Mars Observer was designed in order to obtain detailed information about Mars' surface, atmosphere, climate, gravity field, and magnetic field. The mission consists of a single spacecraft, which will spend one Martian year (687 Earth days) in a low, near polar mapping orbit. The spacecraft will make repeated observations of the entire planet and transmit data back to Earth once a day.

Mars Observer's launch window was scheduled for mid-September 1992 and has a duration of 24-28 days, with two launch opportunities each day. Once at Mars, the spacecraft requires the descending node to be at 2:00 p.m. to maximize scientific returns. Therefore, a month wait at Mars is necessary to perform a minimum DV transfer to the mapping orbit. Data is transmitted back to Earth through the Deep Space Network (DSN) with one DSN tracking pass each day. An addition tracking pass is scheduled once every three days in order to return real time data.

Mars Observer has five mission phases: Launch, Cruise, Orbit Insertion, Mapping, and Mars 1994 Support. Each of these phases will be discussed in detail below.

Launch Phase: Mars Observer was launched in October 1992 from Kennedy Space Center (KSC) aboard a Titan III/ Transfer Orbit Stage (TOS) launch vehicle. The injected mass to Mars performance requirement is 2502 kg. The launch phase lasts from launch countdown until after the injection maneuver when the spacecraft separates from the TOS. At the end of the injection burn, the spacecraft is pointed relative to the earth for communication purposes and relative to the sun for power and thermal control. Early DSN acquisition of the spacecraft will be made from the Canberra, Australia, tracking site.

Cruise Phase: This phase of the mission will last about 11 months and ends at the beginning of the orbit insertion sequence at Mars. The total DV consists of the DV required for mid-course corrections (80 m/s) plus the DV required for orbit insertion at Mars (1367 m/s). Several activities are performed during the cruise phase; initial deployment and checkout of the spacecraft, daily monitoring of subsystems, navigation activities (including trajectory control maneuvers (TCMs)), and limited calibration measurements for the scientific equipment.

Orbit Insertion Phase: This is the period of transition from the interplanetary trajectory to the Mars mapping orbit. To make the most efficient transfer, a series of 7 maneuvers is planned, with a total DV of about 1967 m/s. This phase will last until the spacecraft is established in the mapping orbit, has completed all system checkouts, and is declared ready to begin data collection. The target radius and inclination of the capture orbit are 3950 km and 92.9{ respectively. The intermediate elliptical orbit, called the drift orbit, will have limited scientific activity. However, once the mapping orbit is established, a checkout period of up to 10 days in required before any mapping begins. In addition, before deploying into the mapping configuration, there will be a 7-day gravity calibration period.

Mapping Phase: This phase begins when the spacecraft is declared ready and ends one Martian year (687 Earth days) later and is the period of intense scientific activity. Data is continuously collected and stored by one to two of the three on-board tape recorders. Once a day, the data is played back during the tracking pass and received at one of the DSN tracking sites. Once every 3 days, real time data is collected during the specially scheduled tracking pass. The orbital elements of the mapping orbit are a=3775.3 km, e=0.0070, i=92.87^o, W=31.32^o, w=0.0^o, and t=7058.9 s. The mapping orbit is near polar and sun-synchronous, requiring a total DV of 26 m/s.

Mars Observer will carry a data relay system supplied by the French that will support data return by the Soviet Mars 1994 mission. This phase of the mission overlaps the end of the end of the mapping phase by two months, and the end of the phase has not yet been determined.

The following is a list of hardware elements for Mars Observer:

Mars Observer employs redundancy to avoid single point failures and nearly maximizes the spacecraft dry mass. Also, since Mars Observer uses more modest data rates, there is no competition for the more powerful DSN antennas. The only weakness is the time necessary for orbit insertion at Mars. However, since this is an unmanned mission, the delay is not critical.

Launch Trajectory

Cruise Trajectory and Spacecraft Cruise Configuration

Orbit Insertion Trajectories and Spacecraft Mapping Configuration

1. Blume, William H., Suzanne R. Dodd, and Charles W. Whetsel. Mars Observer Mission Plan. J. Spacecraft, Vol. 28, No. 5, Sep. - Oct. 1991.

2. 2. Beerer, Joseph G., and Ralph B. Roncoli. Mars Observer Trajectory and Orbit Design. J. Spacecraft, Vol. 28, No. 5, Sep. - Oct. 1991.

3. 3. G.E. Astrospace Mars Observer Specifications Sheet.

Last Modified: May 28, 1998
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