Pioneer Venus 2 Press Kit

8/8/2019 Pioneer Venus 2 Press Kit

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NASA NewsNational Aeronautics andSpace Administ rationWashington D C 20546AC 202 755-8370

ForRelease T H U R SD A YJuly 2 7 . 1 9 7 8

PressKit Project P i o n ee r V e n u s 2R E L E A S E N O : 78-101

Con entsG E N E R A L R E L E A S E ..................................... 1 -6M I S S I O N P R O F I L E ..................................... 7 - 2 4P i o n e e r V e n u s M u l t i p r o b e Miss ion .................. 1 3 - 2 4T H E P L A N E T V E N U S .................................... 2 5 - 4 0M A J O R Q U E S T I O N S A B O U T V E N U S ......................... 4 1 - 4 2H I S T O R I C A L D I S C O V E R I E S AB OU T V E N U S .................. 4 3 - 4 5E X P L O R A T I O N O F V E NU S BY S P A C E C R A F T .................. 4 6 - 4 7T H E P I O N E E R V E N U S S PA C E C R A F T ........................ 48-62T h e O r b i t e r Sp a c e c r a f t ............................ 53-58

T h e M u l t i p r o b e S p a c e c r a f t ......................... 5 8 - 6 2VENUS A T M O S P H E R I C P R O B E S ............................ 63-76T h e L a r g e Probe ................................... 6 3 - 7 0The Small Probe ................................... 70-76

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S C I E N T I F I C I N V E S TI G A TI O N S ...................... 77-97O r b i t e r ...................................... 77-85O r b i t e r R a d i o Sc ience ........................ 85-88L a r g e Probe E x p e r i m e n t s ...................... 8 8 - 9 2L a r g e and S m a l l Probe I n s t r u m e n t s ............ 9 2 - 9 3S m a l l P r o b e E x p e r i m e n t s ...................... 9 4M u l t i p r o b e B u s E x p e r i m e n t .................... 9 4 - 9 5M u l t i p r o b e R a d i o S c i e n c e E x p e r i m e n t s ......... 9 5 - 9 6

P R I N C I P A L I N V E ST I G A TO R S AND S C I E N T I F I CI N S T R U M E N T S .................................. 9 7 - 1 0 0L A U N C H V E H I C L E ................................. 1 0 1 - 1 0 2L A U N C H F L I G H T S E Q U E N C E ......................... 1 0 2L A U N C H V E H I C L E C H A R A C T E R I S T I C S ................. 103A T LA S C EN T AU R F L I G H T S EQ U E NC E ( A C - 5 0 ) .......... 1 0 4L A U N C H O P E R A T I O N S .............................. 1 0 5MISSION OPERATIONS ............................. 105-107DATA RET UR N. COMMAND AND TR AC KIN G .............. 108-111P I O N E E R V E N U S T EA M............................. 1 1 2 - 1 1 4CONTRACTORS .................................... 1 1 4 - 1 1 7V E N U S S T A T I S T I C S ............................... 118N 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 p h a s e of t h e P i o n e e r V e n u sMult iprobe s p a c e c r a f t and c r u i s e phases o f b o t h t h e P i o n e e rV e n u s O r b i t e r a n d t h e M u l t i p r o b e s p a c e c r a f t . Much o f t h em 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 nupdated press k i t w i l l be i s s u e d s h o r t l y befo re a r r i v a l a tt 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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National Aeronautics andSpace AdministrationWashington, D.C.20546AC 202 755-8370

For Release:Nicholas PanagakosHeadquarters, Washington, D.C.(Phone: 2 0 2/7 5 5- 3 6 8 0 ) THURSDAYJuly 2 7 , 1 9 7 8Peter WallerAmes Research Center, Mountain View, Calif.(Phone 4 5/9 6 - 5 091)

RELEASE NO: 7 8 - 1 0 1

SECOND VENUS SPACECRAFT SET FO R LAUNCH

NASA will launch the second of two Pioneer spacecraftto Venus next month as part of a detailed scientific studyof that cloud-shrouded planet.

Riding atop an Atlas Centaur rocket, Pioneer Venus 2will be launched from Cape Canaveral, Fla., about Aug. 7for the start of a 354-million-kilometer (220-million-mile)journey to Earth's nearest neighbor.

Pioneer Venus 2 is a multiprobe spacecraft designed tomeasure directly Venus' dense, searing atmosphere from topto bottom. Venus' atmosphere at the surface is 100 timesas dense as Earth's and hotter than the melting points oflead and zinc, 485 degrees Celsius (900 degrees Fahrenheit).

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- 2 -T h i r t e e n m i l l i o n km ( 8 m i l l i o n m i . ) and 2 0 d a ys o u t f ro m

Venus, P io ne er Venus 2 w i l l s e p a r a t e i n t o f i v e a tm os ph er ice n t r y c r a f t . F our of t h e s e p r o b e s w i l l e n t e r V en us ' atmos-p h e r e a t p o i n t s s p r e a d o v er t h e p l a n e t ' s E a r th - f ac i n ghemisphere , t w o o n t h e d ay s i d e an d t w o on t h e n i g h t s i d e .The f i f t h e n t r y pr ob e, t h e t r a n s p o r t e r b us , w i l l a l s o e n t e ro n t h e d ay s i d e .

A no th er c r a f t , P i o n e e r Venus 1--an o r b i t e r d e s i g n e d t oc i r c l e t h e p l a n e t f o r a y e a r o r more--was la un ch ed May 2 0and w i l l a r r i v e a t Venus December 4 . The e n t r y p r o b e s o fPionee r Venus 2 a r e p la nne d t o a r r i v e f i v e da ys a f t e r t h eO r b i t e r . 1

The 30 exper iments aboard P ioneer Venus 1 and 2 a r ep l an n ed a s a c o o r d i n a t e d o b s e r v a t i o n a l sy s te m . The m i s s i o ne mp lo ys t h e l a r g e s t number of s p a c e c r a f t - - s i x - - e v e r d e v o t e dt o o n e p l a n e t and w i l l make t h e most measurements a t t h eg r e a t e s t number o f l o c a t i o n s .

The f l i g h t s a re t h e f i r s t de si gn ed p r i m a r i l y t o s t u dy i n gt h e a t m o sp h er e an d w e a th e r o f a n o t h e r p l a n e t o n a g l o b a ls c a l e . I n f o r m a t i o n g a t h e r e d a t Venus may h e l p u s l e a r nmore a b o u t t h e f o r c e s t h a t d r i v e t h e w ea t he r o n o u r ownp l a n e t .

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- 3-Scientists believe Venus may be an unusually good place

to study the mechanics of atmospheres because the planetrotates very slowly and there are no oceans. The atmosphereappears to be a relatively simple weather machine, and theimportant atmospheric circulation motions appear to be global.Hence, continuous measurements from orbit, combined withthose of the probes from many points in the atmosphere,could provide at least a rough picture of Venusian weatherprocesses.

The five probe spacecraft which make up Pioneer Venus 2will make direct measurements and observations from withinthe planet's atmosphere, providing by f a r the most detailedinformation yet on atmospheric composition, circulation andenergy balance.

The multiprobe spacecraft employs a spin-stabilized,2.4-meter (8-foot)-diameter, structure cylindrical bus,containing most spacecraft support systems. The fourprobes are launched from the bus toward Venus. ThemultiProbe weighs 904 kilograms (1,990 pounds) and carries51 kg (116 Ib.) of scientific instruments.

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-4-W i t h i n t h e b us c y l i n d e r , a t h e r m a l l y - c o n t r o l l e d

equ ipment compar tment houses ins t ru me nts , communica t ionsa nd d a t a - h a n d l in g s y s t e m s , a s w e l l a s n a v ig a t io n , o r i e n t a t i o n ,t h r u s t e r a nd pow er s y s te m s . The e x t e r i o r of t h e busc y l i n d e r i s c o v e r e d w i t h p o w e r - g e n e r a t i n g s o l a r c e l l s .

On i t s four-month journey t o V en us , t h e s p a c e c r a f t w i l lf l y a bo u t t w o - f if t h s of t h e way around t h e Sun between theo r b i t s of Earth and Venus, some 354 m i l l i o n km ( 2 2 0 m i l l i o n m i . ) .

Pioneer Venus 2 i s made up of a t r a n s p o r t e r bu s, al a r g e p r ob e c r a f t ( t h e Sounder Probe) and t h r e e i d e n t i c a lsmal le r p r o b e s p a c e c r a f t ( t h e N o rt h , Day an d N i g h t P r o b e s ) .

T he se s p a c e c r a f t , i n c l u d i n g t h e b u s , will e n t e r a tp o i n t s s p r e a d o v e r V en us ' e n t i r e E a r t h - f a c i n g h e mi s ph e re ,a b o u t 1 0 , 0 0 0 km ( 6 , 0 0 0 m i . ) a p a r t . T h e bus w i l l o b t a i nd a t a o n t h e c o m p o s i t i o n of t h e u pp er mo st p a r t of t h ea tm o sp h e r e b e f o r e b u r n in g u p. The o t h e r f o u r p r o b e s w i l lmake de t a i l e d measurements of t h e a tm os ph er e a t lo wer a l t i t u d e sas t h e y d e s c e n d t o t h e s u r f a c e . The p r ob e s a r e n o t d e s i g n e dt o s u r v i v e a f t e r i m p a ct ; t h e y may r e t u r n s u r f a c e d a t a b r i e f l y ,however.

T h e l a r g e S o un d er Pr o be i s e x p e c t e d t o make t h e f i r s td e t a i l e d i n v e n t o r y of t h e c om p os it i on of Venus ' a tmosphere .

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-5-Because of its high density, temperatures, and corrosive

constituents, the Venusian atmosphere presents a difficultproblem f o r designers of entry craft.of about 41,600 kilometers per hour (26,000miles per hour)add to the problem.

The high entry speeds

A l l four atmospheric probes are geometrically similar.The main component of each is a sperical pressure vesselwhich houses instruments, communications, data, command andpower systems. The large Sounder Probe weighs about 3 1 6 kg( 6 9 8 lb.) and its seven instruments weigh 28 kg (62 lb.).It is about 1.5 meters (5 feet) wide. The smaller North,Day and Night Probes weigh 93 kg (206 lb. ) each, and theirthree experiments weigh 3 . 5 kg (7.7 lb.). Each of thesmaller probes is 0 . 8 m (30 inches) in diameter.

All instruments within the probe pressure vesselsrequire either observing or direct sampling access to thehostile atmosphere. This is oneof the most difficulttechnical problems of the mission.

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-6-NASA's Office of Space Science has assigned project

management of the two Pioneer Venus spacecraft to AmesResearch Center, Mountain View, Calif., and the spacecraftwill be controlled continuously from the Mission OperationsCenter at Ames. The spacecraft werebuilt by Hughes AircraftCo., El Segundo, Calif., and the scientific instruments weresupplied by NASA centers, other government organizations,universities and private industry.

The spacecraft will be tracked by NASA's Deep SpaceNetwork, operated by the Jet Propulsion Laboratory inPasadena, Calif., a government-owned facility managed forNASA by the California Institute of Technology. NASA'sLewis Research Center, Cleveland, is responsible for thelaunch vehicle, which was built by General Dynamics,San Diego, Calif.

Cost of the two Pioneer Venus spacecraft, scientificinstruments,mission operations and data analysis is about$180 million. This does not include cost of launch vehiclesand tracking and data acquisition.

Launch period for the multiprobe flight is 27 days( Auq. 7 throuqh Sex>t. 3 , 1978) , and durina these davsthe launch window opens progressively earlier each day,beginning at 3 : 3 6 a . m . EDT.(END OF GENERAL RELEASE. BACKGROUND INFORMATION F O L L O W S )


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-7 -MISSION PROFILE

The two Pioneer flights to Venus will explore theatmosphere of the planet, study its surface using radarand determine its g l o b a l shape and density distribution.Launched May 20, 1978, the first spacecraft Pioneer Venus 1,an Orbiter, will make eight months or more of remote-sensingand direct measurement. Pioneer Venus 2, a Multiprobe, willseparate into five atmospheric entry craft, eight millionmiles out from the planet, and measure the atmosphere fromtop to bottom in about two hours at points spread over theentire Earth-facing hemisphere of Venus.

The Pioneer Venus Orbiter MissionThe seven-month flight of Pioneer Venus 1 follows atrajectory more than half way around the Sun (through about200 degrees), and will cover about 480 mj-llion kilometers(300 million miles). This trajectory, three months longerthan that o f the Multiprobe, allows a slower arrival speedat Venus, requiring less weight for the orbit insertion motor.It also allows an orbital low point (periapsis) at a latitudeof about 20 degrees north.Launch dates were timed so that the Orbiter arrives at

Launch dates were selected for opti-Venus on Dec. 4, 1978, five days before the arrival of thefive probes on Dec. 9.mum payloads for both Orbiter and Multiprobe missions.Atlas (SLV-3D)/Centaur (D-1AR) two-and-a-half-stage rocket.Air Force Eastern Test Range personnel conduct tracking duringthe near-Earth part of the mission. NASA's Deep Space Network(DSN) is responsible for the remainder.

Two days before arrival at Venus, the spacecraft spinrate will be increased to 30 rpm and the Orbiter will beoriented with its 1 8 , 0 0 0 - N (4,000-lb.)-thrust, solid-fueledrocket engine pointing forward, opposite the direction oftravel at the point of closest approach to Venus.

Launch vehicle for both Pioneer Venus spacecraft is an

On Dec. 4, 1978 (the 198th day after launch), AmesMission Control engineers will command a 28-second orbitinsertion burn. This will reduce spacecraft velocity by3,816 km/hr (2,366 mph), placing Pioneer in a 24-hour orbitaround Venus. The planned orbit will be inclined 7 5 degreesto Venus' equator, with its low point (periapsis) near 20degrees north latitude. The orbit's high point (apoapsis)is expected to be at an altitude of 66,000 km (41,000 mi.),and periapsis initially will be at 300 km (180 mi.) , laterreduced to about 150 km (90 mi.). Planned orbital injectiontime is 1 1 : O O a.m. EST.

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AUG. 7 ,1978

VENUS ATEART H AT L AUNCH

SUN+

DAYS AF TEI\LAUNCH \ VENUS ATA R R I V A L O NDEC. 9 ,19 78


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Within hours after the orbit insertion rocket burn,members of the Orbiter navigation team will have determinedany shortcomings in the orbit. After slowing the spin rateand adjusting orientation, they will command firing ofthrusters to trim up the orbit to acceptable dimensions.Attention in the Mission Operations Center will thenswitch to the probes scheduled to arrive five days later,but fine tuning of the orbit will continue after completionof the probe mission.

In-Orbit OPerationsFor efficient orbital operations during the 243-dayprimary Orbiter mission (one complete Venus rotation on itsaxis), the orbit will have a period very close to 24 hours.This means that most activities will occur at the same timeon Earth every day.

of data return during periapsis. Data return via the high-gain antenna will be at the two highest rates, 1,024 or2,048 bits per second.

This includes the most intensive periods

The 24-hour orbit h a s been divided into two periods,reflecting the kind of measurements being taken.apsis (orbital low point) period is about four hours long.The apoapsis (orbital high point) period is 20 hours long.Since the Orbiter dips into the upper atmosphere itself atperiapsis, which may be as low as 150 km (90 mi.) to makedirect measurements, the periapsis period is the time ofhighest data return.

The peri-

Mission operations will use five data formats duringthe periapsis period.emphasis on certain instruments when desirable; for example,one provides intensive aeronomy coverage at periapsis,another stresses optical coverage.

These formats are designed to permit

The mapping format gives 44 per cent of the data streamto the radar mapper for Venus surface study, and divides therest between the ultraviolet spectrometer and the infraredradiometer.

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PERSPECTIVE V IE W O F P IO N E ER V E N U S O R B I TAPPROACHT R A J E C T O R Y

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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 t wo d a t a f o r m a t si n t h e 2 0- ho ur a p o a p s i s s eg m en t. T h e f i r s t of 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 w h o l e p l a n e t i n u l t r a v i o l e t l i g h t ,w hic h w i l l show t h e f o u r - d a y r o t a t i o n of V e nu s' c l o u d s i nsequence . Known as t h e im a g in g format, it a l l o c a t e s 67 p e rc e n t of t h e d a t a stream t o t h e im a gin g i n s t r u m e n t a n d t h ec l o u d p h o t o p o l a r i m e t e r , a nd d i v i d e s t h e r e s t among t h r e es o l a r w i nd - pl a ne t i n s t r u m e n t s an d 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 to r . T h e o t h e r fo rma t , known a s t h eg e n e r a l f o r m a 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 re x p e r im 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 u d p h o t op o l a ri m e t eran d t h e i n f r a r e d r a d io m e t er . As much as t h r e e - q u a r t e r s o ft h e t o t a l a p o a p s i s p e r i o d w i l l be d e v o te d t o im a gin g, w h ichh a s v e r y l a r g e d a t a r e qu i re m en t s.

S p a c e c r a f t c o n t r o l l e r s h av e d es ig ne d a number of s e q u e n c e su s i n g t h e s e f o r m a t s .t h e y w i l l work w i t h e x p e ri m e n te r s , s e l e c t i n g f o rm a tc om bin at io ns f o r b e s t s c i e n t i f i c r e s u l t s .D u ri ng t h e e i g ht -m o nt h O r b i t e r m i s s i o n ,

D u r in g t h e f i r s t 4 0 d ay s i n o r b i t , t h e O r b i t e r w i l lpass b e hi n d Venus ( o c c u l t a t i o n ) f o r p e r i o d s of up t o 2 3m in u te s . T h i s a l l o w s t h e r a d i o s c i e n c e t e a m t o measuree f f e c t s of Venus' atm osp her 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 hit. S in c e t h e n ar r ow beam s i g n a l i s b e n t by t h e p l a n e t ' sa t mo s ph e re , 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 be commandedas much as 1 7 degrees away f r o m t h e E a r t h - l i n e t o e x t en d t h et i m e of r e c o r d 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 r ou nd 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 a t i o n s , when c om m u nic at i on s are 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 . Cont ro l le r s w i l l then command memory storage, anda f t e r e me rg en ce of t h e O r b i t e r , t h e d a t a memory readoutformat f o r r e t u r n of s t o r e d d a t a .D uri ng t h e e i g h t months o n 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 be m o n i to r e d t h r o u g h t h e c o n t i n u o u s f l o w ofe n g i n e e r i n g d a t a (see O r b i t e r Data H a nd li ng S e c t i o n ) , a n dr e d u nd a 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 fu n c t i o n s ( s uc h a scommand and d a t a r e t u r n ) w i l l be used i f needed . Miss ionsO p e ra t io 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 u t e v e r y1 0 d ay s e i t h e r t o lower p e r i a p s i s a l t i t u d e which 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 whenit d r i f t s from t h e d e s i r e d v a l u e .

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T h e p r i m a r y m i s s i o n e n d s a f t e r 2 4 3 d a y s . S h o r t l ya f t e r w a r d s , t h e O r b i t e r a nd Venus w i l l b e b e h i n d t h e Sunand communicat ions w i l l b e g a r b l e d o r c u t o f f f o r s e v e r a ld a y s. A f t e r em er gen ce fr om t h e s o l a r . b l a c k o u t , t h eo p p o r t u n i t y w i l l b e a v a i l a b l e f o r e xt en de d m is s io n o p e r a t i o n swhich a re n o t c u r r e n t l y a p a r t o f t h e a p pr ov ed miss ion .Pio ne e r V enus M ul t ip robe M iss ion

Pionee r V enus 2 , t h e m u lt ip ro b e s p a c e c r a f t , w i l l belaunched toward Venus on a c i r c u l a r p a r k i n g - o r b i t a s c e n tt r a j e c t o r y f ro m Cape C a n a ve r a l A i r Forc e S t a t i o n by NASA'sKennedy Space C en t e r pe r son ne l . The l aun ch v eh ic l e w i l lh e ad i n a d i r e c t i o n 3 t o 1 8 d e g re e s s o u th o f s t r a i g h t e a s t ,p a s si n g o v er s o ut 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 o f t h es p a c e c r a f t f ro m t h e l a un c h v e h i c l e .The f ou r- mo nt h t r i p t o Venus f o l l o w s a more d i r e c tt r a j e c t o r y th an t h a t of t h e O r b i t e r , g i v i n g t h e p ro b es

approach s peed s o f abo u t 19 , 500 km /hr ( 1 2 , 0 0 0 m ph) . Th i si s 6,500 km/hr ( 4 , 0 0 0 mph) f a s t e r t ha n O rb i t e r a r r i v a l , andi s p o s s i b l e b e ca u se t h e p ro b es a re s lowed a t a tm ospheree n t r y t o a few hundred m i l e s p e r h ou r by 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 .The M u l ti p r ob e f l i g h t w i l l cov er abou t 354 m i l l io 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 o f t h e way a r o un dt h e Sun ( 1 35 d e g r e e s ) i n f o u r mo nt hs a s it 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 etw ee n t h e o r b i t s of E a r t h a ndVenus.Launch pe r i od f o r P ion ee r Venus 2 f l i g h t i s 27 d a y s ,

from Aug. 7 t o S e pt . 3 , 1 97 8. D ur in g t h i s p e r i o d , t h elaunch window opens e a r l i e r each day f r o m 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 , 1978, f i v e d ays 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 remote and d i r e c t s e n s i n g i ns t ru m e n ts t oe s t a b l i s h c or re sp o nd in g d a t a on t h e Venus spac e env i ronm ent ,c l o u d s a nd u p pe r a tm os ph er e 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 e as u re m en t s i n t h e a t m o sp h e r e.P ionee r V enus 2 w i l l be la unch ed by an A t l a s (SLV-3D)C e n t a u r ( D - 1 A R ) tw o-a nd 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 rl i f t o f f , b ur no ut o f t h e 1 , 9 1 7 , 0 0 0 - ~ ( 4 3 1 , 0 4 0 - 1 b . ) - t h r u s t ,

s t age -and-one-ha l f A t l a s b o o s t e r w i l l o c cu r i n a b o utf o u r m i n u te s . S t a g e s e p a r a t i o n a nd 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 ta u r s ec on d s t a g e w i l l t h e n t a k e p l a c e .- more -


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PIONEER VENUSTRAJECTORIES

ORBITER LAUNCHMAY/JUNE 1978

/7PROBE LAUNC HAAUGUS T

ORBITER LAUNCHDVENUSTR n R F I d1INfV-lVENUS AT PROBEENCOUNTERDECEMBER 1978

ORBITER ARRIVES

EARTH AT ORBITER ENCOUNTER/ ENCOUNTERPROBE RELEASESEQUENCE


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A t s i x m in u t e s a f t e r l i f t o f f , t h e A nt ig ua s t a t i o nb e g in s t r a c k i n g . The h y d r o g e n -f u e l e d C e n t a u r e n g in e w i l lb ur n f o r ab o ut 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 t o f f a t9 m i n u t e s , 4 2 s e co n ds a f t e r l i f t o f f . T h i s b e g i ns t h e 18-m in ute c o a s t p e r i o d i n c i r c u l a r p a r ki ng o r b i t a t 1 6 7 km( 1 0 4 m i . ) a l t i t u d e . A t a b o u t l a u n ch p l u s 1 3 m i n u t e s ,A n t ig u a w i l l end i t s t r a c k i n g coverage: a t a b o ut 2 0 m i n u t e sa f t e r l a u n c h , t h e A sc en si on s t a t i o n b e g i n s t r a c k i n g a n d a tl a u n c h p l u s 2 4 minu tes M u l t ip r o b e- C e n ta u r c o m b in a t io n p a s sbeyond Ascens ion range .

A t 2 7 minutes and 3 0 s e c o n d s , C e n t a u r b e g i n s i t s secondb u r n a n d 2 m in u te s a n d 8 s e c o n d s 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 g in e c u t s o f f p u t t i n g t h e M u lt ip r ob e o nt r a j e c t o r y t o Venus. About 27 .6 m i nu te s a f t e r l a u nc h an A i rF o r ce 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 ut e s o ft r a c k i n g c o v e r a g e .A t 29 .7 m in ut es a f t e r l a un ch , C en ta ur o r i e n t s t h e

M u lt ip ro b e 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 o f p e r p e n d i c u l a rt o t h e e c l i p t i c ( E a r t h ' s o r b i t p l an e) w i th i t s f o r w a r d e n dp 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 o nd s a f t e r t h e s e co nd C e nt au r 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 ,an d 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 in u 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 l ti p ro b et o 1 5 rpm.D u ri n g p ow er ed f l i g h t , as w i th P io n e e r V e n u s 1, l a u n c hv e h i c l e and s p a c e c r a f t w i l l be m o n i t o r e d f ro m t h e P i o n e e rM i s s i o 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 n

T 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 ce n si on .T h i rt y -t w o m i n u te s a f t e r l a un c h , a f t e r C e nt au r -M u lt ip r ob es e p a r a t i o n , m i ss io n c o n t r o l w i l l s h i f t f rom t h e Ames M is s io nDi r e c t o r a t Cape C a na v er al t o t h e F l i g h t D i r e c t o r a t t h eP i o n e e r M i s s i o n O p e r a t i o n s C e n t e r ( P M O C ) a t Ames ResearchC e n te r i n Cal i fo rn ia . Commands t o a nd d a t a r e t u r n e d f ro mth e P io n e e r V e n u s w i l l l e a v e a n d a r r i v e a t E a r t h v i a t h eg l o b a l n e t o f 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 c e i v e commands f ro m a n d r e l a y d a t a t o t h e PMOC a tAmes.A t 50 m i n u te s a f t e r l a u n c h , t h e DSN's C an b er ra 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 and 1 0 m in u te 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 th ro ug h t h e s p a c e c r a f t ' sa f t omni a n t e n n a i s 256 bps.- more -


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E N T R Y P O I N T S F O R PI O NE E R - V E N U SA T MO SPH E R E PR O B ES


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F or t h e f o l l o w in g t w o weeks ,communicat 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 o u se k e ep i n g, "s i n c e t h e probe and Bus i n s t r u m e n t s make no i n t e r p l a n e t a r ymeasurements. They a re d e s i g n e d t o measure t h e Venus a tmosphere .Data w i l l be 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 y s a f t e r l a u n c h , t h e s pa ce n a v i ga t io 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 a t o r y w i l l ha ve c a l c u l a t e d t h eM ul ti pr ob e Venus t r a j e c t o r y p r e c i s e l y , an d c o n t r o l l e r s a tt h e PMOC a t Ames w i l l command t h e t h r u s t e r f i r i n g seq ue ncef o r t h e f i r s t t r a j e c t o r y c o r r e c t i o n maneuver. About 1 4 daysa f t e r l a u n c h , t h e t w o B us ins t rum ent s w i l l be checked ou tf o r t h r e e h ou rs a t a d a t a r a t e of 1 , 0 2 4 bps . Twenty da ysa f t e r l a u nc 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 e c o n d c o u r s ec o r r e c t i o n .About 6 0 days a f t e r l a u n c h , t h e se v en i n s t r u m e n t s a ndt h e sys tems on t h e Large Probe w i l l b e ch ec ke d 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 a nd 1 28 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 nd s ys te m s on each of t h eSmall P r o b es f o r a n h o ur of o p e r a t i o n each a t a d a t a r a t e of6 4 and 1 6 bp s. They perf orm s i m i l a r checks on the t w o i n s t r u -m ent s aboard t h e Bus a t 512 b p s . The Bus communicat ions andpower system w i l l be used f o r t h r e e checks .About 9 4 d a y s a f t e r l aunch ( 3 0 d a y s b e f o r e a t m o s p h e r ee 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 yc o r r e c t i o n m a n e u v e 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 ra 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 medium -gain h o r n a n t e n n al o o k s a t E a r t h . T h i s a l l o w s a h i g h e r d a t a r a t e f o r probes e p a r a t i o n m an eu ve rs .Tw enty -seven days be fo re e n t r y , t h e Bus and Large Probei n s t r u m e n t s a re c h e c k e d o u t .T w en t y- fo u r d a y s b e f o r e a t m o s p h e r i c e n t r y , a n d 1 3 m i l l i o nk m ( 8 m i l l i o n m i . ) f r o m Venus, c o n t r o l l e r s r e o r i e n t t h es p a c e c r a f t so t h a t t h e L ar ge P ro be w i l l e n t e r t h e a t m o s p h e r ew i t h i t s h e a t s h i e l d a l ig 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 means 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 an n edL a r g e Pr obe e n t r y t r a j e c t o r y be ca us e t h e Large Probe i sc e n t e r e d o n t h e s p i n a x i s . The L ar ge P ro be i s t h e n l a u n c h e dby a pyro techn ic - sp r ing m echan i sm toward i t s e q u a t o r i a l e n t r yp o i n t on V en us ' d a y s i d e , b ec om in g a n i n d e pe n d e n t s p a c e c r a f t .

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-19-The n e x t 2 3 days f r o m a t m o s p he 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 o f t h e S m a l l Probes by chang ing i t sf l i g h t p a t h , p o i n t i n g it toward t h e c e n t e r o f V e nu s. A t 2 2d a ys 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 o b e i n s t r u m e n t s a r e checkedo u t . A t 2 0 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 d so t h a tt h e t h r e e S m a l l P r ob e s c a n b e t a r g e t e d f o r t h e i r e n t r y p o i n t s

-- o n e on t h e d ay s i d e a t m id -so uth ern l a t i t u d e s , t h e s e c o n don t h e n i g h t - s id e , a l s o a t m id -s ou th er n l a t i t u d e s , an d t h et h i r d o n t h e n i g h t s i d e a t hi gh n o r t he r n l a t i t u d e s .M i s s i o n o p e r a t i o n s t h e n commands l a u n c h o f t h e t h r e e S m al lProbes . A f t e r t h e t r a n s p o r t e r Bus i s spun up t o a p p r o x i m a t e l y48 rpm, t h e probes a r e l au n ch ed by r e l e a s i n g t h e clamps t h a th o l d t h e m . C e n t r i f u g a l fo rce of t h e Bus s p i n t h r ow s t h ep ro be 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 y t 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 u n c h p r o c e s s , t h e S m a l l Probes r e t a i n t h e48-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 o t h e Bus.

W ith l a u n c h of a l l f o u r p r ob e s, 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 -- each w i t h i t s own instrument and commanda nd d a t a s y s t e m -- a re headed f o r Venus.

E i g h t e e n d a y s be 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 85 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 Probet o p r ov i de a r a d i o s i g n a l r e f e r e nc e f o r p r e c i s e c o m p u t a t i o n so f t h e p ro be d e s ce n t t r a j e c t o r i e s . ( T r a j e c to r y d a t a w i l l b eu s ed t o m e a su r e wi n ds i n V en u s' a tmosphe re . )From t h i s p o i n t o n, t h e f o u r probes w i l l be commandedby onboard t imers and o t h e r s e n s o r s a nd e l e c t r o n i c s , an dt h e y w i l l n o t b e h ea r d f ro m by c o n t r o l l e r s on E a r t h u n t i l2 2 m i n u te s b e f o r e a t m o s p h e r i c e n t r y .A t e n t r y minus e i g h t da y s, f i n a l a d ju s t m en t s w i l l bemade t o t h e Bus ' e n t r y an gl e by ground command, and a te n t r y m in us two d a y s , t h e Bus s y st e ms 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 be checked .A pp ro xi ma te ly t wo 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 ci n s t r u m e n t s w i l l be w a r m e d up and commanded i n t o t h e o p e r a t i o nmode f o r e n t r y .On Dec. 9 , 1978, a t a b o u t 2 p.m. EST, t h e f o u r p r o b e sw i l l a r r i v e a t Venus and e n t e r t h e atmosphere . The L a r g eProbe w i l l descend t o V en us ' s u r f a c e i n 55 m i n u t e s a n d t h e

t h r e e S m a l l P r ob e s i n a b o u t 57 m i n u t e s , d e p e nd i n g o n e n t r ya n g l e . - more -

1


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eE N T R Y

F IREJORT ARL A R G E P R OB E D E S C E N T S E Q U E N CE

BDEPLOY PILO T CHUTERELEASE AFT COVER

EXTRACT CHUTE BAG

DE P L OY MAIN CHUT E

H I%RELEASECHUT EAE ROSH ELL/PR ESSUR E VESSE LSEPARATION


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L a r q e P r o b e E n t r y E v e n t sA t 2 . 5 hou r s be fo re e n t ry , t h e La rge P robe 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 an d r a d i o r e c e i v e r . Tw enty-two m i n u te s b e f o r e e n t r y , t h e p r o b e w i l l b e g i n t r a n s m i s s i o nof r a d i o s i g n a l s t o E a r th . A t e n t r y m in us 1 7 m i n u t e s , t h e

L ar ge P ro be 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 bps . The commandu 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 st r um e n tsa b oa rd , p l u s in 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 te s b e f o r et h e p ea k e n t r y d e c e l e r a t i o n p u l s e o f 320 G , t h e p r o b e w i l lbe t r a v e l i n g 4 1 , 6 0 0 km/hr ( 2 6 , 0 0 0 m p h) . E n t r y o c c u r s a t2 0 0 km ( 1 2 0 m i . ) a l t i t u d e , w here t h e p ro be e n c o un t er s t h et e n u o u s t o p o f t h e a tm o sp h er e.The t i m e r w i l l command da t a s t o r a ge f o r t h e a tmosphe r i cs t r u c t u r e e x p e r im e n t d u r i n g e n t r y c o mm u ni ca ti on s b l a c k o u t .T h i r t y - e i g h t s ec on ds a f t e r e n t r y , t h e L ar ge P ro be 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 - t h r e e se co nd s a f t e re n t r y , a t an a l t i t u d e of 6 6 km ( 4 0 m i . ) , a l l i ns tr um en tss 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 t e s l a t e r , a t 4 7 k m(28 m i . ) a l t i t u d e , t h e p a ra c hu t e i s j e t t i s o n e d , a nd t h ea e ro d yn a mi ca ll y s t a b l e p r e s s u r e v e s s e l d e sc e nd s t o t h es u r f a c e i n 39 m i n u t e s , i m p a ct i ng 55 m i n u te s a f t e r e n t r y .

A s t h e p r ob e d e sc e nd s , t h e a tm os ph er e g e t s s t e a d i l y h o t t e rand d e n s e r , u n t i l a t t h e s u r f a ce 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 s t h a ta t t h e E a r t h ' s s u r f a c e . The L arg e P ro be j e t t i s o n s i t sp a r a c h u te t o s p e ed i t s d e s c e n t t h ro u gh t h i s v e r y d e n se a tm os -p h e r e , s o t h a t it r e ac h e s 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 it.

D u ri ng d e s c e n t , t h e L ar ge P r o b e ' s s e v en i n s t r u m e n t sw i l l h av e o b t a i n e d d a t a t o d e te r m in e a l t i t u d e a nd c o mp o si ti ono f c lo u d l a y e r s , a tm os ph er e c o n s t i t u e n t s , t e m p e r a tu r e , p r e s -s u r e , d e n s i t y , wind f lo w and v a r i a t i o n s of h e a t f lo w i n t h ea tmosphe re .The Large Probe w i l l i mp ac t t h e s u r f a c e a t abou t 36km/hr ( 2 2 mph) . None of th e prob es i s des igned t o s u r v i v eimpac t .

Smal l Probe EventsThe t h z e S m a l l Prc.-,br:, t w w i l l . enter t h e planet'sa tmosphere a t a b o u t 4 1 , 6 0 0 km/hr ( 2 6 , 0 0 0 mph). However,b ec au se t h e i r e n t r y p o i n t s a r e s pr ea d over a n e n t i r e hemi-s p h e r e o f V e nu s, a nd t h e y a r e l a u nc h e d s i m u l t a n e o u s l y f ro mt h e Bus, t h e a n g l e 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 atm os ph er ev 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 in g and d u r a t i o n so f maximum d ec e l e r a t i on pu l s e s v a ry wide ly .

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Peak deceleration forces vary from 2 0 0 G to 565 G. Entrytimes also differ by up to 10 minutes, and descent times byone minute. As with the Large Probe, entry is defined asoccurring at an altitude of 2 0 0 km (120 mi.).Three hours before atmospheric entry, the stable oscil-

lator in the radio transmitter for one-way Doppler trackingand the battery on each Small Probe are warmed up by commandsfrom the onboard command unit. Twenty-two minutes beforeentry, each Small Probe begins transmission of radio signalsto Earth. Seventeen minutes before entry, the Small Probesbegin transmitting data at 64 bps. The command unit initiateswarmup and calibration for the three instruments on each SmallProbe.Five minutes before entry, the two cables and weightsof the yo-yo despin system are deployed to reduce the spinrates of the Small Probes from 48 to 15 rpm. The high spinrates imparted by the Bus are needed to disperse the probes

to entry points widely spaced over the planet. However, thiswide dispersion a l s o means that the Small Probes enter Venus'high upper atmosphere somewhat tilted to their flight paths.The "spindown" of the probes is needed to make it easier foraerodynamics forces to line up the axes of the probes withtheir entry flight paths.heating at the edges of the probes' conical heat shieldsbecomes serious. Cables and weights are jettisonedimmediately after spindown.

This must occur quickly before

Five minutes before the peak deceleration pulse ofatmospheric entry, the command unit orders the "blackout"format for storage of spacecraft data, plus heat shieldtemperature and accelerometer measurements for the atmos-pheric structure experiment. This is to assure no l o s s ofdata during the 10-to-15-second communications blackout atentry.

Within the first minute (18 to 46 seconds) after entry,the nephelometer window is opened, and the atmosphericstructure and net flux radiometer housing doors are openedand instrument booms deployed.At this time, the upper descent phase begins, with theprobes in the altitude range of 72 to 65 km (43 to 39 mi.)and all instruments operating. The instrument compartment

doors on each side of the Small Probe afterbodies serve todespin the probes.serves to prevent the spin rate from falling to zero rpmenabling instruments to make observations over a full circleof probe rotation.

A small vane on the pressure sensor inlet

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A t e n t r y plus 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 t m o s p h e r ei n t e r f e r e s w i t h r a d i o t r a ns m i ss 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 rs a t a n a l t i t u d e of 30 k m (1 8 m i . ) .From this p o i n t , t h e t h r e e S m a l l P r o b e s d e sc e nd i n t oV en us ' i n c r e a s i n g l y d e n s e lower a t m o s ph e r e , i m p a c t i n g o n t h e

s u r f a c e a t 3 6 h / h r ( 2 2 mph) from 56 t o 57 m i n u t e s a f t e r t h ee n t r y t i m e of each p r o b e . U n l ik 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 the s u r f a c e . The d e n s i t yo f t h e a t m o s ph e r e i s s o g r e a t t h a t t h e d ra g o f t h e s e aero -d y n a m i c s u r f a c e s s lows them t o t h e d e s i r e d d e s c e n t s pe e d.L i k e t h e L a r ge P r o b e , t h e S m a l l P r o b e s a r e n o t d e s i g n e d t os u r v i v e on t h e s u r f a c e .B us Even t s

E i g h ty m i nu t es 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 Venusa t m o s p h e r e , t h e Bu s w i l l e n t e r o n t h e da y s i d e o f t h e p l a n e ta t h i g h l a t i t u d e s i n t h e s o u t h e r n h em is ph er e. U n li k e t h ep r o b es , 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 pe ed 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 two m i nu t es a f t e r e n t r y . T heBus c a r r i e s two 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 n d 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 e n 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 a n d u p p e r at mo s-p h e r e f r o m 20 0 km ( 1 2 0 m i . ) down t o 1 1 5 k m ( 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 ea su re m en ts b e tw e en1 5 0 and 1 1 5 km . The B us , w i th i t s more p o w er f ul 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 .

A l l d a t a f ro 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 to n e , C a l i f . , a n d Can-b e r r a , A u s t r a l i a , and 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 t e r sw i l l spend 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 . T h e i n v e s -t i g a t o r s w i l l be e s p e c i a l l y i n t e r e s t e d i n comparing r e s u l t sfrom t h e w id e ly -s pa ce d p r ob e f l i g h t p a t h s o n t h e d a y a n d n i g h ts i d e s a n d i n b o t h h e m is ph er es of Venus.

A tm os ph er ic w in d 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 be c a l -c u l a t e d f ro m m ea su re m en ts o f t h e p r o b e v e l o c i t i e s , t h r o u g ht r i a n g u l a t i o n m ea su rem en ts from f o u r s t a t i o n s a t once. TwoSTDN s t a t i o n s a t Guam and San t i ag o , C h i l e , w i l l record Busa n d p r o b e d a t a a l o n g w i t h t h e D S N 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 th i n s i z e , massa 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 much hot te r ,i t s atmosph ere much de ns er , and i t s r o t a t i o n much s lower t hant h a t of 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, 74 5 k m (7920 m i . ) . The mass of Venus is0 . 8 1 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 V enus i s5.26 grams pe r cub ic c m c o m p a r e d w i t h E a r t h ' s 5 .5 grams perc u b i c c m .Because Venus i s c l o s e r t o t h e Sun, it rece ives a b o u tt w i c e a s much energy a s Earth. However , it i s more r e f l e c t i v et h a n E a r t h b e c a u s e o f i t s c loudy a tmosphere . A s a r e s u l t oft h e s e two compe t ing f ac to r s , Venus abso rbs abou t t h e sameam ount o f s o l a r e n e r g y a s E ar th . Thus Venus would be exp ec tedt 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 esu r f ac e o f Venus i s v e r y h o t , a b o u t 480 d e g r e e s Z ( 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 tu r e o f V enus assumes t h a tt h e a t mo s ph 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 lower a t m o s p h e r e a n d t h e s u r f a c e . However, t he a tmosphe rer e s t r i c t s t h e p a ss a ge of h e a t r a d i a t i o n from t h e s u r f a c e a nd t h elower a tmosphere back i n t o spac e . The h ea t i s t r a p p e d . E a r t hh a s a m od es t g re en h ou se 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 p e r a t u r eby about 35 d e g r e e s C ( 95 d eg re es F . ) , b u t i n some p a r t s o f t h ei n f r a r e d s pe ct ru m h e a t c a n es c ap e by d i r e c t r a d i a t i o n fro m t h eE a r t h ' s s u r f a c e t o spac e . Because of i t s d e n s i t y , c o m p o s i t i o nand c lo ud s , th e Venus a tmosphere i s v e r y t h i c k , a nd b e c a us e iti s m o s t l y c a r 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 ut go in 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 en g t h s.One of t h e m o s t puzz l i ng a s pe c t s o f Venus i s i t s l a c k ofwa te r . I f Venus 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 ofVenus g o , i f a ny 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 er e an 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 hy dro ge n a nd oxygen.hydrogen e scaped i n t o space f rom t h e t o p o f t h e Venus a tmosphe re,and t h e he av i e r oxygen d i f f us ed down t o t h e o x id i ze d c r u s t .D e t a i l e d a n a l y s i s shows 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 Venust o have l o s t an ocean o f water by such a r o u t e .formed c l o s e enough t o the Sur , so t h a t t h e t e m pe r at ur e p r ev e nt e dw a t e r from b e i ng i n c o r p o r a t e d i n t o t h e s o l i d mater ia l t h a t f o r m e dt h e p l a n e t .w i t h i n i t s r o c k s t o fo rm e a r l y d ee p oceans l i k e t h o s e o f E a r th .D i r e c t measurements of ga se s wi th in t h e Venus a tmosphere maypo in t t oward one o f t w o a l t e r n a t i v e s : E i t h e r t h a t wate 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 wateroutg asse d and was subseq uen t ly l o s t .

The

Perhaps Venus

I f s o , Venus would never have had enough wate r

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O r b i t a n d R o t a t i o n of VenusT h e r o t a t i o n of Venus 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 po s i t e t o t h e d i r e c t i o n of t h e p l a n e t ' sr e v o l u t i o n a b o u t t h e Sun a nd t o t h e r o t a t i o n o f m ost o t h e r

p l a n e t s . Venus t u r n s o n i t s a x i s on ce i n 2 4 3 . 1 E a r t h d a y s .S i n c e Venus' r o t a t i o n o n i t s a x i s and r e v o lu t io n i n o r b i ta r o u nd t h e S un a r e i n op 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 of a s o l a rday on Venus i s 1 1 7 E a r t h days (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 ay s o f n i g h t ) .The o r b i t s of E a r t h and Venus a r e t i l t e d t o e a c h 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 o u t 6 degreesf r o m 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 sc om pa re s 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 hi ch 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 r e s m a l l .Some s c i e n t i s t s b e l i e v e t h a t Venus ' p e r io d o f r o t a t i o ni s t i e d t o t h e r e v o l u t i o n of t h e E a r t h and Venus arou nd t h eS un . Venus p r e s e n t s t h e same hem isphere tow ard Ear th a t e a c hc lo 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 e tw 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 l o c ke d t o t h e c l o s ea p p r o a c h e s o f E a r t h and Venus, t .hen t h e i n t e r n a l d i s t r i b u t i o n ofm a s s 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 es Venus r o t a t e so slowly when m o s t 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 body h i t Venus a n d s t o p p e d i t s r o t a t i o n . T h i sl a r g e body m igh t have been ca p t u r ed 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 o s 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 slowly i n a n o p p o si 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 f or me d f ro 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 co mb in ed i m p a c ts o f t h e s e f r a g m e n t s n e v e rhad much r o t a t i o n . A c c o rd 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 mo s ph e re may h a ve sl ow ed r o t a t i o na nd 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 un t in g f o r i t s backwardr o t a t i o n .Radar a s t r o n o m e r s have mapped a n ar e a 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 be a r ug ge d s u r f a c e . A c co r di n g t o t h e r a d a r r e s u l t s , t h e rea re huge sha l low c r a t e r s a s w e l l a s an enormous volcano whichmay be a s l a r g e i n a r e a , t ho u gh 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 t e m ' s l a r g e s t d is c o ve r e d so f a r ) . Radara s tr o no m er s a l s o d e t e c t e d what a p p e ar s t o be an enormous canyon.Th i s chasm i s 1 4 0 0 k m (870 m i . ) l o n g , 1 5 0 k m ( 9 5 m i . ) w i d e , andsevera l k i l o m e t e r s d e e p .- more -


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Venus' I n t e r i o r and A bs en ce o f M ag ne tic : F i e l dU n l i k e t h e E a r t h , V enus has no s i g n i f i c a n t m ag ne tic f i e l d .

C on ve ct io n c u r r e n t s i nThe g e n e r a t i o n of E a r t h ' s f i e l d i s a t t r i b u t e d t o a s e l f - s u s t a i n i n gdynamo i n t h e f l u i d core o f t h e p l a n e t .t h e core g i v e r i s e t o e l e c t r i c c u r r e n t s t h a t produce t h e e x t e r n a lm a g n e t i c f i e l d .J u p i t e r , p r e d i c t s t h a t s l o w - s p i n n i n g p l a n e t s l i k e Venus shouldn o t h av e m ag ne ti c f i e l d s .T h i s t h e o r y , w h ic h a l s o seems t o ap p l y t o

Venus i s a p la n e t whose shape cou ld be very close t o as p h e r e acco r d i n g t o r a d a r measurements .t o be almost a p e r f e c t c i r c l e .i n t o vie w a s d o p o i n t s o n t h e e q u at o r , c i r c u l a r i t y a round t h epo les canno t be measu red .shape , and of a s a t e l l i t e makes it d i f f i c u l t t o d e t e r m i n e t h ei n t e r n a l d e n s i t y d i s t r i b u t i o n of t h e p l a n e t .t h e i n t e r i o r a re based on i t s s i m i l a r i t y t o E a r t h , c o n s i s t i n gof a l i q u i d c o r e , a s o l i d mant le and a s o l i d c r u s t .t r u e n a tu r e o f t h e i n t e r i o r o f t h e p l a n e t i s ve ry much i nd o u bt b e c au s e s c i e n t i s t s d o n o t know V en us ' t h e r m a l s t r u c t u r eo r t h e n a t u r e of t h e m a t e r i a l s w hich make up i t s mass.

They s h o w i t s e q u a t o rB ec au se t h e p o l e s d o n o t r o t a t eThe l a c k o f i r r e g u l a r i t i e s i n

M o s t models ofBut t h e

The Atmosphere of VenusCarbon d iox ide i s t h e dominant gas i n t h e V en us ia natmosphere . T h e r e a re a l s o t r a c e s of wa te r , carbon monoxide,h y d r o c h l o r i c a c i d a nd h yd ro ge n f l u o r i d e .been found. Free oxygen has never

The c l o u d s w hic h o b s c u r e t h e s u r f a c e o f V enus c o n s i s t o ft h i c k h a z e s of d r o p l e t s b e l i e v ed t o be made of s u l f u r i c a c id .Venus ' c louds a r e p a l e y e l l ow a nd v e r y r e f l e c t i v e , r e t u r n i n gi n t o s pa ce some 7 5 p e r c e n t o f t h e s u n l i g h t f a l l i n g on them.Space probe measurements have shown th a t t h e r e a r e d i s t i n c tc l o u d l a y e r s much h i g h e r t h a n t e r r e s t r i a l c louds . Pho tog raphst ak en i n u l t r a v i o l e t l i g h t revea l a f ou r- da y r o t a t i o n of t h em ark in gs i n t h e s e c l o u d s . T h i s r o t a t i o n i s l i k e t h a t o f t h ep l a n e t , i n a r e t r o g r a d e d i r e c t i o n . U nu su al d yn am ic s o f t h eatmosphere a r e r e q u i re d t o a c co u nt f o r t h i s high-speed c loudmot ion .The g e n e r a l l y a c c e p t e d f i g u r e f o r a tm o s ph e r ic c a r b o nd iox ide on Venus i s 9 7 p e r c e n t . However, measureme nts madeby e a r l y Ve ne ra s p a c e c r a f t (USSR) d i f f e r f ro m r a d i o o c c u l a t i o nmeasu remen t s sugges t ing t h e p r e s e n c e o f a b o u t 70 p e r c e n tc a rb on d i o x i d e i n t h e Venusian a tmosphere . And, i f t h e r ei s much ar go n i n t h e atmosphere , t h e amount of c a r b o n d i o x i d eco u l d be a s l o w a s 2 5 p e r c e n t .

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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 clouds. At the cloud tops it is only 0.0001 per 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 never

have had much water to outgas in the first place if it wasformed 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.by 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 be

sufficient to evaporate all of Earth's oceans.

This prevents heated water vapor from rising

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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 350 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 250 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.This could have happened to Venus. If the primitiveatmosphere 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 30 million years perhaps 90 per cent of the watercould have been lost to the planet, but all could not belost in this way.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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100

v)w-BO

-EICJw

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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 asignificant magnetic field, the solar wind interacts direc.tlywith the upper atmosphere and the ionosphere of the planet.Among the atmospheric regions of Venus, the upper atmosphereabove the cloud tops is best understood. It has been investigatefrom Earth and from flyby and orbiting spacecraft. Above 150 km(90 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 the

surface 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.Mariner 10 found two clearly defined layers in the nighttimeionosphere: a main layer at 1 4 2 km (87 mi.) altitude and alesser layer at 124 km (76 mi.). The peak intensity of the lattewas about 78 per cent of the higher layer. On the dayside therewas one main layer at 1 4 2 km (87 mi.) and several minor layers,

including one at 128 km (78 mi.) and another at about 180 km(110 mi.). The Venera 9 and 10 orbiters obtained similar resultsbut single layers seem to be the most common.- more -


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SOLAR WIND - VENUS INTERACTIONS

BOW SHOCKT RANSI T I ON

- -~ -/ ~ R E F A C T I O I \

OPAUSE W A V E

SOLAR

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From a practical standpoint, Venus has no intrinsicmagnetic field. The field of Venus is less than 1/10,000 o fEarth'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 sharpboundary to the ionosphere at 350 to 500 km (210.to 05 mi.).This is believed to be caused by the interaction of the solarwind with Venus' atmosphere. On the night side of the planet,the ionosphere extends high into space and probably into aplasma tail stretching away from the Sun.

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 127 degrees C (260 degrees F). At sucha temperature, the thermal escape of helium gas would be negligiblAccordingly it is thought that if helium outgassed from the rocksof Venus as it did on Earth the gas might have accumulated inthe upper atmosphere of Venus.about 800 km (480 mi.) and contains up to 10,000 atoms percubic centimeter.

A corona of hydrogen begins at

Haze Lavers

At least two tenuous layers of haze can be seen in highresolution pictures of the limb (edge of the disc) of Venus.They extend from equatorial regions to higher latitudes. Theymay be associated with temperature inversions in the highatmosphere, and may result from processes similar to those inEarth's atmosphere which produce layers of aerosols in thestratosphere. Aerosols are solid or liquid particles suspendedin an atmosphere.region 8 0 to 90 km (50 to 5 6 mi.) above the surface of Venuswhere the atmospheric pressure is between 50 and 0.5 millibars.(Pressure at Earth's surface is 1000 millibars). These hazelayers are extremely tenuous. At the topmost haze layer, ifthe atmosphere is mainly carbon dioxide, the temperature shouldbe - 7 5 degrees C . However, temperatures determined fromoccultations differ appreciably above 60 km (37 mi.), suggestingtemperature inversions that separate the haze layers from thetopmost convective cloud deck as well as the upper from thelower haze layers. In the region above 50 km (30 mi.), thedaytime atmosphere is about 15 degrees C ( 5 9 degrees F)warmer than the temperature at night.

The stratified layers of haze are in the

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The Cloud LaversB e l o w t h e up p e r a tm o s p h er e i s t h e 18-km ( 1 1 - m i . ) - t h i c kr e g i o n c o n t a i n i n g t h e c l o u d s o f Venus v i s i b l e fr om E a r t h . W hi leth e c lo u d s o f V en us l o o k e x t r e m e ly o p aq u e , t h e y a re i n f a c t v e r ytenuous . Veneras 9 and 1 0 d ete rm in ed t h a t v i s i b i l i t y w i t h in t h e

c l o u d s i s between 1 and 3 km ( 0 . 6 t o 1 . 8 m i . ) . They a re morel i k e t h i n h az es t h a n t e r r e s t r i a l c l ou d s . The p a r t i c l e s makingup t h e c l o u d s of Venus a re s p h e r i c a l a n d a b o u t o n e t o t w om ic ro ns i n d i a m e te r . T he se d r o p l e t s a p p a r e n t l y c o n s i s t o fs u l f u r i c a c i d , w i t h c o n c e n t r a t i o n s v a r y i n g f ro m 50 t o 5 0 0p e r c u b i c c e n t i m e t e r .The p r es e n c e of s u l f u r i c a c i d c l o u d s e x p l a i n t h e e x tr em ed r y n e s s o f t h e V enu s u p p e r a tm o s p he r e . N e a r ly a l l t h e wate rhas c he mi ca l ly bound up i n t h e sulfuric acid d r o p l e t s . T h ed e n s i t y of Venus ' a tmosphere a t t h i s l e v e l i s a b o u t o n e - t e n tht h e d e n s i t y of E a r t h ' s a t m o s p h e r e a t sea l e v e l . S u l f u r i c a c i dc lo u d s r e m a in a s c l o u d s o v e r a w i de r r a n g e o f t e m p e r a t u r e t h a n

water c l o u d s , a l t h o u g h h i g h t e m p e r a t u r e s c a u s e some of t h ew a t e r t o e v a p o r a t e f r o m t h e d r o p l e t s . T he re i s e v i d e n c e oft h e p r e s e n c e of f l u o r i n e i n t h e Venus a t m os p he r e. T h i s e l e m e n tp r o b a b ly c o m b in es w i th w a t e r i n t o t h e e x tr em e ly s t a b l e andc o r r o s i v e f l u o r o s u l f o n i c a c i d . But n one of t h e s e a c i d s c a na cc ou nt f o r t h e a b s o r p t io n of u l t r a v i o l e t r a d i a t i o n by t h ec l o u d s . T h e r e m u s t b e an unknown u l t r a v i o l e t a b s o r b e r i n t h ec l o u d s w h ic h g i v e s r i s e t o t h e d a r k m ark in gs s e en i n u l t r a v i o l e tp i c t u r e s o f V enu s.O n e s p e c u l a t i o n i s t h a t t h e d a r k r eg io n s s ee n i n u l t r a v i o l e tl i g h t a r e o x y g e n -d e p l e te d r e g io n s w h er e a s i g n i f i c a n t amount ofu l t r a v i o l e t -a b s o r b i n g s u l f u r i s b e in g p r o d u c ed . T h e r e a p p e a r s

t o be a whole s e r i e s of compounds o f su l f u r , oxygen and ha lo -q en s t h a t e n t e r i n t o t h e c h em is tr y of t h e atmosphere of Venus.The P io n e e r Ven us m e a su r em e n ts o f t h e c o n s t i t u e n t s of t h ea tmosphere of Venus with a mass spe c t r om ete r and gas chromatographs ho ul d c o n t r i b u t e g r e a t l y t o o u r u n d e r s t a n d i n g of t h e s e c h e m i c a lp r oc e ss e s t h a t a r e r e s p o n s i b l e f o r t h e V en usi an c l o u d s an d t h e i rmark ings .The da rk markings of t h e c l ou d s , s ee n i n u l t r a v i o l e t l i g h t ,h av e c h a r a c t e r i s t i c f or ms t h a t ha ve b ee n s t u d i e d fro m E a r t h .There a re h o r i z o n t a l Y-shaped f e a t u r e s w h ic h s o m e t i m e s have at a i l . T here a r e f e a t u r e s t h a t look l i k e a r e v er s e d l e t t e r C .T h e f e a t u r e s i n t h e f o r m of a r ever se l e t t e r C a p p e a r moreo f t e n on t h e e v e n in g t e r m i n a t o r t h a n o n t h e m or ni ng t e r m i n a t o r .O t h e r f e a t u r e s a r e l i k e a r e v e r s e d C w i t h a b i s e c t i n g b a r .Somet imes the re a r e t w o p a r a l l e l e q u a t o r i a l b an ds . Thep a t t e r n s a re a l s o almost a lways symmetrical a b ou t t h e e q u a t o rof Venus. The arm s of t h e s e f e a t u r e s a re a l w ay s o pe n i n t h ed i r e c t i o n o f t h e i r r e t r o g r a d e m otio n wh ich va r i e s between

1 8 0 and 4 7 0 kph ( 1 1 2 t o 265 m p h ) .- m o r e -


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VENUS ATMOSPHERE

'""I

20 I C L E A RV ATMOSPHERE1 SU R F A C Ei5 i o 7'5 looWIND SPEED m/s

W E A K L YI O N I Z E D

M A I NI O N 2A T ONW E A K L YI O N I Z E DL A Y E R S

UPPERH A Z E SL O W ERH A Z E S

TROPOPAUSEC L O U D S

W I N DS H E A RL O W H A Z E SA ER O SO L S

D U S T

UPPERATMOSPHERE

CLOUDSILOWERATMOSPHERE


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s iasI n t h e u p p e r a t m os p h er e t h e e f f e c t s o f s o l a r he a t in g a re. g n i f i c a n t , a nd t h e C -b ar, C- a n d Y -s ha pe d f e a tu r e s a r e a l ls o c i a t e d w i t h t h e s u b -s o la r p o i n t , w hich i s t h e p o i n t w he reth e S un s h i n e s down o n t h e Ven us a tm o s p h e r e f ro m d i r e c t l yo v e r h e a d . H ow eve r, t h e f e a t u r e s move a r o u n d t h e p l a n e t a n d

a re n o t f i x e d w i t h r e s p e c t t o t h e s u b - so l ar p o i n t .A b i g q u e s t i o n a b o u t V e nu s' a t m os p h er e i s w h e t h e r t h ea p p a r en t mo ti on s o f t h e u l t r a v i o l e t m a rk in gs a r e a r e s u l t o fa c t u a l m ovement o r m e r e ly a wave motio n. The ev id en ce tod ayp o i n t s t o an a c t u a l movement o f mass; i . e . , w in ds . B u t t h e r ei s some e v i d e nc e o f wave m o t io n s , d i u r n a l t i d e s a nd p a r a l l e le q u a t o r i a l b e l t s .The d i v i s i o n b etw ee n t h e h i g h wind v e l o c i t i e s o f t h es t r a t o s p h e r e , and t h e n ea r c a l m o f t h e d e n se s u r f a c e a tm o sp h er eseems t o come a t a bo ut t h e 5 6 km ( 3 6 m i . ) l e v e l . The b i g c ha ng ei n wind v e l o c i t y t h u s a p p e a rs t o t a k e p l a c e a t t h e b o tt om of t h e

c l o u d s w h er e t h e r e m u st b e a s h e a r zo ne . T hu s, t h e c lo u d b o tt o m sa r e e x p e c te d t o b e e x t r e m el y r a gg e d.The S o v i e t p r o b e s m e as u re d t h e am ou nt o f s o l a r r a d i a t i o ndown t o t h e s u r f a c e . Above 50 km ( 3 1 m i . ) , s c a t t e r i n g a p p ea rst o b e by t h e c l ou d p a r t i c l e s . B e l o w a b o u t 25 km (1 5 m i . ) , t h es c a t t e r i n g i s R a yl ei gh s c a t t e r i n g ; i . e . , by much sm a l l e r a i rm o l e c u l e s . A t t h e s u r f a c e , w i t h t h e S u n 's p o s i t i o n a b o ut 3 0d e g r e e s from o v er h ea d , t h e i n t e g r a t e d f l u x w a s measured asb e i n g a b o u t e q u a l t o t h a t o n a n o v e r c a s t d ay on t h e E a r t h a tsea l e v e l i n m i d - la t i t u de s .The h i g h v e l o c i t y w i nd s i n t h e Venus a t m os p h er e m ig h t a r i s e

b e ca us e t h e p l a n e t h a s s uc h a mass iv e and deep a tmosphere . Large-s c a l e e d d i e s c o n t a i n i n g a l o t o f e n e r g y c o u l d t r a n s p o r t momentumfrom low t o h i g h a l t i t u d e s w i t h a h i g h a m p l i f i c a t i o n . The i o nw ind s p e e d s i n t h e d e n s e l o w e r a tm o s p h er e pr o du c e d by t h e h e a tf ro m t h e Sun a nd t h e r o t a t i o n of t h e p l a n e t a r e a m p li f i e d i n t ot h e t h i n u p pe r a t m o sp he re .L o w e r Atmosphere

T h e p e n e t r a t i o n of Veneras 9 and 1 0 i n t o t h e lower a tmospherep r od u ce d new i n f o r m a t i o n a b o u t t h i s r e g i o n . A t a b o u t 50 km ( 3 0 m i . )a l t i t u d e , t h e wind v e l o c i t y a p p e ar s t o b e ab o ut 1 3 0 kph ( 8 0 mph).A t t h e l a n d in g s i t e of Venera 9 , t h e l o c a l wind v e l o c i t y v a r i e dfrom 1 . 2 t o 2.5 kph ( . 9 t o 1 . 4 m ph ); a t t h e V e ne ra 1 0 s i t e , itv a r i e d from 2 . 9 t o 4 . 7 kph ( 1 . 8 t o 9 . 2 mph) . The two la nd er st h u s c o n fi r m ed a l o w w i n d v e l o c i t y c lo s e t o t h e s u r f a c e , a s w e l la s l i t t l e d u s t c o n te n t i n t h e l o w a tmosphere .- more -


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There a r e s t i l l many u n r e s o l v e d q u e s t i o n s a b o u t t h eatmosphere of Venus t h a t n e ed t o b e a ns w er ed , s u c h as :0 How does t h e Venus wea the r machine r e a l l y work?0 I t i s r e a l l y a g r e en h o us e e f f e c t t h a t makes V enusso h o t c om pa re d w i t h t h e E a r t h ? O r i s t h e r e adynamic cause?

Did Venus once have a more m o d e r a t e s u r f a c et e m p e r a t u r e ?What c a u s e s t h e d a r k m a r k in g s i n t h e Ven us c lo u d s ?

0 What a r e t h e c o n s t i t u e n t s o f t h e Venus a t mo sp h er e?T he rm al e m i s s i o n f ro m t h e u p p er a t m o s p he r e d i f f e r s v e r yl i t t l e be tween n i g h t and day and be tween l o w and h ig h l a t i t u d e .

T h i s i n d i c a t e s a dy na mic a c t i v i t y w i t h i n t h e a t m os ph e re , a nds u g g e st s t h a t h e a t i n s u b s t a n t i a l a mounts i s b e in g t r a n s f e r r e da ro un d t h e p l a n e t h o r i z o n t a l l y .a t a l l l e v e l s b e ca u s e s p a c e c r a f t ha ve d e t er m in e d t h a t t h e s o l a rr a d i a t i o n p e n e t r a t e s th ro ug h t h e c l ou d s a nd , t h e r e f o r e , a f f e c t st h e a t m o sp h e re down t o t h e s u r f a c e .most i m p o r t a n t a b o v e 56 km ( 3 4 m i . ) ; d y n a m i c e f f e c t s below t h a t .

There a re dynamic a c t i v i t i e sD i r e c t s o l a r h e a t in g i s

Over th e whole of t h e p la n e t t h e r e i s a l s o t h e e f f e c to f t h e a tm o s ph e re a t t h e e qu a t or r i s i n g a s i t i s w a r m e d bys u n l i g h t , a nd s i n k i n g n e a r t h e P o l e s , a s it c o o l s .

The Sur face of VenusRadar h a s re v e a l e d l a r g e - s c a l e f e a t u r e s t h a t s u g ge s tt e c to n i c s a n d im p a c t m o ldin g o f V e nu s ' t o p o g r ap h y . D e t a i l so f t h e s u r f a c e h a ve be en p ro v i d e d by t h e two S o v i e t l a n d e rs p a c e c r a f t .The r a d a r o b s e r v a t i o n s r e v e a l a l a r g e - s c a l e g r a n u la rs t r u c t u r e , s u g g e s t iv e o f a r o ck - st r ew n d e s e r t . L ar ge b u ts ha ll ow c i r c u l a r f e a t u r e s , m ost l i k e l y c r a t e r s , a r e f ou n d i ne q u a t o r i a l r e g i o n s . Some a re a s of h ig h r a d a r r e f l e c t i v i t y a r ei n t e r p r e t e d a s e x t e n s i v e l a v a f l o w s an d m ou nt ai no us a reas . Am a jo r chasm s t r e t c h e s 1 4 0 0 km ( 8 7 0 m i . ) n o r t h a n d s o u t h a c r o s s

t h e e q u a t or .A t f i v e d e gr ee s s o u t h l a t i t u d e and 320 d e g r e e s l o n g i t u d e

i s t h e h i g h m o u n t a i n B e t a w i t h a c r a t e r e d to p l i k e t h e l a r g eM a r t i a n v o l c a n o e s . T h e r e a r e a l s o a r c u a t e r i d g e s . One i s a tl e a s t 800 km ( 4 8 0 m i . ) l o n g . T h e r e a r e m o u n ta ino u s a r e a s w hichmay be vo l ca n i c o r a r e s u l t of c r u s t a l p l a t e m ovements.- more -

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P h o to g r a p h s fd r y r oc ky s u r f a c eunknown processes .r o c k s w i th r o u n d e dth e s e r o c k s may b et a k en p l a c e on the

rom o ne S o v i e t l a n d e r s p a c e c r a f t c o n f ir m at h a t h a s b ee n f r a c t u r e d a n d moved a b o u t byT h e s e c o n d l a n d e r p r od u ce d a p i c t u r e o fe dg es and p i t t e d s u r f a c e s . The forms ofe x pl a in e d by v o l c a n i c a c t i v i t i e s ha vi ngs u r f a c e .

T h e e x i s t e n c e of c r a t e r s o n Venus s u g g e s t s t h a t i t s s u r f a c eh a s n o t b ee n s u b j e c t e d t o t h e major t e c t o n i c c ha ng es e x p e r i e nc e don E a r th , b u t t h a t i t h a s p r o b a b ly e v o lv e d som ew hat a lo n g t h esame l i n e s a s Mars. Some o l d c ra te r e d t e r r a i n i s p r e s e r v e dw h i l e o t h e r p a r t s h a ve b ee n m o d i f ie d by t e c t o n i c s a nd vo l ca n is m .Venus migh t , inde ed , have evo lved t o a s t a g e b e t w e e n t h a t o fMars and t h a t of t h e E a r t h .Venera 9 l a n d e d a t 3 3 d e gr ee s n o r t h l a t i t u d e . I t s p i c t u r eshows heaps of r o c k s , m o s t l y a b o u t 30 c m ( 1 2 i n . ) o r more i n

s i z e , an d w i t h r a t h e r s h a r p e dg es . T h e f o r m at i o n o f t h e s e rocksi s b e l i e v e d t o be assoc ia ted w i t h t e c t o n i c p r o c e s s e s . The l a n d e ri s b e l i e v e d t o b e on t h e s i d e of a h i l l i n which t h e r e i s somedownward movement of t h e r oc ks . T h e s h a r p e d g e s a nd l a c k o fr o u n d in g of t h e r o c k s a t t h i s s i t e s u gg e st t h a t t h ey wereformed f rom breakage of h a r d , l a y e r e d r o ck s , p o s s i b l y a l av af l o wVenera 1 0 l a n d e d a t 1 5 d eg re es n or t h l a t i t u d e , i n an areaw i t h a much smoother su r f ac e . Th is i s b e l ie v e d t o be a p l a t e a uo r p l a i n o f g r e a t e r r e l a t i v e a g e t h a n t h e s i t e of Venera 9 .T h e r e a r e s o m e r o c k y e l e v a t i o n s w hic h a r e c o v e r e d w i t h ar e l a t i v e l y d a r k , f i n e - g r a i n e d s o i l . T h i s i m p l i e s t h a t t h e

rocks have b ee n w e a t he r e d , p o s s i b l y by ch e m i c al a c t i o n w i t ht h e a tmosphere . I t i s u n l ik e l y t h a t t h e g e n t l e w in ds a t t h es u r f a c e c o u ld have b e e n r e s p o n s i b l e f o r t h e w e a t he r i n g.G e n e r a l l y a t t h i s s i t e t h e m ate r i a l of t h e Ve nu si an s o i l i sd a rk , b u t t h e r e a re o u t c r o p s of l i g h t e r - c o l o r e d r o ck p e n e t r a t i n gt h e s o i l . Some o f t h e da rk s o i l f i l l s d e p re ss io n s of t h eo u t c r o p s . T h i s s u r f a c e i s i n t e r p r e t e d a s being much o l d e r andmore w e at h er e d t h a n t h e s u r f a c e s ee n a t t h e V e n e r a 9 s i t e . Thewea ther ing p ro ce ss may be a chem ica l i n t e r a c t i o n be tw ee n t h eh o t r o c k s a n d t h e a tm o sp h e re , p o s s i b l y by m i n e r a l a c i d s an dw a t e r v a p o r .Measurements made by t h e s p a c e c r a f t i n d i c a t e t h a t t h esar face r o c k s h a v e a d e n s i t y b e tw ee n 2 . 7 and 2.9 grams perc u b i c c e n t i m e t e r , w hic h i s t y p i c a l of t e r r e s t r i a l b a s a l t i cr o c k s .

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Surface temperatures appear to be high enough to makeportions of the surface glow a dull red. They are high enoughto melt zinc, but not most common rocks. The Venus rocks atthe two landing sites are about as radioactive as terrestriallavas and granites. This suggests that Venus, like Earth,has differentiated by heating to form a dense core and alighter crust.

Though it has dramatic major features, the surface issmoother than that of Earth and Mars. Radar-measured minimumto maximum height differences are 10 km (6 mi.)-- the heightof Mt. Everest. This compares with 20 km (12.4 mi.) on theEarth, from the bottom of the Mariannas Trench to the topof Everest. It compares with 30 km (18.6 mi.) on Mars, fromthe floor of the Hel las basin to the peak of Olympus Mons.Craters on Venus seem to be shallower than on the other worldsof the inner solar system.On the Moon and Mercury, and to a somewhat lesser extenton Mars, the ratio of craters diameter to depth is about 10to 1. On Venus, according to the radar surveys, the ratiois more like 100 to 1. The craters on Venus seem to beextremely shallow; the reason is not known. It could resultfrom plastic deformation of the hot surface or from someweathering process.

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MAJOR QUESTIONS ABOUT VENUS

0 A par t f rom ca rbon d i ox id e , o f w ha t does th e low er a tm os-p h e r e c o n s i s t , a nd how a r e i t s c o n s t i t u e n t s d i s t r i b u t e d ?Venus probably has l e s s t h a n s e ve n p e r c e n t o f g a s e so t h e r t h a n c a rb o n d i o x i d e i n i t s lower a tmosphere . M o s tl i k e l y c a n d i da t es f o r o t h e r ma jo r g a s e s a r e a rgon andn i t r o g e n . T h e r e a r e no measurements of l o w e r a tm osphereg a s e s o t h e r t h a n t h e S o v i e t m ea su re me nt s o f c a r b ond i o x i d e a n d w a t e r v a p o r .

0 Of w h at m a t e r i a l s a r e Venus ' c l ou ds made?The v i s i b l e cl o u ds p ro ba bl y c o n s i s t of s u l p h u r i c a c i dd r o p l e t s , p e r h a p s f or me d by s u l f u r compounds f r om t h es u r f a c e .

0 What o t h e r c l o ud l a y e r s a r e t h e r e ?Some k i n d s o f c l o u d p a r t i c l e s a b s o r b s o l a r u l t r a v i o l e tr a d i a t i o n . T h is i s needed t o e x p l a in t h e u l t r a v i o l e tp h o t o g r a p h s w hi ch show d a r k r e g i o n s . T h e s e d i f f e r e n tk i n ds of c lo u d p a r t i c l e s co u ld be m e t a l h a l i d e s o r s u l f u r .

0 What c a n t h e lowermost a tm osphere t e l l u s a b o u t t h ep l a n e t ' s s u r f a ce and i n t e r i o r ?S u r f a c e c o n s t i t u e n t s ( p o s s i b l y h yd ro ge n f l u o r i d e an dm e rc u ry a n d s u l f u r c ompound s) may b e d e t e c t a b l e i n t h ebottom 20 km ( 1 2 m i . ) o f t h e h o t , d e n se at m os p he r e.

0 How d o e s t e m p e r a t u r e , p r e s s u r e a n d d e n s i t y v a r y g l o b a l l ya b o ut t h e p l a n e t ?0 Why i s Venus ' lower a tmosphere so h o t ?

T h i s i s p r o b a b l y d u e t o a ru na wa y gr e e n h o u s e e f f e c t i nw hi ch h e a t f r om t h e S un i s m o r e e a s i l y a bs o rb e d th a nr e r a d i a t e d .0 What r o l e do v a p o r i z a ti o n - c o n d e ns a t i o n c y c l e s p l a y i n t h ea t m o sp h e re , a n d how do t h e s e p r o c e s s e s a f f e c t V e nu s 'weather?0 What a r e t h e c o mp o si ti on a nd t e m p er a tu r e p r o f i l e s of t h eupper a tmosphere?0 How does t em p era tu re va ry i n spa ce and t i m e i n t h e u pp era tmosphere?

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0 What a r e t h e ro l e s o f g l o b a l c i r c u l a t i o n a nd l o c a lt u r b u l e n c e i n s t a b i l i z i n g t h e up p er at mo sp he re ?0 What a r e t h e e f f e c t s o f t h e n e u t r a l p a r t i c l e s o n io no -

s p h e r e c o m p o s i t i o n ?0 How h i g h d o e s s u p e r r o t a t i o n ( f o u r- d a y r o t a t i o n ) of t h ec l o u d t o p s e x t e n d ?0 S i n c e Venus h a s n o m a g ne t ic f i e l d , t h e s o l a r wind i n t e r -a c t s d i r e c t l y w i t h t h e u p p e r a t m o s p h er e . What m ec ha ni sm sd oe s t h i s c r e a t e , and do t h e y a f f e c t t h e l o w e r a t m o s p h e r e ?0 Where d i d Venus ' a tm osp her e come from and wher e i s itgo ing?

The ma in so urc es o f Venus ' a tmosphe re p roba b ly a r e o u t -g a s s i n g from t h e i n t e r i o r , g a s e s from t h e o r i g i n a l s o l a rn e b u l a a n d some s o l a r wind p a r t i c l e s .

0 Where i s t h e wate r t h a t may have once been on Venus?The obv ious answer s a r e t h a t it e i t h e r " l e a k e d " t o s p a c eb e c a u s e o f h i g h Venus h e a t i n g , o r it w a s n e ve r t h e r e .Bu t numerous ques t i ons r ema in .

0 Why does V en us ' a t mo s p he r e d i f f e r so much from t h a t ofi t s " tw i n " p l a n e t , E a r t h ?0 I s a l l Venus t e r r a i n r e l a t i v e l y low com pared t o E a r t h a ndMars o r d o e s V en us ' " i n v i s i b l e h em i sp h er e" c o n t a i n h i g hmoun ta ins and deep c an y on s c o mp a ra b le t o t h o s e o n E a r t hand Mars?0 I s Venus a s c l o s e t o a p e r f e c t s p h er e a s t h e e q u a t o r i a lmeasu remen t s sugges t ?0 Does V enu s' i n t e r i o r c o n t a i n l a r g e c o n c e n t r a t i o n s of h i g hd e n s i t y m a t e r i a l .

T he l o c k i n g o f V en us ' r o t a t i o n t o E a r t h ' s o r b i t s u g g e s t ssuch m a s s c o n c e n t r a t i o n s .0 What i s t h e s u r f a c e t o po g ra p hy ?0 What i s t h e c o m po s it io n o f t h e s u r f a c e ?

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HI STORI CAL DI SCOVERI ES ABOUT VENUS

684 BC1 6 1 0

1 7 6 1

1 7 9 2

1807

1890

1 920

1 9 2 2

1932

1 9 4 2

1955

1 956

1957

N in ev ah t a b l e t s record o b s e r v a t i o n s of Venus.Us ing t h e n e w ly - in v e n t e d t e l e s c o p e , G a l i l e of i n d s t h a t V enus e x h i b i t s p h a s e s l i k e t hos e oft h

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Pioneer Venus 2 Press Kit