Lunar Prospector Status Report #25

March 19, 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. On March 13 GMT (Thursday evening local), the spacecraft experienced penumbral eclipse as the moon (and the spacecraft orbiting it), saw the earth partially block the sun. No power or thermal problems occurred during the event. Also on March 13 (Friday afternoon local), attitude and spin trim maneuvers were performed.

During the penumbral eclipse, there was a visible drop in solar array current and the battery showed a slight discharge before entering its normal 46 minute eclipse as it passed over the night side of the moon. Recharge after that eclipse was nominal.

On DOY 072 (last Friday), the spin axis was precessed about 2 degrees to keep the sun just above the spacecraft equator for thermal reasons. Also, the spin rate was trimmed to correct for small changes to the spin rate which occurred during last week's orbit trim maneuver.

Commands were sent as shown below (all times GMT on DOY 072):
2100 Thruster heaters commanded on
2104 Loaded maneuver parameters
2126 Fire A1/A4 thrusters (13 pulses) to precess spin axis 1.7 deg
2131 Thruster heater commanded on
2140 Loaded maneuver parameters
2150 Fire T1 thruster for 0.81 sec
2151 Safe thrusters

The results of the spin axis reorientation are still under investigation as the engineering team is reviewing the attitude data (both pre- and post-maneuver) to account for natural precession of the spin axis. The spin trim was exactly on target, changing the spin rate from 12.17 rpm to 11.95 rpm.

Current spacecraft state (00:00 3/19/98 GMT):

Orbit: 797
Downlink: 3600 bps
Spin Rate: 11.95 rpm
Trajectory:
Periselene: 84 km
Aposelene: 115 km
Period: 118 minutes
Inclination 90.4 deg
Occultations: 40 minutes
Eclipses: 46 minutes