Mariner - Journey Around the Sun

8/8/2019 Mariner - Journey Around the Sun

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MARINER: Journey Around the SunThe Mariners are a series of l ightweight unmanned deep space probes in

constant comm unication with the Earth, designed for planetary flyby m issions;they all derive their power from the Sun and are capable of performing mid-course maneuvers. It is the objective of the Mariner missions to conductscientific observations in the vicinity of the near planets and to explore theinterplanetary environm ent, with the secondary goal of developing the equip-men t and techniques involved in th e construction of spacecraft for long-distance,long-duration flights. In addition, the advances in space science and spacetechnology achieved by the Mariner series will have application to a varietyof scientific and technical endeavors for many decades to come, as will therefinem ent of celestial parameters and general knowledge of th e solar systemthat has resulted and will continue to result from the flights of the Mariners.


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On May 3, 1966, the new NASA/ JPL 210-foot antenna atGoldstone, California, picked up a telemetry signal fromover 197 million miles out in space. It was the faint signalof Mariner IV, which for many months had been beyondthe reach of the 85-foot antennas that had tracked the space-craft on its journey to Mars. Since the end of th e Mars mis-sion, only the carrier signal had been detectable on farfh.Now the telemetry data could again be extracted and ana-lyzed- he spacecrafts message could be understood andinte rpre ted , The result was an unexpected repo rt on the en-vironment of deep space and on Mariners own remarkableoperating performance.


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IV photograph of Mars, Picture No . 1IV photograph of Mars, Picture No. 11


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First Trip to MarsThe journey of NASAs Mariner IV began on Novem ber 28, 1964, when it was

launched on a t rajectory to Mars. It s main objective was to f ly close enoughto the planet to obtain and return information about Mars and its vicinity.During and af ter a trip that took 8 months and covered 325 mil l ion miles,Mariner sent back to Earth a wealth of data about interplanetary space andabout the environment of the planet. It took a total of 21 unprecedented close-up television pictures of the Martian surface. Furthermore, it reported backon its own condit ion and the functioning of i ts systems and instruments. Theresults indicated nearly perfect spacecraft performance.*The stations of the Deep Space Network had been tracking the probe faith-fully since launch, and they continued t o follow it for 2% months after itsencounter with Mars. The spacecraft was transmitt ing over a high-gain antennathat focused the signal into a narrow but powerful beam. The antenna, how-ever, had a f ixed posit ion on the spacecraft, and unless it was pointing at theEarth, the signal could not be picked up by the conventional equipment ofthe Deep Space Network. Mariner also carried a low-gain antenna. This typeof antenna transmits the radio signal over a broad area; it does not have tobe aimed so precisely, bu t its power is not concentrated and the received signalis therefore weaker. On October 1, when the high-gain antenna was no longerpoint ing a t the Earth, the received signa! became too weak to prodEce mean-ingful information. On that date, the spacecraft s transmitter was switchedfrom the high-gain to the low-gain antenna, the ground eq uipment was turnedoff, and the first cha pter in the life of Ma riner IV was ended.*For further details, see Report From Mars: Mar iner /I/ 1964.1965, Jet Propulsion Labora-tory, NASA EP-39; available from the Superintendent of Documents, U.S. GovernmentPrinting Office, Washington, D.C., 0402.

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.Mariner IV orbif arcund the Su n

Keeping TrackHaving successfully completed its designed mission, Mariner IV cont inued

its journey around the Sun. If Mariners systems kept on operating, and ifthe signal could be tracked from t ime to t ime, the spacecraft could become acoherent radio source-a radio beacon in deep space.

The f i rst at tempt to receive a signal was made on November 1, 1965. Onthat date, the Deep Space Station at Goldstone turned on its receiver, slewedits antenna to the proper posit ion, and picked up once again the unm istakableMariner signal. To be sure, it was a weak signal, but it told a great deal. Itindicated, for example, that it was stil l carrying telemetry information, eventhough that information could not be deciphered. But the fact that there wasa signal a t al l meant that Mariner was generating power; therefore, it mustStill be facing the Sun. And if it was facing the Sun, then the att itude-controlsystem- the mechanism that kept the spacecraft locked in posit ion withrespect to the Sun-was sti l l functioning. Furthe rmore, the solar cells must beworking, and the transmit ter must st i l l be operat ing.

Mariner was designed and bui l t for an 8-month tr ip through the environmentof space. Although it successfully completed its original mission, no one knewhow long the machine would cont inue to funct ion properly. In December, theDeep Space Station at Goldstone again tuned in on the signal f rom Mariner,and again the indications were posit ive. Mariner was sti l l working, sti l l trans-mitt ing. After that, the spacecraft was checked about once each month. withthe same favorable results.

During this period, a number of commands were sent to the spacecraftin order t o keep it f ixed on the star Canopus, which it had been designed t ouse as an att itude-control reference. The commands were sent blindly; sincetelemetry could not be extracted from Mariners signal, there was no wayof tel l ing whether th e spacecraft had accepted and acted upon the commands.

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Solar corona

Through the CoronaThe fact that Mariner remained in good working condition as it traveled

around the Sun provided scientists with an opportunity to pe rfor m a new kindof exper iment. The orbit it was following would take the spacecraft behindthe outer atmosphere of the Sun-the corona; if Mariners signal were changedin some way as it passed through the corona, perhaps it would provide us withnew and signif icant information. A similar occultation experiment had beensuccessfully performed at M ars and had produced im portant information aboutthe Martian atmosphere.

There would be serious diff icu lties connected with such an experiment, how-ever. The deep space tracking antenna could not point directly at the Sun,because the radio noise generated by the Sun would drown out any othersignal. Furthermore, it would be extremely diff icult t o determine just howmuch of the signal distortion came from the corona and how much from thespacecraft transmitter. the ground receiver, or the tracking antenna.

In spite of a l l the dif f icult ies, the exper iment was begun on March 26 , 1966.A radio signal fro m the 100-kilowatt transmitter at Goldstone was sent throughthe corona to the spacecraft. The spacecraft returned the signal, again throughthe corona, and it was picked up by the new 210-foot antenna. The returnedsignal was then analyzed. The experiment was repeated frequently betweenMarch 26 and Apr i l 12, when the spacecraft had passed beyond the corona.The results, while stil l inconclusive, are extremely interesting. The signal wasstrongly distorted by the solar corona-a piece of information that will be use-fu l in the design of future missions and may add to our understanding of thephysics of the corona. It was the f irs t t ime tha t communicat ion had been estab-l ished with a man-made object on the opposite side of th e Sun.

The experiment was significant in yet another way: it employed the new210-foo t tracking antenna. Although the 21 0 had not been fu l ly completedat the t ime of the exper iment, it wa s used, under laboratory conditions,because without the increased gain and narrower beamwidth it provided, theexperiment could not have been performed to begin with.

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.NASA1JPL 210-foot advanced antenna system

The 210It had long ago become evident to scientists and engineers that the value

of a spacecraft depends not only upon the amount of information it is capableof t ransmit t ing but also upon how much of that t ransmit ted informat ion canbe received on Earth. Unless we can follow and control its progress from theEarth and receive and analyze the data the spacecraft generates, even thegreatest advances in spacecraft engineering are of l i t t le practical use to us.It is therefore v ital that the development of Earth-based tra cki ng instrumen-tation and facil it ies keep pace with the refinement of spacecraft technology.The terminat ion of intel l igible communicat ion with Mariner IV on October 1,1965 dem onstrated tha t the reach of the existing Deep Space Network antennaswas not suff icient to keep up with the distances advanced spacecraft werecapable of traversing. Either spacecraft power would have to be increased,or larger Earth-based antenna systems would have to be used.

Although no one had anticipated Mariners remarkable performance, it hadalready been decided to increase the ca pab ility of the Deep Space Networkto meet the requirements of future spacecraft. Construction of the Goldstoneadvanced antenna system was begun nearly three years before the launchof Mariner IV. Its design concept was based on well established antennadesigns-in particu lar, the 85-foot antennas of the Deep Space Network an dthe radio-astronomy antenna a t Parkes, Australia. The new system employsbasically the same operating an d signal-processing techniqu es as these smallerantennas, but it has six and a half t imes more receiving sensit ivity than itspredecessors, and its transmitted beam is six and a half t imes more concen-trated. This capabi l i ty extends the tracking period, and hence, the useful l i fet imeof a spacecraft, by nearly two and a half t imes. Under certain c ondit ions, it ca nreach the edge of our solar system.The giant reflector of the new space tracker has a diameter of 210 feet,and, together with its supporting structure, weighs over 5 mill ion pounds. Inspite of this enormous weight, it can be rotated in a complete circ le and i tsposit ion can be changed from horizontal to vertical in 3 minutes. It is capableof pointing at a moving target with a precision equivalent to that needed toput a bul let inside a thimble at 200 feet.

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Mariner IV telemetry being analyzed at th e JP L Space Flight Operations Facil i ty

Mariner Reports AgainOn May 3. May 21, and again on June 5 and July 1. he new trackin g antenna

was used to pick up the signal from Mariner IV . Now there was no solar coronato interfere with or distort the radio waves, so that the signal was interpret-able even though it was barely above the noise level. The telemetry informa-tion was extracted from the signal and anaiyzed, and the performance of thespacecraft was evaluated fro m the resul ting informa tion, jus t as it had beendurin g the m ission to Mars. By this t ime, no one was surpr ised when theresults indicated that all systems were working properly. The temperature waswi th in 2 degrees of the expected value; tape recorder pressure was normal;the radio transmitter was working wel l ; everything was as it should be. Thesignal also indicated that o ut of the 12 bl ind comm ands sent to M ariner ear lier,all but one had been received. The star sensor was not locked onto the starCanopus, and while th is was an unfortun ate loss in terms of celestia l mechanics,it did not affect the func tioning of the spacecraft or of the science instruments.By May 21 , Marine r had been in space for 539 days and had traveled nearly740 mil l ion mi les.

Monday, June 6, 1966, was a special day in the l i fe of Mariner IV, fo r itwas on th at day that the probe corr ip leted a ful l orb i t around the Sun.

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Mariner Venus 67

To Venus: Another MarinerIn June 1967, another Mariner spacecraft wi l l be launched on a t rajectory

that wi l l br ing it within some 2000 miles of the planet Venus. The launchvehicle for the Mariner Venus 67 mission will be an At las D.Agena D com-bination, the same vehicle that was used for Mariner IV. The Agena stagewill be slightly modified to meet the requirements of the Venus mission. Thespacecraft that wi l l perform this mission is c losely related to Mariner IV-i tis , in fact , a spare from the Mars mission, modif ied for the f l ight to Venus.One of the objectives of the 1967 Venus mission is to demonstrate thefeasibi l i ty of convert ing a spacecraft designed to investigate the planet Marsinto one that can conduct similar investigations of the planet Venus. Theprimary scient i f ic purpose of the mission is to obtain data about the planetand its environmen t and to add to our knowledge of the interplanetary med iumbetween the Earth and the Sun. A further s ignif icant contr ibut ion to be madeby Mariner Venus 67 is the expected improvement in the science of orbitdetermination and the accuracy of space navigation.Because Mariner Venus 67 will be travelir;g toward the Sun rather thanaway from it and will be encountering different environmental condit ions,several of the spacecraft components and experimental instruments will haveto be changed or relocated from the original Mariner Mars design. Forexample, the total area of the solar panels will be reduced, their structuremodif ied, and the conf igurat ion of the solar cells adapted to minimize heatingeffects. So that the antennas can function a t top eff iciency with as lit t leobstru ction by the spacecraft itself as possible, the att itud e of Marine r Venus 67will be opposite fro m that of Mariner IV-wh at is top for the Mars probewill be bottom for the Venus craft. This change in orientation, as well asthe different temperature condit ions and degrees of solar intensity to whichthe spacecraft will be subjected, will requ ire changes in the rma l shielding andother temperature-control devices. In addit ion, the posit ion of the trappedradiation detector will be reversed to have the same solar direction as onMariner IV, the plasma probe will be relocated to permit an unobstructedview of the Sun, and the posit ion of the ultraviolet photometers will be f ixedso that the instruments face the planet a t encounter.

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TAPE

Venus encounter t rajectory

Some of the science instruments carr ied on Mariner Venus 67 wil l beident ical to those of Mariner IV, and some wil l be ent irely new. The experimen tsto be performed wi l l include invest igat ions of the interplanetary magnet icf ield, the solar wind, the distr ibu t ion of hydrogen and oxygen in the upp eratmosphere of the Earth, charged-particle f luxes, solar X-rays, the abundanceof electrons and hydrogen ions in space, and the magnet ic f ield conf igurat ionnear the planet. When the spacecraft encounters Venus, a number of addit ionalexperiments wi l l be performed to invest igate the concentrat ion of hydrogenand oxygen in the exosphere, th e electron conce ntration in the ionosphere, thedensity of the atmosphere at various levels, and the diameter and mass ofthe planet.The Venus m ission wi l l also provide an unusual opportunity to enhance ourknowledge of celestial mechanics. It wil l , in fact , be the f i rst t ime that theinvestigation of celest ial mechanics wi l l be approached as a scientif ic experi-ment. The close proximity of the spacecraft to the planet will have a signif icantef fect on the spacecraft s orbit , which, af ter the encounter, wi l l br in g Marinercloser to the Sun than man has ever before penetrated. By correlat ing the

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r A G E N A D/

ATLAS/AGENA ADAPTER NOSE FAIRING -/

Atlas/ Agena launch vehicle

new orbital data with the data available from earlier missions, scientists wil lbe able to obtain more accurate information, not only about Venus but alsoabout the Moon and the Earth. An attempt wi l l be made to continue thetracking of Mariner Venus 67 fo r as long as possible after encounter, sinceevery additional day of telemetry received and analyzed may mean furtherrefinement of our knowledge of the solar system.

A ComparisonMariner I V Mariner Venus 67*

Science experiments

Solar panelsSpacecraft weightHigh-gain antennaSolar vanesTape recorder

Flight time toencounter

Communicationdistance atencounterClosest approachdistance

Trapped radiation detectorsHelium magnetometerSolar plasma probeCosmic ray telescopeCosmi.c dust detectorIonization chamberS-band occultationTelevision70 square feet total area28,224 solar cells574 poundsFixed position412.84 inches/second tape speed8Y3 days playback time10,700 bi ts/ second record rate5,250,000 bits capacity228 days216,303,650 kilometers(134,401,000 miles)6114 miles

Trapped radiation detectorsHelium magnetometerSolar plasma probeUltraviolet photovetersDual-frequency occu!tationS-band occulta tionCelestial mechanics43.6 square feet total area17,640 solar cells543 poundsMovable to tw o positionsNone0.08 incheslsecond tape speed32 hours playback time66% bi ts/ second record rate960,000 bits capacity114-130 days79,000,000 kilometers(49,000,000 miles)1875 miles

*Prelaunch estimates.-

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1967 trajectories and posit ions

1967:A Busy Year19 67 will b e a year of increasing solar activity. The effec t of this activity

on the interplanetary medium is of great scientif ic interest. Pioneer VI andPioneer VII, launched in 1965 and 1966, respectively, will be in orbit aroundthe Sun in 1967, and the simultaneous presence in space of Mariner IV andMariner Venus 67 wil l provide an unprecedented opportunity t o take scient i f icadvantage of this part of the 11-year solar cycle, The closest approach to theEarth of Mariner IV will occur on September 9, and there are plans to t rackthe spacecraft cont inuously for a few weeks dur ing the Summ er of 19 67,when its signal will be strongest. An attempt wi l l be made at that t ime toconduct several engineering experiments in ad dit ion to receiving interplanetaryscience inform ation. Th is means that the Deep Space Network will be trac k-ing the two spacecraft-one travel ing between the Earth and the Sun and theother outside the Earths orbit-at the same tim e. The fac t tha t scientistswi l l be able to correlate the data from several di f ferent areas in space wi l lgreatly increase the value of the information received from each spacecraft.

The 1967 act iv i t ies wi l l be based on past experience in the f ield of spacef l ight operat ions. Both the Mariner Venus 67 mission and th e reacquisi tion ofMariner IV wi l l be conducted by the same team responsible for the Mars mission,applying the same techniques tha t were used at that t ime.A Summing Up

Mariner IV has drastically revised our ideas about Mars and has increasedour knowledge of the solar system; it graphical ly demonstrates the cont inuingadvances that are being made in spacecraft technology; and it has even addedto our store of informat ion about the Earth. Among the many things that wehave learned as a res ult of M ariners journey aroun d the Sun are the following.

Mars has a relatively thin atmosphere, and there is no detectable magneticf ie ld wi th in 6000 miles of the planet. The Mart ian surface is cratered and ismo re Moonl ike than Earthl ike in appearance. In addit ion to this ent irely newinformation, we have also learned more about the mass of Mars and of theEarth and about their exact sizes; locations, and orbits. We have been ableto redefine radial locations of points on the Earth and to refine our knowledgeof celestial parameters such as the astronomical unit. We have new infor-mat ion about the act iv i ty of the Sun, the part ic les it ejects into space, solarand galactic cosmic rays, and the solar wind. We have a better understandingof interplanetary magnetic f ields, cosmic dust, and trapped radiation in thevicinity of Earth and Mars.

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Mars Venus

In returning these scientif ic data to Earth, Mariner IV has proved aboveall else that it is an extremely rel iable spacecraft . Since launch (to June 5,19 66 ) i ts various subsystems have accumulated a combined total of 24 2,5 00operat ing hours. Broken down into key electronic part operat ing hours, thisfigure means over 42 mil l ion transistor, 1 45 mil l io n resistor, 59 m il l ion capac-itor, 89 mil l ion diode, 5 mil l ion transformer, and 1 mil l ion relay part hours,with but one failure-a resistor on the plasma probe experiment. Based onpresent informat ion, fai lure rates compu ted from these f igures are either equalor superior to those of any other complex electronic system cont inuously func-t ioning in space.

Only a small port ion of the data transmit ted by M ariner IV has been analyzedand interpreted; many m ore mon ths wi l l be required to co mplete the task.Furthermore, as long as Mariner IV cont inues to funct ion, it wil l cont inue toprovide a l l elements of NASA with informat ion, both about i tself and abouthitherto unexplored regions of interplanetary space.

Mariner Venus 67 may modify our ideas about Venus just as Mariner IVchanged many of our concepts of Mars. Because we know even less aboutVenus than we did about Mars, it is reasonable to assume that we shall obtainmuch new, and perhaps unexpected, knowledge about the planet. In addit ionto the technical and engineering informat ion about the spacecraft i tself andspacecraft navigat ion in general, we expect to learn more about the size andmass of Venus, the ef fects of various interplanetary phenom ena in the vic ini tyof the planet, and the scale height, density, and composit ion of the planet satmosphere. We ant ic ipate improvements in the ephemerides of Venus andof the Earth, further ref inement of the ast ronomical uni t , and more data aboutthe extent of the Earths hydrogen cloud. In the course of i ts journey aroundthe Sun, Mariner Venus 67 should also enable us to draw some conclusionsabout the orbital perturbat ions of the planets.

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Continuing activit ies in fhe Mariner series are being conducted for the Na-tional Aeronautics and Space Administrations Office of Space Science andApplications by the Jet Propulsion Laboratory. They are made possible by thesupport and assistance of scientif ic institutions, industrial concerns, and gov-ernment agencies, including NASAs Lewis Research Center and their primecontractors, Lockheed Missiles and Space Corporation an d G eneral DynamicsfConvair; Goddard Space Flight Center and agencies at Cape Kennedy; the agen-cies of the Au stralian, South African, and S panish Goirernments which operateoverseas space comm unication stations; many hun dreds of A merican ind ustrialcontractors and vendors: and a number of scientists in various fields of endeavor.


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NA TI0NA L AERONAUTICS AND SPACE ADMlNlSTR ATlONJet Propulsion Laboratory I California Institute of Technology I Pasadena, Ca lifornia