the tiros 6 meteorological satellite system

8/4/2019 The TIROS 6 Meteorological Satellite System

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C O N T R A C T NO. NAS5-1335

THE TIROS VI METEOROLOGICALSATELLITE SYSTEM

POST-LAUNCHEVALUATION REPORT

(NASA-CR-139067) THE TIROS 6METEOROLOGICAL SATELLITE SYSTEM Postlaunch evaluation report (Radio Corp. ofAnerica) 133 pPrepared for theGODDARD SPACE FLIGHT CENTERNATIONAL AERONAUTICSAND SPACE ADMINISTRATIONWASHINGTON, D.C.

N74-76281

By theASTRO-ELECTRONICS DIVISIONDEFENSE ELECTRONIC PRODUCTS

R A D IO C O R P O R A T I O N O F A M E R I C APRINCETON, NEW JERSEY

Unclas00/99 50558

AED R-2261 Issued: December 15, 1964


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C O N T R A C T N O . NAS5-1335

THE TIROS VI METEOROLOGICALSATELLITE SYSTEM

POST-LAUNCHEVALUATION REPORT

Prepared for theGODDARD SPACE FLIGHT CENTERNATIONAL AERONAUTICSAND SPACE ADMINISTRATIONWASHINGTON, D.C.

By theASTRO-ELECTRONICS DIVISIONDEFENSE ELECTRONIC PRODUCTS

R A D I O C O R P O R A T I O N O F A M E R I C APRINCETON, NEW JERSEY

AE D R-2261 Issued: December 15 , 1964


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PREFACE

This report contains the results of the Post-Launch EvaluationProgram for the TIROS VI Meteorological Satellite System. Theprogram was conducted by the Astro-Electronics Division (AED) ofthe Rad io Corporation of Am eric a for the Godd ard Space FlightCenter of the National Aeronautics and Space Administration, underContract No. NAS 5-1335.The report contains an evaluation summary of overall systemoperation and separate detailed evaluations of the performance ofthe subsystems and of the ground support activities. Accounts aregiven of investigations, ana lyses, and tests conduc ted in connectionwith such areas, and recommendations fo r improvem ents that are de-sirable are included.Brief functional descriptions of the subsystems are given in thisreport. More detailed descriptions of the equipment and of thedesign and technical developm ent of the TIROS system are containedin or referred to in the TIROS VI final engineering report. Otherdocuments which may be useful to the reader of this report arereferred to in the text and listed in a bibliography on the final page.

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TABLE OF CONTENTSSection Page

PREFACE HiI. INTRODUCTION . SYSTEM DESIGN Hl. EVALUATION SUMMARY 1IV. TV PICTURE SUBSYSTEM IV1

A. Function IV1B. Performance Evaluation IV3

1. General IV3a. Camera System No. 1 IV3b. Camera System No. 2 IV32. Satellite Components IV6

a. TV Cameras IV6(1) Camera No. 1 IV6(2) Camera No. 2 IV14b. Tape Recorders IV18c. TV Transmitters IV18

3. Ground Station Components IV20V. INSTRUMENTATIONCONTROL SUBSYSTEM Vl

A . Function VlB. Performance Evaluation V2

1. General V22. Shutter Problem V23. Emergency Telemetry Problem V6

VI. TELEMETRY AND TRACKING SUBSYSTEM VI1A. Function VI1B. Performance Evaluation VI4


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TABLE O F C O N T EN T S ' (Cont inued)Section

VII.

vm.

IX.

REFERENCEINDICATO R SUBSYSTEMSA.B.

c.1. AttitudeIndicator Subsystem ,

SATELLITE DYNAMICS CONTROLA.B.

C.

D.

E.

DeSpin Mechanism ,

SpinUp Rockets

Attitude Prediction, Measurement and Control . . ,

ANTENNASA.

B.3. Ground Station Antennas

Pagevnivnivni

. . . VII12VH4VII44vini

vini, . . vrni. . . vnii, . . Vin2. . . VIII3, . ., . ., . . VIH7. . . Vni7, . . ?, . . Vin8. . . vrn8, . . vin io. . . Kl. . K l

, . . K l, . . Kl, . . K2

K2

VI


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T A BL E O F C O N T E N T S (Continued)Section Page

X. ELECTRICALPOWER SUPPLY SUBSYSTEM XlA. Function XlB. Performance Evaluation X2

1. General X22. SolarCell Array X23. Storage Battery X3

XI. SATELLITE THERMAL RESPONSE XI1A. Function XI1B. Performance Evaluation XI1

. GROUND SUPPORT 1A. Launch Support XII1

1. Launch Operations 12. Orbital Data 2

B. Command and Data Acquisition Stations 21. Introduction 22. Operational Evaluation 3

a. General XII3b. Wallops Island Station 4c. Pacific Missile Range Station 6d. Alaska Station 6e. Princeton BackUp Station 6

C. TIROS Technical Control Center 91. Introduction 92. Operational Evaluation 10

APPENDIX AEXTENDED OPERATIONA L EVALUATION AlBIBLIOGRAPHY A5

V ll


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LIST O F I L L U S T R A T I O N S

Figure Page11 Early Orbit Pictures, Both Cameras 1412 Hurricane Daisy; Camera 2, Remote; Orbit 236,

Oct. 4, 1962 1613 Typhoon Karen; Camera 1, Remote; Orbit 827,Nov. 14, 1962 1614 Cellular Formation West of Australia; Camera 2,

Remote; Orbit 726, Nov. 6, 1962. 1615 Pictures Taken During First Four Months of 1963 1716 Mosaic of Alaska and Western Canada Showing Moon'sShadow During Solar Eclipse of August 20, 1963. Mosaic

Comprises 11 TIROS VI Pictures Taken During RemoteSequence of Camera 1 On Orbit 4456 19

17 Path of Hurricane Arlene as its Intensity Decreased fromHurricane to Tropical Storm (August 7) and IncreasedAgain to Hurricane (August 8, 9, and 10) 11018 Hurricane Arlene on August 3, 1963, Orbit 4658, Camera

1, Remote 11019 Typhoon Gloria, Orbit 5191, Camera 1, Remote 111110 Tropical Storm Debra (left) and Hurricane Edith. Pictureof Debra from Orbit, 5045, Camera 1, Remote;Edith from Orbit 5463, Camera 1, Remote 111111 Geophysical Conditions and Surface Detail Recorded byTIROS VI 1131 The TIROS VI Meteorological Satellite 22 TIROS VI Baseplate, Top View Showing ComponentLocations and IR Dummy Weights 4

IV1 Camera System No. 1 Pictures, Taken Before (top)andA fte r Defocusing on Orbit 5664 . IV9

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LIST OF I LLU S TRA TIONS (Continued)Figure Page

IV-2 Results of Vidicon Tests, Showing Effects of DecreasingFocus Current (Electromagnetic Defocusing) IV-10IV-3 Results of Vidicon Tests, Showing Effects of IncreasingG3 Voltage (Electrostatic Defocusing) IV-11IV-4 Results of Vidicon Tests, Showing Effects of Decreasingand Increasing Vidicon Elec trode Voltages IV-13IV-5 Orbit 766, Ca me ra 2, Direct. Final Direct Frame

Received from Ca mera No. 2 . IV-15IV-6 Cam era System No. 2 Pictures from Orbit 1071,Showing Rapid Loss of Focus Leading to Loss ofUseful Pictures IV-17IV-7 Evidence of End-of-tape Sensor Interfering withRecording of First Picture in Re m ote Sequences IV-19IV-8 Probable Radar Interference Observed on Orbit 4726(Camera 1, Remote, Frame 25) IV-19IV-9 Typical TIROS VI Remote Pictures Indicative of NormalTape Recorder Performance IV-20V-l Shutter-Control C ircu it, B lock Diagram V-lV-2 Shutter-Pulse Logic Circuit Before and AfterModification V-5

VI-1 Typical TIROS VI Telem etry Readout VI-5Vn-1 Representative Attitude-Indicator (H-l) Data from theTIROS VI Vn-5Vn-2 North-Indicator Sun Sensor, Showing how anIncompletely Scribed Sensor could Re sult in a 10-Degree Error in Indicated Sun Direction Vn-6

Vin-l Picture-Center Points on Orbit 5286. Satellite Spin-U pTook Place Just Before Frame 12 Vin-6VHI-2 Normal Point Right Ascension versu s Days AfterLaunch Vin-11Vm-3 Decimation versus Days After Launch VDI-15

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LIST OF ILLUSTRATIONS (Cont inued)Figure Page

X-l Calculated Energy Available and Actual Energy Used,versus Days After Launch X-3X-2 Satellite Battery Voltage versus Days After Launch X-3X-3 Ratio of Telemetered Solar Cell Patch Voltage to

Calculated Patch Voltage versus Days After Launch .... X-7XI-1 Temperature of Solar-Cell Array versus Days AfterLaunch XI-3XI-2 Top and Side Temperatures of Structure versus DaysAfter Launch XI-3XI-3 Temperature of Baseplate versus Days After Launch .. .. XI-5XI-4 Battery Temperature versus Days After Lau nch XI-5XI-5 Temperature of Clock No. 2 versus Days AfterLaunch XI-7XI-6 Gam ma Angle and Percent Suntime versus Days AfterLaunch XI-7XI-7 Plot of Predicted Top-Surface Temperatures versusGam ma Angle XI-12A-l Orbit 6886, Camera 1, Remote A-4A-2 Orbit 9335, Camera 1, Direct A-4


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LIST OF TABLESTable Page

IV-1 Picture M easure me nts, Cam era System No. 1 IV-4IV-2 Picture Measurements, Camera System No. 2 IV-7VI-1 Telemetered Parameters of the TIROS VI Satellite VI-3VI-2 TIROS VI Telemetry Calibration Voltages VI-4

VIII-1 TIROS VI Spin-Up Data VIH-3Vin-2 Changes Made in TIROS VI Attitude-Prediction ProgramDuring Operating Life of the Satellite VIII-17

XI-1 Locations and Characteristics of TIROS VI TemperatureSensors XI-9XI-2 TIROS Predicted and Telemetered Top Temperaturesfor Maximum and Minimum Sun Times XI-11A-l Summary of TIROS VI Performance During Post-Operational Evaluation Period A-3


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I. INTRODUCTION

The TIROS VI satellite was successfully launched from Cape Kennedy (a t thattime Cape Canaveral), Florida on September 18 , 1962 at 8:53:09 GMT (3:53:09A . M . EST), and injected into a nearly circular orbit having an inclination of58.319 degrees, an apogee of 442.18 statute miles, and a perigee of 425.13statute miles. The anomalistic period of the orbit was 98. 73 minutes, andits eccentricity was 0. 0019. This was the sixth consecutive launching andorbiting of a TIROS satellite in as many attempts.The primary mission of the TIROS VI satellite was to provide increased photo-graphic coverage of the tropical latitudes, especially of the Caribbean area, dur-in g th e 1962 autumnal hurricane season. The satellite, operating in conjunctionwith the previously launched TIROS V satellite, provided early detection and ob-servation of many of the major hurricanes an d typhoons that appeared duringthat period. Some of these storms were first detected before they had reachedhurricane force, and their paths and developments into severe storms were fol-lowed continuously in pictures returned from many orbits. The operational lifeof TIROS VT exceeded that of any previous TIROS satellite, continuing until Oc-tober 11, 1963 and providing operational data for nearly 13 months in space.TIROS VI was thus able to observe the autumnal hurricanes and tropical stormsof 1963 as well as those of 1962.The TIROS VI satellite carried two one-half-inch vidicon television cameras,one equipped with a wide-angle lens and the other with a medium-angle lens.Each camera was part of an independent camera system which could beoperated by ground command either to take pictures while in contact with aTIROS ground station or to take and record pictures over areas outside thecommunications range of the ground stations, fo r subsequent transmission toone of the ground stations. In addition to the television systems, the satellitecarried instrumentation and electronics for telemetry and beacon transmissions,for dynamics control, and for attitude determination. The dynamics controlsubsystems maintained the desired satellite attitude and kept the satellite'sspin rate within the desired range of 8-to-12 rpm. Electrical power was sup-plied by a solar-energy conversion array and storage batteries.In addition to the primary mission of hurricane watching, the satellite providedroutine observation of the locations and movements of the world's weather sys-tems during 389 days of producing meteorologically useful pictures. In this

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period, TIROS VI transmitted a total of 66, 674 pictures to the ground stations,of which 58,667 were useful fo r meteorological purposes, thus exceeding theperformance of all previous TIROS satellites both in total picture production andin the total number of useful pictures produced. From th e useful picture se-quences, 2122 nephanalyses w ere prepared by the U. S. Weather Bureau, and276 storm advisories and bulletins were issued.The satellite was also used to provide direct weather observations for otherNASA programs and for scientific projects in which NASA was participating. M ostnotable among thes e was the direct support given to the Project M ercury Man-ned Space Flight Program for the MA-8 flight, in October 1962, and the MA-9flight, in May 1963.After October 15, 1964, although the satellite no longer produced meteorologi-cally useful pictures, it was programm ed once every two days to obtain dataconcerning the longevity of the various components in the space env ironment,,This extended evaluation continued successfully until June 24 , 1964, when, after655 days (9412 orbits) of operation in the space environment, the satellite nolonger responded to command. An account of the extended evaluation period isgiven in Appendix A of this report. *TIROS VI was the first TIROS satellite to be equipped with one-year timing de-vices for silencing the beacon transmitters after 12 months of orbital operation.On September 14, 1963, just four days before the satellite had been in space forone year, the beacon transm itters turned off as scheduled. The command andcontrol subsystem and TV picture subsystem No. 1 continued to operate normal-ly . Because this event had been anticipated an d adequate planning had been madebeforehand, it was possible to continue regular satellite interrogations, usingephemeris data to locate and track th e satellite. Regular programming and in-terrogation of the satellite continued fo r nearly one month following beacon turn-off. Many useful pictures were obtained during that period before defocusing ofthe vidicon in camera No. 1 took place on October 11 , 1963.

* * * * *Shortly after the launching on September 18 , 1962, satellite separation from thethird-stage rocket occurred normally and the de-spin mechanism reduced th einitial injection spin-rate successfully. Since the actual passage of the satellitewas in close co rrelation w ith the predicted orbit, the Pacific Missile RangeCommand and Data Acqu isition Station, located at San Nicolas Island, California,

*On December 23, 1964, while this report was in the reproduction cycle,TIROS VI responded to interrogation, providing 63 video fram es to the WallopsIsland CDA station. An account of this interrogation is given in Appendix A.Future successful interrogations of TIROS VI will be rep orted separately, asthey occur.

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experienced no difficulty in acquiring '.lie satellite on the first orbit and in veri-fying separation and spin down.Both the Wallops Island and the PMIl Command and Data Acquisition Stationssuccessfully interrogated the satellite on the first three orbits, and receivedremote pictures of excellent quality. The taking of useful direct pictures wasnot possible during the first three orbits because of the low solar illumina-tion angle and the high nadir angles occurring while the satellite was withinrange of the ground stations; direct pictures were, however, programmed,to demonstrate that th e subsystems were perform ing norm ally. During theremainder of September 1962, 18,373 direct and remote pictures weretaken.On September 19, the second day of TIROS VI operation, the satellite transmit-ted a total of 604 pictures, of which 5-1 were considered useful for meteorologi-cal purposes. From these, twenty-one nepha nalyses were prepared, represent-ing a record for one day's interrogation of a meteorological satellite. Thepictures received showed the presence of a cloud vortex off the Irish coast an dshowed additional vortices in the Norlh and South Atlan tic, over the desert re-gion of the Sudan, and off the Pacific Coast of North America. Many land mas-se s were identified, including th e coasts of Siberia, Pakistan and California, th esouthern tip of India, coastlines along the Mediterranean and Red Seas, an d por-tions of Braz il, C olumb ia, Venezuela and Chile. Special storm advisories weresent to Brazil, giving the location of a storm in the South Atlantic, and to AirForce detachments in the Pacific, giving the Locations of several cloud vorticesin that area. The quality of these early-orbit photographs from both camerasis indicated in Figure 1-1.Engineering checkout of all satellite systems was performed using the AED back-up ground station during the first week of operation. The timing accuracies ofboth programmer clocks aboard the spacecraft were v erified during 11 orbits oc-curring between September 21 and September 23. On September 26, the magne-tic-attitude-control switch was commanded to step through all 12 positions; theswitch circuits responded nor m ally , pe rm ittin g the ground stations to obtaincalibration data for future attitude-con trol program min g. During this period,the satellite continued to transm it pic iur es of excellent q uality, a high percent-age of which were meteorologically useful . Routine nephan alyses we re pre-pared on a daily basis and special storm bulletin s and we ather advisories we resent to Brazil, Florida, Puerto Rico, Au stralia , and Hawaii, and to Air Forcedetachments in the Pacific.During late September and early October, TIROS VI and TIROS V provided oper-ational support for the Project M erc ury MA-8 spaceflight. The two satellitestransmitted more than 5000 pictures .n support of the MA -8 launch and recoveryoperations.

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. Red Seo and Nile River;Camera I, RemoteOrbit 777, Sept. 26, 7962

b. Saudi Arabia and Arabian Sea;Camera 7, Remote;Orbit 745, Sept. 28. 1962

. Vortex South of Australia;Camera 2, Remote;Orbit 274, Oct. 7, 7962

d. Persian Gulf and Gulf of Oman;Camera 2, Remote;Orbit 073, Sept. 23, 7962

Figure 77 Early Orbit Pictures, Both Cameras

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On October 1, 1962, Tropical Storm Daisy was observed in the Atlantic Oceaneast of Cuba and its position and description were reported to the weather centersat San Juan, Puerto Rico and Miami, Florida. TIROS VI continued to monitor theprogress of Daisy through the next several days as it approached the coast of theUnited States from the southeast, obtaining pictures of its configuration as itswinds increased from tropical storm to hurricane intensity. A picture taken ofDaisy during this period is shown in Figure 1-2.Observations of typhoons, tropical storm s, an d other major weather systemswere made throughout the remainder of 1962. Among these were TyphoonsDoreen, Frieda, E m ma , Gilda, and Ivy during October of that year; and Ty-phoons Jean, Caroline, and Karen during Novem ber. A photograph of TyphoonKaren is shown in Figure 1-3. On November 28 , 1962, Typhoon Lucy was ob-served in the Pacific Ocean; a special weather alert giving the location anddescription of the cloud patterns associated with Typhoon Lucy was sent to theJoint Typhoon Warning Center at Guam.On November 12, a loss of focus became apparent in the pictures taken bycam era sy stem No. 2, the medium -angle cam era system, and, 12 dayslater, useful picture transmission from this camera system ceased altogetheras the result of vidicon filament failure . During its two and one-half monthsof operation, this cam era system transmitted more than 12, 300 pictures,which were still classified as good to excellent when the malfunction developed.The quality of the late photographs returned by camera system No. 2 priorto defocusing is evidenced by the frame shown in Figure 1-4.The wide-angle camera system continued to provide TV pictures of very goodquality. During the first four months of 1963, the satellite photographed stormsystems in the Atlantic, Pacific, and Indian Oceans, and over the continents ofNorth an d South America, Asia, and Africa. Based on these photographs,storm advisories were broadcast to many parts of the world by the U. S.Weather Bureau. Examples of the photographs taken during this period areshown in Figure 1-5.Beginning on May 12, 1963, thirty-nine orbits of TIROS VI were programmedto provide meteorological support to the Project Mercu ry M A-9 manned orbitalspaceflight. Of the 1246 pictures received from the satellite during this period,1146 were analyzed in direct support of the M ercury flight. Thirty-seven neph-analyses were prepared from this data and transmitted directly to Project M er-cury meteorologists. In addition, 253 of the pictures were forwarded to theProject M ercury meteorologists via photo-facsimile transmission, to supple-ment the nephanalyses.The TIROS VI satellite entered its second tropical storm season and continuedits observations of major weather systems during the summer of 1963. In June,1963, Tropical Storm Emily was observed off the southwest coast of Mexico,

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Figure 1-2. Hu rricane Daisy;Camera 2, Remote;Orbit 236. Oct. 4, 1962

Figure 1-3. Typhoon Karen;Camera 1, Remote;Orbit 827, Nov. 14, 1962

Figure 1-4. Cellular Formation West of Australia; Camera 2, Remote; Orbit 726, Nov. 6, 7962

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. Vorfex Over MidAtlantic;Camera 2, RemoteOrbit 3154, April 22. 1963

b. Twin Vortex Over North Atlantic;Camera 1, Remote;Orbit 3183. April 25, 1963

. Vort ex Sout hwest of Australia;Camera 1, Remote;Orbit 1677, Jon. 11, 1963

d. Storm Syste m W e s t of California;Camera 1, Remote;Orbit 2006, Feb. 2,1963

Figure 15. Pictures Tak en During First Four months of 1963

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and a well-developed storm vortex was kept under observation during the periodfrom July 5 to July 9. On July 15, Typhoon Wendy was observed in the PacificOcean, 500 miles northeast of the Philippines.On July 20, 1963, the satellite was programmed to take pictures of the moon'sshadow crossing the surface of the earth during the solar eclipse of that date.A mosaic of pictures showing the moon's shadow over Alaska and Western Cana-da is presented in Figure 1-6.The appearance of Hurricane Arlene in the Caribbean area in early August markedthe beginning of the 1963 hurricane season. This storm , fir st observed by TIROSVI on August 2, was monitored by the satellite for a period exceeding one week,and its position an d description wer e continuously reported to the Miami, Floridaand San Juan, Puerto R ico wea ther stations as the storm progressed through theCaribbean. The coverage afforded by weather-satellite observations of Arleneis illustrated in the map of Figure 1-7, on which the sightings made by TIROS VIare designated. During the period from August 2 to August 7, Arlene decreasedbelow hurricane intensity and was reclassified as a tropical-depression. Theapparent remnants of the storm were observed on August 7. How ever, onAugust 8, as Arlene approached the east coast of the United States, its windsagain increased to hu rrica ne velocity. Sightings from TIROS VI on August 8, 9,and 10 showed Hurricane Arlene as its intensity reached a maximum and then asit veered away from the coast and moved on a northeasterly course into theNorth Atlantic. A picture of Arlene as it appeared on August 3 is shown inFigure 1-8.During September of 1963, TIROS VI continued monitoring weather systemsthroughout the world, sighting and tracking Typhoon Gloria over a one-weekperiod in the early part of the month and transmitting pictures of Tropical StormHester on September 12. Typhoon Gloria is shown in Figure 1-9. In the middleof September, the new TIROS Command and Data Acquisition Station at Fairbanks,Alaska became operational. The TIROS VI satellite was used in the initial check-ou t interrogations made by the Alaska ground station, and was interrogated on aregular basis by that station after the station had become fully operational.On September 14 , 1963, just four days before the satellite had completed oneyear of orbital operation , the one-year timers silenced both of the satellite'sbeacon transmitters as scheduled. How ever, accurate ephemeris data an d ade-quate planning for this event permitted the ground stations to continue regularinterrogation of TIROS VI, and the satellite continued to provide operationalsupport by transmitting picture data of very good quality. Significant storm sobserved after beacon turn-off included Typhoon Jennifer, Hurricane Debra,Hurricane Edith, and Hurricane Flora. Debra and Edith are shown in Figure1-10.

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"

""I*

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Figure /-7. Path of Hurricane Ar/ene as ifs /nfensify Decreased from Hurricane to Tropical Storm(August 7) and Increased Again to Hurricane (August 8, 9, and 10)

Figure 1-8. Hurricane Arlene on August 3, 7963, Orbit 4658, Camera 1, Remote

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Figure /-9. Typhoon Gloria, Orbit 5797,Camera 7, Remote

Figure / -70. Tropical Storm Debro (left) an d Hurricane Edith. Picture of Debra from Orbit, 5405,Camera 7, Remote; Edith from Orbit 5463, Camera 7, Remote

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The TIROS VI pictures contained exceptional detail of surface phenomena andthey recorded, in addition to weather data, a number of geophysical events.Several photos of this type are shown in Figu re 1-11. Figure 1-11 (a) showsa cloud of fine particles, believed to be a dust storm, extending over theArabian Sea. Snow cover on the Himalaya M ountains is shown in Figure I-11 (b). Ice covering Jam es Bay and Hudson Bay is shown in Figure I-11 (c).Figure 1-11 (d) is representative of the detail observed in land masses inthe TIROS VI pictures.On October 11, 1963, after TIROS VI had operated for 389 days in orbit, normalpicture taking finally ceased because of a malfunction in the electronics associ-ated with the wide-angle cam era system. Although it was still possible to obtainpicture data, the pictures w ere out of focus and were no t useable for meteorolo-gical purposes. As stated previously, interrogations were continued on a limitedbasis for an additional 10 months to observe the long-term characteristics of thecomponents and subsystems. A summary of this extended evaluation period,which lasted until late June 1964, is given in Appendix A of this report.

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a. Dust Storm Over Arabian Sea b. SnowCovered Himalaya Mountains

. Hudson Bay and James Bay;Outlines of IceLocked Bays Visible

d. Northeastern Coast of North America fronCape Cod to Gulf of St. Lawrence

Figure I. Geo physi cal Conditions an d Surface Detail Recorded by TIROS VI

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II. S Y S T E M DESIGN

The TIROS VI spacecraft (Figure IIl) was approximately 42 inches in diameter,22.5 inches high (excluding anten nas) and weighed approximately 280.5 pounds.As on the previous TIROS spacecraft, solar cells were mounted on most of the topand side surf ace s of the spacecraft to provide power for the subs ystem s. Ap prox imately half of these cells were of the highefficiency "gridded" construction.The comm and receiving antenna was attached to the space craft's "top" surfac e,and a fourelement transmitting antenna was attached to the exterior of the baseplate. Since TIROS VI carried no IR sub system , the support arms an d sensorsof the omnidirectional infrared experiment, which had been mounted on TIROSthrough V, were omitted from TIROS VI.The TIROS VI Meteorological Satellite System was essentially similar in designto th e previous TIROS Series II satellite system, TIROS V. However, a oneyeart iming an d beacondisabling capability was added to the TIROS VI satellite in orderto meet NASA's requirem ent that all satellites be equipped with a "failsafe",positive means fo r automatically and permanently disabling beacon transmittersafter one year of operation in orbit. Two oneyear timers were installed onTIROS VI to implement this requireme nt. Eac h of the timers was connected ina m anner to disable both beacon transm itters at the end of the oneyear period.The TIROS VI satellite did not carry th e NASA infrare d experiment. This satellite was thus similar to the TIROS V satellite and the operation, power profiles,and thermal profiles of the two satellites were essentially th e same. Dummycomponents having the same weights and approximately the same for m s as theactual infrared subsystem components were fabricated an d mounted on the TIROSVI baseplate in the positions normally occupied by the infrared components.Thus, the weight, balance, and flight characteristics of TIROS VI were also approximately the same as those of TIROS V.Th e TIROS VI subsystems were nearly identical to the TIROS V subsystems. Aminor modification was made in the vidicon cathode circuit of the TVpicturesub syste m , to elimin ate a potential source of noise and to improve reliability.A min or addition was made in the beacon "turnon" circuit, to make it less susceptible to spurious command.

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Figure / / - 7 . The TIROS V/ Mefeoro/ogico/ Satellite

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A photograph of the satellite baseplate, showing the subsystem components, ispresented in Figure II-2. The satellite contained a wide-angle and a medium -angle TV -cam era system, each system consisting of a 500-line, one-h alf-inchvidicon TV came ra, a came ra electronics unit, a magnetic video-tape rec ord er,and a TV transmitter. The lens for the wide-angle camera had a 104-degreefield-of-view , on the diagonal, corresponding to a surface coverage of approxi-mately 800 statute miles square at the mean orbital altitude of 435 miles. Themedium-angle camera lens had a 76-degree field-of-view, on the diagonal,corresponding to a surface coverage of approximately 500 miles square atorbital altitude. The video signals produced by the cameras in scanning 500lines on a square image area durin g a two-second readout period had a frequencyspectrum extending from d-c to a maximum of 62. 5 kilocycles (250 lines persecond multiplied by 250 picture elements per line). The output of each cam erasystem could be transmitted directly to an interrogating ground station or re-corded on magnetic tape for later transm ission to the ground. In either case,the video signal was first frequency-modulated on an 85-kc subcarrier. Thelower sideband of this modulation fell within the optimum response of the mag-netic tape recorder. The video subcarrier was frequency-modu lated on a235-Mc carrier for transm ission to the groun d.Both modes of TV-picture subsystem operation (direct and remote), as well asthe auxiliary functions (telemetry read-out, magnetic attitude control, firing ofspin-up rockets, and temporary turn-off and subsequent turn-on of the beacontran sm itters), were controlled by the Command and Data Acquisition (CDA) groundstations by means of the instrum entation control subsystem. This subsystemprovided for the programming of satellite operations in the ground equipment inadvance of a com mu nications contact with the satellite, and for the automatic andrapid generation and transmission of the programmed commands to the satelliteduring the contact. The satellite-borne portion of the subsystem received,demodulated, and distributed the commands to the individual control circuits ofthe satellite.The satellite contained two beacon transmitters, one operating at 136. 23 Me andthe othe r at 136.92 Me. Thirty-three of the satellite's most significant operatingparameters and six calibration voltages were telemetered to the ground stationby modulation of the beacon carriers at the start of each satellite-to-ground con-tact. Attitude-indicator data, which provided a means for determining the attitudeof the satellite's spin axis, was also sent to the ground complex by modulation of thebeacon transmitters. As mentioned above, provision was made for automaticallyand irrevocably turning off the beacon transmitters at the end of one year of opera-tion in orbit.A set of nine sun sensors, equally spaced about the periphery of the satellite,provided sun-pulse signals from which the angle (mea sured on the satellite's base-plate) betw een the TV-cam era radial and the sun-direction vector could be

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1 - Tape Recorder Power Converter2 - TV Camera Control Package3 - Beacon Transmitter4 - Command Receivers5 - One Year Timer6 - Electronic Clock7 - Attitude Control Switch8 - Voltage Regulator9 - De-Spin Timer and (hidden)TV Transmitter No. 110 - TV Transmitter Power Converter

11 - Tape Recorder12 - Telemetry Switches13 - Tape Recorder Electronics14 - Power Supply Protection Unit15 - Auxiliary Control Unit16 - TV Camera No. 2 (medium angle)17 - TV Transmitter No. 218 - TV Camera Electronics19 - RF Matching and Coupling Net-work an d (hidden) Storage Batteries20 - TV Camera No. 1 (wide angle)

Figure 11-2. TIROS VI Baseplate, Top View Showing Component Locations and IR Dummy Weights

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determined fo r each TV picture. This information, which was combined with thevideo subcarrier and transmitted by the TV transmitters, was used together withspin-rate data to establish the north direction on each TV picture.Four means for controlling the satellite's dynamics were carried on the satellite:a precession damper, a de-spin mechanism, a set of spin-up rockets, and amagnetic attitude-control device. These devices were of identical design totheir counterparts used on the TIROS V satellite.The satellite's ope rational spin rate (8 to 12 rpm) was dictated by a maximum,above which the TV pictures would exhibit "smearing", and a minimum, belowwhich the gyroscopic stabilization of the spin axis would begin to lose effective-ness. Satellite spin-down from the relatively high orbit-injection spin rate (125rpm, nominal), required for stabilization of the third-stage rocket and spacecraftcombination, to an operational spin rate (8 to 12 rpm) was achieved by activationof the de-spin mechanism, which automatically deployed a pair of spin-reducingweights four to seven minutes after the satellite had separated from the third-stage rocket.The precession dampers were uncaged after th e separation of the satellite fromthe third-stage rocket, to dampen any "wobble" caused by precession or nutation.The precession dampers were also effective in quickly reducing any wobble whichaccompanied de-spin and spin-up.Five pairs of spin-up rockets were installed about the periphery of the baseplate.The firing of pairs of these rockets was controlled by the ground station so thatthe satellite spin rate could be increased after it had been reduced by interactionof the magnetic dipole of the satellite with the earth's magnetic field.The attitude-control device consisted of a 250-turn coil of wire, wrapped aboutthe periphery of the satellite, and a 12-position switch that controlled the amountand direction of current in the coil. Using this device, the satellite's magnetic-dipole strength could be set by ground command. The spin-axis attitude could bechanged a maximum of 15 degrees per day using this control over the magneticinteraction between the satellite and the earth.Electrical energy for operation of the satellite's electronic circuits was providedby the solar-cell array and by storage batteries. During the "daylight" portionof the orbit, the solar array supplied the satellite's energy needs and maintainedthe battery charge. During the "night-time" portion of the orbit, the batteriessupplied electrical power to the satellite's subsystems.Initially, the TIROS VI ground complex consisted of two primary Command andData Acquisition (CDA) stations, a back-up CDA station, and selected stationsof NASA's Minitrack Network. One of the Minitrack stations, located at

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Santiago, Chile, was provided with a limited com ma nd (clock-start) capability toextend the remote picture-taking capability to orbits on which the satellite was outof contact with either of the CDA stations. Later in the satellite's operating life,a new CDA station, located at Fairbanks, Alaska, was placed in operation andused to command the satellite. The locations and the operations of the otherstations in contact with the satellite were the same as for TIROS V.The primary CDA stations were used fo r commanding or programming the satel-lite's picture-taking sequences, for receiving and processing sun-angle and tele-metry data, and for receiving and processing the TV pictures and IR data trans-mitted by the satellite.The back-up CD A station, located at the Astro-Electronics Division of RCA, hadthe same capabilities as the pr im ary C DA stations. This station was used asnecessary during the operational period of TIROS VI to perform engineering checksof satellite operation. In addition, the back-up station assumed CDA responsibilityduring periods when the Wallops Island station was precluded from operation.The stations of the NASA Minitrack Network tracked the satellite to obtain ephem -eris data for use by the CDAstations in satellite acquisition and tracking.The areas of the earth to be photographed by the satellite were determined bythe U.S. Weather Bureau and specified by requests to NASA. These requestswere examined at the NASA TIROS Technical Control Center (TTCC), located atthe Goddard Space Flight Center, and became the basis for the operating pro-grams prepared by TTCC. Detailed program instructions were teletyped fromTTCC to the cognizant CDA station, where they were used in programming thestation's command and control equipment. The program instructions specifiedthe areas to be photographed, the camera system or systems to be used, theorder in which the camera systems were to be used, and the number of "set-pulses" to be sent to the satellite's clocks so that remote picture-taking couldbegin at the desired point in the orbit.When the satellite came within communication range of the CDA station, thepre-set program was read out and transmitted to the satellite at high speed.High-speed transmission of the preset program com ma nds allowed time bothfor the playback of data that had been stored by the satellite and for the takingof direct pictures, during the period of each ground station-to-satellite contact.

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III. EVALUATION SUMMARY

The successful launching and operation in orbit of TIROS VI extended therecord of the TIROS program to six successes in six attempts, an d reaffirmed th evalidity of the fundamental design of the system and of the engineering and testphases of the program. The performance of the TV-picture subsystem wasnotable for its duration and for the excellent quality of the pictures. TIROS VIwas th e first meteorological satellite to provide useful picture data for morethan one year in orbit. The high quality of the pictures is apparent from the il-lustrations in Section I of this report.On September 14, 1963, just four days before the operating life of TIROS VIreached one year, th e one-year timers activated and turned off the satellite'sbeacon transmitters; however, th e television and control functions of thesatellite continued to be normal, and by using ephemeris data to predict th esatellite's position, the ground stations were able to continue interrogationof the satellite and to obtain TV pictures of good quality until October 11 , 1963,when the wide-angle camera (camera No. 1) defocused. Altogether, in oneyear and 24 days of operation in orbit, the TIROS VI satellite transmitted atotal of 66, 674 TV photographs to the ground stations, of which 58, 667(8 8 percent) were useful fo r meteorological analysis.Camera system No. 1 performed extremely well over this entire period, pro-ducing 54,097 pictures, of which 47,536 were meteorologically useful. Thegeneral quality of these pictures was excellent an d decreased only slightlywith time in orbit. While the operating life of camera system No. 2 wasshort compared with that of camera system No. 1, it nevertheless produced12,338 pictures, over 90 percent (11,131) of which were meteorologicallyuseful .The TV picture subsystem tape recorders and transmitters operated normallyduring th e operating life of the satellite. The only persistent problem encounteredin TV picture subsystem operation was the receipt of one or two blank frames out ofthe 32 frames in many of the picture sequences. This problem was found to berelated to response of the camera shutter control circuit to spurious commandsand was investigated in connection with the evaluation of the instrumentationcontrol subsystem. The cause of the end of useful operation of camera systemNo. 1, after more than a year in orbit, was the failure of an elemental part

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in th e focus current regulator. Operation of camera system No. 2 ended suddenly, giving indications that a vidicon filament failure had occurred. (Vidiconlife tests conducted in order to determ ine the cause of this fa ilure , and of asimilar failure of one of the TIROS V cameras, are described in Section IV ofthis report.)The instrumentation control subsystem performed normally with th e exception of anisolated malfunction of the control circuits fo r emergency telemetry readout. Theaccuracy of the camera clocks in initiating remotepicture sequences was good. Theproblem of missing video frames, mentioned above in connection with the TV picturesubsystem, was extensively investigated; th e results of this investigation and the design changes made to increase th e immunity of the instrumentation control circuits tospurious com mands are discussed in this report. The cause of abnormal operation ofth e spinup rocket control switch was investigated but could not be positively attributedto any malfunction of the switch or of the control circuit. In spite of the problem,normal spinrate increases were achieved in two of the three spinups that were programmed during th e 13month useful life of the satellite, and the required operationalspin rate was maintained.Th e attitudeindicator an d northindicator subsystems performed satisfactorily. Onoccasion, "sunpulses", caused by direct sunlight falling on the lens of the horizonscanner, appeared in the HI data but were easily distinguishable from th e horizonpulses and did not hinder interpretation of the data. A fixed error existed in thetime of triggering of one of the sun sensors in the north indicator subsystem.The nature of this problem was quickly recognized and the fixed error presentedno problem in the use of the data.The performance of the dynamics control subsystem was excellent. A combination of low despin ratio ( 0.072, as compared with th e design value of 0.079)and of the low initial spin rate (99 rpm, as compared with th e design value of12 5 rpm) imparted by the thirdstage rocket resulted in a low spin rate afteroperation of the "Y oYo" despin mechanism.* However, a pair of spinuprockets, f ired on orbit 33, increased th e spin rate to 10.66 rpm, near th e center of the operational range of 8 to 12 rpm .Three pairs of spinup rockets were fired during the operational period of thesatellite. The first two firings produced normal spinrate increases. On orbit5283, (September 14, 1963), after the satellite had been in operation in orbit forapproximately a year, a programmed spinup produced a low spinrate increase. Because this spinup was accompanied by a significant increase in

*The low separation spin rate had the greater effect. Even if the despin ratioha d been 0.079, the spin rate after despin would have been only 7. 82 rpm,starting fro m the low separation spin rate of 99 rpm.

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nutation, it is believed that one rocket either failed to f ire or misfired, possiblyas the result of degradation due to long exposure in the orbital environment.The precession damping me chanism perfo rme d extrem ely well, rapidly reducingthe nutation angle of the satellite's spin axis below 1 degree after the initial spindown an d after the spinups.Both th e accuracy of predicting satellite attitude and the control afforded oversatellite attitude were excellent. Further refine m ent of the prediction programled to even more accurate predictions than had been obtained during operation ofthe previous TIROS satellites. The long evaluation period permitted a more detailed study of the effects of magnetic biasing, the results of which are presentedin this report.The electrical power supply subsystem performed normally, supplying sufficientenergy for the satellite's needs except for one period, when th e practice of pro gramming camera No. 2 simply to expend excess energy was continued into aperiod of low solar input to the solar energy converter. The low solar input(caused by an unfavorable su n angle and a small percentage of orbit time spentin sunlight) resulted in low available energy, so that th e energy used exceededth e calculated energy available for the brief period in which the extra program ming of camera No. 2 was continued. When this type of programming wasstopped, the availab le energy again exceeded the energy used. The battery busvoltage remained within specified limits throughout th e operational period.The thermal response of the satellite was in good agreement with th e predictedresponse. Component temperatures remained well within design limits andsolararray temperatures remained within th e range required fo r good conversion efficiency.The operation of the DA ground stations was satisfactory. The stations quicklyadapted to the heavier programming loads placed on them by the concurrentoperation of two satellites, an d continued to operate efficiently. The qualityof photographic negatives remained high an d consistent.


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IV. TV PICTURE S U B S Y S T E M

A. FUNCTIONThe TV-picture subsystem for TIROS VI consisted of the satellite equip-ment for taking, storing, and trans m itting televisio n meteorological pic turesand the ground equ ipment necessary fo r receiving, displaying, an d recordingthe pictures. The satellite equipment comprised two separate and independentTV -cam era chains, identical except for the cam era lenses. Camera systemNo. 1 was provided with an Elgeet wide angle lens, with a 104-degree diagonalfie Id-of-view, corresponding to a ground-area coverage of approximately 800miles square. Camera system No. 2 was provided w ith a Tegea-Kinoptic medium -angle lens, with a 76-degree diagonal field-of-view, or a ground area coverage ofapproximately 500 miles square.

Each camera chain consisted of the TV camera, a camera-electronics package,a m agnetic tape record er, and a radio transmitter. Each T V chain was capableof independent picture-taking in either of two modes. The direct mode of opera-tion was used when pictures were to be taken w hile the satellite was within com-munications range of one of the CDA ground stations. In this mode, pictures weretaken and, without being record ed, were transm itted directly to the interrogatingground station. When pictures were to be take n over an area of the earth remotefrom the CDA ground stations, the remote mode of camera operation was used.In this mode, the satellite was programmed to start taking pictures after a spe-cific delay period, corresponding to the time required for the satellite to reacha position in its orbit over the area of interest. The pictures taken remotely werestored by the tape recorder until the satellite again came within range of a CDAground station. Upon interrogation of the satellite by the ground station, the re-corded pictures were played back by the recorder and transmitted.In both modes of picture-taking, the camera generated an analog video signalwith a spectrum of approximately 62. 5 kc. This analog signal produced lineardeviation of an 85-kc subcarrier oscillator in the recorder-electronics uni t .When direct pictures we re being taken, the frequen cy-m odulated video subcar-rier was fed directly to the 235-Mc TV transm itter for FM transmission to theground station. When remote pictures were being taken, the video subcarrierwas recorded on magnetic tape. Upon receipt of an appropriate comm and from aground station, the video subcarrier was p layed back by the recorder and fed tothe TV transmitter.

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Each satellite transmission of direct or remote pictures was accompanied bysun-angle data that originated in the nine sun sensors, spaced about the periph-ery of the satellite. A separate subcarrier of 10 kc, modulated on the 235-Mc TV carrier, conveyed the sun-angle information. The sun sensors producedpulses of three characteristic widths as the satellite rotated and each sensor, inturn, scanned the sun. The pulse widths were assigned to the sensors in a man-ner such that a combination of any two consecutive pulses was unique and permit-ted the orientation of the TV camera with respect to the sun to be determined.The pulses produced by the sensors were converted to 10-kc bursts of the sameduration s as the original pulses. In the direct mode of picture-taking, these10-kc bursts were combined with the video subcarrier before it was fed to theTV transmitter. During remo te picture-taking, the 10-kc bursts were recordedon a separate channel of the tape recorder. When the tape recording was playedback for transmission of recorded data to the ground station, the 10-kc burstswere reconstituted (to ensure a sun-pulse subcarrier frequency of exactly 10 kc)and then com bined with the video subcarrier. The combined video subcarrierand sun-angle signal were applied to the TV transmitter. This data, in additionto satellite attitude data, was used to determine the orientation of each pictureframe during interpretation on the ground.The antennas and the coupling and matching network wer e identical in design tothose used for the TIROS V satellite.The TV transmissions from the satellite were received at the CDA ground sta-tion by two receivers connected for polarization-diversity reception. Bandpassfilters we re used to separate the video subca rrier and the sun-angle subcarrier.The video subcarrier was demodulated and the video signal applied to videoelectronics circuits for display on a kinescope and to a magnetic tape recorderfor storage. A time-reference output from the video electronics was applied toan index computer which generated, in binary form, a frame number fo r displaywith each picture. The index com puter also provided, from signals originatingin the ground eq uipme nt, index data identifying th e satellite camera or tape re-corder associated with each frame , fo r display with the TV picture. Provisionwas made for photographing the kinescope display, including the index data, witha 35-millimeter camera.The sun-angle data, after being separated from the video signal, was fed to asun-angle computer, which provided sun-angle data in binary form to be dis-played and photograp hed along with the TV pictures and other index data.The ground-station equipment was essentially the same as that which had beenused for TIROS V.

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. PERFORMANCE EVALUATION1. General

a. Camera System No. 1The performance of camera system No. 1 was very good over a periodof 389 days of operation in orbit. During this period 54,097 pictures were taken,

6,188 in the direct mode and 47, 909 in the remote mode, of which a total of4 7,5 3 6 (87.7 percent) were meteorologically useful . The sudden demise of thiscamera system on orbit 5664 was caused by a change in electrical focus, probably as the result of a sudden reduction in focus current. Up to the time of failure, pictures taken by this camera system in both th e direct and the remotemodes of operation were of good to excellent quality an d were rated high inuseability. Although some problems were encountered with unprogrammed shutteroperation, resulting in instances of "double exposure" and in blank frames, theseoccurrences were relatively infrequent. N o difficulties of any significance wereencountered in tape recorder operation. The TV transmitter operated reliablyand without malfunction.The generally high quality of pictures taken by camera system No. 1 over th eoperational period is evident in the pictures presented in Section I of this report.An analysis was made of pictures selected at intervals throughout the operationalperiod. For this analysis, the selected frames were projected from photopositives and measurements were made of the picture dimensions and of the deviation of the vidicon image axis (as indicated by the crossed reticle marks)from the center of the scanned area. The aspect ratios (width/height) were determined f rom the measurements. These data are listed in Table IV1.At no time did centering, size or aspect ralio deviations reveal system linearityvariations greater than th e standard limits of +10 percent, nor did these deviations become severe enough to detract f rom picture usefulness.

b. Camera System No. 2

Camera System No. 2 returned ll!, 338 pictures, 278 in the direct modean d 12, 060 in the remote mode, of which 11,131 (90. 2 percent) were meteorologically useful. On November 12, 1962 (orbit 8(>8),the directpicture capability ofsystem No. 2 was lost. At approximately th


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TABLE IV-1. PICTURE MEASUREMENTS, CAMERASYSTEM NO. 1

OrbitNo.

18

207

425

598

807

1029

1200

1401

1604

1805

2002

FrameNo.

113225

1516301631

216311330223212291231

413291-T

10-T24-T1-D

16 -D31-D

CenteringDeviation (%)

Vert.1.852.603.524.655.082.581.471.852.600.360.361.452.241.500.712.191.131.130.371.50

1.110.371.111.49

2.201.851.85

Horiz.1.0600.3601.4501.162.270.3900.352.500.350.380.381.100.730.810.811.1001.100.370.370.750.750.750.750.750.75

SizeDeviation (%)

Vert.0.803.470.661.333.461.3303.341.335.475.488.133.333.331.874.000.905.330.194.54

2.662.661.330.50

2.00.400.40

Horiz.2.660.661.870.130.670.131.330.6700.403.470.670.671.331.330.670.530.531.332.640.802.662.660.400.531.330.532.541.33

Aspect Ratio(NormalH/V - 1)

0.9800.9610.9850.9640.9750.9700.9600.9800.9600.9900.9900.9640.9900.9681.0010.9800.9920.9530.9700.9800.9891.0001.0000.9700.9900.9601.0000.9700.980

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TABLE IV-1. PICTURE MEASUREMENTS, CAMERASYSTEM NO. 1 (Continued)OrbitNo.22222406

2650

2852

3029

3158

3405

3600

4011

4393472650135206543755345638

FrameNo.17291

1631

517313

1531

820311

1631

27

16301

1631

21630

CenteringDeviation (%)

Vert.01.851.851.111.11

0-0.78

0.370.740.7200.72

00.354.253.52

-0.77-0.380.360

3.01.02.53.02.04.02.5

Horiz.0.750.760.750.750.751.471.471.471.572.301.521.141.141.141.831.141.830.810.811.200.811.830.741.471.601.601.592.05.51.01.03.03.06.5

SizeDeviation (%)

Vert.0.9350.670.400.802.67

0.270.27

1.472.0002.002.67

0.670.6702.800.402.002.330

1.00.51.05.02.02.03.5

Horiz.1.600.9350.670.530.530.931.871.873.082.661.200.530.670.670.670.671.870.8001.870.800.130.132.00

2.262.663.01.01.52.02.02.51.0

Aspect Ratio(NormalH/V = 1)

0.9900.9801.0001.0000.9611.0000.9900.9900.9720.9700.9610.9810.9550.9550.9610.9610.9610.9700.9490.9490.9590.9810.9640.989

0.9901.0000.9751.0000.991.0000.9950.9950.980

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During the first mo nth of operation, the pictures from camera system No. 2 hadbeen of very good quality. The nature of the failure indicated a sudden filame ntfailure in the cam era vidicon tube.Both the tape recorder and the TV transmitter in camera system No. 2 operatednormally. No problems were encountered with either of these units.The camera system No. 2 pictures were evaluated by analyzing frames selectedat random . These fra m es were projected and m easure me nts were made to de-termine the centering, aspect ratio, an d size deviations from the normal. Theresults of this analysis are given in Table IV-2. As with camera system No. 1,the size, aspect ratio, and centering va riations of camera system No. 2 neverexceeded the standard limits of +10 percent overall system linearity, and didnot detract from picture usefulness.2. Satel l i te Components

a. TV Cameras(1) Camera No. 1

The operating life of camera No. 1 in both modes was exceptionallylong and the camera produced pictures of excellent quality throughout its life.Normal camera programming frequency was in use during most of the operatingperiod. Several problems were encountered but none were serious enough or pro-longed enough to reduce the usability of the pictures significantly until thefinal failure during orbit 5664 on October 11, 1963. The failure on orbit 5664and several instances of temporary abnormal operation were investigated. Theresults of these investigations are described in the following paragraphs.Throughout the operational period of camera No. 1, there were occurrences ofprogrammed remote frames fo r which no video was received. This problem , whichhad also been encountered in the operation of the TIROS V satellite, was tracedto spurious direct-cam era com m ands that occurred while the satellite cameraswere operating in the remote recording mode.Because the shutter travels alternately in one direction and then the other inmaking successive exp osures, a logic circuit is employed to dete rmine the di-rection in which the shutter must travel to make each exposure. This circuitconsists of a bistable multivibrator which is enabled durin g the entire period ofremote operation and which , in normal operation, changes state just before eachshutter operation. The circuit which drives the shutter is enab led only duringa four-s econ d gating period which includes the two-second picture-readout inter-val. If a spurious direct-camera command is received when the "direction-sensing"

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TABLE IV-2. PICTURE M E A S U R E M E N T S , C A M E R ASYSTEM NO. 2

OrbitNo.

4

14

100250

335

425

550

598

684

768

857

FrameNo.

241117

163032

16281631

214163117311016311

161

1631

CenteringDeviation (%)Vert.1.52.21.51.51.91.91.93.11.41.12.50.71.13.281.850.801.852.6000.800001.20.4

Horiz.0.32.22.63.02.61.82.61.92.22.23.22.23.01. 130. 750.800.3800.800. i1. 10.70.80.41.2

SizeDeviation (%)Vert.0.41.41.41.92.42.42.42.00.40.90.200.52.662.1300.84.261.330.8000.71.40.40.20.6

Horiz.0.51.52.01.92.82.83.56.43.31.81.62.24.101.602.00.82.000.801.02.42.51.20.11.4

Aspect Ratio(NormalH/V = 1)

0.9530.9900.9901.0000.9810.9810.9720.9530.9810.9900.9811.0000.9901.01.00.9901.0001.00.9600.9901.0000.9811.0001.0000.9901.0000.990

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multivibrator is enabled but power is not applied to the solenoid, then the direction-sensing circuit changes its state but the shutter does not operate. The nextgenuine shutter pulse (occurring in the two-second interval when the shuttersolenoid is energized) causes the circuit to attempt to drive the shutter in thesame direction in which it last moved, and the exposure is lost.The several ways in which spurious shutter pulses can be produced, and thechanges in the control subsystem which have been made to prevent future occur-rences of this kind, are explained in Section V of this report, in which the evalua-tion of the instrumentation control subsystem is presented. In addition to increas-ing the immunity of the entire control subsystem to spurious commands, the mod-ifications made will reduce the susceptibility of the shutter circuit to system noise.On October 11, 1963, a fte r 389 days of successful operation in orbit, cam eraNo. 1 ceased producing usable pictures. The loss of useful pictures was notedon orbit 5664, during the playback of a remote sequence of pictures. Aftertaking eight normal pictures, the camera underwent a drastic change in focus.Beginning with frame No. 22, the pictures were reduced in size from precedingfra me s as w ell as being badly out of focu s. Figure IV -l(a ) and (b) show fra me s28 and 24, taken shortly b efo re defo cus ing took place. Figure IV-l(c) showsframe 22*, the first fram e in which defocusing was present.Tests were immediately conducted at AED to determine the failure mode whichwould most closely approximate the observed picture degradation of the No. 1came ra system. Three differe nt failure modes in which focus could be lost weresimulated in laboratory tests. In the first mode, the vidicon was defocused electro-magnetically by simply decreasing focus current while holding al l other test val-ues constant.In Figures IV-2(a), IV-3(a), and IV-4(a), th e normal operating condi-tions of the TIROS camera are given and a normal frame taken under these condi-tions is shown. The frame in Figure IV-2(b) was taken with all values except focuscurrent maintained th e same as in Figure TV-2(a). The focus current was re-duced from 101 milliamperes to 92.5 milliamperes. In Figure IV-2(c), the con-ditions were again the same, except that focus curre nt was reduced to 88 milli-amperes.For the second failure mode, the vidicon was defocused electrostatically by in-creasing the voltage applied to the G3 electrode while all other operating con-ditions and values remained normal (as in Figure IV-3(a). Figure IV-3(b) showsthe result of increasing the voltage applied to grid G3 from 192 volts to 245 volts.A further increase to 300 volts resulted in the defocusing shown in Figure IV-3(c).*The remote frames are numbered in the order of playback, which is the reverseof the order of taking the pictures.

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. Orbit 5664, Camera 1, Remote,Frame 28

b. Orbit 5664, Camera 1, Remote,Frame 24

. Orbit 5664, Camera 7, Remote,Frame 22

*Frames are numbered in order of playback

Figure IV1. Camera System No. 7 Pictures, Taken Before (above) and After Defocus/ng on Orbit 5664

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Normo/ Operating ConditionsFocus current = 707 maGrid No. 3 Voltage = 792 vo/fsLight source 2500 footlambertsOperating temperature = 30CShutter triggering rate = 30 seconds

. Normal Operating Conditions Except:Focus current = 92.5 mo

c. Normal Operating Conditions Except:Focus current = 88 ma

Figure IV2. Results of Vidicon Tests, Showing Effects of Decreasing Focus Current(Electromagnetic Defocusing)

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. Normal Operating ConditionsFocus current = 70? maGrid No. 3 Voltage = 792 voltsLight source 2500 footlambertsOperating temperature 30Shuffer triggering rote = 30 seconds

. Normal Operating Conditions Except:C3 Voltage = 245 volts

Normal Operating Conditions Excep t:G3 Voltage = 300 volts

Figure IV3. Results of Vidicon Tests, Showing Effects of Increasing C3 Voltage(Electrostatic Defocusing)

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The third failure mode simulated a malfunction of, or a change of input voltage to ,the chopper circuit in the camera power supply, resulting in reduced or increasedvoltages on all of the vidicon electrodes. Figure IV-4(a) shows a normal raster.In Figure IV-4(b), the target voltage, the G3 electrode voltage, and the G2 electrodevoltage have been decreased to about 15 percen t below their normal values. InFigure IV-4(c), these voltages have been decreased furth er to 20 percent belownormal. In Figure IV-4(d), the voltages have been increased to 25 percent abovenormal by increasing the input voltage to the chopper transform er to the maxim umpossible value of 24. 5 volts.From the evidence presented in Figures IV-2 through IV-4 it was concluded thatelectromagnetic defocusing, as the result of reduced focus current, most closelyapproximated the changes in picture focus and dimensions of the TIROS VIcamera No. 1 pictures. Increases in the G3 voltage, causing electrostatic de-focusing, would almost certainly be accompanied by changes in the other electrodevoltages. Thus the second failure mode is improbable. The third mode of failure,although more probable than the second, does not produce the effects typical ofthe TIROS VI pictures after orbit 5664. A comparison of Figures IV-l(c), IV-2,IV-3 and IV-4 shows that the TIROS VI pictures displayed the effects of electro-magnetic defocusing caused by decreased focus current.On October 16 , 1963, special program ming devised by AED evaluation engineerswas employed at the Wallops Island CDA station to interrogate cam era system No. 1of TIROS VI. This programming was designed to apply a sudden electrical stressto the focus current regulator circuit in an attempt to "shock" the circuit intonormal operation. This attempt, and other attempts made on October 22 and 25,were unsuccessful, and no further meteorologically useful picture data were ob-tained from camera No. 1.The reduction of focus current is attributed to degradation of a circuit elementin the focus current regulator. (Testing has indicated* that the other possiblecause of reduced focus current, namely vidicon filament degradation, leadsrapidly to total filament failure and total loss of focus current.) Failure modetests carried out in connection with the failure of camera system No. 2 of TIROSV revealed several circuit-element failure possibilities in the regulator circuitwhich would result in reduced focus current. The results of these tests have beenreported in the TIROS V evaluation report, in connection with the camera 2 failureof TIROS V. Briefly, a decrease in d-c current gain (Ip;/Ig) of either of thecurrent-regulating transistors, as the result of aging, or the failure of thezener diode that is used as the source of reference voltage, could bring aboutthe decrease on focus current. Determination of the specific circuit elementwhich caused degradation of camera system No. 1 can not be m ade.

*Refer to evaluation of camera system No. 2 in "TIROS V Meteorological SatelliteSystem Post-Launch Evaluation Report."

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. Normo/ Operating ConditionsFocus current = 107 moGrid No. 3 Voltage = 792 voltsLight source = 2500 rooMomberfsOperating temperature = 30 Shutter triggering rate = 30 seconds

Electrode Voltages Reduced by 75 PercentG7 Voltage 26 voltsC2 Voltage = 257 vo/sG3 Voltage ~ 763 voltsTarget Voltage = 0.85 volt

Electrode Voltage s Reduced by 20 PercentG l Voltage ~ 25 voltsC2 Voltage = 242 voltsG3 Vo/foge = 754 voltsTarget Voltage = 0.80 vo/ t

d. Electrode Voltages Increased by 25 PercentGl Voltage = 39 voltsG2 Voltage = 378 voltsG3 Voltage = 240 voltsTarget Voltage = 7.25 volts

Figure IV4. Results of Vidicon Tests, Showing Effects of Decreasing an d IncreasingVidicon Electrode Voltages

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Camera system No. 1 continued to operate in this defocused condition for anadditional 10 months in orbit, with only a very gradual change in the appearanceof the pictures. This condition indicates that, after the initial, sudden decrease,th e focus current stabilized, giving further evidence of a focus current regulatorproblem rather than of vidicon filament degradation.Documentation of the 10-month post-operational period is given in A ppendix A ofthis report.

(2) Camera No. 2During early orbits, camera No. 2 operated normally in both

modes, yielding pictures of good quality and use ability. (See Figures 1-1, 1-2,and 1-4.) On November 12 , 1962 (orbit 808) programming for direct-picturesequences failed to produce an y pictures. Since only the remote mode of opera-tion was being programmed during most of this period, no immediate effect ofthis loss was felt. However, at approximately the same time, a loss of focus ofthe remote pictures began and gradually grew more pronounced. This conditionpersisted and, on orbit 1080 (November 30), pictures could no longer be obtainedfrom camera No. 2. The last pictures received were taken during orbit 1071.The loss of direct-picture capability occurred sometime between orbit 766 onNovember 9, the orbit on which the last direct picture was received, an d orbit808 on November 12, on which no direct pictures could be obtained. The finaldirect picture received on orbit 766 is shown in Figure IV-5. The problem wasinvestigated by examining picture and telemetry data received by the San NicolasIsland ground station on November 12 , during orbits 808 and 809, and by testingcamera operation in both the direct and the remote modes during orbit 823 onNovember 13. The frames from orbits 808 and 809 contained no video, eventhough the satellite had been at attitudes in which the cameras were pointed to -ward the earth during shutter operation. During orbit 809, direct camera 1operation was programmed to occur within five minutes of direct camera 2operation. The direct pictures taken by camera 1 clearly showed earth areas,confirming that the satellite attitude was suitable fo r taking pictures in whicheither cloud cover or the earth's surface should be visible. The camera 2direct pictures did not contain video. Telemetry data verified the presence ofvidicon high voltage and of filament current , indicating that the problem lay else-where, and leading to the conjecture that direct pictures could not be takenbecause the shutter would not operate in the direct mode. Since power is appliedto the shutter drive circuit through separate and independent circuits in directand remote operation, it was plausible that the shutter might operate normallyduring remote operation but not during direct operation.

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Figur e /V-5. O r b i t 766, Camera 2, Direct. Fina l Direct Frame Received from Camera 2This possibility was tested on November 13 (orbit 823) by using special program-ming to operate camera system No. 2 in a "direct-remote" mode. In this dualmode (which is used only fo r emergency operation or evaluation testing), th e cam-era system is turned on in the direct mode to warm up the camera, th e tape recordersignal electronics circuits and the transmitter. Instead of programming th e takingof direct pictures, however, the camera clock is programmed to start a remoterecording sequence almost immediately, so that th e remote sequence begins whilethe system is still in direct camera operation. In this mode, power is not appliedto the tape transport (because the TV transmitter is operating) and although th eshutter pulses are initiated by the camera clock, unregulated minus 26-volt powerto operate the shutter circuit is applied from the same source as in the direct modeof operation. Picture data obtained in this mode is transmitted directly to theground station because the transmitter and tape recorder signal electronics areoperating.On orbit 823, four frames were taken in the "direct-remote" mode, after whichdirect operation was ended, allowing the camera system to record the remainingfram es in the normal remote sequence. The four frames taken in the "direct-remote" mode were without video, while th e remaining frames contained videoshowing earth details.This test further confirmed that, even though th e satellite attitude was suitable forobtaining recognizable video signals, and even though pictures could be taken in theremote mode immediately thereafter, camera system No. 2 could not produce avideo signal in the direct mode. It further confirmed the suspicion that the problem

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was related to application of minus 26-volt power to the shutter circuit in the directoperating mode. Minus 26-volts is applied to several other circuits, includingtelemetry circuits, through the K2 relay in the direct mode. Since these othercircuits functioned normally, the K2 relay has not been suspected. It is th erefo reprobable that diode CR312, through which minus 26-volts is applied to the shuttercircuit during direct operation, failed. Such a failure could only be considereda random failure, because the 1N538 diode used in this application has a surge-current rating of 9 amperes for 160 milliseconds. The load current during shutteroperation is only 3 amperes for 30 milliseconds.The gradual defocusing, which began on November 12, accelerated on November29 and culminated in the failure of camera No. 2 during orbit 1071, on November30. The rapid decrease in focus during orbit 1071, leading to the loss of usefulpictures, is evident in the four frames shown in Figure IV-60 By the timeframe 14 was taken, all picture definition had been lost. Further attempts to ob-tain pictures from camera system No. 2 were unsuccessful. The failure wasattributed to the same condition which had caused gradual progressive defocusingover a two and one-half week period. Telemetry data indicated that the vidiconfilament current and focus current (the focus coil and the vidicon filament areconnected in series) had decreased to zero. The investigation of this problemwas centered on failure-mode testing of the focus current regulator and of thevidicon filament. (This testing was also applicable to the failure of camera No. 2on TIROS V, which had given similar indications symptomatic of vidicon filamen tor focus current regulator failure.)Simulated element failures of the focus current regulator circuit revealed thatany probable element failure in either the regulating circuit or in the referencevoltage circuit would result in a quiescent value of focus (and filament) currentrather than zero current.Accelerated life testing of vidicon filamen ts was carried out over a period of oneyear. These tests and the results obtained are described in the TIROS V evaluationreport. Plots of filament resistance versus cycles of filament voltage applicationshowed that, as the filament approaches failure, its resistance increases at anexponential rate. The defocusing of camera No. 2 followed such an exponentialincrease, the terminal conditions of which are evident in Figure IV-6. Further-more, in the testing of six filaments, one failed after 2680 cycles, while all ofthe others continued to function for well over 15,000 cycles. Thus it is possiblefor some vidicon filam ents to be comparatively short lived.Because no failure mode of the focus current regulator that resulted in total lossof focus current could be found, and because the degradation of vidicon filamen tsduring aging tests followed a characteristic similar to that of the camera No. 2vidicon in its last two and one-half weeks of operation, the loss of focus in cameraNo. 2 vidicon was attributed to failure of the vidicon filament.

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. Cam era 2, Remote, Frame 25* . C am e r a J, Remote, Frame 23

. Cam era 2, Remote, Frame 21 d. Camera 2, Remote, Frame 74

Frames are numbered in order of playback

Figure IV6. Camera System No. 2 Pictures from Ofoit 7 0 7 7 , Showing Rapid Loss of Focus Leadingto Loss of Useful Pictures

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b. Tape RecordersThe tape recorders in both camera subsystems operated normally. No

significant problems were encountered. Except for infrequent and isolated in-stances of signal dropouts, possibly due to deterioration of the magnetic coatingon the tapes, the pictures had good resolution and the flutter was well within speci-fied limits. Projected photographic transparencies of remote pictures from orbitsspaced throughout the operational period were examined fo r general quality andfor any evidence of tape recorder degradation. In the pictures examined, beginningon orbit 641, there was evidence that the first part of the first picture in a remotesequence was being recorded on the portion of the tape containing the metallic end-of-tape sensor. This evidence included tape dropouts, picture tearing, and loss ofsynchronizing signal during the first part of the picture. In frame 32 of orbits2683 and 3144 (Figure IV-7), dropouts occurred which caused synchronizationproblems in the ground station equipment.One other condition that was noted in the frames examined is shown in frame 10 oforbit 4726, Figure IV-8. White spots appeared on this f rame (and on frames 25,28 , and 30 of this same orbit) at a rate of about 200 spots per second. Since thesespots did not recur on later pictures, it is believed that they were caused by localground station interference. Further, because of the regularity and spacing of thespots, it is probable that the interference source was a pulse radar. In general,the remote pictures give evidence of excellent performance of the satellite taperecorders as shown in Figures IV-9.

c. TV TransmittersThe FM telemetry transmitters used on TIROS VI for transmitting th evideo signals were identical to the units used on the TIROS IV and V satellites,having a minimum power output of two watts at the operating frequency of 235

megacycles per second.The information contained in pass summaries and reports of signal strengths fromthe PMR and AED ground stations indicated that the received power levels weregenerally greater than the levels calculated for the minimum value of transmitterpower.There was no indication of reduction in the output power of the transmittersthroughout the operational period of the satellite. The good picture quality reportedby all ground stations indicated proper operation of the modulator sections of thetransmitters.

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. Orbif 2683, Camera J, Remote,Frame 32

b. Orbit 3144, Camera 7, RemoteFrame 32

Figure IV7. Evidence of End ofTape Sensor Interfering with Recording of First Picturein Remote Sequences

Figure /V 8 . Roo'ar Interference Observed on Orbit 4726(Camera 7, Remote, Frame 25)

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. Orb/f 480, Camera 2, Remote . Orbit 293, Camera 2, Remote

Figure /V9. Typical TIROS VI Remote Pictures Indicative of Normal Tape Recorder Performance

3. Ground Station ComponentsThe ground station components of the TV subsystem performed satisfactorily.Although failure rates did increase with the increased use of the ground station to

program and interrogate two operational satellites, data losses were infrequentbecause of improved techniques and increased efficiency of operating personnel.More detailed information concerning operation of the ground station componentsduring TIROS VI operation is contained in Section of this report.

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V. I N S T R U M E N T A T I O N - C O N T R O L S U B S Y S T E M

A. FUNCTIONThe instrumentation-control subsystem consisted of the satellite and ground-station com pone nts required fo r remote control of satellite operations by the Com-mand and Data Acquisition (CDA) ground stations. The limited-comm and (clock-start) capability, which had been added at the NASA Minitrack Station in Santiago,Chile, for TIROS III operation, was again used for TIROS VI. This capabilityallowed the satellite to take pictures du ring orbits when it was beyond the remote-picture clockset capability of the primary CDA stations.

The control subsystem permitted th e satellite to be programmed fo r direct or re-mote picture-taking sequences, for playback of remotely acquired TV data, fortelemetry reado ut, and for initiation of dynam ics-control functions, i .e., mag-netic attitude control, the firing of spin-up rockets, and back-up activation of theTEAM and de-spin mechanisms. In addition, the control subsystem provided acapability for turning off the satellite's beacon transmitters.The satellite-borne components of the instrumentation-control subsystem in-cluded two command receivers, two camera-control units, an auxiliary-controlunit, two timing and sequencing (clock) units, and a magnetic attitude control.All of these com ponen ts were essentially the same as those which had been usedon TIROS V.The ground-station components included a comm and trans m itter, a control-tonegenerator, a command programm er, an antenna programm er, a master clock,a re mote-picture time-set unit, a clock-set-pulse demodulator, and a relay pow ersupply. These compo nents were the same as those used fo r TIROS V operation.The ground-station equipm ent controlled the programming of the tracking an-tennas, the initiation of commands to the satellite, and the operation of the TVand data recorders.The satellite could be operated in any one of three modes; nam ely, direct, remote,and playback. Direct operation was program me d when it was desired to takecloud-cover photographs of the area surrounding the interrogating CDA station.Remote operation permitted the satellite to be preset while in contact with a CDAstation, so that it would take photographs over a geographically remote areaand store the photographs on magnetic tape. Playback operation permitted play-back of recorded cloud-cover photographs, including the related north-indicatordata. When the satellite was neither in contact with a CDA station nor in a re-mote picture-taking sequence, it was in a standby condition, in which power con-sumption was at a minim um.

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The various modes of satellite operation, the program sequences that could beused in each mode, and the functions that could be performed in each mode aredescribed in detail in the TIROS VI final report.

. PERFORMANCE EVALUATION1. General

The instrumentationcontrol subsystem performed reliably and without malfunction throughout th e operational period of the satellite and for many monthsthereafter. When, after almost 13 months of successful orbital operation, th eoperational life of the TV picture subsystem ended, th e instrumentationcontrolsubsystem continued to function normally, permitting postoperational evaluations of the satellite subsystems that remained fully or partially operational.The high percentage of useful pictures returned by TIROS VI (greater than 87 percent for camera No. 1 and greater than 90 percent for camera No. 2) indicatesthe excellent performance of the subsystem. The satellite responded to all commands with good sensitivity, indicating a uniform satellite antenna pattern aswell as very good performance of the command receiver. The camera controlan d auxiliary control circuits functioned normally. However, it became evidentduring operation of TIROS VI, (and of its contemporary, TIROS V), that increasedimmunity of the camera control circuits to spurious command signals would improve total system performance. Such spurious signals were encountered withincreasing frequency during operation of TIROS IV, V, and VI. The occurrenceof spurious commands had been consistently higher in areas of concentratedpopulation where the greatest radio activity would be expected. Although theorigins of these signals are not definitely known, it can be assumed that theyarose from a variety of causes, including aircraft communications in the VHFwave bands, amateur radio transmissions, accidental transmissions from theground stations, crossmodulation products of command transmission by twoground stations, and many other coincidental products of cross modulation oftw o or more radio waves. The motion of the satellite, giving rise to a doppermodulation of signals arriving at its command antenna, could account for a greatvariety of modulations in the frequency range to which the control circuits areresponsive.

2. Shutter ProblemA problem encountered on TIROS V and TIROS VI as the result of spuriouscommand was the receipt of some frames which were devoid of video. An addi

tional, but very infrequent, problem was the receipt of frames containingmultiple images, indicating multiple exposures of the vidicon during one picturetaking interval.

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Both problems were investigated in connection with the TIROS V evaluationeffort an d both were found to be related to operation of the camera shutter. Theblank frames occurred when the direction-control multivibrator of the shuttercontrol circuit (Figure V -l) received spurious pulses. (The shutter normallymoves across the face of the vidicon alternately in one direction and then theother in making successive exposures. The direction of movement is controlledby the state of a bistable multivibrator.) In response to the spurious pulses, themultivibrator changed state in the time between genuine shutter pulses. Theshutter did not actually operate during a spurious pulse because power for driv-ing the shutter is available fo r only a short period beginning just before and end-ing just after a genuine shutter pulse. When the next genuine shutter pulse oc-curred, the circuit attempted to drive the shutter in the same direction inwhich it had last traveled. Under these conditions the shutter could notmove, and the exposure was lost. The occurrence of this condition wasrandom, depending on the number and the timing of the spurious commandsignals.The multiple exposures mentioned earlier resulted from the arrival of spu-rious shutter com ma nds while the minus 26-volt driving power was availableto the shutter circuit. Arriving at that time, the spurious pulses caused theshutter to operate, exposing the vidicon faceplate. The genuine shutter pulsealso exposed the vidicon shortly afterward, well within the vidicon's storageperiod, and the images resulting from both exposures were present in thereadout.As the first phase of the investigation into the shutter problem, the shutterdrive circuit was tested to determine its susceptibility to system noise orsystem transients. The circuit was found to have a high degree of immunityto such spurious inputs. As a result of these tests, it was suspected thatactual shutter pulses were reaching the shutter control circuit.The investigation of the spurious shutter commands was then directed to theshutter-pulse logic circuit in the camera control unit. A functional diagramof this circuit is shown in Figure V-2(a). By considering the operation ofthis circuit, several ways in which a spurious shutter pulse could be pro-duced with no shutter command input become apparent. When the commandfor direct camera operation is received, minus 24.5-volt power is appliedto the circuit.

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SHUTTER P O W E R(2 6 V DC )

S H U T T E RPULSE"

S H U T T E RD I R E C T I O NC O N T R O L

0B I S T A B L E

M U L T I V I

the tiros 6 meteorological satellite system

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