Mars Global Surveyor

Mars Global Surveyor is a joint mission of NASA and Jet Propulsion Laboratory, intended to chart the Planet Mars.
Elle is the first American mission successful since the probes Viking twenty years before.

Chronology of the mission

Mars Global Surveyor was manufactured by Lockheed Martin in a factory of Denver, Colorado. This probe weighed 1 050 kilograms with its full tanks.

The probe was launched the November 7th 1996 starting from the base of the Cap Canaveral in Florida by a rocket Delta-7925. It accomplished a voyage of almost 750 million kilometers in 300 days.

While arriving near Mars, the probe ignited its principal engine during 22 minutes to join its Orbite insertion. This operation slows down the probe and allowed the Gravitation planet to capture it. This orbit was strongly eccentric, its Périapse was with 262km above the northern hemisphere and its Apoapse with 54 026km above the southern hemisphere; its period was 45 hours. After insertion, the probe carried out a series of changes of orbit to reduce its périapse in extreme cases higher from the Martian atmosphere, with a Altitude of approximately 100 kilometers. During each passage, the probe lost altitude by aerodynamic braking. The probe used this technique of braking for 4 months, which enabled him to lower its apoapse at an altitude of approximately 450 kilometers.

The October 11th the team of flight carried out an operation to go up the périapse above the atmosphere. This stop of braking was carried out because the pressure exerted by the atmosphere caused a light bending of one of both solar panels. This panel had been slightly damaged shortly after launching. The atmospheric Freinage was taken again the November 7th after it was concluded that this braking did not cause any problem in the condition which it occurred ata rate more reduced than that envisaged in the original plan of mission.

With the new plan of mission, braking started again at an altitude of 135 km to reach 120,5 km rather than that of 110 km initially envisaged. This slightly higher altitude made it possible to reduce by 66% the pressure exerted by the atmosphere on the probe. Six months of braking made it possible to reduce the period of the 12 noon orbit to 6 a.m. Between May and November 1998, braking was stopped to make it possible the orbit to derive towards its correct position with respect to the Sun. These six months were to use to collect the greatest possible number of scientific data; these data were taken between 2 to 4 times per day at the point of orbit low.

Finally, of November 1998 to February 1999, atmospheric braking was taken again to reach the orbit of 450 km; at this altitude, the probe made the turn of Mars in 2 hours. Braking was designed to finish at the same time as the orbit reaches its position wanted compared to the Sun for the operations of cartography. In this position, the probe always crosses the equator located on the side day at 14:00 local time of Mars and moves south towards north.

The operations of cartographies, began the March 3rd 1999 and lasted one year Martian complete, i.e. the two years equivalent terrestrial. The probe carried out a full rotation around Mars every 117,65 minutes at an average altitude of 378 kilometers. The selected orbit was a polar Orbite quasi circular such as the probe always crosses the equator located on the side day of the south towards north at 14:00 local time of Mars. Altitude was selected in order to make the orbit synchronous with the Sun in such way that all the images taken by the probe of the same part of surface of Mars but on different dates are taken with conditions of identical illuminations. With each turn of orbit, the probe moves 28,62° towards the east because of the rotation of Mars. After 88 orbits, the probe is found roughly at the same place above surface but shifted 59km towards the east, which makes it possible to uniformly cover all surface with planet.

The January 31st 2001, the probe finished its main mission. NASA approved an extension of the mission. Mars Global Surveyor continued to send data, in particular thanks to its camera MOC (in English Mars Orbiter Camera ). Moreover, the probe been used as communications satellite to relay the data coming from more recent missions. Indeed, the March 30th 2004, the probe photographed the traces of wheels of the rover Spirit , with the Sol 85 of its mission.

In April 2005, Mars Global Surveyor became the first orbitor Martian to take stereotypes of other vessels in orbit around red planet. It succeeds in taking photographs of the American probe Mars Odyssey and of the European orbitor Mars Express.

Since the November 9th 2006, Mars Global Surveyor does not answer any more. After more 10 years in space, MGS, following a reorientation of one as of its Solar panels, saw its power radio broadcast to lower 42 dB. It ceased emitting the 3 et 4 November, and the 5 the probe announced qu 'it passed in passive mode. That is to say the electric output is lacking because of a bad position of the solar panel, or an anomaly of this last caused the reorientation of the probe to expose it to the sun, and the principal antenna then lost its alignment with the Earth. In this situation, the probe would have to use its secondary antenna to contact the Earth… what it still did not do.

Other assumptions are evoked by the director of MGS Thomas Thorpe of JPL of NASA: the shock of a microphone Meteorite or the breakdown of stellar sensors of orientation.

NASA tried to locate the probe, between the Friday the 17th and on Monday, November 20, thanks to Mars Reconnaissance Orbiter (MRO) without success.

November 21st 2006, NASA announced that the Mars Global Surveyor mission is definitively finished. This mission was longest and most productive of the missions sent towards red planet. The probe appearing enduring by functioning five times longer than envisaged (10 years instead of 2). In April 2007, NASA indicated that an human error in the programming of the trip computer would be at 'origin of its loss. This last would have reorientated the probe exposing one of the batteries to the sun and leading to appauvrissment of the two batteries.

Results

This mission studied the whole of Martian surface, the atmosphere and the internal structure of planet and returned us more data over Mars than all the other joined together missions.

Among the important discoveries, Mars Global Surveyor photographed ravines and flows of remains which suggest that there can be sources of water liquid, comparable with an aquifer on the surface or close to surface. The similar formations on Earth are formed by running water but over Mars the temperature is normally too cold and the too thin atmosphere to maintain water in the liquid state. Nevertheless, certain scientists suppose that over Mars, of water can sometimes spout out basement, erode drains and channels and form ponds before freezing or evaporating.

The results of the Magnétomètre show that the Magnetic field Martian is not generated overall by the core of planet but by zones located in the crust. New data of temperature and the large-plans of Phobos show that the surface of this satellite is made up of pulverulent remains on a thickness of at least a meter, result of million years of meteoritic bombardments.

The altimeter-laser made it possible to the scientists to obtain the first images in three dimensions of the cap of ice of the north pole Martian.

References

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