K3PGP Experimenter's Corner

Lunar Prospector Status Report #21

Feburary 27, 1998 - 7:00 p.m. EST (4:00 p.m. PST)

There will be an LP press conference next Thursday, March 5, at 10 am PST; televised on NASA TV to discuss some of the preliminary science results.

The spacecraft continues to perform very well and all instruments continue to collect good data. Only 2 commands were sent this past week. On Feb 21, commands were sent to tweak the gain setting on the Gamma Ray Spectrometer.

Because LP is no longer in the initial verification period after launch (nominally one month), we no longer get 24 hr/day coverage support from the DSN. This past week we were impacted by several launch events, all which also use the 26-m antenna network at the DSN for support. Coverage this past week totaled about 76 %.

The project is currently working on plans for the first orbit trim maneuver, where the s/c velocity will be changed at specific times to re-circularize the orbit to the nominal 100 ± 20 km orbit. This is expected to be executed some time next week.

Also, we are planning for the March 13 partial eclipse of the moon. On March 13, from 0214-0626 GMT [the evening of March 12 local time], the moon will have the Sun partially blocked by the earth. The spacecraft orbiting the moon will enter and exit the penumbral shadow twice as it circles the moon during this period (see accompanying figure).The partial blockage of the sun will mean that the solar cells will not be generating full power during this time, and as the spacecraft will be having 46 minute long shadows each orbit just from passing behind the moon, the reduced energy from the sun will slow the recharging of the spacecraft battery. We don't expect any problems but procedures are being written to allow us to safely monitor the spacecraft during this event.

Lunar Prospector's apparent trajectory (right to left) through the Earth's penumbral shadow cone at lunar distance, as viewed along the sun-earth line at the time of the 3/13/98 lunar eclipse. The motion depicted reflects a combination of the path of the moon in it's orbit about the earth as well as Lunar Prospector's orbit about the moon. The umbra region represents total blockage of the sun by the earth, while the penumbra region represents partial earth shadowing. The darkened segments along the spacecraft trajectory correspond to times when the spacecraft is in the moon's shadow each orbit.

Another item of astronomical interest, during the solar eclipse this morning, we lost about 9 minutes of data as the moon passed in front of the sun. This is not because of the eclipse itself, but the ground radio telescopes pointing at the spacecraft are also pointing almost right at the sun. This causes the ground receivers to pick up radio noise from the sun, making it hard to recognize the data.

Current spacecraft state (00:00 2/27/98 GMT):

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

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