earth orbital science space in the seventies

8/8/2019 Earth Orbital Science Space in the Seventies

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TABLE OF CONTENTS

INTRODUCTIONPART 1. RESEARCH IN SPACE PHYSICSThe Interplanetary Monitoring Platforms (IMPS)The Sm all Scientific Sate llite (SSS or S3)Satellites in the Transition Region, TheAtmosphere Explorers (AEs)Cooperative Programs in Space SciencePART 2 RESEARCH IN SPACE ASTRONOMYScrutinizing Our Ne arest StarThe O rbiting S olar Observatories (OSOs H, I,J: an d K)Surveying he GalaxyThe Remo tely Con trolled Observatory (OAO)The Search for X-Ray S.~urces,The S mall AstronomySatellite (SAS)The High Energy Astronomy Observatory (HEAO)The Noisy Sky, the Radio Astronomy Explorer (RAE)IN RETROSPECT


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INTRODUCTIONFrom 100 miles up, the universe lwks muchdifferent th,.. it does from the Earth's surface.However, the things seen from satellite orbitdepend strongly upon the "eyes" used. To anastronaut in orbit, the sky is a black domesprinkled with hard points of l ight and dominatedby the Sun and Moon. The Earth below unrolls as apanorama fill ing almost half the sky. In reality, theastronaut sees more than an Earth-bound scientistbut he sees litt le that is really different But whenultraviolet detectors, radiation counters, andmagnetometers replace human eyes in orbit theEarth's magnetic envelope and radiation beltsbecome visible; the Sun, the sta~s, nd the othergalaxies are seen in light that never penetratesthe curtain of the atmosphere.

It was, of course, the presence of this atmosphericcurtain that stimulated scientists first to climbmountains with their instruments, then place themon balloons, and more recently install them inrockets and satellites. Radiation detectors carriedaloft by balloons proved that cosmic rays came fromouter space rather than the Earth itself. Satellitediscoveries of the radiation belts, the solar wind, themagnetosphere (the magnetic envelope around theEarth that wards off the bulk of the space radiation),the X-ray stars, and many other space phenomenahave radically changed our view of the solar systemand of the universe as a whole. Yet, after morethan a decade of scientific satellites, what can Earthorbital science do for an encore? What remainsundiscovered? I f we knew. space science would becut and dried. Scientists no longer dare say, as

many did toward the end of the last century, that thetask of Science was complete except for adding afew decimal places here and there. I n fact, Earthorbital science has just begun to exploit thepote.~tialof satellite instrument carriers. We arejust beginning to understand in detail whattranspir?~ bove the atmospheric blanket that, until1957, clo.lded and distorted our view of the universe.The main rask of the next decade, therefore, islearning the how and why of the phenomena wehave discovered.Some General Objectives of Earth Orbital Science.Since one cannot plan unexpected discoveries, theobjectives of Earth orbital science are necessarilyrather general:Understand better the nature of the spaceenvironment and the hazards it may pose to menand machines.Identify the forces that shape the Earth'senvironmentUnderstand better the origin and evolution of thecosmic environmentrn Carry out experiments that cannot be doneon Earth; that is, use space as a new laboratoryenvironmentAn Overall Strategy. The strategy of Earth orbitalscience is two-pronged: one thrust for "spacephysics," another for "space astronomy." Thefirst deals primarily with the near-Earthenvironment; the second with the Sun and otherstars beyond. As the historicel summaries (below)show, the strategies in both areas have evolved in

Step l n c ~ s e sn Roficicncy- I Step Increases in Proficiency-Space Physics Examples S P ~ ~ A S ~ ~ ~ Y ExamplesIn situ measurements at o rbital altitudesTopside sounding of the ionosphereIn situ measurements n cislunar spaceLarge sa tellites carrying many relatedexperimentsSmall, modular, highly automatedsatellites for synoptic, in situ

meast!rementsLow altitude, in situ measurements ramself-propelled satellitesGroup flights of two or more satellit esto measure correlative phenomena

Explorer 1.1958Alouette 1. 1%2Explorer 18, 1963Orbiting GeophysicalObservatory 1, 1%Small Sc ientificSat ellite . 1971'AtmosphereErplorerC, 973'Proposed

Instrument platforms providing glimpsesof Earth, Sun, and stars at ultrav ioletand radio wavelengthsPointable instrument platforms for abovepurposesUnstab ilized nstrument platforms givingbrief views of E arth, Sun, and stars at

X-ray and gamma-ray wavelengthsPointable instrument p latforms for abovepurpasesUnstabilizedand stabilized instrumentplatforms carrying infraredinstrumentation

Sounding rockets.Explorer satellites,over many yearsOAO 2.1968'RAE 1. lW fSmall AstronomySat ellite . 1970'High Energy Astro-nomical Obser-vatory, 1974*Propased

Satellite m m swucd in this booklet.

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the direction of ever-more-sophisticated spacecraftcarrying instruments with wider ranges and betteraccuracies.Turning these strategies into action, NASA hasbegun the design, construction, and testing of thespacecraft l isted i n Table 1.In the field of space physics, an entirely newkind of spacecraft, the Atmosphere Explorer C, willbe able to penetrate the fringes of the atmospherewithout being slowed and quickly removed fromorbit by air drag. A small, on-board engine makesup for frictional losses. In addition, the same engine

can change the orbit in stepwise fashion, giving asingle satellite the perspective of several differentsatellites in fixed orbits. With the bigger launchvehicles now available another innovation becomesfeasible. NASA hopes eventually to orbit smallgroups of satellites in close flight patterns to detectthe so-called correlative phenomena i n space, suchas the strange "gravity waves" caused byelectromagnetic, gravitationai, 2nd thermodynamicforces working in concertNASA strategy in space astronomy calls not onlyfor additional Orbiting Astronomical Observatories(OAOs), Orbiting Solar Observatories (OSOs), and

Radio Astronomy Explorers (RAEs) to expand

surveys of the celestial sphere in the ultravioletand radio regions of the spectrum, but also for newinstruments o extend our knowledge at very shortwavelengths. Tbe Small Astronomy Satellite (SAS)and High Energy Astronomical Observatory (HEAO)will search the sky looking for X-ray, gamma-ray,and cosmic-ray sources of energy. Some of thesesources have already been seen fleetingly bysounding rcc!:ets and spinning satellites. Becausethey may hold the key to understanding how starsand galaxies get their energies, scientists wish totake longer looks from better stabilized spacecraftEvery time we look at the universe with a new

instrument we see a new facet of a cosmos that isever more complex and mysterious. Our hope is thatsomewhere in the solution of the great puzzle thatnature has presented us we wil l discover thephysical laws that control the cosmos as well asthe key to our own fate.

TABLE 1. NASA's Planned Program in Earth Orbital Science*

The letters designate spacecraft flight models.After a successful bunch. a number is assigned;for example OSO H would become OSO 7.

Space PhysicsInterplanetary MonitoringPlatform (IMP)Small Scientific Satellite (SSS)Atmosphere Explorer (AE)--Space AstronomySmall AstronomySatell ite ( 9 s )Orbiting AstronomicalObservatory (OAO)Radio Astronomy Explorer (RAE)High Energy AstronomicalObservatory (HEAO)Orbiting Solar Observatory (OSO)

75

E

76

K

71

A

BC

H

7-2

H

C

El

73

J

C

I

74

D

AJ


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Part OneRESEARCH IN SPACE PHYSICSThe scientific discipline of space physics is usuallydivided into three parts: (1) Atmospheric physics;(2) Ionospheric physics; and (3) Particles and Fields.It is tempting to divide the volume immediatelyabove the Earth's surface in a similar fashion-likean onion-with the atmosphere on the bottom, next,the ionosphere, and, finally, the radiation beltsand magnetosphere. However, this division is highlyartificial because the eiectrically charged atomsand molecules in the ionosphere coexist with theirneutral counterparts in the atmosphere. (Fig. 1)Further, all three regions are dominated by a singleforce-the Sun-and there is considerableinterchange of energy and particles between thethree regions.

Although sounding rockets began to probe theseregions frequently in 1946, when a large supply ofcaptured German V-2 rockets were equipped withscientific instruments rather than high explosivewarheads, the brief glimpses of high altitudephenomena only whetted the scientist's appetites.The several score scientific satellites launchedsince 1957 have describer' :he gross features of theEar',nls environment, but they have also revealedtile great complexity of the dynamic, Sun-stirredregions surrounding the Earth. Some of theimportant unsolved problems in space physicsfollow.

GEO~~AGNET~CIELD FADINGOUT SLOWLY. EMElilwfPACESURROUNDING EARTH WITH

Figure 1. During the first decade of space flight our conceptof the Earth changed markedly, as indicated by theconceptual drawings on the left and right


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dissociates many molecules, and the cause-and- region bu t also the solar ultraviolet light, wh icheffect relations at higher altitudes. As AEC's actually causes the reactions. Because thecomplement of instruments indicates, one must satellite will dip far enough into the atmospherelook not only at the particle population in this for air drag to be a measurable quantity, anTABLE 4. Design Features and Vital Statistics, SSS-ASpacecraft Functions Design FeaturesCommunications

Power supply

Pulsecode-modulation (PCM) telemetry at 136.830 MHzTwo-level transmitter; In or 5 watts Command receiver at148.980 MHzSolar cells plus silvetcadmium battery. 800 2x2 cm n-p cellsand 1116 2x3 cm n-p cells on top. side. and skirt facets25-30 watts at beginning of life.

Attitude control

ISpin-stabiiizsd satellite wi th magnetic torquing.

Guidance and control

Data handling

Structure

I Passive thermal control using various thermal coatings.Spacecraft bo t tm protected wi th superinsulation.Sun and Earth sensors. SCADS (Scanning Celestial AttitudeDetection System) determines attitude from guide stars towithin 0.1". From the ground, 80 PCM commands plus backuptone commands.Modular, general-purpose data handling system. Incorporatesa buffer memory, central processor, and enables thereprogramming of the telemetry format in-flight Taperecorder.26-faceted polygon with 8-f?cet skirt around bottom. Fourradial instrument booms and central magnetometer boom ontop along spin axis. Weight: about 115 pounds. Polyhedronapproximates a sphere 27 inches in diameter.

Launch vehicle I %OutTracking and dataacquisition network I San Marco Range during launch. Space Tracking and DataAcquisition Network (STADAN) thereafter.TABLE 5. Scientific Instrumentation, SSS-AInstrument Scienti fic ObjectivesChannel multipliers,scintillators, solid-state detectors inan electrostatic analyzerTwo-axis flurgate magnetometersand two searchcoil magnetometersA.C. and D.C. electric feld detectors(actually spheres on ends of booms)

Measure the relationships betweentrapped particles, the geomagneticfield, and the aurorasCorrelation of magnetic fields withcharged particle measurementsmade in above experimentMeasure particle-wave interactions

Principal InvestigatorD.J. Williams (Goddard SpaceFlight Center)L.J. Cahill (University of NewHampshire)D.A Guinett (University of Iowa)and N.C. Maynard (Goddard SpaceFlight Center)


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accelerometer has been included in the payload.Of course, this instrument will also recordvelocity changes caused by the small onboardhydrazine engine. These data, combined withprecision tracking of the spacecraft from theground, wil l be useful to aerodynamicists designingspace shuttle craft that must fly back and forththrough the transition region as they carry cargoto orbital vehicles and stations.

between the Earth's equatorial plane and a planethrough the poles. AE-D will be placed in polarorbit; while the third of the new AEs, AE-E, isdestined for an equatorial orbit. In this way,the transition region will be mapped at mostlatitudes when the perigees of these three orbitscarry the AEs into different parts of the upperatmosphere. To attain these inclinations, differentlaunch sites are required:

AE-C and AE-D are scheduled for flight i n AE-C Mid-inclination Cape Kennedy1973 and -974, respectively. Plans call for p ~ t i i n g AE-D Polar inclination Western Test RangeAE-C into an elliptical orbit i-ic lined midway AE-E Equatorial inclination An equatorial siteTABLE 6. Design Features and Vital Statistics, AE-C *Spacecraft FunctionsCommunications

Power supply

Attitude control

Propulsion

Guidance and control

Design FeaturesPulsecodemodulation (E M ) telemetry.8600 bits sec. Transmitter frequencies:136 and 22% MHz PCM commandfrequency: 148 MHzn-p solar cells on ? ~ pnd sides ofspacecraft. Nickel-cadmium battery.Provides 1M) wars.Spin and despln modes, 0-10 rpm. Spinaxis perpendicular to orbital plane.Momentum wheels. magnetic torquers, andnutation darnprs control attitude and spin.Hydrazine engine prcduces about 5 poundsof thrust. Propellant tank will carry430 pounds of fuel.Horizon scanners and solar aspectsensars.

Data handling I Encoders. Two tape recordersStructure Cylinder 54 inches in diameter and40 inches high. (Fig. 8) Weight:about 1000 pounds, including propellantand instruments.Launch vehicle I &ItaTracking and dataacquisition network Space Tracking and h : a AcquisitionNe~workSTADAN).'Some of these data. particularly weights. maychange as design and fabrication progress


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- - - - - - pp - -TABLE 7. Scientific Instrumentation, AE-C

Neutral mass spectrometer(closed sxrce)

Neutral mass spectrometer(open source)

Langmuir probe

Photometer (extremelrltraviolet range)

Spectrometer (extremeultraviolet)

Ion spectrometer

Neutral temperature probe

Photoelectron spectrometer

Accelerometer

1 Scientific ObjectivesMeasurement of the concentrationsof neutral atoms: H, He. N, 0.Ar; molecules N,, Ot; and thelocal temperature.Measurement of the

I densities of neutral constituents.1-50 amu.' Measurement of electron densityand temperature.

Measurement of ultraviolet lightemitted by the upper atmosphereairglow in several bands between180 and 1100Angstrom units.Recording of the continuousspectrum i n the extreme ultra-violet from 170-1700 AMeasurement of ionic compositionin upper atmosphere. 1-64 amu.Measurement of the temperatureof the neutral atmosphere.Measurement of ionic density,composition and temperature.Measurement of the density andenergy distribution of photoelec-trons in the upper atmosphere.

Measurement of atmosphere-induced decelerations and theneutral air density.

I InvestigatorsD.T. Pelz (Goddard SpaceFlight Center)

AO. Nier (University ofMinnesota)

LH. Brace (Goddard SpaceFlight Center)D.F. Heath (Goddard SateFlight Center)

H.E. Hinteregger (Air ForceCambridge ResearchLaboratories)J.H. Hoffman (Universityof Texas)N.W. Spencer (Goddard SpaceFlight CentedWB Hanson (Universityof Texas)J.P. Ooering (JohnsHopkins University)

K.S. Champion (Air ForceCambridge ResearchLaboratories)

COOPERATIVE PROGRAMS IN SPACE SCIENCEThe upper atmosphere and the space betweenthe Earth and the M oon is such a fertile regionfor space research that several foreign countrieshave built their own satellites. However, thecosts of launch vehicles. launch ranges, andworld-wide tracking and data acquisition networksare high. Therefore, many countries prefer toenter into cooperative agreements with the UnitedStates, under which the United States providesthose elements of technology missing in theirspace programs. It is a two-way street, though,because American scientists often get opportunitiesto fly instruments on these foreign spacecraft.Further, the foreign efforts permit the UnitedStates to make better use of its scientific

resources. The NASA cooperative satellite effortlaunched its first satellites in 1962, when GreatBritain's Ariel 1and Canada's Alouette 1wereorbited successfully. So surcessful have thesecooperative programs been that the number ofcountries involved has expanded. In fact, tt-,esatellites now being prepared for flight are sonumerous that a table is in order to describethem (Table 8). It should also be noted that theUnited States has many cooperative agreementswith foreign countries invo lving sounding rocketresearch.

NASA also supports other agencies of theUnited States government, such as the Air Forcand Navy, in their space research programs.Table 8 also includes these programs.


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* WI-Wallops Island Range. Virginia.WTR-Western Test Range. California.4 N o t an orbital vehicle. but larger than most sounding rockets.Will fly higher and carry a greater payload than most sounding rockets.

TABLE 8.SatelliteDesignationAeros

AFCRL

ANS

Barium ioncloud*

lS lS B. C

San Marco-CSolrad-10

U K 4

UK-5

Launch ScheduleCountry orU.S. AgencyGermany

Air Force

Netherlands

Germany

Canada

Italy

Navy

Great Britain

Great Brita in

For NASA Cooperative Programs-ScientificLaunchDae1972

1971

1974

1971

197I.19721971

1971

~n

1973

VehicleScout

Scout

Scout

Scout

Delta

Scout

Scout

Scout

Scoit

Satellites

Scientific 0bjectivesMeasure the relationship betweenthe state of the upper atmosphereand absorption of solar ultra-violet radiation.Study magnetic storms throughmeasurement of felds andparticles in inner magnet*sphere.Study stellar spectra in therange 15W3300A. and X-raysin ranges 0 2 4 kev and 240 kev.Using a released barium ion cloud,study physical properties ofmagnetosphere at several Earthradii.Measure distribution of electronsand ions in ionosphere, theparticles that interact with th emMeasure equatorial atmosphericparameters between 100 and 500miles.Monitor solar X-ray and ultra-violet emissions and solarflares. Monitor stel lar X-rays.Investigate interactions amongplasma, charged particle streams,and electromagnetic waves inthe upper atmosphere.Investigate galactic and extragalactic

X-ray sources. Measure positions,spectra, intensities, and timevariations from 0 3 to over 300 kev.

NASA Involvement*RangeWTR

WI

WTR

W1

WTR

SanMarcaWI

WTR

WI

Networknone

STADAN

STADAN

Opticaltracking

STADAN

STADANadd othersSTADAN

STADAN

STADAN


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i l lustrate the effect of wavelength, considerthe Radio Astronomy Explorer (RAE) satellite. Inorder to detect and determine the origin of low-frequency radio waves i n space, the RAEantennas had to be 1500 feet long. Even then,sharp images of radio stars, analogous to thosebright points we know in visible l ight, are sti l limpossible. At the short wavelength of thespectrum, images are hard to form for a differentreason. X-rays cannot be focussed by conventionaltelescopic lenses. Telescopes that form imagesof stars at these short wavelengths must bebased upon the property of reflection rather thanrefraction. Such telescopes are often quite large.Thus, a second major problem of space astronomyhas been the sheer size of some of theinstruments.

The following pages wi l l demonstrate that preatprogress has been made in solving the problemsof instrument size and pointing. Because theSun was the first target of space astronomy,NASA's new OSOs will head the list of projects.Then, mo re or less in the order in whic h technicalproblems were solved, the new OAOs and RAEswill be covered. Two new astronomical spacecraftcomplete the l ist: the Small Astronomy Satell i te(SAS) and the High Energy AstronomicalObseNatory (HEAO1.I

SCRUTI NIZING OUR NEAREST STARThe Sun is so close and such a powerful radiatorof energy that one wonders why adequate0b se ~a tio ns annot be made from terrestr ia lobservatories. Of course, the atmosphere is theculprit, blocking most wavelengths except thevisible band and some portions of the radiospectrum. Even where the atmosphere is relativelytransparent, i ts turbulence compromises s cientif icobservations. Consequenily, until instrumentson rockets and satellites took a look, solarphysicists were essentially color blind-at leastin terms of the ultraviolet, some of the infrared,and most of the rest of the electromagneticspectrum.

The OSOs have found the Sun to be most"expressive" at the short wavelengths. X-rays andultraviolet light are indicative of solar processesmore energetic than those that em it visiblelight. For example, solar flares seem to announcetheir development by emitting X-rays andultraviolet light b efore they can be seen visually.he pol lo Telescope Mount (ATM). a manned mission. is coveredin another booklet in this series

Solar flare prediction is valuable to us 93,000,00(,miles away from the Sun because magneticstorms and solar radiation affect not only ourastronauts out in space but also terrestr ialcommunications and possibly our weather andother phenomena. The Sun is also an astrophysicallaboratory-the only star we can see in detail.By studying i t we have learned a great dealabout the evolution of al l stars. There is sti l l muchwe do not know, however, as the following listshows:Some Unsclved Problems of Solar Physics. hat is the relationship between the Sun'smagnetic field and solar activity? Can solar flaresbe forecast by analyzing changes i n the Sun'sfield?. ow are solar cosmic rays generated? Howare the charged partic les accelerated to s uch h ighenergies? Are solar flares the principal sourcesof solar cosmic rays?. hy do flares, prominences, and other signs ofsolar activ ity follow the classical :!;.vpot cycle?. ow is energy transferred i n the S~n ' t ;atmosphere?. oes the solar constant-that is, the amo untof energy reaching the Earth-vary wit h the sunspotcycle?

THE ORBITING SOLAR OBSERVATORIES,OSOs, H, I, J, an d KThe primary objective of OSO-H is the acquisitionof high resolution spectrograms from the solarcorona in white l ight du ring one complete solarrotation. A secondary objective is the recordingof the spectrum of solar and cosmic X-raysbeyond the first solar rotation.

As a spacecraft family, the OSOs are uniquein that the ir top portions (the sails) p ointperpetually at the Sun, while the bottom wheelsspin gyroscope-like t o stabilize the space craft(Fig. 10). Of course, a mo tor on the spacec raftturns the sail a t just the r ight speed so thatthe sail and its instruments always look at theSun. Gas jets at the r ims of the wheel and sailportions controi the satell i te's atti tude. The sunwardside of the sail is obviously the best place tomount solar cells for electrical power generation.Other design features are presented in Table 9.The success of the OSO program can beinferred from the number of successful satell i testhat have been orbited:


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earth orbital science space in the seventies

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