Lunar Prospector
Mission type | Lunar orbiter |
---|---|
Operator | NASA |
COSPAR ID | 1998-001A |
SATCAT no. | 25131 |
Mission duration | 570 days |
Spacecraft properties | |
Bus | LM-100 |
Manufacturer | Lockheed Martin |
Launch mass | 296.4 kilograms (653 lb)[1] |
Dry mass | 126 kilograms (278 lb) |
Power | 202.0 W |
Start of mission | |
Launch date | January 7, 1998, 02:28:44 Lockheed Martin Space Systems | UTC
Orbital parameters | |
Reference system | Selenocentric |
Eccentricity | 0.00046 |
Periselene altitude | 99.45 kilometers (61.80 mi) |
Aposelene altitude | 101.2 kilometers (62.9 mi) |
Inclination | 90.55 degrees |
Period | 117.9 minutes |
Epoch | January 16, 1998[1] |
Lunar orbiter | |
Orbital insertion | January 11, 1998, 10:28 UTC |
Impact site | 87°42′S 42°06′E / 87.7°S 42.1°E |
Orbits | ~7060 |
Instruments | |
Gamma ray spectrometer (GRS) Lunar Prospector neutron spectrometer (NS) Alpha particle spectrometer (APS) Doppler gravity experiment (DGE) Magnetometer (MAG) Electron reflectometer (ER) | |
Official insignia of the Lunar Prospector mission Discovery program → |
Lunar Prospector was the third mission selected by
Data from the mission allowed the construction of a detailed map of the surface composition of the Moon, and helped to improve understanding of the origin, evolution, current state, and resources of the Moon. Several articles on the scientific results were published in the journal Science.[5][6]
Lunar Prospector was managed by
In 2013 an unidentified object was discovered in an unstable orbit around the Earth, and assigned the provisional number WT1190F. After it crashed into the Indian Ocean it was identified as probably the translunar injector of Lunar Prospector.[8]
Spacecraft and subsystems
This article needs additional citations for verification. (July 2020) |
The spacecraft was a graphite-epoxy drum, 1.36 m (4 ft 6 in) in diameter and 1.28 m (4 ft 2 in) high with three radial 2.5 m (8 ft 2 in) instrument booms. A 1.1 m (3 ft 7 in) extension boom at the end of one of the 2.5 m booms held the magnetometer. Total initial mass (fully fueled) was 296 kg (653 lb). It was spin-stabilized (nominal spin rate 12 rpm) with its spin axis normal to the ecliptic plane. The spacecraft was controlled by six
Communications were through two
The probe also carried a small amount of the remains of
Mission profile
Following launch on January 7, 1998 UT (January 6 EST) aboard a four-stage
The mission ended on July 31, 1999 at 9:52:02 UT (5:52:02 EDT) when Lunar Prospector was steered into a deliberate collision in a permanently shadowed area of the Shoemaker crater near the lunar south pole. 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 such plume was observed.
The Lunar Prospector mission was the third mission selected by NASA for full development and launch as part of NASA's Discovery Program. Total cost for the mission was $63 million including development ($34 million), launch vehicle (~$25 million) and operations (~$4 million).
Instruments
The spacecraft carried six instruments: a
Gamma Ray Spectrometer (GRS)
The Lunar Prospector
The GRS was a small cylinder which was mounted on the end of one of the three 2.5 m (8 ft 2 in) radial booms extending from Lunar Prospector. It consisted of a bismuth germanate crystal surrounded by a shield of borated plastic. Gamma rays striking the bismuth atoms produced a flash of light with an intensity proportional to the energy of the gamma ray which was recorded by detectors. The energy of the gamma ray is associated with the element responsible for its emission. Due to a low signal-to-noise ratio, multiple passes were required to generate statistically significant results. At nine passes per month, it was expected to take about three months to confidently estimate abundances of thorium, potassium, and uranium, and 12 months for the other elements. The precision varies according to element measured. For U, Th, and K, the precision is 7% to 15%, for Fe 45%, for Ti 20%, and for the overall distribution of KREEP 15% to 30%. The borated plastic shield was used in the detection of fast neutrons. The GRS was designed to achieve global coverage from an altitude of approximately 100 km (62 mi) and with a surface resolution of 150 km (93 mi).[11]
The instrument mapped the distribution of various important elements across the Moon. For example, the Lunar Prospector GRS identified several regions with high iron concentrations.[12]
The fundamental purpose of the GRS experiment was to provide global maps of elemental abundances on the lunar surface. The GRS was designed to record the spectrum of gamma rays emitted by:
- the radioactive decay of elements contained in the Moon's crust; and
- elements in the crust bombarded by cosmic rays and solar wind particles.
The most important elements detectable by the GRS were uranium (U), thorium (Th), and potassium (K), radioactive elements which generate gamma rays spontaneously, and iron (Fe), titanium (Ti), oxygen (O), silicon (Si), aluminum (Al), magnesium (Mg), and calcium (Ca), elements which emit gamma rays when hit by cosmic rays or solar wind particles. The uranium, thorium, and potassium in particular were used to map the location of KREEP (potassium, rare-earth element, and phosphorus containing material, which is thought to have developed late in the formation of the crust and upper mantle, and is therefore important to understanding lunar evolution). The GRS was also capable of detecting fast (epithermal) neutrons, which complemented the neutron spectrometer in the search for water on the Moon.
Neutron Spectrometer (NS)
Based on the Lunar Prospector Neutron Spectrometer (NS) data, mission scientists have determined that there is evidence for lunar water ice in the polar craters of the Moon,[13] an estimated 3 billion tonnes (800 billion US gallons).
The neutron spectrometer was a narrow cylinder colocated with the Alpha Particle Spectrometer at the end of one of the three radial Lunar Prospector science booms. The instrument had a surface resolution of 150 km (93 mi). The neutron spectrometer consisted of two canisters each containing helium-3 and an energy counter. Any thermal neutrons colliding with the helium atoms give an energy signature which can be detected and counted. One of the canisters was wrapped in cadmium, and one in tin. The cadmium screens out thermal (low energy or slow-moving) neutrons, while the tin does not. Thermal neutrons are cosmic-ray-generated neutrons which have lost much of their energy in collisions with hydrogen atoms. Differences in the counts between the two canisters indicate the number of thermal neutrons detected, which in turn indicates the amount of hydrogen in the Moon's crust at a given location. Large quantities of hydrogen would likely be due to the presence of water.
The NS was designed to detect minute amounts of water ice which were believed to exist on the Moon. It was capable of detecting water ice at a level of less than 0.01%. For the polar ice studies, the NS was slated to examine the poles to 80 degrees latitude, with a sensitivity of at least 10 ppm by volume of hydrogen. For the implanted hydrogen studies, the NS was intended to examine the entire globe with a sensitivity of 50 ppmv. The Moon has a number of permanently shadowed craters near the poles with continuous temperatures of −190 °C (−310.0 °F). These craters may act as cold-traps of water from incoming comets and meteoroids. Any water from these bodies which found its way into these craters could become permanently frozen. The NS was also used to measure the abundance of hydrogen implanted by solar wind.
The Alpha Particle Spectrometer (APS)
The Alpha Particle Spectrometer (APS) was a cube approximately 18 cm (7.1 in) colocated with the neutron spectrometer on the end of one of the three radial 2.5 m (8 ft 2 in) Lunar Prospector science booms. It contained ten silicon detectors sandwiched between gold and
The APS was designed to detect radon outgassing events on the surface of the Moon. The APS recorded alpha particle signatures of radioactive decay of radon gas and its byproduct product, polonium. These putative outgassing events, in which radon, nitrogen, and carbon dioxide are vented, are hypothesized to be the source of the tenuous lunar atmosphere, and may be the result of the low-level volcanic/tectonic activity on the Moon. Information on the existence, timing, and sources of these events may help in a determination of the style and rate of lunar tectonics.
The APS was damaged during launch, ruining one of the five detecting faces. Additionally, due to sunspot activity peaking during the mission, the lunar data was obscured by solar interference. The information was eventually recovered by subtracting out the effects of the solar activity.
Doppler Gravity Experiment (DGE)
The Doppler Gravity Experiment (DGE) was the first polar, low-altitude mapping of the lunar gravity field. The
The purpose of the Lunar Prospector DGE was to learn about the surface and internal mass distribution of the Moon. This is accomplished by measuring the
This experiment provided the first lunar gravity data from a low polar orbit. Because line-of-sight tracking was required for this experiment, only the near-side gravity field could be estimated using this Doppler method. The experiment was a byproduct of the spacecraft
The downlink telemetry signal was transmitted at 2273 MHz, over a ±1 MHz bandwidth as a right-hand circularly polarized signal at a nominal power of 5 W and peak power of 7 W. Command uplinks were sent at 2093.0542 MHz over a ±1 MHz bandwidth. The transponder was a standard Loral/Conic S-Band transponder. An omnidirectional antenna can be used for uplink and downlink, or a medium gain helix antenna can be used (downlink only). Since the spacecraft was spin-stabilized, the spin resulted in a bias in the Doppler signal due to the spacecraft antenna pattern spinning with respect to the Earth station of 0.417 Hz (27.3 mm/s) for the omnidirectional antenna, and −0.0172 Hz (−1.12 mm/s) for the medium gain antenna. LOS data was sampled at 5 seconds to account for the approximately 5 second spin rate of the spacecraft, leaving a residual of less than 0.1 mm/s.
The detailed data collected has shown that for low lunar orbit the only stable or "frozen orbits" are at inclinations near 27º, 50º, 76º, and 86º.[15]
Electron Reflectometer and Magnetometer (MAG/ER)
The Magnetometer and Electron Reflectometer (collectively, MAG/ER) detected anomalous surface magnetic fields on the Moon, which are in stark contrast to a global magnetosphere (which the Moon lacks). the Moon's overall magnetic field is too weak to deflect the solar wind, but MAG/ER discovered a small surface anomaly that can do so. This anomaly, about 100 km (62 mi) in diameter, has therefore been referred to as "the smallest known magnetosphere, magnetosheath and bow shock system in the Solar System."[16] Due to this and other magnetic features of the Moon's surface, hydrogen deposited by solar wind is non-uniformly distributed, being denser at the periphery of the magnetic features. Since hydrogen density is a desirable characteristic for hypothetical lunar bases, this information may be useful in choosing optimal sites for possible long-term Moon missions.
The electron reflectometer (ER) and
The ER determined the location and strength of magnetic fields from the
The ER and the electronics package were located at the end of one of the three radial science booms on Lunar Prospector. The MAG was in turn extended further on a 0.8 m (2 ft 7 in) boom—a combined 2.6 m (8 ft 6 in) from Lunar Prospector in order to isolate it from spacecraft generated magnetic fields. The ER and MAG instruments had a combined mass of 5 kg (11 lb) and used 4.5 watts of power.
See also
- Lunar resources
- Luna-Glob, a current Russian lander program
- Prospector (spacecraft)
- Resource Prospector (rover)
- List of artificial objects on the Moon
References
- ^ a b c "Lunar Prospector". NASA Space Science Data Coordinated Archive. Archived from the original on 2019-01-15. Retrieved 2023-01-09.
- ^ "NASA - NSSDCA - Spacecraft - Details". nssdc.gsfc.nasa.gov. Archived from the original on 2019-08-12. Retrieved 2018-07-04.
- ^ "Eureka! Ice Found At Lunar Poles". NASA. Archived from the original on 2020-08-03. Retrieved 2018-07-04.
- ^ "Ice on the Moon". nssdc.gsfc.nasa.gov. Archived from the original on 2019-10-24. Retrieved 2018-07-04.
- PMID 9727968.
- PMID 9727967.
- OCLC 61137782.
- ^ Berger, Eric (2016-01-14). "Fiery space debris that hit Earth in November likely from Moon rocket". Ars Technica. Archived from the original on 2019-03-24. Retrieved 2019-03-24.
- ^ "Gene Shoemaker - Founder of Astrogeology | U.S. Geological Survey". www.usgs.gov. Archived from the original on 2022-04-28. Retrieved 2022-04-28.
- ^ "Gene Shoemaker | American astrogeologist | Britannica". www.britannica.com. Archived from the original on 2022-04-25. Retrieved 2022-04-28.
- PMID 9727970.
- ^ "Iron Distribution - Lunar Prospector". NASA. Archived from the original on 2008-06-26. Retrieved 2008-07-14.
- ^ "Neutron Spectrometer Results". NASA. Archived from the original on 2008-05-31. Retrieved 2008-07-14.
- ^ "Doppler Gravity Experiment Results". NASA. Archived from the original on 2008-07-12. Retrieved 2008-07-14.
- ^ Bell, Trudy E. (2006-11-06). Phillips, Tony (ed.). "Bizarre Lunar Orbits". Science@NASA. NASA. Archived from the original on 2021-12-04. Retrieved 2017-09-08.
- ^ "Magnetometer / Electron Reflectometer results". NASA. Archived from the original on 2010-05-27. Retrieved 2008-07-14.
External links
- "Lunar Prospector website". NASA. Archived from the original on 1998-01-09. Retrieved 2006-04-24.
- "GRS results". Lunar Prospector website. NASA. Archived from the original on 2006-02-11. Retrieved 2006-04-24.
- "Alpha Particle Spectrometer results". Lunar Prospector website. NASA. Archived from the original on 2005-12-26. Retrieved 2006-04-24.
- "MAG/ER results". Lunar Prospector website. NASA. Archived from the original on 2010-05-27. Retrieved 2006-04-24.
- "Neutron Spectrometer results". Lunar Prospector website. NASA. Archived from the original on 2008-05-31. Retrieved 2006-04-24.
- "DGE results". Lunar Prospector website. NASA. Archived from the original on 2008-07-12. Retrieved 2006-04-24.
- "Eureka! Ice Found At Lunar Poles". Lunar Prospector website. NASA. Archived from the original on 2006-12-09. Retrieved 2006-04-24.
- Lunar Prospector Mission Profile by NASA's Solar System Exploration
- Isbell, Douglas; Morse, David; Rische, Becky (1999-10-13). "Press release on Lunar Prospector impact". NASA. Archived from the original (txt) on 2015-12-13. Retrieved 2006-04-24.
- Exploring the Moon: Lunar Prospector Mission