| MISSION_DESCRIPTION |
Mission Overview
================
The Lunar Prospector (LP) Mission consisted of a spin-stablized
orbiter spacecraft designed to perform continuous mapping of the Moon
from a circular polar orbit. LP was selected as the third mission in
NASA's Discovery program in February, 1995. The spacecraft was
designed and built in about 2 years by Lockheed Martin Missiles and
Space in Sunnyvale, CA. It was delivered for launch in late 1997
[BINDERETAL1998]. The LP spacecraft was launched on January 7, 1998
(UTC). The primary mapping mission began on January 16, 1998 and
lasted for one year. During most of the mapping mission, the
spacecraft mapped the surface from a 118-minute, circular, polar orbit
100 km above the moon's surface [BINDER1998]. Starting on 12/19/98
the spacecraft was maneuvered into a 40 km orbit as a transition into
a low altitude extended mission orbit. The transition orbit was used
to collect gravity data in order to verify the moon's gravity model in
preparation for conducting the extended mission orbit.
The extended mission began on January 16, 1999. The objective of the
extended mission was to provide higher resolution mapping from a
circular, polar orbit averaging 30 km above the moon's surface. The
spacecraft was maneuvered in its 30 km extended mission orbit starting
on January 29, 1999. The Lunar Prospector mission ended on July 31,
1999 when the spacecraft was intentionally impacted into a crater near
the south pole. The impact site was targeted for one of the hydrogen
deposits detected by Lunar Prospector's Neutron Spectrometer. The
intent of the impact event was to generate a plume of dust and vapor
from the deposit to try to confirm the presence of water through a
series of earth-based and space-based spectral observations. The
impact of Lunar Prospector occurred at 9:52 UTC on July 31, 1999.
There was no evidence of a dust plume, a water vapor plume, or an OH
plume.
The science goals of the Lunar Prospector Mission were to map the
Moon's surface composition and its magnetic and gravity fields, and to
determine the frequency and location of gas release events. Special
emphasis was placed of the search for polar ice deposits.
To meet these science goals the LP spacecraft carried five science
instruments mounted on three booms. The instrument package included a
Gamma Ray Spectrometer (GRS), a Neutron Spectrometer (NS), an Alpha
Particle Spectrometer (APS), a Magnetometer (MAG), and an Electron
Reflectometer (ER). A sixth science investigation was a Doppler
Gravity Experiment (DGE) that used tracking data for mapping the
gravity field. The gravity data was derived from tracking the LP
spacecraft with the NASA Deep Space Network (DSN) with ground stations
in California, Spain, and Australia [KONOPLIVETAL1998].
The LP science team consisted of the PI, Alan Binder, and five Co-I's,
and was divided into three groups. The Spectrometer Group consisted
of William Feldman and Binder. The Magnetics Group consisted of
Robert Lin, Mario Acuna, and Lon Hood. The Gravity Group consisted of
Alexander Konopliv.
Mission Phases
==============
LUNAR PROSPECTOR LAUNCH
-----------------------
The Lunar Prospector spacecraft was launched on January 7, 1998 at
2:28:44 UTC on a Lockheed Martin Launch Vehicle 2 (Athena 2) from the
Spaceport Florida commercial pad (Pad 46) at Cape Canaveral, Florida.
After about 1/2 of an orbit around the Earth, a 64 second burn by the
spacecraft's Trans Lunar Injection stage sent LP on a 105 hour cruise
to the moon. The spacecraft was turned on at 56.5 minutes after
launch.
Spacecraft Id: : LP
Target Name : MOON
Mission Phase Start Time : 1998-01-07
Mission Phase Stop Time : 1998-01-07
Spacecraft Operations Type : ORBITER
LUNAR PROSPECTOR CRUISE
-----------------------
The Lunar Prospector spacecraft was inserted into a translunar
trajectory after reaching a parking orbit around Earth. The Cruise
Phase to the moon lasted about 105 hours. The three spacecraft booms
were deployed starting about 5 hours after launch. All five science
instruments were turned on during cruise and collected science data
for instrument check out and calibration. The MAG/ER was activated at
about 1.33 hours after launch and the APS at about 3.5 hours after
launch. The GRS and NS needed to degas and were not turned until
about 24 hours after launch. Two trajectory correction maneuvers were
performed during the Cruise Phase.
Spacecraft Id: : LP
Target Name : MOON
Mission Phase Start Time : 1998-01-07
Mission Phase Stop Time : 1998-01-11
Spacecraft Operations Type : ORBITER
LUNAR PROSPECTOR ORBIT INSERTION
--------------------------------
The Lunar Prospector spacecraft was inserted into orbit by an initial
Lunar Orbit Insertion (LOI) engine burn at 11:45 UTC on January 11,
1999. The initial capture orbit had a 11.8 hour period. Three
additional engine firings put the spacecraft into its mapping orbit,
which was a 100 +/- 20 km circular polar orbit with a 118 minute
period. All five science instruments were operating and collecting
data during the Orbit Insertion Phase.
Spacecraft Id: : LP
Target Name : MOON
Mission Phase Start Time : 1998-01-11
Mission Phase Stop Time : 1998-01-16
Spacecraft Operations Type : ORBITER
LUNAR PROSPECTOR PRIMARY MISSION
--------------------------------
The Lunar Prospector Primary Mission lasted for one year as originally
planned. The nominal mapping orbit during the Primary Mission had an
altitude of 100 km above the moon's surface. Orbit maintenance
maneuvers were required every 56 days to correct for changes in the
mapping orbit due to lunar gravity anomalies.
The basic mapping strategy during the Primary Mission was for the
science instruments to collect data continuously. The data were
downlinked to Earth immediately and simultaneously transferred to a
solid state recorder and then downlinked 53 minutes later. These
delayed data frames were interleaved into the real-time data stream.
The purpose of the delayed stream was to receive data acquired on the
lunar farside when communications with the Earth were blocked by the
moon. Late in the Primary Mission as the spacecraft batteries began
to degrade and eclipses limited recharge time by the solar panels, the
spacecraft transmitter was cycled off and on to conserve power. The
transmitter was switched off when the spacecraft was on the lunar
farside and communications with the Earth were not possible. This
transmitter cycling began on September 16, 1998 and continued
periodically throughout the rest of the Primary Mission and into the
Extended Mission.
At the start of the Primary Mission the LP spacecraft attitude as
measured by the spin axis direction (+Z, which is perpendicular to the
top of the spacecraft bus and in the direction of the omni antenna)
was pointed to within a few degrees of north ecliptic pole. In
October 1998, the spacecraft orientation was flipped by 180 degrees so
that the spin axis pointed toward the south ecliptic pole. The
reorientation was done so that the APS instrument could collect data
that it missed due to an anomaly on one of its faces and to test for
any asymmetries in the response of the other spectrometers. The
maneuver was initiated on October 5, 1998 with the spacecraft turning
90 degrees (spin axis parallel to the ecliptic). This intermediate
orientation provided calibration data for the GRS instrument. On
October 7, 1998, the spacecraft turned the final 90 degrees. The
spacecraft maintained the ecliptic south orientation for the rest of
the mission except for special procedures. On November 15, 1998, the
spacecraft was turned by 80 degrees to avoid possible damage to the
solar panels due to dust from Leonids meteor shower. This orientation
minimized the cross sectional area of the solar panels in the
direction of the shower. On November 19, 1998, the spacecraft was
turned back to the attitude with the spin axis nearly parallel to the
ecliptic south pole. There was no apparent damage to the spacecraft
from the shower.
Spacecraft Id: : LP
Target Name : MOON
Mission Phase Start Time : 1998-01-16
Mission Phase Stop Time : 1999-01-16
Spacecraft Operations Type : ORBITER
LUNAR PROSPECTOR EXTENDED MISSION
--------------------------------
The Lunar Prospector Extended Mission started on January 16, 1999 and
continued until July 31, 1999. The nominal mapping orbit during the
Extended Mission had an average altitude of 30 km above the moon's
surface.
Near the start of the Extended Mission, noise in the Alpha Particle
Spectrometer instrument started to affect the Neutron Spectrometer
causing the NS instrument to saturate. As a result, the APS was
turned off on February 8, 1999 to allow the NS to collect clean data.
The APS instrument was turned on again on April 21, 1999 and was
collecting good data without noise. However, noise from the APS again
began affecting the NS in mid-May 1999. As a result, the APS was
turned off on May 24, 1999 and it remained off for the remainder of
the mission.
During the final week of the Lunar Prospector mission a number of
events took place in preparation for the final impact event. On July
26, 1999, a small orbit correction maneuver raised periselene up about
5 km to maintain the spacecraft's circular orbit. In preparation for
a lunar eclipse on July 28, 1999 where the spacecraft could not fully
recharge the battery between nighttime passes, all non-critical
subsystems were turned off. The three spectrometer instruments were
powered off before the eclipse and they remained off for the last
three days of the mission. On July 29, 1999, the spacecraft was spun
up to 23.7 rpm (from the nominal 12 rpm). This was in preparation for
later maneuvers that targeted the spacecraft for impact. On July 30,
1999 aposelene was raised to put the spacecraft into a more elliptical
orbit. This was done so that the impact approach was as steep (about
6.3 deg) as possible to hit the crater floor. On July 31, the final
maneuver occurred to lower periselene beneath the lunar surface such
that the spacecraft impacted the target point of -87.7 deg latitude,
42 deg longitude. The impact occurred at 09:52 UTC.
Spacecraft Id: : LP
Target Name : MOON
Mission Phase Start Time : 1999-01-16
Mission Phase Stop Time : 1999-07-31
Spacecraft Operations Type : ORBITER
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| MISSION_OBJECTIVES_SUMMARY |
The overall goal of the Lunar Prospector (LP) Mission was to perform
global mapping of the Moon in order to better understand the Moon's
origin, evolution, current state, and resources. Specifically, LP
mapped the surface abundances of key elements (U, Th, K, O, Si, Mg,
Fe, Ti, Ca, Al, Gd, Sm, and H). As part of the elemental abundance
mapping, LP determined that water ice exists in permanently shadowed
areas near the lunar poles. LP made high-resolution measurements of
the near-side crustal gravity field and measured long-wavelength
gravity anomalies for the entire Moon. LP provided global
measurements of lunar crustal magnetic fields and the induced dipole
moment. LP also attempted to determine the frequency and location of
gas release events, as one of the major sources of the thin lunar
atmosphere.
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