This Week in NASA History: Lunar Prospector

ASK OCE — January 12, 2007 — Vol. 2, Issue 1

On January 6, 1998, the unmanned Lunar Prospector embarked on a one-year lunar polar mission. Its primary objective was to ascertain whether or not water ice was buried inside the lunar crust.

The spacecraft was developed as part of the Discovery Program a series of low-cost missions. In addition to the presence of water, Lunar Prospector also gathered data regarding the existence of other natural resources, such as minerals and gases. Such elements might prove useful in building and sustaining a future human lunar base or for producing fuel for the launch of possible future spacecraft from the Moon to the rest of the solar system.

Lunar Prospector was specifically designed for a low-polar orbit investigation of the lunar surface. In addition to mapping the surface and investigating the possibility of polar ice deposits, it took measurements of the Moon’s magnetic and gravity fields. The spacecraft carried 5 instruments: a Gamma Ray Spectrometer (GRS), a Neutron Spectrometer (NS), a Magnetometer (MAG), an Electron Reflectometer (ER), and an Alpha Particle Spectrometer (APS). The ship had no onboard computer; all control was performed from Earth on a 53-minute delay. Lunar Prospector also had a single onboard command and data handling unit.

During Lunar Prospector’s 105-hour trip to the Moon, its three instrument booms were deployed. The MAG and APS collected calibration data, while the GRS, NS, and ER collected calibration data in cis-lunar space. Once in orbit around the Moon, Lunar Prospector was inserted into a 3.5-hour period intermediate orbit. A day later, it was put into a preliminary mapping orbit, and then on January 16 it was inserted into a near-circular 100 km altitude nominal lunar polar mapping orbit. Data collection was periodically interrupted during the mission for orbital maintenance burns, which took place about once a month to recircularize the orbit.

In March of 1998, Lunar Prospector detected intriguing evidence of the possible presence of water ice at both lunar poles. The possible lunar water ice was estimated at an overall range of eleven million to 330 million tons. The data gathered indicted that perhaps twice as much water existed at the Moon’s north pole as its south pole.

The mission ended on July 31, 1999, when Lunar Prospector was deliberately targeted to collide with a shaded portion of a crater near the lunar south pole. Scientists hoped that the impact would release water vapor from suspected ice deposits in the crater that would be observable from Earth. No plume was observed.