Viking Mission to Mars

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An Educational Publicationof theNational Aeronautics andSpace AdministrationNF-76/6-75

TO INCREASE KNOWLEDGE ABOUT ONE OF OURSISTER PLANETS

miles) from Earth on the other side of the Sun. Each3400-kilogram (7500-pound) spacecraft will belaunched by the Kennedy Space Center atop a TitanIII/Centaur rocket during a 30-day launch periodbetween mid-August and mid-September 1975.

The National Aeronautics and Space Administra-tion will launch two spacecraft to Mars in 1975 tosoft-land on the surface and test for signs of life. Several days after the spacecraft go into orbit

around Mars, each will separate into two elements-a lander and an orbiter. Each lander, containing itsown scientific laboratory, will descend to the Martiansurface to conduct experiments and televise its sur-

The two Viking mission spacecraft will travel some700 million kilometers (440 million miles) throughspace on nearly a year's journey, arriving when theplanet is about 330 million kilometers (206 million

Earth based photograph of Mars.

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roundings. The orbiters will observe and map Marsfrom above and relay to Earth data radioed from thelanders.

fortable climates-similar to that on Earth-thechances of finding life are substantial. We will havestrong reason to believe that many inhabited solarsystems-perhaps billions-lie around us in theGalaxy.he lander's science instruments will collect data

for transmission to Earth, direct or via the orbiter,including panoramic, stereo color pictures of its im-mediate surroundings; molecular organic and in-organic analyses of the soil; and atmospheric,meteorological, magnetic, and seismic character-istics. It will also make measurements of the atmos-phere as it descends to the surface.

Viking exploration may also settle a question ofequal importance for determining the probability oflife arising out of nonliving chemicals: Is it possiblethat Mars is lifeless today, but was once the site ofa rich variety of life that disappeared later in thehistory of the planet?

The entire lander system will be heat-sterilizedbefore launch to assure that Mars will not be con-taminated by Earth microorganisms. Sterilizationwill assure that chances of contaminating Mars areless than one in a million.

The question turns on the abundance of water.Mars is relatively dry today, but discoveries byMariner 9 of volcanism and riverbeds on Mars sug.gest that the planet could have had a substantialsupply of water that at times became available inliquid form. The water could have remained longenough to permit some form of organism to evolve,only to be snuffed out later when the vital gases andwater on Mars disappeared. If that happened, wemay still find traces of one-time life on the surface.

IMPORTANCE OF VIKINGIs Earth truly a unique life-supporting planet in

the immense totality of creation? There is growingevidence to the contrary. Our Galaxy contains 100billion stars, many of which are surrounded byfamilies of planets, according to the best astronom-ical evidence. In studying these stars with tele.scopes, man has been able to verify that the basicchemicals of which Earth is composed are foundthroughout the universe. In just the last century, ithas been proven that the ratio of these elements inour own solar system is consistent with the overallratio generally observed throughout the universe.

Even if no signs of life, extant or extinct, are foundon Mars, it is crucially important to study the natureof other planets presumed to have originated atabout the same time and by the same processes asEarth. In this context, finding that Mars is withoutlife could be nearly as important as the discovery oflife forms. The study of a planet-not too dissimilarfrom Earth-which has evolved in the absence of lifewould provide us with a yardstick with which to de.termine, for example, how the atmosphere of Earthhas been influenced by the advent of biological proc-esses. Comparative planetology will be of great valuein understanding our own Earth, and in formulatingmeasures to protect our own environment.

Further, radio astronomers have detected simpleorganic compounds in interstellar space. Recent de-tection of complex organic compounds has in-creased our confidence that life could evolve onother worlds. But science cannot calculate the prob-ability of encountering extraterrestrial life in thissolar system and in other solar systems on the basisof this evidence. We cannot tell conclusively by labo-ratory studies or theoretical reasoning whether theevolution of life is vanishingly improbable or quitelikely. We can only estimate the probability by look-ing around us for signs of extraterrestrial life. Thenearest reasonable planet on which to look is Mars.

These possibilities make the exploration of Marsthe most important objective of planetary explora-tion for many decades to come.

PREVIOUS MARS MISSIONSThe Mariner Mars flights have supplied most of

the Martian data which permit us to plan and de-sign the Viking mission. These data include atmos-pheric composition, atmospheric structure, surfaceelevations, atmosphere and surface temperatures,topography, figure of the planet, and similarinformation.

Mars is dry, cold and less favorable than theEarth for the support of life, but it is not implacablyhostile. Life could exist in the harsh climate of Mars,and if it does, we will know that on planets with com-2


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As a result of the Mariner missions, much ex-perience has been gained also in conducting anorbital mission, inserting a spacecraft into plane-tary orbit, and processing large quantities of digitaldata. The design of the Viking orbiter is based onthe Mariner spacecraft, with many of the subsys-tems being nearly identical.

The Mariner flights have provided the logicalsteps in the exploration of Mars which had to pre-cede Viking, just as Viking is a necessary preludeto eventual sample return by automated rovingvehicles and possible manned missions to Mars.VIKING LAUNCH

The launch period was selected to provide a mini.mum-energy trajectory from Earth to Mars. Oppor-tunities for such flights occur at approximately 25.month intervals. The Titan booster is a two-stage liquid-fueledrocket, with two additional large, solid-propellant

rockets attached. It is a member of the Titan familyused on NASA's manned Gemini program. The Cen-taur is a liquid oxygen-liquid hydrogen, high-energy upper stage used on unmanned Surveyorflights to the Moon and on Mariner flights to Mars.

In separate launches at least 10 days apart, twoTitan/Centaur rockets will lift off from their Floridapads, each placing the Centaur upper stage and theViking spacecraft into a 180-kilometer (115-mile)parking orbit. After coasting for 30 minutes, theCentaur will reignite to send the spacecraft on itsjourney to Mars. At liftoff, the solid rockets provide 9.1 millionNewtons (2.16 million pounds) of thrust. When the

solids burn out, the first stage of the Titan boosterignites. After that comes second-stage ignition asthe first stage shuts down. The Centaur ignites onsecond stage shutdown to inject the spacecraft intoorbit. Then after a 3D-minute coast around theEarth into position for restart, the Centaur reignitesto propel Viking on its Mars trajectory. Once thismaneuver is completed the spacecraft separatesfrom the Centaur which subsequently is deflect~daway from the flight path to prevent its impact onthe surface of Mars.

Viking Titan/Centaur launch vehicle prior to proof launch.

Shortly after separating from the Centaur, theorbiter portion of the combined orbiter-lander space-craft orients and stabilizes the spacecraft by usingthe Sun and a very bright star in the southern sky,Canopus, for celestial reference.JOURNEY THROUGH SPACE

Viking may have to make several flight correctionsduring its journey. These corrections will be basedon navigation information acquired from Earth-based tracking of the spacecraft. Thus by firing itsorbit-insertion engine several times in a prede-

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termined direction the spacecraft's trajectory will bealtered to insure interception of Mars.

TRACKINGThe Deep Space Network (DSN) supporting Vik

ing will consist of two networks, each with threestations having 26-meter (85-foot) antennas andone network of three stations with 64-meter (210foot) antennas. The 64-meter stations are locatedin California, Australia, and Spain. During most othe Viking interplanetary flight, the spacecraft wilbe in contact with one of the stations. During orbitaloperations at Mars, there will be continuous trackingof the spacecraft by one of the larger DSN stations.

Power is produced by solar panels which open upafter injection toward Mars, spanning more than 10meters (33 feet) tip to tip. Batteries are used whenthe panels are shaded from the Sun or when peakpower is demanded. In turn, the batteries arecharged by the solar panels. Small attitude controljets on the ends of the orbiter's four solar panelskeep the spacecraft stabilized and oriented.

The orbiter wi II furnish electric power to the landeruntil separation. The lander has a set of recharge-able batteries which will be charged during Mars sur-face operations by two radioisotope thermoelectricgenerators (RTG's) being provided by the EnergyResearch and Development Administration (ERDA).The RTG's convert heat produced by the nuclearsource into electricity, making the landers independ-ent of solar energy.

In addition to tracking the precise path of thespacecraft, this system processes three kinds odata: engineering telemetry, science, and commandsto the spacecraft to initiate or change programmedoperations.

Communication with Viking will take longer andlonger as the spacecraft gets farther away fromEarth. When it reaches Mars, a one-way messagewill take 20 minutes. This means a roundtrip minimum of 40 minutes will pass before a commandfrom Earth can be received by the spacecraft in response to its initial transmission. For this reasonautomation is essential. Operations that cannot binterrupted, such as the soft landing, will be performed completely automatically by an onboard preprogrammed computer.

Information concerning flight performance istransmitted to Earth throughout the flight. An on-board computer controls all spacecraft operationsand supplies commands for trajectory correctionsin addition to controlling the orbiter's scientificequipment while in orbit. At the same time, groundcontrollers will be monitoring all phases of the mis-sion via the worldwide tracking facilities.

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INJECTION INTO MARS ORBIT AND LANDING LANDINGAs the spacecraft nears the planet, it is maneu-

vered into the proper attitude for being placed inorbit. The engine will be fired for nearly an hour toplace the combined orbiter and lander in a highlyelliptical orbit of 1500 kilometers (930 miles) by33,000 kilometers (20,500 miles) and with a periodof approximately 24 hours to match Mars' rate ofrotation.

The Viking lander instruments, weighing about91 kilograms (200 pounds), are divided into twoareas of investigation, those used during the atmos-pheric entry phase prior to landing and those usedon the Martian surface. Entry data will provide in-formation on the composition of the upper atmos-phere and on the pressure, temperature, and densityof the lower atmosphere.

The spacecraft will be tracked for at least 10 daysafter achieving orbit to obtain detailed informationfor a precise landing, as well as to check out pre.selected landing sites. Mission controllers will haveas many as 50 days to further study the planet toconfirm optimum landing sites.

When a landing area has been determined, thelander's power is turned on, and the lander withinits aeroshell separates from the orbiter. The aero-shell shields the lander against the intense heat gen-erated as it decelerates during the high-speed entrythrough the thin CO2atmosphere.

The lander is prepared for separation after con-firmation of a landing site based on observationaldata from Mariner 9 as well as Viking observations.An ideal landing area would be relatively low, warm,wet, safe, and interesting.

During descent and landing, the lander maintainscommunication with the orbiter, which serves as arelay station between Mars and Earth.

A 50-foot parachute is deployed to further decel-erate the lander at about 6000 meters (20,000 feet)above the surface. Shortly thereafter, the aeroshell isjettisoned. The parachute is jettisoned about 1.6kilometers (1 mile) above the surface, and the termi-nal propulsion system begins firing its three engines.This is a rocket subsystem similar to that used bythe Surveyors to soft-land on the Moon.

Mission sequence of events.

The engines, firing about 30 seconds, slow thelander for a soft landing and shut down just as thefoot pads touch the surface.

As soon as the lander is on the surface, all sys-tems except those necessary for science operationsare shut down to conserve power. The lander's com-puter immediately determines its attitude on the sur-face to provide information necessary for aligningthe S-band transmitting/receiving antenna withEarth.

Scientific data and monitoring information areimmediately relayed to Earth via the orbiter. At thesame time, the two 35-watt (electric) nuclear-fueledgenerators are recharging the lander's batteries sooperations can be continued for at least 90 days.

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The lander instruments consist of a gas chro-matograph/mass spectrometer for detecting andidentifying organic molecules, the building blocksof life, in the soil; a biology instrument capable ofperforming three different life detection experi-ments; three meteorology sensors; a seismometer;an X-ray fluorescence spectrometer for inorganicchemical analysis of surface material; two facsimilecameras; and magnets, plus a collector head on aboom to collect soil samples and measure surfaceproperties.

The cameras will give the 66 principal scientistsparticipating in Viking a vastly improved view, incolor and stereo, of the Martian topography and sur-face structure. Of even greater interest to lifescientists will be the results obtained from theorganic and inorganic analyses of the Martian soil,and from the three life-detection experiments.

Lander instruments will also determine the tem-poral variations of atmospheric temperature andpressure, and wind speed and direction; seismo-logical characteristics of the planet; the atmosphericcomposition and its variation; and the magnetic andphysical nature of the surface. Exploded view of the Viking spacecraft.

ORBITER VIKING INVESTIGATIONSWhile experiments are proceeding on the surface,

the Viking orbiters will be circling overhead, observ-ing the landing site, so that local measurementsmade by the landers may be correlated with overallsurface effects. The orbiters will look for conditionssuch as buildup of dust storms, cloud formation,variations in temperature and humidity, and thepassage of the seasonal wave of darkening.

THE SEARCH FOR LIFEIf life exists on Mars, it is probably in the form of

microorganisms. To search for evidence of theirexistence in the surface samples, three different in-vestigations will be performed. The biology instru-ment will examine three different soil samples, whichwill also be analyzed by the molecular analysis in-strument for organic content and by the X-ray fluo-rescence spectrometer for chemical composition.

The Viking orbiters each carry about 65 kilo-grams (144 pounds) of instruments, consisting oftwo high-resolution television cameras, an infraredspectrometer and an infrared radiometer. These in.struments will be employed to survey landing sitesboth before and after lander deployment to providedata on surface temperature, atmospheric waterconcentration, the presence of clouds and duststorms and their movement, the topography andcolor of the terrain, and other information to de-scribe the broader aspects of the landing site andits relationship to the overall planet characteristics.This information will then be integrated with thelander data for a better understanding of what ishappening on the surface.

Photosynthetic Analysis. Photosynthesis is theprocess by which organic compounds, such as car-bohydrates, are formed by combining basic com-pounds like carbon dioxide, water, and salts, usingthe Sun as a source of energy. It is a basic life.sustaining process; plant life on Earth consumescarbon dioxide during photosynthesis.

In the Viking experiment, a soil sample is inocu-lated with carbon dioxide gas that has been labeledwith a radioactive tracer. The soil and gas are thenallowed to incubate in simulated Martin sunlight for

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a period of time. Later, all remaining gas is flushedout of the chamber and the sample is heated to 6000C (about 11000 F). The heating will liberate any ofthe labeled carbon dioxide incorporated into organicmolecules in a photosynthesis process, and theliberated gas can then be measured. A substantialquantity of labeled gas would indicate that a photo-synthetic process had taken place, which would bestrong evidence of the presence of living plant-likeoganisms.

bon gases that can be measured. A sharp rise in theproduction of such metabolic gases would be strongevidence that life is present.

Biology instrument.

Metabolic Analysis. It is possible that Mars organ.isms sustain life by obtaining nourishment fromorganic materials rather than through photosyn-thesis. Therefore, an analysis very similar to thephotosynthesis reaction analysis has been planned,which will "feed" organic compounds containingradioactively labeled carbon to the soil sample--sugar, as an example. If organisms are in thesample, and they can consume the food offered tothem, they will discard-as waste-radioactive car.

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Respiration. As metabolism takes place, the com.position of the gaseous environment is in a state ofcontinuous change. For this analysis, which is closelyrelated to the metabolic conversion analysis alreadydescribed, a soil sample is moistened with nutrients.

MOLECULAR ANALYSISThis investigation will perform a chemical analy-

sis of the Martian atmosphere and soil. The chem-istry is important in all scientific aspects of under-standing the planet, but particularly so for biology.All known life is organic (composed of substancessuch as sugars, fats and proteins).

A sample of the Martian atmosphere is pumpedinto the chamber headspace above the sample andmonitored. Changes in the composition of the gaseswill again be evidence of the existence of life as aresult of cellular respiration.

The composition of the atmosphere is importantin understanding the overall chemistry of the planetand in attempting to trace the history of itsformation.n the event of positive results from one or moreof these experiments, a control sample will be pre-

pared to further verify the evidence. The controlsample is heat-sterilized to insure that all livingorganisms are destroyed before analysis is made.Then, if the result is changed, scientists can berelatively certain that the original result was due tothe existence of living organisms.

Both the atmospheric and soil analysis consist ofdetecting and identifying specific molecules byusing a device called a gas chromatograph-massspectrometer. For the atmospheric analysis, themethod is simply to "sniff" the Martian atmospherewith the mass spectrometer. The device is sensitive

Block diagram of the biology instrument.SOl L SAMPLE

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PHOTOSYNTHETICANAL YSIS METABOLIC ANALYSIS METABOLIC PROCESS8


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Typical photograph taken with one of the lander cameras.

to one part per 10 million, and will detect any vola.tile chemical whose molecular weight is less than200. Seasonal variation in atmospheric compositionmay strongly influence, or be evidence of, biologicalactivity, as might unusual isotope ratios or com-pounds in unstable equilibrium with the environ-ment.

tion will identify rock types in the vicinity of thelander and is important in determining the degreeof differentiation that has occurred on the planet.The inorganic composition and character of the sur.face are important to the biologists as well as togeochemists and planetologists.

The analysis will be performed by an X-ray fluo-rescence spectrometer. The instrument consists oftwo radioisotope X-ray sources which bombard thesurface material, inducing X-ray fluorescence, andfour thin-window proportional counters which de-tect and differentiate the spectrum of the inducedfluorescence. The instrument is capable of quanti-tative analysis for most major, minor, and sometrace elements with a sensitivity range of 0.02 per-cent to 2.0 percent depending upon the element.

The soil analysis is more complex. The instrumentcontains several tiny ovens; each can receive a soilsample from the soil processor. The ovens areheated to 5000 C (about 9000 F). During heating theorganic compounds are vaporized and analyzed. Ifa living system has not evolved on Mars, the organicanalysis may help explain and provide knowledgeof prebiological organic chemical evolution. A highyield of organic material would support a positiveactive biology result or, in the absence of a positiveactive biology finding, suggest the possible presenceof organisms which did not respond to the condi-tions in the biology instrument; a high yield oforganic material in the absence of a positive resultfor active biology could be indicative of earlier bio-logical activity.

The sample to be analyzed will be obtained by thesurface sampler and delivered to the instrument bythe soil processor and be a part of the same sampleexamined for organic content and living organisms.IMAGING SYSTEMINORGANIC CHEMISTRY

Viking will extend our knowledge of Mars byexamining unique sites at a higher resolution thanpreviously obtained. The Viking visual imaging sys.

This investigation will perform an elementalanalysis of the Martian soil. The elemental composi-

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tem on the orbiter will obtain pictures with a resolu-tion of about 39 meters (130 feet) per TV line at theorbiter minimum altitude of 1500 kilometers (930miles), permitting one to distinguish objects aboutthe size of a football stadium.

The facsimile camera operates by using a smallmirror which scans a vertical line and projects theimage light intensity onto a pre-selected detector.After that line is scanned, the camera is turned about0.10 and another vertical line is scanned. This proc-ess is repeated many times to build up an imagefrom the many scan lines. The detector is a smallphotocell that converts the light in the picture imageto an electronic signal which is then transmitted toEarth. The picture is obtained by reversing the proc.ess, converting the electronic signal to a light whichis scanned over a film to prepare a negative formaking the photograph.

The orbiter system consists of two identicalcameras, each composed of a telescope, filters, TVtube, and appropriate electronics.

Prior to initiation of the landing sequence, theorbiter cameras will aid in confirmation of the pre-selected landing sites or, if necessary, in the identi-fication of suitable alternatives. After landing, thelander observations will be available to verify andextend the interpretation of orbiter camera picturesfor a more detailed understanding of the physicaland chemical character of the surface in areas otherthan the landing sites. Valuable data are also ex-pected relative to variable features such as clouds,dust storms, and seasonal albedo changes.

ENTRY SCIENCEAs the lander enters the atmosphere and de-scends to the Martian surface, there will be an op-

portunity to learn about the structure and chemicalcomposition of the atmosphere.

Atmospheric chemical composition will bemeasured at short intervals during the lander aero-shell's descent to identify changes in compositionat different altitudes. This investigation will showthe proportions of gases such as carbon dioxide,nitrogen, oxygen, argon, and of particles such asions and electrons. Pressure, temperature, anddensity variations with altitude will be measured

Picture 1 is taken by Camera 1 and stored in thetape recorders. Picture 2 is then taken by Camera2 and, while it is being put in the tape recorder,Camera 1 is prepared for taking Picture 3 by erasingthe previous picture from the TV tube. This processis repeated until the required pictures are acquired.

LANDER CAMERAClaw and camera systems tested.On the Viking lander, two facsimile cameras will

substitute for man's eyes. They can be directed tolook down at the ground nearby or perform a 3600panoramic scan of the entire landscape.

The cameras will take pictures in high qualityblack-and-white and color, and in the near infraredregion of the spectrum. Pictures taken by the twocameras can also be combined to yield stereoscopicviews of the areas.

The pictures will convey a great deal of informa-tion about the geological character of the surface ofMars, and could identify any higher form of life thatmay exist. Clouds and dust storms may be seen.The cameras will help in selecting the places wherethe surface sampler is to dig for soil specimens to beanalyzed by the other instruments. Pictures of thedigging itself will provide information on the physicalproperties of the soil.10


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absorbs all colors except yellow. The infrared spec-trometer can determine that the particular part ofthe infrared light has been absorbed and how muchhas been absorbed. This in turn tells the scientiststhat there is water vapor in the atmosphere and howmuch.THERMAL MAPPING

The intensity of the infrared energy that is radi-ated by the Mars surface is an indicator of the sur-face temperature. The infrared thermal mapper onthe Viking orbiter can measure the radiated energyand therefore provide scientists with the datanecessary to determine the surface temperature ofMars. Similar measurements were made byMariners 6 and 7 and 9; however, these measure-ments cover narrow strips of the surface. The Vikingthermal mapper will cover large continuous areas ata better resolution than previously obtained.Thermal mapping data will contribute significantlyto the selection of landing sites and provide a tem-perature map of much of the planet at varioustimes, both day and night. In addition, scientistsmay be able to locate features such as volcanoes,using the temperature information provided.

during the descent at low altitude, to determine theatmosphere's vertical structure.

These investigations are divided into two phases:the aeroshell phase (entry) and the parachute phase(descent). During the aeroshell phase, atmosphericcomposition, temperature, pressure, and densitywill be observed. To accomplish this phase of thestudy, temperature and pressure sensors, a mag-netic sector mass spectrometer, and a retardingpotential analyzer are mounted on the aeroshell.After aeroshell separation, temperature and pres-sure sensors mounted on the lander itself will con-tinue the measurements to the Mars surface andprovide supporting data on the surface for the dura-tion of the mission.

RADIO SCIENCEThe radio communications system can be used

as a scientific instrument by measuring the altera-tions of the radio signals caused by the planet andits atmosphere.The mass spectrometer measures the relativeamounts of the gases making up the atmosphere as

well as identifying the molecules. The retarding po-tential analyzer measures both the concentrationand the energies of upper atmosphere ions and elec-trons. Atmospheric density is derived from the pres-sure and composition data together with theaerodynamic drag on the spacecraft as indicated bythe accelerometers.

Viking Orbiter science scan platform.

WATER DETECTIONThe Mars atmospheric water detector on the

Viking orbiter can detect very small amounts ofwater vapor with a high resolution.

The water detector is an infrared spectrometerwhich operates on the following principle: If watervapor is in the atmosphere, it will absorb a particularpart of the infrared light that is produced by the Sunin much the same manner that ozone in our atmos-phere absorbs the ultraviolet light, or a yellow filter

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Full scale lander model.

54-meter (210-foot) antennas of the Deep SpaceNetwork; the large antenna at Britain's Jodrell Bankwill also receive signals for an experiment in longbaseline interferometry.

As the radio signal passes through the atmos-phere, the signal is changed and observation of thetype of change will help characterize the atmosphere.

The radio system-including the radar-will beused for measuring the gravitational field of Mars,determining the axis of rotation, measuring the sur-face properties, and performing certain relativity ex-periments. It will also be used to determine thelocation of the lander on the ground.

WEATHER STATION ON MARSWeather has been an important factor in shaping

the thermal history and geological character ofMars. The meteorological conditions also affect anylife that may exist on the planet. Like Earth's, thedynamic weather conditions on Mars undergo cyclicchanges both daily and seasonally.A special radio link, the X-band, is very useful for

studying charged particles, the ions and electrons.This is particularly so for measurements of the iono-sphere of Mars. It also will be used for solar coronaexperiments when Mars and the Earth are lined upwith the Sun.

Periodic measurements will be made of theatmospheric temperature, pressure, and the windspeed and direction for the duration of the mission.PHYSICAL AND SEISMIC CHARACTERISTICS

Geological measurements will be made of thehe radio data will be received by the three large12


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Viking orbiter thermal test model.

physical and magnetic properties of the surface andof the internal seismic activity. Scientists do notknow the level of motion within Mars, but will samplefor periods long enough to establish whether it is anactive planet or not. Such information could shedlight on the early history of Mars.

measured by small but powerful magnets mountedon the lander soil sampler. These magnets will comeinto contact with the surface during soil sampleacquisition, then will be maneuvered in sight of theViking cameras to be viewed with and without a4x magnifying mirror. Pictures of clinging particleswill be evidence of magnetic material in the soil.

A sensitive miniaturized seismometer is mountedon the lander. The seismic background and thelarger events, such as Mars quakes or meteoroid im-pacts, are measured with a three-axis device capableof detecting ground motion transmitted through thelander legs. The instrument uses a rapid data modeduring special seismic events to obtain much moredata during those periods.

The cameras will also photograph the footprintsof the lander and the trough made by the sample,enabling scientists to study the cohesive propertiesof the soil, its porosity, hardness, and particle size.Such observations will help them to deduce informa-tion about the physical properties of the planet'ssurface. Observations of the trough over severalweeks' time will also give an indication of particletransport and the erosion potential of Martian winds.he magnetic properties of the planet are

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Each orbiter and each lander has a narrow-beamantenna and a broad-beam one. The narrow beam,high-data-rate antennas must be carefully orientedtoward Earth. To accomplish this, the antennas aresteerable. Due to the planet's rotation, the antennaon the lander must be moved continuously duringeach transmission period. The fixed, broad beam,low-data-rate antennas are used to receive signalsfrnm F~rth

the Deep Space Network. Lewis Research Center,Cleveland, Ohio, is responsible for the Titan!Centaur launch vehicle and the integration of thespacecraft to the launch vehicle. Launch operationswill be handled bv the Kennedv Soace Center.

Major contractor is the Martin Marietta Corpo-ration, Denver, Colorado, which is responsible forthe lander and systems integration and builds theTitan III booster. General Dynamics/Convair, SanDiego, California, builds the upper-stage Centaur.he lander-to-orbiter communication link is anultra-high-frequency (UHF) system that is used for

rapid, high-volume transmission. The orbiter recordsthese data and then plays them back to Earth overits S-band system. The X-band system on the orbiteris used for radio science only. The orbiter/landerUHF system begins operating when the lander sepa-rates from the orbiter, and continues operatingthrough the descent and landing. The relay link willbe activated again each day when the orbiter passesover the lander.

VIKING SCIENCE TEAMSTeams of scientists were selected by the National

Aeronautics and Space Administration to direct theViking scientific investigations. These scientists in-teract with project engineers who are responsiblefor hardware design, test, and fabrication of flighthardware-

Scientists and engineers working together deter-mine details of the investigations and instruments;the compromises that must be made because ofweight, power, or data constraints; and the ultimateflexibility of experiments.

MANAGEMENT RESPONSIBILITIESViking management is under the overall direction

of the Office of Planetary Programs, Office of SpaceScience, NASA Headquarters. Langley ResearchCenter, Hampton, Virginia, exercises overall projectmanagement and is responsible for the lander por-tion of Viking. The Jet Propulsion Laboratory, Pasa-dena. California. is resDonsible for the orbiter and

Each science team has a leader who is also amember of the Science Steering Group that developsthe scientific policies and contributes to the overallcoordination of Viking science requirements.

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* u.s. GOVERNMENT RINTINGOFFICE: 1915-0-579-587--6

Viking Mission to Mars

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