Lunar Prospector Status Report #12

January 16, 1998 - 1:00 p.m. EST (10:00 a.m. PST)

The Lunar Prospector spacecraft has been successfully placed into what might be termed its "final mapping orbit," according to the Mission Control Center (MCC) at NASA's Ames Research Center.

The results of yesterday's trim maneuvers (for details, see Mission Status Report #11, dated Jan 15, 5 p.m. PST) were such as to place the spacecraft into a 99 km x 100 km altitude orbit, with an inclination of 90° and a period of 118 minutes. The orbit is (lunar) polar in location, and almost perfectly circular in nature. It is virtually "right on" the targeted 100 km (62.5 mile) circular mapping orbit that was planned and anticipated pre-launch. It is certainly well within the 100 ± 20 km (62.5 ± 12.5 mile) orbit that is considered to be the most desirable mapping orbit/altitude.

Of course, the current orbit of the Lunar Prospector spacecraft is subject to degradation with time -- in fact, it will change continuously over time as the gravity anomalies of the Moon pull on the spacecraft, thereby modifying its altitude and its resulting orbit. To address this situation, missions operations personnel will be firing the spacecraft thrusters at periodic intervals to reboost the vehicle to its desired, circular mapping orbit. At the present time, it is believed that the Lunar Prospector spacecraft will remain within the mapping orbit limits (at 100 ± 20 km altitude) for about two weeks. Since one of the mission experiments is to learn more about the gravity model of the Moon, the time required between burn maneuvers is uncertain at present. MCC personnel will be gaining knowledge on this aspect of the operation as the Lunar Prospector mission progresses.

The initial estimate of the spin axis pointing after yesterday's reorientation shows it to be about 2.7 degrees from the target, but well within acceptable limits.

The current state of the spacecraft is as follows: the vehicle is on orbit #48; its spin rate is 12.09 rpm; its spin axis attitude is latitude -- 87.1°, longitude -- 218°; the orbit period is 118 minutes. Earth occultations are of 44-minute duration; there are currently no solar eclipses.

Now that the Lunar Prospector spacecraft is in its final mapping orbit, further mission status reports will be issued on a weekly basis, barring any unforeseen events or anomalous situations.

David Morse
Ames Research Center
Moffett Field, CA 94035