Lunar Prospector

Lunar Prospector was a robotic NASA mission launched in 1998 as part of the Discovery Program. Its primary goal was to perform a low-altitude polar orbit investigation of the Moon, mapping its surface composition and locating potential resources. The mission provided key data that revolutionized understanding of the lunar polar regions and confirmed the presence of water ice. It concluded with a controlled impact into a permanently shadowed crater in 1999.

Spacecraft Design

The spacecraft was a simple, spin-stabilized, graphite-epoxy drum built by Lockheed Martin under the management of NASA's Ames Research Center. Its design emphasized low cost and reliability, carrying a suite of five scientific instruments mounted on three 2.5-meter booms to minimize interference from the spacecraft body. These instruments included a Gamma Ray Spectrometer, a Neutron Spectrometer, a Magnetometer, an Electron Reflectometer, and an Alpha Particle Spectrometer. Power was provided by a body-mounted solar array charging nickel-cadmium batteries, and communication was handled via a S-band transponder with the Deep Space Network.

Mission Objectives

The mission's core objectives were defined by the Discovery Program's mandate for focused, cost-effective science. Key goals included globally mapping the elemental composition of the lunar surface, particularly for thorium, potassium, uranium, iron, titanium, oxygen, silicon, aluminum, magnesium, and calcium. A primary focus was the search for evidence of polar ice deposits within permanently shadowed craters. Additional objectives included measuring the lunar magnetic field and gravity field, and detecting the release of lunar outgassing events, which could indicate low-level volcanic or tectonic activity.

Orbit and Operations

Launched on an Athena II rocket from Cape Canaveral Space Launch Complex 46, the spacecraft entered an initial 105-hour phasing loop trajectory before being captured into a 12-hour lunar orbit. Mission controllers at Ames Research Center then used a series of orbital maneuvers to lower it into its primary, near-circular 100 km altitude polar orbit, which it achieved on January 16, 1998. This orbit allowed for global mapping every 118 minutes. In December 1998, the orbit was lowered to approximately 40 km, and later to 30 km, to obtain higher-resolution data, particularly for the gravity field investigations.

Discoveries

The Neutron Spectrometer data provided strong evidence for the presence of hydrogen, interpreted as water ice, in the permanently shadowed regions of both lunar poles, with a higher concentration at the lunar north pole. The Gamma Ray Spectrometer produced the first global maps of mare and highland elemental abundances, revealing the Procellarum KREEP Terrane as a unique geochemical province rich in heat-producing elements. The Magnetometer and Electron Reflectometer mapped remnant crustal magnetic fields, creating the most detailed atlas of lunar magnetic anomalies to date. The mission also refined models of the lunar gravity field, identifying several new mass concentrations.

Impact and Legacy

The mission was deliberately terminated on July 31, 1999, by commanding it to impact the interior of Shoemaker crater near the lunar south pole. Scientists from the University of Texas at Austin and other institutions observed the event using the Keck Observatory and the Hubble Space Telescope in hopes of detecting a plume of water vapor, though no definitive signature was observed. The mission's data remains a foundational resource for planetary science and influenced the site selection for subsequent missions like the Lunar Reconnaissance Orbiter, LCROSS, and the Artemis program. It demonstrated the high scientific return possible from low-cost, focused Discovery Program missions.

Category:NASA space probes Category:Discovery Program Category:1998 in spaceflight Category:Missions to the Moon