Pioneer Venus Press Kit

8/8/2019 Pioneer Venus Press Kit

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NASA NewsNational Aeronautics andSpace AdministrationWashington D C 20546AC 20 2 755-8370

PressKit

ForRelease 1 0 a.m. EDT. TUESDAY.May 9 . 1 9 7 8

Project P i o n e e r V en usRELEASE N O : 78- 68

ContentsGENERAL RELEASE .................................. 1-11M I S S I O N PROFILE .................................. 1 2 - 2 9

P i o n e e r Venus O r b i t e r M i s s i o n .................. 1 2 - 2 0P i o n e e r V en us M u l t i p r o b e M i s s i o n ............... 20-29THE PLANET VENUS ................................. 3 0 - 4 4MAJOR QUESTIONS ABOUT VENUS ...................... 45-46HISTORICAL DISCOVERIES ABOUT VENUS ............... 47-49EXPLORATION O F VENUS BY SPACECRAFT ............... 5 0 - 5 1THE PIONEER VENUS SPACECRAFT ..................... 52-66T h e O r b i t e r S p a c e c r a f t......................... 57-62

T h e M u l t i p r o b e S p a c e c r a f t...................... 62-66VENUS ATMOSPHERIC PROBES ......................... 67-80T h e L a r g e Probe ................................ 67-74The S m a l l P r o b e s ............................... 7 4 - 8 0


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S C I E N T I F I C I N V E S T I G A T I O N S ........................ 81-100O r b i t e r ........................................ 81-89O r b i t e r R a d i o S c i e n c e .......................... 8 9 - 9 2L a r g e P r o b e E x p e r i m e n t s ........................ 92-96L arge and S m a l l I n s t r u m e n t s .................... 9 6 - 9 7Sm a l l Probe E x p e r i m e n t s ........................ 98-99M u l t i p r o b e R a d i o S c i e n c e E xper i m en t s ........... 99-100P R I N C I P A L I N V E S T IG A T O R S AND S C I E N T I F I C

I N S T R U M E N T S .................................... 1 0 1 - 1 0 4L A U N C H V E H I C L E ................................... 1 0 5 - 1 0 6L AU NC H F L I G H T S E Q U E N C E ........................... 1 0 6LA UN CH V E H I C L E C H A R A C T E R I S T I C S ................... 1 0 7A T L A S CE NT AU R F L I G H T S E Q U EN C E ( A C - 5 0 ) ............ 1 0 8L A U N C H O P E R A T I O N S ................................ 1 0 9M I S S I O N O P E R A T IO N S ............................... 109-111DATA RET URN . COMMAND AND TR AC KI NG ................ 1 1 2 - 1 1 5P I O N E E R V E N U S T EA M ............................... 1 1 6 -1 1 8C O N T R A C T O R S ...................................... 1 1 8 - 1 2 1V EN U S S T A T I S T I C S ................................. 1 2 2

N O T E T O E D I T O R S :T h i s press k i t covers t h e l a u n c h and c r u i s e p h a s e s of b o t ht h e P i o n e e r V e n u s O r b i t e r and th e M u l t i p r o b e s p a c e c r a f t .Much of t h e m a t e r i a l i s a l s o p e r t i n e n t t o t h e V e n u s e n c o u n t e r .b u t a n u p d a t e d pre s s k i t w i l l b e is s u e d s h o r t l y b e f o r ea r r i v a l a t t h e p l a n e t i n D e c e m b e r 1 9 7 8 .


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NfEANewsNational Aeronautics andSpace AdministrationWashington, D.C.20546AC 202 755-8370

Ni cho l a s PanagakosH e a d q u a r t e r s , W a s h i n g t o n , D .C .(Phone: 20 2/75 5-3 6 80 1

Pe t e r WallerA m e s R e s e a r c h C e n t e r , M o u n t a i n V i e w , C a l i f .(Phone: 415/9 65-509 1)

RELEASE N O : 78-68

P I O N E E R VENUS 1 LAUNCH SET FOR MAY 2 0

For Release:1 0 a . m EDT, T U E S D A Y ,May 9 , 1 9 7 8

NASA i s p r ep a r i n g t o l au nc h t h e f i r s t o f t w o s p a c e c r a f tt oward Venus t h i s mon th for a d e t a i l e d s c i e n t i f i c s t ud y oft h a t c lo u d- sh ro u de d p l a n e t .

P i onee r Venus 1 w i l l be l aunch ed a bou t May 20 from N A S A ' sKennedy S p a c e C e n t e r , F l a . , a t o p a n A t l a s C e n t a u r r o c k e t .

T he s e c o nd s p a c e c r a f t , P i o n e e r V enus 2 , w i l l b e l a u n c h e dt ow ar d t h e p l a n e t t h r e e m on th s l a t e r , about Aug. 7 .

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Pionee r Venus 1, an o r b i t e r , w i l l re ac h Venus on Dec. 4 ,1 9 7 8 , and P ionee r Venus 2 , a m u l t i p r o b e s p a c r a f t , w i l l a r r i v ef i v e d ay s l a t e r a f t e r s p l i t t i n g i n t o a bus and four a tm os -p h e r i c e n t r y p r ob e s, 1 3 m i l l i o n k i l om e t e r s ( 8 m i l l i o n m i l e s )and 20 d ay s o u t from t h e p l a n e t .

T he f l i g h t s may s h e d new l i g h t on s o m e of t h e m os tp u z z l i n g q u e s t i o n s i n p l a n e t a r y s c i e n c e , s uc h a s t h e f o l lo w i n g :

a Why do t w o p l a n e t s w i t h about t h e same mass, p r o b a b l yf or me d o u t o f s i m i l a r m a t e r i a l s a nd s i t u a t e d a t c om pa ra bled i s t a n c e s fro m t h e S u n, h a v e a t m os p h er e s t h a t ha v e e v o lv e dso d i f f e r e n t l y ?

0 Why i s t h e s u r f a c e o f Venus ba ke d by a s e a r i n g h e a t ,w hi le E a r t h l u x u r i a t e s i n a c l i m a t e f r i e n d l y t o l i f e ?

The answers t o b o t h o f t h e s e q u e s t i o n s d ep en d o n a nu n d e r s t a n d i n g of t h e f a c t o r s t h a t g o ve rn t h e e v o l u t i o n ofa p l a n e t ' s a t m o s p h e r e .

I n f o r m a t i o n g a t h e r e d by t h e t w o i n s t r u m e n t - l a d e n P i o n e e r sa t Venus may a l s o h e l p u s l e a r n more a b o ut t h e f o r c e s t h a td r i v e t h e w e a t h e r o n o u r own p l a n e t .

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The f l i g h t s a re t h e f i r s t on es d ev ot ed p r i m a r i l y t o as t u d y of t h e a t m os p he r e a nd w ea t h e r of a n o t h e r p l a n e t on ag l o b a l s c a l e . They w i l l em plo y t h e l a r g e s t num ber of v e h i c l e se v e r u s e d i n s u c h s t u d i e s , a nd make m ea su re m en ts a t t h eg r e a t e s t n u m b e r of l o c a t i o n s .

- The f l i g h t s a l s o w i l l seek t o l e a r n more a b o u t t h ec h a r a c t e r i s t i c s of Venus ' s uppe r a t mosphe re and i ono sph e re ,a s w e l l a s t h e l ower a t mosphe re . They w i l l s t u d y t h e i n t e r -a c t i o n s of t h e s e r e g io n s w i t h t h e s o l a r wind -- t h e c o n t i n u o u sstream o f i o n s a n d e l e c t r o n s f l o w i n g o u t w a r d f r o m t h e Sun --a n d t h e s o l a r m a g n e t i c a n d e l e c t r i c f i e l d s .

C i r c l i n g t h e p l a n e t f o r a t l e a s t e i g h t m o nt hs , t h eP i o n e e r Venus O r b i t e r w i l l make t h e l o n g e s t o b s e r v a t i o n sy e t o f V e nu s. I t w i l l b e t h e f i r s t U.S. s p a c ec r a f t t o o r b i tt h e p l a n e t .

To rea ch Venus, th e O r b i t e r w i l l f l y m o r e t h a n h a l f waya r o u n d t h e S un on i t s seven-month jo ur ne y, some 4 8 2 . 8 m i l l i o nkm ( 3 0 0 m i l l i o n m i . ) , t r a v e l i n g o u t s i d e t h e E a r t h ' s o r b i t f o rthe f i r s t t h r e e m onth s, and i n s i d e it f o r t h e l a s t f o u r m o n t h s .T h i s w id e- sw in gi ng f l i g h t p a t h w i l l a l l o w a s l ower approacht o t h e p l a n e t , p e r m i t t i n g a s ma l l e r o r b i t a l i n s e r t i o n m otora n d more s p a c e c r a f t w e i g h t .

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A t Venus , the O r b i t e r w i l l f o l l o w a h i g h l y - i n c l i n e d( 7 5 - d e g r e e ) , 2 4-h ou r o r b i t p l a n n e d so t h a t s p a c e c r a f t ev e n tsa r e t i m e d w i t h t h o s e on E a r t h . A t p e r i a p s i s ( o r b i t a l l o wp o i n t ) , t h e s p a c e c r a f t w i l l d i p a s low a s 1 5 0 km ( 9 0 m i . )a l t i t u d e , e n t e r i n g V en us ' t h i n up p er at m os p he re . I t s o r b i t a lh i g h p o i n t o r a p o a p s i s w i l l b e 6 6 , 6 0 0 k m ( 4 1 , 0 0 0 m i . ) fromt h e p l a n e t .

The O r b i t e r w i l l make d a i l y p i c t u r e s in u l t r a v i o l e tl i g h t of V en us ' c l ou d s f o r s t u d i e s o f t h e i r f ou r- da y r o t a t i o n .

E x p e r i m e n t e r s w i l l u s e p r e c i s e o r b i t m ea su rem en ts t oc h a r t Venus ' g r a v i t y f i e l d f o r c a l c u l a t i o n o f p l a n e t a r ys h a pe a nd d e n s i t y v a r i a t i o n s . The 1 2 O r b i t e r s c i e n t i f i ci n s t r u m e n t s w i l l m ake a va r i e ty of o t h e r r e m o t e - se n s i n g a n dd i r e c t m ea su re me nt s o f t h e p l a n e t ' s a tm o sp h er e an d su r r ou n d -i n g e n v ir o n m en t .

The O r b i t e r ' s p r i m a r y m i s s i o n o f e i g h t m on th s i n Venuso r b i t w i l l c o v e r o n e c o m p l e t e r o t a t i o n of Venus on i t s a x i s-- 2 4 3 E a r t h d a y s . I t c i r c l e s t h e Sun i n 2 2 5 d a y s .

The O r b i t e r ' s com panion s p a c e c r a f t , t h e M u l t i p ro b e , i smade up of a t r a n s p o r t e r Bus, a L a r ge P r ob e an d t h r e e i d e n t i -c a l s m a l l e r p r o b e s .

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The O r b i t e r s p a c e c r a f t , l i k e t h e M u l ti p ro b e b u s , con-s i s t s p r i n c i p a l l y o f a s p i n - s t a b i l i z e d , 2 . 4 - m e t e r ( 8 - f o o t ) -d i a me t e r , f l a t c y l i n d e r c o n t a i n i n g m ost s p a c e c r a f t s ys te ms .

Above t h e c y l i n d e r , o n a 1 -m ( l O - f t . ) m a S t a l i g n e d w i t h t h es p i n a x i s , i s t h e d e s p u n , na rro w-b ea m, p a r a b o l i c d i s h a n t e n n a .T h e d i s h i s u s ed f o r h ig h -s p ee d d a t a t r a n s m i s s i o n a nd f a c e st ow ar d t h e E a r t h t h r o u g ho u t t h e m i s s io n , w h i l e t h e s p a c e c r a f ts p i n s b e n e a t h i t .

W i th in t h e c y l i n d e r i s a t h e r m a l l y - c o n t r o l l e d e q u i p m e n tcom par tm en t , wh ich house s t h e 1 2 O r b i t e r s c i e n t i f i c i ns t r um en t s ,a m i l l i o n - b i t d a t a memory a nd t h e c o m mu n ic a ti o ns a n d d a t a -h a n d l in g s y st e m s . O t h e r O r b i t e r s y st e ms a r e t h e S u n a n d s t a rs e ns o rs f o r s p a c e c ra f t o r i e n t a t i o n ; t h r u s t e r s t o make spin-r a t e , o r i e n t a t i o n an d c o u rs e c o r r e c t i o n s ; t h e s o l i d - f u e lo r b i t a l i n s e r t i o n motor; a nd t h e b a t t e r y a nd pow er s y st e m .The e x t e r i o r o f t h e c y l i n d e r i s c o a t e d w i t h p o w e r - g en e r a ti n gs o l a r c e l l s . A 4 . 6 - m ( 1 5 - f t . ) boom e x t e n ds r a d i a l l y o ut wa rdt o p l a c e two m ag ne to me te r s e n s o r s b ey on d s p a c e c r a f t m a g n e t icf i e l d s .

The O r b i t e r ' s l a un c h w e i gh t is abou t 580 k i logram s ( 1 , 2 8 0pounds ) wi th 4 5 kg ( L O O lb.) o f s c i e n t i f i c i n s tr u m e n ts . W eigh ti n o r b i t a f t e r moto r b ur n w i l l b e 372 kg ( 82 0 l b . ) .

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The O r b i t e r ' s d e s t i n a t i o n , V e n u s , i s t h e s ec on d p l a n e tfr om t h e S un , a nd t h e c l o s e s t on e t o E a r t h . B e ca us e o f i t sh i g h l y r e f l e c t i v e c l o u d c o v e r , Venus i s t h e b r i g h t e s t o b j e c ti n t h e s k y a f t e r t h e S un and t h e Moon. I t s y e a r i s 2 2 5 E a r t hd a y s . I t s mean d i s t an ce f rom t h e Sun i s 1 0 8 . 2 m i l l i o n km( 6 7 . 2 m i l l i o n m i . ) . T h i s i s n e a r l y t h r e e - q u a r t e r s of E a r t h ' sd i s t a n c e f ro m t h e S u n .

When Venus i s c l o s e s t t o Ea r t h , d i r e c t l y be tween E a r t ha nd S u n, t h e p l a n e t i s o n l y 4 2 m i l l i o n km ( 2 6 m i l l i o n m i . )away. W h i l e Ear t h and Venus a r e a l m o s t t w in s i n s i z e andm a s s , t h e y a r e e xt re m el y d i f f e r e n t i n o t h e r ways . E a r t h i sa w a t e r - r i c h p l a n e t o n w hich l i f e t h r i v e s . Venus i s a d r ya nd d e s o l a t e w o rl d, a p p a re n t ly w i t h o ut l i f e . S c i e n t i s t sw an t t o know how two s i m i l a r p l a n e t s c a n e v o l ve s o d i f f e r e n t l yand i f t h e r e i s any chance of E a r t h b ec om in g l i k e V en us .

A v a i l a b l e e v i d e n c e s u g g e s t s t h a t V enus h a s a d r a m a t i -c a l l y ru gg ed s u r f a c e , b u t i t i s l e s s m o u n ta i no u s t h a n E a r t hand M a r s . I t s s u r f a c e t e m p e r a t u r e i s h o t t e r t h an t h e m e l ti n gp o i n t s of l e a d a nd z i n c , a b o u t 4 7 0 d e g r e e s C ( 9 0 0 d e g r e e s F . ) ,a nd t h e a t m o s p he r i c p r e s s u r e i s a b o u t 1 0 0 t i m e s t h a t of E a r t h .S u r f a c e f e a t u r e s o n V enus c a n n e v e r b e s e e n b e c a u s e of i t spe rmanent c l ou d co ve r . The a t mosphe re o f Venus app ea r s t ob e p r e d o m i n a n t l y c a r b o n d i o x i d e -- a b o u t 9 7 p e r c e n t . O nlyminute amounts of w a t e r v a p o r h a v e b e e n d e t e c t e d i n i t .

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Venus h a s no s i g n i f i c a n t m a gn e ti c f i e l d . S o t h ep l a n e t ' s u pp er a tm os ph er e i n t e r a c t s d i r e c t l y w it h t h e s o l a rwind. Venus i s o n e of t h e t h r e e p l a n e t s i n o u r s o l a r sy ste mwhich h a s no moons, the o t h e r s b e i n g M er cu ry a n d P l u t o .

The m a s s , d i a m e t e r and m ean dens i ty of E a r t h and Venusa r e a lmos t i d e n t i c a l . V e n u s ' h i g h o v e r a l l d e n s i t y s u g g e s t sa d e n s e core something l i k e E a r t h ' s n i c k e l - i r o n core.

V enus r e c e i v e s a l m o s t t w i c e a s much s o l a r r a d i a t i o n a sE a r t h . B u t w i t h o u t t h e t r a p p i n g of s o l a r h e a t by i t s atmos-p h e r e , th e p l a n e t ' s p o l a r r e g i o n s would ha ve h a b i t a b l e t e m -p e r a t u r e s . T h i s t r a p p i n g i s c a l l e d a g r e e n h o u s e e f f e c t ,which means t h a t Venus ' a tmosphere a l l o w s pas sag e of incom ings o l a r r a d i a t i o n , b u t r e s t r i c t s r a d i a t i o n of h e a t o u t w a r d .

T h e t e m p e r a t u r e a t th e p o l e s of Venus i s o n l y a b o u t 1 0d e g r e e s C ( 1 8 d e g r e e s F . ) l e s s t ha n t h a t a t t h e e q u a t o r . B othi t s d ay a n d n i g h t h e m i s p h e re s h a v e t h e same t e m p e r a t u r e .H en ce, V en us ' m a s s i v e a t m os p h er e c o n t a i n s c i r c u l a t i o n mech-a n is m s w hich d i s t r i b u t e s o l a r h e a t e v e n l y o v e r t h e w h o l e p l a n e t .

I n a d d i t i o n t o c a r b o n d i o x i d e a nd water t r a c e s , Venus 'a tm osphere a l s o h a s some c a r b o n m o no xi de , h y d r o c h l o r i c a c i da n d h y dr o ge n f l u o r i d e .

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Venus ' pe rm anen t c l ou ds a r e v e r y t e n u o u s , s o m e th i n gl i k e t e r r e s t r i a l smog. They a r e almost twice as d e e p a sE a r t h ' s c l o ud l a y e r , a b ou t 1 8 km (11 m i . ) t h i c k , a n d a r eb e l i e v e d t o be composed mainly of s u l f u r i c a c i d d r o p l e t s .

Somewhere below t h e bot tom of t h e m ain c l o u d l a y e r s ,t h e t e m p e r a t u r e becomes g r e a t enough f o r th e s u l f u r i c a c i dd r o p l e t s t o e v a p o r a te i n t o w a te r va po r an d s u l f u r i c a c i dv a p o r . A c l e a r a tm o sp h er e r e s u l t s . Enough s u n l i g h t g e t st h r o u g h t h e c l o u d s s o t h a t t h e s u r f a c e a p p e a rs a s b r i g h t a so n a n o v e r c a s t da y on E a r t h .

From t h e M ar in e r cl o u d p h ot o gr a ph s i n u l t r a v i o l e t l i g h t ,it a p p ea r s t h a t t h e s t r a t o s p h e r e of Venus i s i n c o nt in u ou sh i g h - s p e e d m o t i o n .( 2 2 0 mph) , c i r c l i n g t h e p l a n e t i n f o u r E a r t h days. However,t h e S o v i e t V e ne ra l a n d e r s showed t h a t win d s p e e d s i n t h e d e e pa t m o s p h e r e a r e e x t r e m e l y s l o w . I n t h e r e g i o n b et we en a tm os -phere t o p a n d b o tt om , a n a b r u p t c h an ge i n wind v e l o c i t y a p p e a r st o t a k e p l a c e . T h i s s e e m s t o o c cu r a t a b o u t 56 k m (3 6 m i . )above t h e s u r f a c e , b e t w e e n t h e ba s e of t h e c l o u d s a n d t h ec l e a r a t m o s p h e r e below them.

The clouds seem t o move about 360 km/hr

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Some major q u e s t i o n s r e l a t i n g t o E a r th a nd V enu s a r et he s e :

0 L i k e Venus , the E a r t h h a s a " g r e e n h o u s e e f f e c t "w h i c h a p p e a r s t o b e growing due t o i n c r e a s e s i n c ar bo nd i o x i d e i n o u r a t m os p he r e. T h es e i nc rea s e s come f r o m l a r g e -sca l e b u r n i n g of f o s s i l f u e l s s i n c e 1 8 5 0 . Could t h e E a r t h ' sg r e e n h o u s e e f f e c t become s t r o n g e n o u g h t o c a us e s e r i o u s ,pe rmanent r i s e s i n t e m pe r at u re ?

0 Si nc e Venus p resum ably fo rmed a s c l o s e t o E a r t h a si t i s t o d a y , w e m i g h t e x p e c t V e n u si a n o c e a n s l i k e our own.Y e t t h e r e i s a l m o s t n o water on Venus. Where d i d t h e waterg o , i f it e v e r e x i s t e d ?

One theory i s t h a t g r e a t e r s o l a r h e a t i n g v a p o r i z e d a nyo c e a n s , a n d f o r c e d w a t e r v a p or i n t o t h e s t r a t o s p h e r e . T h e r ei t would have s p l i t i n t o h ydroge n an d oxygen by s o l a r u l t r a -v i o l e t r a d i a t i o n . T he l i g h t - w e i g h t h y d ro g e n w ou ld t h e n h a v ee s c a p e d t o s p a c e l e a v i n g t h e o x yg e n b e h in d . B u t t h e r e seemst o be so l i t t l e f r e e oxygen l e f t , t h a t s c i e n t i s t s wonderwhere it a l l went .

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management of t h e t w o P i o n e e r Venus s p a c e c r a f t t o A m e sR e s e a r c h C e n t e r , M o u nt ai n V i e w . C a l i f . , a nd t h e s p a c e c r a f tw i l l be c o n t r o l l e d c o n t i n u o u s l y f rom t h e M is s io n O p e ra t i o n sC e n t e r a t Ames. T h e s p a c e c r a f t were b u i l t by H ughes A i r c r a f tCo., E l S egundo, C a l i f . , a nd t h e s c i e n t i f i c i n s t r um e n t s weres u p p l i e d by NASA c e n t e r s , o t h e r g ov er nm en t o r g a n i z a t i o n s ,u n i v e r s i t i e s and p r i v a t e i n d u s t r y .

T h e s p a c e c r a f t w i l l b e t r a c k e d by NASA's Deep Space N e t -w or k, o p e r a t e d b y th e J e t P r o p u l s i o n L a b o r a t o r y , P a s a de n a ,Ca l i f . NASA's L e w i s R e s e ar c h C e n t e r , C l e v e l a n d , i s r e s p o n s i b l ef o r t h e l au n ch v e h i c l e , w hich w a s b u i l t by G e n e r a l D yn am ics ,San Diego, C a l i f .

C o s t o f t h e two P i o n e e r Venus s p a c e c r a f t , s c i e n t i f i ci n s t r u m e n t s , m i s s i o n o p e r a t i o n s a n d d a t a a n a l y s i s i s a b o u t$ 17 5 m i l l i o n . T h i s does n o t i n c l ud e c o s t of l a u n c h v e h i c l e sa n d t r a c k i n g a n d d a t a a c q u i s i t i o n .

Launch p e r io d f o r t h e O r b i t e r f l i g h t i s 2 2 days (May 2 0t h r o u g h J u n e 1 0 , 1 9 7 8 ) , an d d u r i n g t h e s e d ay s , t h e t i m e o flaunch window opening v a r i e s be tween 6 : 0 8 and 9 : 2 4 a . m . E D T .T he window v a r i e s i n l e n g t h f r o m 1 5 m i n u te s t o o n e h o u r .

Launch p e r i o d f o r t h e M u lt i pr o b e f l i g h t e x t en d s fromAug. 7 t o S e p t . 3, 1978.

( E N D O F GENERAL RELEASE. B AC KGR OUND I N F O R M A T I O N FOLLOWS.)


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M I S S I O N PROFI LE

r i l l ehe t w o P i o n ee r f l i g h t s t o V enus p l o r e t h ea t m os p he r e o f t h e p l a n e t , s t u d y i t s s u r f a c e u s i n g r a d a ra n d d e t e r m i n e i t s g l o b a l s ha pe and d e n s i t y d i s t r i b u t i o n .The f i r s t s p a c e c r a f t , P i o n e e r Venus 1, a n O r b i t e r , w i l lmake e i g h t months o r m ore o f r e m o t e - se n s i ng a nd d i r e c tmeasurement . P i on ee r Venus 2 , a M u l t i p r o b e , w i l l s e p a r a t ei n t o f i v e a tm o s ph er ic e n t r y c r a f t , e i g h t m i l l io n m i l e s o u tfro m t h e p l a n e t , a n d m e a su r e t h e a t m o s p h e r e f ro m t o p t ob ot to m i n a b o u t two h o u r s a t p o i n t s s p r e ad o ve r t h e e n t i r eE a r t h - f a c i n g h e m i s p he r e o f V e nu s.

The P i o n e e r V en us O r b i t e r M i s s io nThe P io ne er Venus O r b i t e r w i l l be l a u n c h e d i n t o a c i r -cula r p a r k i n g orbit a s c e n t t r a j e c t o r y from Cape C a n a v e r a l ,F l a . , h e ad i ng i n a d i r e c t i o n v a r y in g from 3 t o 1 8 d e g r e e s

s o u th of d u e e a s t d u r i ng t h e f i r s t 1 5 d a y s o f t h e l a u n c hp e r i o d . I t w i l l p a s s o v er s o u t he r n A f r i c a s h o r t l y a f t e rs ec on d s t a g e r e s t a r t and b u rn o u t. L a t e r , t h e la un c h d i r e c -t i o n w i l l b e e i t h e r 1 0 d e g r e e s o r 30 d e g r e e s n o r t h of d uee a s t , d e p en d in g on t h e l a u n c h d a t e .T he s ev en -m o nth f l i g h t t o V enu s w i l l f o l l o w a t r a j e c -t o r y more t h a n h a l f way a r o un d t h e S un ( t h r o u g h a b o u t 2 0 0d e g r e e s ) , a n d w i l l c o v e r a b o u t 4 8 0 m i l l i o n k i l o m e t e r s ) 3 0 0m i l l i o n m i l e s ) . T h i s t r a j e c t o r y , t h r e e m on ths l o n g e r t h a nt h a t o f t h e M u l ti p ro b e, a l lo w s a s lo w er a r r i v a l s pe ed a tV e n u s , r e q u i r i n g l e s s w eig ht f o r t h e o r b i t i n s e r t i o n motor.

I t a l s o a l l o w s a n o r b i t a l l o w p o i n t ( p e r i a p s i s ) a t a l a t i t u d eof a b o u t 20 d e g r ee s n o r t h .F o r t h e f i r s t 8 2 d a y s , P io n e e r V en us 1 w i l l f l y o u t -s i d e t h e E a r t h ' s o r b i t . I n Augus t , i t w i l l c r o s s b ac k i n -s i d e t h e o r b i t of i t s home p l a n e t , a nd t h e n , d u r i n g t h el a s t f o u r m on th s o f t h e j o u r n e y , w i l l c r o s s t h e 4 2 m i l l i o n k m( 2 6 m i l l i o n m i . ) b et we en t h e o r b i t s of t h e E a r t h a nd V enuson a l on g , c ur v i ng t r a j e c t o r y . T h i s f l i g h t p a t h w i l l b es i m i l a r t o t h a t of i t s c om pa nio n s p a c e c r a f t , t h e Venus M u l t i -p r o b e . T he M u l t i p r o b e w i l l b e l a u n c h e d a f e w d ay s a f t e r t h eO r b i t e r crosses back i n s i d e E a r t h ' s o r b i t .

L aun ch p e r i o d f o r t h e O r b i t e r f l . i g h t i s 2 2 days (May 20t h r o u g h J u n e 1 0 , 1 9 7 8 ) . D u ri ng t h e s e d a y s , t h e l aunch win-dow opening t i m e s v a r y f r o m 6 : 0 8 t o 9 : 2 4 a . m . EDT. The win-dow v a r i e s i n l e n g t h f ro m h a l f a n ho ur t o a n h ou r f o r t h ef i r s t 1 8 l a u n ch d a ys , b u t e x t e n d s t o two h o u r s o n t h e l a s ttwo days of t h e p e r i o d .- m o r e -


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Launch da tes a r e t imed s o t h a t t h e O r b i t e r a r r i v e s a tVenus on D e c . 4 , 1978, f i v e d a ys b e f o r e t h e a r r i v a l o f t h ef i v e p ro b es on Dec. 9 . Launch da tes were s e l e c t e d f o r op-timum p a y l o a d s f o r b o t h O r b i t e r a n d M u l t i p r o b e m i s s i o n s .B o th P i o n e e r Venus s p a c e c r a f t w i l l be l aunched bya n A t l a s (SLV-3D) / C e n t a u r ( D - l A R ) two-and-a-hal f -s tagel a u n c h v e h i c l e . A i r F o r c e E a s t e r n T e s t Range personnelw i l l c on d uc t t r a c k i n g d u r in g t h e n e ar -E a rt h p a r t o f t h em is s io n . NASA's Deep Sp ac e Network (DSN) w i l l b e r e s p o n s i b l ef o r t h e r e m ai n de r .A f t e r l i f t o f f , b u r n o u t o f t h e 1,9 17 ,0 00 -n ew to n ( 43 1, 04 0-p o u n d ) - t h r u s t , o n e - a n d - o n e - h a l f - s t a g e A t l a s b o o s t e r w i l lo c c u r i n a b o u t f o u r m i n u t e s . O n e- ha lf m i n ut e b e f o r e t h i se v e n t , t h e 1 0 . 4 - m e t e r ( 3 4 - f o o t ) - l o n g a er od y na m ic n o s e f a i r i n gw hich p r o t e c t s t h e s p a c e c r a f t w i l l s p l i t l en g th w is e a nd b ej e t t i s o n e d j u s t a f t e r le a v i n g t h e a tm os ph er e. S t a g e s e pa r a-

t i o n a n d i g n i t i o n o f t h e 130,000-N ( 3 0 ,0 0 0 -l b .) t h r u s t C e n t a u rsecond s t a g e w i l l t h e n t a k e p l a c e . S h o r t l y a f t e rw a r d t h eA n t ig u a s t a t i o n b e g i n s t r a c k i n g . The h y dr og e n- fu el ed C e n t a u re n g i n e w i l l b u r n f o r a b o u t f i v e m i n u t e s. The C e n ta u r e n g i n esw i l l t h e n s h u t down a t 173-km (107 .5 -m i.) a l t i t u d e , and t h eO r b i t e r a n d t h e C e n ta u r w i l l c o a s t f o r a b o u t 1 2 m i n ut e s i nc i r c u l a r p a rk i ng o r b i t . A n ti gu a t r a c k i n g w i l l e n d a b o u t 1 3m i nu te s a f t e r l au n ch . The A sc en si on I s l a n d s t a t i o n , j u s tbelow t h e e q u a t or i n t h e So ut h A t l a n t i c , p i c k s u p t h e C e nt au r-Venus O r b i t e r a b o u t 1 0 m i n u t e s l a t e r . A bo ut 23 m i n u t e s a f t e rl a u n c h , t h e C e n t a u r e n g i n e r e s t a r t s a nd b u r n s f o r a b o u t 2 . 5m in u te s , p u t t i n g t h e O r b i t e r on i t s Venus f l i g h t p a t h . Dur-i n g t h e n e xt 2 . 3 m i n u t e s , C e n t a u r w i l l o r i e n t t h e s p a c ec r a f tw i t h t h e f or w ar d ( a n t en n a ) e nd p o i n t i n g t o c e l e s t i a l n o r t hb u t t i l t e d 20 d e g r e e s t o w ar d t h e S u n. A t t h i s p o i n t , t h eP i o n e e r Venus O r b i t e r s e p a r a t e s f ro m t h e C e n t a u r , a n d t h es p a c e c r a f t command r e g i s t e r t h e n b e g i n s t o f u n c t i o n .

J u s t a f t e r s e p a r a t i o n , a b o u t 28 m i n ut e s a f t e r la u n c h ,t h e command re g i s t e r w i l l command s to ra ge o f t e l em et r y d a taand s t a r t t h e t h r u s t e r - f i r i n g s eq ue nc e f o r s p in u p t o 6.5 rpm.T he O r b i t e r ' s m i l l i o n - b i t d a t a memory c a n s t o r e i n f o r m a t i o nf o r 68 m i n u t e s a t a b i t r a t e of 2 5 6 b p s a f t e r i t i s t u r n e don.Twenty -e igh t m inu tes a f t e r l a u n c h , a n d a f t e r C e n ta u r-O r b i t e r s e p a r a t i o n , m i s si o n c o n t r o l w i l l s h i f t f r o m t h em i s s i o n d i r e c t o r a t Cape C an av er al t o t h e f l i g h t d i r e c t o ra t t h e P i o n e e r M i s s io n O p e r a t i on s C e n t e r (PMOC ) a t AmesResea rch Cen te r , M ounta in V i e w , C a l i f . Commands t o space -c r a f t and incom ing da ta w i l l g o v i a t h e g l o b a l n e t o f D S Nt r a c k i n g s t a t i o n s . DSN s t a t i o n s w i l l rece ive commands from,a nd r e l a y d a t a t o , t h e PMOC a t A m e s .

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A t l a un c h p l u s a b o u t o ne h o u r , t h e D S N s t a t i o n a tC a n b e r r a , A u s t r a l i a , w i l l a c q u i r e t h e s p a c e c r a f t , and 1 0m i n u t e s l a t e r w i l l have e s t a b l i s h e d command o f t h e Venusbound O r b i t e r and v e r i f i e d t h e s p a c e c r a f t ' s h e a l t h . F l i g h tc o n t r o l l e r s a t A m e s w i l l t h e n command t h e s p a c e c r a f t t e l e -m et ry p r o c e s s o r i n t o th e l a u n c h - c r u i s e f o r m a t ( h a l f s c i e n c e ,h a l f e n g i n e e r i n g ) . Gaps i n t r a c k i n g c o v e ra g e w i l l b e d u et o e a r l y f l i g h t a l t i t u d e s be tw een w i de ly s e p a r a te d g l o b a lt r ac k in g s t a t i o n s .

W i t h C a n b e r r a a c q u i s i t i o n , A m e s m i ss io n d i r e c t o r s w i l lt u r n o n t h e p la sm a a n a l y z e r ( s o l a r w i n d i n s t r u m e n t ) t o maken e a r - E a r th o b s e r v a t i o n s . They w i l l v e r i f y t h e s p i n p er io dand Sun an g l e and check sp a c e c r a f t wobb le. When t h e wobb leh a s s u bs id e d t o a n a c c e p t a b le l e v e l , t he y w i l l command t h ef i r i n g o f p y r o t e ch n i c s t o de p lo y t h e th r e e - s e c t i o n , h in g ed ,4 . 7 - m (1 5 .5 -f t . ) magnetom eter boom. Deployment of th e booms l o w s s p a c e c r a f t s p i n from 6 . 5 t o 5 rpm. Immedia te ly a f t e r -w a r d s , t h e magnetometer i s t c r n e d o n . W it h t h e boom deployed,c o n t r o l l e r s w i l l b e a b l e t o command s p a c e c r a f t s p i n u p t o 1 5rpm i n e n s u i n g w e e k s .

Approx im ate ly 1 8 h ou rs a f t e r l au nc h , t h e O r b i t e r w i l lbe o r i e n t e d s o t h a t i t s s p i n a x i s i s w i t h i n t w o d e g r e e s ofa r i g h t a n g le t o t h e e c l i p t i c . M i ss io n e n g i n e e rs c a n nowcommand operation of t h e h ig h - ga i n a n t e n n a d e s p i n sy st em t op o i n t t h e narrow -beam a n t e n n a a t E a r t h . T he a n t e n n a m a s t ,which i s a l ig n e d w it h t h e s p a c e c r a f t s p i n a x i s , i s commandedt o s t o p r o t a t i n g s o t h a t t h e a n te nn a d i s h p o i n t s a t E a r t hw h i le t h e s p a c e c r a f t c o n t i n u es t o s p i n u nd er i t . E l e v a t i o no f t h e d i s h i s a d j u s t e d s o t h a t i t c e n t e r s o n E a r t h .

N in e a nd o ne -h al f h o u rs a f t e r l au n c h , t h e O r b i t e rp i c t u r e - t a k i n g f o r m a t i s t u r n e d o n , a n d o n e - h a l f h o u r l a t e r ,t h e e l e c t r o n i c camera, t h e C lo ud P h o to p o l a r im e t e r , u s i n gi t s i ma gi ng mode, b e g i n s t o t a k e p i c t u r e s of E a r t h a sP io ne er moves away.S u b s eq u e n tl y , m i s s i o n o p e r a t i o n s w i l l t u r n on t h egamma r a y b u r s t d e t e c t o r an d t h e e l e c t r i c f i e l d d e t e c t o r .

M id co ur se C o r r e c t i o n s a nd C r u i s eD ur ing t h e f i r s t f i v e d ay s, t r a j e c t o r y s p e c i a l i s t s a t

NASA's J e t P r o p u l s i o n L a b o r a t o r y, P a sa d en a , C a l i f . , w i l lc a l c u l a t e t h e p r e c i s e t r a j e c t o r y , e s t a b l i s h i n g t h e p r e c i s eE a r t h d e p a r t u r e v e l o c i t y and d i r e c t i o n . Ames c o n t r o l l e r sw i l l t h e n command f i r i n g o f r a d i a l a n d /o r a x i a l t h r u s t e r s t oe l i m i n a t e e r r o r s i n a im in g a t V enus, S p a c e c r a f t o r i e n t a t i o nmay be c ha ng ed somewhat f o r e f f i c i e n t a c c e l e r a t i o n , a nd t h e nr e tu r n ed by f u r t h e r t h r u s t s t o i t s c r u i s e p o s i t i o n , p er pe n-d i c u l a r t o t h e e c l i p t i c .-more-


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Once t h e s p a c e c r a f t i s i n a c r u i s e mode, t h e s i x s c i e n -t i f i c i n s t ru m en ts p la nn ed f o r u s e a t Venus w i l l be checkedo u t p e r i o d i c a l l y . C o n t r o l l e r s w i l l c ha ng e p o i n t i n g d i r e c -t i o n o f t h e h i g h- g ai n a n t e n n a d i s h e ve r y f i v e d a y s t o t w oweeks o r more, t o keep i t c e n t e r e d o n E a r t h .T wenty d a y s a f t e r l a u n c h , a s ec on d c o u r s e c o r r e c t i o nc a n be made, a nd 30 d a ys b e f o r e t h e s p a c e c r a f t a r r i v e s a tVenus, n a v i g a to r s can command a t h i r d c o u rs e c o r r e c t io n f o ra p r e c i s e i n s e r t i o n i n t o o r b i t a rou nd t h e p l a n e t . S e v er a lweeks a f t e r l au n ch , c o n t r o l l e r s w i l l command t h e sp a c e c ra f tt o s pi nu p t o 15 rpm, a r a t e which w i l l be m a in ta in ed u n t i ltwo days before Venus a r r i v a l . I t p r o v i d e s s o l a r windmeasurements .T w o d ay s b e f o re a r r i v a l a t Venus, t h e s p a c e c r a f t s p i nr a t e w i l l b e increased t o 30 rpm a n d t h e O r b i t e r w i l l beo r i e n t e d w i t h i t s 18,000-N ( 4 , 0 0 0 - l b . ) - t h r u s t , s o l i d - f u e l e dr o c k e t e n g i ne p o i n t i n g f or w ar d, o p p o s i t e t h e d i r e c t i o n of

t r av e l a t t h e p o i n t of c l o s e s t a p pr oa ch t o Venus.On D e c . 4 , 1978 ( t h e 1 9 8 t h d ay a f t e r l a u n ch , i f l au n choccurs on May 2 0 ) , Ames M i s s i o n C o n t r o l e n g i n e e r s w i l l com-mand a 28-second o r b i t - i n s e r t i o n b u r n . T h i s w i l l r e d u c es p a c e c r a f t v e l o c i t y b y 3 ,8 16 k m/hr ( 2 , 3 6 6 mph) , p l a c i n gP i on e e r i n a 2 4-h ou r o r b i t a r o u n d V en us . T he p l a n n e d o r b i tw i l l b e i n c l i n e d 7 5 d e g r e e s t o V en us ' e q u a t o r , w i t h i t s l o wp o i n t ( p e r i a p s i s ) ne a r 20 d e g r e e s n o r t h l a t i t u d e . Theo r b i t ' s h i gh p o i n t ( a po a p si s ) i s e x pe ct ed t o b e a t a n a l t i -t u d e of 6 6 , 0 0 0 km (41 ,0 00 m i . ) , and p e r i a p s i s i n i t i a l l y w i l lbe a t 300 km (180 m i . ) , l a t e r r e du c e d t o a b o u t 1 5 0 k m (90 m i . ) .P lan ned o r b i t a l i n j e c t i o n t i m e i s 11:OO a . m . EST.W i t h i n h o u r s a f t e r t h e o r b i t i n s e r t i o n r o c k e t bu rn ,members of t h e O r b i t e r n a v i g a t i o n t e a m w i l l h a v e d e t e r m i n e dany sh or tc om in gs i n t h e o r b i t . A f t e r s l ow in g t h e s p i n r a t ean d a d j u s t i n g o r i e n t a t i o n , t h ey w i l l command f i r i n g oft h r u s t e r s t o t r i m up t h e o r b i t t o a c c e p t a b l e d i m e n s i o n s .A t t e n t i o n i n t h e M is si on O p e ra t i o n s C e n t e r w i l l t h e ns w i t c h t o t h e p r o be s s c h ed u le d t o a r r i v e f i v e d ay s l a t e r ,b u t f i n e t un in g o f t h e o r b i t w i l l c o n t i n u e a f t e r com ple t ionof t h e p r ob e m i s s i on .

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I n - O r b i t O p e r a t i o n sF o r e f f i c i e n t o r b i t a l o p e r a t i o n s d ur i ng t h e 243-dayp r i m a r y O r b i t e r m i s s i o n ( o ne c o m p le t e V enus r o t a t i o n o n i t sa x i s ) , t h e o r b i t w i l l h a v e a p e r i o d v e r y c l o s e t o 2 4 h o u r s .T h i s means t h a t most a c t i v i t i e s w i l l o c c u r a t t h e same t i m eon E a r t h e v e ry d ay . T h i s i n c l u d e s t h e m os t i n t e n s i v e p e r i o d so f d a t a r e t u r n d u r in g p e r i a p s i s . D ata r e t u r n v i a t h e h ig h-g a i n a n t en n a w i l l be a t t h e t w o h i g h e s t r a t e s , 1 , 0 2 4 o r2 , 0 4 8 b p s .The 2 4-hou r o r b i t h a s be en d i v i d e d i n t o two p e r i o d s ,r e f l e c t i n g t h e k i n d o f m e as ur em en ts b e i n g t a k e n . T h e p e r i -a p s i s ( o r b i t a l low p o i n t ) p e r i o d i s a b o u t f o u r h o u r s l o n g .The a p o a p s i s ( o r b i t a l h i g h p o i n t ) p e r i o d i s 20 h o u r s l o n g .S i n c e t h e O r b i t e r d i p s i n t o t h e up pe r a tm os ph er e i t s e l f a tp e r i a p s i s , w h ic h may b e a s low a s 1 5 0 k m ( 9 0 m i . ) t o maked i r e c t m e as ur em e nt s, t h e p e r i a p s i s p e r i o d i s t h e t i m e ofh i g h e s t d a t a r e t u r n .M i ss io n o p e r a t i o n s w i l l u s e f i v e d a t a f o r m a t s d u r i n gt h e p e r i a p s i s p e r i o d . T he se f o r m at s a r e d e si gn e d t o p e r m i te m ph as is o n c e r t a i n i n s t r u m e n t s when d e s i r a b l e ; f o r e xa mp le ,o n e p r o v i d e s i n t e n s i v e a eronom y c o v e r a g e a t p e r i a p s i s ,a n o t h e r s t r e s se s o p t i c a l c ov er ag e.The mapping format g i v e s 4 4 p e r c e n t of t h e d a t a s t r e a mt o t h e r a da r m ap pe r f o r Venus s u r f a c e s t u d y , a nd d i v i d e s t h er e s t b etw een t h e u l t r a v i o l e t sp e c t r o m e t e r a nd t h e i n f r a r e dr ad iometer .N o r m a l l y , c o n t r o l l e r s w i l l u s e o n l y two d a t a f o r m a t si n t h e 20 -h ou r a p o a p s i s se g m en t . T h e f i r s t o f t h e s e w i l l bef o r t a k i n g p i c t u r e s of t h e whole p l a n e t i n u l t r a v i o l e t l i g h t ,which w i l l show t h e fo u r -d a y r o t a t i o n of V en us ' c l o u d s i nsequence. Known a s t h e im a g in g f o r m a t , it a l l o c a t e s 6 7 p e rc e n t of t h e d a t a stream t o t h e i m ag in g i n s t r u m e n t a nd t h ec l o ud p h o t o p o l a ri m e t e r , a nd d i v i d e s t h e r e s t among three

s o l a r w i n d -p l a ne t i n s t r u m e n t s a nd t h e a s t r o n o m i c a l e x p e r i -m e n t ' s gamma b u r s t d e t e c t o r . T he o t h e r f o r m a t , known a s t h eg e n e r a l f o r ma t , a l l o c a t e s d a t a r e t u r n among a l l O r b i t e r ex-p e r i m e n t s e x c e p t t h e p i c t u r e - t a k i n g c l o ud p h o t o p o l a r im e t e rand t h e i n f r a r e d r a d io m e t er . A s much a s t h r e e - q u a r t e r s oft h e t o t a l a p o ap s is pe r io d w i l l b e d e v o t e d t o imaging, whichh a s v e r y l a r g e d a t a r e q u i r e m e n t s .S p a c e c r a f t c o n t r o l l e r s h a ve d e s i g n e d a number of s e q u en c e su s i n g t h e s e f o r m a t s . D uri ng t h e ei gh t- mo nt h O r b i t e r m i s s i o n ,t h e y w i l l w ork w i t h e x p e r i m e n t e r s , s e l e c t i n g f o r m a t c om bin a-t i o n s f o r b e s t s c i e n t i f i c r e s u l t s .

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O R B I T IN S P A CE C RA F T O R B I T P L A N ETIME FROM PERIAPSIS, hours

202 '2119

>E IAPSISA ORBIT PERIOD = 24hoursPERIAPSIS ALTITUDE = 2 0 0 k mV E NUS RADIUS = 6050 km (3750 mi) APOAPSIS k13

I I I I I I I I I I 1 I I I-1 0 1 2 3 4 5 6 7 8 9 10 11 12DIS T ANCE , V E NUS RADI I


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During t h e f i r s t 4 0 days i n o r b i t , t h e O r b i t e r w i l lp a s s b eh i n d Venus ( o c c u l t a t i o n ) f o r p e r i o d s o f up t o 23m i n u t e s . T h i s a l l o w s t h e r a d i o s c i en c e t e a m t o m ea su ree f f e c t s o f V e n us ' a t m o s p he r e down t o a p p r o x i m a t e l y 50 km( 3 1 m i . ) on t h e s p a c e c r a f t r a d i o s i g n a l a s it p a s s e s t h r o u g hi t . S i n c e t h e nar row beam s i g n a l i s b e n t b y t h e p l a n e t ' sa t m os p h er e , t h e a n t e n n a ' s d i s h r e f l e c t o r c a n b e commandeda s much a s 1 7 d e g r e e s away f ro m t h e E a r t h - l i n e t o e x t e n d t h et i m e o f r e c o rd i n g t h e s i g n a l a s it i s r e f r a c t e d a ro un d t h es o l i d p l a n e t .

A l s o d u r i n g o c c u l t a t i o n s , w hen c om m u ni ca ti on s a r e c u to f f , t h e Venus O r b i t e r w i l l s t o r e d a t a i n i t s m i l l i o n - b i tmemory . Con t ro l l e r s w i l l then command memory storage, anda f t e r e me rg en ce o f t h e O r b i t e r , t h e d a t a memory r e a d o u t f o r -m a t f o r r e t u r n of s t o r e d d a t a .

D ur in g t h e e i g h t m onths on o r b i t , h e a l t h of t h e s p a c e -c r a f t w i l l b e m o n i to r e d t h ro u g h t h e c o n t i n u o u s f l o w o f e n g i -n e e r i n g d a t a ( s e e O r b i t e r Data H a nd li ng S e c t i o n ) , a nd re -d u n da n t s ys te m s f o r t h e m o s t c r i t i c a l f u n c t i o n s ( s u c h a scommand and d a ta r e tu r n ) w i l l b e u s ed i f n ee d ed . M i s s i o n sO p e r a t i o n s e n g i n e e r s a l s o w i l l t r i m t h e o r b i t a b o ut e ve ry1 0 d ay s e i t h e r t o low er p e r i a p s i s a l t i t u d e w hich i s c o n s t a n t l yr a i s ed by s o l a r g r a v i t y o r t o a d j u s t t h e o r b i t a l p e r io d wheni t d r i f t s from t h e d e s i r e d v a l u e .

The p ri m a ry m i s s i o n e n ds a f t e r 2 4 3 d a y s . S h o r t l y a f t e r -w a r ds , t h e O r b i t e r a n d Venus w i l l be be hind t h e Sun and com-m u n i c a t i o n s w i l l b e g a rb l ed o r c u t o f f f o r s e v e r a l day s.Af t e r emergence f rom t he s o l a r b l a c ko u t , t h e o p p o r tu n i t y w i l lb e a v a i l a b l e f o r e x te n de d m i ss i o n o p e r a t i o n s wh ich a r e n o tc u r r e n t l y a p a r t of t h e a pp ro ve d m i s s io n .

P i o n e e r V enu s M u l t i p r o b e M i s s i o nP i onee r Venus 2 , t h e m u lt i p ro b e s p a c e c r a f t , w i l l b elaunched toward Venus on a c i r c u l a r p a r k in g - o rb i t a s c e n tt r a j e c t o r y f rom Cape Canavera l A i r Force S t a t i o n by N A S A ' sK ennedy S p a ce C e n t e r p e r s o n n e l . T he la u n c h v e h i c l e w i l lh ea d i n a d i r e c t i o n 3 t o 1 8 d e g re e s s ou th of s t r a i g h t e a s t ,p a ss i ng o v e r s o u t he r n A f r i c a s h o r t l y a f t e r s e p a r a t i o n of t h es p a c e c r a f t fro m t h e l au n c h v e h i c l e .T he fo ur -m o nt h t r i p t o V enus f o l l o w s a more d i r e c tt r a j e c t o r y t h an t h a t o f t h e O r b i t e r , g i v in g t h e p ro be sa p p r o ac h s p e e d s o f a b o u t 1 9 , 5 0 0 h / h r ( 1 2 , 0 0 0 m p h ) . T h i si s 6 , 5 0 0 h / h r ( 4 , 0 0 0 mph) f a s t e r t h an O r b i t e r a r r i v a l , andi s p o s s i b l e b e c a u s e t h e p r o b e s a r e s lowed a t a t mosphe ree n t r y t o a few hundred m i l e s p e r h o ur b y t h e b r a k i n g ofa t m o s p h e r i c f r i c t i o n .

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P I O N E E R V E N U STRAJECTORIES

ORBIT ER L AUNC HMAY/JUNE 1978

ORBITERENUSATA U N C HqVENUS ATD P A P C I A l l h l P UVENUS AT PROBEENCOUNTERDECEMBER 1978\ORBITER ARRIVES

-/ ART H AT ORBIT ER H+M"TEFENCOUNTERPROBE RELEASESEQUENCE


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- 2 1 -

T h e M u l t i p r o b e f l i g h t w i l l c o v e r a b o u t 3 5 4 m i l l i o n km( 2 2 0 m i l l i o n m i . ) , g o i ng a b o u t t w o - f i f t h s of the way aroundt h e Sun ( 13 5 d e g r e e s ) i n f o u r m on th s a s i t c ro sses t h e 4 2m i l l i o n km ( 2 6 m i l l i o n m i . ) b et we en t h e o r b i t s of E a r t h a ndVenus.

L au nc h p e r i o d f o r P i o n e e r V enus 2 f l i g h t i s 27 d a y s ,from Aug. 7 t o S e p t . 3 , 1 97 8. D ur in g t h i s p e r i o d , t h ela un ch window open s e a r l i e r each day f rom 3:36 a . m . t o1 2 : 1 6 a . m . EDT. T h i s l a u n c h p e r i o d w i l l a l l o w t h e p r o b est o a r r i v e a t Venus on D e c . 9 , 1 97 8, f i v e da y s a f t e r a r r i v a lo f t h e O r b i t e r . The e a r l i e r O r b i t e r a r r i v a l w i l l a l l o wt h e O r b i t e r ' s r em ot e and d i r e c t s e n s i n g in s t r u m e nt s t oe s t a b l i s h c o r r es p on d in g d a t a on t h e Venus s p a c e environment,c l o u d s an d u pp er a tm o sp he re t h a t c a n b e c o r r e l a t e d w i t h t h ep r o b e m ea su re m en ts i n t h e a t m o s p h e re .P i o n e e r V e n u s 2 w i l l be l aunched by an A t l a s (SLV-3D)C e n t a u r ( D - l A R ) tw o-and o n e - h a l f - s t a g e l a u n c h v e h i c l e .A f t e r l i f t o f f , b u rn ou t o f t h e 1 , 9 1 7 , 0 0 0 - N ( 4 3 1 , 0 4 0 - l b . ) -t h r u s t , s t a g e - a n d - o n e - h a l f A t l a s b o o s t e r w i l l o cc ur i n a b o u tf o u r m i nu t es . S t a g e s e p a r a t i o n an d i g n i t i o n of t h e 130,000-N( 3 0 , 0 0 0 - l b . ) - t h r u s t C e n t au r s e co n d s t a g e w i l l t h e n t a k e p l a c e .A t s i x min ut e s a f t e r l i f t o f f , t h e An t ig u a s t a t i o n b eg in st r a c k i n g . T he h y d r og e n - fu e l ed C e n t a u r e n g i n e w i l l b u r n f o ra b ou t f i v e m in ut es w i t h t h e f i r s t e ng in e c u to f f a t 9 m i n u t e s ,4 2 s ec on ds a f t e r l i f t o f f . T h i s b e g in s t h e 18-m inute c o a s tp e r io d i n c i r c u l a r p ar ki ng o r b i t a t 167 k m (104 m i . ) a l t i t u d e .

A t a b o u t l a u nc h p l u s 1 3 m i n u t e s , A n t i gu a w i l l end i t s t r a c k -i n g c o v e r a g e ; a t a b o u t 20 m i n u t e s a f t e r l a u n c h , t h e A s c e n si o ns t a t i o n b e g in s t r a c k in g and a t l a u n c h p l u s 2 4 m i n u t e s M u l t i -probe-Cen taur com bina t ion pa ss beyond Ascens io n r ang e .

A t 2 7 m i n u t e s a n d 30 s e c o n d s , C e n t a u r b e g i n s i t s s e c o n db u r n a n d 2 m inutes and 8 seconds l a t e r ( l a u n c h , p l u s 2 9 . 6m i n u t e s ) i t s e n gi ne c u t s o f f p u t t i n g t h e M u l t ip ro be o n t r a -j e c t o r y t o V en us . A b ou t 2 7 . 6 m i n u t e s a f t e r l a u n c h a n A i rF o r c e Range I n s t r u m e n t a t i o n A i r c r a f t b e g i n s f i v e m i n u te s oft r a c k i n g c o ve ra g e.A t 2 9 . 7 m i n u t e s a f t e r l au n ch , C e n ta u r o r i e n t s t h eM u lt ip ro be s p i n a x i s t o w i t h i n 1 2 d e g r e e s of p e r p e n d i c u l a r

t o t h e e c l i p t i c ( E a r t h ' s o r b i t p la n e) w i t h i t s fo rward endp o i n t e d n e a r t h e s o u t h e c l i p t i c p o l e . One h un dr ed t h i r t y -f i v e s ec on ds a f t e r t h e se co nd C en t a ur en g i ne c u t o f f , a l s oa t l a u n c h p l u s 31.9 m i n u t e s , P i o n e e r s e p a r a t e s f ro m C e n t a u r ,and t h e s p a c e c r a f t command r e g i s t e r i n i t i a t e s t h e s p i nu ps eq ue nc e. S p a c e c r a f t t h r u s t e r s t h e n s p i n up M u lt ip r ob e t o15 rpm.-more-


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- 2 2 -

D u ri ng po we re d f l i g h t , a s w i t h P i o n e e r V e n u s 1, l a u n c hv e h i c l e an d s p a c e c r a f t w i l l b e m o n i t or e d f ro m t h e P i o n e e rM i s s io n C o n t r o l C e n t e r a t Cape Canavera l v i a DSN an d E a s t e r nT e s t Range t r a c k i n g s t a t i o n s , i n c l u d i n g A nt ig u a a nd A s c en s io n .T h i r t y - t w o m i n u t e s a f t e r l a u n c h , a f t e r Cent au r -Mul t i -

p ro be s e p a r a t i o n , m i s s io n c o n t r o l w i l l s h i f t from t h e A m e sM i s s i o n D i r e c t o r a t Cape C an a ve r al t o t h e F l i g h t D i r e c t o ra t t h e P i o n e e r M i s si o n O p e r a t io n s C e n t e r ( P M O C ) a t A m e sR e s e a rc h C e n t e r i n C a l i f o r n i a . Commands t o and d a t a r e t u r n e df ro m t h e P i o n e e r V en us w i l l l e a v e a n d a r r i v e a t E a r th v i a t h eg l o b a l n e t of t h e DSN t r a c k i n g s t a t i o n s . The s t a t i o n s i nt u r n r e ce i v e commands f rom and r e l a y d a t a t o t h e PMOC a t A m e s .A t 50 m i n u t e s a f t e r la u n c h , t h e DSN's C a n b e rr a s t a t i o na c q u i r e s t h e s p a c e c r a f t an d 1 0 m i n u t e s l a t e r command capa-b i l i t y i s e s t a b l i s h e d . D a t a r a t e t hr ou gh t h e s p a c e c r a f t ' sa f t omni antenna i s 256 b p s .Fo r t h e fo l lo w in g two weeks communica t ions be tweens p a c e c r a f t and E a r t h w i l l b e p r i m a r i l y " h ou s ek e ep i ng , I' s i n c et h e p r o b e an d Bus i n s t r u m e n t s make n o i n t e r p l a n e t a r y m ea su re -ments . They a r e d e s i g n e d t o measure t h e Venus a t mosphe re .Data w i l l b e s p a c e c r a f t h e a l t h a nd e n g i n e e r i n g me as ur em en ts .F i v e d a ys a f t e r l au n ch , t h e s p a c e n a v i g a t i o n s e c t i o n a tt h e J e t P r o p u l s i o n L a b o r at o ry w i l l h av e c a l c u l a t e d t h e M u lt i-p ro be Venus t r a j e c t o r y p r e c i s e l y , and c o n t r o l l e r s a t t h e PMOCa t A m e s w i l l command t h e t h r u s t e r f i r i n g s e qu en ce f o r t h ef i r s t t r a j e c t o r y c o r r e c t i o n m an eu ver. A bout 1 4 d ay s a f t e rl a u n c h , t h e tw o Bus i n s t r u m e n t s w i l l b e checked o u t f o r t h r e eh o u r s a t a d a t a r a t e o f 1 , 0 2 4 b p s . Tw enty d a y s a f t e r l a u n c h ,o p e r a t i o n s e n g i n e e r s w i l l make a s ec on d c o u r s e c o r r e c t i o n .About 60 days a f t e r l a u n c h , t h e s e v en i n s t r u m e n t s an dt h e s y st em s o n t h e L a r ge P r ob e w i l l b e c he ck ed o u t f o r t h r e eh o u r s a t d a t a r a t e s of 256 and 1 2 8 b p s. C o n t r o l l e r s a t PMOCc he ck o u t t h e t h r e e i n s t r u m e n t s a n d s ys te m s on e ac h o f t h eS m a l l P r o b e s f o r a n h o ur o f o p e r a t i o n e ac h a t a d a t a r a t e of6 4 and 1 6 bp s . They per form s i m i l a r c h e c k s on t h e two i n s t r u -men t s aboa rd t h e Bus a t 512 bps. T h e Bus communications andpower system w i l l b e u se d f o r t h e s e c h ec k s.About 9 4 d ay s a f t e r l au nc h I 3 0 d a y s b e f o r e a t m os p he ree n t r y ) , c o n t r o l l e r s w i l l i n i t i a t e t h e t h i r d t r a j e c t o r y co r -r e c t i o n m a n eu ve r. A t a b o u t t h e same t i m e , t h e s p a c e c r a f ti s o r i e n t e d so t h a t t h e a f t - f a c i n g m edium -gain h o r n an t e n n al o o k s a t E a r t h . T h i s a l lo w s a h i g h e r d a t a r a t e f o r p r ob es e p a r a t i o n m a n e u v e r s .

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E N T R Y P O I N TS F O R P IO N E ER - V E N U SATMOS P HE RE P ROBE S


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T w en ty -s ev en d a y s b e f o r e e n t r y , t h e B us a nd L a r g eP r o b e i n s t r u m e n t s a r e c h e c k e d o u t .T w en ty -f ou r d a y s b e f o r e a tm o s p h e r i c e n t r y , a n d 1 3m i l l i o n km ( 8 m i l l i o n m i . ) from V enus, c o n t r o l l e r s r e o r i e n tt h e s p a c e c r a f t s o t h a t t h e L a rg e P ro be w i l l e n t e r t h e a tm os-

p h e r e w i t h i t s h e a t s h i e l d a l i g n e d w i t h i t s e n t r y f l i g h tp a t h . T h i s m e a n s a l i g n i n g t h e Bus s p i n a x i s w i t h t h e p l annedL ar ge P ro b e e n t r y t r a j e c t o r y b e ca u se t h e L ar ge P r ob e i s cen-t e r ed o n t h e s p i n a x i s . The L a r ge P r o be i s t h e n l a u n c h e d b ya pyr o t e chn i c - s p r i n g mechanism t oward i t s e q u a t o r i a l e n t r yp o i n t o n V e nu s' d ay s i d e , be co min g a n i n d e p e n d e n t s p a c e c r a f t .

The nex t 2 3 d a ys f ro m a t m o s p h e r ic e n t r y , t h e Bus i sm an eu ve re d f o r s e p a r a t i o n of t h e S m a l l Prob es by chang i ngi t s f l i g h t p a t h , p o i n t i n g i t t ow a rd t h e c e n t e r o f V e nu s. A t2 2 d ay s b e f o r e e n t r y t h e t h r e e S m a l l P r ob e i n s t ru m e n t s a rec h e c k e d o u t . A t 20 d ay s b e f o r e e n t r y t h e Bus i s r e o r i e n t e dso t h a t t h e t h r e e Sm a ll P ro be s c an b e t a r g e t e d f o r t h e i re n t r y p o i n t s -- one on t h e day s i d e a t m i d - s o u t h e r n l a t i t u d e s ,t h e s ec on d o n t h e n i g h t s i d e , a l s o a t m i d - s o u t h e r n l a t i t u d e s ,and t h e t h i r d on t h e n i g h t s i d e a t h i gh n o r t h e rn l a t i t u d e s .Mi s s i on op e r a t i o n s t hen commands l au nch of t h e t h r e e S m a l lP r o be s . A f t e r t h e t r a n s p o r t e r Bus i s s pu n up t o a p p r o x i -m a t e l y 48 rpm , t h e p r o b e s a r e l au n ch e d by r e l e a s i n g t h ec la mp s t h a t h o l d them . C e n t r i f u g a l f o r c e o f t h e Bus s p i nth ro ws t h e p ro b e s t a n g e n t i a l l y from t h e Bus i n t o t h e i r e n t r yt r a j e c t o r i e s . A s a r e s u l t of t h i s l a un ch p r o c e s s , t h e S m al lP ro b es r e t a i n t h e 48-rpm s p i n e s t a b l i s h e d w h i l e a t t a c h e d t ot h e B us.

Wi th l aunch of a l l f o u r p ro b es , f i v e s p a c e c r a f t --i n c l u d i n g t h e Bus -- e a c h w i t h i t s own i ns t ru m en t and com-mand and da ta sys tem -- a r e h e ad e d f o r V en us .E i g h t e e n d a y s b e f o r e e n t r y , a f t e r S m a l l P r o b e s e p a r a t i o n ,c o n t r o l l e r s w i l l r e t a r g e t t h e Bus f o r e n t r y . Bus e n t r y i sd e l a y e d a b o u t 8 5 m i n u t e s a f t e r e n t r y of t h e l a s t S m a l l . P r o b et o p ro v id e a r a d i o s i g n a l r e f e r e n c e f o r p r e c i s e c om pu ta '2 on sof t h e p ro be d e s c e n t t r a j e c t o r i e s . ( T r a j e c t o r y d a t a w i l l beu s e d t o m e a s ur e w i n d s i n V e n us ' a t m o s p h e r e . )From t h i s p o i n t on , t h e f o u r p r ob e s w i l l be commandedby onboard t ime r s a nd o t h e r s e n s o r s an d e l e c t r o n i c s , a nd

t h e y w i l l n o t b e h e ar d f rom by c o n t r o l l e r s on E a r t h u n t i l22 m i n u te s b e f o r e a t m o s p h e r ic e n t r y .A t e n t r y m in us e i g h t da y s, f i n a l ad j u st m e n ts w i l l bemade t o t h e B U S ' e n t r y an gl e by ground command, and a t e n t r ym in us tw o d a y s , t h e Bus s y st e m s a nd s c i e n t i f i c i n s t r u m e n t sw i l l b e checked .

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A p p ro x im a te ly two h o u r s b e f o r e Bus e n t r y , t h e s c i e n -t i f i c i n s t ru m e nt s w i l l b e warmed up and commanded i n t o t h eo p e r a t i o n mode f o r e n t r y .On Dec. 9 , 1 9 7 8 , a t ab ou t 2 p.m. EST, t h e f o u r p r o b esw i l l a r r i v e a t Venus and en te r t h e a t m o s p h e r e . T h e L a r g eP r o b e w i l l d e sc e nd t o V en us ' s u r f a c e i n 55 m i n u te s an d t h et h r e e S m a l l P ro be s i n a b o u t 57 m i n u t e s , d e pe n di ng on e n t r ya n g l e .

L a r q e P r o b e E n t r v E v e n t sA t 2 .5 h o u rs b e f o r e e n t r y , t h e La rge P rob e command u n i tw i l l o r d e r warmup o f t h e b a t t e r y a nd r a d i o r ece ive r . Twenty-two m i n u te s b e f o r e e n t r y , t h e pr o b e w i l l b e g i n t r a n s m i s s i o no f r a d i o s i g n a l s t o E a r t h . A t e n t r y m i n u s 1 7 m i n u t e s , t h eLarge P r ob e b e g i n s t r a n s m i t t i n g d a t a a t 256 b ps . The com-mand u n i t i n i t i a t e s warmup of t h e s ev en s c i e n t i f i c i n s t r u -m en ts ab o ar d, p l u s i n s t r u m e n t c a l i b r a t i o n . F i v e m i n u t e sb e f o r e t h e p eak e n t r y d e c e l e r a t i o n p u l s e o f 3 2 0 G , t h e p r o b ew i l l b e t r a v e l i n g 4 1 ,6 00 km/hr ( 2 6 , 0 0 0 m p h ). E n t r y o c c u r sa t 200 km ( 1 2 0 m i . ) a l t i t u d e , w here t h e p r ob e e nc o u n te r s t h et e n u o u s t o p of t h e a t m o s p h e r e .T h e t i m e r w i l l command d a t a s t o r a g e f o r t h e a t m o s p h e ri cs t r u c t u r e e x p er i m en t d u r i n g e n t r y c om mu ni ca tio ns b l a c k o u t .T h i r t y - e i g h t s e c o n d s a f t e r e n t r y , t h e La rg e P r ob e b e g i n st h e d e s c e n t p h a s e, d e p lo y s i t s p a r ac h u te and j e t t i s o n s i t sf or w ar d a e r o s h e l l - h e a t s h i e l d . F o r t y - th r e e s ec on ds a f t e re n t r y , a t a n a l t i t u d e of 66 km ( 4 0 m i . ) , all i n s t r u m e n t ss h o u l d b e o p e r a t i n g . S e v e nt e en m i n u te s l a t e r , a t 4 7 km (2 8m i . ) a l t i t u d e , t h e p a ra c hu te i s j e t t i s o n e d , a n d t h e a e ro -d y n a m i c a l l y s t a b l e p r e s s u r e v e s s e l d es ce nd s t o t h e s u r f a c ei n 39 m i n u t e s , i m p a c t i n g 5 5 m i n u t e s a f t e r e n t r y . A s t h ep r o b e d e s c e n d s, t h e at m o s ph e r e g e t s s t e a d i l y h o t t e r andd e ns e r , u n t i l a t t h e s u r f a c e i t s t e m p e r a t u r e i s 4 7 0 d e g r e e sC ( 9 0 0 d e g r e e s F . ) , and i t s p r e s s u r e i s n e a r l y 1 0 0 t i m e st h a t a t t h e E a r t h ' s s u r f a c e . The L ar ge P ro be j e t t i s o n s i t sp a r a c h u t e t o s p e e d i t s d e s c e n t t h r o ug h t h i s v e r y d e n s e atm os-p h e r e , s o t h a t i t r eaches t h e s u r f a c e b e f o r e h e a t d e s t r o y s i t .D u ri ng d e s c e n t , t h e L a r g e P r o b e ' s s e v e n i n s t r u m e n t sw i l l h av e o b t a in e d d a t a t o d e t e rm i n e a l t i t u d e an d co m po s it io n

o f c l o u d l a y e r s , a tm o sp he re c o n s t i t u e n t s , t e m pe r a tu r e , p r e s-s u r e , d e n s i t y , wind f l o w and v a r i a t i o n s o f h e a t f lo w i n t h ea tm osphere .The Large P r o b e w i l l i m pa c t t h e s u r f a c e a t a b o u t 3 6km/hr ( 2 2 m ph) . None o f t h e p ro be s i s d e si gn e d t o s u r v i v ei m p a c t .

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S m a l l P r o b e E v e n t sT h e t h r e e S m a l l P r o b e s , t o o , w i l l e n t e r t h e p l a n e t ' sa t mosphe re a t a b o u t 4 1 , 6 0 0 km/hr ( 2 6 , 0 0 0 mph) . H o w e v e r ,b e ca us e t h e i r e n t r y p o i n t s a r e s p r e a d o v e r a n e n t i r e hem i-sp he re o f Venus, and t he y a r e l a u n c h e d s i m u l t a n e o u s l y f r o mt h e B u s, t h e a n g le s of t h e i r f l i g h t p a t h s i n t o t h e a tm osp he rev a r y g r e a t l y . T h i s means t h a t e n t r y h e a t i n g an d d u r a t i o n sof maximum d e c e l e r a t i o n p u l s e s v a r y w i d e l y . P e ak d e c e l e r a -t i o n f o r c e s v a r y f rom 20 0 G t o 5 6 5 G . E n t r y t i m e s a l s o d i f f e rby up t o 1 0 m i n u t e s , a n d d e s c e n t t i m e s by one mi nu t e . A s w i t ht h e L a rg e P r o be , e n t r y i s d e f i n e d a s o c c u r r i n g a t a n a l t i t u d eo f 200 km ( 1 2 0 m i . ) .T h re e h o u rs b e f o r e a tm o s p he r ic e n t r y , t h e s t a b l e o s c i l -l a t o r i n t h e r a d i o t r a n s m i t t e r f o r one-way D op ple r t r a c k i n ga nd t h e b a t t e r y o n e ac h S m a l l P r o b e a r e warmed up by commandsf rom t h e onboard command u n i t . Twenty-two m inu tes b e fo ree n t r y , e a c h S m a l l P r o b e b e g i n s t r a n s m i s s i o n o f r a d i o s i g n a l st o E a r t h . S e v en t ee n m i n ut e s b e f o r e e n t r y , t h e S m a l l P r o b e sb e g i n t r a n s m i t t i n g d a t a a t 6 4 b p s . T he command u n i t i n i t i a t e swarmup a nd c a l i b r a t i o n f o r t h e t h r e e i n s t r u m e n t s o n ea c h S m a llP r o b e .

F i v e m i n ut e s b e f o r e e n t r y , t h e t w o c a b l e s a n d w e i g h t so f t h e y o-yo d e s p i n s y s te m a r e d ep lo ye d t o r e d u c e t h e s p i nr a t e s o f t h e S m a l l Probe s f rom 48 t o 1 5 rpm. The h i gh s p inr a t e s i m p a r t e d by t h e Bus a r e ne eded t o d i s p e r s e t h e p r o be st o e n t r y p o i n t s w i d el y sp a c ed o v e r t h e p l a n e t . However, t h i sw ide d i s p e r s i o n a l s o means t h a t t h e S m a l l Probes e n t e r V en us 'h igh upper a tmosphere somewhat t i l t e d t o t h e i r f l i g h t p a th s .The "spindown" of t h e p r ob e s i s needed t o make it e a s i e r f o ra ero dy na mic f o r c e s t o l i n e up t h e a x e s of t h e p ro b es w i t ht h e i r e n t r y f l i g h t p a t h s . T h i s m us t o c cu r q u i c k ly b e f o r eh e a t i n g a t t h e e dg es of t h e p ro b e s ' c o n i c a l h e a t s h i e l d sb ec om es s e r i o u s . C a b l e s a n d w e i g h t s a r e j e t t i s o n e d imme-d i a t e l y a f t e r sp indown.

F i v e mi nu te s b e f o r e t h e p e ak d e c e l e r a t i o n p u l s e o fa t m o s p h er i c e n t r y , t h e command u n i t o r d e r s t h e " b l a c k o u t "f or m at f o r s t o r a g e o f s p a c e c r a f t d a t a , p l u s h e a t s h i e l dt e m p e r a t u r e a n d a c c e l e r o m e t e r m e as ur em e nt s f o r t h e atmos-p h e r i c s t r u c t u r e ex p er im e nt . T h i s i s t o a s s u r e no loss ofd a t a d u r i n g t h e 1 0 -t o- 15 -s ec o nd c om m u n ic at io n s b l a c k o u t a te n t r y .t h e neph elcme ter window i s o p en ed , a nd t h e a tm o s p h e r ic s t r u c -t u r e a nd n e t f l u x r a d i o m e t er h o u si n g d o o r s a r e opened andin s t ru m en t booms deploy ed .

W it h in t h e f i r s t m in ut e ( 1 8 t o 4 6 s ec on ds ) a f t e r e n t r y ,

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A tp r o b e s iand a l lt h i s t i m e , t h e up pe r d e s c e n t p h a se b e g i n s , w i t h t h en t h e a l t i t u d e ra n ge o f 7 2 t o 65 km (4 3 t o 39 m i . )i n s t r u m e n t s o p e r a t i n g . The i n s t r u m e n t c om pa rt me ntd o o r s on e ac h s i d e o f t h e S m a l l P ro be a f t e r b o d i e s s e r v e t od e s p i n t h e p r o b e s. A s m a l l v an e on t h e p r e s s u r e s e n so r i n l e t

s e r v e s t o p r e v e n t t h e s p i n r a t e from f a l l i n g t o z e r o rpme n a b l i n g i n s t r u m e n t s t o make o b s e r v a t i o n s o v e r a f u l l c i r c l eo f p r ob e r o t a t i o n .A t e n t r y p l u s 1 6 . 4 m i n u t e s , a s t h e t h i c k e n i n g a tm o sp h er ei n t e r f e r e s w i t h r a d i o t r a n s m i s s i o n , t h e d a t a r a t e i s r e d u c e dt o 1 6 b p s . T h i s o c c u r s a t a n a l t i t u d e o f 30 km ( 1 8 m i . ) .From t h i s p o in t , t h e t h r e e S m a l l P r o b e s d e s c e n d i n t oV en us ' i n c r e a s i n g l y d e n s e l o we r a tm o s p he r e , i m p a c t i n g o n t h es u r f a c e a t 36 km/hr ( 2 2 mph) from 56 t o 57 m in ut es a f t e r t h ee n t r y t i m e o f e a c h p r o b e . U n l i k e t h e L a r g e P r o b e , t h e S m a l lP ro be s r e t a i n t h e i r h e a t s h i e l d s t o t h e s u r f a c e . The d e n s i t y

of t h e a t m os p h er e i s so g r e a t t h a t t h e d r a g o f t h e s e ae r o-dynam ic s u r f a c e s s lo w s them t o t h e d e s i r e d d e s c e n t s p e ed .L i k e t h e L a r g e Pr obe , t h e S m a l l Probes a re n o t d e s i g n e d t os u r v i v e o n t h e s u r f a c e .Bus Events

E i g ht y mi nu te s a f t e r a l l p r o b e s h a v e e n t e r e d t h e V enusa tm osphere , t h e Bus w i l l e n t e r o n t h e d ay s i d e o f t h e p l a n e ta t h ig h l a t i t u d e s i n t h e s o u t h e r n h e m is p h er e . U n l i k e t h ep r o b e s , t h e Bus h a s no h e a t s h i e l d f o r h ig h -s p ee d e n t r y , a ndi s e x p e c t e d t o b u r n u p o n e t o t w o m i nu te s a f t e r e n t r y . TheBus c a r r i e s t w o e x p e r i m e n t s o n t h e c o m p o s i t i o n o f t h e a tm os -p h e r e , a nd i o n a n d a n e u t r a l mass s p e c t r o m e t e r . T h es e i n s t r u -m en ts m e as u re c o n s t i t u e n t s o f t h e i o n o s p h e r e an d up p e r at mo s-p h e r e f r o m 200 km ( 1 2 0 m i . ) down t o 1 1 5 km ( 6 9 m i . ) , makingt h e m i s s i o n s ' o n l y a t m o s p h e r i c c o m p o s i t i o n m e as u re m en t s b e tw e e n1 5 0 and 1 1 5 km . The Bus, with i t s more p o w e r f u l t r a n s m i t t e r ,r e t u r n s t h i s d a t a t o E a r t h a t 1 , 0 2 4 b p s .

All d a t a fro m t h e p r o b e m i s s i o n s w i l l be recorded s i m u l -t a n e o u s l y by t h e D S N s t a t i o n s a t G o l d s t o n e , C a l i f . , a nd Can-b e r r a , A u s t r a l i a , a nd more t h a n 50 m u l t i p r o b e e x p e r i m e n te r sw i l l s p e nd a y e a r o r more a n a l y z i n g t h e s e d a t a . The i n v e s -t i g a t o r s w i l l b e e s p e c i a l l y i n t e r e s t e d i n com paring r e s u l t sf ro m t h e w i d e ly - s pa c e d p r o b e f l i g h t p a t h s o n t h e da y a nd n i g h ts i d e s a n d i n b o t h h e m i s p he r e s o f V e nu s.

A tm os ph er ic wind v e l o c i t i e s a nd d i r e c t i o n s w i l l b e c a l -c u l a t e d fro m m ea su re me nts o f t h e p r o be v e l o c i t i e s , t h ro u g ht r i a n g u l a t i o n m ea su re me nt s fro m f o u r s t a t i o n s a t o n c e . T w oS TDN s t a t i o n s a t Guam and Sa nt ia go , C h i l e , w i l l r e c o r d Busand p robe d a t a a l o n g w i t h t h e DSN s t a t i o n s .-more-


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THE PLANET V E N U SVenus i s t h e p l a n e t m ost s i m i l a r t o E a r t h i n s i z e , m a s sa nd d i s t a n c e f ro m t h e S un . B u t i t s s u r f a c e i s m u c h h o t t e r ,i t s a tmosphere much d en se r , and i t s r o t a t i o n m u c h slower t h a n

t h a t o f E a r t h .The d i a m e t e r of Venus i s 1 2 , 1 0 0 k m (7519 m i . ) , comparedw i t h E a r t h ' s 1 2 , 7 4 5 km ( 7 9 2 0 m i . ) . The m a s s of Venus i s0 .81 t i m e s t h a t o f t h e E a r t h . The mean d e n s i t y o f Venus i s5 .26 g rams pe r cu b i c c m compared w i t h E a r t h ' s 5 .5 g r ams pe rc u b i c c m .

Because Venus i s c l o s e r t o t h e Sun, it receives a b o u tt w i c e a s much energy a s Ear th . However , it i s m o r e r e f l e c t i v et h a n E a r t h b e c a u se of i t s c l o u d y a t m o s p h e r e . A s a r e s u l t o ft h e s e two c o m pe ti ng f a c t o r s , Venus a b s o r b s a b o u t t h e s a m eamount of s o l a r e n e r g y as E ar th . Thus Venus would be ex pe c te dt o h av e a t e m p e r a t u r e v e r y s i m i l a r t o E a r t h ' s . I n f a c t , t h es u r f a c e o f V enus i s v e r y h o t , a b o u t 480 d e g r e e s 2 ( 9 0 0 d e g r e e s F ) .

T h i s t h e o r y f o r t h e h i g h t e m p e r a t u r e o f V enus assumes t h a tt h e a t m o sp h e re a l l o w s t h e p a s s a g e o f t h e i nc om in g s o l a r r a d i a t i o nt o t h e l o w e r a tm o sp h er e and t h e s u r f a c e . However, t h e a t m o s p h e r er e s t r i c t s t h e p a s s a g e o f h e a t r a d i a t i o n fro m t h e s u r f a c e a nd t h el o w e r a t m o sp h e re b a ck i n t o s p a c e . The h e a t i s t r a p p e d . E a r t hh a s a m od es t gr ee nh o us e e f f e c t t h a t r a i s e s i t s s u r f a c e t e m pe r at u reby abou t 35 deg rees C ( 95 d eg re es F . ) , b u t i n some p a r t s of t h ei n f r a r e d s pe ct ru m h e a t c a n e s ca p e by d i r e c t r a d i a t i o n from t h eE a r t h ' s s u r f a c e t o s p ac e . B ec au se o f i t s d e n s i t y , c o m p o s i t i o nand c l o ud s , t h e Venus a t mosphe re i s v e r y t h i c k , a nd b e c a u s e iti s m o s t l y c ar b o n d i o x i d e , it i s e s s e n t i a l l y opaque t o o u t g o i n gh e a t r a d i a t i o n a t a l l i m p o r t a n t w a v e l e n g t h s.One of t h e m os t p u z z l i n g a s p e c t s o f V enus i s i t s l a c k ofw a t e r . I f V enus i s a s d r y a s it seems, w he re d i d t h e o c e a n s o fVenus g o , i f an y e v e r e x i s t e d ? One s p e c u l a t i o n i s t h a t t h ew a t e r rose i n t o t h e u p pe r a t m o sp h e re a n d w a s d i s s o c i a t e d bys o l a r u l t r a v i o l e t r a d i a t i o n i n t o h yd ro ge n a nd o xyg en . Theh y dr og e n e s c a p e d i n t o s p a c e f ro m t h e t o p o f t h e Venus a t m o s p h e r e ,a nd t h e h e a v i e r o xy ge n d i f f u s e d down t o t h e o x i d iz e d c r u s t .D e t a i l e d a n a l y s i s s hows t h a t it m i g h t n o t be p r a c t i c a l f o r Venus

t o h av e l o s t a n o c ea n of water by such a r o u t e . P e r h a p s V enusformed c l o s e e no ug h t o t h e Sun so t h a t t h e t e m pe r at u re p r e ve n te dw a t er from b e in g i n c o r p o r a t e d i n t o t h e s o l i d m a t e r i a l t h a t f o r m e dt h e p l a n e t . I f s o , Venus would ne ve r have had enough w a te rw i t h i n i t s r o c k s t o form e a r l y d ee p o c e an s l i k e t h o s e o f E a r t h .D i rec t measurement s o f ga se s w i t h i n t h e Venus a t m osphe re mayp o i n t to ward o ne o f two a l t e r n a t i v e s : E i t h e r t h a t w a t e r w a sn o t i n c o r p o r a t e d i n t o V enus a s much a s on E a r t h , o r t h a t watero u t g a s s e d a n d w a s s u b s e q u e n t l y l o s t .- more -


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O r b i t a n d R o t a t i o n of VenusThe r o t a t i o n o f V enus i s v e r y s lo w a nd i n a r e t r o g r a d ed i r e c t i o n , t h a t i s , o p p o s i t e t o t h e d i r e c t i o n o f t h e p l a n e t ' sr e v o l u t i o n a b ou t t h e Sun an d t o t h e r o t a t i o n o f m o s t o t h e rp l a n e t s . Venus t u r n s o n i t s a x i s o nc e i n 2 4 3 . 1 E a r t h d a y s .

a ro un d t h e Sun a r e i n o p p o s i t e d i r e c t i o n s , t h e l e n g t h o f a s o l a rday on Venus i s 1 1 7 E a r t h d a y s ( 58 .5 E a r t h d a y s of " d a y l i g h t "58.5 E a r t h d a y s of n i g h t ) .S i n c e V enus' r o t a t i o n on i t s a x i s a nd r e v o l u t i o n i n o r b i t

T h e o r b i t s of Ear th and Venus a re t i l t e d t o each o t h e ra b o u t 3.5 d e g r e e s . V en us ' a x i s i s t i l t e d a b ou t 6 d e g r e e sfrom p e r p e n d i c u l a r t o t h e p l a ne of t h e p l a n e t ' s o r b i t . T h i scom pares w i t h E a r t h ' s a x i a l tilt of 23.5 d e g r e e s w h ic h p r o d u c e so u r s e a s o n s . T hu s, s e a s o n a l e f f e c t s on Venus a re smal l .Some s c i e n t i s t s b e l i e v e t n a t V enus' p e r i o d of r o t a t i o n

i s t i e d t o t h e r e v o l u t i o n o f t h e E a r t h and Venus around t h eSun . Venus p re se n t s t h e same h e m i s p h e r e toward E a r t h a t eachc l o s e s t a p p r o a c h ; t h a t i s , e a c h t i m e t h e p l a n e t p a s s e s b etw ee nSun and E a r t h . I f t h e r o t a t i o n of Venus i s locked t o t h e closea p p r o a c h e s of E a r t h a nd Venus, t h e n t h e i n t e r n a l d i s t r i b u t i o n o fmass w i t h i n Venus s h o u l d b e s l i g h t l y asymmetric.Why do e s Venus r o t a t e so s l ow ly when most o t h e r p l a n e t sr o t a t e i n p e r i o d s of h o u r s r a t h e r t h a n m on th s? One s p e c u l a t i o ni s t h a t a l a r g e b ody h i t Venus and s topped i t s r o t a t i o n . T h i sl a r g e bo dy m i g h t h a ve b e en c a p t u r e d a s a s a t e l l i t e i n t o ar e t r o g ra d e o r b i t and l a t e r im pac ted w i t h Venus t=, t o p i t sn or ma l r o t a t i o n a nd r o t a t e it s lo w ly i n a n o p p o s i t e d i r e c t i o n .I t c o u l d b e t h a t Venus w a s formed f r o m l a r g e f r a g m e n t s ,and a s a r e s u l t of t h e combined impacts of t h e s e f r a g m e n t s n e v e rh a d much r o t a t i o n . A c c o r d i n g t o a n o t h e r s u g g e s t i o n , s o l a r t i d a le f f e c t s i n V en us ' d e n s e a t m os p h e re may h a ve sl ow e d r o t a t i o nand t h e n " t u r n e d t h e p l a n e t o v e r " , a c c o u n t in g f o r i t s backwardr o t a t i o n .Radar as t ron om ers hav e mapped a n a rea on t h e E a r t h - f a c i n g

s i d e of t h e p l a n e t a s l a r g e a s A s i a and have found w h a t a p p e a r st o b e a r u gg e d s u r f a c e . A c co r di ng t o t h e r a d a r r e s u l t s , t h e r ea re h u g e s h a l l o w c r a t e r s a s w e l l a s an enormous volcano whichmay be as l a r g e i n a r e a , t h o u g h n o t a s h i g h , a s Olympus Monson Mars ( t h e s o l a r s y s te m ' s l a r g e s t d i s c o ve r ed so f a r ) . R adara s t r o n o m e r s a l s o d e t e c t e d wh at a p p e a r s t o be an enormous canyon.T h i s chasm i s 1 4 0 0 k m (870 m i . ) l o n g , 1 5 0 km (9 5 m i . ) w i d e , andseve ra l k i l o m e t e r s d e e p .

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Venus' Interior and Absence of Magnetic FieldUnlike the Earth, Venus has no significant magnet,e fie d.The generation of Earth's field is attributed to a self-sustainingdynamo in the fluid core of the planet. Convection currents in

the core give rise to electric currents that produce the externalmagnetic field. This theory, which also seems to apply toJupiter, predicts that slow-spinning planets like Venus shouldnot have magnetic fields.Venus is a planet whose shape could be very close to asphere according to radar measurements. They show its equatorto be almost a perfect circle. Because the poles do not rotateinto view as do points on the equator, circularity around thepoles cannot be measured. The lack of irregularities inshape, and of a satellite makes it difficult to determine theinternal density distribution of the planet. Most models ofthe interior are based on its similarity to Earth, consistingof a liquid core, a solid mantle and a solid crust. But thetrue nature of the interior of the planet is very much indoubt because scientists do not know Venus' thermal structureor the nature of the materials which make up its mass.

The Atmosphere of VenusCarbon dioxide is the dominant gas in the Venusianatmosphere. There are a l s o traces of water, carbon monoxide,hydrochloric acid and hydrogen fluoride. Free oxygen has neverbeen found.The clouds which obscure the surface of Venus consist ofthick hazes of droplets believed to be made of sulfuric acid.Venus' clouds are pale yellow and very reflective, returninginto space some 75 per cent of the sunlight falling on them.Space probe measurements have shown that there are distinctcloud layers much higher than terrestrial clouds. Photographstaken in ultraviolet light reveal a four-day rotation of themarkings in these clouds. This rotation is like that of theplanet, in a retrograde direction. Unusual dynamics of theatmosphere are required to account for this high-speed cloudmotion.The generally accepted figure for atmospheric carbondioxide on Venus is 97 per cent. However, measurements madeby early Venera spacecraft (USSR) differ from radio occulationmeasurements suggesting the presence of about 70 per centcarbon dioxide in the Venusian atmosphere. And, if thereis much argon in the atmosphere, the amount of carbon dioxidecould be as low as 25 per cent.

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Adding to the uncertainty is the fact that the percentagesdetermined by the Veneras were obtained by sampling theatmosphere in regions where there are sulfuric acid droplets.The presence of the acid may have contaminated these measurements.It is therefore possible to argue that the carbon dioxide isconsiderably less than 97 per cent, with the remainder beingmade up by some combination of nitrogen and argon.

The amount of carbon dioxide is important because it playsa major role in the interpretation of the microwave spectrumof the planet. If the atmosphere is 9 7 per cent carbon dioxide,the microwave observations permit the presence of as much as0.1 per cent water below the clouds. Some instruments on themost recent Veneras 9 and 10 indicated that water vaporconstituted about 0.1 per cent of the atmosphere below themain c l o u d s . A t t h e c l o u d t o p s it is only 0.0001 p e r cent,however. But, if there is another gas in the atmosphere ofVenus that is not a good microwave absorber, the planet'satmosphere might contain more water than is now believed.

Carbon dioxide is also important to theories about theevolution of the atmosphere of Venus, and to the radiativeproperties of the present atmosphere and its dynamiccharacteristics.The atmospheres of both Venus and Earth are assumed tohave originated from gases that were released from the interiorsof the planets which were hot when the planets first formed. Inthe case of Earth, most of the outgassing may have occurred soonafter formation, from the heat of formation. Venus may neverhave had much water to outgas in the first place if it was

formed from parts of the solar nebula that were poor in water,Or it may be that Venus formed with as much water as the Earth,but this water has now been lost.The Earth holds its water in its oceans because it is muchcooler than Venus and there is a "lid" on its atmosphere. Thislid is the very cold tropopause where the temperature riseswith altitude. This prevents heated water vapor from risingby convection to cooler heights where it could be dissociatedby solar ultraviolet radiation. But if Earth were moved tothe same distance from the Sun as Venus, conditions couldchange drastically. The additional solar energy would besufficient to evaporate all of Earth's oceans.

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If Venus had been formed from the same mix of materialsas Earth and then outgassed its volatiles, we would expect itto have an atmosphere about 3 5 0 times as massive as Earth's.Carbon dioxide would account for a surface pressure of about100 atmospheres, and water vapor would account for about 150atmospheres. On Earth most of the 100 atmospheres of carbondioxide is tied up in carbonate rocks which are chemicallystable at terrestrial temperatures, but unstable at Venustemperatures. Earth's oceans, if vaporized, would result inan atmospheric pressure of about 2 5 0 atmospheres. Venusdoes indeed have nearly 100 atmospheres of carbon dioxide,but the water is apparently absent. There are no oceans,and the atmospheric water vapor is a minor constituent.One of the major questions to be answered by Pioneer Venusis just how much water vapor is present. Water vapor wouldbe broken down by solar ultraviolet radiation into oxygenand hydrogen. The hydrogen would escape into space leavingthe oxygen behind. Effectively the oceans would be leakinginto space.

atmosphere of Venus consisted mostly of steam (because theplanet is closer to the Sun than Earth), the resultingconvective atmosphere could not have had a barrier toconvection. The water vapor would have dissociated intohydrogen and oxygen. Calculations suggest that withinabout 3 0 million years perhaps 90 per cent of the watercould have been lost to the planet, but all could not belost in this way.

This could have happened to Venus. If the primitive

Furthermore, there is no easy way to explain whathappened to the leftover oxygen other than that it reactedwith the surface rocks. Yet without running water tocontinually expose fresh rocks for oxidation, the processmight be insufficient to remove all the oxygen. Continentaldrift might be a possible mechanism to expose fresh rocks.There is a question, too, of what happens to the oxygen nowreleased in the upper atmosphere by photodissociation ofcarbon dioxide to produce the carbon monoxide observedspectroscopically. The incorporation of oxygen with sulfurto form the sulfuric acid droplets does not seem to accountfor all the missing oxygen.

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On Venus, because of the high surface temperatures,reactions between rocks, minerals and the atmosphere areexpected to be much faster than on Earth.the action of running water constantly exposes new rocks tothe action of the atmosphere and aids oxidation and otherreactions between the rocks and the atmosphere. This is nothappening on Venus. If fresh rocks are not being exposed bysome other mechanism, the atmosphere of Venus may not haveachieved equilibrium with surface materials.

However, on Earth

The Venus atmosphere can be divided into three distinctregions:the ionosphere and the exosphere; a region of clouds; and aregion from the base of the clouds to the surface.a region above the visible cloud tops which includes

Upper AtmosphereThe upper atmosphere of Venus has an ionosphere which isdifferent from that of Earth. Because Venus does not have a

significant magnetic field, the solar wind interacts directlywith the upper atmosphere and the ionosphere of the planet.Among the atmospheric regions of Venus, the upper atmosphereabove the cloud tops is best understood.

from Earth and from flyby and orbiting spacecraft. Above 150 km( 9 0 mi.) it is more rarefied than the atmosphere of Earth at thesame height. Like Earth's atmosphere, it is ionized by incomingsolar radiation to produce positively-charged ions and freeelectrons of an ionosphere, which is thinner and closer to thesurface of the planet than Earth's ionosphere. Like Earth'sionosphere, the ionosphere of Venus has layers at which thenumber of electrons per cubic centimeter (electron density)peaks. In Earth's ionospheric layers, the peak electron densityis about 100,000 to 1,000,000 electrons per cubic centimeter, andoccurs at an altitude of about 2 5 0 to 300 km (150 to 180 mi.).The major ion is singly-charged carbon dioxide.

It has been investigated

Mariner 10 found two clearly defined layers in the nighttimeionosphere: a main layer at 1 4 2 km ( 8 7 mi.) altitude and alesser layer at 1 2 4 km ( 7 6 mi.). The peak intensity of the latterwas about 7 8 per cent of the higher layer. On the dayside therewas one main layer at 1 4 2 km ( 8 7 mi.) and several minor layers,including one at 1 2 8 km ( 7 8 mi.) and another at about 180 km(110 mi.). The Venera 9 and 10 orbiters obtained similar results,but single layers seem to be the most common.- more -


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SOLAR WIND - VENUS I N T E R A C T I O N S

gJOLAR TRANS I T I ONREG ION - -,- R ~ R E F A C T I O NIONOPAUSE WAVEPLASMAI/


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From a practical standpoint, Venus has no intrinsicmagnetic field. The field of Venus is less than 1 / 1 0 , 0 0 0 ofEarth's field. There is a region of rarefaction (lesseneddensity) of the solar wind flow at Venus, and the characteristicsof the plasma there indicate that Venus absorbs part of the fluxof the solar wind. On the dayside of Venus, there is a sharp

- boundary to the ionosphere at 3 5 0 to 5 0 0 km (210 to 3 0 5 mi.).This is believed to be caused by the interaction of the solarwind with Venus'- the ionosphere extends high into space and probably into aplasma tail stretching away from the Sun.

atmosphere. On the night side of the planet,

Temperatures have been measured in regions above the visiblecloud layers by radio occultation. The temperature of theexosphere (region where particles escape the planet) was derivedfrom density variation with altitude found by the ultravioletexperiments of spacecraft. From observations of the ultravioletradiation from hydrogen and helium atoms, it is calculated thatthe temperature of the exosphere of Venus when Mariner 10 flewpast the planet was about 1 2 7 degrees C ( 2 6 0 degrees F). At sucha temperature, the thermal escape of helium gas would be negligible.Accordingly it

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Pioneer Venus Press Kit