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NASA SP-280

THE INTERPLANETARYPIONEERS

VOLUME HI: OPERATIONS

-SP-280) T H E I N T E R P L A N E T A R YESS. V O L U M E3: O P E R AT I O N S ( N A S A )

HF $0.95; SO D $1.75 domesticaid or C S C L 22B

N73-20882

UnclasH1/31 66438

NATIONAL AERONAUTICSAND SPACE ADMINISTRATION



NASA SP-280

THE INTERPLANETARY PIONEERS

VOLUME HI: OPERATIONS

by

William R. Corliss

Scientificand TechnicalInformat ionOffice 1972N AT I O N A L A E R O N A U T I C SAND SPACE ADMINISTRATION

Washington, D.C.



For sale by the Superintendent of Documents,U.S. Government Printing Office, Washington, D.C. 20402Price $1.75 domestic postpaid or 81.50 GPO Bookstore, Stock Number 3300-0451Library of Congress Catalog Card Number 74-176234



Foreword

SO M EE X P L O R A T O R Y E N T E R P R IS E Sstar t withfanfare and end with a quietburial; some start with hardly a notice, yet end upsignificantly ad-

vancing m an kind 's knowledge.The Interplanetary Pioneers more closelyfit the latter description. Whenthe National A eronaut icsand Space A d-ministrat ion star ted theprogram a decade ago it received li t t le publica t tent ion .Y et thefour spacecraft , designated P ioneers6, 7, 8, and 9,have

fa i thful ly l ived up to their name as defined by Webster, "to discover orexplore in advanceof others." These pioneering spacecraft werethe firstto system atically orbit the Sun at w ide ly separated points in space, col-lect ing informationon condit ions far from the Earth 's disturbing influ-ence. From them w e have learned much about space,the solar wind,andthe fluctuating bursts of cosmic radiat ion of both solar and galacticorigin.

These P ioneers have proven to be supe rbly reliablescientific explorers,send ing back informat ionfar in excess of their design l i fe t imes over aperiod tha t covers m uch of the solar cycle.

This publicat ion at te m pts to assem ble afull accoun ting of this rem ark-able program . Writ t en by W ill iam R . Corliss, unde r contract w ithNASA, i t is organized as Volume I: Sum m ary (NA SA SP-278) ;VolumeII: System Design and Development (NASA SP-279);and Volume III:Operat ions andScientificResul ts (NASASP-280). In a sense it is neces-sarily incomplete,for un t i l the last of these remoteand fa i th fu l sentinelsfalls silent, the finalword is not at hand .

H A N S M A R KDirectorA m e s Research CenterNa t i ona l Ae ronau t i c sa n d

Space Admin i s t ra t ion

III



Page intentional*L e f tBlank



Contents

Page

Chapter 1. PIONEER OPERATIONS 1

Chapter 2. PRELAUNCHACTIVITIES 3Facilities Involved in Pioneer Prelaunch Activities 3Organizations and Their Responsibilities 4Significant Events in the Pioneer Prelaunch Phase 9

Prelaunch Schedules—Planned and Actual 13The Actual Prelaunch Phases and How They Compared 17

Chapter 3. LAUNCH TO DSS ACQUISITION 25Performance of the Delta Launch Vehicle 26Tracking and Data Acquisition 36Spacecraft Performance 44

Chapter 4. FROM DSS ACQUISITION TO THE BEGINNING OF THE

CRUISE PHASE 45Sequence of Events 45Pioneer Operations—Acquisition to Cruise Phase 49

CHAPTER 5. SPACECRAFT PERFORMANCE DURING THE CRUISEPHASE 55

Pioneer-6 Performance 55Pioneer-7 Performance 68Pioneer-8 Performance 73Pioneer-9 Performance 74

References 75

Chapter 6. PIONEER SCIENTIFICRESULTS 77The Goddard Magnetic Field Experiment (Pioneers 6, 7, and 8) 78The MIT Plasma Probe (Pioneers 6 and 7) 85The Ames Plasma Probe (All Pioneers) 90The Chicago Cosmic-Ray Experiment (Pioneers 6 and 7) 97The GRCSW Cosmic-Ray Experiment (All Pioneers) 102The Minnesota Cosmic-Ray Experiment (Pioneers 8 and 9) IllThe Stanford Radio Propagation Experiment (All Pioneers) . . . . 115Radio Propagation Experiments Using the Spacecraft Carrier

(All Pioneers) 124

PRECEDINGPAGE BLANK NOT FILMED



C H A P T E R 1

Pioneer Operations

T H I SV O L U M E D E S C R IB E Sthe long chain of events that began withthearrival, checkout,and launch of the Pioneer spacecraftat Cape Ken-

nedy and culminated in the publicat ion of resul ts in thescientific jour-nals. There were five major l inksin the chain, each beginningand end-ing with a critical event:

P hase 1. P relaunch O perations— B egan w ith the arrival of the space-craf t at the Cape an d ended wi ththe launch

Phase 2. Launch to DSSAcquis i t ion—Spacecraf tusu ally acquired firstby Deep Space Sta tion (DSS)at Johannesburg

P hase 3. Near-Earth O perat ions— Com m enc ed with DSS acqu isit ionand ended with completionof all or ienta t ion maneuvers

P hase 4. No m inal and E xten de d Cruise—F rom com plet ion of orienta-t ion m aneuversto end ofuseful spacecraf t life

Phase 5. Presentation of Scientificand Engineer ing Resul ts—Beganassoon as the scientific ins t ruments were turnedon and ended only whenthe data became superseded

Scientificda ta m ay remain v iablefor decades, with informationof va luestil l being extractedaf te r the spacecraftitself has s topped transm it t ing.

The operational historiesof the five Pioneer spacecraft could be re-

lated separately, a l though this would resul t in f ive highly repet i t ivechapters, and the com parison of spacecraft perform an ce and cooperat ivespacecraft activities wouldbe difficult. The descriptions of spacecraftoperations, therefore, are organized with a chapter assigned to each ofthe fivephases established above.

A Pioneer launch requiredthe coordinat ion of thousands of peoplelocated not only at the laun ch sitebut also at the tracking stationsaroundthe world and at thecommunicat ion focal poin tsat the Jet Propuls ionL aboratory 's Space F l ight O perat ions F aci l i ty (SFO F)and the A m e sResearch Center. Some measureof organiza t ionhad to be superimposedon these people and the operations they performed withthe Pioneerspacecraft, the Delta laun ch vehicle , and the Deep Space N etw ork. Am esResearch Center, as the overall program manager, established principlesand generalspecificationsfor all ope ration al phases. The two m ostsignif-icant of the A m e sspecificationswere:



C H A P T E R 2

Prelaunch Activities

T H ES U C C E S S F U LC O M P L E T I O Nof spacecraftpreship review signaled thebeginning of prelaunch activit ies. The spacecraft w as carefully

packed and shipped to Cape K e n n e d yby air. I ts arr ival at the Capei n i t i a t ed a 6- to 10-weekseries of testsand checkout proceduresto assure

the readiness of the spacec raft and i ts co m pa tibi l i ty with the Delta laun chvehic le , the Deep Space Network (DSN), and equipmentalong the AirForce's EasternTest R a nge . If all we nt wel l, the pieces did fit together,and the spacecraft was laun che dsuccessfully. Of course, the real picturewas more complicated.

Basically, one mus t view Cape K en ne dy as a product ion l ine wherespacecraft and launch vehicles meet ,are tested, and fired. Such a com-plex enterprise requires rigorous scheduling anddefini t ion of responsi-bili t ies, leading, in this case, to the launches of the Pioneer spacecraftwithin the i r narrow laun ch windows.

FACILITIES INVOLVEDIN PIO NEER PR ELAUNCH ACTIVITIES

More people and facil i t ies par t ic ipated dur ing the Pioneer pre launchand launch a ct iv i t ies tha n at an y other t im e in the m ission. Alth oughCape K e n n e d yand the Eastern Test Range's downrange stat ions werethe focal points d ur in g this phaseof operat ions,the DSN andSFOF were

all involvedin various tests and during various checkout procedures.A sthe m o m e n t of launch approached, moreand more of the NASA andAir Force general-purposefacilities "came on the l ine" for the launch.R adars , optica l in s t ru m en ta t ion , and te lem etry an ten na s a t the Capeand downrange were al l ,in effect, w a i t i n gfor the Del ta and its Pioneerpayload dur in gthe m inu te s before laun ch. L ikewise , c r i tica l ante nn asa tsome of the DSN 's Deep Space Sta tion s brokeoff from t r ack ing M ar ine rsan d Pioneers alreadyout in space an d swung toward the points wherethe n ew P ioneer wa s expected to come over the horizon.

The major facilities concerned with a Pioneer launchare describedin some detai lin Vol. I I . Here, only the m a j o r func t ions are rei terated.

Cape Kenn ed y.— T h eCape provided facil i t ies for spacecraft tests,checkout , an d inte gration . F ac ili t ies were also providedfor m a t i n g ofspacecraft w i t h l au n c h vehicle and for launch vehicle assemblyan dl aunch . The P ioneer Elec t r ica l G round Suppor t E qu ipm en t (EGSE)



T HE I N TE R P L A N E TA RY P I O N E ER S

provided an interface betweenthe spacecraft and the launch pad en-vironm en t. F igure 2-1 shows L aun ch Com plex 17,from which all fivePioneers were launched.The AE, AM, AO, and Mbuildings are seen

in the aerial view presentedin figure 2-2. Figure 2-3 was taken frominside the M ission Director 's Center.USAF Eastern Test R an ge(ETR)-This facility provided t racking

and data acquisition servicesfrom launch through n om inal D SS acquisi-tion a t Johannesburg.

The Deep Space Network(DSN)-The DSN supplied tracking, dataacqu isition, and transm ission of com m and signals to the spacecraft . In-cluded in the DSN is theDeep Space Ins t rumenta t ion Faci l i ty (DSIF)which encompassesall of the DSSs, the SFOF, and the Ground Com-munica t ions Fac i l i ty (GCF) .F or fur ther informat ionsee Ch. 8 ,Vol. I I .The Pioneer Ground Opera t ional Equipment(GOE) at selected DSSstations provided aninterface between the spacecraft and the general-ized DSS equipment .

ORGANIZATIONS AND THEIR RESPONSIBILITIES

Hundreds of people from governm ent and in du stry applied their

ta len ts and t r a in ing dur ing the tes t ing and checkouts that led to aPioneer launch.They operated the facil i t ies listed above, or they werepar t of the launch crews associated withthe Delta and the spacecraft .

F I G U R E2-1.—Aerial viewof Launch Complex 17 at Cape Kennedy.



PRELAUNCH ACTIVITIES

F I G U R E2-2.—Aerial viewof part of the Cape Kennedy complex. The buildings in theforeground are, f rom le f t to right, M, AO, AM, and AE.

F W U R F .2-3.—The Mission Director's Center at Launch Complex 17.



D T HE I N T ER P L A N E TA RY P I O N E E R S

They also had to be given direct ionsand schedules. Ames ResearchCenter, as the arm of NA SA m an ag ing the P ioneer P rogram , providedboth. The P ioneer F light O pera tions S pecifications issuedby A m e s1

established the pre launc h-phase respon sibilit ies as follows.Ames Research Center Prelaunch Responsibilities

1. Plan and d o c u m e n t the Pioneer space flight operations.2. Prepare and d o c u m e n t a Pioneer spaceflight operations test plan.3. Plan and schedule acceptance, integration,and operational readi-

ness tests.4. D e t e r m i n e r e q u i r e m e n t sand i n i t i a t e tasks an d procurements re -

quired to provide the necessary aidsand mater ia ls used dur ingtests,such as tapes co nt a in ing s imu la ted spacecraf t te lem etry and t rackingda ta .

5. Par t i c ipa tein equipment prepara t ion , acceptance , in tegra t ion ,andoperational readiness tests.

6. Direct c ond uct of , m on itor, and review acceptance, integrat ion,and operational readiness tests.

7. Prepare and update proceduresfor mission-dependent act ivi t iestobe performed dur ingthe flightoperations.

8 . P lan for and in i t ia tetasks and proc urem en ts required to providethe necessary G OE, the com m un icat ion s ne t be tween the s ta tions sup-por t ing the m ission , the m ission-depend entdisplays, and the off-linedata-processingsystem.

9. Develop procedures for flight ope ration s associated w it h m ission-d e p e n d e n t e q u i p m e n tfor handl ing on- l ine an d off-line data , for theanalysis of spacecraft , exper im en t , and G OE per forman ce , and fo rd i s semina t ing informat ion to the spacecraf t cont rac tor and exper i -menters .

Jet Propulsion Laboratory Prelaunch Responsibilities

1 . M a n a g eand coordinateact ivi t iesof DSN.2. P rovide personnel to opera te m iss ion- inde pen den t equ ipm en t and

Pioneer G O E (except dur in g Type-I I or ien ta t ion) dur ing acceptance ,i n t eg ra t ion , and operat ional readinesstests, and d u r i n g flight opera-t ions at DSIF.

3. Provide personnelto opera te m iss ion- indepen den t equ ipm en t dur-

ing acceptance, integrat ion,and operational readiness testsat SFOF.

'The basic documents are Pioneer Specifications PC-046, for Block-I Pioneers, andPC-146, for Block-II Pioneers. See Bibliography in Vol. II. Many of these activities,particularly those invo lv ing planning, occurred prior to the shipment of the spacecraftto the Cape. The actual equipment preparations and tests prior to launch are coveredin detail in the next section.



8 THE INT ERPLANETARYP I O N E E R S

Experimenters' Prelaunch Responsibilities

1. Provide data for plans and procedures preparedby A m e s for ex-per im ent prepara t ion, acceptance , in tegra t ion, opera t ional readinesstests, and flight operations.

2. Provide requirementsfor use byAmes in the preparat ion of weeklyand dai ly operat ions plansand in the c o n d u c tof the mission as it per-ta ins to the scientifici n s t r u m e n t s .

3. Stanford m ust providea field crew as required to operate the t rans-mitter at StanfordUnivers i tydu r ing equipm en t prepara tion, acceptance ,integrat ion, operat ional readiness testsand dur ing flight operat ionsofthe Pioneer spacecraft .

NASA Headquarters Prelaunch Responsibilities

1. R evie w operations readinessof the Pioneer Project priorto l aunch .2. Advise the P u b l i c I n f o r m a t i o nOffice on procedures to be followed

for Pioneer.3 . Pa r t i c ipa t ein l aunch operat ionsat ETR.4. Par t i c ipa tein flightoperat ionsat SFOF.

Goddard Space Flight Center Prelaunch Responsibilities1. Prepare and s u b m i tthe P ioneer opera t ions requirem en tsto E T R .

K enned y Space Center P relaunchResponsibilities

1. Plan the launch operat ions.2. Provide technical d i rec t ionand i m p l e m e n t a t i o nof the l a u n c h

operat ion.3. Coo rdinate ac t ivi t ies between NA SA , contractors,and ETR groups.

McDonnell-Douglas3 Prelaunch Responsibilities

1 . Prepa re p l ann ing ,reference, and predictive powered-flighttrajec-tories.

2. R ev iew techn i ca l docum en t st ha t re la te to laun ch opera t ionsandt ha t hav e been preparedby other e lem entswi th in the Pioneer Program.

3. Prepare l a u n c h c o u n t d o w n d o c u m e n t a t io n .

Eastern Test Range (USAF) Prelaunch Responsibilit ies1. Rev iew t echn i ca l r equ i r emen t sand documents that re la te to

launch operat ionsand t h a t have been preparedby other e lementswi th inthe Pioneer Program.

'Delta con t r ac to r.



PRELAUNCH ACTIVITIES

2. Provide crewsas required to operate ETR stat ions support ingthePioneer P rogram du rin g integrat ionand operational readiness testsanddu ring the launc h coun tdow n and powe red-fl ight phase of the P ioneer

mission.From these assignmentsof responsibi l i ty came detai led schedulesofprocedures te l l ing ind ividu alsin all organizat ions involved what theyshould do and when. Although the proliferation of plans, task assign-ments , and schedulesm ay seem overly complex,it is th is k in d of paper-work that permits large groupsof people from diverse organizat ionstofunct ionsuccessfully.

SIGNIFICANT EVENTS IN THE PIONEER PRELAUNCH PHASEThe prelaunch phaseof act ivi t iesconsisted of m a n y h u n d re d sof sepa-

rate i temsan d events ; so m a n y, in fact, tha t the checkout an d count -down lists were printed by computers . In addition to the extens ivepla n n in g ac tivitie s ju st described, two other groups of processes andevents s tand out as im por ta nt :

(1) Training in operational procedures(2) P reparat ion and test ing of the spacecraft, laun ch vehicle, and

other mission-dependent hardware

Training in operat ional procedures wa s m ost im po rta n t d uri n g thepreparations for the launch ofPioneer A in 1965, w he n the P ioneerProgram was new to ETR and DSNpersonnel. The Delta, of course,was a f ami l i a r sight at the Cape; and the ETR and DSN hadalreadyhand led space craft m ore com plex tha n the P ioneers. Some of the "dif-ferent" aspects of the Pioneer launches were:

(1) The un usua l o r i en ta t ion m aneuversfol lowingl aunch(2) The narrow lau nc h win do w associatedw i t h in je c t in g the space-

craf t into an orbit roughly parallel to the plane of the ecliptic(3) The ejec t ionof the Test and Training Satelli tes (TETR) from

Block-I I Pioneers(4) The occultationsan d flights through the Earth 's m agne t ic ta i l

The orientat ion maneuvers, especial ly, requiredcareful t r a i n ing a tthe G oldstone DSS site an d, in the case of Pioneers 6 and 9, at Joh ann es-

burg an d G oldstone, respect ively, where "part ial" Type-II orien tat io nm ane uvers were carr ied out .

The prelaunch preparat ion and testing of the spacecraft , launchve-hicle, an d associated hardware commenced withthe arr iva l of thespacecraf t at the Cape. These highly impor tant checksand double-checks were performed prim ari ly by Am es, TR W ,Goddard, and Ken -



10 THE I N TE R P L A N ETARY P I O N E ER S

nedy personnel . Although the actua l operat ions varied slightly frommission to mission, the following listof major tasksis representative.4

Pioneer Prelaunch Tasks

Task 1. Receip t , unpacking,and i nven to ry ingof spacecraft and as-sociated e q u i p m e n t at hangar

Task 2. Verif icat ion of mechanical condit ion of the spacecraf t ,ground hand l ing equ ipment ,an d EGSE

Task 3. Validat ion of EGSETask 4. Spacecraf t pn eum atic system leak testTask 5. Spacecraf t a l ignment checksTask 6. Solar-array performance testTask 7. Performance checksof cri t ical uni t parametersnot accessible

dur ing an In tegra ted Sys temsTest (1ST)Task 8. In tegra tedSystemTest (see discussion below)Task 9. Prepara t ion of spacecraft for m at in g w ith third s tageTask 10. M a ti n g of space craf t to inert third s tageTask 11. In sta l la t ion of EGSE in blockhouse and i ts val id at ionTask 12. M a t i n g of spacecraft and third stage to rest of l aunch ve-

hicle at the l a u n c h padTask 13. P rel im ina ry spacecraf t on-s tand e lec t rica lan d radio-

•Vequency testsTask 14. Verif icat ion of spac ec raf t / laun ch vehicle com patibi l i ty with

the rangeTask 15. Nose fair ingfit checkTask I f i . P re l imin ary on-stand In tegra ted SystemsTestTask 17. Flight readiness dem onstrat ion w itha spacec ra f t / l aunch-

vehicle pract ice coun tdow nTask 18. Replacement of iner t third s tage witha l ive third stage

and f ina lspacecraft preparationsTask 19. Veri f ica t ion tha tthe exper iments are opera t ing to the satis-

fact ion of the exper imentersTask 20 . Spacecraft radio-frequency subsystem testTask 21. Integrated SystemsTestTask 22. Final spacecraf t checkprior to dyn am ic ba lanc ing (en ta i ls

moving spacecraf t backto hangar)

Task 23. Spacecraf t dy n am ic balance checkTask 24. Mat ing of spacecraft w itli live thir d stageTask 25. Dyn am ic ba lance testof spacecraf tand third stageTask 26. Reins ta l la t ion of EGSE in blockhouse and revalidation

' TRW Space Technology Laboratories: Test Program Plan, Pioneer SpacecraftProgram. Aug. 1964.



PRELAUNCH ACTIVITIES 11

Task 27. Ma t ing of spacecraftand live third stage to launch vehicleon pad

Task 28. Spacecraft on-stand electricaland radio-frequency tests

Task 29. F inal launc h vehic le /spacec raf t / range radio-f requency com-pat ib i l i ty testTask 30 . F inal on-stand Integrated SystemsTestTask 31. Preparat ion of spacecraft for pre-term inal count ( includes

instal lat ionof live pyrotechnics)Task 32. Perform jo in t launch vehic le /spacecraf t / range pre- terminal

countTask 33. Terminal c o u n t an d l aunchThe Integrated SystemsTest, or 1ST, was performed at least twice

for each spacecraft at the Cape.This test (a ct ua lly a check for laun chreadin ess) was described in Ch. 6, Vol. II. Each spac ec raft was subjectedto at least one 1ST before it left the TRW Systems plan t for the Cape.A successful 1ST demonstrated that the spacecraft met al l spacecraftperformance requirements .I t provided a baseline upon whichto gagespacecraft operat ional con dit ion— a background against which to spottrend s. It was because of this diagnostic va lue th at the 1ST was re-peated twice or more before launch.The final 1 ST was"on-stand;" that

is , carried out when the spacecraftwas mated to the Delta rocketon thelaunch pad. The on-stand 1ST was the finalcomprehensive spacecraftcheck before launc h. R ec api tu la t in gthe 1ST description in Vol. II, the1ST was asclose to a rea listic operational testas one could get prior tolaunch and yet be independen t of the Delta, the ETR, and the SFOF.A m in im um of hard line s were used; radio lin ks were used instead tos imula te ac tual communicat ion l inks ( f ig .2 — 4 ) .Sun-sensor pulses werealso simulated. Basically,a successful 1ST was a vote of confidencein thespacecraft ,even though int erfac es w iththe Delta and DSNwere not tested.

The opera tional readine ss tests were dress rehearsals th at dem onstratedt h a t al l personnel , equipment, andfacil i t ies par t ic ipat in g in a P ioneerl a u n c h were ready to suppor t the mission. While the 1ST was a space-craf t test , the operational readiness test encompassedthe en t i re Pioneersupersystem; that is , the spacec raft and i ts instru m en ts, the D elta , andthe DSN (fig. 2-5). The even t sand tasAs performed and sim ula ted wererepresenta t iveof the ac tua l m ission eve nts. The m ost cr it ic al "dryruns"were those s i m u l a t i n gthe Type- I I o r i en ta t ion maneuverin con junc t ionw i t h the G oldstone DSS. An othe r s im ulate d si tu at ion brought StanfordUnivers i ty i n t o the sys tem, permit t ingoperators there to practice withthe spacecraft and ground equipment under real is t ic condit ions. Ofcourse, the normal missionw as simulated too,via ersatz commandsandte lemetry sent over NA SA's wor ldwide c om m unicat ion sys tem(NASCOM) an d along ETR communica t ion channe l s .



12 TH E I N T E R P L A N E TA RY P I O N E E R S

FinuRK 2-4 .—Pioneer F.wired for on-stand checkout at the Cape.

Two operat ion al readiness tests were plann ed for each prelaunchphase. With Pioneer6, lor example , the first operational readiness testwas scheduled for 48-hr dura t ion , w i th4 hr devoted to Cape and ETRactivit ies, 13 hr for first-pass ev en ts at Jo han ne sburg , and 9 hr for theType-I I or ien ta t ion m ane uver comm anded f rom Goldstone . F or Pio-neers 6 and 9 the part ial Type -II o rientat ion m ane uver was sim ulatedat Johanne sburg. N orm al cruise operat ions were sim ulated at a l l s ta-t ions. The second operational readiness test just beforel i f t o f f was a



P R E L A U N C H ACTIVITIES 13

F I G U R E2-5.—Scene in control room at SFOF in Pasadena, Calif., during Pioneer-Boperational readiness test.

repeat of the first, except that everything was to be compressed into a24-hr period. If all systems passed the second operational readiness test,a launch readiness review w as held by the Pioneer Mission Director(fig. 2-6). The "go/no-go" decision was made at this final meeting.

If the decision w as "go," the actual countdown began.

PRELAUNCH SCHEDULES—PLANNED AND ACTUAL

The Pioneer spacecraf t arrived at the Cape 6 to 10 weeks prior tothe planned launch. As the various tests were successfully passed, eventsm u l t i p l i e d crescendo-like as the day of launch approached. F — 2, F— 1,and F— 0 days were fil led w i t h critical tests. The Pioneer project pre-pared schedules to lend some order to these events. The first "working"schedu le of importance was the Detailed Task Sequence prepared byA m e s Research Center a few months before the spacecraft w as shippedto Cape Kennedy. The Detailed Task Sequence was published as aPioneer specification. In the case of Pioneer D, which is used as anexample here, Specification PC—153contains the Detailed Task Sequenceshown in table 2-1. Although the Detailed Task Sequence was presented



14 THE INTERPLANETARY PIONEERS

NATIONAL AERONAUTICS AND SPACE ADMINISTRATION

AMES RESEARCH CENTER MOFFETT FIELD, CALIFORNIA

Mission Readiness ReviewPioneer C

Date: December 6, 1967Place: E & 0 Building Conference Room 116Time: 0930 EST.Chairman: Charles F. Hall, ARC Pioneer Project Manager

AGENDA

Time, EST.

093009451000102011001115

113512051305

13251410144014551515

1600

16451705

Item

IntroductionMission ObjectivesLaunch Operations StatusLaunch Vehicle Status

COFFEE BREAKLaunch Vehicle/TTS Status

TTS Spacecraft StatusLUNCH

Summary of Pioneer CapeActivities

Pioneer Spacecraft StatusPioneer Instrument Status

COFFEE BREAKPioneer Post Launch ActivitiesT & DS Support

ETRMSFNDSNNASCOM

Interstation ConferenceStation ReportsSummary of Mission Status

Pioneer Program Office Comment

C. F. HalI/ARCC. F. HalI/ARCJ. Nielon/ULOW. McCall/ULO

J. Tomaselio/T. Longo/GSFCP. Burr/GSFC

R. W. Holtzclaw/ARC

B. O'Brien/TRWJ. Lepetich/ARC

C. F. Hall/ARCJ. Thatcher/JPLR. Norman/ULOD. Bonnell/GSFCJ. Thatcher/JPLJ. Thatcher/JPL

J. Thatcher/JPLC. t. Hall/ARCJ. Mitchell/M. Aucremanne/HQ

F I G U R E2-6.—Reproduction of the schedule for the Pioneer-C Mission Readiness R e-view held at the Cape.

on a.t ime base and was muchmore detai led than the general Block-I Ispecifications,PC—146, i t was not a working schedule in the sense thatit specified who, w h a t , when , andwhere.

The Detai led Task Sequence wasnex t rendered in to more specific

schedules. It is impractical toreproduce the i tem-by-i tem details, butthe reader can get a "feel" of these working-level schedules from thePioneer-D F — 2, F— 1, and F— 0 day schedules in tables 2-1 and 2-2.Detailed descript ionsof the tasks to be performed—inte rms of switchesto be thrown, meters to be read, calibrations to be made, etc.—had toaccompanythese schedules.



P R E L A U N C HACTIVITIES 15

TABLE 2-1.—Planned Pioneer-D Typical Detailed Task Sequence "

Da?e Location Task

Oct.Oct.

2918

Oct.Oct.Oct.

Oct. 24

Oct. 25

Oct. 28

Oct. 31Oct. 31Nov. 1

SFOF Flight path analysis and command group acceptance testSFOF Spacecraft performance analysis area/science analysis and

command group acceptance testSFOF SFOF integration testETR DSS hangar and on-stand compatability testETR Practice on-stand 1ST

SFOF First operational readiness test

ETR Preliminary electrical and radio-frequency checks

ETR DSS hangar and on-stand compatability test

SFOF Second operational readiness test

ETR Practice countdown (pre-fairing installation)

ETR Practice countdown (post-fairing installat ion)

0725 EST07300730090011201210

13201440144017101840

ETRDeltaSpacecraf tDeltaSpacecraftDelta

SpacecraftDeltaSpacecraftDeltaETR

Nov. 4 (major F —2 day milestones)

Countdown initiationTask 2, engine checksTask I, preparations and spacecraft checksTask 3, electrical systems checksTask II, pneumatic pressure and fill valve lead checkTask 5, stray voltage checks

Task III, service magnetometerTask 6A, class B ordnance installation and hookupOrdnance installationTask 6B, squib installationB u i l t - i n hold (8 hr, 15min)

Nov. 5 (major F — 1 day milestones)

0700 EST Spacecraft Task V, remove Red Tag items and protective coversCountdown initiationTask 7B, second-stage final preparationsTask 9A, Second-stage propellant serv ic ing setup

Task 7A . f a i r i ng erectionTask 6C, FW-4 (third stage) hookupTask 7B , f a i r i ng installationTask III, umbilical checksTask 9B, second-stage propellant servicingTask "('.. blast-band installationTask 10, first-stagef ue l i ngTask 60, ordnance checksB u i l t - i n hold (4 hr, 35min)

Nov. 6 (major F — 0 day milestones)

2349 (Nov. 5) Spacecraft Task VII, spacecraft radio-frequency checksCountdown initiationTask 11, launch-vehicle radio-frequency checksSpacecraft standby status checksTask 12,class-A ordnance i n s t a l l a t i on an d hookupTask IX. ordnance armTask IX, sustained operation

072507300730083011301200133014001730174519002015

022402290309031903190404

ETRDeltaDelta

DeltaDeltaDeltaSpacecraftDeltaDeltaDel taDeltaETR

ETRDeltaSpacecraftDeltaSpacecraftSpacecraft



16 THE INTERPLANETARYP I O N E E R S

TABLE 2-1.—Planned Pioneer-D Typical Detailed Task Sequence—Continued

Date

0.549

0549064907490809During holdD u r i n g hold0847

093709420947

Location

Delta

SpacecraftDeltaDeltaETRDeltaDeltaETR

ETRETRETR

Task

Tasks 13 to 15, launch-vehicle f inal preparation andtower removal

Task X , spacecraf t t e rm ina l coun tTask 16A, l iqu id oxygen setu pTask 17, beacon checksBui l t - in hold (57m i n )Task 16B , liquid oxygen fillTask 13, second -stage p ressure fillEnd of holdBui l t - i n hold (5 m i n )End of holdLiftoff

• Adopted from Pioneer SpecificationPC-153.00. Cross checks between ac tual w orkin gschedules and the ac tu al sequence of eve nts at the Cape for Pioneer D reveal severalminor changes in plans. Arabictask num bers apply to the launch vehic le ; R om ann u m e r a l s are assigned to spacecraft tasks.These tasks are defined in great detail inG oddard and Am es doc um en ts. P ioneer Spec ification PC-153.00 covered on ly flightoperations; p reparationof the spacecraft, launch vehicle,and other hardwareare typi-fied in Figure2-7.

TABLE 2-2.—Spacecraft Co un tdow n De tai led Schedu le*

TimeCountdown

time Task

F — 2 d a yschedule0420 EST T— 24300450 T - 2400

05050550

11101110

111013101310

143014301530

T-2385T —2340

T —2020T —2020

T-2020T — 1 9 0 0T — 1 9 0 0

T—1820T-1820T — 1 7 6 0

F — 1 d a y schedule0040 EST T-15500110 T-1520

All personnel reportto Hangar A M .Area-17 personnel report to Spacecraft Coordinator in

blockhouse.Area-17 personnel reportto Levels8B and 9 .Start Task I , preparat ionsan d spacecraft an d e x p e r i m e n t

checks.CompleteTask I.TR W personnel not required in Task I I report to block-

house.Begin Task II , f inalpn eum at ics pressur izat ion.Task II complete .Begin Task III , magnetometer service.

Task I I I complete .Begin Task IV, ordnance ins ta l la t ionand checks.Complete Task IV.End of F — 2 dayactivi ty, secure Level8B .

Crew arrives at blockhouse30 min prior to start of Task V.Begin Task V, R ed Tag remova land finalp repara t ions .



P R E L A U N C HACTIVITIES 17

TABLE 2-2.—SpacecraftC o u n t d o w nDeta iled Schedule— Cont inued

Time

034003400950095010101040

F —O d a y18551905

2205220522152215223522552300230000350045

0045020002150240025503050405043004350440

04420445

Countdowntime

T-1370T— 1370T-1000T— 1000T — 980T — 950

scheduleT — 525T — 515

T-335T — 335T-325T-325T — 305T — 285T — 280T — 280T — 185T— 175

T — 1 7 5T — 100T — 85T — 60T-45T-35T-35T— 10T —5T-5

T-3T_0

Task

Comple teTask V.T RW a n d NASA observers on stand as required.Task V I pre para tion s; spacec raft crew reports to blockhouse.Begin Task VI, umbi l ica l checks.Task VI comple te .End of F— day activi ty,secure Level8B .

Crew arrives at blockhouse 10 min prior to s tar t of Task VII .Begin Task V I I ,spacecraft systems checks.

Complete Task V I I .Begin Task V I I I ,spacecraft s t andby status preparations.Complete Task V I I I .Begin Task IX, ordnance Connectionand final secure.Arm ordnance.Secure.Complete Task IX .Spacecraft susta ine d operat ion.Stand personnel requiredfor Task X report to road block.Start Task X , t e r m i n a l c o u n t d o w n .

Tower r emova l preparations.Tower removal .RF checks (receiver2) .RF checks (receiver1) .Receiver1 and 2 finalfrequency report.Bui l t - i n hold (60 m i n ) .Begin t e rmina l coun t .Spacecraft to internal power.B u i l t - i n hold (5 m i n ).Resume count .

Spacecraft go/no-go report .Lif toff .

• As issued to spacecraft lau n ch team at Cape K en ne dy for the la un ch of Pioneer D .Delta , DSN, and ETR events not shown , a l thoughthey participate in some tests ,suchas the operational readiness test.

THE ACTUAL PRELAUNCH PHASESAND HOW THEYCOMPARED

Each of the fiveprelaun clr phaseshad its own i n v e n t o r yof anecdotesan d specia l c i rcum stanc est h a t m a d e it slightly different from the others.O f course, the spacecraft , the Delta, the DSN , and the ETR al levolved be tween P ioneerflights so t h a t the ingred ien t s w ere somew hatdi ffe ren t for each launch.A brief narrativefor each lau nc h follows w ithemphasis on eve nts not app ea ring on the plan ne rs ' cha rts in tables 2-1



18 THE I N T E R P L A N E TA RY P I O N E E R S

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20 THE I N TE R P L A N ETA RY P I O N E ER S

and 2—2. A typical scheduleof actual prelaunch eventsis presentedin figure 2-7.

Pioneer-A Prelaunch Narrative

Both the prototype and flight models were sentto the Cape. Theprototype arrived October 1, 1965, and was used for practicing pre-launch operat ions. Whenthe prototype modeland an inert Delta thirdstage were matedto the launch vehicle (Delta35) on November 29,it was discovered thatthe um bi l ica l w i ringwas improperly connected.Modif ica t ionswere m adeto correct this.

The Pioneer-A flight model was delivered for mat ing w i th the Deltathird stage on December 5. During prel iminary al ignment checkout, aTotal In dicator R un ou t of 0 .25 in . was noted, indicat ing a physicalm ismatch. The a t tach f it ting was shaved down to br ing the a l ignm en tw i t h i n tolerance. Tests an d checkouts proceeded normally throughF — 1 day ("norm ally" m ea n ing only m inor, easi ly corrected problem s).

December 15, F — 0 day, was relat ive ly calm w ith visibi l ityof only0.125 to 2 miles . Countdown commenced30 min early at 1630. Every-t h ing we nt smooth lyu n t i l T — 90 min w h e n the second-stage um bil ica lplug was in ad ve rte n tly pulled , ca using loss of power to the D elta second

stage and the spacecraf titself. No one wascer ta in w hat would h appenif the plug were reinserted,and it was considered possible that someunforeseen signal could cause serious damageby firing some of theordnance. The spacecraftand the Delta were revalidated.The bui l t - in60-min hold and u l t ima te ly the launch window had to be extendedwhile fu r the r checks were m ade. The term ina l count resumed at 0145,December 16, at T — 35 m i n .

At T — 2 min an abnorma l i t y in the radio gu idance equ ipmen t

caused another hold. The situation seemed to correct itself,and thecou nt was recycled to T— 8 m i n . Liftoff occurred at 0231:20 EST,Dec em ber 16, 1965 (fig . 2-8).

Pioneer-B Prelaunch Narrative

The pre lau nc h opera tions for P ioneer B were com parat ively un-even t fu l . The flight spacecraf t arrived at Bui ld ing AM on July 17,1966. O n Augus t9, it wasdiscovered that, whenthe Chicago cosmic-rayexper iment warmedup, a connection opened, part ial ly disabling theexp erim en t. As a result , the expe rime nt indica ted a non -existen t lowradiat ion level at al l time s. The expe rime nt f lew in this con dit ion.

O n F— 2 day, August 15, a receiver lockup problemwas encounteredon the two S-band upl inks . Ul t imate ly,the trouble w as traced to anan t enna on Building AM that was not pointed toward the launch pad.

F — 0 day, A ugu st 17, had superb w eather, w ith 5-knot wind s an d



P R E L A U N G HACTIVITIES 21

FIGURE2-8.—The launch of Pioneer A on Delta 35.

a visibil i ty of 10 m iles. The co un tdo w n proceeded n orm ally to T— 3m i n , when a hold was called due to the loss of c o m m u n i c a ti o n s d o w n -range on the ETR . Co m m un ica t ion s were resto redaf te r 2 m i n , andl i f t o f foccurred at 1020:17 EST.

Pioneer-C Prelaunch Narrative

Pioneer C was the first of theBlock-I I spacecraft .In addi t ion, th isflight was the first tocarry a TETR m o u n t e d in the Delta second stage.The P ioneer-C fl ight m odel was received a t B ui ld ing AM on Novem ber1 1 , 1967. The 1ST of N o v e m b e r15 identified a faul ty decoder whichwas replaced. O n N o v e m b e r22, the Ames plasma probe was removedto correct a wir ingerror.



PRELAUNCH ACTIVITIES 23

Pioneer-D Prelaunch Narrative

This spacecraft was the first to incorporate the convolutional coderexperiment and the Ames magnetometer. Pioneer D arrived at Build-

ing AM on October 6, 1968. The beginning of the countdown was de-layed for 2 days while tests and adjustments were made to the second-stage programmer. A s soon as the programmer was accepted for flight,F — 2 day activities commenced. The countdown proceeded smoothlyto 0900 EST when anomalies appeared in the experimental data andexperimental performance. Holds were called to investigate these prob-lems which were found to be due to radio and electrical interferencef rom the launch vehicle. No troubles were encountered during F—1

day countdown activities. A t 1850 EST, November 7, 1968, F — 0 d a ychecks began. Spacecraft power w as turned on at 1920. Spacecraftsystems checks (Task VII) ran ahead of schedule, and a 20-min holdw as called at 2015 to give the spacecraft receiver additional time towarm up. The terminal count began at 0050, November 8. Followinga hold of 9.5 m in due tohigh sheer winds aloft , the Delta l if ted offa t 0446:29.

Pioneer-E Prelaunch Narrative

O n July 18, 1969, the Pioneer-E spacecraft w as received at Cape Ken-n e d y (fig. 2—9). There were no unusual prelaunch events. A s t u d y ofthe launch vehicle test s u m m a r y indicates a normal sequence of pre-launch events although a number of minor problems arose—as theyusual ly d o — a n d were corrected. Nothing in the prelaunch tests andcheckout presaged the fa i lure of the launch vehicle af ter l iftoff.

Spacecraf t and radio-frequency checks, Task VII, began at 0835 EDTo n F — 0 day, August 27, 1969. Except for a thunderstorm that tem-porari ly delayed work, weather w as excellent, with a vis ibi l i ty of 8miles and light winds. The terminal countdown w as u n e v e n t f u l . Lif t -off was at 1759:00 EDT, August 27, 1969.



Intentionally LeftB)ank



C H A P T E R 3

Launch to DSS Acquisition

T H E P H A S EOF P I O N E E RO P E R AT I O N Sstretching from launchto DSSacq uisition lasted less th an 1 hr, but i t was the on ly time wh en all

four Pioneer systems operated together. Even this observation is aforced onebecause the spacecraftan d scientific ins t rum en t systems were

essentially passive du ring powered flight and the coast phase. O nlyhousekeeping data were telemetered,and al l scientific ins t ruments wereo f f . The spacecraft cameto life only when the Travelling Wave Tubes(TWTs) were switchedon, the booms were deployed, and the Type-Iorientat ion maneuver was ini t iated. By this t ime, the spacecraft hadbeen spun up and hadseparated from the Delta third stage.The ground-based DSN was involved in a configurat ion cal led the Near-EarthP hase N etw ork which, du ring this phase, incorporated som e facili t iesfrom the Air Force Eastern Test Range and the NASA M ann ed SpaceFl ight Network (MSFN). Figure3-1 i l lustrates the chronology andterm inology involved in this phase of the mission.

It is best to view Pioneer operationsfrom several vantage pointssoth at the operation s of all four systems can be apprec iated. F irst , thesequence of eventsis portrayed schematical lyin figure 3 — 2 .The n o m i n a lt ime f r a m e for one of the launches is added to the picture in table 3 — 1 .O f course, the t im i n g of the critical events variedfrom mission to mis-sion because the bu rn and coast t im es changed w ith each laun ch , and

the Delta rocket w as upgraded during the program. The nomina l t imeframe, with its critical events, provides a yardstick against which tomeasure the successof this portion of the l aunch . Al t i tud eand distancedownrange are also important diagnost ic parameters . However,theDSN stat ions wait ing downrange tendto see the picture as hav ing anadd it ional sp at ial dim ension (f ig. 3-3) .This is not surpris ing becausethe t rackingof spacecraftin orbit or far out in space is essent ia l ly four-d i m e n s i o n a l ( inc luding t ime) , whereas range t racking,as on the ETR,was more nearly three-dimensionalin character; thatis, al t i tude , range,an d t ime. In fact, one of the critical displaysat the Cape is an impac tpoint predictor— a two-dime nsional display."Handover" from the Near-Earth Phase Network to the DSN was facilitated by "predicts" sentahead to DSS-51 (Johannesburg) to tell its acqu i si tion-a id an te nn aswhere to look in the western sky. Once the acquisi t ion aid had thespacecraft ,the 85-ft. parabolic an te n n a was slewed to it .

25

PRECEDING PAGE BLANK NOTFILMED



26 T HE I N T ER P L A N E TA RY P I O N EE R S

Deltalaunchvehicle

Near-Earthphasenetwork

Spacecraft

Instruments

Launch MECO DSSh- co acquisition

W/

///////H

'///Housekeeping telemetry only

// / // /// / / / /

//// / /

///,

Booms' //deploy./

TWTs on

Instruments off

In s t rumen t son

F I G U R E3-1.—Status of the four Pioneer systems from launch through DSS acquisi t ion.

PERFORMANCEOF THE DELTA LAUNCH VEHICLE

The Delta la un ch vehicle performed superbly duringthe f irs t fourPioneer launches.The fifth mission, PioneerE, had to be aborted bythe Range Safety Officer w h e n the vehicle began to stray off course. I twould be repeti t ious to narrate each launch in detai l . Instead, tables3-2 and 3-3 sum m arize Del ta "mark events"and stage performance,

respectively. A series of figures (figs. 3-4 to 3-7) portrays the Deltaovera l l metr ic performancefor the four successful missions. O f course,none of the flights wa s flaw less, but thedeviat ions wereall minor com-pared to the fa i lure on the final flight.These per tu rba t ionsare s u m -marized below along witha descript ionof the loss of Pioneer E.

Pioneer-6 Launch Vehicle Performance

All m ission objectives were achievedan d vehicle flight wa swell w i th inthe "three-sigma" limits.5 A ll l iquid enginesand solid motors performedsatisfactorily, inc luding the spinup rockets. Second-stage thrustmis-align m en t in pitch was excessive, however, and alig n m en t procedureswere to be modified onfu tu re Delta f l ights . Another minor deviat ion

5 Theoretically, the "three-sigma" l imi t s encompass 99.86 percent of all observations.



L AU NCH TO DSS ACQUISITION 27

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Pioneer-9 Launch Vehicle Performance

This w as essentially a perfect launch from the Delta viewpoint.

Pioneer-E Launch Vehicle Performance

Ignition and l iftoff were normal. The three solid, thrust-augmentationengines operated properly and were jettisoned simultaneously and atthe proper moment. At 63 sec into the flight, the first-stage hydraulicpressure decreased from 3150 to 3000 psia. Then the pressure beganfluctuating. A t 213 sec, the pressure dropped to zero, and all first-stagecontrol was lost. Telemetered propulsion parameters began to indicateviolent vehicle maneuvers.

With the first-stage hydraulic pressure lost, the main engine pitcheddown, yawed left , an d rolled counterclockwise. A s a result, the second-stage gyros were driven out of their limits during second-stage ignitionand separation. The ignition and initial performance of the second-stageengine were approximately normal, but the damage was done, and thesecond stage was far offcourse.

Afte r main engine cutoff , the predicted impact point on the plotboardbegan to move at a 45° angle to the right and downrange. The Range

Safety Officer sent "arming" commands to downrange stations to ensurethey had the capability for vehicle "destruct." A t 483.9 sec, the deviationfrom the planned course wa s toogreat, and the vehicle w asdestroyed.

TRACKING AND DATA ACQUISITION

A s a Pioneer spacecraf t and its launch vehicle rose from the launchpad at Cape Kennedy, they were tracked downrange by a variety ofradio an d optical tracking devices. Until the spacecraft w as "handed

over" to the Johannesburg DSS station, the pooled radars, optical track-ers, guidance equipment, and telemetry receivers of the Air Force ETRand some stations of NASA's DSN and MSFN were crucial to missionsuccess. We examine now how these resources were put together andhow they funct ionedduring this phase of each Pioneer mission.

Tracking and Data Acquisition Requirements and Station Configurations

Tracking an d telemetry data are needed to assess the performance ofboth the launch vehicle and the spacecraft and also for ensuring rangesafety. All of the "mark events" an d launch vehicle positions, velocities,and headings described in the preceding section are obtained throughtrackingan d analysisof telemetry data.

The facil i t ies assigned to each of the Pioneer missions from launchihrough DSS acquisition are listed in table 3 — 4 .The ETR was thepri-




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mary agency responsiblefor providing m etric ( trac king) data d uringthis phase of operations. The MSFN stations, listedin tab le 3-4, pro-vided redu nd an t radar support . M etric requirem en ts were me t by track-

ing the C-band beacon aboardthe Delta and the S-band telem etry signalfiom the space craft. Froml i f t o f fto 5000-ft al t i tude, ETR optical equip-m en t provided add it ional m etric data.

During this"powered"phase of flight, telemetry came primarilyfromthe first andsecond stagesof the launch vehicle.These w e r e P D M / F M /FM l inks operat ingat 228.2 and 234.0 MHz, respectively.ETR stations1, 3, 9.1, 12, 13, and the R ange In strum en tation Ships (R IS) acquiredthis te lemetry.

The ETR R e a l Time Computer Faci l i ty(RTCF) at the Cape, whichused CDC 3600 and 3100 computers duringthe Pioneer flights, proc-essed the m etr ic dataflowing back from downrange sitesand convertedthem into"predicts"forstation s whichhad not yetacquired the spacecrafta n d / o r laun ch vehicle stages.

Dur ing the Pioneer flights, Building AO (fig . 3-8) con tained jointJPL—AFETRfacilities that were vital to mission analysisand control.Briefly, these facilitieswere:

(1) A joint operations center consistingof status displays,a t iming

system, and consoles.During the early portion of the Pioneer mission,control was transferred to the SFOF.

(2) A joint communication center, which providedthe local ter-minals and interfacesfor voice, teletype ,and data circuitsto and fromCape facilities, the SFOF,and the ETR.

Flight Operations—Trackingand Data Acquisition

The scenariosof t rack ingand dat a acq uisition a ctivities vary slightly

for each laun ch . Short n arra tive s rather tha n tables seem inorder here.Pioneer 6.—Liftoff occurred at 0731:20 G MT, December16, 1965.Grand Bahama r i sewas at 0732:15,but its receiver was in and out oflock until 0737:33.At 0751, control was transferred from the SFOF toDSS-51, Johannesburg, for the planned part ial Type-II orientat ion.The Johannesburg acquisi t ionaid antenna acquired the spacecraftat0759. In it ial telem etry indicated tha t the auto m atic Type-I orientat ionwas underway. At 0804:14, the spacecraft signaled that theType-IOrientat ionwas complete.At 0807, the Johannesburg receiverwas trans-ferred from the acquisition aid an tenna to the 85-ft dish.

There were some minor problemswith telemetry coverage duringthis flight. Stations did not acquire and lock onto the spacecraft signalas early as predicted; however,the signal was tracked longer thanan-ticipate d (fig. 3-9). This anomalous performancewas scheduled forlater inve stigation . The first and only indic ation of third-stage ignition




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in near real t ime was the dropout of vhf telemetry as the third-stagep lume engul fedthe second stage.RF propagation problems precludedreceipt of rea l - tim e data f rom Ascension Is land. W hena report was

finally received,it indicated onlya 50-percent burn t ime .All other track-ing and telemetry data, however, indicateda normal third-stage burn.L ater, i t was fou n d that som eone had read the wrong scale on theDoppler plot a t Ascension. F inal ly,the Coastal Crusader obtainednoDoppler data from eithe r the 136-M Hz De lta beacon or thespacecraftS-band carrier due to equipment problems. The parking orbit para-meters computedfrom downrange t racking data are tabula ted in table3-5.

Pioneer 7.—This mission's launch windowopened at 1518; liftoff was

at 1520:17, A ugu st17, 1966. G rand B aham a roseat 1521. NominalJo-hannesburg r ise was 1547, but acceptable two-way Doppler was notachieved un til 1558:24. Telem etry in dica ted tha t the Type-I o rienta-tion had been completedand had required 28 gas pulses.

Near-Earth trackingwas generally excellent, exceptfor some drop-outs as indicated in figure 20a. Due to an operator error aboard theSword K n o t , the spacec raft separation m ark eventwas not recorded.This error was a t t r ibuted to thefact tha t the Sword K no t d id n ot re-ceive mission instructionsuntil F—1 day. Early in the launch phase,the spacecraft S-band telemetry signal was some 20 dBhigher thanexpected.

Pioneer 8.—Under an overcast sky,liftoff occurred at 1408:00 GMT,Dec em ber 13, 1967. The flight appea red to be on tim e u n til 480 sec in tothe flight, when the African Dest ruc t L inewas crossed 6 to 8 seclaterthan predicted. At DSS—51 (Johan nesbu rg) , only one-way dow nl inkcontact was made to check the spacecraft status, wh ichwas normal .B e-cause of the short pass and excessive tracking ratesat Johannesburgcaused by the location of the t rajectory,DSS—41 (Woomera) was con-sidered the primary stat ion for first acquisition. Woomera rise andacquisition were at 1455:42. Two-way lockwas established at 1510:52.Telemetry indicated thatthe Type-I orientat ion had been completedsuccessfully.The f irst com m and to thespacecraftwa s sen t at 1535.

A special third-stage telemetrysystem was flown on this mission.I tprovided better data on the eventsfrom third-stage spinup throughspacecraft separation. The third stage proveddifficult to track because

it apparen t ly began tumbl ingafter spacecraft separat ion.The parkingorbits given in table 3— 5 were computed from Antigua data . Predic tsfor DSS—51 and DSS—41 were also generatedfrom Ant igua da ta wi ththe ad dition of nom inal third-stage burn param eters.

Pioneer P.-Liftoff occurredat 0946:29, Nove m ber8, 1968.At 0948:40,DSS-71 (Cape Kennedy)and ETR station reported they had lost the




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hide, the Pioneer-E spacecraft,and theTETR-C impacted in theAtlant icat 11°30.23'N, 55°42.1'W.

During the period following main enginecutoff, the radars trackedsomething that veeredof f at a 45° angle to the r ight of the vehicle trajec-tory. The ident i tyof this object couldnot be de te rmined .

Analysis of telemetry from ETR stations, DSS-71 (Cape K e n n e d y ) ,and downrange MSF N sta t ions indicated thatthe spacecraft was operat-ing normal lyat the t ime the des t ruc t comm andwas sent .

SPACECRAFT PERFORMANCE

The spacecraft were ne arly do rm an t durin g the so-called "powered-

flight" stages. Ab out 5 m in- before launch, thespacecraft was put onin te rna l power, that is, the bat tery.The spacecraft low-gain an ten na2was connected to the t ransm itter driverra ther than one of the TWTsin order to conserve battery power. Consequently, only about 40 mWof signal power was broadcast un til the TW T was switched on. House-keeping telemetry during launchwas set at 64 bps-a relat ivelylowrate—in order to increase the likelihood of obtaining good diagnosticdata at a lowpower level if the TWT failed to turn on properly.

Assoon as the

spacecraftseparated

fromthe Delta third stage,thebooms and Stanford an ten na au tom at ica l ly deployedand locked into

position. Powerwasapplied to the TW T and theorien tation subsystem ,again automatically.The Type-I orientation maneuver then beganandproceeded in the m an ne r describedin Ch. 4,Vol. II . When the low-gainantenna was switched from the transmitterdriver to the TWT, the telem-etry signal from the spacecraft fadedfor about a minute whi lethe TWTwarmed up. B y the t ime Johanne sburgrose, the spacecraftwas trans-m it t ing about 7W. I t w asfully operation al and had completed oneType-Iorientationm ane uver. Upon acquisit ion,the firstcom m ands generally sentwere: (1) sw itch to 512bps, and (2) repeat theType-I orientationmaneuver.

Pioneers 6 through 9 successfully went through the above sequenceof events w i ththe exceptionof Pioneer 9 wh ich experiencedthe switch-ing problem described ea rlier.



C H A P T E R 4

From DSS Acquisition to the Beginning of

the Cruise Phase

SEQUENCE OF EVENTS

T H E P E R I O DOF S E V ER A L H O U R Sbe tween the initial acquisition of thespacecraft by one of the DSSs and the begin nin g of the c ruise phase

encom passed several eve nts crucial to the success of the m ission:(1) Two types of orientat ion m ane uvers(2) Experiment turn ons(3) The first thorough assessmentof space craft operation al condition

in flight(4) The first passes overall participating DSSs.

Prior to DSS acquisi t ion, the spacecraft autom atical ly w en t throughthe Type-I or ienta t ion maneuver.This event was started by micro-switches triggered when the deploying appendages locked into position.B y the t ime the spacecraftwas acquired by DSS, spacecraft powerwason and the t r ansmi t t e r w as sending te lemetry.In addit ion, the spinaxis was almost perpendicular to the Sun line by virtue of the automaticType-I or ienta t ion maneuver.

The first command dispatchedaf te r a two-way lock had been estab-lished was usually that which changedthe telemetry bit rate fromFormat C, 64bps, to Format C, 512bps. Next , a command in i t ia t ingthe Type-I orientat ion m ane uver was sent torefine the a l ignment madeautomat ica l lyprior to acquisition and, more impor tant , to preclude thepossibility tha t the autom at ic or ienta t ion sequence m ay have term inatedpremature ly. The third in the series of prepara tory commandsw asUndervoltage Protect ionOn, but this was sent only if analysis by theSpacecraftAn alysis and Com m and (SPAC) G roup ( located at the SFOFduring laun ch) was con fiden t tha t the spacecraft power level wa snor-

m al an d that the spac ecraf t wa s ope rating properly. F ollowing the space-craft 's exec ution of Un de rvoltage P rotection O n, the Pionee r was readyfor exper iment turn on and the a l l - important Type-II or ienta t ionmaneuvers.

Experiment Turn-On

The Pioneer scientific instruments were turnedon by c o m m a n ddur ing the first pass over Johannesburg (DSS-51). The planned

45




sequences for the Block-I and Block-II spacecraftare indicated below.Usually, experiment turn-ons were separatedby other spacecraft statuscommands, instrument cal ibrat ion commands, and, in the case of Pio-

neer 6, the part ial Type-II orientat ion commands.The actual eventsaredescribed laterfor each missionin chronological order.

Exper imentTurn-On Sequences

Block I Block II

A m e s plasma Goddard cosmic dustG oddard m agnetometer Ames plasmaMIT plasma Am es m agnetometer

Chicago cosmicray . TR W electric fieldGRCSW cosmicray GRCSW cosmicra yStanford rad io propaga tion Sta n ford radio propagation

The reasoning behindthe above sequencesw as that those instrumentsm easur ing im portan t n ear-Ear th phenom ena, par t icular ly in the trans i-tion region as the spacecraft passed throughthe magnetosphere, shouldbe tu rned on and calibrated first. General ly, about20 m in were sched-uled between each exper iment turnon. The Stanford Radio Propaga-

t ion Exper im en t , which requiredthe t ransmissionof signals from Stan-ford Universi tyat Palo Alto, was usual ly not tu rned on u n t i l jus t be-fore the firstGoldstone (DSS-12) pass.

Orientation Maneuvers

The purpose of the Type - I I maneuve rwas the ro ta t ion of the space-craf t spin axis abou t the Sun l ine un t i l the spin axis w as perpendicu la rto the plane of the eclipt ic . As expla ined more ful ly in Vol. I I , thism a n e u v e r w as normally control led from Goldstone wherethe Opera-t ions O rienta t ion Director (OOD) m axim ized the te lemetry s ignal re-ceived from the Pioneer ' s h igh-gain te lemetry antenna. General ly,hundreds of Type-II orientat ion commands were relayed to the space-craf t , each giving riseto a pulse of gas from the or ienta t ion subsystem .Usual ly, there wa s som e jock ey ing back and forth across the peak inthe signal-strength-reception curve.O n occasion, the normal Type-IIorien tat ion process was interrupted for an otherType-I maneuver toremove any spin-axis m isalignm en t inad ver tent ly in troducedby crosscoupl ing dur in g Type-II m ane uvers . O f ten , or ienta t ion m ane uverswere commanded evenaf ter the beg inn ingof the cruise phase to "trim"spacecraf t a l t i t ude and correct for drift, solar pressureeffects, and otherper turbat ions .

Prel iminary trajectory analysisin the cases of Pioneers 6 and 9 indi-cated that the so-called "partialType-II orientat ion" would be desir-



F R O M A C Q U I S I T I O N TO C R U I S E P H A S E 4 7

able earlyin the flight topreclude an unfavo rab l espacecraf tor ien ta t ionlater in the flight. As discussed in Ch. 4, Vol. II, the low-gain omnidirec-t ional an tenna usedfor com m unica t i on ea rlyin the flight had avery

low gain with in a 10° cone a ft along the spin axis. D urin g the partialType-II or ien ta t ion m an eu ve r, the gas pulses torqued the spin axissufficiently so that G oldstone an ten na s wo uld not be looking up thiscone at the spacecraft dur in gthe final Type-II or ienta t ion maneuver.

The par t ia l Type-II or ienta t ion m aneuvers we re perform ed dur ingthe first passes of the spacecraf t .F or Pioneer 6, Johannesburg (DSS—51)was responsible for this special m an eu ver (table 4-1).But on the Pio-neer-9 flight, it wasdecided to wai t 4 hr un t i l the spacecraft had beenacquired by G oldstone (DSS-12), wherethe OOD and histeam werealready s i tuated for the final Type-II or ienta t ion m an euve rs , whichcustomari ly took place a pass or two later over Goldstone.

The f inal Type-II or ien ta t ion m aneuvers werealways directed fromG oldstone. Special equ ipm en tfor this task as well as the OO D an d histeam were positioned here.The OOD began th is maneuver when con-trol was t ransferred to him from the Space Flight Operat ions Director( S F O D ) . His first commands were : (1) Fo rma t C, 512 bps, whichprovided m axim um engineer ing te lem etryto check spacecraft s ta tus an d(2) Type-I orientat ion, to t r im the orientat ion with respect to the Sunline. If all seemed to be going well,the c o m m a n dwas given to reducethe engineering telem etry rate to 16 bps so tha t no data w ould be losti f the high-gain antennawas switched on and i t happened to haveGoldstonein one of them i n i m aof its lobed gain pa t tern . (See an ten n apatte rns in Ch. 4, Vol. II . ) N ext , the OO D com m and ed the space craft

TABLE4—1.—DeepSpace Stations P articipatingin Orien ta t ionManeuve r s

Or ien ta t i on Pioneer Pioneer Pioneer Pioneerm a n e u v e r s 6 7 8 9

In i t i a lacquis i t ion DSS-51a DSS-51 USS-41 DSS-51InitialType-I or i en t a t i on ' ) DSS-51 DSS-51 DSS-41 DSS-51P a r t i a l

Type-II orientation DSS-51 - - DSS-12Fina lType-II orientation DSS-12 DSS-11 DSS-12 DSS-12

"DSS-11, Goldstone; DSS-2. Goldstone; DSS-tl, Woomera; DSS-51, Johannesburg.6 The first Type-I orientation is a u t o m a t i c and occurs before and during DSS acqui-

sition.



48 THE I N TE R P L A N ETARY P I O N E ER S

to switch from the low-gain om nidirect ional an ten n ato the high-gaindirect ional antenna.This an t enna had to be used if telemetry was tobe received from deep space. The spacecraft was now ready for the final

Type-II orientat ion commands.B y direction of the OOD, blocksof Type-II orientation commands

were tran sm itted to the spacecraft. B ecause each separate com m an dreleased a single gas pulse which torquedthe spin axis onlyabout 0.3°,blocks of up to 30 commands had to be used to achieve noticeablechanges in the signal strength detectedby the Goldstone stat ion.Inpractice, each block of commands was followed by a shortperiod ofanalysis, during which primary interestwas focused on the plot of re-

ceived signal stren gth ve rsus the n um be r ofType-II commands t rans-mi t t ed .As fur ther blocksof comm ands were sent,the plots would showdefini te m i n i m a and maxima character is t icof the Pioneer high-gaina n t e n n a . The major lobe was usual ly easy to recognize by its size.Nevertheless,further commands were issued beyond this peak unti l thesignal strength had been roughly halved.This procedure insured thatthe main lobe had t ruly been found , and it permit ted the OOD'sengineers to compu te the n u m b e r of commands be tweenthe m a x i m u mand half-power point.It was then possible to re tu rn to the m a x i m u mby t r ansmi t t inga fixed n u m b e rof commands .

Interspersed withthe above sequence of blocks of commands wereoccasional Type-I o rien tat ion com m ands which, as m en tioned earlier,were necessary to reduce theeffects of cross-coupling betw een the twodegrees of freedom.These Type-I m ane uvers were com m anded only a tm a x i m a in the an tenna pa t t e rn wherethe spacecraft telem etry couldbesafely switched to 512 bps. Only at 512 bps wass ta tus data t ransmit tedfaster than the autom at ica l ly genera tedType-I gas pulses.

A few reversals of the Type-II torquing sequence were also com-m anded to insure the OO D that the ent i re or ien ta t ion subsystem wasworking satisfactorily. I t would have been disastrous to reach thehalf- 'power point on the other sideof the s ignal -s trength m axim umand findthat bac ktracking to the m axim um w as im poss ible .

Usually, the Type-II m ane uvers were in ter rupted severa l t im esfora half hour or more in order toassess the performance of thescientificins t ruments . FormatB and thehighest bit rate commensura te wi ththe

spacecraftsignal s trength were comm andedduring these periods.Upon the successful complet ion of the Type-II or ien ta t ion m aneu ver,

the Type-I or ienta t ion commandwas given once more.Then, the space-craf t was placed in its cruise mode, witha te lemetrybit rate of 512 bps,Fo rma t B . Spacecraftstatus was checked a final t im e, and, to t e rmina tethe m aneuvers , the O O D sent the O rienta t ion P ower O ff com m and. The



F R O M ACQUISITION TO C R U I S E PHASE 49

OOD then transferred mission control to SFOD at the SFOF, and thecruise phase began.

The P ioneer orientat ion m ane uvers were unique . Despite consider-

able ini t ial skepticism aboutthe feasibil i ty of the whole concept, them a n e u v e r sproved relativelyeasy to carry out and control in practice.Other small and moderately sized spacecraft, American and foreign, haveadopted similar alti tude -con trol strategies.

Predicts

Upon acquisi t ion, the SP AC group at the SFO F in P asaden a beganto generate orbital data.The first orbit based on data from the first

acquisition station w as usually available about 1.5 hr af ter launch.O rbital data were teletyped to Am es R esearch Cen ter where stat ion lookangles were computedfor DSS—41, DSS—51, and DSS—12. Earth-space-craft-Sun angle computat ions were also computedand teletyped to theSFOD and the OOD at Goldstone.

PIONEER OPERATIONS—ACQUISITION TO CRUISE PHASE

The Pioneerflights generally adheredto the scenario jus t described.Each, however, wasdi ffe ren t in several ways. The best tec hn ique todescribe thesespecific differencesand , in addit ion, conveythe flow ofevents , is by chronologically recordingthe highlights of each flight fromDSS acquisition to the beginning of the cruise phase.Tables 4— 2to 4-5assemble these important events.For the purpose of i l lustration,Pioneer6 eventsare presented in more detai l thanthe other threeflights.

TABLE4-2.—Highlights of the Pioneer-6 Flight:

Acquis i t ion to CruiseDate,G M T Event and remarks

Dec. 16, 19650759 Init ial downlink acquisi t ion byDSS-51.0800 First tele m etry signals indic atedt h a t the Type-I or ienta t ionwas in progress

and spacecraft n o r m a l .0804 Type-I orientation completed.An e s t i m a t e d386 ±6 gas pulses were required,

corresponding to a rotation of 64.1°± 1.0°.

0813 Type-I or ienta t ion command given.No gas pulses indicatedby te lemetry in -ferring that the autom at ic Type-I m aneuver had beensuccessful.

0824 Undervoltage ProtectionO n c o m m a n d tr a n s m i t t e d .0825 In it ial dow nlin k acq uisi t ion at DSS-42.0835 The signal receivedfrom the spacecraft began to fade rapidly and"lock" w as

lost by the com puter. Telem etry indicated thata signal w as present in bothreceivers. Although both spacecraft fai lurean d poor spacecraft orientation




TABLE4-2.—Highlights of the Pioneer-6 Flight:Acquisition to Cruise—Continued

Date,G M T Event and remarks

were suspected at first, the problem was finallya t t r i b u t e dto a normal butunforeseen phenomenonof coherent operations.

0851 Firstof 33 counterclockwiseType-II orienta t ion commands sentfrom DSS-51as part of partial Type-II orientation maneuver.No change in signals t rength was noted. The infere nc efrom the spacecraft an tenna pa t te rn wastha t the spin axis had changed eitherfrom 125° to 135° or from 60° to 70°with respect to the North Ecliptic Pole.

0914 Am es P lasm a Exper imen t turned on.

0931 First of 32 addi t ional Type-II or ienta t ion com m ands sent .0957 MI T P lasm a Experim en t turned on. Received signal strength increased 2 dB ,

assuring the OOD that the first change had beenfrom 125° to 135°. Withthe spacec raft axisnow between 140°and 150°, the par t ia l Type-II orienta-tion maneuver was terminated.

1013 Form at-A comm and executed.1031 Chicago Cosmic-R ay Expe rim en t turne d on.1050 GR CSW Cosmic-Ray Exper im ent tu rnedon.1110 Stanford R adio P ropagat ion Exper iment turn ed on.1130 Type-I orientation com m an d sent. Single gas pulse indicated.

1255 Spacecraft pene trated m agnetosphere 12.8 radiifrom Earth.1710 Earth-solarwind bow shock penetrated at 20.5 Earth radii.1912 First Stanfordradio propagation data on teletype.2003 First acquisitionby DSS-12.2100 Fi rst comm andl ink t ransfer, DSS-51 to DSS-12.

Dec. 17, 1965 ,2008 Second acquisit ionby DSS-12.2120 Control transferredfrom SFOF to DSS-12 for completion of Type-II or ienta-

tion m a n e u v e r.Also, first data sent to exper imentersfrom Ames Tape Proc-essing Station.

2128 Type-I orientation com m and sent. Seven gas pulses coun ted.2130 Telemetry changedto 16-bps m ode.2137 Spacecraf t commandedto Format C, 16 bps.2158 Spacecraft transm itter switchedto high-gain an tenna .2210 Blockof 33 counterclockwise Type-II or ien ta t ion comm ands sent1 min apart .2250 Telem etry bit rate changed to 512 bps.2254 Type- I o r ien ta t ion comm and givento correct for cross coupling. Four pulses

noted from spacecraft telemetry.2321 Block of 67 counterclockwise Type-II orienta tion com m ands dispatched1

min apart.

Dec. 18, 19650031 Ten more Type- I I com m ands sen t.0048 F our gas pulses noted wh en Type-I orien tation sequence was repeated.0114 Blockof 15counterclockwise Type-II or ienta t ion com m ands sent .0137 O n l yone gaspulse counte d when Type-I or ienta t ion sequencewas repeated.



F R O M ACQUISITION TO C R U I S E PHASE 51

TABLE4—2.—Highlightsof the Pioneer-6 Flight:Acquis i t ion to Cruise—Concluded

Date,

GMT Event and remarks

0144 Block of 3 clockwise Type-II orientation commands sent to assure OOD thatbacktracking to max imum antenna lobe was possible.

0148 Open-ended block of counterclockwise Type-II orientation commands started.A total of 27 were sent.

0220 Three gas pulses noted as Type-I orientation sequence was repeated.0223 Block of 10 clockwise Type-II orientation commands sent.0345 Second block of 10 clockwise Type-II orientation commands sent.0409 One gas pulse noted when Type-I orientation sequence was repeated.

0411 Orientation Electronics Off command executed.0413 Format-A command executed.0424 Mission Control returned to SFOF. Orientation maneuvers over; cruise phase

began.

TABLE4-3.—Highlights of the Pioneer-7 Flight:Acquisi t ion to Cruise

Date,GMT Event and remarks

Aug. 17, 19661548 Initial acquisition by DSS-51. First telemetry indicated that Type-I orienta-

tion maneuver was in progress and that the spacecraft was functioningn o r m a l l y.

1557 Coherent, two-way lock established by DSS-51.1600 Bit rate commanded from 64 to 512 bps.1611 First acquisition by DSS-42.1621 Signal received from spacecraft dropped rapidly.1625 Due to ground station problems at DSS-51, the command l i n k was transferred

to DSS-42. Apparently, DSS-51 was tracking Pioneer 7 on a sidelobe of theground antenna.

1702 Spacecraft entered Earth's shadow as indicated by bus-voltage telemetry.1739 Spacecraft emerged f rom Earth's shadow.1746 Battery on spacecraft turned off for 11 m in due tohigh charging current over-

heating partially discharged battery.1810 Undervoltage Protection On command transmitted.1815 Experiment turn ons began. Completed at 2015.

Aug. 18, 19660426 First acquisition by DSS-11. (DSS-12 was engaged in tracking other space-

craft.)

Aug. 19, 19660429 Second acquisition by DSS-11. Type-II orientation maneuvers commanded

from DSS-11 during second pass. Required 191 Type-II commands.




TABLE4-4.—Highlights of the Pioneer-S Flight:Acquis i t ion to Cruise

Date,G M T E v e n t and remarks

Mar. 29 , 19681443 DSS-51 acquired first spacecraft te lemetry. Telemetry indicated that al l

spacecraft subsystem s we re perform ing no rm ally.1455 In itial ac quisition at DSS-41.1457 DSS-41 acquired one-way lock.1535 Spacecra f t com m andedfrom 64 to 512 bps.1538 Telemetry indicated periodicfluctuation inpr imary bus voltage.1550 Goddard CosmicDust Exp erim en t turne d on. B y 2030, al l expe rime nts were

on.Orientation power turned on during third pass overDSS-12.

Apri l 1, 19681900 Orien ta t ion poweron.

Type-I orienta t ion m an euv er performed autom at ical ly. Twen ty-eight gaspulses noted.

1945 Type-I or ienta t ion m an euv er com m anded. Two valve pulses noted.2000 A n o t h e rType-i or ien ta t ion m aneuv er comm anded .O n l y one valve pulse this

t ime.

2030 Type-II or ienta t ion counterc lockwise com m and sent . Novalve pulse recorded.2045 Type-II or ienta t ion c lockwise com m and sent . On e valve pulserecorded, asexpected.

2100 Again a counterc lockwisevalve pulse was atte m pte d, and again the telem etryshowed that noneactual ly occurred.

2115 Type-II orienta t ion counterc lockwise com m and sent throughother spacecraftdecoder. Still the valve did not pulse. The im plication was tha t the Sun-sensor thresholds had degraded just as they had on P ioneers 6 and 7 despitethe thicker cover glasses tried on Pioneer 8. (See Ch. 4, Vol. II.)

2130 Type-I or ienta t ion com m and dispatched. Telem etry indicated a singlevalve

pulse.2145 C o m m a n d sent to turn off orientation powerand enter cruise mode.

TABLE4-5.—Highlights of the Pioneer-9Flight:Acquisi t ion toCruise

Date ,G M T E v e n t and remarks

Nov. 8, 19681012 M om en tary signal picked up at DSS-51.1024 In i t ia l acquis i t ionby DSS-51. Ac quis i t ion delayedby a mal func t ion ingdriver.

Predictswere also late. F irst telem etry (one -way m ode) ind icated spacecraftsystemswere all performing n ormal ly.

1030 Two-way coherent mode established between DSS-51 and spacecraft.1045 Spacecraf t commandedto switch from 64 to 512 bps.



FROM ACQUISITION TO CRUISE PHASE 53

TABLE4-5.—Highlights of the Pioneer-9 Flight:Acquis i t ion to Cruise—Concluded

Date ,

G M T Event and remarks

1046 Type-I o ri e n ta t io n m a n e u v e r co m m a n d e d .1047 Three-way lock withDSS-51 and DSS-42 established.1100 Undervol tage Protect ion On command sent .1130 Firs t exper iment turnedon. On the firstpass over DSS-12, a part ial Type-II

or ienta t ion m an euv er was perform ed. Atotal of 58 counterclockwise pulseswere t r ansm i t t ed , ro ta t ingthe spacecraft spin axisan estimated 15°.

Nov. 9, 19682215 First of the final Type-II or ienta t ion commands were t ransmitted from

DSS~12.A to ta l of 250 coun terclockw ise pulses were comm anded beforeth esignal m a x i m u m w as reached. Three test clockwise pulses were initiatedtoinsure tha t the re turn to s igna l max imum cou ldbe made . A total of 26clockwise pulses brought the spin axis back to maximum after the 6.7-dBpoint beyond them a x i m u m was reached.

Nov. 10, 19680600 Type-II orientat ion complete. Pioneer9 enters cruise mode.



Page Intentionally Left Blank



C H A P T E R 5

Spacecraft Performance During the CruisePhase

TH E P I O N E E RS P A C E C R A F T W E R ED E S I G N E Dfor a m i n i m u m life of 6months each, and each greatly exceeded thisgoal. In fact , each

spacecraft f u nc t i o n e d we llfor several years , co nf irm ingin their longevi-ties the design decisions m ade b y Am es and TR W System s in the early1960's. This chap te r is concerned wi th spacecraf t performancein orbitaround the Sun: How did each subsys tem perform in prac t ice? Whatcomponents and designfea tures finally encountered t rouble?This intro-spection is well w or th w hi le becausethe basic P ioneer design philosophyhas proved so successful t h a t mu c hof it is being applied to other space-

craf t dest ined for the outer p lanets , suchas the Jup i t e r fly-by probes,P ioneers F /G , w hich require years ra ther th an m on thsof successfuloperat ion.

As a chronological frameworkfor the following discussionof space-craf t performance, table5-1 provides a list of major engineeringandscientificevents du r ingthe cruise phase.An engineering event ,of course,is one invo lv ingsubsystem performance; say,the fa i lure of a key com-ponen t . B ecause im provem ents in g round suppor t eq u ipm ent have beenso cri t ical to ex tend ing P ioneer opera t ionto greater and greater dis-tances, some of these changesare also presented in the chronology. Ascientif ic ev e n t m i gh tbe a solar flare or the passing of the spacecraf tbehind the Sun.Thus, table 5-1 also ident i f ies astronomical events ofsignificanceto the ne xt chap ter which dealsw i t h scientificresults.

P IONEER-6 PERFORMANCE

The nom ina l P ioneer-6 mission ex tendedfrom the laun ch date (De-

cember 16, 1965) to J u n e 13, 1966—a to ta l of 180 days. However, be-cause spacecra f t pe r fo rmanceat the end of 180days con t inued to begood and the 210-ft dish at DSS-14 became ava i l ab lefor long distancetracking, the mission w as exten ded . (All subsequentPioneer missionswere also extended,as spacecraf tl i fe t imes greatly exceededthe 180-daydesign leve l.)

Al though each Pioneer surpassedthe goals set for it,each of the space-craf t provided it s share of minor problems.O n Pioneer 6, for example ,

55




56 THE INTERPLANETARYPIONEERS

TABLE5-1.—Major Events During the Cruise Phasesof Pioneers 6, 7, 8, and 9

Date, GMT Event

Pioneer 6

Dec. 23, 1965 F irst G oddard m agne tom eterflip c o m m a n dexecuted.Dec. 24, 1965 First D ut y Cycle Store mode co m m an de d due to first lack of DSS

coverage.Jan . 3, 1966 First acquisi t ion by a DSS stat ion w itho ut G OE equipm ent; DSS-61

(Robledo. Spain).Jan. 13, 1966 Space craft con trol shared between Am esand SFOF for the first t ime.Feb. 23 , 1966 Transfer of mission controlto Ames completed.

M a r. 2, 1966 In fer ior con junc t ionor syzygy, with spacecraft 1.84° belowSun asseen from Earth .Mar. 17, 1966 B it error rate a t DSS-12 reaches lO'3; spacecraftbit rate reduced from

256 to 64 bps.Apr. 13, 1966 Bit rate reduced from 64 to 16 bps. Pioneer 6 34.2 million km from

Ear th .Apr. 29, 1966 Spacecraft receiver 2 switched to high-ga in a nten na .May 8, 1966 B it rate reduced from 16 to 8 bps. Pioneer 6 55.3 million km from

Ear th .May 20 , 1966 P erihelion; spacecraft64 701 502 km from Ear th , 121 821 430 km (0.814

AU) from Sun.J u n e 4, 1966 Type-I or ienta t ion maneuver ; numberof gas impulses indeterminate(4 to 10) . Type-I I o r ien ta t ion m ane uverto confirm spacecraft al t i-tude .

J u n e 9, 1966 Type-II orientat ion m an euv erfor the purpose of a t t a in ing a morefavorable spacecraft al t i tude for the extended mission. Bat teryswitchedoff .

July 11, 1966 Stan ford radio propagat ion expe r ime nt turnedoff because spacecraftwas too far away.

Dec. 16 , 1966 Magnetometerflipped by c o m m a n d .

Nov. 23, 1968 Superior con junc tion . Exce llent scientif ic data acquired as spacecraftpasses behind the S u n .Nov. 28, 1969 First s im ult an eo us trackin g of Pioneers 6 and 7 in "radial-spiral"

exper iment .July 6, 1970 Magnetometer data all zeros.Oct. 26, 1970 First s im ulta ne ou s track ing of Pioneers 6 and 8 in "radial-spiral"

exper iment .Oc t . 30, 1970 B it rate of 64 bps now standard.

May 19, 1971 Pioneers6 and 8 al igned wi th Ear th .

Pioneer 7Aug. 25, 1966 Magnetometerflipped byc o m m a n dfor first t ime.Aug. 31, 1966 TWT 2 switchedin to replace erratic TWT 1.Sept. 20, 1966 Syzygy, P ioneer 7 enters Earth 's magn etic tai l .Nov. 6, 1966 Went to 64 bps becauseof high error rate.Jan . 19, 1967 L un ar occ ultat ion passfrom DSS-12.Mar. 16 , 1967 Type-II orientat ion maneuvers.



SPACECRAFT PERFORMANCE 57

TABLE5—1.—MajorEvents During the Cruise Phasesof Pioneers 6, 7, 8, and 9—Concluded

Date, GMT Event

Mar. 21, 1967 Bit-error rate of 10" 3 reached with 85-ft antenna. Goldstone trackingcontinued using narrowed bandwidth and lowered noise tempera-tures.

June 13, 1967 Battery commanded off.A u g . 17, 1967 Type-H orientation maneuvers.Jan. 23, 1968 DSS test with linear polarization cone.Feb. 16, 1969 Lack of Sun pulses noted in spacecraft telemetry. These returned later.M ay 7, 1969 Undervoltage problems. (See text.)Nov. 10, 1969 Aphelion.

Nov. 28, 1969 First simultaneous tracking of Pioneers 6 and 7 in "radial-spiral" ex-periment. Battery turned off.

Pioneer 8

Jan. 17, 1968 Syzygy, Pioneer 8 in Earth's tail.

Jan. 25, 1968 Magnetometer flipped by command for first time.

Jan. 27, 1968 Spacecraft emerges from geomagnetic tail.

Feb. 9, 1968 Type-I and partial Type-II orientation maneuvers.

Mar. 30, 1968 Type-I and Type-II orientation maneuvers revealed that Sun-sensor D

w as inoperative. Battery turned off.June 27, 1968 Another orientation maneuver attempt showed that Sun-sensors A, B,

and C were also out of action.

Sep. 21, 1969 Battery commanded off.

Jan. 20, 1970 Began electromagnetic interference tests to determine whether God-dard cosmic-dust experiment was being affected by spacecraft.

Oct. 26, 1970 First simultaneous tracking of Pioneers 6 and 8 in "radial-spiral" ex-periment.

M ay 19, 1971 Pioneers 6 and 8 aligned with Earth.

Pioneer 9

Jan. 14, 1969 Solar-array temperature on this inbound fl ight had begun rising, caus-ing the primary bus voltage to decrease. Battery was disconnected.

Jan. 30, 1969 Inferior conjunction or syzygy.

Feb. 5, 1969 Special test using Type-I and Type-II orientation commands showedt h a t the spacecraft orientation subsystem w as working well, in fe r-ring that the Sun-sensor ultraviolet filters had solved the Sun-sensordegradation problem.

A p r. 8, 1969 First perihelion at 0.754 AU, which was within the 0.8-AU design goal.(an. 20, 1970 Began electromagnetic interference tests to determine whether God-

dard cosmic-dust experiment was being affected by spacecraft.

Sep. 29, 1970 Ames magnetometer turned off temporarily to eliminate 1.9-dB degra-dation of Stanford radio propagation experiment.

Dec. 18, 1970 Syzygy.




the gas leak in the orien tation con trol subsystem caused som e concern.The degradation of the Sun sensors plagued every Pioneer until Pio-neer 9's ultravioletfilters finally solved theproblem. Future designers of

long-lived spacecraft shouldbenefi t from Pioneer experience; therefore,these summaries of engineer ing performanceare organized on a sub-system basis.6 Many of the observations concerning spacecraft design alsoapp ly to the rest of the space cra ft in the series.

Orientation Control Subsystem

The ini t ial Pioneer-6 orientat ion maneuvers have already beende-scribed in Ch. 4. The orientation control subsystemoperated flawlessly

during these maneuversan d also during the at t i tude adjus tments madein June 1966 to prepare the spacecraft for the extended mission. Thefact that these maneuvers were executedsuccessfully at the end ofnomin a l life indica ted tha t the gas leak that had developed duringthelaunch phasedid not compromise the mission at all. The shape of thegas pressure curve drawnfrom telemetered data (fig.5 — 1 )impl ies tha tthe gas leakage ratewas propor t ional to a pressure less thanthe bot t lepressure itself. The inf ere nc e is tha t gas escaped through the relief valveor a poorly sealed nozzle valve. At the conclusion of the June 9, 1966,m a n e u v e r,the gas pressure w as approx imate ly100 psi, and leakage w asapparently near zero. A reconstruction of the Pioneer-6 spin rate is pro-vided in table 5-2. A pp ar e n tly the gas leak was responsible forslightchanges in the spin rate.

Thermal Control Subsystem

N o problems arose withthis subsystem; a ll temperatures werem a i n -t a ined well wi th in the des ign l imi ts . Al l temperature measurementsgradual ly rose as the spacecraf t approached perihelion 155 days af te rlaunch, fal l ing slowly af te rwards . Approx imate ly on e m o n t h af te rlaunch, predict ions were made of spacecraft temperatures at 0.9 and 0.8A U based upon kn ow n orb i tal condit ions and the resul ts of the the rm al-vacuum tests.All except three parametersfell within 2.5 percent of thepred ict ions (f ig. 5-2) . The ni trogen t em pe ratur e was off 4 percent andthe two Sun-sensor temperatures, 6 percent , a t 0.814 AU. In addit ion,the upper part of the solar array ran at a higher-than-expected tempera-

ture. Minor discrepanciesin spacecraf t the rm al -vacuum sim ula t ionan dthe prot rus ion of the Sun-sensor shields acc ounte dfor these larger-than-expected devia t ions .

6 These per fo rmance summar ie sare based largely upon discussionsin the TRW Sys-tems final report: Pioneer Spacecraft Project , Final ProjectReport, Rept. 8830-28,Dec. 1969.



S PA C E C R A F T P E R F O R M A N C E 59

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TABLE5-2.—Early Pioneer-6 Spin-Rate History

Estimated spinStage rate, rp m

After boom de ploym en t 58. 88After the automatic Type-I orientation 59. 01Before the partial Type-II orientation 58. 99After the par t ia l Type-II orientation 59. 11Before the J u n e 1966 m ane uve rs 57. 77After the June 1966 maneuvers 51. 79

Electric P ower SubsystemIni t ia l te lemetry conf i rmed tha tthe spacecraft power supplywas op-

era t ing no rm ally (fig. 5-3). Du ringthe au tomat i c Type-I orientat ionmaneuver, the pr imary bus showed evidence of a r ipple, but severalgroups of high-bit-rate, Format-C, telem etry da ta tak en laterin therevision did not indicate an y ripple.

Right af ter boom deployment , the ba t t e ry w as recharged at an aver-age 0 .1 A. Fif teen m in later, the charging current dropped to 0.024 A,

and a f t e r 4 hr the bat te ry w as tr ickle charging or floating. OnJune 9,1966; the bat te ry was switched offthe pr imary bus as aprotective measure.The spacecraft load history is summarized in table 5-3 and figure 5-4.

Over the years the performanceof the solar array has been degraded bysolar particles, but th is has not been considered a serious problem be-cause of the favorable orbit.

TABLE5-3.—Pioneer-6 Electrical L o a d History

Day offlight

11233

3953

156171171208

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64 T H E I N TE R P L A N E TA RY P I O N E ER S

Communications Subsystem

The performance of this subsystem was generally better than pre-dicted during the first 6 months of flight (fig. 5-5). The data in table

5-4 substan tiate this observationfor the March 1966period. Figure 5-1shows the actual bit-error rate for the same period. During these 6

Mar 4 8 12 16 20 24

FIGURE5-5.—Pioneer-6 telemetry bit-error rate during part of Mar. 1966.




months about 3500 commandsfrom the Earth were executedsatisfac-torily by thespacecraf t .

Housekeeping te lem etry indicateda sl ight upward dr i f t of the helix

cur ren t of TW T 1 dur ing the first 6 months . From 7 m A af ter in i t i a lstabilization, the curre nt level crep t up to betwee n 7.50 and 7.75 m Aduring the first 175days. In early 1971,the level had reached an 8.0-mAaverage.The TWT threshold lies within this range,but no fur ther dr i f thas been noted,and no degradation of TW T per formancew as apparen t .The operat ing life of this TW T exceeded the life tests made by them a n u f a c t u r e r.

Infer ior c o n j u n c t i o nor syzygy occurred on March 2, 1966, at 0530for Pioneer 6. As the spacecraft m oved nearerthe Sun , the bit-error raterose as indicated in figure 5-6. The radio noise contributedby the Sunhad , of course, adverselyaffected the signal-to-noise ra tioand thus thebit-error rate. Signal deteriorationwas most severe within 2.5°of theSun. B y mid-1969, the high-gain antenna characteris t icshad degradedto a level equal to those of the low-gain antenna.A mal func t i onin re-ceiver2 prevented the use ofchanne l7.

Structure Subsystem

The spacecraft s tructu re subsystem fun ction edperfectlydu r in g separa -t ion an d boom dep loym en t. The stab il i ty of the signal received by theDSS stations showed fu r the r t ha t the spacecraft was aligned and bal-anced with high precision.

Data Handling Subsystem

Dur ing the first 6 m o n t h sof operat ion, all of the various m odes, for-mats , and bit ra tes were commandedfor one reason or another (f ig.5 — 7 ) .This

subsystem responded properlyto all comm ands . Dur ingthefirst 200 days of operat ion, the spacecraft procured nearly3 bil l ion bi tsof i n fo rma t ionfor t ransmiss ionto Ea rth (table 5-5). These bits fellin the following categories:

Category Bits , mil l ionsSciencedata 2060Engineer ingda t a 160Par i ty check bits 370

Data ident i f ica t ionbits 260Other 20

Total . 2870

About 96 percent of the scientific data were t ransmit tedin Forma t A ,less than 4 percent in Format B , and less than 0.03 percentin Fo rma t D.




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SPACECRAFTP E R F O R M A N C E 67

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F I C U R F .5-6.—The effect of prox imi ty of Pioneer 6 to the Ear th -Sunline of the telemetry data error rate.

The R eal-Tim e Mode of da ta t ransmiss ion was em ployed pred om inan t lywhenever DSS stations wereavailable—in fact, almost all data receivedat Earth arrived via this mode. The Duty Cycle Store Mode providedabout 18 percent of thedata coverage, but because of inte rm it te n t sam-pling of stored data, this mode contributed less than 0.05 percent ofthe da ta receivedat Earth (fig. 5-8).




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Distance from Earth, AU

FIGURE5-7.—Distance limitations for Pioneer-6 telemetry.

PIONEER-7 PERFORMANCE

As the spacec raft beganthe long c ruise phase,all spacecraf tsubsystemsappeared to be o p e ra t i ng no rm a l ly.O n Augus t 25, 1966, however, TW T1 began to disp lay an om alous pe r fo rman cein the noncoherent modeofopera t ion a l though opera t ionw as n o r m a l in the coherent mode.F orexample , the he l ix cur ren t jum pedto 10.2 m A compared to the n o m i n a l6.1 m A, and the te m pe ratu re rose to 180° F against the n orm al 101° F .O n Au g u s t 31, 1966, Am es person ne l dec idedto swi tch in TWT 2.ThisTWT behaved n orm ally in every respect . Except for thisdifficulty, over-come by r e d u n d a n c yin the des ign, spacecraf t performance dur ingthebasic 180-daymission wasexc ellent. Som e subsystem details follow.




TABLE5-5.—Summary of Pioneer Data Acquis i t ionThrough 1969*

Flight

Pioneer 6Pioneer 7Pioneer 8Pioneer 9

Total

Time in solarorbit, months

48402514

127

Bil l ions of bitsacquired

3.0302.2606.0326.518

17. 840 c

DSN telemetrysupport, hrs

6330627144552275

29173

Books ofprinted data b

154118306332910

a Adapted from Table 2, JPL Space Programs S u m m a r y 37-61, Vol. II, p. 13.l>Data printed in a lpha -numer i c fo rmin 1000-page books.« O f this total, 72 percent was scientific information, 6 percent engineering in for-

m a t i o n , and 22 percent pa r i t y and data iden t i f ica t ion .

Orientation Subsystem

The orientat ion subsystemw as turned off at 1102 G MT, August19,1966, af te r complet ing the usu al series of Type-1 and Type-II orienta-t ion m aneuvers . Telemetry indica teda gas leakage rateof about 9 cc /h r,which was well within the specified maximumof 15cc/hr. Some of thesetelemetered dataare listed below. B y 1970, essentiallyall of the ni t ro-gen had leaked away (table 5-6).

O n February 16, 1969, telemetryfrom the spacecraf t indica ted tha tthe space craft wa s no longer gen erat ing Sun pulses. The precise tim eof failure is u n k n o w n , but i t was between February9 and 16. Theopinion w as that Sun-sensorE had degraded during the 914 days offlight to thepoint where the Sun no longer activated it .This fai lure was,all Sun sensors except those of Pioneer 9 w ith ult rav ioletfilters. The lackof course, part of the ultraviolet degradation problem encountered withof a reference Sun pulse has negated the magnetometer exper imentand

precluded anisot ropy m easurem ents w i th the GR CSW exper im ent .

Communication Subsystem

The pe r fo r m a nceof this subsystemhas been excellent exceptfor thedifficulty of opera t ing TW T 1 in the coherent mode, whichwas m e n -tioned above.All five of the coaxial switches were activatedonce—suc-cessfully. Throughout the mission the redundant receivers weread-dressed o cc asion ally; these, too, worke dflawlessly. On J anua ry 4, 1967,

receiver 2 was connected to the high-gain antenna. After January10, allcom m ands were tran sm it ted to the spacecraft through this receiver.It is inte resting to com pare the perform ance of the P ioneer-7 telem -

etry l ink wi th tha tof Pioneer 6. This is done in tables 5-7 and 5—8, byind ica t ing the d i s tanceat which te lemetrybit rate had to be reducedto keep the bit-error rate below 10~3.




TABLE 5—6.—Sun-SensorE Degradation

Date

Aug. 19, 1966Sept. 2, 1966Oct. 5, 1966Nov. 10, 1966Dec. 15, 1966Jan. 15 , 1967Feb. 15, 1967

G as pressure,psia

21122112 to 20482048 to 19831983 to 1918

191818531789

Bott letemperature,°F

26.323.923.923.921.521.519. 1

TABLE5-7.—Comparative Telemetry Link Performance,Pioneers 6 and 7

Threshold, bps

512256

64168

Pioneer-6range, 10° km

12.418.3

34.357.079.5

Pioneer-7range, 106 km

12.215.0

32.359.176.8

Predictedrange, 106 km

1217

336080

TABLE5—8.—ReceivedCarrier Strengths at DSS Receivers

R a n g e , 106

km

15

1020406080

Pioneer-6signal

s t rength , dBm

-127.5— 139-145—151.5-158-162-164

Pioneer-7signal

s t rength ,dB m

— 127— 139-145.5-152—158.2— 162

-

Predictedsignal

s t rength ,d B m

-125.5-139.4— 145.5— 151.5— 157.5— 161-163.5

Electric Power Subsystem

During all phases of flight the spacecraft power supply operated aspredicted. During the eclipse of the Sun by the Earth, which began ap-proximately 100 m in af te r l if toff, the battery supplied 1.76 A. By the



72 THE I N T E R P L A N E TA RYP I O N E E R S

end of the eclipse, the solar-array temperaturehad dropped to —130° Fand the busvoltage to 24.3 V. Entering sunlight again,the solar arraypicked up the load and began recharging the battery. The cold solar

array generateda bus voltage of about 35 V and acurrent . that saturatedthe current sensorat 0.562 A. To avoid overchargingthe battery whilethe solar array warmedup, the battery was commandedoff for 11 min.When the battery was reconnected, the voltage haddropped to 33.6 Vand the recharging currentto 0.130 A. Equil ibrium condit ions weregradually at tained,and all parameters were normal.

On May 7,1969, near the 1.125 AU aphelion, tests ind icate d th attheundervoltage relaywas being tripped whenthe MIT plasma experi-m e n t was switched to its high power mode.The implication was tha tthe 9-W extra power req uirem en t exceeded the capa bilities of the de-graded solar array.To provide the required power,the Goddardmagnet-ometer and Stanford radio propagation experim ents were turne d of f.This was acce ptable becausethe magnetometer data were useless withoutthe pulses from Sun-sensorE, which was out of action, and the space-craft was beyond the range of the Stanford expe rim en t. The M IT in-s t rument wasleft in a low-power m ode which prevente dit from operat-ing in itsfour highest en ergy steps.

Thermal Control Subsystem

Performancehere has also been excellent. Tem pera tures of the Sunsensors did not deca y as rap id ly as prior an alysis had ind icate d.This wasatt ribu te d to the con servative approach used in the analysis. In thisinstance a conduction path to the spacecraft was not included in theanalysis because it was to difficult to take into account.

During the ascent phase,the af t , uninsula tedend of Pioneer 7 was

i l lumined by the Sun.Plat form temperatures during this phase were afew degrees higher than thoseof Pioneer 6 which was i l lumined on itsinsulated end.After the qrientat ion maneuvers, Pioneer 7 continued tooperate a little warm er as described below .

The equil ibrium temperaturesat various pointson the spacecraftarelisted in table 5-9 for the Pioneer-6 and Pioneer-7 nights.It is interest-ing to note that the Pioneer-7 platformran a fewdegrees warmer thanPioneer-6 and that the solar-array temperaturewas a little lower. Theinference is th at P ioneer 7 was better in sulated than P ioneer 6.

Structure Subsystem

Performancewas good throughout the mission.The absence of rippleon the prim ary bus and signal stab ility at the DSS receivers inferredprecision balanceand al ignment .




TABLE5-9.—Equilibrium Temperaturesat 1 AU ,Pioneers 6 and 7

Telemetry measurement

Sun-sensorASun-sensor BReceiversTWT 1 (operating)TWT 2 (in reserve)TWT converterTransmitter driverDigital telemetry unitData storage unitEquipment converter

BatteryUpper solar panelLower solar panelPlatform 1Platform 2Platform 3Wobble-damper boomHigh-gain antennaLower actuator housingNitrogen bottle

Pioneer 6, °F

588057

103707652626462

60414183575254647327

Pioneer 7, "F

558262

106798152646767

6027278660 '5263647928

Data Handling Subsystem

All formats, modes, and bit rates were usedsuccessfully dur ing themission.


The Earth-escape hyp erbo la for P ioneer 8 was less en ergetic th anplanned. Insteadof occurring at roughly 500 Earth radii, syzygy tookplace at 463 Earth radii. The heliocentric orbit was less eccentric andmore inclined thanthe planned orbit ,but the differenceswere not sig-nif icant . The spacecraft performed normally exceptfor the deviationsnoted below.

Early in the mission, troublewas experienced withthe Am es plasm aprobe, and it wassubse quen tly turne d off . However,the difficulty wasul t imate lytraced to a corona discharge resultingfrom outgassing. Later,

the Am es exper im entwas switched backon, and it operated wi thoutfur ther trouble.

Receiver2 drif ted some what, witha drif t of 10 kHz being measured3monthsafter launch.

During an orientation maneuver in March 1968, Sun-sensorD wasfound to be inoperative. On another orientat ion at tempt in June 1968,




Sun-sensors A, B , and Cwere also foundto be out of commission. Theheavier Sun-sensor covers installedon Pioneer 8 had obviously notsolved the degradation problem.


P ionee r 9, an in bo un d flight, was subjected to increa sing solar rad ia-tion, higher solar-array temperatures, and, consequently, falling busvoltages. To preven t the discharge of the b attery , it wa s switched outon January 14, 1969.

To check the effects of the ul t raviole t n i ters ne wly ins ta lledon theSun sensors, a special test was conducted on February 5, 1969, the 89th

day of flight. Telemetry indicated that Type-Iand Type- I I commandswere executed properly.The ultraviolet nitershad apparently solvedthe Sun-sensor deg radation problem.

The spacecraft reached perihelion at 0.754 AU on April 8, 1969. Thespacecraft wa s designed to pe ne trate to only 0.8 AU . It reached 0.754A U without overheat ing a l thoughthe cosmic-ray expe rim en t reached90° F, its upper l imi t .

A ll spacecraf t systems operated normal ly throughoutthe n o m i n a l180-day mission. Duringthe extended missionin May 1969, the com-munica t i onrange reached 130 mill ion km (78m illion miles) using on lythe 85-ft DSS an ten na s, and a bit-errorrate of 10—3. This extension ofthe com m unicat ion range can be a t t r ibuted to threefactors:

(1) Use of l inea r polarizersat some DSS stations(2) I m p r o v e m e n tof noise temperaturesat the DSSs ta t ions(3) Use of the Convolutional Coder Uniton Pioneer9

L ate r in 1969, the com m un ica t ion range was extended st i llfu r the r to152 mil l ion km (95 mill ion miles) by allowing the bit-error rate toincrease to 10—-. D urin g part of 1970, an improved, low-temperaturecone (an "ultracone") was instal ledat DSS—12. W ith th is im provem en t ,the com m unica t ion r angewas ex tended to 260 mil l ion km (162 m il l ionmi le s ) .

Decoder 2 began operating improperlyin 1969 and is no longer usedfor normal opera t ions .

ConvolutionalCoder Unit (C CU) P erform ance

The CCU, whichis described in Vol. II , wasadded to PioneersD andE as an en gineering e xpe rim en t. I t can be switched in or out ot thete lemetrys t ream . CCU perform anc e has been good, con tr ibut ing abou t3 dB to the com m unica t ion power budget . Ineffect, the CCU has nearlydoubled Pioneer-9 's communicat ion range.

B e t w e e n the November6, 1968, launch and December 10, 1968, the



SCIENTIFIC R E S U LT S 75

spacecraft operated in the uncoded m ode at 512 bps exce pt for CCUf u n c t i o n a lchecks. Since Decem ber10, the CCU hasbeen in almost con-s t an t use except when the spacecraf tis being workedby a DSSw i t h o u t

Pioneer GOE.About January7, 1969, Pioneer 9 was far enough awayfor the CCUto provide a "codinggain" for DSS stat ion s con figured for receiving cir-cularly polarized waves.7 Up to March 6, 1969, GOE-equipped DSSstat ions t racked Pioneer 9 approximately 1000 hr with the CCU in op-eration; 680 of these hours werein the coding-gain region. As a resultof the CCU's coding gain, 4.43 X 108 addit ional bi ts were received dur-ing this period. The 3-dB gainat 5 12 bps w asverified by direct compari-son with uncoded dataat 256 bps. The CCU exper iment has been sosuccessful on P ioneer 9 th at conv olut ional coding is being applied toother spacecraft .

REFERENCE

I . LUMB,D. R. : Test and Prel iminary Fl ight Resul t son the Sequential DecodingofConvolut ional Encoded Data fromPioneer IX . IEEE paper, In ternat ional Confer-ence on Communications, 1969.

7 The Pioneers t ransm it l inear lypolarized signals. A loss is incurred w h e n a DSSantenna receiving circularly polarized signals is used.



C H A P T E R 6

PIONEER SCIENTIFIC RESULTS

T H EC O M P L E T E S C I E N T I F ICL E G A C Yof the Pioneer Program will not bek n o w n for m any years.Scientific papers based uponthe data telem-

etered back from deep space are s t i l l being published in abundance. In-deed, all four successfully launched spacecraf tare stil l activeand con-t inue to add to our scientific store. The Pioneer scientific record oftoday, though incomplete, is impressive; some 137 contributions arelisted at the end of this volum e.These papers and som e of their im plica-tions are sum m arize d in the followin g pages.

The first Pioneer was l aunched in December 1965to add to the sub-s tant ia l f u n d of information that Earth satel l i tesan d planetary probeshad alrea dy discovered d ur in g the first 8 yr of the Space Age. It is im -practical to review here the state of our knowledge of interplanetaryspace as of 1965. However, G lasstone's Sourc ebo okon the Space Sciences11

was published about the same t imeas the launch of Pioneer 6, and thereader is referred to it for background informat ion.

To set the stage prope rly, a brief d escription of the cosm ic set tin g ofthe Pioneer drama is in order. The Sun controls most of what happensin in terplanetary space .In 1965 solar act ivi ty was low and supposedlygoing to get even lower. O f course, the P ioneers were originally plannedto support the world's IQSY program. However, solaract ivi ty, as meas-ured by the sunspot number, beganto c l imb in 1966; by 1969 it hadreached its peak. The Pioneers, therefore, have already monitored solaractivity in deep space for over half a solar cycle. As solar act ivi ty buil tup in the late 1960's, solar flares appeared .moref requent ly, engul f ingwith the i r p lasma an d cosmic radiat ion someof the Pioneers and,onoccasion, the Earth too.These flares were of great interest to science,and the P ioneers, located stra tegic ally arou ndthe Sun, in effect made

the whole solar systema laboratory for Earth-bound scientists.The moreimpor t an t of these flares were noted in the chronology of the last chap-ter. Thus, the physical bac kdrop for the P ioneer program was one ofincreasing solar ac t iv i ty—more plasma-producing flares, more solarcosmic rays, and, in general , more opportunit iesto u n r a v e l the effectsof the Sun on thei n t e r p l a n e t a ry m ed iumand the Ear th .

8D. Van Nostrand, Princeton, 1965.

77





THE GODDARD MAGNETIC FIELD EXPERIMENT(PIONEERS 6, 7, AND 8)

The magne t i c field in in terplanetary spaceis in t im ate ly associa tedwith the hot , ionized plasma that s treams outwardfrom the Sun . I nfact , it is customary to speak of the solar magnetic l inesof force as"imbedded" in the plasma.Thus, data from the Pioneer magnetometersmus t be s tudied in co n j u nc t i on w i th m eas ure me n t s m ad eby the space-craft 's plasma ins t ruments !The G R CSW cosm ic-ray anisotropy experi-m en t was also related to the m agne tom eter in the sense th at cosmic-rayisotropy could beaffected by changes in the s tructure of the magneticfield. In add i t ion , on the Block-II Pioneers,the TRW Systems electric

field exper imen t registers m an yof the same magne tohydrodynamicphenomena tha tare signaled by the magne tome te ran d plasma probes.The m agnetom eter therefore views onlyone dimension of the in terplane-tary plasma which,as we shall see, turns out to be a most complexmedium indeed .

B y Decem ber 1965 whe n P ioneer6 was launched, satelli tes, suchasI M P 1 (Explorer 18) and space probes, had al ready conf i rmed thetheore tical pred iction of a basically spiral solar m agn etic field imb edd edor "frozen" in the streaming solar plasma.The Sun's rotat ion aboutitsaxis imposed the so-called "water sprinkler" patternon the outward lyrush ing plasm a (fig. 6-1). At th e dist an ce of the Earth , the solar plasm ahad a veloci ty of ab out 400 km /sec , and the wa ter-sprinklereffect ben tthe solar magnetic l ines of force unti lthey were incl ined about 45° tothe Sun-Earth line. The IMP 1 magnetometer showed further that thedirect ion of the solar magneticfield would be first directed outwardandthen inward, each condit ion last ing several daysas the Sun 's ro ta t ioncarr ied the ne wly dubb ed"sectors" past the Earth (fig.6 — 1 ) . It wa s first

thought that the sectors might be associated withlarge p l a sma-emi t t i ngareas of the Sun , but some recent theories suggest that smallnozzle-likeregions may be responsible. The sectors also evolve w ith tim e (ref.1) ;there were four separate sectors during the latter part of the 1960's, butthe i r pa t te rn var ied . The P ioneer spacecraf t were ideal p la t f orm sfromwhich to m on itor these gross s truc ture s of inte rpla ne tar y space and alsoinvest igatean y m icros t ruc ture superimposed uponthe sectors.

First Results from Pioneer 6A t app r o x i ma t e l y11 Earth radi i ,the magne tome te rreported a marked

increase in m ag n et ic field fluctuations as shown in figure 6-2 (ref . 2) .9

W ith the p en et rat ion of the ma gne topause at 12.8 Eart h radi i , the f ield

"The first Pioneer-6 r e su l t s were communica tedat a special Pioneer-6 symposiumconvened by the American Geophysical Union in 1966.



79

,IAU

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80 T HE I N T ER P L A N E TA RY P I O N EE R S

9.0 Geocentric distance (/?£•)68°SE longitude of S/C

75

Pioneer 6Magnetic Field data

Dec 16,1965

1100 1130 1330

FIGURE 6-2.—Observat ions of geomagnetic field magnitude near the bounda ry of theregular field, the magnetopause, at a distance of 12.8 R E near the sunsetterminator. The observed magnitude is larger than the theoretically ex-

pected because of the compression of the Earth's magnetic field by thesolar wind. Note the abrupt transition from strong and regular fields toweak and rap id ly fluctuating fields. The lowermost "noise" curve measuresthe rms deviation (y) over a 3O-sec interval of one component of themagnet ic field. Note tha t the increase in noise level as the magnetopauseis approached and the signif icant ly higher noise level when within themagnetosheath. From: ret. 2.

P ioneer-6 results were com pared w ith m agnetom eter readingsfrom

I M P 3 (Explorer 28) (ref. 3) . This was the first time that accuratemeasurementsof the in te rp lane ta ry m agne t icfield had been made fromtwo widely separatedspacecraft . B y considering corotation delays(dueto the Sun's rotat ion ) excellent agreeme nt w as fou n d between the twosets of data. Using these observations, B urlagaand Ness (ref.4) ident i -fied a tangential discontinuity.

General ly, then, ear ly Pioneer magnetometer data tendedto confirmthe Earth shock structure,the magnetopause ,and the spiral sectorstruc-ture of the in te rp lane ta ryfield inferred from previousspacecraf t nights.The strong experimental supportfor a f i lamentary f ines t ructure w asperhaps the m ost intere st ing resultfrom the first fewm o n t h sof flight.

Further Observationsof the GeomagneticTail

O utward-bound P ioneers 7 and 8 carried G oddard m agnetom etersthrough the region whe re the geom agnetic tail wa s expected to exist.



SCIENTIFIC RESULTS

20.00 U T

81

19.00 UT

Pioneer 6Dec 30,1965

Magnetic field andcosmic ray anisotropy

directions projected intoecliptic (viewed fromNorth ecliptic pole)

Field line azimuth

16.00 UTDirection of cosmic rayanisotropy Maximumflux from arrowhead

FIGURE 6-3.—Comparison of interplanetary magnetic field andsolar cosmic-ray anisotropic directions projectedonto the ecliptic plane. From: ref. 29.

This region was crossed by P ioneer 7 between Septem ber 23 and O ctober3, 1966, at distances rangingfrom 900 to 1050 Earth radi i. S im ul tane -ously, results from Ex plorer 33 de m on strated the existence of a tail outto 80 Earth radii .The Pioneerflights presented addi t ional oppor tuni t iesto explore this s trange region "dow nw ind"from the Earth.

A coherent , well-ordered geomagnetic tai l with an imbedded neutralsheet was notobserved by Pioneer 7 (ref. 5) . However, the rapid fieldreversalsrecorded (fig.6 — 4 )are character is t icof the n e ut ra l sheet regionobserved closer to Earth . The con clusion of Ness and his collea gue s atGoddard was tha t the geometry of the tail changes to a complex setof in termingledf i lamentary f luxtubes at severa l hun dre d Ear th radi i.

In a later paper, F airfield com pared P ioneer-7 data w ith thoseob-tained during the same periodfrom Explorers 28 a'nd 33 in the regioncloser to Earth (ref. 6). Comparisons revealed periods when Pioneer 7was recording the s teady, h igher-magni tude solaror anti-solar fieldscharacteristicof the tai l but qui te different f rom the fieldsconnec t ingpast the satellites. The presence ofthese" isolated intervals was inter-preted as due to the tail swee ping back andfor th across the spacecraft inresponse to changing di rec t ionsof p lasma flow. Discon t inuousfea turesof the tai l were foundto connect pastthe three spacecraft at velocitiescom parable to the m easured veloci t ies of thesolar w i n d .



82 THE I N T E R P L A N E TA RY PIONEERS

A Y 1

J^^^

AZ

' ^^^^J^^1500 1600 1700 1800Pioneer 7 Sept 27, 1966

F I G U R E6 — 4.—Detailed 30-sec averaged m agne t icfield observations by Pioneer 7 on Sept.27, 1966, when the field or ien ta t ion and its rapid reversals are character-istic of the neu t r a l sheet region of the geomagnetic tail . From: ref. 5.Throughout the g-h r inte rva l f rom 1500to i800 the field is observed tobe directed either away f rom the Sun (0=i80°) or toward the Sun

Pioneer 8 passed throughthe tail region at 470 to 580Ear th radi i inJanuary 1968. The results here were similar to those obtained fromP ioneer 7 at 100 Eart h rad i i (ref . 7) . The geom agnetic tai l m ay lose thec lea rcu t structure plot ted by Explorer 33 at 80 Earth radi i before itreaches 500 Earth radi i .

Mesoscale and Microscale Structures

Whereas the macroscale s t ructuresof the i n t e rp l ane t a ryf ield—thoses t ruc tures persis t ing 100 hr and more—genera l lyfit theoret ical expecta-t ions quite well, mesoscale structures(1 to 100 hr) andm icroscale stru c-tures (<1 hr) presented new exper imenta l and theoretical problems

and results. Some relevant observationsand interpretations arising fromP ioneer m agne tomete r da tafollow.Direct ional disc on tinuit ie s were correlated early w ith solar cosm ic-ray

anisotropies and expla ined in terms of spaghetti-l ike flux tubes or fila-ments . More thoroughanalysis of Pioneer datahas replaced this typeofmodel witha "discontinuous" model (ref .8) . The newm odel recognizes



84 T H E I N T ER P L A N E TA RY P I O N E E R S

I IDay 356. hr 0-12

-, 2-, 1+. 2+Day 357, hr 12-23

Oo, Oo, 0+, Oo

10

f(Hi) 5X10" 4 2X10 3 5X10 "3 10' 2

I I I Ir(sec) 1800 720 180 60

f(Hz)5X10 4 2X10' 3 5X10' 3 10' 2

I I I Ir(sec) 1800 720 180 60

F I G U R E6-5.—Power spectra of the interplanetary magnetic field components and mag-nitude for two 12-hr periods in Dec. 1965. The dotted l ines indicate in-verse-square dependency. Data are from Pioneer 6, i0 6 km from Earth.From: ret. lO.

observations based on Pioneer-8 telem etry represent ab out wh atonewould expect from a general model of a solar disturbance propagatingthrough space.

(1) A rather s teadyfield of 4 to 6 y wasobserved during the earlyhours of February25.

(2) The field increased rapidlyto near 10 y between 2000and 2022,then it rose slowlyto abou t 14 y.

(3) L ong-period variat ion s were observed betw een 0200and 0500,February26.




(4) A very quie t field of abo u t 6 y occurecl between 2000and 0500,February 27.

(5) The nex t g roup of te lem ete red d a taat 2149, February27, again

revealed a high field (over 10 y). Large variat ion s were noticed.(6) In the last t ime interval telemetered, between 0200, February 28,and 0500, February29, the field h addropped to norm al values .

THE MIT P LA SMA P ROBE(PIONEERS 6 AND 7)The pre l iminary MIT data presented at the American Geophysica l

Un ion P ioneer-6 Sym posium indicate d tha t , f i rs t , sharp changes in theplasma densi ty precededthe dram at ic changesin the magnet icfield re-corded by the G oddard m agnetom eter, and, second,the peaks in n u m b e r

densi ty were fol lowedby periods of increased bulk veloci ty (ref . 14) .The early theoret ical conc lusions dra w nfrom these coordinated measure-m ents have alread y been coveredin the preceding sect ion.

The MIT group later published additional correlations between theplasma-probe and m agnetom eter da ta ( ref. 15) .In this s tudy ,the simul-taneous changesin plasma and magne t ic pa ramete r s were foundto beconsistent with what one would expect from tangential discontinuit ies .High-velocity shears were observed across these discontinuities,thelargest being about80 k m/s e c .The disc on tinuit ie s observedby the M ITplasma probe were un doubted lydue to the same filament boundaries ordiscontinuities discussedin the papers published by the Goddard group.

The MIT plasma-probeand Goddard magnetometer data also showedtha t these disc on tinu it ies hav e preferred direct ions in space, w ith atendency for the solar wind to be fast from the west and slow from theeast. This east-west asym m etry in solar wind veloci ty is a na tura l resul tof the rotat ion of the Sun—thewater-spr inklereffect again. Slow stre am sof plasma tend to spiral more tightly,and fast s t reams are straightenThe con dition exists wh ere by slowand fast plasma streams tendto pushagainst one another. Fast plasma streams push slow plasma awayfromthe Sun and to theeast; fast plasma, in tu rn , is pushed toward the Sunand to thewest. The east-westasymmet rywas shown s triking ly when 3-hraverages of solar wind speed were correlated againstflow angle in theplane of the ecliptic for a 27-day stretch of da ta ( ref . 16) .Figure 6— 6shows a conspicuous peakat zero lag, a posi t ive correlat ion confirmingthe predicted in-phase relat ionship.

The correlation of plasma-probe and magne tomete r da tahas con-t inued to be a-f ru i t fu l way to s tudy the deta i led s t ructureof the solarplasma. For example, the generalform of theoret ical relat ion betweenthe size of a sudde n geom agne tic pulse and the associated change in solarwind stagna tion pressurew as c on f i rmedin this w ay (ref . 17) . Formisanowas also shown that data from the two P ioneer ins t rum en ts m ay be



SCIENTIFIC RESULTS 87

0.5 T

F I G U R E6-6.—Correlation between Pioneer-6 measu remen t s of solar wind speed andangle in the ecl ipt ic plane as a func t ion of lag time. From: ref . 16.

this region. The second region, 1.5-Earth radii thick, was boun de d atthe outer edge by the magnetopause .The electron distr ibutionin thisregion could be expla ined by two models. Using the the rmodynamicm odel presentedby Howe, the dis t r ibut ion m atched thatof a Maxwell ian

having a pressure of abou t 300 e V / c m3

, with the temperature para l le lto the local m agne tic field ab ou t twice that perpen dicular to the f ield.In the third region, the magne toshea thitself, the following parameterswere typical:

(1) Thermal electron energy—40eV(2) Electron speed-2700 k m / s e c(3) Electron temperature- 100 000°KHowe also com pared the results of the M IT and Am es plasma probes

in this region. M IT velocity m easurem en ts were consis tent ly about20k m / s e c higher and well outside the uncer ta in t i esof the MIT experi-m e n t . There was also clear disagreementin the measu remen tof theout-of-the-eclipticf low angle. The densi ty pulse detected by the Amesinstru m en t w hen the shock was crossed could not be de tected by theM IT probe. I t should be recalled, however, that thesetw o i n s t rumen t s




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12 13 14 15 16 17 18 19 20 21

Earth radii

F I G U R E6-8. Pioneer-6 magnetosheath proton observations showing velocity, thermalspeed, and number density. From: ref. 20.




are quite different in concept and that one would expect to have toreconcile discrepancies at this stage of their development.

Passage Through the Earth's TailThe passage of Pioneer 7, an outward bound spacecraft, through the

Earth's magnetic tail was recounted in the preceding section. Duringthis passage on August 17 and 18, 1966, data from the MIT probe clearlyindicated the existence of a tail and the traversal of the neutral sheet(ref. 21). There was also some evidence of a second neutral sheet near

the magnetopause. The data were found to be in general agreement withexpectations from a quasistatic model of the geomagnetic tail, based on

a balance of particle and field pressures (fig. 6—9). Also shown in figure6 — 9is the apparent correlation of a period of low particle flux with theterrestrial observation of a geomagnetic bay (insert).

THE AMES PLASMA PROBE (ALL PIONEERS)

The Block-I and Block-II plasma probes (called quadrispherical elec-trostatic analyzers) built by Ames Research Center record the energy

spectra of electrons and positive ions in the solar plasma as functionsof azimuth and elevation angles (see ch. 5, Vol. II). For a more com-plete understanding of the interplanetary medium, it is essential torelate plasma probe results to the magnetometer data and, of course,the somewhat different perspectives apparent to the MIT Faraday-cupplasma probe and the TRW Systems electric field detector.

Some Early Results

Like the other Pioneer-6 experimenters, the Ames plasma-probe grouppresented preliminary results at the 1966 Pioneer-6 Symposium spon-sored by the American Geophysical Union (ref. 22). Figures 6-10 and6 — 1 1show tw o basic types of data acquired by the Ames plasma probe—energy spectra and angular spectra. The energy spectrum (fig. 6-10)indicates a proton peak at 1350 V , corresponding to a proton velocityofapproximately 510 km/sec. The second peak in the curve was due toalpha particles. However, analysis of subsequent data revealed the possi-

ble presence of singly ionized helium in the solar w i n d — t h e first timethis had been detected. In the angular spectra (fig. 6-11), collector 5consis tent ly recorded, higher fluxes than collector 4. The inference wasthat a ne t southward convect ivef low of plasma existed with respect tothe plane of the ecliptic. There w as also an obvious velocity dependencein ecliptic longitude. It was quite apparent from early Pioneer-6 meas-




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urements tha tthe common assumpt ionsof solar radial flow of plasmaand thermal isotropy were not valid.

The early data also revealed an average solar wind electron tempera-ture of about 100000°K dur ing quie t t imes whenthe solar wind was

blowing a t abou t 290 km /sec , w i th a m ax im um ion tem perature of50 000° K . In terplan etary electrons always seem ho tter th an ions d urin gquie t periods.

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characteristics.

Observations of the Earth's Wake

Pioneers 7 and 8 were outward-bound missions and, as i l lustrated infigure 6-12, swept through the Earth's tail earlyin their flights. In s t ru -ments on both spacecraft detected evidenceof the Earth 's tai l or wake




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with the i r magnetometersan d plasm a probes.The Am es plasma probesdetected the wakes at about 1000 and 500 Earth radii for Pioneers 7and 8 ,respectively ( re f . 23 ) .In each casethe norm al ly quiescent p lasma

ion energy spectra were in te r rupte dby the abrupt changesin the m a g n i -tude an d c urve shape th at one wo uld expect near the tai l b ounda ries.In figure 6-13, thetypical quiescent ion spect rum is comparedwi th

t h a t measured in the Earth 's wake by Pioneer 7. The peaks of the"disturbed" spectraare usual ly one or two orders of m a g n i t u d e lessthan those of quiescent spectra. Further, thereis often a different kindof doub le peak ( ind icatedby the dashed l ines) which infers t h a t the

8 Typical' interplanetary ion spectrum

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ions cm •'sec'1. In this case the first peak of the curve ( the H* peak)

occurs at — $00 V and the second at — '500 V. The second peak is in-terpreted as a high energy tail of the proton energy distribution. Analysisof successive ion spectra show tha t the higher energy dis t r ibu t ion of tengrows at the expense of the lower energy distribution. At t imes only partof the distribution is seen as indicated by the two variations. From: ref.

23-




(4) Possiblythe tai l m ight have d is in tegra ted in t o "bundles"at thesedistances.

(5) I f m agn etic m erging occurred, subsequ ent accelerat ionof

pinched-off gas m ay have caused the disturbe d cond itions m easured.

Plasma Instabilities

Prior to P ioneer 6, few spacecraft were capableof making deta i ledmeasurements of the solar wind. Consequently, the col l is ionless inter-planetary plasma was treated as a s ingle magnetofluid. However, theA m e s plasma probes have revealed thatthe solar proton distributionis defini te lyanisotropic, with the temperature parallel to the local mag-

ne t i c field being larger than tha t perpendicularto the local magneticfield (ref. 24). From these data and basic theory, i t can be shown thatthe anisotropy can be produced by the approximate conservationofmagnetic mom e n t and thermal energy as the collisionless solar plasmaf lowsoutward and the imbedded magne t icfield weakens .The positiveion distributions measured were also unstable with respectto the genera-tion of low-frquency whist lers .The conclusion was that a generalizedform of "firehose" in sta bi l i t y m ust occur withthe growth of whist lersnear the ion cyclotron f requency.

THE CHICAGO COSMIC RAY EXPERIMENT (PIONEERS6 AND 7)

The Chicago cosmic-ray telescopeon the B lock-I P ioneers providedthe oppo r tun i t y for scient is tsto inves t iga tethe direction of arr ival ofcosmic-rayparticles near the plane of the ecliptic. The experiment alsohad a short enou gh t im e resolut ion so th at rapid f luctuations in cosm ic-ray in tens i tycould be recorded. The first test case came shortlyaf ter the

launch of Pioneer 6 whensolar-flare protons were detected on Decem-ber 30, 1965. These ear ly results—someof t h em unexpec t ed—werere -ported at the Pioneer-6 Sy m posium by the Chicago group (ref . 25 ) .

Anisotropy of Solar-Flare Proton Flux

The solar f lare th at erup ted ab ou t 2 weeksaf te r the launc h of P ioneer6 was given an im porta nc e rat in g of 2. Theeffects were noted for alm osta week, as ind ica ted in figure 6-15. In te rpla n eta ry cond it ions during

most of th is period were rem arka blyfree of solar-flare blas t effects capa-ble of m o d u l a t i n g the galactic cosmic-rayflux. Solar protons in theenergy range 13 to 70 MeV firstarrived at the spacecraf t at about 0300UT, December 30 , 1965, with lower energy particles arriving later.Theanisotropy of these protons was str iking (f ig.6-16), with the averagedirec t ion ofpart icle flow ab o u t hal fway between the Sun l ine and the




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angle on e would expect if the particles travelled alongthe "water-sprinkler" spiral l ines. However,the detai led data reveala more com-plex situation:

(1) The direct ion of the peak ampl i tudew as highly variable, chang-in g direction by as m u c h as 90° with in 10 m i n .

(2) Rela t ive to the in tens i t i e sin other directions,the peak i n t ens i tyvaried rapidly.

(3) Occasionally,the angula r d i s t r ibu t ionw as strongly peaked with-in a 45° sector.

(4) Rare ly, tw o int en si ty peaks 180° apart were noted.The strong coll imationof solar protons with energies greater than13

M eV infers tha t there are fewi r regulari t iesin the propagation path fromthe Sun that could scatter the protons. However, therapid changes indirec t ion of the peak flux vector supports the conclusionfrom Goddardm agnetom eter an d GR CSW cosm ic-ray anisotropy da ta tha t there are




m a n y short-term, rather localized changes in the Earth's magnetic field.(See discussion of the possible filamentary character of interplanetary

space under these other experiments.) The double intensity peak noted

on occasion implies t h a t some back-scattering does occur out beyondthe spacecraft's orbit.

Rapid Intensity Variations

During part of the solar-flare event (about 7 hr), the proton measure-ments at energies of the order of 600 keV displayed large-scale, quasi-periodic bursts with periods of about 900 sec and characteristic rise andfal l times of roughly 100 to 200sec. In addition, quasi-periodic fluctua-tions were noted in the 13 to 70 MeV energy range with periods of 3.5to 4 hr. It is possible that these fluctuations indicate the existence ofAlfven waves in the inner solar system.

Sector Structure of Interplanetary Space

Corotation effects were noted early in flight by the Chicago instru-ment, supporting the joint observations of several other Pioneer 6 in-struments and similar instruments on spacecraft elsewhere in the solarsystem. For example, proton intensity structures detected at Pioneer-6were noted some 2 hr later at the IMP-3 (Explorer 28) Earth satellite.

Proton flux increases over the period from December 1965 throughSeptember 1966 have been unambiguously associated with specific solarflares ( ref . 26). Enhanced solar proton fluxes in the energy range 0.6 to13 M eV have been recorded from specificactive regions from ranges asgreat as 180° in longitude. The enhanced fluxes were characterized bydefini te onsets when their associated active centers reached points 60°to 70° east of the central solar meridian. Cutoffs occurred 100° to 130°

west. Coupled with the detection of associated modulations of the galac-tic cosmic-ray flux, these observations again point to the existence ofcorotating magnetic regions associated with the active centers on theSun (fig. 6—17) .Observations seem to show that solar-flare protons prop-agate along the spiral interplanetary field from the Sun's western hemis-phere. Present evidence supports the view that the solar protons arisefrom processes continually occurring in the solar active centers.

The protons from flares located at ranges over 60° in longitude seemto propagate rapidly through the corona into the interplanetary mag-netic field. The short transit and rise times cannot be explained by iso-tropic diffusion across coronal magnetic fields. To account for theseobservat ions, a newquasi-stationary model w as suggested in which somefield lines rooted in or near the active center are spread out in the coronaover a range of about 100° to 180° in longitude and then extended intoi n t e r p l a n e t a r yspace by the solar wind.




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Differential Energy Spectra

B y correlat ing measurements from Chicago cosmic-ray telescopesaboard Pioneer 7 and O G O s 1 and 3, the Chicago group has shown thatprotons and he l ium nuc le iin th e 1 to 20MeV/nuc leon rangeare pres-en t during the so-called "quiet t imes" often observedin in terp lanetaryspace from 1964to 1966 (ref. 27 ) . F urth er,the observed hel ium nuclei.flux was shown to increasefrom 1964 to 1965 and then decreasefrom1965 to 1966—in accord with the observed variation of galactic heliumnucle i by terrestrial detectors.In contrast , the proton flux detected keptincreasing duringthese 3 yr.

These results i n fe r that most of the particles observed by the space-

craf t at the t i m e of so la r min imumare of galactic origin.As the newsolar cycle bega n, solar particles (m ostly protons) beganto e n h a n c e thegalact icproton Hu x. The H /H e rat io rosefrom 2 in 1965 to ab ou t 10 in1966.

Relativistic Electronsin the GeomagneticTail

NASA's scientif ic satell i tes have establ ished that a neutral sheet(where the Ear th ' s magnet icfield is essen tially ni l ) exists w ith intheEarth 's ta i l betwe en ab out 11 and 80 Earth radi i . Sa tel l i tes have alsodetected high energy electrons s treaming along this sheet . Duringitspassage through the geomagnetic tai lin August 1966, Pioneer 7 ob-served relat ivis t ic electronsconfined w ithin th is ne utral sheet at a bou t19 and 38 Ear th radi i ( ref . 28) .The two high-energy-electron peaks(>400 MeV) , shown in figure 6-18, were coin cide nt w ith P ioneer-7

passages acrossthe neutral sheet .The relativistic electronf luxes did notextend outs ide the neutra l sheet ,and the evidence points to accelera-

tion of the electrons by the spl i t magnetic field within the sheet. Theorigin of this u n i q u e fea ture in n a t u r e is stil l controversial.

THE GRCSW COSMIC R AY EXPERIMENT ( A L L P I O N E E R S )

The pr imary miss ionof the GRCSW e x p e r i m e n t was the measure -m e n t of anisotropy in the dis t r ibu t ion of cosmic rays withinthe solarsystem but still far enough away from the Earth to avoid i ts perturbingmagnet ic field. The construct ion of a theoret ical model describinghowcosmic rays are propagated throughthe solar system depends upon thea c c ur at e m e a s u re m e n tof cosmic rays with energies less than 1000 MeV.Because the weaker cosmic rays, especially those originatingon the S u n ,are affected by the solar magnetic field and the plasma in which it isimbedded , the G R C S W d a t a m u s tbe e x a m i n e d in con junc t ion wi ththe resul ts of the Pioneer plasmaand magne tomete r exper iments . Some




Pioneer 7 magnetosphere passage

2000 0000 0400 0800 1200 1600 2000

Aug 17,1966 Aug 18, 1966 Aug 21,1966

FIGURE6-18.—The intensity of electrons >400 keV as a funct ion of time as the space-craft emerges from the cusp region until passage into the magnetosheath(ref. 28). A typical cosmic ray background flux is shown on the right forAug. si. For comparison the magnetic field strength and electron con-centration reported by Lazarus et al. (ref. 21) are shown on the samescale. NS-i = neutral sheet passage no. i.

of these interrelationships have already been discussed in the precedingsections.

General Structure of Interplanetary Space

The early data from Pioneer 6 revealed thatthe low-energy cosm ic-rayflux ( 13 M eV /nu cleo n) exh ibi ted cons iderable an isot ropy. I t wa s th isanisot ropy wh ich , when com bined wi thGoddard magne tomete r da ta ,ledto the original concept of the filamentary structure described earlier inconnect ion wi ththe Goddard magnetometer ( ref .29). The close corre-lat ion of these two sets of data can be seen in figure 6-3. According tothis model, cosmic raysof low energy are forced to flow inside thesetwist ing tubes, as shown in figure 6-19. The changing cosmic-rayaniso-tropies were ascribed to the experiment 's sampling of the fluxes in thevarious tubes as they swept past the spacecraft . The tubes themselveswere est ima ted to be between 0.5 and 4 mil l ion km in diam eter. A s the



104 T H E I N T E R P L A N E TA RY P I O N E E R S

Direction ofcorotation

" Typical dimension • 3 X 10 6 km•-21 Gyro-radii for 13 MeV: 1.6 Gyro-radii for 1 BeV

Cosmic ray skin depth ~ 1 Gyro-radius~6 min for a 400-km/sec plasma

F I G U R E6-19.—A simplified model of the f i lamentary structure of the interplanetarymagnetic field. Each filament can be thought of as a bundle of tubes offorce. The cosmic raysof low energy are constrained to travel along thefilament by the magnetic field. From: Hart ley; et al.: J. Geophys. Res.,vol. 71, J u l . i, 1966, p. 3301.

reader will recall , later magnetometer data suggested thatthe f i lamentmodel shouldbe replaced by a "discontinuity" model .

The ex te n t of the an isotropy of low-energy solarprotons during earlyflight w as striking. Since scattering normally reduces anisotropy, theseresults im ply tha t l i t t le scatt ering transpired since the cosmicrays wereinjected into the in te rp lane ta ryf ield near the Sun . In contrast, theanisotropy of relativistic cosmic rays is known to be obliterated quickly.

In 1967, R ao, M cC racken , andHart ley (ref . 30) sum m arized theseanalyses of Pioneer anisotropy data collected during 1965 and 1966 forthe period when solarflare effects were not seen. Con sidering on ly cosmicrays in the vic in i ty of 10 MeV/nucleon, their conclusions were:



SCIENTIFICR E S U LT S 105

(1) The 10 M eV /nu cle on cosm ic rays possessed a den sity gradientdirected toward the Su n; i .e., de n sity increases sunw ard, as expec ted.

(2) These low-energy cosmic raysare predominantly of solar origin

even dur ing the sunspo t m in im um .(3) The den si ty gradientf requent lyreversesin the range 10<E< 1000

MeV.(4) Cosm ic radiat ion betw een10 and 105 M eV corotates w iththe Sun.

Studiesof the large-scale, stead y-sta te struc tureof interplanetary spacehave also been made by comparing Pioneer data with thosefrom otherspacecraft (ref . 31). Comparisonof Pioneer cosmic-ray telemetry withcomparable data from tlie IMP 3 (Explorer 28) Geiger counter showedclose agreemen t w hen the spacec raft were lined up w ith the sun. W henseparated by 50° in a z i m u t h ( in late 1966) the var ia t ionsin cosmic-rayflux appeared to be due m ain ly to galact ic cosmic rays. B alasubrahm an-yan and his colleagues concluded that there exist numerous, long-livedregions of modula ted cosmic-ray flux fo l lowing the general spiral con-figuration of the i n t e rp lane t a ry m agne t icfield as is corotates with theSun .

A Closer Lookat the Anisotropy-Magnetic Field RelationshipThe early paper of M cCracken and Ness ( ref . 29 ) , which in t roduced

the f i lamentconcept, was modif ied by another jo in tpaper in 1968 (ref.32) . The m ain thru st of this paper w as that the observed anisotropiesof low-energy cosmic rays couldbe divided intotwo groups:

(1) Equil ibrium anisotropies which are most evident toward the endof a solar-flare even t .The maximum cosmic- rayflux is always directedaway from the Sun (fig. 6-20), and the anisot ropy ampl i tudeis low(5 to 15 perce nt) . P erhaps of m ostsignificanceis the fact that the aniso-tropies are not dependen t uponthe deta i led natureof the interplane-tary magne t i cf ield.

(2) Nonequil ibrium anisotropies which change direct ion in t ime andhave ampl i tudes between20 and 50 percent. These anisotropies areal igned—paral lelor ant ipara l le l—tothe magnet icfield.

These obse rvations were inte rprete d as possible evidenc e of com plexloops in the m agn etic field.

Cosmic-RayPropagation Processes

The G R C S W group published two general papers relat ing Pioneercosmic-ray data to cosmic-ray flareeffects and energetic-storm-particleevents (refs. 33 and 34) . The data used came from Pioneers6 and 7and covered 29 solar flares occurring between December16, 1965, andO ctober 31, 1966. Som e of the m ore im po rta n t conclusions expressed inthis paper were:




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(1) Solar cosm ic rays are norm ally extrem ely anisotropic w ith thedirect ion of maximum flux al igned paral lel to the magnetic f ield vectorduring the firstpar t of the solar ev en t.

(2) D ur ing the late portion of the flare, thecosm ic raysare in diffu-

sive equi l ibr ium.(3) Under some c i rcumstances ,the propagat ion of cosmic rays fromthe Sun toEar th is com plete ly dom inatedby a "bulk motion" propaga-tion mode. Here,the cosmic raysdo not reach the spacecraf t unt i lthem agnetic regime into w hich they were injected en gulfs the E arth.

(4) In two cases, the anisot ropyand cosmic-ray t im esof flight in ferdiffusion of the cosmic ray s to a point on the w estern portion of thesolar disk before injec t ion into the m agn etic f ield.

(5) Simul taneous observat ionby both Pioneers when separatedby54° of azim uth indica te den s i ty gradientsof abou t two orders of magni-t u d e per 60°sector duringthe in itia l stagesof a solar flare.

(6) A s tudy of cosmic-ray scat ter ing w ith inthe solar system indica tesa mean free pa th of a bou t 1.0 AU for large-angle scattering.

The second paper dealt with the energetic-storm -particle even t wh ichwas defined as the very marked enhancementof cosmic raysin the I to




10 M eV range nearthe onset of a strong terrestrial m agn etic s torm . Datarelating to seven such eve nts were e xtractedfrom Pioneer-6 and Pioneer-7 telemetry. The da ta ind ica teda near one-to-one correspondencebe-

tween the energetic-storm -part icle events and the begin ning of a F orbushdecrease (fig.6-21). It was shown further that the bulk of the energetic-storm-part icles are apparently not t rapped in the magnetic regimeasso-ciated with the Forbush decrease.The P ioneer cosmic-ray data tendtosupport the P arker "blast w ave" m odelin which the charged particlesare accelerated by the magnetic f ield within the shockf ront . Fur the rdiscussion can be found in reference35.

The GRCSW group also comparedthe characteristicsof corotatingthe flare-inducedForbush decreasesas derived from cosmic-ray data ob-ta ined from Pioneers 6 and 7 .(ref. 36).The results of this inv est igat ionare summarizedin table 6 — 1 .

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FIGURE 6-21—Temporal variat ions of the cosmic-ray countingrates and the cosmic-rayanisotropy ampl i t ude during the period Jan . 17-21, 1966. Note that themajor portion of the energetic storm-particle event occurred after theonset of the small Forbush decrease. The solid wedges re fer to t imes atwhich major changes wereobserved to occur in the anisotropic n a t u r eof the cosmic radiation. From: ref. 34.




TABLE6—1.—Comparison of theProperties of Corotating andFlare-Initiated Forbush Decreases**

Corotating Forbushdecrease

Flare-initiated Forbushdecrease

Not accompanied by solar-generated cosmic rays

Onset time difference due tocorotation

No amplitude dependence over*—.60° of solar azimuth

Accompanied by solar cosmic raysand an energetic storm particleevent

Probably simultaneous onset up to•—100° off the axis of the Forbushdecrease

Amplitude varies by a factor of•—4.0 over—60° of solar azimuth

"Adapted from reference 36.•>The energy dependence of both classes of events is esentially the same.

Galactic Alpha-Particle Flux

Some limited studies of the galactic alpha-particle flux measured bythe Pioneer-6 GRCSW cosmic-ray experiment have been reported (ref.37). A n examination of the time dependence of alpha particles in the124- to 304-MeV range shows that these particles exhibit the same re-

current Forbush decreases previously observed in the galactic protonflux.

Studies of Specific Solar-Flare Events

Several solar-flare events have been examined in detail in the lightof GRCSW cosmic-ray data and readings taken at several ground sta-tions. B y way o fillustration, the results of the studies of the January 28,1967, and March 30, 1969, events are summarized below (ref. 38). Thesalient features of the firstevent were:

(1) The probable location of the responsible solar flare was about60 ° beyond the west limb of the Sun.

(2) Low-energy particles (< 100 MeV) recorded by the Pioneers andthe high-energy particles (> 500 MeV) detected at Earth arrived af terdiffusion across the interplanetary magnetic field. Both groups of parti-cles displayed remarkable isotropy.

(3) The flux that would be observed by a detector ideally located inazimuth would be greater than 2000 particles cm-—2 sec-—1 sr-— 1 above 7.5

MeV.(4) Pioneer observations indicated low-energy injection commencing

several hours before the high-energy main event.Rei ff has written a running account of the March 30 , 1969, event (ref.

39). Solar act ivi ty w as high during most of March; several active regionscapable of generating solar flares were under surveillance. On March 30,




after the m ost active of these regions had rotate d be hin d the west l im bof the Sun, terrestrial radio telescopes recorded the largest 10-cm burstfrom the corona inscientific history. W ith in ab ou t 2 hr, the cosm ic-ray

ins t rumenta t ionon Pioneers 6, 8, and 9 noted a sharp increase in low-and high-energy protons. A bo uta day later, Pioneer7 recorded the sameincrease in flux. Apparen t ly a large solar flare had occurred on theother side of the Sun. The fluxes recorded by Pioneers 8 and 9 aswellas those on Ea rth sate llites subsided w ith in a few days; by April 5,Pio-neer-6 and -7data followed suit.

B y April 10, the ac tive region of the Sun which produced theseeffectsw as only 20° be hind the eas t l im b. Onceagain a f lare erupted. Withina half hour, cosm ic-ray inten si t ies at P ioneers 6 and 7 jum pe d m ore thanan order of magni tude . Terres t r ia l ins t rumentsand those on Pioneers 8and 9 showed l i t t le change.The relative locationsof the Earth and thespacecraft are indica ted on figure 6-22. Eviden t ly the f lare^gen eratedradiation first en gulfed P ioneers6 and 7. Two days later, Pioneers 8 and9 and terrestr ial in stru m en ts were recording increases while levelsat theother Pioneersdropped to near-normal levels.The motion of the act iveregion and solar rotation had combined to t u rn the spray of radiat ionmore than90°.

In 1971, a keypaper was pu blishe d by M cCracke n and his colleaguesdescribing thedecay phase of typ ica l solar flares (ref. 40). Some of theim por tan t conc lus ionsfrom th is paper fol low:

(1) A t t imes less than4 days af te r the in jec t ionof a solar flare, theanisotropy at 10 MeV t ends to be direc ted ra dia l ly awayfrom the Sun.After 4 days, this anisotropyis directed 45° east of the spacecraft-Sunline. This s i tua t ion impl ies the d o m i n a n c eof convection overdiffusionin the escapeof solar cosmicrays la te in flare life.

(2) A posi t ive radia l c osmic-ray de nsi ty gradien t existsat la te t imes(more than 4 days) near the Earth 's orbit . This drives a diffusivecur-rent a long the in te rplan eta ry m agn et ic l ines toward theSun.

(3) The observed tem poral va riat ion of cosm ic-ray flux can beascribed to (a) con vec tive rem oval of the cosm ic rad iat ion , and (b)the corotation of the cosm ic-ray popula t ion .

(4) The observed rate of change of cosmic-rayflux is cr i t ica l lyde-penden t upon the local valueof the gradient in heliocentr ic longitudefor energies less than10 MeV.

(5) Cosmic-ray spectra indica te tha tthe in f luence of the longitudegradient upon the observed temporal decay increases toward lowerenergies.

(6) La te in the solar flare, the spectral exponent nearJO MeV isdependent upon the longitude of the observer relative to the centroidof the cosmic-ray pop ulat ion injectedby the flare.



110 TH E I N T E R P L A N E TA RY P I O N E E R S

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THE MINNESOTA COSMIC RAY EXPERIMENT(PIONEERS 8 AND 9)

The Minnesota cosmic-ray telescopesreplaced the Chicago instru-m ents on the B lock-I P ioneerflights. The energy range of the Minnesotain s t rumen twas considerably higher (4 MeV/nuc leon to over 2 B e V /n u c l e o n ) . The research results publishedto date are primari ly con-cerned w ith galactic cosm ic rays rathe r th an the lower-energy particle soriginating on the Sun, although papers on solar cosmic rays are inpreparat ion.

Composition of Galactic Cosmic RaysA lthough the so-called "M (m ed ium ) nuc lei," carbon, nitrogen , and

oxygen are the most ab un da n t nuc le iin cosmicrays except for hydrogenand helium, their relat ive abundances have beenin quest ion unt i lre-cently. New measurementsof cosmic-ray nitrogenfrom balloons andPioneer8 have provided better est ima tes (ref . 41 ) .The energy spe ctrumof nitrogen was found to be iden tical with thoseof the other M nucle iover the range of 100 M eV to over 22 B eV /nu cle on . Theratio of nitro-gen nuc lei to all M nu cle i was fou n d to be about 0.125, con stan t to w ith-in 10 percen t over the above en ergyrange (fig. 6-23). Assuming that

some of the nitrogen in the cosmic-rayflux originates in f ragmentat ionreactions with inte rstellar m atte r and kn ow ing the proper cross sections,one can compute a "source" N/M ratio less than about 0.03. However,the solar atmospheric valuefor the N/M ratio is about 0.10—adisturb-ingly higher value.The impl icat ionis that galacticand solar c osmic raysm ay originate in fundamental lydifferent processes.

The Pioneer-8 instrument also identifiedand measured fluorine nucleiin the galactic cosm ic rays (ref. 4 2) . The fluorine abu nd an ce was 1 to 2

percent that of oxygen for energies above 500 MeV/nucleon.These da taon fluo rin e are con sistent w ith the hyp othesis tha t the fluorine is createdby the f ragmenta t ionof heavier nucleias they traverse roughly4 g / c m2

of hydrogen in their flights through the galaxy.In a later paper, the Pioneer-8 data were usedto estimate the chemical

composition and energy spectra of cosmic rays wi th a tomic numbersfrom 3 to 30 ( ref . 43) .Briefly, the results wereas follows. The rat io oflight to m edium e lem en t s ( L /M rat io )w as 0.25± 0.02 and wascons tan tw ith energy overthe range of 100MeV/nuc leonto over 22 BeV/nuc l eon .N o significant var ia t ions in the ind iv idua l L i /M , B e /M , and B /Mratios were observed as a funct ion of energy. These ratios were 0.086,0.037, and 0.150, respe ctive ly (fig.6-24). However, the B e / ( L i+ B)ratio was considerably less thanthat predicted f rom known fragmenta-tion parameters, suggesting that someB e7 had decayed in flight. Thechemical composition of the heavier cosmic rayswas roughly what one



112 THE I N T E R P L A N E TA RY PIONEERS

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would expectif they or ig inatedfrom the f ragmenta t ionof iron in galac-

tic space (table6-2).

Primary Electronsin the 0.2-MeV to 15-BeV Range

The P ioneer-8 cosm ic-ray telescope m easured prim aryelectrons at theextreme low end of the energy spectrum(ref. 44). On Apri l 8 and 9 ,1968, the Minnesota experiment was reconfigured by a series ofgroundcom m and s for this invest igat ion. Two readings were take n in thelow-energy range between200 and 600keV. The results proved to becon-

sis tent wi t h an extrapola t ion of data measured previouslyin the 2- to20-MeV range (fig.6-25).

Anisotropies and Gradients

Although Pioneer 8's orbit takes it only from 1.0 to 1.12 AU, the Min-nesota in str um en t is sensi t ive eno ugh to est im ate cosmic-ray radial gradi-



114 T H E I N T E R P L A N E TA RY P I O N E E R S

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table 6-3. In general, the cosmicray an isotropy seem s closeto zero; how-ever, i t may beslightly po sitivein som e energy ranges.The data indicatetha t there are nosignificant anisotropies above 240 MeV.

Effects of Solar Modulation

Pioneer 8 m e a s u r e m e n t sof protons and hel ium nucle i were usedinconjunc t ion w i th da tafrom balloons and terrestrial cosmic-ray monitors



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of 4.43 cm—3 (ref. 46).AsPioneer 6 moved fartherout into space, it soonbecameapparent thatthe firstvalues reported we re unu sua lly highdueto high solar activity.The spread in measured valuesof the total inter-plan eta ry electron c on ten t is shown for Pione er 6 in figure 6-28. Theelectron numberdensity can be computed from the slopes of the l inesdrawn through these scattered points.The data in the figureyield anelectron numberdensity of 5.47 ±4.1 cm -3. A similar procedureforPioneer-7 data leadsto the valueof 8.02±3.8 cm —3 (ref . 47) .

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Plasma Pulsesand Clouds

The measurements p lo t t edin figure 6-28 ow e their variation pri-mari ly to changes in solar act ivi ty and, consequently,the quan t i ty of

electrons injected into interplanetary space. Some of these injections—called plasma pulsesor clouds—are fair ly well-defined.Many have been"mapped" after a fashion by the Stanford radio propagation experiment .Koehler has reported on the analysisof three plasma pulses occurringon October 24, 1966, Nove m be r10, 1966, and J anua ry 25, 1967 (ref. 48 ) .

O n October 24, 1966, the in tegra ted e lec t ron content measuredbe-tween the Ear th an d P ioneer 6 was un usu ally high, as shown in f igure6-29. The difference be tween the elec t ron contenton October 24 andOctober 26, a "control" day with the usual electron content , is plot tedin figure 6-30. As a firstapprox imat ion ,the curve is t r iangular in shapeand can beexpla ined as due to arectangular pulseof increased electrondens i ty t ravel l ingrad ia l ly outward from the Sun and crossing the prop-agation path. The peak electron contentwas 40 X 1010 elec t rons /m3.Dividing by the 10.7 X 'O8 km propagat ion path ,the peak increaseinelectron dens i ty over the backg round comes to 33 elec trons/c m3. Thispart icular pulse t ravel led the length of thepropagation pa th in about9 hr, leading to a calculated velocityof 330 k m / s e c . This figure corre-

sponds well withthe plasm a velocity m easured d ur ingthe same periodby the Am es plasm aprobe.

The event of Novem ber 10 was somewhatdi ffe ren t in t h a t the curvecorresponding to that in figure6 — 3 0was flat-topped. The inte rpret ationw as t h a t the pulse w as shorter than the propagation pa th in this case.The flat-top,wh ich representsa constant electron content, occurs beforethe leading edge reaches the spacecraftan d af te r the t rai l ing edge haspassed the Ear th .

The largest of the th ree pulses was no ted on Ja n ua ry 25 . Its peakelec t ron contentwas 56 X ' O 1 0 e l ec t rons /m3 above the background .I n -d ica t ionswere tha t this w as approx imate lya spherical pulse5.2 X 10°km in d i a m e t e rt r ave l l i ngat 350k m / s e c .

The Stanford group madea more deta i led s tudyof the plasma cloudejected by the J u l y 7, 1966, solar Hare ( ref . 49) . Al thoughthe radiopropaga t ion exper imentw as being operated beyon dits n o m i n a l maxi -m um range, the descr ip t ionof the plasma cloud derived fromthe meas-

urements i scompa t ib l ew i t h the MIT plasma probe which also meas-ured the passageof a plasm a shockat the sam e t im e ( ref . 19) .The shapean d e x t e n t of the passing plasma cloudw as calculated from the inte-grated e lec t ron content measuredfrom Pioneer 6. Three cloud shapes-each deducedfrom a di ffe ren t da ta channe l—seemedto fit the data ( f ig .6—31). Each cloud modelhas a double s t ructureto account for the two




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average density levelsdetected by the MIT i n s t r u m e n t .The secondcloud in figure 6-31 was t hough t to be the most probableconfigurat ion.Although a unique reconstruct ionof the cloud is impossible with theavai lable da t a , the most l ikely models are consis tent wi ththe generalconclusion t h a t the shock f ronts of the plasm a c louds e jec tedfrom theSun have rad i iof curva tu re of abou t 0.5 AU by the t ime they reach theEar th .

The January 20, 1967, Lunar Occultations

When the Moon occulted the Pioneer-7spacecraft on Jan ua ry 20 ,1967, radio signals sen tfrom the 150-ft Stanford a n t e n n a w e rediff ractedby the edge of the l u n a r disk an d also refracted by the lunar ionosphere(ref. 5 0 ) . The geometry of the situation ispor t rayed in figure 6 — 3 2 .O fcourse, if there is no lunar ionosphere at all, only the classical Fresnel




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diffraction pattern wil l be measured (f ig.6—33). If an ionosphere ispresent, however, its refractive effects will displace the diffraction pat-tern in time. In this case, thedifference in the angles of refraction forthe 49.8- and 423.3-MH z signals w ere usedto com pute e lec t ron d en si ty.

The ray path f rom the Stan ford an ten na to Pioneer 7 was par t ia l lyin the shadow of the Moon during immersion but wasfully i l luminatedduring emersion. The angles of ref rac t ion w ere — 2.3 m icroradiansand

• — 5.7 microradians for immers ion and emersion, respectively. Theminus sign indicates thatthe electron density increases with height nearthe surface of the Moon, and that a tenuous ionosphere may be created—at least on the sun l i t side—by the interact ion of the solar wind wi ththe lunar surface .

Solar-Wind Flow Patterns

B y taking measurements dur ingtw o periods each day,first using aPioneer spacecraft ahead of Earth and then another behind it, corotat-in g solar-windflow patterns are clearly visible (ref. 51).The den sity pat-terns observed a re not con sisten t w ith the hy pothe sis of steady coro tatingf lows—there arelarge tran sie n ts wh ich occurtoo rapidly. The Stanfordgroup has observed that identif iable features recur with nearly but not

exactly the sam e period on successive solar rota tions .Croft suggests thatthese pat te rns m ight be due to the corotat ion of thin steady stream s thatfluctuate indirect ion.These data might also indicate that some corotat-ing regions are of lowdens i tyand featureless w hile othersare dense andhighly disturbed.

RADIO PROPAGATION EXPERIMENTS USING THE SPACECRAFTCARRIER (ALL P IONEERS)

With the Stanford radio propagat ion exper imentit is possible tomeasure the in tegra ted e lec t ron densi ty betweenthe spacecraf t and theEarth, as described in ch. 5, Vol. II . H ow eve r,useful scientifici n fo rma-t ion can a lso be obta ined concerning t rans ient space phenomena byobserving changesin the Faraday rota t ionof the spacec raft S-band trans-mit ter. Levyand his associatesat the Ca l i fo rn i a In s t i tu t eof Technologyand the Univers i tyof Southern Cal i fornia have usedthe DSN 210-ftan tenna a t Golds tone to measure t rans ien t Faraday ro ta t ions dur ingsolar occultat ion of P ioneer 6 (ref . 52 ). The geom etry of the occulta-tion is shown in figure 6-34. As the spacecraf t l ine of sight approachedthe Sun, the S-band telem etry signal passed through increa singly den seregions of the solar corona. B y N o v e m b e r 16, however, the signal-to-noise ratio had deteriorated to the point where the e x p e r i m e n thad tobe discont inued un t i l the s ignal was reacquired on No vem ber 29. Atthree points (m arkedA, B, and C on fig.6 — 3 4 )be tween6 and 11 solar



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radi i , F arada y rotat ion tra n sien ts were recorded (f ig.6—35). The dura-t ion of each eve nt was ab out 2 hr. The tran sien ts were poorly correlatedw i t h solar (lares, but it wasnoted that burstsof radio noise in the deka-meter range occurred prior to the observat ion of the Faraday rotat ionp henomena .

Later s tudiesof these t r ans ie n t sat G S F C by Scha t ten led to the corre-lation of Levy 's three events wi thspecific Class-1 solar flares and sub-Hares which preceded the events ( ref . 53) . Schat ten in terpre ted Levy 'sevidence in t e rms of a m agn e t ic bo t t le expan d ingfrom the corona toperhaps 10 to 3 0 solar radi i before contract ing back towardthe corona.Resembl ingan elongated bl is ter,the m agne t ic bo t t leand i ts electronicconte nt w ould cause the observed F araday rotat ion tra nsien ts .

TRW SYSTEMS ELECTRIC FIELDEXPERIMENT(PIONEERS 8 AND 9)

The Pioneer Electric Field Exper iment i sphysically associated withthe Stanford Radio Propagat ion Exper iment , u t i l iz ingits short 423-M Hz a n t e n n a as a de tec to r ; but scientif ically it is more closely alliedwith those exper iments measur ing character is t icsof the i n t e rp l ane t a ryplasma; i.e., the Ames p lasma exper imentand the A m e s and Goddard

magnetometers .The electr ic f ield expe r imen t w as added late in theBlock-II programand wasthus ra ther l im i tedin its a l lo tmentsof weight ,power, an d te lemetry capaci ty.The engineering designand phys ica lopera t ions of this exp e r imen tare described in ch. 5, Vol. I I .

Early in the d e v e l o p m e n tof space physics, scientists concentrated pri-m a r i l y upon m ea sur in g solar p lasmavelocity, densi ty, an d t empera tu re .P l a s m a dynam ics, i n c l ud in gthe s t udy of plasma wavesan d other "co-operat ive" phe nom en a, was gene ral ly not em phasized. I t was recognized,of course, that wavesan d m a n y other dy na m ic phenom ena weren otbeing detected withthe usual plasma ins trum en ts. Earth satel li tes soonbegan carrying vlf (very low f requency) radio l i s t en ing exper imentsan d high-sensit ivity i n s t r um en t s l ik ethe "LEPEDEA" ana lyzers .Thesei n s t r u m e n t sbegan to reveal the t rue complex i tyof the plasma environ-m en t ne ar the E arth. I t was, there fore, desirable to in stal l a vlf or elec-tric f ield e x p e r i m e n ton the B lock-I I P ioneers . F or tun ate ly, th is provedpossible.

N e a r the Ear th ' s orbit the solar wind is very di lu te , and the plasma is

t ru ly collisionless.I n d i v i d u a l electrons an d positive ionsa re in f luencedon ly by dc electromagnetic f ields or by f ields due to the organizedmot ion of plasma par t ic lesin the form of ac plasma waves.The PioneerElectric Field e xpe r i men t w as designed to detect these microscopicplasma p h e n o m e n a .The overa l l size of the Pioneer spacecraftand i tsappendages is sm all compared to the Debye length in in te rplan et ary




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space and also the m i n i m u m w a v e l e n g t hfor any undamped p l a smaoscillation. Thus, the spacecraft actua l ly represents a "microscopic"measur ing pla t form immersed in plasma phenomenaof m u c h greater

f u n d a m e n t a lsize. The 423-MHz an t enn ais a relat ively insen si t ive,butadequate, cap acit ively coupled sensor tha t detects plasma waves sweep-ing past the Pioneers in in te rpla n et ary space.

W hile m agne tom eters have helped scientis ts un de rstand m icroscopicelectromagnetic phenomena in space, the Pioneer Electr ic Field experi-m e n t is primari ly electrostat icin na tu re—in fact , it was the first low-f requency (under 20 kHz) electr icfield e x p e r i m e n tto be flown indeepspace. The Pioneer ins t rument detects densi tyfluctuations with in theplasma rather than the mot ions of cur ren t systems indicated by mag-netometers .In this sense,the electric field exper iment a l lowsus to s tudythe plasma froman ent i re lydi fferent vantage point thanthe more con-ven t iona l plasma probes and magnetometers . Electrostat ic plasma phe-nomena cancarry considerable energy indeep space and stronglyaffectoverall plasm a be havior. The follo w ing discussion of the resu lts ob-ta ined from th is exper iment underscoresthe impor tance of these ex-t remely s imple , l ightweight ins t rumentsin our unders tanding of thein te rp lane ta ry medium.

Presentation of Early Results

The initial results from the Pioneer-8 ElectricField experiment werereported by Scarf et. al. ( re f. 54) .These experimental data were treatedin three categories.

B r o a d b a n dmeasurements .—Duringthe spac ec raft 's passage across theEarth 's magnetosphere,very low ampl i t ude vlf oscillations werede-tected. O n D ecem ber 14, P ioneer 8 f irst enc ountered the stream ingplasma in the dis tan t m agne toshea th ,as indicated in figure 6—36. Theelectric fieldexper iment detected some plasmawaves before the A m e splasma probe registered its first bursts of plasma around 2140 UT.A p p a r e n t l ythe crossingof the magnetospherewas com pleted ab out 0230on December 15 when bo th the electric field e x p e r i m e n tand the A m e splasma probe indicated enhancedact ivi ty. Almost coincident wi ththepene t ra t ion of the magnetoshea th , Ear th -based magne t icfield ins t ru -menta t ion reported a magnetic disturbance(a sudden commencemen t ) .Wi t h i n m i n u t e sof the terrestr ial indicat ion,the Pioneer electricfielde x p e r i m e n t also detected the dis tu rbance . Ev iden t ly,the p h e n o m e n as t i m u l a t i n g terrestr ial magnetic s torms alsoin tens i fy i n t e r p l a n e t a r yplasmawaves.

The 400-Hzc h a n n e l . — W h e nthe preceding broadban d data are com-bined w i th in form at ionfrom the nar row-bandwid th 400-Hz channe l ,




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one obta ins a measure of the spect ra l wid thof the low-frequency noiseband .

Telemetry from the 400-Hz chan ne l revealeda regular modula t iontha t was qu ick ly associated w ith the spa ce craft 's spin ra te, m ore pre-cisely with the ins tan tan eou s posit ionin space of the Stanford an tenna .The effect w as greates t when th is antennawas pointed towardthe Sun .Apparen t ly,the physical causeof the modula t ion is a Sun-al igned space-charge cloud surroun ding the non -con duc ting spacecraft.

Despite the modu la t i on ,the 400-Hz chan nelis clearly sen sitiveto theplasma waves detected by the broadband channel . Fur ther conclus ionswere notdrawn at the t im e th is in i t ia l paperw as wri t ten .




The 22-kHz chan nel.— The n arrow-ban dw idth 22-kHzchannel pro-vides information about plasma osci l lat ions when the electron concen-trat ion is relat ive ly low. There is a natural noise backgroundat this

frequency, but i t usually lies well below the experiment 's threshold.R arely, however, inte nse burs ts of 22-kH z noise a ctiv ate the receiver.The noise burst portrayedin figure 6-37 is typical. Althoughrare, thesenoise bursts do not appear to be random, being weaklycorrelated wi thsolar and geomagneticac t iv i ty and strongly correlated with proximityto the Earth 's magnetosphere.

The fol lowing tentat ive observat ions were presentedby Scarf et al.(ref . 5 4 ) :

(1) Even when the Sun is quiet , low-frequenc y electric waves(>100Hz) can be detected in the solar wind al though the lowest levelsare near the in-flight background.

(2) Wave ampli tudes at the lowest frequencies vary markedly withchanging conditionsin in te rp lane ta ry space .These electric field changesare correlated with local changesin the plasma environmentas regis-tered on the Am es plasmaprobe.

(3) As Pioneer 8 moved away from the Earth, theeffects of corota-tion and solar-wind travel t imes were evident when comparing disturb-

ances recorded at both the Ear th and thespacecraf t .(4) L arge-ampl i tude h igh-f requency waves, de tec ted whenthe space-

craf t was far from Ear th , are apparent ly the resul t of bursts of inter-planetary, but Earth-associated, electron oscillations.

Shock Structures

At the 1969 Summer Advanced S tudy Ins t i tu teat the Univers i tyofCalifornia at Santa Barbara, further resul ts were presented on the shock

structures detected by the Pioneer electr icfield exper im ent ( ref . 55) .Data from Pioneers8 and 9 and OG O 5were used to demons t ra te theseveral types of shock structures fo un d in the high M ach -num ber solarplasma colliding withthe Earth 's magnetosphere.The most commonstructure reported was a la rge-ampl i tude magnetohydrodynamic pulsehav ing a characteris t ic length equalto the in i t ia l gradient and a t rai l -in g wa vetra in . Energyin these shock structuresis apparently dissipatedvia electrostat ic wav e turb ule nc e which arisesfrom instabi l i t ies . Further

thoughts conce rning these inte ract ions were presentedin a second paperat this sam e m eetingby Scarf and his associates (ref. 56).

Measurementsin the Distant GeomagneticTail

The plasma-probeand electric-fielddata recorded as Pioneer 8 crossedthe Earth 's geom agneticta i l d ur in g Ja n ua ry 1968 were reportedin 1970




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by the researchers at Am e s and TRW Systems (ref. 57).Both instru-ments recorded disturbances nearthe ta i l boundaries between500 and800 Earth radii downstream. The major conclusionof this paper was

tha t ta i l breakupand f i e ld - l ine - reconn ec t ionphenomena beg in wi th in500 Earth radi i .

Multi-Instrument Correlationof Space Disturbances

The initial results from the Pioneer-8 electricfield experiment showedclearly their close correlat ions w ith te rrestr ial ly detected m agn etic act iv-i ty. B ecause the other P ioneer in stru m en ts also record space even ts(froma di ffe ren t perspect ive) , correlat ions betweendifferent onboard ins t ru-ments should also be obvious in many instances.Scarf, in his 1970review paper, i l lus t ra ted a three-way correlationduring a Forbush de-crease. Figure 6-38 indicateshow the Pioneer-8 magnetometer, electric-field exper iment , and the Minnesota cosmic-ray exper imentsall re-corded the sam e even t .

An other in tere s t ing corre la t ion betweendi ffe ren t i n s t r u m e n t s (ondifferent spac ecra ft this tim e) wa s revealed by Siscoe et al. (ref. 5 8).They i l lustrated the strikin g correlation betwee n P ioneer-8 electric-field data and the solar-wind parameters recorded by Explorer 35 (in

lun ar orbit) in late F ebru ary 1968 (fig.6—39). Siscoe et al. noted thatthe electric-field noise d ataare of two types: (1) burs ts or spikes lastingless tha n 10 sec, and (2) persisten t signals typ ically lastin g a day ormore. The first type of data coincide with plasmaand magnet ic-f ie lddiscontinuities, whereasthe la t ter are available for comparison. Thepersisten t signals, on the other ha n d, correlate loosely w ith solar-w inddensi ty, whe ther the d ens i ty increases are due to in te rpla ne tary shocks(t he so-called "snowplow" effect) or other processes.

This m ulti-space craf t correlat ion stud y also provedof va lue in defin-ing the spat ial ex te n t of the Ea rth's in flue nc e. Siscoe and his associatesshowed thata huge wa ke region surroun dsthe dis tant geomagnet ic ta i l(ref. 59) . This analysis indicated tha t Pioneer 8 did not encounter un-disturbe d solar wind for several m ont hs fol lowing launc h. In a laterpaper, Siscoe used thisfact to expla in the ear ly anomalousE-field ob-servat ions (ref . 59) .

In later papers, new typ es of correlation stud ies were presented(refs.60 and 61). Nearly simultaneous wave observation fromOGO 5 andPioneer 9 were compared and used to provide an in-flight cal ibrat ionfor the s im ple P ioneer in s t rum en t . Ana lys isof these wave observationssuggested that the wave spectrum varies with radial distancefrom theSun.

In concluding the discussionof the electr ic-f ield experim en t ,it shouldbe noted again tha t the exper iment had only very l imited telemetry



134

16

THE I N T E R P L A N E TA RYPIONEERS

Pioneer 8, hourly samples

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I ' l l I

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T5, Pioneer 8(E D >14MeV)

F I G U R E 6-38.—Pioneer 8 magnetometer data (top) and electric-field data (middle)reveal interplanetary shock. Cosmic-ray readings (bottom) show att end-ant Forbush decrease.

capacity assigned, andtha t the interpretation of results is somewhatcomplicated by intera ctions of the inte rplan eta ry m edium with thespacecraft. F or example, the exper iment was too limited for the un-am biguous dete rm ination of plasm a wave modes in in terplan etaryspace.




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THE GODDARD COSMIC DUST MEASUREMENTS

(PIONEERS 8 AND 9)Dur ing the early days of the Space Age, cosmic dustw as thought to

be a serious ha zar d to m en an d m ac hin es ope rat ing outside the E arth 'sprotec t ive a tmosphere . More accura te measurementsof cosm ic dust p ar-ticles have since shown thesefears to have been unwar ran ted .Sensitiveex te rna l surfaces on long-lived Ea rth satel l itesm ay suffer some degrada-



136 THE I N TE R P L A N E TA RY P I O N EE R S

t ions , but nei ther m ann ed n or unm an ne d spacecraf t have been com-promised. Ne vertheless, cosmic d ust p articlesdo exist, and their presencein space de m and s ascientific explanat ion.

Are cosmic dust particles productsof cometary disintegrat ionor thedebris from collisions within the asteroid belt? Most of our insightintothis question at present comes from ground-based photographic andradar m easurem ents of m eteor t ra i ls .These data suggest that almost allcosmic dust trajectories are heliocentric with the orbital characteristicsof comets rather than asteroids. Further,the particles seem"fluffy" andof low densi ty.The P ioneer cosmic dust e xper im en t , wh ichflew on Pio-neers 8 and 9, was designed to help answer this quest ionof particleorigin

w ith in s i tu datafrom

deep space.The exper iment itself (described in detai l in Vol. II) was designedand tested by a team of scientistsand engineersat Goddard Space FlightCenter. Arraysof plasma and acoustical sensorscan measure part icledirections, energies, and, through atime-of-flight technique, velocities.The early results from Pioneer 8 described below have beenreportedby the Goddard group ( ref. 62 ) .

Dur ing the first 390 days of continuous exposureof the Pioneer-8sensors,-numerous events (severalper day ) were recordedby the f ron tsensor a rray alone,the rear sensor array alone,or the microphone sensoralone. These data weren ot completely analyzedat the t ime the refer-enced papers w ere w ri t te n . However,six time-of-flight even ts involvingboth f ront and rear sensor arrays were also registered.These are con-sidered highly im po rta n t to the question of cosmic dust origin becauseorb i ta l in format ioncan bederived from the measurements .

The six time-of-flight even ts in a space of 390 days representa ra te3.8 X 10* lower tha n the rate recorded by atime-of-flight exper iment onO G O 1. I t i s surm ised that the h igh O G O -I ra te was due to coincidentnoise pulses in thatexper iment—noisewas a serious problem w ith earlyscientific sate llite cosmic du st expe rim en ts. Early P ioneer-8 results con-firm expecta t ionsfrom zodiacall ight measurem ents .

From a knowledge of thespacecraft t rajectory and orientat ion at theinstant of each event and the telemetered data indicat ing t imes of f l ightand the specific sensors activated in the front and back arrays, i t waspossible to derive the particle orbits shown in table6 — 4 .These data in -

dicate a com etary origin for the six part icle even ts , reinf orcin g the con-clusions derivedfrom ground-based observations.

The m ost inte rest in g of the six even tsreported in the two papersoccu rred on A pril 13, 1968. A pp are n tly, onefront sensor segment andtwo rear sensors responded, inferr ing thatthe particle partially disinte-grated upon first impact , showeringthe rear array with a conical spray




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of debris. No such f ragmenta t ionwas observed during laboratory testsw ith particlesfired from an elec trostatic accelerator.In view of the possi-ble f r iable nature of cosmic dust material , this typeof event was not

unexpected. The much higher rates of sol i tary front and back arrayevents also tend to indicatefluffy particles withpoor penetrating powers.The A pril 13, 1968, eve nt was no table in twoother aspects: (1) its

im pact energy exceeded80 ergs, more than any other particle recorded;and (2) i t was theonly part icle that act ivatedthe acoustical sensor.Thus, inde pen de nt m easurem en ts of the part icle m ass were possiblefrom the energy and m om entum equat ions .These were 2.3 X 10— 11 and1.6 X 10-11 grams—relativelygood agreement for this kind of experi-m e n t . From th is informat ionan orbit for the particle can be computed(fig. 6-40). However, it is cautioned that the response of the acousticsensor to thepostulate d sprayof debris is u n k n o w n and was assumed tobe the same as that of a solid particle.

Summariz ing, the early Pioneer-8 cosmic dust datatend to confirmthe hypotheses that cosmic du stis alm ost exc lusivelyof cometary originand ra therfluffy or friable in character.

In a paper presented at the Xlllth Plenary Meet ingof COSPAR inM ay 1970, Berg and Gerloff summarized Pioneer resultsto tha t date(ref. 63) .

(1) The m icrophone m icrom eteoroid detectors em ployed on m an yearly space craft also respon dto the cosm ic rays gene ratedby solar flares.This effect was responsible for the m u c h higher micrometeoroidfluxes"measured" by these craft in the early da ysof space science .

(2) The m icrom eteoroid f lux betwe en 0.7 and 1.1 AU is2±0.5 X10—4 particles/m 2-sec-2?rsr and shows a cutoff at a mass of 5 X10-"g (fig.6-41).

(3) Among the eight detected particles for which orbits could becomputed weretwo that t ravel in the orbital planesof known com e ts(Encke and Grigg-Skellerup).

THE PIO NEER CELESTIAL MECHANICS EXP ER IMENT( A L L PIONEERS)

All spacecraft l aunchedout of the Earth 's g ravi ta t ional"well" provide

oppor tuni t ies for improving solar system cons tan t s and ephemerides .Al though the Pioneerspacecraf tdid not pass close to any other planets,their t rajectories we reaffected by the Moon. Fu r ther,the l aunch of fours imi lar spacecraft ,of know n massan d equipped w i th t rack ing a ids , in toheliocentr icorbi ts made poss ible more accurate determinat ionsof theAstronom ical U ni t (AU )as well as the Earth 's ephemeris .



SCIENTIFICRESULTS 139

Nominal particle

trajectory

April 13, 1968

F I G U R E6-40.—Postulated orbit for the particle recorded on Apr. rg, 1968. This was at ime-of-f l ight event. From: Berg, 1969.




-18-12 - 1 0 - 8 - 6 - 4

Log particle mass in grams-2

FIGURE6-41.—Micrometeoroid fluxes as functions of mass. The heavy lines representexperimental data, while the shaded areas are theoretical. Pioneer dataagree well with theory. From: ref. 63.

The three formal objectivesof the experiment were:(1) Obtain primary determinations of the masses of theMoon and

Earth and of the AU(2) Improve the ephemeris of the Earth(3) Investigate the possibility of a General Rela t iv i ty test, using

Pioneer orbits and data (ref. 64).The source of all data for this experiment is the Deep Space Network.

The spacecraft carried no special equipment for this experiment. DSN




two-way coherent Doppler data, judged as "good" by the tracking sta-tions, were put on magnet ic tapes .The tapes also contained missionda ta, suchas the specific DSN station responsiblefor each group of data .O bvious m istakes were edi ted from the tapes.

Al though the Pioneers , unl ike the Mariners , made no midcoursemaneuvers , they did carry out the two types of or ienta t ion maneuversdescribed in Vol. I I . Tracking data indicate that some trajectory per-turbat ions resul tedfrom these maneuvers . For tunate ly,the or ienta t ionm a n e u v e r swere usually concluded w ithina day or two oflaunch. Fromthe trackin g da ta on P ioneer 7, i t is app aren t tha t the Type-II orienta-t ion maneuver executedon August 19, 1966, changed the spacecraftvelocity only by a few hun dre d m il lim ete rs per second. More seriouswas the gas leak on Pioneer 6, which provided an unknown sourceofuncompensa t e d mom e n tumt ransfer—in other words, a source of thrustt h a t con fused the an alyses. The gas leak rendered the first 6 m onth s ofPioneer-6 tracking data uselessin te rms of the objectivesof the experi-men t .

In the first paper published on the Pioneer celest ial mechanicsex-periment, Anderson and Hilt (ref .64) reported the following preliminaryEarth-Moon data:

G eocentric gravi ta t ional constant= GE —398601.5±0.4 k m3/ s e c2

Lunar gravi ta t ional constant= GM =4902.75±0.12 km3/ sec2

Earth-Moo n m ass rat io= / * . —x =81.3016±0.0020

The uncertaint ies were bel ievedto represent realistic standard errors.The authors reported tha t mostof the sys temat icerrors in the determina-tion of M^1 probably camefrom the single-precision numerical computa-t ions performedon an IBM 7094. These computat ions were being con-verted to double-prec ision as thepaper was being w ri tten .

SOLAR WEATHERMONITORING

Solar events stronglyaffect all that t ranspiresin in terplan etary spacefrom the edges of the Sun 's extensive coronato well beyond the Earth 'sorbit . The chief carriers of solar distu rba nc es are the solar plasm a (solarw i n d ) , the Sun 's m agnet icfield, and theburs tsof cosm ic rays tha toftenaccompany solar activity.The interactions of these phenomena with theEarth are not obvious as far as theordinary ci t izenis concerned. Rarely,he wi l l read or hear that intense magnetic s torms tr iggeredby solar



142 THE I N TE R P L A N E TA RY P I O N E ER S

activity are hamper ing long dis tance communicat ion,but in generalthe Earth is well insulatedfrom any obvious effects of solar activitybyits magnetosphere and atmosphere.

During intense magnetic storms, while mostpeople go about theirbusiness unknowingand unc onc erne d, solar-induced electromagn eticeffects wreak havoc withradio and long-landline communicat ion.Highf requency radio link s depe ndin g upon forward-or back-sca ttering proc-esses in the upper atmosphere areoften impossible to use.There is alsoevidence tha t m agn etic s torm s som etim es open circuit breakers an dcause other d isruptionsin large electric powergrids, part icularly in thenorthern lat i tudes. Companiesengaged in searching for minerals withmagnetic detectorsare often forced to suspend operations. Accurateforecasts ofm agnet ic s to rm sare useful (and worth money)in the sensethat prepara t ionscan be m a d e for use of other communicat ion c i rcui tsand forotherwise reduc ingthe impac tof the storm.

Because of these terrestrialeffects, several groups are interested in"solar weather"; i.e., the status of the interplanetary magneticfield,plasma fluxes, and cosmic rad iat ion levels .The interest transcends purescience. NASA, for example, is concerned with solar events that mightcompromise manned space missions, particularly thosethat leave the

shelter of the Earth 's magnetosphere.The Environmenta l ScienceServ-ices Adminis t ra t ion (ESSA) desires advance informationon magnet icstorms and the in jec t ionof new charged part icles intothe Earth's beltof t rapped radia t ion.These are the events that sometimes upset terres-t r i a l communica t ionsan d have some not-so-well-understoodeffects onthe planet 's weather.The D e p a r t m e n tof Defense (DOD) has s imi larinterests for m ili tar y reasons.

Pioneer solar weather reports beganin Ja n ua ry 1967. Usua lly, they

are sent once a day to ESSA's Space Disturbance Forecast CenteratBoulder, Colorado,to D O D ' s N O R A D ,and to other agencies. However,when m ann ed f lights are im m in en t , reports are sent hourly to NASA 'sApollo Mission Control Center at Houston, Texas. The reports include:

(1) The corotat ion de lay, the expected t im e in days betwee n themeasu remen tof a dis tu rbanceat the spacecraf tand its arrival at Earth

(2) Solar-windvelocity,dens i ty,and t empera tu re(3) Cosmic-ray inte nsi t ie sin several energy b an ds(4) The general condit ion of the interplanetary magnetic f ield.

REFERENCESI .BURLACA,L. F. ; ANDNESS, N. F. : Mac ro and M icrostructu re of theInterplanetary

Magnetic Field. Can. J. Phys., vol.46, 1968, p. 8962.2. NESS, N. F.; S C E A R C E ,C. S.; AND C A N T A R A N O ,S. C.: Preliminary Results from the

Pioneer 6 Magne t i c Field Exper imen t . J. Geophys. Res., vol.71, Jul. i, 1966.




25. F A N ,C. Y .; ETA L . :Anisotropy and Fluxuations of Solar Proton Fluxes of Energies0.6-iOO MeV Measured on the Pioneer VI Space Probe. J. Geophys. Res., vol. 71,Jul. i, 1966.

26. F A N , C. Y.; F.TAL.: Protons Associated with Centers of Solar Activi ty and Their

Propagation in Interplanetary Magnetic Field Regions Corotating with the Sun.J. Geophys. Res., vol. 73, Mar. i, 1968.

27. F A N , C. Y.; ET AL.: Diffe ren t ia l Energy Spectra and Intensity Variation of i-20MeV/Nucleon Protons and Helium Nuclei in Interplanetary Space (1964-1966).Can. J. Phys., vol. 46, May 15, 1968, p. 8498.

28. R E T Z L E R ,J .; ANDS I M P S O N ,J. A.: Relativist ic Electrons Confined within the NeutralSheet of the Geomagnetic Tail. J. Geophys. Res., vol. 74, May i, 1969, p. 2149.

29. M C C R A C K E N ,K . G .; AN DNESS, N. F.: The Collimation of Cosmic Rays by the Inter-planetary Magnetic Field. J. Geophys. Res., vol. 71, Jul. i, 1966.

30. R A O , U. R.; M C C R A C K E N ,K. G. ; AND H A R T L E Y ,W. C.: Cosmic-Ray Propagation

Processes, 3. The Diurnal Anisotropy in the Vicin i ty of lO MeV/Nucleon. J.Geophys. Res., vol. 72, Sept. i, 1967, p. 4343.

31. B A L A S U B R A H M A N Y A N ,V K.; F.T AL:Co-Rotating Modulations of Cosmic R ay Inten-sity Detected by Spacecraft Separated in Solar A z i m u t h . NASA TM-X-63654, 1969.

32. M C C R A C K E N ,K. G. ; RAO, U. R.; AN DNESS, N. F.: Interrelationship of Cosmic-RayAnisotropies and the Interplanetary Magnetic Field. J. Geophys. Res., vol. 73,Jul. i, 1968.

33. M C C R A C K E N ,K. G. ; RAO, U. R. ; ANDB U K A T A ,R. P. : Recurrent Forbush DecreasesAssociated with M-Region Magnetic Storms. Phys. Rev. Letters, vol. 17, Oct. 24,1 9 6 6 , p. 928.

34. M C C R A C K E N ,K. G. ; RAO, U. R.; AN DB U K A T A ,R. P. : Cosmic-Ray Propagation Proc-esses, i. A Study of the Cosmic-Ray Flare Effect. J. Geophys. Res., vol. 72,Sept. i, 1967.

35. R A O ,U. R. ; M C C R A C K E N ,K . G .; AN DB U K A T A ,R. P. : The Acceleration of EnergeticParticle Fluxes in Shock Fronts in Interplanetary Space. Can. J. Phys., vol. 46,1968, p. 8844.

36. B U K A T A ,R. P. ; M C C R A C K K N ,K. G. ; ANDR A O ,U. R.: A Comparison of the Character-istics of Corotating and Flare-Initiated Forbush Decreases. Can. J. Phys., vol. 46,May 15, 1968, p. 8994.

37. B U K A T A ,R. P. ; ET AL.: Pioneer VI Observations of Forbush-Type Modulation

Phenomena in the Galactic Alpha Particle Flux. Paper presented at nth Intl.Conf. on Cosmic Rays (Budapest) , 1970.38. B U K A T A ,R. P. ; ETA L . :Neutron Monitor and Pioneer 6 and 7 Studies of the Janu-

ary 28, 1967, Solar Flare Event. Solar Phys., vol. lO , Nov. 1969, p. 198.39. R E I F F, G. A.: Radio Propagation Experiments w i t h Interplanetary Spacecraft. J.

Spacecraft and Rockets, vol. 6, May 1969.40. M C C R A C K F . N ,K. G.; ETAL.: The Decay Phase of Solar Flare Events. Solar Phys.,

'97'•4 1 . L . E Z N I A K ,J. A.; F.T AL.: Observations on the Abundance of Nitrogen in the

P r i m a r y Cosmic Radiation. Astrophys. and Space Sci., vol. 5, Sept. 1969.4 2 . L . E Z N I A K ,J .; ANDW E B B E R ,W. R . : Observations of Fluorine Nuclei in the Primary

Cosmic Radiation Made on the Pioneer 8 Spacecraft. Astrophys. J., vol. 156, May1969, p. L73.

43. L E Z N I A K ,J. A.; VO NR O S E N V I N G E ,T. T.; AN DW E B B E R ,W. R.: The Chemical Com-position and Energy Spectra of Cosmic Ray Nuclei with 7 = 3-30. Acta Physica,v o l . 29, Supplement i, 1970.

44. B E E D L E ,R. E.; ET AL.: Measurements of the Primary Electron Spectrum in theEnergy Range 0.2 MeV to 15GeV. Acta Phys ica , vol. 29, Supplement i, 1970.




45. L E Z N I A K ,J. A.; W E B B E R ,W. R.; AN DR O C K S T R O H ,J.: A Compar ison of Solar Modu-lat ion Effects on Protons, Electronsand He l ium N uc le i . P aper p resen tedat nthIntl. Con f. on CosmicR a y s (B uda pes t ) , 1970 .

46. S T A N F O R DU N I V E R S I T VAN DS T A N F O R D R E S E A R C H IN S T I T U T E :The Interplanetary Elec-

t ro n N u m b e r D e n s it yfrom P r e l i m i n a r yAnalys is of the Pioneer V I Radio Propa-ga t ion Exper imen t .J. Geophys. Res. , vol .71, J u l . i, 1966, p. 3325.

47. K O E H L E R ,R . L .: In te rp lan e ta ry Elec tron Con ten t M easured B e tween Ear th andPioneer VI and VI ISpacecraft Using R ad io P ropaga tionEffects. Stanford ElectronicLaboratory SU-SEL-67-051, 1967.

48. K O E H L E R ,R. L . : R adio P ropaga tion M easurem ent sof Pulsed P lasma S t reamsfromthe Sun Using Pioneer Spacecraf t .J. Geophys. Res., vol.73, Aug. i, 1968.

49. L A N D T ,J. A.; ANDC R O F T ,T. A.: A Plasma Cloud Following aSolar Wind Shockon 7 Ju ly 1966 M easuredby Rad io Propaga t ionto P ionee r 6. Stanford ElectronicsLaboratory SU-SEL-7&-OOi ,1970.

56.P O M A L A Z A - D I A Z ,J. C.: M e a s u r e m e n tof the L un ar Ionosphereby Occul t a t ionof thePioneer V II Spa ce craft . Sta nf ord Electronics L aboratory SU-SEL-67-Og5, 1967.51. C R O F T ,T. A.: P a t t e r n s of Solar Wind Flow Deducedfrom In te rp lane ta ry Dens i ty

M e a s u re m e n t s Ta ke n d u r i n g21 R o t a t i o n sof the Sun in 1968-70. S t a n f o r d U n i -versity SU-SEL-70-063, 1970.

52. L E V Y ,G. S.; FT AL . : P ionee r 6—Measuremen t o f Transient Faraday Rota t ionP hen om en a O bserved d ur in g Solar O cc ultat ion . Science, vol. 166, Oct 31, 1969.

5 3 . S C H A T T E N ,K . H.: Evidenc e for a Coronal M agn etic B ottle at ip SolarRadii.NASA-TM-X-638n, 1969.

54.S C A R F ,F. L.; ET A L . :Initial R e s u l t sof the Pioneer 8 VLF Elec t r ic F ie ld Exper im en t .

J. G eop hys. R es., vol. 73, N ov . i, 1968.55. S C A R F ,F. L. ; F R E D R I C K S ,R. W.; AND K E N N E L ,C. F.: AC Electric and Magne t i cFie lds and Col l is ionless Shock St ruc tures . P ar t ic les and Fie lds in the Magne tosphere .R . M. McCormac, ed ., D. R eidel P ub l ishin g Co.; D ordrecht , 1970, p . iO z.

56. S C A R F ,F. L.; ETAL. :AC Fie ldsand W ave -P ar t ic le In terac t ions . Par t ic lesand Fieldsin the Magne tosphere .R . M . M cCorm ac, ed.,D . R eidel P ubl ish ing Co., Dordrecht ,'97°, P -275-

57. S C A R F ,F. L.; ETAL .: P ioneer 8 Elec t r i c F ie ld M easurem ent sin the Distant Geo-magnet ic Tail. J. G eophys. R es. vol.75, J u n e i, 1970,p. 3167.

58. S I S C O E ,G. L.; ETAL.:VL F Elect r ic Fie ldsin the I n t e r p l a n e t a r y M e d i u m : P i o n e e r

8. TRW Systems 10472-6016-RO-OO, '97 '-59. S I S C O E ,G. L.: ETA L . :Evidence fo r a G eom agne t i c W ake a tsO O RE. J. Geophys. Res.,vol. 75, Oct . i, 1970, p. 5319.

60.S C A R F ,F. L.; G R E E N ,I. M.; AND C R O O K ,G. M.: The Pioneer 9 Electr ic Field Ex-p e r i m e n t : P a r t i , Near Ear th Observat ions .TR W Systems i0472-60ig-RO-00,'970.

61. S C A R F,F, L.; AND S I S C O E ,G. L.: The Pioneer 9 Elect ric Fie ld Expe r im en t : P ar t2,Observat ions be tween 0 .75and i .O AU. TRW Systems i0472-6i20-RO-00, 1970.

62 . B E R G ,O. E.; K R I S H N A S W A M Y ,K. S.; ANDS E C R E T A N ,L .: Cosmic Dust RadiantsandVelocities from Pioneer.8 . Goddard Space Fl ight CenterX-6i6-6g-i45 and X-6i6—69-233, 1969.

63. B E R C ,O. E.; ANDG E R L O F F ,U.: M o r e Than Two Ye a r s of Micrometeor i te DatafromTw o P ioneer Satel l i tes . P aper presenteda t Xlllth P l e n a r y 'M e e t in gof C O S PA R( L e n i n g r a d ) ,M ay 1970.

64. A N D E R S O N ,J. D.; AND HILT, D. E.: I m p r o v e m e n tof Astronomical ConstantsandEphemerides from Pioneer Radio Track ing Da ta .Am. Astronaut. Society Paper68-130, 1968.



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HOWARD, H. T.; AN DKOEHLER,R . L . : Interplanetary Electron Concentration an d Varia-bility Measurements with Pioneer VI and VII. The Zodiacal Light and the Inter-planetary Medium. J. L. Weinberg, ed., NASA SP-isO, 1967, pp. 361-364.

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Index

Ames magnetometer,23, 127A m e s plasma probe, 127

scientific results, 90 , 92-97, 130Ames Research Center, 1, 2, 6, 7, 9,

13,55, 133(See also Ames magnetometer, Amesplasma probe)

Cal i fornia Ins t i tu teof Technology, 124Cape Canaveral (Cape K e n n e d y ) ,3, 4,

5 , 1 3 , 3 7Celestial mechanics experiment results ,

138, 140-141Chicago cosmic-ray experiment, 20

scientific results,97-102

Communicat ion subsystem performance,64-65, 66, 69, 70, 71

Convolutional coder,23per formance ,74-75

Cosmic dust , 135-138, 139, 140(See also Goddard cosmic-dustex-p e r i m e n t )

Cosmic rays, 97-115(See also Chicago cosmic-ray experi-m e n t , G R C S W cosmic-ray experi-

ment, Minnesota cosmic-ray experi-m e n t )

Data-handling subsystem perform anc e,65, 67-68, 73

Deep Space N e t w o r k ( D S N ) , 3, 4, 6,7, 9, 25, 115, 124

launch conf igurat ion,37(See also Trackingand data acquisi-t ion)

Delta launch vehicle,3, 4, 11, 17, 25

per formance ,26—36D e p a r t m e n t of Defense, 142DSN. See Deep Space Network.Ear th , magnet ic field, 78-83, 86-87,

88-91, 92, 95-97, 102, 129-131Eastern Test Range (ETR), 3, 4, 8-9,

11, 17, 25, 36, 37, 38, 39

Electrical Ground SupportEquipment( E G S E ) , 3, 10

Electric-power subsystem performance,60, 62, 63, 71-72

Environmental Science Service Admin-istrat ion (ESSA),142Goddard cosmic-dust experiment, scien-

tific results, 135-138, 139, 140Goddard magnetometer, 72,103, 127

scientific results, 78-85, 86, 103, 133,134

Goddard SpaceFlight Center (G SF C) ,2, 8, 9, 127

G R C S W cosmic-ray experiment,78

scientific results, 102-110Ground Opera t iona l Equipment(GOE), 4, 6, 7

Internat ional QuietSun Ye a r ( I Q S Y ) ,77

Jet Propulsion Laboratory (JPL), 1, 2,6-7, 38, 39

(See also Deep Space Network, JP Lcelestial mechanics experiment)

JPL celestial mechanicsexperiment, sci-entif ic results, 138, 140-141

Launch sequence,27, 30Launch vehicle. See Delta launch ve-

hicle.Magnetometers. See Goddard magne-

tometer.Manned Space Flight Network

(MSFN) , 25 , 37 , 38McDonnell-Douglas Astronautics Co.,2,

8Micrometeoroids. See Cosmic dust.MIT Faraday-cupplasma probe, 72

scientific results, 85-90, 119NASA Communicat ions Network

(NASCOM), 11NASA Headquarters, 8, 142

151



152 INDEX

Orientation, Type I maneuver, 25, 41,44, 45, 46-49

(See also specific spacecraft, flightoperations)Type I I maneuver, 7, 11, 12, 46-49(See also specific space craft, flightoperations)

Orientation subsystem perform ance ,58,59, 60, 69

(See also Sun-sensor degradation)Pioneer A. See Pioneer 6.P ioneer B. See P ioneer 7.Pioneer C. See Pioneer 8.Pioneer D. See Pioneer 9.Pioneer E, 12, 22, 26

flight operations, 43-44launch-vehicle performance,30, 36prelaunch narrative,23

Pioneer 6, 21flight operations, 38, 40, 41, 49-51gas leak, 58, 59launch-vehicle per formance , 26-28,

29/30prelaunch narrative, 20spacecraft performance, 55-56, 58-

68, 70t rajectory, 32

Pioneer 7, flight operations, 41, 43, 51launch-vehicle performance, 28, 30prelaunch narrative, 20-21spacecraf t performance,56-57, 68-

69, 71-73trajectory, 33

Pioneer 8, 14flight operations, 41-52launch-vehicleperformance, 28, 30pre lau nc h activities, 18-19pre launch narrat ive , 2 1 — 2 2spacecraf t performance, 57,73-74t rajectory, 34

Pioneer 9, cou ntd ow n sche dule, 16-17detailed task sequence, 13, 15-16

flight operations, 41, 43, 52-53launch-vehicle performance,30, 36prelaunch narrative, 23spacecraft performance,57, 74—75trajectory, 35

Plasma probes.See Am es plasm a probe,MIT Faraday-cup plasma probe.

Radio propagation experiments, scien-tific results, 12 4

(See also Stanfordradio propagationexper iment )

SFOF. See Space Flight OperationsF a-cility.

Solar weather monitoring,141—142Space Flight Operations Facility

(SFOF), 1, 3, 4, 6, 7, 11, 13, 38, 45Stanford radio propagation exper iment ,

scientific results, 115, 118-124, 125Structure subsystem performance, 65, 72Sun, magnetic field, 78-85, 92, 95-97,

100, 103-105plasma, 78, 81, 83, 85-90, 92-97,

100, 119-124, 129-135solar weather, 141-142

Sun-sensor degradation, 58, 69, 71, 73-74

Test an d Training Satellite (TETR),9, 21, 44

Thermal control subsystem performance,58-61, 72, 73

Tracking an d data acquisit ion, launchto DSS acquisition, 36-44

launch trajectories,32-35Pioneer-6 ground track,29

(See also Deep Space Network)TR W Systems, 2, 7, 9, 55, 133TR W Systems electricfield detector, 78

scientific results, 90, 127-135Universi ty of Southern Cal i fornia ,124U.S. Air Force, 2

(See also EasternTest R a n g e )

U . S . G O V E R N M E N T P R I N T I N GOFFICE: 1 9 7 3 O 466—192



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