e-Pulsar - Apr

e-Pulsar Apr - May 98

LUNAR ICE

"Lunar Prospector" By Michael Carroll

Lunar Prospector The past 12 months have been a banner year for astronomy with one incredible discovery after another - and March was no exception. On the 5th, NASA announced that data returned by the Lunar Prospector spacecraft had confirmed the presence of water ice at the lunar poles. Data indicates the ice is mixed in with the lunar regolith at 0.3 to 1 percent.

This may not seem like much until you consider where it was discovered. There are two areas giving indications of ice, the first is between 10 and 50 thousand square km in size at the north pole. The second is 5 to 20 thousand square km around the south pole. The instrument that detected the ice can get a reading to a depth of about half a meter. These numbers give an estimated bottom figure volume of ice of 10 BILLION kilograms - possible as much as 1,200 billion! That’s a lot of water!

Lunar Prospector is part of NASA’s Discovery program. Total mission cost is $63 million. It has five main science instruments: the Gamma Ray Spectrometer, Magnetometer, Electron Reflectometer, Alpha Particle Spectrometer, and a Neutron Spectrometer. The spectrometer can determine hydrogen abundance and location on the surface to within 50 parts-per-million. This was the instrument that confirmed the presence of water on the Moon.

The spacecraft is a graphite-epoxy drum, 1.4 meters in diameter and 1.22 meters high with three radial instrument booms. It is spin-stabilized and controlled by 6 hydrazine monopropellant 22-Newton thrusters. There is no on-board computer. After launch a January 7th, 1998 from Kennedy Space Center, LP cruised for 110 hours, then was inserted into a 100 km altitude lunar polar orbit with a 118 minute period. Though the nominal mission duration is one year, a two year extended mission is possible, during which LP’s orbit will be lowered to 50 km and 10 km altitude to obtain higher resolution measurements.

LP is the first US space mission to the Moon in over 20 years. Hopefully, it won’t be the last!