At 9:28 p.m. (EST) on January 6, 1998, Lunar Prospector (LP)
blasted off to the Moon aboard a Lockheed Martin solid-fuel, three-stage
rocket called Athena II. It was successfully on its way to the Moon for
a one-year, polar orbit, primary mission dedicated to globally mapping
lunar resources, gravity, and magnetic fields, and even outgassing events.
About 13 minutes after launch, the Athena II placed the Lunar Prospector
payload into a "parking orbit" 115 miles above the Earth. Following
a 42-minute coast in the parking orbit, Prospectorís Trans Lunar Injection
(TLI) stage successfully completed a 64-second burn, releasing the spacecraft
from Earth orbit and setting it on course to the Moon, a 105-hour coast.
The official mission timeline began when the spacecraft switched on 56
minutes, 30 seconds after liftoff. Shortly after turning the vehicle on,
mission controllers deployed the spacecraftís three extendible masts,
or booms. Finally, the spacecraftís five instruments -- the gamma-ray
spectrometer, alpha particle spectrometer, neutron spectrometer, magnetometer
and electron reflectometer -- were turned on. On Sunday, January 11, at
7:20 a.m. (EST), Lunar Prospector was successfully captured into lunar
orbit, and a few days later began its mission to globally map the Moon.
Lunar Prospector is a small,1.3m in diameter X 1.4m tall bus with three
2.5 meter science masts carrying its five science instruments and isolating
them from the spacecraft's electronics, spin-stabilized spacecraft in
a polar orbit with a period of 118 minutes at a nominal altitude of 100
km (63 miles). Since the Moon rotates a full turn beneath the spacecraft
every lunar cycle (~27.3 days) as it zips around the Moon every 2 hours,
Prospector visits a polar region every hour and completely covers the
lunar surface twice a month. Prospector's one-year-long primary mission
with an optional extended mission of a further 6 months at an even lower
altitude enables large amounts of data to collect over time. For some
science instruments, a significant amount of time is required to obtain
high quality usable data. Thus, Prospector's polar orbit and long-mission
time render it ideal from the standpoint of globally mapping the Moon.
Lunar Prospector Scientific Goals
As a Discovery-class mission, Prospector's scientific goals
were carefully chosen to address outstanding questions of lunar science
both efficiently and effectively. In the Post-Apollo era, NASA convened
the Lunar Exploration Science Working Group (LExSWG) to draft a list of
the most pressing, unanswered scientific riddles still facing the lunar-science
community. In 1992, LExSWG produced a document, entitled "A Planetary
Science Strategy for the Moon." The following lunar science objectives
were listed: How did the Earth-Moon system form? How did the Moon evolve?
What is the impact history of the Moonís crust? What constitutes the lunar
atmosphere? What can the Moon tell us about the history of the Sun and
other planets in the Solar System?
Lunar Prospector mission designers carefully selected a set of objectives
and a payload of scientific instruments which would address as many of
LExSWGís priorities as possible, while remaining within the tight budget
confines of NASAís "faster, better, cheaper" Discovery Program.
Lunar Prospector's identified critical science objectives are:
- "Prospect" the lunar crust and atmosphere for potential
resources, including minerals, water ice and certain gases,
- Map the Moonís gravitational and magnetic fields, and
- Learn more about the size and content of the Moonís core.
The six experiments (five science instruments) which address these objectives
- Neutron Spectrometer (NS) --Map hydrogen at several signature energies
and thereby infer the presence or absence of water.
- Gamma Ray Spectrometer (GRS) -- Map 10 key elemental abundances, several
of which offer clues to lunar formation and evolution.
- Magnetometer/Electron Reflectometer (Mag/ER) -- These two experiments
combine to measure lunar magnetic field strength at the surface and
at the altitude of the spacecraft and thereby greatly enhance understanding
of lunar magnetic anomalies.
- Doppler Gravity Experiment (DGE) -- Make an operational gravity map
of the Moon for use by future missions as well as LP by mapping gravity
field measurements from changes in the spacecraftís orbital speed and
- Alpha Particle Spectrometer (APS) -- Map out-gassing events by detecting
Radon gas (current outgassing events) and Polonium (tracer of recent,
i.e. 50 years).