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Lunar Prospector Status Report #27

April 1, 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 Tues., March 31 (PST), mission controllers executed an attitude reorientation trim maneuver. In doing so, the spacecraft's spin axis was reoriented about 5 degrees so that the Sun shines on the top half of the spacecraft. The maneuver required 23 pulses, as detailed by the timeline below:

Tues., March 31, 2:32 p.m. (PST) Thruster heaters on
Tues., March 31, 2:37 p.m. (PST) Maneuver parameters loaded
Tues., March 31, 2:58 p.m. (PST) Thrusters A1 and A4 fired (23 pulses) to rotate spin axis 4.7 degrees
Tues., March 31, 3:01 p.m. (PST) Thruster parameters reset

The Lunar Prospector engineering team is still investigating the results of the spin axis reorientation by reviewing pre-and post-maneuver attitude data. Calibration data for the Earth-Moon Limb Crossing Sensor requires updating based upon flight data. Until this recalibration is complete, the precise attitude and performance of the maneuvers cannot be analyzed.

The current state of the vehicle (as of 4:00 p.m. (PST) on Wed., April 1, 1998), according to Mission Operations Manager Marcie Smith, is as follows:

Spacecraft Orbit Number: 968
Data Downlink Rate: 3600 bps
Spin Rate: 11.96 rpm

Spin Axis Attitude
Longitude: (see above)
Latitude: (see above)

Trajectory
Periselene: 93.4 km
Aposelene: 105.9 km
Period: 118 minutes
Inclination: 90.2 degrees

Occultations: 25 minutes in duration
Eclipses: 47 minutes in duration (maximum)

At present, Lunar Prospector is aligned with the Moon-Sun line. This means that the spacecraft passes directly over the local noon and midnight points on the Moon, experiencing the hottest temperatures and longest eclipses of the entire mission. In about three months, when the Earth (and thus the Moon) have continued around the Sun, the spacecraft's orbit plane will be perpendicular to the Moon-Sun line, and there will be a period of a few weeks with no eclipses before the next eclipse season begins.

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