The Ariel I Satellite

8/7/2019 The Ariel I Satellite

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TH E A R IEL I S A T E L L I T E

Robert C . Baumann, ChiefSp ace cra ft Integration and Sounding Rocket Division

The A r i e l I Satel l i te (Figure 1) i s an integrated scient if ic labo ra-to ry spe cifica lly designed to obtain knowledge of the ionosphere and i tscomplex relat ionship to the sun.

This scient if ic labora tory in space is completely self-containedand oth er than a sing le command function op er at es independently of ex-te r na l contro l .

The re a r e no opportuni ties to repa i r o r adjust the ins t rumenta t ioni n thi s lab orato ry once the rock et leaves the launching pad. Considerbeing unable to se rv ice your automobile, adju st your television s et ,have your washing machine rep aire d, fo r a perio d of a yea r . Howmany i tems in everyday use would be op erat ive after one year with nomaintenance?p r e s entation.

I will give data on A r i e l ' s opera t ion s ta tus la te r in my

Let us now tur n our at tent ion to the components that go into makingthis labora tory in space . F i r s t we sh a l l look a t the e lec t ronics , thenbr ie f ly a t the s t ruc ture and assoc ia ted hardware .

The var ious e lec tronic sub-systems a r e represe nted by the Arie l Ifunctional diag ram (Fig ure 2). I wil l not go into detai l on the vario usprobes , sensors , or experim ent condit ioning circ ui ts since they ar e con-side red pa rt of the experiment instrumentation. I wil l , however, go intol imited detai l on the oth er su b-sy stem s indicated.

The power sys tem for Arie l consists of four so lar paddles, twoba tter y pac ks of 10 Nickel-cadmium ce lls ea ch , a shunt voltage lim ite r,a bat tery charging curren t l im iter , a ba t tery switching network, anundervoltage detector s yste m and four co nve rters .

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The four s ol ar paddles a r e covered with p on n si l icon solar cel lsa n d , p r i o r to radiat ion damage i n space, we re capable of providing, de-pending on Ariel 's aspect to the sun, f rom 0.5 to 2 amp eres a t 15 vol t s ,which is 7.5 to 30 watts of power.

The shunt voltage l im ite r regulates the s ola r paddle-bat terycharging voltage to 14.5 vo lts.

The bat t ery charging cu rre nt l imi ter reg ulates the bat tery chargingcu rre nt to a va lue not i n excess of 0.5 ampere.

The batte ry switching network sele cts the ba tter y with the highestvoltage to operate the satelli te.

The undervoltage detector s yste m includes an undervoltage de tec tor ,a con ve rte r, a rela y and the shut-down tim er . Operation of this s yste mtu rn s off A rie l en tirely , with the exception of the ti m e r , fo r approxi-ma tely 18 hou rs, to provide maximum power fo r recharging the bat terie s.

The conver t e r s a r e DC to DC con vert ers which supply regulatedvol tages to Ar ie l ' s e lec t ronic subsystems.

A rie l contains a high speed and a low speed encoder system. F orincreased reliabili ty, operation of the HS encoder i s independent of theoperation of the LS encoder.fac i l i ta te corre la t ion of data.

However, the two a r e synchronized to

The high speed encoder information is tra ns m itte d continually whilethe low speed encoder information is recorded on the tape recorder .

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To give you a n indicat ion a s t o the com plexity of the En cod er sub-systems they contain:

520 t r a n s i s t o r s860 r e s i s t o r s125 capaci tors

59 diodes4 digital osc l.7 analog oscl .

TOTAL - 1575 electronic components

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Ar iel contains a prog ram me r whose main function is to contro l thctra ns mi ss ion of the HS and LS encoder data to the ground.

To t ransm i t the data s tore d by the tape rec or de r , an R F commandis sen t to Arie l from a ground stat ion.corded during the 100-minute orbi t i s played back in approximate ly2 minutes. The tape reco rde r automatical ly goes back into the re cor dmode.

The data which has been re -

A means for automatical ly removing the tape recorder drive motorpower is incorpora ted i n the system to protec t aga inst overloads. TheRF command f r om the ground rese ts the c i rcu i t s o that if the overloadi s remo ved the sy ste m will again function.

Ar ie l ' s Command Receiver i s basica l ly a double-super-heterodyneunit with an amplitude-modulation detec tor. It per form s the s inglecom man d function of tap e re co rd er playback.

Ar ie l ' s phase modula ted t ransm i t te r is ful ly t ran sisto rized anddel ivers 260 mil liwa tts of power to the antenna syste m a t a frequencyof 136.410 megacyles.

Let u s now tu rn briefly to the s t ruc tu re and a ssoc ia t ed ha rdware .In the orbi ta l configurat ion the sate l l i te weighs 133.8 lb s. Ar iel 's

bas i c s t ruc tu re is 23 inches in diam eter by 22 inches high. It i s con-str uc ted pr im ar ily of epoxy-bonded f ilam ents of fib erg las s andmachined-wrought aluminum al loys.

Fig ure 3 shows the main s truc tura l shelf . Notice the machinedbr ac es which perform the dual task of supporting the shelf and str uc tu reand provid e mounting su rfa ce s for the appendages.

F igure 4 shows the f iber glas s upper and lower do me s, and thecyl indrical mid-skin sect ion pr io r to therma l coat ing.

The appendages ar e shown in Figu re 5. Notice the f iberglass inert iabooms and the aluminum s olar paddle ar m s . T w o of the paddle a r m shave two hinges , while two only have one.the appendage to be folded within the nose cone envelope and la te r toassume orbi tal configurat ion.

The hinges in a l l ca se s allow

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Figure 6 shows some of the electronic sub- sys tem s, the de-s pinmechanism, the tape re cord er ,one of the bat ter y packs ,and the escape-ment mechanism that was used to restrain the experiment sensorbooms erection.

F igure 7 shows the experimen ters ' sen sor s and electronics.Using the vario us sub-system s mentioned, adding a few ot he rs , and

wiring th ese a ll together gives the integrated scientific laborato ry nowknown a s Arie l I.

Figure 8 i s a cut-away view of Arie l I. Starting a t the top andmoving clockwise you can see the location of the various experimentsen so rs a s fo llows:

The Ma ss Spectrom eter probeThe Cosm ic Ray AnalyzerThe re a r e three Lyman Alpha dete ctors , one located

on the equa tor, one 45" above and one 45" below theequator.

The El ect ron Density boomThe Aspect Sensor AssemblyThe X -r ay gauge-a second se ns or is located on theThe Electron temper ature probe-a second sens or is

low er dome d ire ctl y below the one shown.located on the spin axis at the bottom of thesatel l i te .

Over one year ago, on April 26, 1962, Ar iel was p laced into orbit .F igure 9 shows some of the housekeeping data obtained up to April 15,1963.angle have been monitored.c i r c l e s .

The percent t ime in sunl ight , temp eratur e, spin rate , and aspectActual data points a r e shown a s sm a l l

The P T 1 payload temp eratu re is the tempera ture me asur ed in UCLstack #2 on the main shelf of Ariel and is indicative of average satel l i tetempera ture . The curve follows the theo retical percen t of t im e in sun-l ight curve rath er well . Ar iel ' s internal temp eratur e ha s ranged fro mapproxim ately +20 to +50" C.

The initial spin rate of approximately 38 rpm decayed to approxi-mately 27 rp m and then incre ased a s shown. Solar pr es su re on th e

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so lar paddles, and Ar iel ' s aspe ct with resp ect to the su n, contr ibute tothe spin ra te increase .

The so lar aspect angle is measu red from the equator of the satel-li te . The angle var ies fr om approximately 42 degr ees above the equatorto approximately 40 de gre es below the equator. Initially the actual datawas v ery close to the theoret ical data; now, however, current data showsconsiderable var iat ion , possibly due to radiation damage to the aspe ctsensor s o la r ce l l s.

Ar iel starte d to malfunct ion on Ju ly 12, 1962. We on the projectfee l that this i s not comp letely unrelated to the Ju ly 9, 1962 high altitud enuclear explosion.

Information about the s atel l i te 's pe rform ance since launch i s showno n F i g u r e 1 0 .

Low-speed data stor e lost in mid-August.The boom e lectro n tem pera ture equipment was funct ional on Apri l 1,

1963. The bas e electro n tem pera ture equipment started inte rmit te ntmalfunction at approxim ately July 9 , 1962. Approximately 7570 of theboom prob e data and 25% of the base probe data was lost upon the mal-function of the low-speed data s to re .

X-r ay spectrom eter-suspected cal ibrat ion change occu rred on, orn e a r , Ma y 4 , 1962. The ex iste nc e of this change is not yet confirme d,but a catas trop hic fai lure occu rred approximately on November 1 , 1962.Approximately 1070 of data los t due to lo ss of low-speed data sto re .

Cosmic ray - geig er counter lost about Sep tem ber 1. Cherenkov75% of d ata lo st due to l oss of

dete ctor st arted to degrade during f i rs t 10070 sunlight p er io d due tooverheating.low-speed data store .

Lost in mid-December.

Elec t ron densi ty - failed M arch 1963 - approximately 75% of datalo st due to lo ss of low-speed data s tor e.

Lyma n alpha failed on launch.Aspect - functioning.

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Spin ra te - inter mitte nt operation during fi rs t half of August andf i r s t half of Novem ber. Op eratin g since then.

Of the ele ctron ic sub -sy ste ms mentioned ea rl ie r, the followingwe re o perating pro pe rly on Ap ril 15, 1963.

1. The power system .2. The high speed encoder.3.4. The trans mitte r.5. Undervoltage det ecto r.6. Recycle t imer .

The command receiver - l as t t ime t r i ed , February 8.

Of questionable op eratin g status a r e the following:

1. The low speed enco der.2.3. The programm er.

The tape record er control circ uits .

Fig ure 11 shows the perc ent of time of o pera tion in the variou soperational modes.

In con clusion, he re a r e a few st at is t ic s related to Ari el I:The equivalent total number of 24-hour days of operation with

modulation, hence, useful data, to 17 Ap ril 1963 wa s 174 days . Thetape re co rd er operated for approxim ately 100 days. The undervoltagesyste m had operated 62 t imes a s of 17 Ap ril 1963. pote ntially adding46 days to the satellite's life.

As of Ap ril 13, 1963 922 hours of usable data have been digitized,and have been sen t to the expe rimenters .mat ely 180 million data points.)

(Th is is equivalent to ap prox i-

On Ap ril 11, the satell ite made its 5000th orb it of the e ar th , whichis equivalent to approxim ately 140 million miles.

The sate l l i te has one year "kil ler" t i m e rs , which have a toleranceof * l o% or 36.5 days. One might, ther efor e, normally expect Ari el Ito cea se tra nsm itting som etim e between now and July 19, provided the"killer" ti m er s work and no undervoltages oc cu r between now and then.

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The Ariel I Satellite

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