The Mariner Missions (2024)

The Mariner Missions (1)TheMariner Mars Missions

Mariner 4

The Mariner Missions (2)Spacecraft Specifications

Mariner 4 images

Detailed Information on the Spacecraft, Experiments, and Data Sets

Introduction

Mariner 4 was the first spacecraft to obtain and transmitclose range images of Mars. After its launch on November 28, 1964 and ajourney of hundreds of millions of kilometers, Mariner 4 passed within9844 kilometers of Mars on July 14, 1965. Beginning at a range of 16,900 km,the probe acquired a surface image composed of 200 lines, consisting of200 pixels each (average resolution was about 3 km/pixel) every 48 secondsuntil, at a range of 11,900 km, 22 television pictures of the Martian surfacehad been stored on the spacecraft's 4-track tape recorder (the last 3 ofthese pictures were beyond the terminator). It took 4 days to transmitthe image information to Earth and the spacecraft returned useful data untilOctober 1965, when the distance from Earth and its antenna orientationtemporarily halted the signal acquisition. Data acquisition resumed inlate 1967 and continued until December 20, 1967.

Objectives

Mariner 4 was designed with 3 main objectives in mind.First, the probe was to conduct field and particle experiments in interplanetaryspace, including measurements of the Martian magnetic field, cosmic dustand cosmic rays, and the solar wind. Secondly, Mariner 4 was to provideclose range images of Mars in order to provide us with the most detailedsurface pictures ever obtained of the planet, hopefully revealing geologicand atmospheric processes. Finally, as interplanetary probes were stilla new technology, the mission would provide experience in operational andengineering techniques required for long term interplanetary missions.An interesting spin-off of the last objective was the development of theradio-occultation experiment which obtained approval only after the spacecraftwas already launched. The experiment took advantage of radio waves fromthe spacecraft propagating through the Martian atmosphere as the spacecraftpassed behind the planet. Variations in the amplitude, frequency, and phaseof the returned signal allowed calculations of atmospheric density, temperature,and scale height as functions of altitude.

Results

Other than some degradation of the plasma probe and afailed Geiger counter, the Mariner 4 mission was a success. The relayedsurface images revealed a cratered and moon-like surface, contrary to evenconservative estimates of the Martian topography (it was later learnedthat the images were of a geologically older region of the planet). Theimages covered about 1% of the surface within a discontinuous band stretchingfrom 40oS, 96oWto 40oN, 187oW.It was not conclusively determined whether or not Mars had an intrinsicmagnetic field, but to date it is generally accepted that Mars is essentiallywithout an intrinsic magnetic field of any significance. One of the greatachievements of the Mariner 4 mission was the modification of mission planswhile the spacecraft was in transit in order to accomodate the radio-occultationexperiment. Not only did the experiment indicate surface pressures of 4.1to 7.0 mbar (for comparison Earth has a surface pressure of 1013 mbar),but the experiment revealed the benefits of maintaining some flexibilityin mission plans even after a spacecraft is launched.

Mariner 6 & 7

The Mariner Missions (3)Spacecraft Specifications

Detailed information on Mariner 6 Spacecraft, Experiments and Data Sets

Detailed information on Mariner 7 Spacecraft, Experiments and Data Sets

Introduction

Mariner 6 and Mariner 7 were identical spacecraft launchedon February 24, 1969 and March 27, 1969 respectively, and their missionswere entirely devoted to the flyby study of Mars. The probes passed closestto Mars on July 30 and August 4 of the same year (Mariner 7 took a moredirect path than Mariner 6 and "caught up" to Mariner 6, arrivingonly 5 days behind). The spacecraft each acquired a series of far encounterimages, composed of 704 lines consisting of 945 pixels each, as they approachedthe planet and a series of near encounter images (same numbers of linesand pixels/line) upon arrival. The far encounter photos had resolutionsranging from 4 to 43 km per pixel, while the near encounter images hadresolutions as good as 300 m per pixel. In total, 143 far encounter imagesand 58 near encounter images were transmitted. Due to advances in technology,Mariner 6 and 7 carried computers that could be reprogrammed from Earthduring the mission and the probes were able to transmit data at a rateof almost 2000 times that of Mariner 4. These spacecraft were heavier thanany planetary probes previously launched by NASA and they were carriedinto space by the Atlas-Centaur rocket.

Objectives

The probes were designed to concentrate entirely on Mars.Measurements of atmospheric composition, pressure, density, and temperaturewere made and the radio-occultation experiment designed during the Mariner4 mission was once again implemented. Surface images of greater qualityand quantity were hoped to provide a more complete picture of the Martiansurface and, when combined with the atmospheric data, to allow planningfor future missions in search of life on Mars. A celestial mechanics experimentwas also included in the mission, which, by analysis of the extremely accuratetracking data of the paths of the spacecraft, provided a precise measurementof the mass of Mars. Finally, as long range interplanetary mission technologywas still in its infancy, the missions provided valuable experience inthe engineering and mission operations required for long-term flight awayfrom the sun.

Results

In transit to Mars, likely due to a battery rupture, contactwas temporarily lost with Mariner 7 on July 30. After a 7-hour silence,contact was restored, but it soon became evident that the instrument responsiblefor reporting the orientation of the television cameras had been damagedand was no longer functioning. Without this information the Mariner 7 camerascould not be pointed properly and, with the Mars encounter close at hand,a solution was needed quickly. On August 1, manual calibration by groundcrews brought Mars into the view of Mariner 7 cameras and, on August 2,Mariner 7 began to relay far encounter images of Mars. The restorationof the Mariner 7 imaging system was a prime example of the expertise beingdeveloped by mission operators during these early interplanetary missionsand the event stood as a testament to the importance of having a reprogammablecomputer on the spacecraft.

The mission was a complete success. In total, 201 imagesof Mars were acquired; the near encounter images covering about 10% ofthe Martian surface. In the near encounter sequences, the two spacecraftviewed different areas of the planet with Mariner 6 imaging a band fromthe equator to 10oS, spanning 60oWto 320oW, and Mariner 7 imaging the edgeof the polar cap at 60oS, 0oWas well as a band from 10oN to 30oS,spanning 20oW to 105oW.The images essentially deflated any of the theories proposing the existenceof artificial canals on the surface and the images also showed a lack ofany correlation between geographical features and the light and dark areasseen by far encounter images and Earth based images. The images still didnot show the widely varied terrain that was hoped for, but later missionsrevealed the truth about the exciting surface of Mars. Atmospheric experimentsindicated the presence of dust suspended in the atmosphere, carbon dioxideice and water ice clouds, carbon monoxide, ionized hydrogen, and ionizedoxygen. Among the species not detected were ozone and nitrogen; both ofwhich would have been beneficial to the existence of life similar to thaton Earth. Surface temperatures as warm as 280-290K (290K is about 17oCelsius or 63o Fahrenheit) were detectednear the equator, and it was found that, as one would expect, the darkerareas of lower reflectance were generally warmer than the lighter coloreddeserts of higher reflectance. The radio-occultation experiment reinforcedthe findings of Mariner 4 with atmospheric pressure falling between 3.8to 7.0 millibars and this experiment also detected an ionosphere on onlythe sunlit side of the planet.

Mariner 9

The Mariner Missions (4)Spacecraft Specifications

Detailed Information on the Spacecraft, Experiments, and Data Sets

Introduction

Originally, Mariner 9 was to have an identical companion,Mariner 8, but on May 8, 1971, 365 seconds after launch, Mariner 8's Centaurmain engine shut down and the upper stage of the rocket, along with Mariner8, fell into the Atlantic about 560 km north of Puerto Rico. Mariner 9was the first of NASA's Mars orbiters. The spacecraft, which weighed morethan Mariner 6 and 7 combined, was launched on May 30, 1971 on top of anAtlas-Centaur launch vehicle. After a journey of more than 600 millionkilometers, Mariner 9 arrived in Mars orbit on November 14, 1971 and beganthe most ambitious Mars exploration mission yet attempted. Mariner 9 carriedsophisticated instrumentation similar to that of Mariner 6 and 7, but alarger propulsion system was required for controlling the spacecraft duringits time in Mars orbit. By the end of 349 days in Mars orbit, 7329 images(including images of Mars' two moons, Phobos and Deimos) had been relayedback to Earth and a total of 54 billion bits of data had been transmitted.Mariner 9 completely revolutionized our view of Mars and the informationfrom this mission would later serve as the foundation for the Viking program.

Objectives

Mariner 9 was designed to provide the most complete viewof Mars ever obtained with mission experiments similar to those of Mariner6 and 7. Atmospheric structure, composition, density, and pressure wereto be analyzed again using techniques similar to those used on previousMariner Mars missions. Mission goals were to map over 70% of the Martainsurface with resolutions ranging from 1 km per pixel to as good as 100m per pixel during successive Mars orbits from an altitude of about 1,500km. The spacecraft would also look for signs of volcanic activity denotedby heat anomalies on the surface using infrared radiometry. Mars' two moons,Phobos and Deimos, were also to be analyzed by Mariner 9. Mariner 9 wasessentially designed to refine the findings of previous missions and totake away the veil of uncertainty which had so far concealed the Martainsurface.

Results

Mariner 9 far exceeded its expectations in every way.Upon its arrival in November, the spacecraft was presented with a Martianatmosphere full of dust which obscured the view of the surface. The opaqueness,explained as dust storms, of the Martian atmosphere had been previouslyobserved from Earth during Martian southern hemisphere summers and nowwith Mariner 9 in orbit, the existence of these dust stroms was confirmed.With a reprogrammable computer on board, Mariner 9 was kept in orbit untilthe dust began to settle out of the atmosphere and the systematic imagingof the planet's surface began in January of 1972. The 7329 images, coveringabout 80% of the planet, revealed the surface and atmosphere of Mars tobe as varied as planetary scientists had hoped. Some of the observed featuresincluded ancient river beds, craters, massive extinct volcanoes, canyons,layered polar deposits, evidence of wind-driven deposition and erosionof sediments, weather fronts, ice clouds, localized dust storms, morningfogs and more. With evidence of flow features, and therefore the possibiltyof a time when water was in liquid form on the surface of Mars, the questionof the existence of life on Mars was intensified. It was clear that Marshad brought about many more questions which a lander would be best suitedto answer.

In addition to the vast array of images obtained, manyother observations were made. These observations included: a lack of evidencefor volcanic activity, irregularities in Mars' gravity field, propertiesof the daytime ionosphere, atmospheric pressures ranging from 2.8 to 10.3mbar, measurements of atmospheric water vapor content, altitude measurements,detection of seasonal upper atmosphere ozone, and an ultraviolet spectrumof Phobos. In total, 54 billion bits of data were relayed back to Earthby Mariner 9. For comparison, this was 27 times the amount of data retrievedby all previous Mariner Mars missions combined.

The results of the Mariner 9 mission paved the way forthe Viking program. Confirmation of atmospheric pressure allowed engineersto design the Viking landers for a safe descent, and the fantastic imagesand data retrieved fueled the fire for further Mars exploration. The possibilityof life on Mars was an irresistable mystery and, on August 20, 1975, theViking program was launched with a variety of experiments... includingexperiments designed to search for signs of Martian life.

A Listing of Mariner 4,6,7,9 References

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The Mariner Missions (12)
Author/Curator:
Dr. David R. Williams, dave.williams@nasa.gov
NSSDCA, Mail Code 690.1
NASA Goddard Space Flight Center
Greenbelt, MD 20771
+1-301-286-1258

NASA Official: Dave Williams, david.r.williams@nasa.gov
Original Page Author: Malcolm J. Shaw, Malcolm_Shaw@pcp.ca
Last Updated: 06 January 2005, DRW
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