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Lunar Prospector Status Report #11

January 15, 1998 - 8:00 p.m. EST (5:00 a.m. PST)

The Lunar Prospector orbit trim maneuvers and spacecraft attitude reorientations scheduled for today were successfully completed this afternoon (p.m. PST), Thurs. Jan 15, 1998, according to Mission Operations Manager Marcie Smith.

Final determination of the orbit will not be available for several hours as the navigation team must collect and verify data for one to two orbits. The spacecraft performed nominally, and it is expected that the vehicle is now within the 100 ± 20 km (62.5 ±12.5 mile) altitude orbit desired for mapping. The attitude is also believed to be within a degree of the desired mapping attitude, with the spin axis near normal to the ecliptic plane.

The timeline for today's events was as follows. At 12:31 p.m. PST, the thruster heaters were activated. This was followed by the firing of the thrusters at 1:44 p.m. PST for a 76.6 second burn to reduce the spacecraft speed by 12.1 meters per second, thereby lowering the aposelene from its initial 153 km (95.6 mile) altitude to something close to the desired 100 km (62.5 mile) altitude. At 2:06 p.m. PST, the thruster heaters were again activated, followed by a 16.4 second burn designed to raise Lunar Prospector's speed by 2.6 meters per second, thereby raising the vehicle's periselene by about 7 km (4.4 miles) from its original 92 km (57.5 mile) altitude to what is believed to be a new 99 km (61.9 mile) altitude.

At 3:57 p.m. PST, a period of pulsed thruster firing was initiated to reorient the spacecraft to the desired mapping attitude. In all, 139 pulses were fired to precess the spin axis 31.5 degrees. The target attitude is: latitude -- 89 degrees; longitude -- 296 degrees.

The science instruments remain operational and continue collecting excellent data. The precise results of today's maneuvers will be reported in tomorrow's mission status report when the relevant data has been analyzed and verified by mission operations personnel.

David Morse
Ames Research Center
Moffett Field, CA 94035