Lunar Prospector Status Report #68

February 3 , 1999 - 1:00 p.m. EST (10:00 a.m. PST)

The Lunar Prospector spacecraft is operating well and collecting science data in the extended mission orbit.

On January 31, the moon went through Earth's penumbral shadow (a partial eclipse) from 14:04 to 18:30 GMT. The loss of full sunlight cooled the LP spacecraft and prevented full recharging of the battery between nightside passages each orbit. To prevent excessive battery discharge, the spacecraft transmitter was powered off for much of the event, and the primary heater circuits were powered off for a short time as well. The timeline is given below.

DOY 031 (all times GMT):
15:00 Transmitter OFF. (Enter occultation and nightside eclipse 15:03)
15:45 Exit occultation and nightside eclipse but deep in partial shadow (over 90% of the sun blocked). Transmitter left off - no data
16:40 Transmitter ON for data snapshot. Battery voltage good but propellant tank heater was ON (high load). Tried to command primary heater circuit off, but not enough time before next occultation.
16:42 Exit partial shadow - full sun for a while
16:51 Transmitter OFF. (Enter occultation and nightside eclipse 16:54)
17:37 Exit occultation and nightside eclipse but back in partial shadow (about 30% of sun blocked)
17:39 Transmitter ON for data snapshot. Battery voltage okay but dropping quickly due to heater and transmitter loads.
17:42 Primary heater circuit OFF. Battery voltage began to recover immediately.
17:43 Transmitter OFF 18:05 Transmitter ON. Data snapshot showed battery recharging.
18:11 Exit partial shadow - full sun again 18:18 Transmitter OFF
18:45 Enter occultation and nightside eclipse
19:28 Exit occultation and nightside eclipse 19:29 Transmitter ON. Battery recharging.
19:38 Primary heater circuit ON. Back to normal operations.

Cycling of the spacecraft transmitter continues. The transmitter is powered off for occultations (when the spacecraft goes behind the moon and no data is received at Earth anyways) to reduce battery drain during propellant tank heater events. On January 31, a ground station problem prevented turn on of the transmitter at occultation exit, and 34 minutes of data were lost.

The investigation of the noise in the Alpha Particle Spectrometer (APS) instrument continues. The instrument continues to intermittently see noise which saturates the electronics, occasionally affecting the Neutron Spectrometer (NS) data as well.

The analysis of the orbit data since the maneuver last week show good results. The performance of the thrusters was within 0.5% of predicted and the orbit is evolving as expected. The next maneuver is scheduled for February 25.

Current spacecraft state (0000 GMT 02/03/99):

Orbit: 4750
Downlink: 3600 bps
Spin Rate: 12.09 rpm

Spin Axis Attitude (ecliptic):
Latitude: -88.5 deg
Longitude: 331 deg

Trajectory:
Periapsis Alt: 21 km
Apoapsis Alt: 39 km
Period: 111 min

Occultations: 48 minutes
Eclipses: 42 minutes
Propellant Remaining: 15.95 kg