Voyager Backgrounder 1981

8/8/2019 Voyager Backgrounder 1981

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National Aeronautics andSpace Administration

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VOYAGER BACKGROUNDER .. AUGUST 1981

For f u r t h e r i n f o r m a t i o n : RELEASE NO: 81-116

C h a r l e s RedmondNASA Headquarters. Wa s h i n g t o n . D.C.(Phone: 202/755-3680)

F r a n k Bris towNASA J e t P r o p u l s i o n L a b o ra t o ry . P a sa d en a . C a l i f .(Phone: 213/354-5011)

CONTENTS

VOYAGER SPACECRAFT ......................................... 1-26S t r u c t u r e and C o n f i g u r a t i o n ........................ 3C o m m u n i c a t i o n s ..................................... 8Power .............................................. 15A t t i t u d e C o n t r o l ................................... 20I n j e c t i o n P r o p u l s i o n C o n t r o l ....................... 2 1C e l e s t i a l R e f e r e n c e C o n t r o l ........................ 2 2T r a j e c t o r y C o r r e c t i o n Manuevers .................... 2 3S c i e n c e P l a t f o r m ................................... 24Te m p e r a t u r e C o n t r o l ................................ 25Lo w-E nergy C h a r g e d P a r t i c l e s ....................... 28M a g n e t i c F i e l d s .................................... 29

Computer Command Subsystem ......................... 18

VOYAGER EXPERIMENTS ........................................ 27-42Cosmic Ray ...................................... a . . 2 7 ..I n f r a r e d I n t e r f e r o m e t e r S p e c t r o m e t e r ............... 0P h o t o p o l a r i m e t e r ................................... 31P l a n e t a r y R a d i o Astronomy .......................... 3 2P l a s m a ............................................. 33P l a s m a Wave ........................................ 35R a di o S c i e n c e

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T e l e v i s i o n ......................................... 38TRACKING AND DATA ACQUISITION ............................... 42MISSION CONTROL AND COMPUTING CENTER ........................ 46VOYAGER SUBCONT.CTORS ..................................... .49APPENDIX A: E a r t h - S p a c e c r a f t C o m m u n i c a t i o n s ................ 2APPENDIX B:

U l t r a v i o l e t S p e c t ro me te r ........................... 4 1

N a v i g a t i o n O p e r a t i o n s .......................... 58


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THE VOYAGER S PA C E C R A F T

Th e t w o i d e n t i c a l Voyager s p a c e c r a f t a r e d e s i g n e d t o

o p e r a t e a t g r e a t e r d i s t a n c e s f rom E a r t h an d t h e S un t h a n r e q u i r e d

b y a n y p r e v i o u s m i s s i o n . C om mu ni ca ti on s c a p a b i l i t y , h a r d w ar e

r e l i a b i l i t y , n a v i g a t i o n a n d t e m p e r a t u r e c o n t r o l a r e among t h e

major c h a l l e n g e s t h a t had t o be m e t t o o p e r a t e o v e r t h e t i m e of

t h e m i s s i on , b e ca u se of t h e E a r t h - s p a ce c r a f t d i s t a n c e s i n vo l ve d a nd

t h e wide r a n g e of e n v i r o n m e n t a l c o n d i t i o n s e n c o u n t e re d .

E a c h s p a c e c r a f t a t l au nc h c o n s i s t e d of a m i s s i o n m od ul e

-- t h e p l a n e t a r y v e h i c l e -- and a p r o p u l s i o n . m o d u l e , w h i c h p r o v i d e dt h e f i n a l e n e rg y in c r e m en t t o i n j e c t t h e m i s s i o n m od ul e o n t o t h e

J u p i t e r t r a j e c t o r y . The p r o p u l s i o n module was j e t t i s o n e d a f t e r

t h e r e q u i r e d v e l o c i t y was a t t a i n e d . ( F o r t h e major p a r t of t h e

m i s s i o n , " s p a c e c r a f t " a n d " m is s io n module" w i l l be used i n t e r c h a n g e -

a b l y . I n d e s c r i b i n g t h e p re -l au nc h c o n f i g u r a t i o n and l a u n c h p h a s e ,

" s p a c e c r a f t " w i l l r e f e r t o t h e combined " m i s s i o n module" a n d " p r o -

p u l s i o n m o d u l e . " )

The l a u n c h w e i g ht o f t h e s p a c e c r a f t was 2,066 k i l o g r a m s

(4,556 p o u n d s) , i n c l u d i n g t h e p r o p u l s i o n module w i t h i t s l a r g e ,

s o l i d - p r o p e l l a n t r o c k e t m ot or t h a t weighed 1 , 2 0 7 k i l o g r a m s (2,660

p o u n d s ) . A f t e r i n j e c t i o n t h e m i s s i o n m o d u le w e i g h e d 8 2 5 k i l o g r a m s

( 1 , 8 1 9 p o u n d s ) i n c l u d i n g a 1 1 7 k i l o g r a m s ( 2 5 8 p o u n d ) s c i e n c e

i n s t r u m e n t p a y l o a d ' .

L ik e t h e M a r i n e r s t h a t e x p l o r e d t h e i n n e r p l a n e t s a nd

t h e Vi k i n g M a r s o r b i t e r s , t h e Voyager s a r e s t a b i l i z e d on t h r e e

axes u s i n g t h e Sun an d a s t a r as c e l e s t i a l r e f e r e n c e s .

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Hot g a s j e t s p r o v i d e t h r u s t f o r a t t i t u d e s t a b i l i z a t i o n

and f o r t r a j e c t o r y c o r r e c t i o n maneuver s .

T h r e e e n g i n e e r i n g s u b sy s t e ms a r e programmable f o r o n-

b o a r d c o n t r o l o f most s p a c e c r a f t f u n c t i o n s . The t h r e e a r e t h e

computer command s u b s y s t e m (CCS), f l i g h t d a t a s u b s y s t e m ( F D S ) a n d

a t t i t u d e a nd a r t i c u l a t i o n c o n t r o l su bs ys te m ( A A C S ) . Th e memories

of t h e u n i t s can be u p d a t e d o r m o d i f i e d by ground command.

A n u c l e a r power s o u r c e -- t h r e e r a d i o i s o t o p e t h e r m o -e l e c t r i c g e n e r a t o r s -- p r o v i d e s e l e c t r i c a l power f o r t h e space-c r a f t .

The p o i n t a b l e s c i e n c e i n s t r u m e n t s a r e mounted on a t w o -

a x i s s c a n p l a t f o r m a t t h e end o f t h e s c i e n c e boom. O t h e r b o d y - f i x e d

and boom-mounted i n s t r u m e n t s a r e a l i g n e d t o p r o v i d e f o r p r o p e r

i n t e r p r e t a t i o n o f t h e i r measu r emen t s .

Data s t o r a g e c a p a c i t y on t h e s p a c e c r a f t i s a b o u t 5 3 6

m i l l i o n b i t s -- a p p r o x i m a t e l y t h e e q u i v a l e n t o f 1 0 0 f u l l - r e s o l u t i o np h o t o s .

D u a l - f r e q u e n c y c o m m u n i c a t i o n l i n k s -- S-band a nd X-band-- p r o v i d e a c c u r a t e n a v i g a t i o n d a t a an d l a r g e a mo un ts o f s c i e n c ei n f o r m a t i o n d u r i n g p l a n e t a r y e n co u n t e r p e r i o d s ( u p t o 115,200 b i t s

p e r s e c o n d a t J u p i t e r and 4 4 , 8 0 0 b p s a t S a t u r n ) .

-. .. r -

T h e d o m i n a n t f e a t u r e of t h e s p a c e c r a f t i s t h e 3 . 6 6 - m e t e r

( 1 2 - f o o t ) d i a m e t e r h i g h -g a i n a n t e nn a t h a t , a f t e r t h e f i r s t 8 0 d a y s

o f f l i g h t , a lmos t c o n t i n u o u s l y p o i n t s t oward E a r t h . P e r i o d i c e x c e p -

t i o n s a r e d u r i n g t r a j e c t o r y - c o r r e c t i o n , c a l i b r a t i o n , o r s c i e n c e

d a t a a c q u i s i t i o n a t t i t u d e m a n e u v e r s .

W hi le t h e h i g h -g a i n a n t e n n a d i s h is w h i t e , most v i s i b l e

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.

p a r t s of t h e s p a c e c r a f t a r e b l a c k -- b l a n k e t e d o r w r ap pe d f o rt h e r m a l c o n t r o l a nd mi c ro m et e or o id p r o t e c t i o n . A f e w s m a l l a r e a s

a r e f i n i s h e d i n g o l d f o i l o r h av e p o l i s h e d a lu mi nu m s u r f a c e s .

S t r u c t u r e and C o n f i g u r a t i o n

The b a s i c m i s s i o n module s t r u c t u r e i s a 2 4 . 5 - k i l o g r a m

( 5 4- p o un d ) 1 0 - si d ed al um in um fr am ew or k w i t h 1 0 e l e c t r o n i c s p a c k a g i n g

c o m p a r t m e n t s . T h e s t r u c t u r e i s 47 c e n t i m e t e r s ( 1 8 .5 i n c h e s ) h i g h

a n d 1 7 8 c e n t i m e t e r s ( 7 0 i n c h e s ) a c r o s s from f l a t t o f l a t ; 1 8 8 c e n t i -

meters ( 7 4 i n c h e s ) f r om l o n g e r o n t o o p p o s i t e l o n g e ro n . The e l e c -

t r o n i c s a s se m b li es a r e s t r u c t u r a l e l e m e n t s o f t h e 1 0- s i de d bo x.

The s p h e r i c a l p r o p e l l a n t t a n k t h a t c o n t a i n s f u e l f o r

h y d r a z i n e t h r u s t e r s f o r a t t i t u d e c o n t r o l and t r a j e c t o r y c o r r e c t i o n

m an eu v er s o c c u p i e s t h e c e n t e r c a v i t y o f t h e d ec ag on . P r o p e l l a n t

l i n e s c a r r y h y d r a z i n e t o 1 2 s m a l l a t t i t u d e - c o n t r o l and f o u r TCM

t h r u s t e r s o n t h e m i s s i o n module and t o l a r g e r t h r u s t - v e c t o r - c o n t r o le n g i n e s o n t h e p r o p u l s i o n m o d u l e d u r i n g l a u n c h .

The 3 .6 6- me te r ( 1 2 - f o o t ) d i a m e t e r h i g h - g a i n p a r a b o l i c

r e f l e c t o r i s s u p p o r t e d a b o v e t h e b a s i c s t r u c t u r e b y a t u b u l a r t r u s s

work. T h e a n t e n n a r e f l e c t o r has an a luminum honeycomb core a n d is

s u r f a c e d o n b o t h s i d e s by g r a p h i t e e po xy l a m i n a t e s k i n s . A t ta c h -

m e n t t o t h e t r u s s e s i s a l o n g a 1 7 8 - c e n t i m e t e r ( 7 0 - i n c h ) d i a m e t e r

s u p p o r t r i n g . The Sun s e n s o r p r o t r u d e s t h r o u gh a c u t o u t i n t h e

an te nn a d i s h . An X-band f ee d ho rn i s a t t h e c e n t e r of t h e r e f l e c t o r .

Two S-band f e e d h o r n s a r e mounted back- to -back w i t h t h e X-band

s u b - r e f l e c t o r o n a t h r ee - l eg ge d t r u s s ab ov e t h e d i s h . O ne r a d i a t e s

t n r o u g h t h e s u b - r e f l e c t o r , t r a n s p a r e n t a t S- .band, t o t h e h i gh - g ai n

d i s h . The o t h e r f u n c t i o n s as t h e l ow -g ai n a n t e n n a .

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L o u v e r assembl ies f o r t e m p e r a t u r e c o n t r o l a re f a s t e n e d t o

t h e o u t e r f a c e s of two e l e c t r o n i c s c o m p a r t m e n t s -- t h o s e h o u s i n gt h e p ower c o n d i t i o n i n g a s se mb l y a nd t h e r a d i o t r a n s m i t t e r power

a m p l i f i e r s . T h e t o p a nd b o t t o m o f t h e 1 0 -s i de d s t r u c t u r e a r eenclosed w i t h m u l t i - l a y e r t h er m al b l a n k e t s .

Two Canopus s t a r t r acke r u n i t s a r e m o u n t e d s i d e - b y - s i d e and

p a r a l l e l a t o p t h e u p p e r ring of t h e d e c a g o n .T h r e e r a d i o i s o t o p e t h e r m o e l e c t r i c g e n e r a t o r s a r e a s s e m b l e d

i n t an de m on a d e p l o y a b l e boom h i n g e d o n a n o u t r i g g e r a r r a n g e m e n t

of s t r u t s a t t a c h e d t o t h e b a s i c s t r u c t u r e . The RTG boom i s

c o n s t r u c t e d of s t e e l a nd t i t a n i u m . E a ch RTG u n i t , c o n t a i n e d i n a

b e r y l l i u m o u t e r case , i s 4 0 . 6 c e n t i m e t e r s (16 i n c h e s ) i n

d i a m e t e r , 5 1 c e n t i m e t e r s ( 2 0 i n c h e s ) l o n g a n d w e i g h s 39 k i l o g r a m s

( 8 6 p o u n d s ) .

T h e s c i e n c e boom, s u p p o r t i n g t h e i n s t r u m e n t s t h a t measure

e n e r g e t i c p a r t i c l e r a d i a t i o n , i s l o c a t e d 1 8 0 d e g r e e s f r o m t h e RT G

boom and i s h i n g e d t o a t r u s s e x t e n d i n g o u t f r o m t h e d e c a g o n

b e h i n d t h e h i g h - g a i n a n t e n n a . T h e boom, 2.3 mete r s ( 7 1 / 2 f e e t )

l o n g , i s a b r i d ge w o r k of g r a p h i t e e po xy t u b i n g . A t t a c h e d o n

o p p o s i t e s i d e s of t h e boom a t i t s m i d - p o i n t a r e t h e c o s m i c r a y

and l ow -e ne rg y c h a rg e d p a r t i c l e i n s t r u m e n t s . F a r t h e r o u t on t h e

boom is t h e p lasma sc i ence i n s t r u m e n t .T h e two-axis s c a n p l a t f o r m is mounted a t t h e e n d o f t h e boom

and p r o v i d e s p r e c i s i o n p o i n t i n g f o r f o u r r e mo t e- s en s in g i n s t r u -

m e n t s -- t h e u l t r a v i o l e t s p ec t ro m et e r , i n f r a r e d i n t e r f e r o m e t e r

s p e c t r o m e t e r amd r ad iome te r, p h o t o p o l a r i me t e r ( n o l o n g e r o p e r a t -

i n g o n Vo y a g e r 1) and a two-camera imaging s c i e n c e s u b s y s t e m .

To t a l p l a t f o r m g i m b al l e d we ig ht i s 1 0 0 k i l o g r a m s ( 2 2 0 pouncis) .Wi t h b o t h t h e RTG a n d s c i e n c e booms d e p l o y e d , t h e near-

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e s t boom-mounted ins t rument t o a r a d i a t i o n source i s 4. 8 meters

( 1 6 f e e t ) , w i t h t h e b u l k of t h e s p a c e c r a f t b et we en t h e two. The

c l o s e s t p l a t f o r m - m o u n t e d i n s t r u m e n t i s 6.4 meters ( 2 1 f e e t ) away.

A p a i r of 1 0 -m et e r ( 3 3 - f o o t ) wh i p a n t e n n a s , d e p l o y e d

from a p o s i t i o n o u t s i d e t h e t o p r i n g o f t h e b a s i c s t r u c t u r e an d

e x t e n d i n g down b e tw e e n t h e R T G boom o u t r i g g e r m e mb er s, a r e p a r t of

t h e p l a n e t a r y r a d i o a s t r o n o m y (PRA) i n s t r u m e n t p a c ka g e a nd a r e

s h a r e d w i t h t h e plasma w a v e i n s t r u m e n t (PWS). Th e PRA and PWS

a s s e m b l i e s a r e b o d y - m o u n t e d a d j a c e n t l y.

t u b i n g a n t e n n a s , w h i c h form a r i g h t a n g l e , were r o l l e d f l a t i n

t h e i r h o u s i n g b e f o r e d e p lo y me n t b y s m a l l e l e c t r i c motors.

T h e b e r y l l i u m - c o p p e r

The ma g ne t ic f i e l d s e x pe r im en t c o n s i s t s of a n e l e c t r o n i c s

s u b a s s e m b l y l o c a t e d i n o n e of t h e m i s s i o n module e l e c t r o n i c s b a ys

a nd f o u r m a g n e t o m e t er s -- t w o h i g h - f i e l d s e n s o r s a f f i x e d t o t h e

s p a c e c r a f t and t w o l o w - f i e l d s e n s o r s mo un ted o n a 13-me te r ( 4 3 -f o o t ) d e p l o y a b l e boom. Th e boom, c o n s t r u c t e d of e p o x y g l a s s ,

s p i r a l l e d f ro m i t s s towed p o s i t i o n i n a n a lu mi nu m c y l i n d e r t o form

a r i g i d t r i a n g u l a r mast w i t h one m ag n et o me t er a t t a c h e d t o i t s e nd

p l a t e a n d a n o t h e r p o s i t i o n e d 6 meters ( 2 0 f e e t ) c l o s e r t o t h e

s p a c e c r a f t . T h e mast w e ig h s 2 .26 k i l o g r a m s ( f i v e p o u n d s ) , a few

o u n c e s l e s s t h a n t h e c a b l i n g r un ni ng i t s l e n g t h and c a r r y i n g power

t o and d a t a from t h e m a g ne t o me t e r s. T he boom h o u s i n g i s a 2.8-

c e n t i m e t e r ( n i n e - i n c h ) d i a m e t e r c y l i n d e r , 66 c e n t i m e t e r s ( 2 6 i n c h e s )

l o n g , s u p p o r t e d by t h e RTG o u t r i g g e r . T h e mast u n c o i l s i n h e l i x

f a s h i o n a l o n g a l i n e between t h e r e a r f a c e o f t h e h i gh - ga i n a n t e n n a

a n d t h e RTC boom.

- -. . -

The b a s i c s t r u c t u r e of t h e d i s c a r d e d p r o p u l s i o n m o d u l e


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was a 43 .54-k i log ram (96-pound) a luminum semi-monocoque s h e l l .

The c y l i n d e r , 99 c e n t i m e t e r s ( 39 i n c h e s ) i n d i a m e t e r a n d 89 c e n t i -

meters ( 3 5 i n c h e s ) l o n g , was s u s p e n d e d below t h e m i s s i o n mo du le

s t r u c t u r e by a n e igh t-memb er t u b u l a r t r u s s a d a p t e r.

t h e s t r u c t u r e c o n t a i n ed t h e s o l i d r o c k e t motor t h a t d e l i v e r e d t h e

f i n a l powered s t a g e of f l i g h t . T he r o c k e t , w hi ch w ei gh ed 1 , 1 2 3

k i l o g r a m s ( 2 , 4 7 5 p o u n d s) i n c l u d i n g 1 ,0 3 9 k i l o g r a m s ( 2 ,2 9 0 p o un d s )

o f p r o p e l l a n t , d e ve l op e d a n a v e r ag e 1 5 , 3 0 0 p o u n ds t h r u s t d u r i n g

T h e h o l l o w of

i t s 4 3- se co nd b u r n d u r a t i o n .Mounted o n o u t r i g g e r s from t h e s t r u c t u r e were e i g h t

h y d r a z i n e e n g i n e s t h a t p ro v i de d a t t i t u d e c o n t r o l d u r i n g t h e s o l i d -

motor b u r n . H y dr a zi n e f u e l was s u p p l i e d f r o m t h e m i s s i o n m o d u l e .

A p a i r o f b a t t e r i e s and a remote d r i v e r modu le f o r power-

i n g t h e v a l v e d r i v e r s t o t h e t h r u s t - v e c t o r - c on t r o l e n g i n e s were

p o s i t i o n e d on t h e o u t e r f a c e of t h e c y l i n d r i c a l p r o p u l s i o n modu le

s t r u c t u r e .

A f o u r - sq u ar e - f o o t s h un t r a d i a t o r / s c i e n c e c a l i b r a t i o n

t a r g e t f a c e s o ut wa rd f ro m t h e p r o p u l s i o n mo dule t r u s s a d a p t e r

t ow ar d t h e s c a n p l a t f o r m . The d u al - pu r p os e s t r u c t u r e i s a f l a t

s a n d w ic h o f t w o a l u m i n u m r a d i a t i n g s u r f a c e s l i n i n g a honeycomb

core .

p l a t e s , a n y a m o u n t of t h e e l e c t r i c a l power from t h e RT G s c a n be

r a d i a t e d t o s p a c e a s h e a t . The o u t e r s u r f a c e a l s o s e r v e s a s a

p h o t o me t r i c c a l i b r a t i o n t a r g t ' t f o r t h e re mo te -s en s i ng s c i e n c e

Through power c o l l e c t o r s a n d e m i t t e r r e s i s t o r s b e t w e e n t h e

i n s t r u m e n t s o n t h e s c a n p l a t f o r m .

T h e s h u n t r a d i a t o r and t h e p ro p ul si on -m od ti le t r u s s a d a p t e r

r e m a i ne d when t h e p r o p u l s i o n mo du le was j e t t i s o n e d .

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S t e e l a l l o y / g o l d f o i l p l u m e d e f l e c t o r s e x te n de d f ro m t h e

p r o p u l s i o n m o d u l e t o s h i e l d t h e s t o w e d RTGs a n d s c a n p l a t f o r m from

r o c k e t e x h a u s t d u r i n g e n g in e f i r i n g .Th e s p a c e c r a f t a d a p t e r , a t r u n c a t e d al umi nu m c o n e , j o i n e dt h e p r o p u l s i o n m o d u l e t o t h e C e n t a u r s t a g e of t h e l a un c h v e h i c l e .

T h e a d a p t e r , 7 6 c e n t i m e t e r s ( 3 0 i n c h e s ) t a l l , was 1 60 c e n t i m e t e r s

( 6 3 i n c h e s ) i n d iame te r a t t h e b a s e ( C e n ta u r a t t a c h m e n t ) , 9 9

c e n t i m e t e r s (39 i n c h e s ) a t t h e s p a c e c r a f t s e p a r a t i o n j o i n t a nd

w e i g h e d 36 k i l o g r a m s ( 7 9 p o u n d s) . The a d a p t e r r e ma i ne d w i t h t h e

C e nt a ur r o c k e t s t a g e a t s p a c e c r a f t s e p a r a t i o n .

L a u n c h C o n f i g u r a t i o n

Some m e ch a ni c al e l e me n t s o f t h e s p a c e c r a f t were r i g i d l y

r e s t r a i n e d a g a i n s t t h e s e v e r e v i b r a t i o n d u r i n g l au nc h. A f t e r

l a u n c h , a p p e n d a g e s t h a t had been l a t c h e d s e c u r e l y w i t h i n t h e C e n t a u r

s t a g e n o se f a i r i n g were d e p l o y e d t o t h e i r c r u i s e p o s i t i o n s .

T h e p y r o t e c h n i c s u b s y s t e m p r o v id e d s i m p l e an d p o s i t i v e

d e pl o ym e nt w i t h e x p l o s i v e s q u i b s . D e vi c es s towed s e c u r e l y d u r i n g

l a u n c h an d r e l e a s e d f o r d ep lo ym en t b y t h e p y r o t e c h n i c s u bs y s te m

were t h e s c i e n c e boom, RTG boom and magnetometer boom. U n c e r t a i n t y

c o n c e r n i n g t h e f u l l d ep lo ym en t an d l o c k i n g o f t h e s c i e n c e boom o n

Voyager 2, f i r s t s p a c e c r a f t l a u n c h e d , e x i s t e d f o r s e v e r a l w e e k s .

T h e p y r o t e c h n i c s u b s y s t e m a l s o r o u t e d power t o d e v i c e s

t o s e p a r a t e s p a c e c r a f t from l a u nc h v e h i c l e , a c t i v a t e d t h e prop-

u l s i o n m o d u l e b a t t e r i e s , i g n i t e d t h e s o l i d - p r o p e l l a n t r o c k e t motor,

s e a l e d o f f t h e p r c p e l l a n t l i n e c a r r y i n g h y d r a z i n e from t h e m i s s i o n

module t o t h e propLi3.sion mo du le , j e t t i s o n e d t h e p r o p u l s i o n m c d u l e

a n d r e l e a s e d t h e IRIS d u s t co v er . T h a t su b s y st e m i s no l o n g e r u s e d .

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Communica t ions

C o m m u n i c a t i o n w i t h t h e Vo y a g e r s i s by r a d i o l i n k b e t w e e n

E a r t h t r a c k i n g s t a t i o n s and a d u a l - f r e q u e n c y r a d i o s y s t e m a b o a r d

e a ch s p a c e c r a f t .

T h e u p l i n k o p e r a t e s a t S- ban d o n l y , c a r r y i n g commands

a nd r a n g i n g s i g n a l s from g ro un d s t a t i o n s t o o n e of a p a i r of r e d u n -

d a n t r e c e i v e r s . The d ow nl in k i s t r a n s m i t t e d f ro m t h e s p a c e c r a f t

a t b o t h S-band and X-band f r e q u en c i e s .

The on -boa rd commun ica t io ns sy s t em a l s o i n c l u d e s a program-

m a b l e f l i g h t d a t a s u b sy s t em (FDS), m o d u l a t i o n / d e m o d u l a t i o n s u b s y s t e m

(MDS), d a t a s t o r a g e s u b s y s t e m (DSS) a nd h i g h - g a i n a n d l o w - g a in

a n t e n n a s .

The FDS, o n e of t h e t h r e e o n- bo ar d c o m p u te r s , c o n t r o l s

t h e s c i e n c e i n s t r u m e n t s and f o r m a t s a l l s c i e n c e and e n g i n e e r i n g

d a t a f o r t e l e m e t r y t o E a r t h . The t e l e m e t r y m o du l a t i on u n i t ( T M U )

o f t h e MDS f e e d s d a t a t o t h e d o wn l i nk . The f l i g h t command u n i t

( F C U ) o f t h e M D S r o u t e s g r o u n d commands r e c e i v e d by t h e s p a c e c r a f t .

O n l y o n e r e c e i v e r i s powered a t a n y o n e t i m e , w i t h - t h e _ _r e d u n d a n t r e c e i v e r a t s t an d by . The r e c e i v e r o p e r a t e s c o n t i n u o u s l y

d u r i n g t h e m i s s i on a t a b o u t 2 11 3 m e ga h er t z . D i f f e r e n t f r e q u e n c y

r a n g e s h a ve be e n a s s i g n e d t o t h e r a d i o - f r e q u e n c y s u b s y s t e m of e a c h

s p a c e c r a f t . The r e c e i v e r c a n be u se d w i t h e i t h e r t h e h ig h - ga in o r

l o w - g a in a n t e n n a . Voy a ge r 2's p r i ma r y r e c e i v e r f a i l e d o n A p r i l 5 ,

1978, a nd t h e s p a c e c r a f t i s o p e r a t i n g o n i t s b a ck u p r e c e i v e r , w hi ch

i s a l s o c r i p p l e d w i t h a p a r t i a l f a i l u r e of t h a t p o r t i o n of t h e

r e c e i v e r t h a t a c q u i r e s an d t r a c k s t h e t r a n t i v i t t e d s i g n a l .

(Appendix A c o n t a i n s a d e t a i l e d d e s c r i p t i o n of Voyager 2

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communication problem, the process used to accommodate the operations

limitation imposed by the problem, and some of the communications

fea tures of the Voyager 2 Saturn encounter.)

The S-band transmitter consis ts of two redundant exciters

and two redundant RF power amplifiers, of which any combination is

possible.

one time. Selection of the combination is by on-board failure-

detect ion logic within the computer command subsystem ( C C S ) , with

ground-command backup. The same arrangement of exciter-amplifiercombinations makes up the X-band transmitting unit.

Only one exciter-amplifier combination operat es at any

One S-band and both X-band amplifi ers emp-ley traveling

wave tubes (TWT). The second S-band unit is a solid state ampli-

fier. The S-band transmitte r is capable of operat ing at 9 . 4 watts

or at 28.3 watts when switched to high power and can radiate from

both antennae. X-band power output is 1 2 watts and 21.3 watts.

X-band uses only the high-gain antenna. (S-band and X-band never

operat e at high power simultaneously.

When no uplink signal is being received , the transmitted

S-band f requency of about 2295 MHz and X-band frequency of 8418 MHz

origina te in the S-band exciter's auxili ary oscill ator o r i n a

separa te ultra-stable oscillator (one-way tracking). With the

receiver phase-locked to an uplink signal, the receiver provides

the frequency source f or both transmitters (two-way tracking).

The radio system can also operate with the receiver locked to an

uplink signdl while the downlink carrier f requencies are determined

by the on-board oscil lators jtwo-way noncoherent tracking).

Both the 64-meter (210-foot) and 34-meter (112-foot)


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a n t e n n a s t a t i o n s of t h e Deep S p a c e N e t w o r k c a n r e c e i v e t h e

downlink X-band s i g n a l . T he e n t i r e 6 4 -m et er f 34-meter a n d 26-

meter ( 8 5 - f o o t ) a n t e n n a s t a t i o n s a r e c a p a b l e o f r e c e i v i n g a t S-

band .The X-band dow nli nk was not n o r m a l l y u s e d d u r i n g t h e f i r s t80 d a y s of t h e m i s s i o n -- u n t i l E a r t h was w i t h i n t h e beam o f t h es p a c e c r a f t ' s h i g h - g a i n a n te n na . C om mu ni ca ti on s d u r i n g l a u n c h ,

n e a r -E a r t h and e a r l y c r u i s e ph as e o p e r a t i o n s were c o n f i n e d t o S-

band and t h e l o w - ga i n a n t e n n a . An e x c e p t i o n o c c u r r e d e a r l y i n

t h e f l i g h t when t h e s p a c e c r a f t , on i n e r t i a l c o n t r o l , p o i n t e d t h e

h i g h - g a i n a n t e n n a t ow a rd E a r t h t o s u p p o r t i n s t r u m e n t c a l i b r a t i o n

and a n o p t i c a l n a v i g a i o n/ h ig h - r a t e t e l e co m m un i c a ti o n s l i n k

t e s t . D u r i n g i t s c a l i b r a t i o n s e q u e n c e o n S e p t . 1 8 , 1 9 7 7 , Voy ag er

1 t o o k p i c t u r e s o f Ea rt h- Mo on s y s t e m .

T he h i g h - g a i n a n t e n n a , w i t h 3 . 66 - me t er - di a me t er ( 1 2 f e e t )

p a r a b o l i c r e f l e c t o r , p r ov i d e s a h i g h l y d i r e c t i o n a l beam. T h e

l o w- g ai n a n t e n n a p r o v i d e s e s s e n t i a l l y u n i fo r m c o v e ra g e i n t h e

d i r e c t i o n o f E a r t h .

Under normal c o n d i t i o n s , a f t e r t h e f i r s t 8 0 d a y s o f t h e

m i s s i o n , a l l c o m m u n i c a t i o n s -- b o t h S-band and X-band -- h a v ebeen v i a t h e h i g h - g a i n a n t e n n a . T h e n o r m a l c o m m u n i c a t i o n

c o n f i g u r a t i o n f o r t h e Voyager 2 S a t u r n e n c o u n te r i s f o r t h e X-

band t r a n s m i t t e r t o o p e r a t e a t h i gh power and t h e S -band

t r a n s m i t t e r t o o p e r a t e a t low power. T he o n l y v a r i a t i o n s t o t h a t

c o n f i g u r a t i o n a r e d u r i n g E a r t h - o c c u l t a t i o n e n t r a n c e and e x i t when

t h e S-band i s a t h i g h power and t h e X-band i s a t low -power.

Low-power X-band i s a l s o u s e d d c r i n g two I R I S c a l i b r a t i o n s , when

b o t h t h e S -b an d and X - b a n d t r a n s m i t t e r s a r e a t low power.


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Commanding t h e S p a c e c r a f t

r o u n d commands a r e used t o p u t i n t o e x e cu t i o n s e l e c t e d

f l i g h t s eq uences , t o cause e x e c u t i o n o f d i s c r e t e e v e n t s , o r t o

cope w i t h u n e x p e c t e d e v e n t s . Commands a r e i s s u e d i n e i t h e r a

p r e - d e t e r m i n e d , t i m e d sequence v i a on -b oa rd p r og r am c o n t r o l o r

d i r e c t l y a s r e c e i v e d f r o m t h e ground. Most commands a r e i s s u e d by

t h e s p a c e c r a f t ' s c o m p u t e r command s u b s y s t e m ( C C S ) i n i t s r o l e a s

" s e q u e n c e r - o f - e v e n t s " a n d b y t h e f l i g h t d a t a s u b s y s t e m (FDS) a s

c o n t r o l l e r o f t h e s c i e n c e i n s t r u me n t s .

A l l c o m mu n ic a t i on s b et we en s p a c e c r a f t a n d E a r t h a r e i n

d i g i t a l f o r m. Command s i g n a l s , t r a n s m i t t e d a t 1 6 b i t s p e r s e c o n d

( b p s ) t o t h e s p a c e c r a f t , a r e d e t e c t e d i n t h e f l i g h t command u n i t

and r o u t e d t o t h e C C S f o r f u r t h e r r o u t i n g t o t h e i r p r o p e r d e s t i n a t i o n .

G r o u n d commands t o t h e s p a c e c r a f t f a l l i n t o t w o major c a t e g o r i e s :

d i s c r e t e commands (DC), and coded commands ( C C ) .

A d i s c r e t e command c a u s e s a s i n g l e a c t i o n o n t h e s p a c e -

c r a f t . F o r exam ple , DC-2D s w i t c he s t h e S-band a m p l i f i e r t o h i g h

power: DC-2DR, S-band a m p l i f i e r l o w power; DC-2E, S - b a n d t r a n s m i t s

from h i g h - g a i n a n t e n n a : DC-2ER, S -ba nd t r a n s m i t s l o w -g a i n. C oded

. _ -

commands a r e t h e t r a n s f e r of d i g i t a l da ta f rom t h e computer command

s y s t e m o r f r o m t h e g r o u n d v i a t h e CC S t o use r s u b s y s t e m s . S u b s y s -

tems r e c e i v i n g coded commands a r e f l i g h t d a t a , a t t i t u d e a nd a r t i c -

u l a t i o n c o n t r o l , modulation/demodulation, d a t a s t o r a g e a nd power.

Downlink Tele ine t rv

Data t e lemetered from t h e s p a c e c r a f t c o n s i s t s of e n g i n e e r -

i n g a n d s c i e n c e m e a s u r e m e n t s p r e p a r e ? f o r t r a n s m i s s i o n by t h e

f l i g h t d a t a s u b s y s t e m , t e l e m e t r y m o d u l a t i o n u n i t a nd d a t a s t o r a g e

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s u b s y s t e m . The e n c o d e d i n f o r m a t i o n w i l l i n d i c a t e v o l t a g e s , p r e s -

s u r e s , t e m p e r a t u r e s , t e l e v i s i o n p i c t u r e s and o t h e r v a l u e s m e a s u r e d

b y t h e s p a c e c r a f t t e l e m e t r y sensor s a n d s c i e n c e i n s t ru m e n t s .

Two t e l e m e t r y c h a n n e l s -- low r a t e a n d h i g h r a t e -- a r ep r o v i d e d f o r t h e t r a n s m i s s i o n o f s p a c e c r a f t d a t a . The low r a t e

c h a n n e l f u n c t i o n s o n l y a t S-band a t a s i n g l e 4 0 - b i t s - p e r - s e c o n d

d a t a r a t e and c o n t a i n s real- t ime e n g i n e e r i n g d a t a e x c l u s i v e l y .

I t i s o n o n l y d u r i n g p l a n e t a r y e n c o u n t e r s when t h e h i g h - r a t e c ha n-

n e l i s o p e r a t i n g a t X-band.The h i g h - r a t e c h a n n e l i s o n t h r o u g h o u t t h e m i s s i o n . I t

o p e r a t e s a t e i t h e r S-band o r X-band a nd c o n t a i n s t h e f o l l o w i n g

t y p e s o f d a t a :

O E n gi n ee r in g o n l y a t 4 0 b i t s p e r s e c o n d o r 1 , 2 0 0 b p s

( t h e h i g h e r d a t a r a t e u s u a l l y occurs o n l y d u r i n g

l a un c h a nd t r a j e c t o r y c o r r e c t i o n m an eu ve rs ) t r a n s m i t t e d

a t S-band o n l y .

O Rea l - t ime c r u i s e s c i e n c e a n d e n g i n e e r i n g a t 2 ,560 ,

1 , 2 8 0 , 6 40 , 3 2 0 , 1 6 0 a n d 80 b p s . R e d u c e d d a t a r a t e s

r e s u l t i n r e d u c e d i n s t r u m e n t s a m p l i n g . Data r a t e i s

r e d u c ed o n l y when t h e t e l e c o m m u n i c a t i o n s l i n k c an -

n o t s u p p o r t t h e h i g h e r r a t e .

O Real- t ime e n co u n t e r g e n e r a l s c i e n c e an d e n g i n e e r i n g

a t 7 .2 k i l o b i t s p e r s e co nd ( a s p e c i a l 11 5 . 2 k b p s r a t e

was a v a i l a b l e a t J u p i t e r f o r t h e p l a n e t a r y r a d i o

a s t r o n o m y i n d plasma wave i n s t r u m e n t s ) t r a n s m i t t e d

a t X-band 0. y .

O Real-time e n c o un t e r g e n e r a l s c i e n c e , e n g i n e e r i n g an d

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17/70

T h e d a t a - s t o r a g e s u bs ys t em i s a d i g i t a l t ape recorder which

can r eco rd a t two r a t e s : TV p i c t u r e s , g e n e r a l s c i e n c e a nd

e n g i n e e r i n g a t 11 5 . 2 k bps ; g e n e r a l s c i e n c e a nd e n g i n e e r i n g a t 7 .2

k b p s ; a nd e n g i n e e r i n g o n l y a t 7 . 2 k b p s ( e n g i n e e r i n g i s acqu i r ed

a t o n l y 1 , 2 0 0 b p s , b u t i s f or ma t t ed w i t h f i l l e r t o m a t c h t h e

r e c o r d e r i n p u t r a t e ) . T h e t a p e t r a n s p o r t i s b e l t - d r i v e n . I t s

1 / 2 - i n c h magnetic t a p e is 328 meters (1,075 f e e t ) l o n g and is

d i v i d e d i n t o e i g h t t r a c k s t h a t a r e r e c o r d e d s e q u e n t i a l l y one

t r a c k a t a t i m e . To t a l r e c y c l e a b l e s t o r a g e c a p a c i t y i s a b o u t 5 3 6

m i l l i o n b i t s -- t h e e q u i v a l e n t o f 1 0 0 TV p i c t u r e s . P l a y b a c k i s

a t one of f o u r s p e e d s -- 57.6 , 33 .6 , 21 .6 and 7 . 2 kbps .Downlink t e l e m e t r y d a t a r a t e s a r e m ax im iz ed d u r i n g t h e

S a t u r n e n c o u n t e r by t h e s i m u l t an e o us r e c e i p t a nd p r o c e s s i n g of

t h e r e c e i v e d s i g n a l f rom t h e s p a c e c r a f t by two c o - l o c a t e d g r o u n d

a n t e n n a s (one 64-me te r and on e 3 4 - m e t e r ) . G o l d s t o n e , S p a i n a nd

A u s t r a l i a h av e c o - l o c a t ed s t a t i o n s p r o v i d i n g t h e a r r a y e d

c a p a b i l i t y . Combin ing t h e r e c e i v e d s p a c e c r a f t s i g n a l r e s u l t s i n

a p p r o x i m a t e l y a o ne -l dB i mp ro ve me nt i n s i g n a l - t o - n o i s e r a t i o .

T h a t i s e q u i v a l e n t t o h a v i n g o ne 72 -m et er s t a t i o n a t e a c h

l o c a t i o n . Loss of a 34-meter s t a t i o n d u r i n g an y a r r a y e d t r a c k

would r e s u l t i n a r e d u c t i o n o f d a t a q u a n t i t y or q u a l i t y , b u t n o t

i n t h e loss of a l l d a t a . Loss o f t h e 6 4 -m et e r a n t e n n a w ou ld__-. - - -

r e s u l t i n t h e loss of X-band c a p a b i l i t y , r e du c in g a v a i l a b l e d a t a

t o e n g i n e e r i n g i n f o r m a t i o n o n l y .

T r a c k i n q t h e S p a c e c r a f t f o r N av i g a t i o n

Ve r y p r e c i s e n a v i g a t i o n i s r e q u i r e d t o a c h i e v e t h e d e s i r e d

ma neu ver a nd f l y b y a c c u r a c i e s f o r a m u l t i - p l a n e t / s a t e l l i t e

e nco u n t e r m is o 1 .R a d i o m e t r i c o b s e r v a t i o n s made by a t r a c k i n g s t a t i o n o n E a r t h

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u s i n g r a d i o s i g n a l s t o and from t h e s p a c e c r a f t a re i m p o r t a n t i n

d e t e r m i n i n g t h e s p a c e c r a f t ' s p o s i t i o n and v e l o c i t y . The r a d i o

d a t a c o m b i n e d w i t h p h o t o g r a p h s of se l ec t ed s a t e l l i t e s a g a i n s t t h e

background of known s t a r s taken by t h e cameras p r o v i d e t h e i n f o r -

m a t i o n ne c e s s a r y f o r t h e p r e c i s e n a v i g a t i o n r e q u i r e d . ( Ap pe nd ix

B c o n t a i n s a d e s c r i p t i o n o f t h e Voy ag er n a v i g a t i o n p r o c e s s ,

i n c l u d i n g d e s c r i p t i o n s of t h e t y p e s of da ta used , o r b i t d e t e r m i -

n a t i o n , t r a j e c t o r y c o r r e c t i o n , t h e Voyage r 2 t a r g e t i n g s t r a t e g y

a nd t h e Voyager 2 n a v i g a t i o n s t a t u s a s of Ma y 1 5 , 1 9 8 1 . )

Power

T h e Vo ya g er power s u b s y s t e m s u p p l i e s a l l e l e c t r i c a l power t o

t h e s p a c e c r a f t by g e n e r a t i n g , c o n v e r t i n g , c o n d i t i o n i n g an d

s w i t c h i n g t h e power.

Power source f o r t h e m i s s i o n m od ul e i s a n a r r a y o f t h r e e

r a d i o i s o t o p e t h e r m o e l e c t r i c g e n e r a t o r s ( R T G s ) . T h e p r o p u l s i o n

m od ul e, a c t i v e on l y d u r i n g t h e b r i e f i n j e c t i o n p h a s e o f t h e

m i s s i o n , used a s e p a r a t e b a t t e r y s o u rc e ; no o t h e r b a t t e r i e s a r e

used o n t h e s p a c e c r a f t b ec au se of t h e n e c e s s i t y f o r l o n g m i s s i o n

l i f e .

T h e RTG u n i t s , mounted i n tandem o n a de p l oy ab le boom and

c o n n e c t e d i n p a r a l l e l , c o n ve r t t o e l e c t r i c i t y t h e h e a t r e l e a s e d

by t h e i s o t o p i c d e c a y of P l ut o ni u m- 23 8 . Each i s o t o p e h e a t sou rce

h a s a c a p a c i t y of 2,400 w a t t s t h e r m a l w i t h a r e s u l t a n t maximum

e l e c t r i c a l power ou tpu t of 1 6 0 w a t t s a t t h e b e gi nn in g of t h e

m i s s i o n . T h e r e i s a g r a d u a l d e c r e a s e i n power ou tpu t . T h e t o t a l

p o w e r a v a i l a b l e from t h e t h r e e RTGs on each Vo y a g e r r a n g e s f r o m

a b o u t 4 7 5 w a t t s w i t h i n a few hours a f t e r l a u n c h t o 430 w a t t s

a f t e r t h e s p a c e c r a f t p a s s S a t u r n .S p a c e c r a f t p o w e r requirements f rom l a u n c h t o p o s t - Sa t u r n

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o p e r a t i o n s a r e c h a r a c t e r i z e d by t h i s g e n e r a l power t i m e l i n e :

l a u n c h a n d p o s t - l a u n c h , 2 3 5 t o 2 6 5 wat t s ; i n t e r p l a n e t a r y c r u i s e ,

3 2 0 t o 3 6 5 wat t s ; J u p i t e r e n c o u n t e r , 3 5 0 t o 3 7 0 watts: S a t u r n

e n c o u n t e r , 3 7 7 t o 3 8 2 watts ; a n d p o s t - S a t u r n , l e s s t h a n 3 6 5

w a t t s .

Te l e m e t r y measurements have been s e l e c t e d t o p r o v i d e t h e

n e c e s s a r y i n f o r m a t i o n f o r power management by ground command, i f

n e e d e d .Power f rom the RT G s i s h e l d a t a c o n s t a n t 3 0 v o l t s d c by a

s h u n t r e g u l a t o r . T h e power i s s u pp l i e d d i r e c t l y t o some

s p a c e c r a f t use r s and i s s w i t c h e d t o o t h e r s i n t h e p o w e r d i s t r i -

b u t i o n s u b a s s e m b l y. The m a i n p o w e r i n v e r t e r i s a l s o s u p p l i e d 3 0

v o l t s d c f o r c o n v e r s i o n t o 2.4 k i l o h e r t z square wave used by most

s p a c e c r a f t s u bs y st e ms . A ga in , t h e ac power may be supp l i ed

d i r e c t l y t o u s e r s or c a n b e s w i t c h e d o n or o f f b y p ower r e l a y s .

C om ma nd -a ct ua te d r e l a y s c o n t r o l t h e d i s t r i b u t i o n of power i n

t h e s p a c e c r a f t . Some r e l a y s f u n c t i o n a s s i m p l e o n - o f f s w i t c h e s

a n d o t h e r s t r a n s f e r power from one m o du l e t o another w i t h i n a

s u b s y s t e m .

Among t h e use r s of d c power, i n a d d i t i o n t o t h e i n v e r t e r ,

a r e t h e r a d i o s ub sy st em , g yr os , p r o p u l s i o n i s o l a t i o n v a l v e s , some

s c i e n c e i n s t r u m e n t s , m os t t e mp e ra t ur e c o n t r o l h e a t e r s a n d t h e

m o t o r s t h a t d e lo y ed t h e p l a n e t a r y r a d i o a s t r o n o m y a n t e n n a s .

O t h e r elements of t h e s p a c e c r a f t use t h e 2 .4 khz power.T h e r e a r e two i d e n t i c a l 2;4 k hz power i n v e r t e r s -- m a i n and

s t a n d b y. T h e m a i n i n v e r t e r i s on f rom l a u n c h and remains o n

t h r o u g h o u t t h e m i ss i o n .

t h e mai? i n v e r t e r , t h e power c h a i n , a f t e r a l . 5 - , : econd de lay, i s

I n c a s e of a m a l f u n c t i o n or f a i l u r e i n

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s w i t c h e d a u t o m a t i c a l l y t o t h e s t a n db y i n v e r t e r . Once t h e s w i t c h -

o v e r i s made, i t i s i r r e v e r s i b l e .

A 4 . 8 khz s y n c and t i m i ng s i g n a l f ro m t h e f l i g h t d a t a

s u b s y s t e m i s u s e d a s a f r eq u en c y r e f e r e n c e i n t h e i n v e r t e r . T h e

f r e q u e n c y i s d i v i d e d b y two a n d t h e o u t p u t i s 2 . 4 k h z p l u s - o r - m i n u s

0 . 0 0 2 % . T h i s t i m i n g s i g n a l i s s e n t , i n t u r n , t o t h e c om pu te r com-

mand s u b s y s t e m , w h ic h c o n t a i n s t h e s p a c e c r a f t ' s m a s t e r c l o c k .

Because o f t h e l o n g m i s s i o n l i f e t i m e , c h a r g e d c a p a c i t o r

e n e r g y - s t o r a g e b a n k s a r e u s e d i n s t e a d o f b a t t e r i e s t o s u p p l y t h e

s h o r t - t e r m e x t r a power demanded b y i n s t a n t a n e o u s o v e r l o a d s t h a t

would cause t h e main d c p o w e r v o l t a g e t o d i p below a c c e p t a b l e

l i m i t s . A t y p i c a l h e av y t r a n s i e n t o v e r l o a d o c cu r s a t t u r n - o n o f

a r a d i o power a m p l i f i e r .

F u l l o u t p u t o f t h e RT G s , a c o n s t a n t power s o u r c e , m u s t

be u s e d o r d i s s i p a t e d i n some way t o p r e v e n t o v e r h e a t i n g o f t h e

g e n e r a t o r u n i t s a n d d c v o l t a g e r i s i n g a b o v e a l l o w e d maximum. F u l l

u s e i s c o n t r o l l e d b y a s h u n t r e g u l a t o r t h a t dumps excess RTG o u t p u t

p o w e r a b o v e t h a t r e q u i r e d t o o p e r a t e t h e s p a c e c r a f t . The e x c e s s

power i s d i s s i p a t e d i n r e s i s t o r s i n t h e s h u n t r a d i a t o r mounted

o u t s i d e t h e s p a c e c r a f t a nd r a d i a t e d i n t o s pa ce - as h e a t . -. -.,

Two b a t t e r i e s i n d e pe n d e n t l y s u p p l i e d u n r e g u l a t e d d c

power t o a remote d r i v e r module (RD M) f o r p ow er in g v a l v e d r i v e r st o t h e t h r u s t - v e c t o r - c o n t r o l e n g i n e s o n t h e p r o p u l s i o n m o d u l e

d u r i n g t h e i n j e c t i o n p h a s e of t h e m i s s i o n . The b a t t e r i e s a n d t h e

RDM a r e l o c a t e d i n t h e p r o p u l s i o n m c d u l e t h a t was j e t t i s o n e d a

f e w m i n u t e s a f t e r t h e m i s s i o n

t r a j e c t o r y . Each b a t t e r y w a s

module was placed o n t h e J u p i t e r

composed of 2 2 s i l v e r o x i d e - z i n c

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c e l l s w i t h a c a p a c i t y of 1 , 2 0 0 a m p e r e s e c o n d s a t 28 t o 4 0 v o l t s ,

d e p e n d i n g up on t h e l o a d .

B a s i c r e q u i r e m e n t o n t h e b a t t e r i e s was h i g h power f o r a

s h o r t p e r i o d -- 1 2 m i n u t e s . W i t h a l i f e t i m e of o n l y 6 6 m i n u t e s ,t h e b a t t e r i e s were k e p t i n e r t u n t i l j u s t f o u r s e c o n d s b e f o r e C e n t au r

s e p a r a t i o n a n d 2 0 s e c o n d s before s o l i d r o c k e t i g n i t i o n . A f t e r

a c t i v a t i o n , i n wh ich a n e l e c t r o l y t e was i n j e c t e d i n t o t h e c e l l s ,

t h e b a t t e r i e s were a t f u l l v o l t a g e i n o n e- h al f s ec on d a nd r e a d y

f o r u s e i n t w o seconds .

C o m p u t e r Command S u b s y s t e m

T h e h e a r t o f t h e o n-b oard c o n t r o l s ys t e m i s t h e computer

command subsystem ( C C S ) , w hi ch p r o v i d e s a semi-automatic c a p a b i l i t y

t o t h e s p a c e c r a f t .

The C C S i n c l u d e s t w o i n d e p e n d e n t memories, e a c h w i t h a

c a p a c i t y o f 4 , 0 9 6 d a t a words. Half of each memory s t o r e s r e u s a b l e

f i x e d r o u t i n e s t h a t d o n o t ch an ge d u r i n g t h e m i s s i o n . The s e co n d

h a l f i s reprogrammable b y u p d a t e s from t h e g r o u n d .

Most commands t o o t h e r s p a c e c r a f t s u b sy s t em s a r e i s s u e d

f r o m t h e C C S memory, which, a t a n y g i v e n t i m e , i s loaded w i t h t h e

sequence a p p r o p r i a t e t o t h e m i s s i o n p h a s e. The C C S a l s o c a n

decode commands from t h e g r o un d an d p a s s t h e m a l o n g t o o t h e r space-

c r a f t s ub sy s t em s.

Under c o n t r o l o f a n a c c u r a t e o n- bo ar d c l o c k , t h e C C S

c o u n t s h o u r s , m i n u t es o r s ec on ds u n t i l some p r e - p r o g r a m m e d i n t e r v a l

h a s e l a p s e d a nd t h e n b r a n c h e s i n t o s u b r o u t i n e s s t o r e d i n t h e memory

t h a t r e s u l t s i n commands t o o t h e r s u b s y s t s m s . A s e q u e n c i n g e v e n t

c a n b e a s ing le command or a r o u t i n e t h a t i n c l u d e s many commands

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(e g . manipulating the tape recorder during a playback sequence .The CCS can issue commands singly from one of its two

proces sors or in parallel or tandem from both processors. An

example of CC S dual control i s the execution of trajectory correc-

tion maneuvers.

TCM thrusters are started with a tandem command (both

proces sors must send consistent commands to a single output unit)

and stopped with a parallel command (eithe r processor working

through di fferen t output units will stop the burn).

The CCS can survive any singl e internal fault; each

funct ional unit has a duplicate elsewhere in the subsystem.

Attitude Control and Propulsion

Stabil ization and orientation of the spacecraft from

launch-vehicle separation until end o f the mission is provided by

two major engineering subsystems -- attitude and articulationcontrol ( A A C S ) and propulsion.

Propulsion Subsystem

The propulsion subsystem consisted of a large solid-

propel lant rocket motor for final Jupiter trajectory velocity

and a hydrazine blowdown system that fuels 16 thrusters o n the

mission module and eight reaction engines on the propulsion

module. (The propulsion module was jettisoned after injection.)The single hydrazine ( N 2H4) supply is contained within

a 28-inch-diameter spheri cal titanium tank, separated from the

helium pressurization gas by a Teflon-filied rubber bladder.

tank, located in the central cavity of t he mis sion module's 10-sided

basic structure , contained 104 kilograms (230 pounds) of hydrazine

The

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a t l a u n c h a n d was p r e s s u r i z e d a t 4 20 p s i . A s t h e p r o p e l l a n t i s

co ns um ed , t h e h e l i u m p r e s s u r e w i l l d e c r e a s e t o a minimum of a b o u t

1 3 0 p s i .

A l l 24 h y d r a z i n e t h r u s t e r s u s e a c a t a l y s t t h a t spon-

t a n e o u s l y i n i t i a t e s a nd s u s t a i n s r a p i d d ec om po s i t i on of t h e

h y d r a z i n e .

The 16 t h r u s t e r s on t h e m i s s i o n module e a c h d e l i v e r 0 .2 -

p o un d -t h ru s t . Fo ur a r e u se d t o e x e c u t e t r a j e c t o r y c o r r e c t i o n man-

e u v e r s ; t h e o t h e r s i n two r e du n da n t s i x - t h r u s t e r b r a n ch e s , t o

s t a b i l i z e t h e s p a c e c r a f t on i t s t h r e e a x es .

a t t i t u d e c o n t r o l t h r u s t e r s i s needed a t a n y t i m e .

O n l y o n e b r a n c h o f

Mounted o n o u t r i g g e r s f r om t h e p r o p u l s i o n mo du le a r e

f o u r 1 00 -p ou nd - t hr us t e n g i n e s t h a t , d u r i n g so l id -motor b u r n , pro-

v id ed t h r u s t - v e c t o r c o n t r o l o n t h e p i t c h an d yaw a x e s . F ou r f i v e -

p o u n d - t h r u s t e n g i n e s p r o v i d e d roll c o n t r o l .

Th e s o l i d r o c k e t , w hi ch w ei gh ed 1 , 1 2 3 k i l o g r a m s ( 2 , 4 7 5

p o u n d s ) i n c l u d i n g 1 ,0 3 9 k i l o g r a m s ( 2 , 2 9 0 p o u n d s ) of p r o p e l l a n t ,

d e v el o p ed a n a v e r a g e 15 , 3 00 p ou nd s t h r u s t d u r i n g i t s 43-second

b u r n d u r a t i o n .- -_ -

A t t i t u d e an d A r t i c u l a t i o n Control S u b s y s t e m

The A A C S i n c l u d e s a n o nb o ar d c o mp u te r c a l l e d HYPACE

( h y b r i d p rogrammable a t t i t u d e c o n t r o l e l e c t r o n i c s ) , r e d un d a n t s u n

s e n s o r s , r e d u n d a n t C an op us s t a r t r a c k e r s , t h r e e t w o- ax is g y r o s a nd

s c a n a c t u a t o r s f o r p o s i t i o n i n g t h e s c i e n c e p l a t f o r m .

Th e HYPACE c o n t a i n s t w o r e d u n d a n t 4,09 6-word p l a t e d - w i r e

memories -- p a r t of which a r e f i x e d a n d p a r t r e p r o g r a m m a b l e --r e d u n d a n t processo r s a n d i n p u t / o , t p u t d r i v e r c i r c u i t s .

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I n j e c t i o n P r o pu l s io n C o n t r o l

Because of t h e e n e r gy r e q u i r e d t o a c h i e v e a J u p i t e r

b a l l a s t i c t r a j e c t o r y w i t h a n 82 5- ki lo gr am ( 1, 81 9- po un d) p a y l o a d ,t h e s p a c e c r a f t l au nc he d by t h e T i t a n I11 E / C e n t a u r i n c l u d e d a f i n a l

p r o p u l s i v e s t a g e t h a t a d d e d a v e l o c i t y i n c r e m e n t o f a b o u t t w o k i l o -

meters p e r s e c o n d ( 4 , 4 7 5 m i l e s p e r h o u r ) .

The s o l i d - r o c k e t mo to r i n t h e p r o p u l s i o n m o d u l e was

i g n i t e d 1 5 s ec on ds a f t e r t h e s p a c e c r a f t s e p a r a t e d from t h e C e n t a u r

a n d b u r n e d f o r a b o u t 4 3 s e c on d s. F i r i n g c i r c u i t s t o t h e motor

were armed d u r i n g l a u n c h - v e h i c l e c ou nt do wn .

The f o u r 1 0 0 - po u nd - th r us t e n g i n e s p r o v i d e d p i t c h a n d yaw

a t t i t u d e c o n t r o l and t h e f o u r f i v e -p o u n d- t h r us t e n g i n e s p r o v i d e d

r o l l c o n t r o l u n t i l b u r n o u t o f t h e s o l i d r o c k e t motor. T h e h y d r a z i n e

e n g i n e s r e s p o n d e d t o i n s t r u c t i o n s from A A C S ' s c o m p u t e r. O n l y t w o

p i t c h / y a w a n d two r o l l e n g i n e s a t most were t h r u s t i n g a t a n y g i v e n

t i m e .Before s o l i d r o c k e t i g n i t i o n a n d a f t e r bur 'nout , u n t i l t h e

p r o p u l s i o n m o d u l e s e p a r a t e d f rom t h e m i s s i o n mo du le , o n l y t h e

f i v e - p o u n d - t h r u s t r o l l e n g i n e s were r e q u i r e d f o r a t t i t u d e c o n t r o l

They were o r i e n t e d o n t h e p r o p u l s i o n m o d u l e so t h a t , b y p r o p e r

e n g i n e s e l e c t i o n b y t h e AACS, a t t i t u d e c o n t r o l was m a i n t a i n e d o n

a l l t h r e e axes .

A p p r o x i m a t e l y 11 m i n u t e s a f t e r s o l i d - r o c k e t b u r n o u t , t h e

p r o p u l s i o n m od ul e was j e t t i s o n e d . S e v e r a l s e c on d s e a r l i e r , t h e

p r o p s l l a n t l i n e c a r r y i n g h y d r a z i n e from t h e m i s s i o n m o d u l e t o t h e

p r o p u l s i o n m od ul e was s e a l e d a n d s e p a r a t e d .

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C e l e s t i a l R e f e r e n c e C o n t r o l

T he s u n s e n s o r s , w hi ch look t h r o u g h a s l o t i n t h e h i gh -

g a i n a n t e n n a d i s h , a r e e l e c t r o - o p t i c a l d e v i c e s t h a t s e n d a t t i t u d e

p o s i t i o n e r ro r s i g n a l s t o HYPACE, w hi c h , i n t u r n , s i g n a l s t h e ap-

p r o p r i a t e a t t i t u d e c o n t r o l t h r u s t e r s t o f i r e and t u r n t h e s p a c e c r a f t

i n t h e proper d i r e c t i o n .

t w o a x e s ( p i t c h a nd yaw).

Sun l o c k s t a b i l i z e s t h e s p a c e c r a f t on

T h e s t a r Canopus , o n e o f t h e b r i g h t e s t i n t h e ga l a x y ,

i s u s u a l l y t h e s ec on d c e l e s t i a l r e f e r e n c e f o r t h r e e - a x i s s t a b i l i -

z a t i o n . Two C a n o p u s t r a c k e r s a re mounted so t h a t t h e i r l i n e s o f

s i g h t a r e p a r a l l e l . Only one i s i n u s e a t a n y o n e t i m e . Th e s t a r

t r a c k e r , t h r o u g h HYPACE l o g i c , c a u s e s t h e t h r u s t e r s t o r o l l t h e

s p a c e c r a f t a b o u t t h e a l r e a dy - f i x ed E a r t h o r S u n - p o i n t e d r o l l a x i s

u n t i l t h e t r a c k e r i s l o c k e d o n C a n o p u s . B r i g h t n e s s of t h e t r a c k e r ' s

t a r g e t s t a r i s t e lemetered t o t h e g r o u n d t o v e r i f y t h e c o r r e c t

s t a r h a s b e e n a c q u i r e d .

- ..

T o e n h a n c e d o w n l i n k c o m m un i c a t io n c a p a b i l i t y , t h e S u n

s e n s o r i s e l e c t r i c a l l y b i a s e d ( o f f s e t ) by commands from t h e c o m p u t e r

command subsystem t o p o i n t t h e r o l l a x i s a t o r a s n e a r t h e E a r t h

a s p o s s i b l e . The s u n s e n s o r c a n b e b i a s e d p l u s a nd m in us 2 0 i n

b o t h p i t c h a n d yaw a x e s .

T h r e e -a x i s s t a b i l i z a t i o n w i t h c e l e s t i a l r e f e r e n c e i s t h en or ma l a t t i t u d e - c o n t r o l mode f o r c r u i s e p h a s e s b e tw e en p l a n e t s .

I n e r t i a l R ef er en ce C o n t r o l

The s p a c e c r a f t c a n be s t a b i l i z e d o n o n e a x i s ( r o l l ) o r

a l l t h r e e a x e s w i t h t h e A A C S ' s i n e r t i a l r e f e r e n c e u n i t c o n s i s t i n g

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Appropriate inertial reference modes are used wheneve r

the spacecraft is not on sun/star celestial lock. Such situations

include maintaining inertial reference from Centaur sepa ration

until initial celestial acquisition is achieved; purposely turning

the spacec raft off sun/star lock to do directed trajectory correc-

tion s or sc ience instrument observations or calibrations: providing a

reference when the sun is occulted; and providing a re ference when

concern exists that the Canopus or Sun senso r will detect stray

intensity from unwanted sources -- planets, rings, satellites.Each gyro has associated electron ics to provide position

information about two orthogonal axes (Gyro A : pitch and yaw,

Gyro B: rol l and pitch, Gyro C: ya w and roll). Normally, two

gyros are on for any inertial mode. The gyro s have two selectable

rates, one -- high rate -- for propuls ion-module injection phase:the other for mission-module cruise and tra jectory-correc tion and

science maneuvers.

Trajectory Correction Maneuvers

The Voyager trajectories are planned around eight -trajec- -

tory correct ion maneuve rs (TCM) with each spacecraft between launch

and Satur n encounter. Mission requirements call for extremely ac-

curate maneuvers to reach the desired zones at Jupiter, Satu rn

and the target satellites. Total velocity increment capabili ty

for each spacecraft is abou t 190 mete rs per second ( 4 2 5 miles per

hour .TCM sequencing is under control of the computer command

subsystem (CCS), which sends the required turn angles to the AACS

for positioning the spacecraft at the cor rect orientat ion in space

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a n d , a t t h e p r o p e r t i m e , s e n d s commands t o t h e AACS t o s t a r t an d

s t o p t h e TCM b u r n . A t t i t u d e c o n t r o l i s m a i n t a i n e d b y p u l s e - o f f

s e q u e n c i n g of t h e TCM e n g i n e s and p u l s e- o n s e q u e n c i n g of t w o a t t i -t u d e - c o n t r o l r o l l t h r u s t e r s . P o s i t i o n an d r a t e s i g n a l s a r e o b t a i n e d

f r o m t h e g y r os . A f t e r t h e b ur n, r e a c q u i s i t i o n of t h e c r u i s e c e l e s -

t i a l r e f e r e n c e s i s a c c o m p l i s h e d b y a s e c o n d s e t o f s p a c e c r a f t t u r n s .

A l l TCMs a r e e n ab l ed by ground command.

S c i en c e P l a t f o rm ( A r t i c u l a t i o n C o n t r o l )

Vo y a g e r ' s t w o t e l e v i s i o n cameras, u l t r a v i o l e t spec t romete r,

p h o t o p o l a r i m e t e r an d i n f r a r e d s p e c t r o m e te r a nd r a d i o m e t e r a r e

mounted o n t h e s c a n p l a t f o r m t h a t c a n be r o t a t e d a b o u t t w o a x e s f o r

p r e c i s e p o i n t i n g a t J u p i t e r , S a t u rn and t h e i r moons d u r i n g t h e p l a n -

e t a r y p h a s e s of t h e f l i g h t . T h e p l a t f o r m i s l o c a t e d a t t h e e n d of

t h e s c i e n c e boom. To t a l g i m b a l l e d w e i g h t i s 1 0 0 k i l o g r a m s ( 2 2 0

p o u n d s ) .

C o n t r o l l ed by t h e a t t i t u d e a nd a r t i c u l a t i o n c o n t r o i sub -

s y s t e m ( A A C S ) , t h e p l a t f o r m a l l o w s m u l t i p l e p o i n t i n g d i r e c t i o n s of

t h e i n s t r um e n t s . D r iv e r c i r c u i t s f o r t h e s ca n a c t u a t o r s -- o n e f o re a ch a x i s -- a r e l o c a t e d i n t h e AACS compute r. The p l a t f o r m ' s t w oa x e s o f r o t a t i o n a r e d e s c r i b e d a s t h e a z i mu t h a n g l e mo t io n a b o u t

a n a x i s d i s p l a c e d 7 O from t h e s p a c e c r a f t r o l l a x i s ( p e r p e n d i c u l a r

t o t h e boom c e n t e r l i n e ) an d e l e v a t i o n a n g l e mo t i on a b o u t a n a x i s

p e r p e n d i c u l a r t o t h e a z im u th a x i s and r o t a t i n g wi t h t h e a z i m ut h

a x i s . A ng ul ar r a n g e i s 360 i n a z i mu t h a nd 210 i n e l e v a t i o n .

T h e p l a t f o r m i s s l e w e d o n e a x i s a t a t i m e w i t h s e l e c t a b l e

s l e w r a t e s i n r e sp o ns e t o computer command s u b s y s t e m commands t o

t h e AACS. Slew r a t e s a r e : l.Oo/s; 0.33O/s; .083O/s; a n d a s p e c i a l

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UVS l o w r a t e : .0052O/s. Camera l i n e o f s i g h t i s c o n t r o l l e d t o

w i t h i n 2 . 5 m i l l i r a d i a n s per a x i s .

Te m p e r a t u r e C o n t r o l

The t w o Vo y a g e r s p a c e c r a f t a r e d e s i g n e d t o o p e r a t e f a r t h e r

f r o m E a r t h t h a n a n y p r e v i o u s m a n - m a d e o b j e c t . S u r v i v a l d e pe n ds

g r e a t l y upon k ee p i n g t empe ra tu re s w i t h i n o p e r a t i n g l i m i t s w h i l e

t h e s p a c e c r a f t t r a v e r s e s a n en v i r on m e nt a l r a n g e o f o n e s o l a r c o n s t a n t

a t t h e E a r t h d i s t a n c e t o f o u r p e r c e n t o f t h a t s o l a r i n t e n s i t y a t

J u p i t e r a n d one pe r c e n t a t S a t u r n .

U n p r o t e c t e d s u r f a c e s a t t h e S a t u r n r a n g e , n e a r l y o ne

b i l l i o n m i l e s f rom t h e Sun , can r e a c h 320F below z e r o -- t h et e m p e r a t u r e o f 1 q u i d n i t r o g e n .

B ot h t o p an d b o t t om o f t h e m i s s i o n mo d u l e' s b a s i c d e c a -

gon s t r u c t u r e a r e e n c l o s e d w i t h m u l t i - l a y e r t h e r m a l b l a n k e t s t o

p r e v e n t t h e r a p i d l o s s of h e a t t o s p a c e . T he b l a n k e t s a r e s a n d -

w i c h es o f a l u mi n i z ed M yl ar , s h e e t s o f Te d l a r f o r micrometeroid

p r o t e c t i o n and o u t e r b l a c k K apto n c o v e r s t h a t a r e e l e c t r i c a l l y

c o n d u c t i v e t o p r e v e n t t h e a c c u m u l a t i o n of e l e c t r o s t a t i c c h a r g e s .

A l s o e x t e n s i v e l y b l a nk e t ed a r e t h e i n s t r u m e n t s o n t h e

s c a n p l a t f o r m . Sma l l e r b l a n k e t s a nd t h e r m a l wrap c o ve r e i g h t

e l e c t r o n i c s b ay s , boom a n d b ody-mounted i n s t r u m e n t s , c a b l i n g ,

p r o p e l l a n t l i n e s an d s t r u c t u r a l s t r u t s .

m e n t s of t h e s p a c e c r a f t a r e n o t c l a d i n t h e b l a c k f i l m -- t h e h ig h -g a i n a n t e n n a r e f l e c t o r , p la sm a s e n s o r s , s u n s e n s o r s a nd a n t e n n a

f e e d c o n e s .

On ly a f e w e x t e r i o r e l e -

Te mp e ra t ur e c o n t r o l of f o u r of t h e 1 0 e l e c t r o n i c s com-

p a r t m e n t s i s p r ov i de d by t h e r m o s t a t i c a l l y c o n t r o l l e d l o u v e r a s -

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s e m b l i e s t h a t p r ov i d e a n i n t e r n a l o p e r a t i n g r an ge n e a r room temp-

e r a t u r e . T h e l o u v e r s a r e r o t a t e d o p e n b y b i m e t a l l i c s p r i n g s w h e n

l a r g e a m o u n t s of h e a t a r e d i s s i p a t e d .

p o w e r - c o n d i t i o n i n g e q u i p m e n t a n d t h e r a d i o power a m p l i f i e r s . M i n i -

l o u v e r s a r e l o c a t e d o n t h e scan p l a t f o r m , cosmic r a y i n s t r u m e n t

a nd t h e s u n s e n s o r s .

T h e s e b a ys c o n t a i n t h e

R a d i o i s o t o p e h e a t i n g u n i t s (RHU), s m a l l non-power-us ing

h e a t e l e m e n t s t h a t g e n e r a t e o ne w a t t of t h e r m a l e n e r g y , a r e l o c a t e d

o n t h e ma gn et om et er s e n s o r s a nd t h e s u n s e n s o r s . N o RHUS a r e u s e d

n e a r i n s t r u m e n t s t h a t d e t e c t c h a r g e d p a r t i c l e s . E l e c t r i c h e a t e r s

a r e l o c a t e d t h ro ug h ou t t h e s p a c e c r a f t t o p r o v id e a d d i t i o n a l h e a t

d u r i n g p o r t i o n s of t h e m i s s i o n .

off w h e n t h e i r r e s p e c t i v e v a l ve s , i n s t r u m e n t s o r s u b a s s e m b l i e s

a r e o n a n d d i s s i p a t i n g power.

Many o f t h e h e a t e r s a r e t u r n e d

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VOYAGER EXPERIMENTS

The

objectives:

1.

2.

3 .

4 .

COSMIC-RAY EXPERIMENT

cosmic-ray experiment has four principal sc ientific

To measure the energy spectrum of electrons and

cosmic-ray nuclei.

To determine the elemen tal and isotopic corngosition

of cosmic-ray nuclei.

To make elemental and isotopic studies of Jupiter's

radiation belt s and to explore Saturn's environment.

To determine intensity and d irectional characteri stics

of energetic particles as a function of radial distance

from the Sun, and det ermine location of the modulation

boundary.

-

The cosmic-ray experiment uses multiple solid-state detector

telescopes to provide la rge solid-angle viewing ; the low-energy-

telescope system covers the range f rom 0 . 5 to 9 million electron

volts (MeV) per nucleon; the high-energy telescope system covers the

range from 4 to 500 million electron volts. The elec tron telescope

system covers the range from 7 million to 100 million electron volts.

The cosmic-ray experiment weighs 7.52 kilograms (16.57

pounds) and uses 5.2 wat ts of power.

Dr. Rochus E. Vogt of the California Institute of Technology

is principal investigator.

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LOW-ENERGY CHARGED PA RT I C L E EXPERIMENT

S c i e n t i f i c o b j e c t i v e s of t h e Low-Energy C h a r g e d - P a r t i c l e

E x p e r i m e n t i n c l u d e s t u d i e s of t h e c h a r g e d - p a r t i c l e c o m p o s i t i o n ,e n e r g y - d i s t r i b u t i o n and a n g u l a r d i s t r i b u t i o n w i t h r e spec t to:

1. S a t u r n ' s m ag ne to sp he re ( e x p l o r a t o r y ) and J u p i t e r ' s

magnetosphere ( d e t a i l e d s t u d i e s ) .

I n t e r a c t i o n s of c h a r g e d p a r t i c l e s w i t h t h e s a t e l l i t e s

o f J u p i t e r a n d S a t u r n a nd p o s s i b l y w i t h t h e r i n g s of

S a t u r n .

2 .

3 . M ea su re me nt s o f q u a s i - s t e a d y i n t e r p l a n e t a r y f l u x

and h igh -ene rgy componen ts of t h e s o l a r wind.

4 . D et e r mi na t i on o f t h e o r i g i n and i n t e r s t e l l a r

p r o p a g a t i o n of g a l a c t i c cosmic r a y s ( t h o s e t h a t

come f ro m o u t s i d e t h e s o l a r s y s t e m ) .

5. Measuremen t s of t h e p r o p a g a t io n of s o l a r p a r t i c l e s

i n t h e o u t e r s o l a r s y s t e m .

T h e e x p e r i m e n t u s e s two s o l i d - s t a t e d e t e c t o r s y s t e m s o n

a r o t a t i n g p l a t f o r m mounted o n t h e s c a n p l a t f o r m boom.

i s a l o w - e n e r g y m a g n e t o s p h e r i c p a r t i c l e a n a l y z e r w i t h l a r g e d y n a m i c

r a n g e t o m e a s u r e e l e c t r o n s w i t h e n e r g y r a n g i n g from 1 5 , 0 0 0 e l e c t r o n

v o l t s ( 1 5 K e V ) t o g r e a t e r t h a n 1 m i l l i o n e l e c t r o n v o l t s ( 1 M e V ) :

and i o n s i n t h e e n e rg y r a n g e f rom 1 5 , 0 0 0 e l e c t r o n v o l t s p e r n uc le on

t o 1 6 0 m i l l i o n e l e c t r o n v o l t s p e r n u cl eo n.

One sys tem

The s ec o n d d e t e c t o r s y s t e m i s a l ow-ene rgy p a r t i c l e

t e? .e sc op e t h a t c o v e r s t h e r a n g e from 0.15 m i l l i o n e l e c t r o n v o l t s

p e r n u c l e o n t o g r e a t e r t h a n a bo u t 1 0 m i l l i o n e l e c t r o n v o l t s pe r

n u c l e o n .

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The Low-Energy Charged-Particle Experiment weighs 7 - 4 7

kilograms (16.47 pounds) and draws 3.9 watts during cruise and 4 . 2

watts during planetary encounter,

Dr. S. M. (Tom) Krimigis of the Applied Physics Laboratory,

Johns Hopkins University, is principal investigator.

MAGNETIC FIELDS EXPERIMENT

The magnetic field of a planet is an externally measurable

manifestation of conditions deep in its interior.

The magnetic-fields instruments on Voyager 1 and 2

dete rmin e the magnetic field and magnetospheric structure at

Jupiter and Saturn; they study the interaction of the magnetic

field and the sa tellites that orb it the planets inside that

field and study the interplanetary-interstellar magnetic field.

Four magnetometers are carried aboard Voyager. Two arelow-field, three-axis instruments located on a boom to place them

as far from the spacecra ft body as possible.

of the spacecrafts magnetic field from the external field that is

to be measured. The other two magnetometers are high-field, three- . ..

axis instruments mounted o n the spacecra ft body.

That allows separation

The boom-mounted , low-field instruments measure the

magnetic fields in the range from 0.002 gamma to 50,000 gamma.

(Fifty-thousand gamma equals one-half gauss, about the average

magnetic .field strength at. the s ur face of Earth.)

The high-jfield instruments cover the r ange from 1 2 gamma

to 20 gauss. While the highest field strengths measured by the


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P i o n ee r s p a c e c r a f t a t J u p i t e r were a b o u t 14 g a u s s , s c i e n t i s t s

e x p e c t t h a t l o c a l i z e d , s t r o n g e r f i e l d s may be a s s o c i a t e d w i t h t h e

p l a n e t s o r some o f t h e i r s a t e l l i t e s .

To t a l w e i g ht o f t h e m a g n e t ic - f i e l d s e x p er i m en t i s 5 . 5

k i l o g r a m s ( 1 2 p o u n d s ) . T he e x p e r i m e n t u s e s 3.2 w a t t s of power.

D r . Norman Ness o f NASA's Goddard Space F l i g h t C e n t e r

i s p r i n c i p a l i n v e s t i g a t o r .

I N F R A R E D INTERFEROMETER SPECTROMETER AND RADIOMETER~~

-~Th e I R I S i s d e s i g n e d t o p e r f o r m s p e c t r a l and r a d i o m e t r i c

m ea s ur e me n ts o f t h e J o v i a n , S a t u r n i a n an d U ra n i a n p l a n e t a r y s y s t e m s ,

and t a r g e t s o f o p p o r t u n i t y d u r i ng t h e c r u i s e p h a se s .

S c i e n t i f i c o b j e c t i v e s f o r I R I S a r e :

1.

2.

3 .

4 .

5 .

The

M ea su re me nt o f t h e e n e r g y b a l a n c e of J u p i t e r ,

S a t u r n an d U r a nu s .

S t u d i e s o f t h e a tm o sp h er i c c o m po s i t i o n s o f J u p i t e r ,

S a t u r n , T i t a n a nd o t h e r s a t e l l i t e s , and Uranus .

Te m pe r a tu r e , s t r u c t u r e an d d y na m ic s of t h e a t m o s p h e r e s .M e a s ur e m e nt s o f c o m p o s i t i o n a n d c h a r a c t e r i s t i c s o f

c l o u d s a n d ae roso l s .S t u d i e s of t h e c o m po s i t i on an d c h a r a c t e r i s t i c s o fr i n g p a r t i c l e s ( a t S a t u r n ) a nd t h e s u r f a c e s o f

t h o s e s a t e l l i t e s t h e i n s t r u m e n t w i l l o b s e r v e .

i n s t r u m e n t p r o v i d e s b r o a d s p e c t r a l c o v e r a g e , h i g h

s p e c t r a l r e s o l u t i o n a nd l o w n o i s e - e q u i v a l e n c e - r a d i a n c e t h r o u g h

u s e of d u a l i n t e r f e r o m e t e r s . T h a t a n d t h e v a r i a b l e r e s o l u t i o n

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of the instrument, as well a s the precision of the radiometer,

will allow scientists to acquire information about a wide

variety of scientific questions concerning the atmospheres of

the planets and satel lites , local and global energy balance, and

the nature of satellite surfaces and the rings of Saturn.

The instrument has two fields of view from its position

on the scan platform. The first is centered on the boresight of the

51-centimeter (20-inch) Cassegrain telescope. The second field of

view -- for solar calibration -- is pointed 2 0 degrees off thetelescope boresight. It approximate ly over laps the ultraviolet

spectrometer's occul tation field of view. IRIS pointing is con-

trolled by the scan platform.

Dr. Rudolf A . Hanel of Goddard Space Flight Center is

principal investigator.

PHOTOPOLARIMETER

A great deal of information about the composition of

an objec t can be learned from the way that object reflec ts

light. The light that Voyager's photopolarimeter measu res is

polarized by the chemical s and aerosols in the atmospheres and

small particles on the surfaces.

The photopolarimeter studies aerosol particles in the

atmospheres of the planets and satelli tes, and the textures and

compositions of the surfaces of satellites. It also will measure

size , albedo, spatial distribution, shape and orientation of

part icles in Szturn's rings; and opt ical and geometric t hickness

of the rings.

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The instrument is made up of a 15-centimeter (6-inch)

Cassegrain te lescope, aper ture sector, polar izat ion analyzer wheel ,

fi l t er whe el and a photomultiplier-tube detector. The fil t er

whee l ca rri es eigh t fi l ter s ranging from 2,350-Angstrom to 7,500-

Angstrom wavelength; f ive l inear polar izers (0, 60, 120, 13 5 and

4 5 deg ree s) plus an ope n posi t ion (no polar izer) and a dark s lide.

Th e instrument's field of vi ew can be s et at 3.5 degree s, 1 degree ,

1/4 degree and 1/10 degree.

During the Ju pi te r flyby, Voy age r 2's pho top ola rim ete r

suff ered some radiat ion damag e that affected some of i ts central

logic. A s a consequence some of i t s co lor f i l t e r s and po la r ize rs

cann ot be used. The Satur n encounter w i l l concent ra te on the use

of deep ul t raviolet (2 ,800 Angstroms) and de ep red (7,500 Angstroms)

and perpendicul ar polar izat ions (4 5 and 135 degrees) . Those choice s

wil l re turn much of the scienti f ic data the photopolar imeter

team had counted on.

The ph otopolar ime ter weighs 4.41 ki lograms (9.7 poun ds) and

uses 2.4 watts average power.- --I .

Dr. Ar thu r L. La ne of the Jet Propuls ion Laboratory

is prin cipa l investigator.

PLANETARYRADIO ASTRONOMYThe Plan etary Radio Astronomy experiment co nsis ts of a

stepped frequ ency radio receiver t hat cover s the range from 20

kilo herc z to 40.5 mega hert z, and tw o mono pole ant enna s 10 meters

(33 feet) long, to detect and s tudy a var ie ty of r adio s ign als

emitted by J upit er and Saturn.

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S c i e n t i f i c o b j e c t i v e s o f t h e e x pe r im e nt i n c l u d e d e t e c t i o n

a n d s t u d y o f r a d i o emiss ions f r o m J u p i t e r a n d S a t u r n and t h e i r

s o u r c e s a nd r e l a t i o n s h i p t o t h e s a t e l l i t e s , t h e p l a n e t s ' m ag n e t i c

f i e l d s , a t mo s ph e r i c l i g h t n i n g and plasma r e s o n a n c e . The i n s t r u m e n t

a l s o measures p l a n e t a r y a n d s o l a r r a d i o b u r s t s from ne w d i r e c t i o n s

i n s p a c e a n d r e l a t e s them t o m e a s u r e m e n t s made from E a r t h .

T he r e c e i v e r i s d e s i g n e d t o p r o v i d e c o v e ra g e i n t w o

f r e q u e n c y b a n d s -- o n e c o v e r i n g t h e r a n g e f r o m 2 0 . 4 k i l o h e r t z t o1,345 k i l o h e r t z , t h e se co nd from 1,228.8 k i l o h e r t z t o 40.5 m e g a h e r t z .

T h e r e c e i v e r b a n d w i d t h i s 1 k i l o h e r t z i n t h e lo w -f r eq u en c y r a n g e a nd

2 0 0 k i l o h e r t z i n t h e h ig h- f re qu en cy b an d. T h er e a r e t h r e e s i g n a l

i n p u t a t t e n u a t o r s t o p r o v i d e s w i t c h a b l e t o t a l a t t e n u a t i o n f r o m 0 t o

9 0 d e c i b e l s .

The i n s t r u m e n t w ei g h s 7.66 k i l o g r a m s (16.8 p o u n d s ) a n d

d r a w s 6 . 8 w a t t s of power.

P r i n c i p a l i n v e s t i g a t o r i s D r . James W. Warwick of

R a d i o p h y s i c s , I n c . , B o u l d e r , Colo.

PLASMA E X P E R I M E N T

Plasma, c l o u d s o f i o n i ze d g a s e s , m o v e s t h r o u g h t h e

i n t e r p l a n e t a r y r e g i o n and comes from t h e S un a nd f r o m s t a r s .

T h e p l a s m a e x p e r i m e n t u s e s t w o F a r a d a y c u p plasma d e t e c t o r s ,

o n e p o i n t e d a l o n g t h e E a r t h - s p ac e cr a f t l i n e , t h e o t h e r a t r i g h t

a n g l e s t o t h a t l i n e .

S c i e n t i f i c o b j e c t i v e s o f t h e p la s ma e x pe r i m e n t a r e :

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1.

2 .

3.

4.

T h e

D et er mi ne p r o p e r t i e s o f t h e s o l a r w i n d , i n c l u d i n g

c ha ng es i n t h e p r o p e r t i e s w i t h i n c r e a s i n g d i s t a n c e

f r o m t h e S u n .

S t u d y o f t h e m ag n et o sp h er e s t h a t a r e i n t r i n s i c t o

t h e p l a n e t s t h e m s e l v e s a n d t h a t c o - r o t a t e w i t h t h e

p l a n e t s i n d e p e n d e n t o f s o l a r w i n d a c t i v i t y .

S t u d y of t h e s a t e l l i t e s of J u p i t e r and S a t u r n an d t h e

p l a s m a e n v i r o n m e n t o f Io.

D e t e c t i o n a nd me asu reme nt o f i n t e r s t e l l a r i o n s .

E a r t h - p o i n t i n g d e t e c t o r u s e s a n o v e l g e o m e t r i c a l

a r r a n g e me n t t h a t makes i t e q u i v a l e n t t o t h r e e F a r a d a y c u p s a n d

d e t e r m i n e s m i cr o s co p i c p r o p e r t i e s o f t h e plasma i o n s . Wi th t h i s

d e t e c t o r , a c c u r a t e v a l u e s of t h e v e l o c i t y , d e n s i t y and p r e s s u r e

can be d e t e r m i n ed f o r p la sm a from t h e E a r t h (1 A.U. ) t o beyond

S a t u r n ( 1 0 A . U . ) . Two s e q u e n t i a l e n e r gy s c a n s a r e employed t o

a l l o w t h e i n s t r u m e n t t o c o v e r a b ro ad r a n g e o f e n e r g i e s -- f r o m1 0 e l e c t r o n v o l t s ( e V ) t o 6 , 0 0 0 e l e c t r o n v o l t s ( 6 K e V ) . S i g n i f i c a n t

m e a s u r e m e n t s c a n be made b et we en s u b s o n i c a nd s u p e r s o n i c speeds i n

c o l d s o l a r wind o r h o t p l a n e t a r y m a g ne t o sh e a th .

The v a r i a b l e e n er g y r e s o l u t i o n a l l ows s c i e n t i s t s t o

d e t e c t and s o r t o u t i o n s t h a t f lo w w i t h t h e s o l a r wind a t t h e same

t i m e t h e y a r e m e a s u r i n g t h e s o l a r w i n d ' s p r o p e r t i e s .

Th e i n s t r u m e n t h a s a l a r g e ( 1 8 0 - d e g r e e ) f i e l d of v iew

a t p l a n e t a r y e n c o u n t e r s an d a 9 0 - d e g r e e f i e l d of v i e w i n t h e s o l a r

w i n d ; n o e l e c t r i c a l o r m e c h a n i c a l s c a n n i n g i s n e c e s s a r y .

T h e o t h e r F a r a d a y c u p , a s i d e - l o o k i n g or l a t e r a l d e t e c t o r ,

measures e l e c t r o n s i n t h e r a n g e of 1 f i e l e c t r o n v o l t s t o 6 K e V an d

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s h o u l d i mp r o ve s p a t i a l c ov er ag e f o r a ny d r i f t i n g o r c o - r o t a t i n g

p o s i t i v e i o n s d u r i n g p l a n e t a r y e n c o u n t e r s .

T h e i n s t r u m e n t was d e si g ne d p r i m a r i l y f o r e x p l o r i n g

p l a n e t s ' m a g n e t o s p h e r e s . I t i s c a p a b l e o f d e t e c t i n g h o t s u b s o n i c

p l a s m a s u c h a s h a s b e en o bs e r ve d i n t h e E a r t h ' s m ag n et o sp h er e an d

is e x p e c t e d from i o n s o r i g i n a t i n g i n t h e Mcl hn ou gh- Br ic e r i n g of

Io . T h e i n s t r u m e n t ' s l a r g e a n g u l a r a c c e p t a n c e a l l o w s d e t e c t i o n

o f p l a s m a f l o w s w e l l away f ro m t h e d i r e c t i o n of t h e Su n, s u c h a s

p l a s m a f l o w s t h a t c o - r o t a t e w it h t h e p l a n e t .

The p l a s ma e x p e r i m e n t w e i g h s 9 . 89 k i l o g r a m s (21.8 p o u n d s )

a n d d r aw s 8 . 3 w a t t s o f p ow er .

D r . H e r b e r t B r id g e of t h e M a ss a c hu s e t t s I n s t i t u t e o f

Te c h n o l o g y i s p r i n c i p a l i n v e s t i g a t o r .

PLASMA WAVE

S c i e n t i f i c o b j e c t i v e s o f t h e p la sm a wave e x pe r i me n t a r e

m e a s u r e m e n t s of t h e r m a l p l a s m a d e n s i t y p r o f i l e s a t J u p i t e r a nd_..- -

S a t u r n ; s t u d i e s of w a v e- p a r t i c le i n t e r a c t i o n , a nd s t u d y of t h e

i n t e r a c t i o n s o f t h e J o v i a n and S a t u r n i a n s a t e l l i t e s w i t h t h e i r

p l a n e t s ' m a g n e t o s p h e r e s .

The p l asma-wave in s t ru me n t measures e l e c t r i c - f i e l d

c o m p o n e n t s of l o c a l plasma waves o v e r t h e f r e q u e n c y r a n g e f ro m

1 0 h e r t z t o 5 6 k i l o h e r t z .

The e x p e r i m e n t s h a r e s t h e t w o e x t e n d a b l e 10-me te r

( 3 3 - f o o t ) e l e c t r i c a n t e n n a s p ro v' de d b y t h e p l a n e t a r y r a d i o

a s t r o n o m y e x p e r i m e n t team. T h e t w o g r o u p s u s e t h e a n t en n a s i n

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d i f f e r e n t ways. T h e p la sm a wave e x p e r i m e n t u s e s t h e a n t e n n a s t o

f o r m a Ve e - t y p e b a l a n c e d e l e c t r i c d i p o l e ( w h i l e t h e r a d i o a s t r on om y

e x p e r i m e n t uses t h e m a s a p a i r o f o r t h o g o n a l m on o po le s) .

I n t h e normal f o r m a t , t h e plasma-w ave s i g n a l s a r e p r o - .

cessed w i t h a s i m p l e 1 6 - c h a n n e l spec t rum a n a l y z e r . A t p l a n e t a r y

e n c o u n t e r s t h e s ys t e m p r o v i d e s a s p e c t r a l s c a n e v e r y f o u r s ec on ds .

The p lasma-wave sys te m h a s a b ro ad ba nd a m p l i f i e r t h a t

u s e s t h e Vo yager v i d e o t e l e m e t r y l i n k t o g i v e e l e c t r i c f i e l d

w a v e f o r m s w i t h a f r e q u e n c y r a n g e from 5 0 h e r t z t o 10 k i l o h e r t z

a t s e l e c t e d t imes d u r i n g p l a n e t e n c o u n t e r s .

T h e e x p e r i m e n t i s d e s i g n e d t o p r o v i d e k ey i n f o r m a t i o n

o n t h e w av e - p a r t i c l e i n t e r a c t i o n phenomena t h a t c o n t r o l i m p o r t a n t

a s p e c t s o f t h e dy na mi cs of t h e m a gn e to s ph e re s o f J u p i t e r a nd S a t u r n .

Wa v e- p a r t i c l e i n t e r a c t i o n s p l a y e x t r em e l y im p o r t an t r o l e s a t E a r t h ,

an d s c i e n t i s t s u n d e r s t a n d t h a t a t l e a s t t h e i n n e r m ag n et o sp h er e

of J u p i t e r i s c o n c e p t u a l l y s i m i l a r t o t h a t of E a r t h d e s p i t e t h e

v a s t d i f f e r e n c e s i n s i z e a nd i n t h e e n e r g y o f t r a p p e d p a r t i c l e s .

I n a d d i t i o n , t h e s a t e l l i t e s of J u p i t e r and S a t u r n a p p e a r

t o p r o v i d e i m p o r ta n t l o c a l i z e d s o u r c e s o f plasma a n d f i e l d - a l i g n e d

c u r r e n t s , and t h e y s h ou l d s i g n i f i c a n t l y a f f e c t t h e t r a p p e d - p a r t i c l e

p o p u l a t i o n s .Th e i n s t r u m e n t w e i g h s 1.37 k i l o g r a m s (3.02 p o u n d s ) a n d

d r a w s 1.4 w a t t s o f power i n t h e s t e p f r e q u e n c y mode a n d 1 8 w a t t s

i n t h e s t e p f r e q u e n c y p l u s w a v e f o r m a n a l y z e r mode.

D r . F r e d e r i c k L. S c a r f of TRW D e f 2 n s e a n d Space S y s t e m s

G r o u p i s p r i n c i p a l i n v e s t i s a t o r .

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4

RA D IO S C I E N C E

The spacecraf t ' s communica t ions sys tem i s u s e d t o

c o n d u c t s e v e r a l e x p e r i m e n t s by obse rv in g how the r a d i o s i g n a l s

a r e changed on t h e i r way t o E a r t h .

By measuring t h e way signals d i e o u t and r e t u r n when t h e

s p a c e c r a f t d i s a p p e a r s b e h i n d a p l a n e t or s a t e l l i t e and t h e n

r ea ppe a r s , t h e r ad io s c i en ce team can de t e rmine t h e p r o p e r t i e s

o f p l a n e t a r y a nd s a t e l l i t e a tm o sp he re s and i o n o s p h e re s .

The

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Voyager Backgrounder 1981