Lunar Prospector Status Report #67

January 29, 1999 - 1:00 p.m. EST (10:00 a.m. PST)

The Lunar Prospector spacecraft is operating well.

The noise in the Alpha Particle Spectrometer (APS) instrument has begun again, and this time seems to be affecting the Neutron Spectrometer (NS) as well. As reported last week, Face #3 was turned off on DOY 019. On DOY 022, Face #5 was powered off as well. Data analysis also indicated that there has been cross-talk between the APS and NS, and that the noise in the APS is also saturating the NS. The APS was commanded off on DOY 025, and the noise in the NS disappeared. Because it is believed that the noise from the APS is related to a light leak in that instrument, the APS was turned on before last night's orbit maneuver, when the attitude was changed to provide better shading to the instrument. The data will be collected for a couple of days for analysis by the instrument team, but if the noise continues, the APS will be turned off this weekend. These two instruments share one of the three science booms on the spacecraft, and they also, along with the Gamma Ray Spectrometer, share the same electronics box. The anomaly is under investigation.

The spacecraft was successfully maneuvered into the extended mission orbit last night. Two burn sequences placed the spacecraft in a 15 km x 45 km altitude orbit which will maintain an average altitude above the surface of 30 km. After the orbit change burns, the attitude was precessed slightly to change the sun angle for the spectrometer instruments.

The maneuver timeline is given below. The combined set of maneuvers consumed 1.44 kg of propellant. DOY 029, times are GMT:

06:29 thruster heaters ON
06:35 APS ON 06:39 load maneuver parameters
06:55 fire part 1, A1/A2 thrusters for 40.4 sec, 6.34 m/s raised periapsis, new orbit 43 km x 63 km altitude
07:30 thruster heaters ON
07:32 load maneuver parameters
07:43 fire part 2, A1/A2 thrusters for 71.6 sec, 11.34 m/s lower periapsis, new orbit 15 km x 45 km
08:05 thruster heaters ON
08:20 load maneuver parameters
08:24 fire reorientation, A1/A4 thrusters, 8 0.2-sec pulses, slew 1.5 deg Cycling of the spacecraft transmitter began this morning. 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.

Current spacecraft state (0000 GMT 01/29/99):

Orbit: 4698
Downlink: 3600 bps
Spin Rate: 12.09 rpm

Spin Axis Attitude (ecliptic):
Latitude: -89.3 deg
Longitude: 339 deg

Trajectory:
Periapsis Alt: 17 km
Apoapsis Alt: 43 km
Period: 111 min

Occultations: none
Eclipses: 40 minutes
Propellant Remaining: 15.95 kg

On January 31, 1999, from 14:04 to 18:30 GMT, the Earth will partially block the Sun as seen by the moon. The LP spacecraft will enter and exit partial shadow twice as it circles the moon. Since the LP spacecraft will also be experiencing 42 minute nightside passes once each 111 minute orbit, the loss of full sun between nightside passes will slow battery recharge. The LP project will be closely monitoring the power and thermal subsystems during this event, and power cycling of the transmitter is expected.