Unfortunately, problems with one of the two MGS solar panels forced the aerobraking sequence to proceed more slowly than planned. MGS executed its final aerobraking pass through the upper martian atmosphere on February 4, 1999, and successfully performed its aerobraking exit maneuver later that day. MGS executed its transfer to mapping orbit on February 19, 1999, and achieved the desired mapping orbit with an altitude which ranged from 230 to 274 miles and a period just under two hours.
The primary mapping phase of the MGS mission began in March, 1999. During the mapping phase of the mission, a number of science teams conducted a systematic study of the red planet with instruments of exquisite capability. The mapping phase of the mission concluded in January, 2001 after one complete martian year (687 days). A series of extended mapping missions began on January 31, 2001 and continued until contact with the spacecraft was lost in November, 2006. The extended missions provided the opportunity to study the year to year changes on Mars. Results of the MGS Radio Science Team investigation of the martian atmosphere were posted on this web site as they became available.
Mars and its Valles Marineris
The MGS mission was managed by the NASA Jet Propulsion Laboratory. The purpose of the mission was to study the atmosphere, topography, geology, gravity and magnetic field of the red planet. The mission was approved by Congress as a low-cost replacement for the ill-fated Mars Observer, and the MGS instruments were all copies of instruments which flew aboard the Mars Observer. A summary of the most important discoveries of the MGS mission is available here.
The MGS Radio Science Team employed a technique called radio occultation to probe the martian atmosphere. Twice per orbit, MGS was occulted by Mars (once on entry and once on exit) and an ultrastable radio transmission from the spacecraft to Earth passed through and was perturbed by the thin atmosphere of Mars. The radio transmissions were received by NASA Deep Space Network (DSN) antennas at three locations on Earth, and analyzed at Stanford University with special computer software developed by Team members. DSN Station 43 at Canberra, Australia is pictured in the photo at the right. This antenna is among the larger of the antennas that were normally used to receive radio transmissions from MGS.
Analysis of the perturbations to the phase of the ultrastable transmission by the martian atmosphere yielded profiles of the temperature and pressure of that atmosphere as a function of height above the planet's surface. The atmospheric profiles provided the basis for the MGS Radio Science Team's Daily Martian Weather Report.
To fully appreciate the significance of the MGS radio occultation measurements, think about this. If you were to launch a weather balloon from the surface of Mars, you would be able to measure the temperature and pressure at many heights as the balloon ascended through the martian atmosphere. You would essentially be able to collect one profile each of atmospheric temperature and pressure. Using the radio occultation technique, MGS scientists were able to collect two of these sets of profiles for each orbit of the MGS spacecraft. With 12 orbits per day, Radio Science Team members have been able to produce nearly 22,000 profiles of the martian atmosphere at various locations on the red planet over the course of five martian years!