Pioneer Venus Fact Sheet 1975

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NOTE TO EDITORS. This fact sheet outlines the missionand basic scientific rationale for Pioneer Venus '78.It is suggested that it be retained in your files forfuture reference.

CONTENTS

Pioneer Venus 1978: Summary .................... 1Why Pioneer Venus? ........................... 3History of Pioneer Venus .................... 5The Mission ................................. 5Scientific Objectives ........................... QScientific Instruments ....................... 10The Spacecraft ................................ 13Tracking and Data Acquisition .................. 19Ground Data System .......................... 19Launch Vehicle ................................ 19

For Further Information:Nicholas Panagakor,Headquarters, Washington, D.C.(Phone: 202/755-3680)Peter WallerAmes Research Center, Mountain View, Calif.(Phone: 415/965-5091)

RELEASE NO: 75-274

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SUMMARY

NASA will send both an orbiter and a multiprobe space-craft to Venus in 1978 to determine the characteristics ofVenus's atmosphere and weather.

A better understanding of that cloud-shrouded planet'sclimate, with its constant environment and one-day year,could help scientists solve the mystery of Earth's drivingweather forces.

This knowledge in turn could be of immeasurable valuein predicting food shortages resulting from global climatechanges, and in dealing with changes in our planet's climateresulting from man's tampering.

The spin-stabilized multiprobe spacecraft consistsof a bus, a large probe, and three identical small probes,each carrying a complement of scientific instruments. Theprobes will be released from the bus 20 days prior to arrivalat Venus.

The large probe will conduct a detailed sounding ofthe lower atmosphere, obtaining measurements of the struc-ture, composition, and clouds from 70 kilometers (42 miles)to the surface. Primary emphasis is on the planet's energybalance and clouds. Wind speed will also be measured duringthe descent.

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Entering at points some 8000 km (5000 mi.) apart,the three -- -i probes will provide information on thegeneral circulation pattern of the lower atmosphere.Since the important motions are believed to be global,only a few observations are required. The probe buswill provide data on the Venusian upper atmosphere andionosphere down to an altitude of about 120 km (72 mi.),where it will burn up.

The orbiter mission is designed co globally mapthe Venusian atmosphere by remote sensing and radiooccultation, directly measure the upper atmosphere,ionosphere, and the solar wind/ionosphere interaction,and study the planetary surface by remote sensing.

The orbiter will be placed in a highly inclinedelliptical orbit with the lowest rcint in Venusian mid-latitudes at about 200 km (120 i.) altitude. Operationin orbit should allow investigation over at least oneVenusian year (225 Earth days).

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WHY PIONEER VflNUS?

Understanding Earth's Weather. Many climatologistsand meteorologists say that data on the weather and climatesof both Venus and Mars is of immediate importance. Bothplanets provide simpler (and different) models of how anatmosphere works on a planet, and understanding how theseatmospheres work should help in understanding Earth'sclimate and weather.

Earth's atmosphere and the forces affecting it areso complicated that very little progress has been made inpredicting climate. Climate is such things as: nextyear's weather, a cold summer, a multi-year African drought,a hundred-year cycle of higher-than-normal temperature.

The time for climatology (long-term weather research)is here, scientists say, for these reasons:

M Earth's population will double in the next 35 years.Masses of new population each year will mean great pressureon agricultural resources, such as food and fiber.

Some climatologists feel that recent cooler years maymean a years-long cold cycle. They point out that a 1.5-degree drop in the average temperature would eliminate theCanadian wheat crop, and that the massive Russian wheatdeal, for example, was basically a climatic event, reflec-ting a cold summer and short crop.

New understanding of Earth's atmosphere might even-tually be used for climate control, but more immediately,if an adve-se climate trend is known, agricultural plan-ning could limit its effects.

e The current concern about destruction of theEarth's protective ozone layer by aerosol spray accumula-tions began specifically through space observations of Venus,Professor Richard Goody of Harvard points out. The odds areabout two to one, he adds, that this problem is real, andman cannot afford to take such chances with his environment.

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-4-Planet Atmosphere Modeling. Scientists want to crankdata on the atmospheres of both Venus and Mars into theirtheoretical models for the Earth's upper and lower atmos-pheres--and then compare results with observed effects.Such information for Mars will come with the Viking landing

in 1976; and for Venus from Pioneer Venus.The advantages of Venus are in its simplicity. AsProfessor Verner Suomi of the University of Wisconsin pointsout: Venus's day is nearly the same length as its year (225Earth days), and hence its weather is nearly the same as itsclimate. And hence, much information on its climate shouldbe obtainable through a relatively brief study.Though most people may not realize it, almost nothingis known about thL .eather and climate of Venus, and severalscientific disciplines would find immediate use for some ofthe basic facts on Earth's nearest neighbor.Planets As Laboratories. Venus's simplicity andadvantages of this are shown by four differences from Earth:1. Venus is always covered by clouds, so there isno effect of alternating cloud cover and sunlight.2. Venus has no oceans so there is no effect of theinterrelationship of ocean and land areas.3. Venus has no tilt on its axis, so there are noseasons. (Earth's seasons are a result of its axial tilt.)4. Venus rotates only once in a Venusian year (225Earth days), and this means it does not have a coriolisforce of rotation, which along with solar heating, drivesthe Earth's weather.These simplifying factors make the whole planetand its atmosphere like a laboratory experiment in whichseveral variables are held constant in order to look atother variables, (Scientists do this constantly in theirlaboratories.)

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Questions Important to Man

Scientists raise some other questions of importanceto man that may be answered by the comparative meteorologyof planets.

These are:What mechanisms have kept the Earth's climate rela-tively benevolent for several billion years?Why have the other terrestrial planets taken such

different courses? Mars and Venus spacecraft so far haveprovided hints.

What are the stabilizing and destabilizing feedbackmechanisms that determine a planet's climate? How strongare they?

What has happened in the past on Mars to cause erosionas if there were once rivers?Where is the water that was on Venus originally?Scientists explain that the laws of chemistry andfluid dynamics are universal. Theoretical models of the

Earth's upper and lower atmospheres can be tested over awide range of boundary conditions by seeing how well thesemodels simulate the atmospheres of Mars or Venus.

HISTORY

The Pioneer Venus Project was assigned by NASA'sOffice of Space Science to Ames Research Center, MountainView, Calif. , in January 1972, where system defin4tionwas carried out with competitive studies by two major firms.In February 1974, Hughes Aircraft Co., El Segundo, Califor-nia was selected to build the spacecraft.

MISSIONPioneer Venus is the first NASA mission developed

specifically to investigate the atmosphere of Venus ona planetary scale by direct measurements. Pioneer Venusemploys two spacecraft, an orbit combined with a multi-

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TYPICAL ENTRY POINTS FOR PIONEER--VENUS ATMOSPHERE PROBES


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probe craft, to provide for the first time correlation ofdirect atmosphere measurements with those taken remotelyon a planetary scale over 243 days, or more than oneVenusian year.The project uses two spacecraft systems with manycommon features. A bus-type basic spacecraft has beendesigned to which specific subsystems are added to meetrequirements ot the two planned missions.The two missions have similar launch and interplane-tary phases, but have very different planet encounterphases.A large probe and three small probes integrated withthe bus provides the multiprobe spacecraft. A Venus-orbitinsertion rropulsion unit and a high-gain narrow-beam anten-na for data return are added to the bus to provide the or-biter spacecraft.Low-cc-t concepts of commonality, use of existingdesigns, increased design margins to reduce testing havebeen made possible by use of the relatively large pay-load Atlas-Centaur launch vehicle.Approximate transit time of the Multiprobe Spacecraftis 125 days. At about 20 days before Venus encounter, theMultiprobe Spacecraft will be maneuvered for probe targetingand the probes will be released from the Pus.The Probes will be decelerated aerodynamically andwill have a descent time to the surface of about one hour.They will be designed to operate to, but not on the sur-face. After the Probe release, the Bus will be targetedfor a shallow atmospheric entry to obtain measurements ofthe upper atmosphere prior to burnup, which will occur atan altitude of about 110 km (65 miles).

SCIENCEScientific priority for the Venus mission wasestablished by the scientific community in two documents;"VENUq,: Strategy for Exploration. Report of a Studyof the Space Science Board." National Academy ofSciences, Washington, D.C., 1970.

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"Priorities for Space Research 1971 - 1980. Reportof a Study of the Space Science Board."National Academy of Sciences, Washington, D.C.,1971. /The scientific investigations for the project wereselected by NASA Headquarters in June 1974. For the Multi-probe Mission, this selection followed a tentative selec-tion made in June of 1973.

SCIENTIFIC OBJECTIVESMultiprobe Mission. The scientific objectives forthe Multiprobe Mission are the study of the dense regionsof the Venus atmosphere to find:(a) The nature and composition of the clouds(b) The composition and structure of the atmospherefrom the surface to high altitudes(c) The general circulation pattern of the atmosphereThis requires entry probes that enter at several selec-ted locations for direct measurements of the clouds andlower atmosphere of Venus. Onboard instruments will deter-mine if the clouds consist of condensed vapors or solidparticles; if solids, whether they are ice crystals ordust; the size of the particles; and whether there are

several cloud layers. Measurements will also help deter-mine whether minor constituents are uniformly mixedthroughout the atmosphere; whether any constituents couldmelt or condense to form liquids on the surface of theplanets; if argon, neon, or nitrogen are present in th eatmosphere, where it originated and how the amount presentrelates to the amount of the major constituent, C02 ; whattypes of ions are present in the upper atmosphere; and whatthe photochemistry of that region is. Finally, these entry-probe measurements will help determine the variation oftemperature and composition of the atmosphere with altitude;whether the polar regions are cooler than the equatorialregion; characteristics of the interaction between the cloudsand atmospheric heat sources; the cause of the high surfacetemperature, whether from a "greenhouse" or other effect;the extent to which the atmosphere accounts for a redistri-bution of surface or internal material; variation in tem-perature between the dayside and the nightside of the planetand windspeed profiles from top of the atmosphere to thesurface.

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Besides probing the dense lower atmosphere of Venus,instruments carried on the Pioneer Venus Bus will deter-mine the neutral and ion species at high altitudes.Orbiter Mission. Scientific objectives for thePioneer Orbiter Mission to Venus are:(a) Direct measurement of the detailed structureof the upper atmosphere and ionosphere(b) Investigation of the interaction of the solarwind with the Venus ionosphere and with thesmall magnetic field in the vicinity of theplanet(c) Determination of the characteristics of theatmosphere and surface of Venus on a planetary

scale by remote sensing experiments(d) Determination of the planet's gravitationalfield variations from the spacecraft's orbitabout VenusUnderstanding the physical properties of the upperatmosphere requires information on a planetary scale overa period of time, which only an orbiter can provide. Adetailed investigation of the interaction between thesolar wind and the planet will allow mapping from varyingsolar-aspect angles. Orbiters can also make the beststudies of general characteristics of the Venus surface

and atmosphere on a planetary scale.Large numbers of orbits will provide sufficient data

to calculate the planet's mass distribution and the mechani-cal and other properties of Venus's interior.

SCIENTIFIC INSTRUMENTS

Multiprobe MissionTwelve scientific investigations have been selected

to provide onboard scientific instruments for the LargeProbe, the three Small Probes, and the Probe Bus. Speci-fic investigations and investigators are:

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Large ProbeNeutral Mass Spectrometer John Hoffman - University of

TexasGas Chromatograph Vance Oyama - NASA/ARCAtmosphere Structure Alvin Seiff - NASA/ARCSolar Flux Radiometer Martin Tomasko - University

of ArizonaInfrared Radiometer Robert Boese - NASA/ARCCloud Particle Size Spec- Robert Knollenberg - Particletrometry Measuring SystemsNephelometer (Cloud Jacques Blamont - UniversitySensor) of ParisSmall Probes (3)Atmosphere Structure Alving Seiff - NASA/ARCNephelometer Jacques BlamontNet Flux Radiometer Verner Suomi - Universityof WisconsinBusNeutral Mass Spectrometry Vulf von Zahn - University ofBonn, West GermanyIon Mass Spectrometry Harry Taylor - NASA/GSFC

Radar and Radio Science Teams. Radio Science Team willuse the changing characteristics of the spacecraft communica-tions link, as it passes through the Venusian atmosphere. Theseinvestigations determine atmosphere structure and composition,wind velocities, and atmosphere turbulence. With multipleground station coverage of the entry vehicles, the team willalso determine the horizontal velocity (wind drift) character-istics of the Venusian atmosphere.

Orbiter MissionTwelve scientific investigations have been selectedto provide onboard scientific instruments for the orbiter

spacecraft system. The specific investigations and investi-gators are:Neutral Mass Spectrometer Hasso Neimann - NASA/GSFCIon Mass Spectrometer Harry Taylor - NASA/GSFCRetarding Potential William Knudsen - LockheedAnalyzer Missile and Space Co.

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Electron Temperatu'e Larry 3rpce - NASA/GSFCProbeUltraviolet Spectrometer Alan Stewart - Universityof ColoradoSolar Wind/Plasma John Wolfe - NASA/ARCAnalyserMagnetometer Christopher Russel - UCLAInfrared Radiometer F. H. Taylor - JPLCloud Photopolarimeter James Hansen - GoddardInstitute of

Space StudiesRadar Altimeter Team*Electric Field Detector F. L. Scarf - TRWGamma Ray Burst Detector W. D. Evans - LASLRadio and Radar Science Teams. The Radar Science

Team will analyze the oriboard radar instrument data todetermine Venusian topography and surface characteristics.The Radio Science Team for the Orbiter Mission will analyzechanges in the spacecraft communications link as it passesthrough the Venusian atmosphere, and in many cases is occultedby the planet, to determine characteristics of this atmosphere.Atmosphere composition and density cloud locations, and turbulencecharacteristics will be investigated as well. Planetary andcelestial mechanics values and upper atmosphere drag effectswill also be found.

* Radar Altimeter Team Members: G. Pettengill, MIT:D. Staelin, MIT; W. Kaula, UCLA; W. Brown, JPL.

Interdiscnpli.ary Scientists. Interdisciplinaryscientists have been selected for both the Multiprobe andOrbiter Missions to provide assistance in analyses of theVenusian atmosphere. For the Multiprobe Mission they are:

Dr. Siegfried Bauer NASA/GSFCDr. Thomas M. Donahue University of MichiganDr. Richard M. Goody Harvard UniversityDr. Donald M. Hunten Kitt Peak National ObservatoryDr. James B. Pollack NASA/ARCDr. Spencer NASA/GSFCFor the Orbiter Mission they are:

Dr. Gerald Schubert UCLADr. Harold Masursky U.S. Geological SurveyDr. Thomas M. Donahue University of MichiganDr. G. McGill University of MassachusettsDr. Andrew F. Nagy University of Michigan

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ORIGINAL PAGE 1s01 ' POMR QUALITYL ooneer Venus Or'iltI.Ar

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K -18-The Large Probe and three Small Probes are each totallyindividual spacecraft systems that provide the recuired sub-systems to carry science payloads thrcugh atmospheric entryto the surface of Venus, while maintaining direct communicationlinks with Earth-based DSN stations.The Large Probe. The Large Probe weighs about 286 kg.(630 lbs.), and is 145 cm. (about five feet) in diameter.It will return data at 256 BPS and carry 35 kg. (75 lbs.)of instruments.The forward end of the Large Probe has a carbon phenolicheat shield for heat protection and aerodynamic stabilityduring atmosphere entry, and a parachute descent subsytem.The remaining probe subsytems, data handling, power,thermal protection, communications, and structure, aremounted inside the probe pressure vessel, as is the sciencepayload. The pressure vessel is sealed against the Venusianenvironment. A single, hemispheric omni-directional antennais provided on the aft end of the probe pressure vessel.The Small Probe. The Small Probe configuration isidentical for each of the three Small Probes. Each probeis 71 cm. (28 inches) in diameter, weighs 86 kg. (190 lbs.),transmits data at 16 to 64 bits per second, and carries 8 kg.

(18 lbs.) of instruments.The pressure vessel for the Small Probes seals the SmallProbe subsystems and the science payload from the hostileVenusian atmosphere. No parachute descent system is used forthe free-falling Small Probes.The high-speed aerodynamic designs for both the Largeand Small Probes are similar with a 45 degree conical fore-body (heat shield) used in both designs.

The Orbiter SpacecraftThe Orbiter Spacecraft system, as with the Multiprobe,uses the basic Bus. At the forward end of the Bus is thebearing and power transfer assembly to mechanically despin theparabolic, high-gain antenna. With the spacecraft spinaxis spin-stabilized perpendicular to the ecliptic plane(Earth's orbit plane), the cespun, high-gain antenna reflec-tor will be focused on the Earth during its interplanetary phase

and throughout its orbital lifetime. An orbit insertionmotor will be mounted at the other end of Lhe Orbiter Space-craft to place the spacecraft in Venus orbit. A slightlylarger solar array will be provided to meet the largerpower demand of an orbiting spacecraft. A larger datastorage unit also is being provided.

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All Orbiter Spacecraft scientific instruments willbe on the equipment platform inside the Bus. The magnetometersensor is mounted at the end of a boom to insure no magneticinterference from the spacecraft.

TRACKING AND DAT. ACQUISITION

Tracking and data acquisition for the Multiprobe andOrbiter Spacecraft will be provided by the NASA Deep SpaceNetwork (DSN) operated by NASA's Jet Propulsion Labora~ory,Pasadena, Calif. A subnet of Deep Space Stations with26-meter (85 foot) diameter antenna systems and around-the-world coverage will provide basic tracking support. The64-meter (210 foot) diameter antenna subnet will providecoverage during critical phases of the mission such asreorientation, velocity corrections and Venus encounter.

GROUND DATA SYSTEMThe ground data system for the Pioneer Venus Missionsinvolves facilities of the Deep Space Network which includesthe Deep Space Stations, and the Network Operations facili-ties at JPL, and th b NASA Ground Communications Network andPioneer Mission Operations and Computing Center facilitiesat Ames Research Center.

LAUNCH VEHICLEThe launch vehicle for the Pioneer Venus missions isthe AtlaL SLV-3D/Centaur D-1AR vehicle.The first-stage Atlas is powered by two boosterengines, a sustainer engine, and two small vernier engines.The second stage Centaur employs liquid hydrogen andliquid oxygen as propellants. Primary thrust is providedby two engines which gimbal for pitch, yaw, and roll con-trol, and have a restart capability.

October 1975

Documents

Pioneer Venus Fact Sheet 1975