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Lunar Prospector Status Report #24

March 11, 1998 - 7:00 p.m. EST (4:00 p.m. PST)

The Lunar Prospector spacecraft continues to perform very well, and all instruments continue to collect good data, according to Mission Control at NASA's Ames Research Center. On Sat., March 7 (PST), mission controllers sent commands to fire the spacecraft's thrusters to correct its orbit. In addition, on Tues., March 10 (PST), two commands were executed to tweak the gamma ray spectrometer's HV (high voltage) gain. The current state of the vehicle (as of 4:00 p.m. (PST) on Wed., March 11, 1998), according to Mission Operations Manager Marcie Smith, is as follows:

Spacecraft Orbit Number: 711
Data Downlink Rate: 3600 bps
Spin Rate: 12.18 rpm

Spin Axis Altitude
Longitude: 281 degrees
Latitude: 87.6 degrees

Trajectory
Periselene: 94 km
Aposelene: 106 km
Period: 118 minutes
Inclination: 90.7 degrees

Occultations: 44 minutes in duration
Eclipses: 45 minutes in duration

Last Saturday, mission controllers executed the first orbit trim maneuver, in which two axial burns were fired: one to raise periselene (closest distance from the Moon) and the other to lower aposelene (furthest distance from the Moon). The target orbit (87 X 113 km) was designed to be biased to compensate for periodic perturbations in order to keep the actual orbit as close as possible to the desired 100 + 20 km orbit for as long as possible. The actual maneuver was very close to target, resulting in an orbit of 87.7 X 112.3 km. The precise command timeline was as follows:

Sat., March 7, 7:26 p.m. (PST) Thruster heaters on
Sat., March 7, 7:49 p.m. (PST) Thrusters A3 and A4 fired for 46.5 seconds
Sat., March 7, 7:50 p.m. (PST) Thruster parameters reset
Sat., March 7, 8:32 p.m. (PST) Thruster heaters on
Sat., March 7, 8:53 p.m. (PST) Thrusters A3 and A4 fired for 45.9 seconds
Sat., March 7, 8:54 p.m. (PST) Thruster parameters reset
Tues., March 10, 7:00 a.m. (PST) Gamma Ray Spectrometer command sent

On March 12 (PST), the Moon will see the Sun partially blocked by the Earth. Mission controllers will carefully monitor this event to ensure full battery recharging after normal once-per-orbit passages over the nightside of the Moon. Also on that day, controllers plan to execute small attitude and spin trim maneuvers.

Alison Davis
Lunar Prospector Mission Office
NASA Ames Research Center
Moffett Field, Calif. 94035