Lunar Prospector Credit - NASA

Lunar Prospector was a robotic moon orbiter designed to determine the origin, evolution, and current state of resources of the Moon via low-altitude mapping of its surface composition, magnetic fields, gravity fields, and gas release events. The mission provided a new map that showed in unprecedented detail the chemical composition and the magnetic and gravity fields of the Moon.

Lunar Prospector was the third of NASA's Discovery missions. The mission was led by Lockheed and NASA's Ames Research Centre and the entire cost, including launch vehicle, was less than $63M. After launch, the Lunar Prospector had a 105 hour cruise to the Moon, followed by insertion into a near-circular 100 km altitude lunar polar orbit with a period of 118 minutes. The nominal mission duration was one year. A two year extended mission following this was possible, during which the orbit was to be lowered to 50 km and then 10 km altitude to obtain higher resolution measurements.

The spacecraft's launch mass was 295 kg (fully fueled), 126 kg (dry). The spacecraft was a graphite-epoxy drum, 1.4 meters in diameter and 1.22 meters high with three 2.5 meter radial instrument booms. It was spin-stabilized and used with Sun and limb sensors for attitude determination. It was controlled by 6 hydrazine monopropellant 22-Newton thrusters providing 1430 m/s of delta-V. . Communications were through two S-band transponders and a slotted, phased-array medium gain antenna and omnidirectional low-gain antenna. There was no on-board computer; ground command was through a 3.6 kbps telemetry link. Body mounted solar cells provided 206 W and recharged 15 amp-hr NiH batteries.

The payload included :

Scientific Investigations

Gamma Ray Spectrometer (GRS) - Neutron Spectrometer (NS) - The GRS and NS returned global data on elemental abundances, to be used to help understand the evolution of the lunar highland crust and the duration and extent of basaltic volcanism, and to assess lunar resources. The NS also located significant quantities of water ice which existed in the permanently shadowed areas near the lunar poles.

Magnetometer (MAG) - Electron Reflectometer (ER) - The MAG/ER experiments would return data on the lunar crustal magnetic field and the lunar induced magnetic dipole. These data would help provide an understanding of the origin of lunar paleomagnetism and the degree to which impacts could produce paleomagnetism, and allow constraints on the size and composition of the (possible) lunar core.

Alpha Particle Spectrometer (APS) - The APS instrument would be used to find radon outgassing events on the lunar surface by detecting alpha particles from the radon gas itself and its decay product, polonium. Observations of the frequency and locations of the gas release events would help characterize one possible source of the tenuous lunar atmosphere. Determination of the relationship of outgassing sites with crater age and tectonic features may be possible. This may in turn be used to characterize the current level of lunar tectonic activity.

Doppler Gravity Experiment (DGE) - This investigation would use Doppler tracking of S-Band radio signals to characterize the spacecraft orbit and determine the lunar gravity field. This data would provide information on the lunar interior and, combined with lunar topographic data, would allow modeling of the global crustal asymmetry, crustal structure, and subsurface basin structure. It could also used for planning future lunar missions.

Design Life: One year in lunar orbit. Typical orbit: 100 km lunar orbit, period of 118 min. Length: 1.22 m (4.00 ft). Maximum Diameter: 1.40 m (4.50 ft). Mass: 295 kg (650 lb). Main Engine Propellants: 170 kg (370 lb). Associated Launch Vehicle: Athena-2.

• 1998 January 7 - Lunar Prospector - Program: Discovery. Launch Site: Cape Canaveral. Launch Vehicle: Athena.

  The Lunar Prospector was designed for a low polar orbit investigation of the Moon, including mapping of surface composition and possible polar ice deposits, measurements of magnetic and gravity fields, and study of lunar outgassing events. Data from the 1 to 3 year mission will allow construction of a detailed map of the surface composition of the Moon, and will improve understanding of the origin, evolution, current state, and resources of the Moon. After launch, the Lunar Prospector had a 105 hour cruise to the Moon, followed by insertion into a near-circular 100 km altitude lunar polar orbit with a period of 118 minutes. The nominal mission duration was one year.

• 1999 July 31 - Lunar Prospector, Moon Impact -

  A two year extended mission following the original one-year mission was possible, during which the orbit was to be lowered to 50 km and then 10 km altitude to obtain higher resolution measurements. However this was not funded, and the spacecraft was commanded to crash into the moon.