Lunar Prospector Status Report #93

July 28 , 1999 - 1:00 p.m. EST (10:00 a.m. PST)

The Lunar Prospector spacecraft continues to collect good science data in the extended mission orbit. Two of five science instruments are on: the Magnetometer (MAG) and the Electron Reflectometer (ER). The spectrometers were powered off today as part of the eclipse power sharing activities as described below.

The Lunar Prospector orbit was trimmed successfully Monday. This maneuver raised the altitude of periapsis by about 5 km to allow the spacecraft to safely orbit through the rest of the week. A brief timeline is below. Times are GMT, on DOY 207 [7/26/99]:

13:36 Thruster heaters commanded on
13:39 Loaded maneuver parameter file
14:01 Fire A1/A2 for 9.0 sec (1.44 m/s delta-V, 0.13 kg prop used)
14:04 Safed spacecraft

After the maneuver, the MAG/ER was configured to collect high resolution data during the full moon passage. A total of 27 commands were transmitted with no anomalies.

The LP spacecraft successfully survived today's lunar eclipse. Because the moon passed through the earth's shadow, the time of no sunlight was increased from the once per orbit lunar shadow duration of 36 minutes, to 67 minutes. For another 2:31, the sun was partially eclipsed by the earth, preventing the normal recharge of batteries. The spacecraft was not designed to survive this eclipse.

To increase the chance of survival, the spectrometer instruments were turned off, reducing the load. Because they would get very cold during the eclipse while they were turned off, they will not be turned on again during the last 3 days of the mission. The impact to their science analysis will be negligible. The MAG/ER was left on so that it could continue to get the high resolution full moon data through the end of the mission.

Other non-essential loads were powered off: the pressure transducer which measures the propellant tank pressure, and the earth-moon limb sensor. These were turned back on at the end of the event. Also turned off was the primary heater relay. This prevented the highest load of the spacecraft, the propellant tank heaters, from coming on at a time when the battery was unable to support the load. This relay was turned back on at the end of the event as well.

The spacecraft transmitter is the second highest load on the spacecraft, and it was turned off for every occultation (when the s/c is behind the moon as seen from the tracking station), plus extra time as needed to allow battery recharge. It was turned on as much as power allowed to prevent it from getting too cold as well as to allow collection of data to monitor the spacecraft status.

Activities are listed below, times are GMT, DOY 209 (7/28/99). Umbra is when the entire sun is blocked by the earth as seen from the spacecraft. Penumbra is when only part of the sun is blocked. Occultation times are not listed, but they overlap closely with the lunar shadow events.

07:25 - Pressure Transducer commanded off
07:26 - Earth/Moon Sensor Commanded off
07:33 - Spectrometers commanded off
08:32 - Transmitter commanded off
08:37 - Entered Lunar Shadow
09:02 - Entered Earth Penumbra (first time)
(can't tell from data since sun still blocked by moon)
09:12 - Exit Lunar Shadow
09:22 - Transmitter commanded on
09:30 - Exit Earth Penumbra (first time)
10:16 - Entered Earth Penumbra (2nd time)
10:23 - Transmitter commanded off
10:29 - Entered Lunar Shadow
10:52 - Entered Earth Umbra (can't tell, since sun is already blocked by moon)
11:03 - Exit Lunar Shadow (can't tell, since sun is still blocked by earth)
11:34 - Transmitter commanded on
11:36 - Exit Earth Umbra but only partial sun (3rd interval of Earth Penumbra)
12:06 - Transmitter commanded off
12:20 - Entered Lunar Shadow
12:55 - Exit Lunar Shadow
13:13 - Tranmistter commanded on - battery voltage very low (21.5 V)
13:14 - Primary Heaters commanded off
13:15 - Transmitter commanded off
13:42 - Exit Earth Penumbra
13:54 - Transmitter commanded on - battery charging, at 30.1 V
14:04 - Transmitter commanded off
14:11 - Enter Lunar Shadow
14:47 - Exit Lunar Shadow
14:54 - Transmitter commanded on - battery charging, at 29.0 V
15:52 - Transmitter commanded off
16:03 - Enter Lunar Shadow
16:38 - Exit Lunar Shadow
16:42 - Transmitter commanded on - battery charging, at 29.8 V
17:18 - Battery fully charged (33.0 V); EMS commanded on
17:19 - Pressure Transducer commanded on
17:20 - Primary Heaters commanded on (creates very high load as all
heaters turn on at once)
17:47 - Transmitter commanded off
17:54 - Enter Lunar Shadow
18:30 - Exit Lunar Shadow
18:37 - Transmitter commanded on - battery charging very slowly
(all heaters are on), at 28.7 V
19:14 - Transmitter commanded off
19:46 - Enter Lunar Shadow
20:22 - Exit Lunar Shadow
21:00 - Transmitter commanded on - battery fully charged (33.3 V), heater
load back to normal.

A total of 53 commands were sent with no anomalies.

The spacecraft is still cooler than normal but is warming as expected.

Current spacecraft state (2110 GMT 7/28/99, DOY 209):

Orbit:7028
Downlink:3600 bps
Spin Rate:12.12 rpm

Spin Axis Attitude (ecliptic):
Latitude: -88.7 deg
Longitude: 055 deg

Trajectory:
Periapsis Alt:10.9 km
Apoapsis Alt: 49.1 km
Period:111 min

>Occultations:41 minutes
Eclipses: 36 minutes
Propellant Remaining: 9.38 kg

The next activity is the spin-up, scheduled for tomorrow, 7/29 at 15:32 GMT. This will be the first step in setting the spacecraft up for the targetted impact. Impact is now scheduled for 09:51 GMT on 7/31 (one minute earlier than reported last week). It was moved up to optimize timing with Hubble Space Telescope observations.