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''Lunar Prospector'' was the third mission selected by
NASA The National Aeronautics and Space Administration (NASA ) is an independent agency of the US federal government responsible for the civil space program, aeronautics research, and space research. NASA was established in 1958, succeedin ...
for full development and construction as part of the Discovery Program. At a cost of $62.8 million, the 19-month mission was designed for a low polar orbit investigation of the
Moon The Moon is Earth's only natural satellite. It is the fifth largest satellite in the Solar System and the largest and most massive relative to its parent planet, with a diameter about one-quarter that of Earth (comparable to the width of ...
, including mapping of surface composition including Lunar hydrogen deposits, measurements of
magnetic Magnetism is the class of physical attributes that are mediated by a magnetic field, which refers to the capacity to induce attractive and repulsive phenomena in other entities. Electric currents and the magnetic moments of elementary particl ...
and
gravity In physics, gravity () is a fundamental interaction which causes mutual attraction between all things with mass or energy. Gravity is, by far, the weakest of the four fundamental interactions, approximately 1038 times weaker than the stro ...
fields, and study of lunar outgassing events. The mission ended July 31, 1999, when the orbiter was deliberately crashed into a crater near the lunar
south pole The South Pole, also known as the Geographic South Pole, Terrestrial South Pole or 90th Parallel South, is one of the two points where Earth's axis of rotation intersects its surface. It is the southernmost point on Earth and lies antipod ...
, after the presence of hydrogen was successfully detected. 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''. ''Lunar Prospector'' was managed by NASA Ames Research Center with the prime contractor
Lockheed Martin The Lockheed Martin Corporation is an American aerospace, arms, defense, information security, and technology corporation with worldwide interests. It was formed by the merger of Lockheed Corporation with Martin Marietta in March 1995. It ...
. The Principal Investigator for the mission was Alan Binder. His personal account of the mission, ''Lunar Prospector: Against all Odds'', is highly critical of the bureaucracy of NASA overall, and of its contractors. 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.


Spacecraft and subsystems

The spacecraft was a graphite-epoxy drum, in diameter and high with three radial instrument booms. A extension boom at the end of one of the 2.5 m booms held the magnetometer. Total initial mass (fully fueled) was . It was spin-stabilized (nominal spin rate 12 rpm) with its spin axis normal to the ecliptic plane. The spacecraft was controlled by six
hydrazine Hydrazine is an inorganic compound with the chemical formula . It is a simple pnictogen hydride, and is a colourless flammable liquid with an ammonia-like odour. Hydrazine is highly toxic unless handled in solution as, for example, hydrazine ...
monopropellant 22-newton thrusters (two aft, two forward, and two tangential). Three fuel tanks mounted inside the drum held of hydrazine pressurized by helium. The power system consisted of body-mounted solar cells which produced an average of 186 W and a 4.8 A·h rechargeable NiCd battery. Communications were through two
S band The S band is a designation by the Institute of Electrical and Electronics Engineers (IEEE) for a part of the microwave band of the electromagnetic spectrum covering frequencies from 2 to 4  gigahertz (GHz). Thus it crosses the conventi ...
transponders, a slotted, phased-array medium-gain antenna for downlink, and an omnidirectional low-gain antenna for downlink and uplink. The on-board computer was a Harris 80C86 with 64
kilobyte The kilobyte is a multiple of the unit byte for digital information. The International System of Units (SI) defines the prefix '' kilo'' as 1000 (103); per this definition, one kilobyte is 1000 bytes.International Standard IEC 80000-13 Quant ...
s of
EEPROM EEPROM (also called E2PROM) stands for electrically erasable programmable read-only memory and is a type of non-volatile memory used in computers, usually integrated in microcontrollers such as smart cards and remote keyless systems, or ...
and 64 kilobytes of static RAM. All control was from the ground, the computer echoing each command to the ground for verification there. Once the command was ground-verified, an "execute" command from the ground told the computer to proceed with execution of the command. The computer built telemetry data as a combination of immediate data and also read from a circular queue buffer which allowed the computer to repeat data it had read 53 minutes earlier. This simple solid-state recorder ensured that all data collected during communications blackout periods would be received, providing the blackout was not longer than 53 minutes. The probe also carried a small amount of the remains of Eugene Shoemaker (April 28, 1928 – July 18, 1997), astrogeologist and co-discoverer of Comet Shoemaker-Levy 9, to the Moon for a space burial.


Mission profile

Following launch on January 7, 1998 UT (January 6 EST) aboard a four-stage Athena II
rocket A rocket (from it, rocchetto, , bobbin/spool) is a vehicle that uses jet propulsion to accelerate without using the surrounding air. A rocket engine produces thrust by reaction to exhaust expelled at high speed. Rocket engines work entir ...
, ''Lunar Prospector'' had a 105-hour cruise to the Moon. During the cruise, the three instrument booms were deployed. The MAG and APS collected calibration data, while the GRS, NS, and ER outgassed for one day, after which they also collected calibration data in cislunar space. The craft was inserted into an 11.6-hour period capture orbit about the Moon at the end of the cruise phase. After 24 hours ''Lunar Prospector'' was inserted into a 3.5-hour period intermediate orbit, followed 24 hours later (on January 13, 1998) by transfer into a preliminary mapping orbit, and then on January 16 by insertion into the near-circular altitude nominal lunar polar mapping orbit with an inclination of 90 degrees and a period of 118 minutes. Lunar calibration data was collected during the 11.6- and 3.5-hour orbits. Lunar mapping data collection started shortly after the 118 minute orbit was achieved. The data collection was periodically interrupted during the mission as planned for orbital maintenance burns, which took place to recircularize the orbit whenever the
periselene An apsis (; ) is the farthest or nearest point in the orbit of a planetary body about its primary body. For example, the apsides of the Earth are called the aphelion and perihelion. General description There are two apsides in any ellip ...
or aposelene was more than to from the 100 km nominal orbit; this occurred about once per month. On December 19, 1998, a maneuver lowered the orbit to to perform higher resolution studies. The orbit was altered again on January 28 to a orbit, ending the one year primary mission and beginning the extended mission. 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 Shoemaking is the process of making footwear. Originally, shoes were made one at a time by hand, often by groups of shoemakers, or cobblers (also known as ''cordwainers''). In the 18th century, dozens or even hundreds of masters, journeymen an ...
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, a Neutron Spectrometer, a
Magnetometer A magnetometer is a device that measures magnetic field or magnetic dipole moment. Different types of magnetometers measure the direction, strength, or relative change of a magnetic field at a particular location. A compass is one such device, ...
, an Electron Reflectometer, an Alpha Particle Spectrometer, and a Doppler Gravity Experiment. The instruments were omnidirectional and required no sequencing. The normal observation sequence was to record and downlink data continuously.


Gamma Ray Spectrometer (GRS)

The ''Lunar Prospector'' Gamma Ray Spectrometer (GRS) produced the first global measurements of gamma-ray spectra from the lunar surface, from which are derived the first "direct" measurements of the chemical composition for the entire lunar surface. The GRS was a small cylinder which was mounted on the end of one of the three 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 and with a surface resolution of . 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. 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, an estimated 3 billion
tonne The tonne ( or ; symbol: t) is a unit of mass equal to 1000  kilograms. It is a non-SI unit accepted for use with SI. It is also referred to as a metric ton to distinguish it from the non-metric units of the short ton ( United State ...
s (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 . 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 Cadmium is a chemical element with the Symbol (chemistry), symbol Cd and atomic number 48. This soft, silvery-white metal is chemically similar to the two other stable metals in group 12 element, group 12, zinc and mercury (element), mercury. Li ...
, 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 . 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 colocated with the neutron spectrometer on the end of one of the three radial ''Lunar Prospector'' science booms. It contained ten silicon detectors sandwiched between gold and aluminum disks arranged on five of six sides of the cube. Alpha particles, produced by the decay of radon and polonium, leave tracks of charge on the silicon wafers when they impact the silicon. A high voltage is applied to the silicon, and the current is amplified by being funneled along the tracks to the aluminum disk and is recorded for identification. The APS was designed to make a global examination of gas release events and polonium distribution with a surface resolution of and a precision of 10%. The APS was designed to detect
radon Radon is a chemical element with the symbol Rn and atomic number 86. It is a radioactive, colourless, odourless, tasteless noble gas. It occurs naturally in minute quantities as an intermediate step in the normal radioactive decay chains th ...
outgassing events on the surface of the Moon. The APS recorded
alpha particle Alpha particles, also called alpha rays or alpha radiation, consist of two protons and two neutrons bound together into a particle identical to a helium-4 nucleus. They are generally produced in the process of alpha decay, but may also be prod ...
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 ''Clementine'' mission had previously produced a relatively low-resolution map, but the ''Prospector'' DGE obtained data approximately five times as detailed: the "first truly operational gravity map of the Moon". The practical benefits of this are more stable long-term orbits and better fuel efficiency. Additionally, the DGE data is hoped to help researchers learn more about lunar origins and the nature of the lunar core. The DGE identified three new near-side mass concentration regions. 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 Doppler shift in the S-band tracking signal as it reaches Earth, which can be converted to spacecraft accelerations. The accelerations can be processed to provide estimates of the lunar gravity field, from which the location and size of mass anomalies affecting the spacecraft orbit can be modeled. Estimates of the surface and internal mass distribution give information on the crust, lithosphere, and internal structure of the Moon. 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
S band The S band is a designation by the Institute of Electrical and Electronics Engineers (IEEE) for a part of the microwave band of the electromagnetic spectrum covering frequencies from 2 to 4  gigahertz (GHz). Thus it crosses the conventi ...
tracking, and so has no listed weight or power requirements. The experiment was designed to give the near-side gravity field with a surface resolution of and precision of 5 mGal (0.05 mm/s²) in the form of
spherical harmonic In mathematics and physical science, spherical harmonics are special functions defined on the surface of a sphere. They are often employed in solving partial differential equations in many scientific fields. Since the spherical harmonics form ...
coefficients to degree and order 60. In the extended mission, in which the spacecraft descended to an orbit with an altitude of and then to , this resolution was expected to improve by a factor of 100 or more. 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.


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 In astronomy and planetary science, a magnetosphere is a region of space surrounding an astronomical object in which charged particles are affected by that object's magnetic field. It is created by a celestial body with an active interior d ...
(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 in diameter, has therefore been referred to as "the smallest known magnetosphere, magnetosheath and bow shock system in the Solar System." 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
magnetometer A magnetometer is a device that measures magnetic field or magnetic dipole moment. Different types of magnetometers measure the direction, strength, or relative change of a magnetic field at a particular location. A compass is one such device, ...
(MAG) were designed to collect information on the lunar
magnetic field A magnetic field is a vector field that describes the magnetic influence on moving electric charges, electric currents, and magnetic materials. A moving charge in a magnetic field experiences a force perpendicular to its own velocity and to ...
s. the Moon has no global magnetic field, but it does have weak localized magnetic fields at its surface. These may be paleomagnetic remnants of a former global magnetic field, or may be due to
meteor A meteoroid () is a small rocky or metallic body in outer space. Meteoroids are defined as objects significantly smaller than asteroids, ranging in size from grains to objects up to a meter wide. Objects smaller than this are classified as mi ...
impacts or other local phenomena. This experiment was to help map these fields and provide information on their origins, allow possible examination of distribution of
mineral In geology and mineralogy, a mineral or mineral species is, broadly speaking, a solid chemical compound with a fairly well-defined chemical composition and a specific crystal structure that occurs naturally in pure form.John P. Rafferty, ed. (2 ...
s on the lunar surface, aid in a determination of the size and composition of the lunar core, and provide information on the lunar induced magnetic dipole. The ER determined the location and strength of magnetic fields from the energy spectrum and direction of
electron The electron ( or ) is a subatomic particle with a negative one elementary electric charge. Electrons belong to the first generation of the lepton particle family, and are generally thought to be elementary particles because they have n ...
s. The instrument measured the pitch
angle In Euclidean geometry, an angle is the figure formed by two rays, called the '' sides'' of the angle, sharing a common endpoint, called the ''vertex'' of the angle. Angles formed by two rays lie in the plane that contains the rays. Angles ...
s of solar wind electrons reflected from the Moon by lunar magnetic fields. Stronger local magnetic fields can reflect electrons with larger pitch angles.
Field strength In physics, field strength means the '' magnitude'' of a vector-valued field (e.g., in volts per meter, V/m, for an electric field ''E''). For example, an electromagnetic field results in both electric field strength and magnetic field streng ...
s as small as 0.01 nT could be measured with a spatial accuracy of about at the lunar surface. The MAG was a triaxial fluxgate magnetometer similar in design to the instrument used on Mars Global Surveyor. It could measure the magnetic field
amplitude The amplitude of a periodic variable is a measure of its change in a single period (such as time or spatial period). The amplitude of a non-periodic signal is its magnitude compared with a reference value. There are various definitions of am ...
and direction at spacecraft altitude with a spatial resolution of about when ambient plasma disturbances are minimal. 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 boom—a combined from ''Lunar Prospector'' in order to isolate it from spacecraft generated magnetic fields. The ER and MAG instruments had a combined mass of and used 4.5
watt The watt (symbol: W) is the unit of power or radiant flux in the International System of Units (SI), equal to 1 joule per second or 1 kg⋅m2⋅s−3. It is used to quantify the rate of energy transfer. The watt is named after James ...
s of power.


See also

* Lunar resources * Luna-Glob, a current Russian lander program *
Prospector (spacecraft) Prospector was a proposed lunar probe that was intended to be flown in support of the Apollo lunar missions. History Prospector arose as a result of President John F. Kennedy's desire to rehabilitate the tarnished image of US spaceflight. In 1961 ...
*
Resource Prospector (rover) Resource Prospector is a cancelled mission concept by NASA of a rover that would have performed a survey expedition on a polar region of the Moon. The rover was to attempt to detect and map the location of volatiles such as hydrogen, oxygen and l ...
* List of artificial objects on the Moon


References


External links

* * * * * * *
''Lunar Prospector'' Mission Profile
b
NASA's Solar System Exploration
*

{{Orbital launches in 1998 Missions to the Moon Discovery Program NASA space probes Spacecraft launched in 1998 Spacecraft that orbited the Moon Spacecraft that impacted the Moon 1999 on the Moon