The Lunar Prospector Spacecraft
Lunar Prospector was one of the NASA Discovery Program missions. It was designed to perform a low polar orbit investigation of the Moon. This included mapping the surface composition and locating lunar resources, measuring magnetic and gravity fields, and studying outgassing events. The data from this mission, which carried only scientific instruments, complemented the image data from the Clementine mission, which carried mostly cameras. The information gathered will improve the understanding of the origin, evolution, and current state of the Moon. The mission was launched January 6, 1998, from Cape Canaveral using a Lockheed Martin LMLV2 rocket.
The Primary Mission
Beginning on January 15, 1998, Lunar Prospector spent one year mapping the entire surface of the Moon from a distance of about 100 kilometers (60 miles). The data collected during this phase of the mission greatly improved on the quality of data collected previously. Among the early returns from the instruments were those from the Neutron Spectrometer indicating significant amounts of water ice at the lunar poles.The Extended Mission
The mission was extended for an additional seven months, starting in January 1999. At this time, the orbit of the spacecraft was lowered, first to about 30 kilometers (18 miles) and then to within about 10 kilometers (6 miles) of the lunar surface. This allowed the spacecraft to obtain data at much higher resolutions, greatly enhancing results, particularly those from the magnetic fields and gravity experiments.The Impact Experiment
Originally, the mission was to have ended with the spacecraft crashing into the Moon when its fuel ran out. As the mission neared its end, however, the suggestion was made to use the crash as part of an experiment to confirm the existence of water on the Moon. The spacecraft was successfully directed into a crater near the lunar south pole, thought a likely location for ice deposits, but no water was detected in the resulting impact plume.
Lunar Prospector's Flight Path to the Moon
[Photo No. ACD-97-0047-2]
During the cruise phase, mid-course corrections were performed, the instrument booms deployed, and the instruments calibrated. On arrival at the Moon, the spacecraft went through three changes of orbit to place it into its nominal lunar polar orbit of about 118 minutes. With the correct orbit established, mapping data collection could begin.
More about the Spacecraft
The spacecraft was shaped like a drum and made of epoxy graphite material. It was approximately 1.2 meters (4 feet) tall and 1.4 meters (4.5 feet) in diameter. Total mass, when fully fueled, was about 295 kilograms (660 pounds). It was spin stabilized and maneuvering capability was provided by six thrusters. The power system consisted of body-mounted solar cells and storage batteries. There were three radial booms approximately 2.5 meters (8 feet) long for the instruments. These were located equidistantly around the perimeter of the spacecraft.
There was no onboard computer and only minimal onboard data storage capability. This was done primarily as a cost-cutting measure. Instead, the mission was controlled from the Earth and data from the experiments were downloaded continuously. A small solid-state memory was used to store data temporarily when the spacecraft made a pass over the lunar farside and was out of contact with Earth. An array of two transponders and two antennas was used for communications and data return.
More about the Instruments
The mission carried a complement of five instruments to map the lunar surface. The instruments were all designed to collect scientific data; there were no cameras. One additional experiment, the Doppler Gravity Experiment, used the spacecraft itself as an instrument. Brief descriptions of the instruments and the gravity experiment are provided below.
Gamma Ray Spectrometer
The Gamma Ray Spectrometer (GRS) was contained in a cylinder mounted by itself on one of the spacecraft booms. Its purpose was to map the elemental abundances of the lunar surface. It was designed to record the spectrum of gamma rays and neutrons emitted by the radioactive decay of elements contained in the Moon's crust.
Neutron Spectrometer
The Neutron Spectrometer (NS) was designed to detect minute amounts of water ice that may exist on the Moon. It was also used to measure the abundance of solar-wind-implanted hydrogen. This instrument was a slender cylinder and was mounted on the same instrument boom as the Alpha Particle Spectrometer.
Alpha Particle Spectrometer
The Alpha Particle Spectrometer (APS) was designed to detect radon-outgassing events on the surface of the Moon. These events may relate to lunar tectonic activity. It recorded alpha particle signatures of radioactive decay of radon and polonium. The APS was shaped like a cube and was located, with the Neutron Spectrometer, on one of the instrument booms.
Magnetometer
The Magnetometer (MAG) was used primarily to map weak lunar magnetic fields. Used in conjunction with the Electron Reflectometer, it helped locate and measure the strength of the weak localized magnetic fields on the lunar surface. This box-shaped instrument was attached by a short pole to the Electron Reflectometer, which in turn was attached to one of the instrument booms.
Electron Reflectometer
The Electron Reflectometer (ER) was designed to collect information on the lunar remanent paleomagnetic fields. In conjunction with the Magnetometer instrument, it helped locate and measure the strength of the weak localized magnetic fields on the lunar surface. The ER was connected to its companion instrument, the Magnetometer, and the two instruments were mounted together on one of the spacecraft booms.
Doppler Gravity ExperimentThe purpose of the Doppler Gravity Experiment (DGE) was to learn about the distribution of mass in and under the surface of the Moon. It used Doppler tracking of S-Band radio signals to monitor changes in the spacecraft orbit as a way of measuring/mapping the lunar gravity field. These measurements also provided information on the lunar crust and lithosphere and on the internal structure of the Moon.
Gamma Ray Spectrometer
Neutron Spectrometer
Alpha Particle Spectrometer
Magnetometer
Electron Reflectometer
Mission Summary
The Lunar Prospector mission ran 19 months and successfully completed all of its objectives. The data collected will allow construction of a detailed map of the surface composition of the Moon. The data from this mission was 10 times better than hoped and is far more comprehensive than any data ever collected. The mission ended on July 31, 1999, when the spacecraft was directed to crash into a crater near the south pole as part of an experiment to confirm the existence of water ice on the Moon.