The MSP 98 Orbiter launches aboard a Delta 7425 in December 1998, and arrives at Mars in September 1999. Burnout of the 3rd stage is followed by yo- yo despin of the entire stack, followed by spacecraft separation. At this point both the spacecraft and upper stage have been injected onto a Type 2 trajectory whose aimpoint is biased away from the nominal Mars Orbit Insertion (MOI) aimpoint, to assure that the upper stage has less than a 1E- 4 probabilty of impacting Mars, as required by Planetary Protection regulations.
After separation, the solar panels are deployed and pointed to the sun, and initial acquisition achieved by the Deep Space Network (DSN). During inner cruise, the solar panel is sun pointed, and contact maintained via the Medium Gain Antenna. Approximately 15 days after launch, the largest Trajectory Correction Maneuver [TCM- 1] is executed. This maneuver removes launch vehicle injection errors and the spacecraft's injection aimpoint bias. Provisions have been made to execute up to 3 additional small TCM's during the remainder of cruise, as needed, to shape the orbit and direct the spacecraft to the proper aimpoint for MOI. All TCM's are performed with the monopropellant hydrazine thrusters. As the heliocentric distance increases during cruise, communications moves to the High Gain Antenna.
At Mars arrival, the Orbiter bipropellant engines are used to propulsively insert the spacecraft into an elliptical capture orbit. The biprop engines burn for approximately 16 minutes, until all the loaded oxidizer is exhausted. One minute later, an additional maneuver is executed by the Hydrazine thrusters, if needed, to reduce the orbit period further. Depending on launch date and propellant mass consumed during cruise, the resultant orbit period lies between 19 and 40 hrs, with a nominal periapse altitude of 160 km. A maneuver to lower periapse in preparation for aerobraking occurs at the first apoapse of the final capture orbit. Over the next two months, the energy of the orbit is reduced via successive passes through the atmosphere of Mars, controlled by small Orbit Trim Maneuvers near apoapse. At aerobrake termination, two maneuvers transfer the Orbiter to its final, frozen, near sun- synchronous mapping orbit, at a descending node of approximately 4 PM. This occurs some time prior to the MSP98 Lander arrival in December, 1999.
During the Lander's surface lifetime, the Orbiter
provides command and data relay support, and also engages in a limited amount
of orbital science. In its mapping phase, the Orbiter performs systematic
daily global sounding and imaging of the Mars atmosphere for approximately
one Mars year (687 days). The nadir- mounted science payload consists of
a rebuilt Pressure Modulator Infrared Radiometer (PMIRR), and the Mars Color
Imager (MARCI). Once its mapping mission is complete, the Orbiter will be
available as a communication relay for future Mars landers for up to 3 additional
years. Upon completion of its relay mission, the Orbiter may perform a maneuver
or be placed in a low- drag attitude to satisfy Planetary Protection regulations.
The MSP 98 Lander will be launched on a Delta 7425 in January 1999, and will arrive at Mars in December 1999. Burnout of the 3rd stage will be followed by yo-yo despin of the entire stack, followed by spacecraft separation. At this point both the spacecraft and upper stage will have been injected onto a Type 2 trajectory whose aimpoint is biased away from the nominal entry aimpoint, to assure that the upper stage has less than a 1E-4 probabilty of impacting Mars, as required by Planetary Protection regulations.
After separation, the solar panels will be deployed and pointed to the sun, and initial acquisition achieved by the DSN. Throughout cruise, contact will be maintained via the Medium Gain Antenna, and the solar panels pointed at the sun [with a small offset in inner cruise]. Approximately 15 days after launch, the largest Trajectory Correction Maneuver [TCM-1] will be executed. This maneuver will remove launch vehicle injection errors and the spacecraft's injection aimpoint bias. Depending on the size of the maneuver, it may be necessary to divide this into two smaller maneuvers. Provisions have been made to execute up to 4 additional small TCM's during the remainder of cruise, including one 7 hours prior to entry for final control of the entry angle and landing footprint. Precision approach navigation will be effected via near simultaneous tracking of the approaching Lander and an orbiter at Mars (either the MSP98 Orbiter or Mars Global Surveyor).
After a direct atmospheric entry, the Lander will be slowed by a Mars Pathfinder-heritage aeroshell and parachute, and a controlled propulsive landing effected. For launch during the Lander's primary launch period, landing will occur between 75 and 78S, on the southern polar layered terrain. The first landed day's activities will include deployment of the solar panels, functional checkout, and establishment of communication with the Orbiter and time critical science activities. Routine science activities will commence on the second day following landing. The Lander will be equipped with a UHF relay for downlink via the MSP98 Orbiter and/or MGS, and command uplink via the MSP98 Orbiter. A direct to Earth (DTE) link will also be available for Lander commanding and as a backup downlink. The Lander will carry the Mars Volatiles and Climate Surveyor (MVACS) instrument suite, which will perform in situ investigations to address the science theme "Volatiles and Climate History" on Mars. The Lander will also provide descent imaging with the Mars Descent Imager (MARDI), and accommodate a LIDAR instrument supplied by the Russian Space Agency. The Lander will search for near-surface ice and possible surficial records of cyclic climate change, and characterize physical processes key to the seasonal cycles of water, carbon dioxide and of dust on Mars. The duration of the landed science phase is expected to last no more than approximately 90 days.