The Lunar Prospector was designed for a low polar orbit investigation of the Moon, including mapping of surface composition and possible deposits of polar ice, measurements of magnetic and gravity fields, and study of lunar outgassing events. Data from the 19 month moon mission will allow construction of a detailed map of the surface composition of the Moon, and will improve our understanding of the origin, evolution, current state, and resources of the Moon.
The spacecraft carries 6 experiments: a Gamma Ray Spectrometer (GRS), a Neutron Spectrometer (NS), a Magnetometer (MAG), an Electron Reflectometer (ER), an Alpha Particle Spectrometer (APS), and a Doppler Gravity Experiment (DGE). The instruments are omnidirectional and require no sequencing. The normal observation sequence is to record and downlink data continuously.
Spacecraft and Subsystems:
The spacecraft is a graphite-epoxy drum, 1.37 meters in diameter and 1.28 meters high with three radial 2.5 m instrument booms. A 1.1 m extension boom at the end of one of the 2.5 m booms holds the magnetometer. Total initial mass (fully fueled) was 296 kg. It is spin-stabilized (nominal spin rate 12 rpm) with its spin axis normal to the ecliptic plane. The spacecraft is controlled by 6 hydrazine monopropellant 22-Newton thrusters, two aft, two forward, and two tangential.
Three fuel tanks mounted inside the drum hold 138 kg of hydrazine pressurized by helium. The power system consists of body mounted solar cells which produce an average of 186 W and a 4.8 amp-hr rechargeable NiCd battery. Communications are through two S-band transponders, a slotted, phased-array medium gain antenna for downlink, and an omnidirectional low-gain antenna for downlink and uplink.
There is no on-board computer, all control is from the ground, commanding a single on-board command and data handling unit. Data are downlinked directly and also stored on a solid-state recorder and downlinked after 53 minutes, to ensure all data collected during communications blackout periods are received.
Following launch on 7 January 1998 UT (6 January EST) aboard a three-stage Athena 2 rocket, the Lunar Prospector had a 105 hour cruise to the Moon. During the cruise, the three instrument booms were deployed. The MAG and APS collected calibration data, while the GRS, NS, and ER outgassed for one day, after which they also collected calibration data in cis-lunar space. The craft was inserted into an 11.6-hour period capture orbit about the Moon at the end of the cruise phase.
After 24 hours Lunar Prospector was inserted into a 3.5-hour period intermediate orbit of the moon, followed 24 hours later (on 13 January 1998) by tranfer into a 92 x 153 km preliminary mapping orbit, and then on 16 January by insertion into the near-circular 100 km altitude nominal lunar polar mapping orbit with an inclination of 90 degrees and a period of 118 minutes. Lunar calibration data was collected during the 11.6- and 3.5-hour orbits. Lunar mapping data collection started shortly after the 118 minute orbit was achieved. The data collection was periodically interrupted during the mission as planned for orbital maintenance burns, which took place to recircularize the orbit whenever the periselene or aposelene was more than 20 to 25 km from the 100 km nominal orbit, about once a month. On 19 December 1998, a maneuver lowered the orbit to 40 km to perform higher resolution studies. The orbit was altered again on 28 January to a 15 x 45 km orbit, ending the 1 year primary mission and beginning the extended mission. The mission ended on 31 July 1999 at 9:52:02 UT (5:52:02 EDT) when Lunar Prospector was deliberately targeted to impact in a permanently shadowed area of a crater near the south pole of the moon. It was hoped that the impact would liberate water vapor from the suspected ice deposits in the crater and that the plume would be detectable from Earth, however, no plume was observed.
The Lunar Prospector mission was the third mission selected by NASA for full development and construction as part of NASA's Discovery Program. Total cost for the mission was $62.8 million including development ($34 million), launch vehicle (~$25 million) and operations (~$4 million).