Prospecting the Moon
by John Gruener
Lockheed Martin Space Mission Systems and Services		 Prospector Logo

Lunar sample analyses have often been used to correlate lunar remote sensing data from spacecraft and earth-based measurements. During the Apollo program, roughly 20% of the lunar surface was chemically mapped from orbit by scientific instruments in the command/service module. More recently, data from the Galileo and Clementine spacecraft have increased our knowledge of the global chemical composition of the lunar surface. Now, Lunar Prospector is ready to continue the exploration of our nearest planetary neighbor. Is there water ice on the Moon? How did the Moon evolve? Are there resources on the Moon that could be used by future human explorers? These are only a few of the questions Lunar Prospector hopes to answer.

On October 24, Lunar Prospector will be launched on a three-stage Lockheed-Martin Launch Vehicle Two (LMLV2) from Spaceport Florida's Pad 46 at Cape Canaveral. This will be the first commercial launch from the Florida Spaceport complex and the first spacecraft that NASA has sent to the Moon since the Apollo program. One hour after launch, a Star 37 solid rocket motor will provide the trans-lunar injection (TLI) burn over Borneo and the South Pacific that will propel Prospector towards the Moon. During the approximately 123 hour flight to the Moon, Prospector will establish its cruise attitude, deploy its science booms, turn on the science instruments, and fires its onboard thrusters to correct any launch errors.

As it nears the Moon, Prospector will fire its onboard thrusters to accomplish lunar orbit insertion (LOI). Initially, Prospector will be placed in a 12-hour elliptical lunar orbit. The spacecraft will then be lowered to a 3.5-hour elliptical orbit, and finally to 100 km circular polar orbit. This polar orbit will have an orbital period of 118 minutes and will be the primary mapping orbit for Lunar Prospector's one year mission.

Dr. Alan Binder of the Lunar Research Institute (LRI) is the Principal Investigator for the Lunar Prospector mission and leads the project team that includes personnel from NASA, Lockheed-Martin, Los Alamos National Laboratory, JPL, the University of California at Berkeley, and the University of Arizona. The Lunar Prospector mission will be controlled from Ames Research Center.

Dr. Binder designed Lunar Prospector's science payload to address many of the highest priority experiments proposed for lunar mapping missions by NASA's Lunar Exploration Science Working Group (LExSWG). In addition to their scientific value, the instruments were also chosen based on their ability to operate on a simple, spin-stabilized spacecraft, and for their low mass, power, and data rate requirements.

The instrument that will likely generate the most interest early in the mission is the neutron spectrometer (NS). The primary goal of this experiment is to map the hydrogen abundance on the lunar surface, and in particular locate water ice deposits that may be present in the permanently shadowed regions near the lunar poles. The sensitivity of NS is such that it can detect a cup full of water in one cubic meter of regolith. Two other spectrometers with Apollo heritage will also be flying on Prospector. The gamma ray spectrometer (GRS) will gather data on the distribution of the elements U, Th, K, Fe, Ti, Si, O, and Al in the lunar surface to a depth of > 10 cm. It may also be possible to map the distribution of Ca and Mg. The Prospector GRS bismuth-germanate crystal is about twice as sensitive as the Apollo sodium-iodide GRS. The third spectrometer is an alpha particle spectrometer (APS) and will be used to detect releases of radioactive 222Rn and 210Po gas. Though these gases are released in very small amounts (as measured by the Apollo APS), it is believed that they could act as tracer gases for other carrier gases such as N2, CO, CO2 that may be coming out of the Moon in larger, useable amounts. While Lunar Prospector is in its 100 km orbit, the spatial resolution of the three spectrometers will be about 150 km. However, a lower orbit in an extended mission could improve this resolution.

Other science experiments that will be conducted by Lunar Prospector include mapping the global magnetic and gravity environments. The magnetometer/electron reflectometer (MAG/ER) will measure the magnetic field flux at both the orbital altitude and on the lunar surface. The MAG measures vector fields at orbital altitudes with about 0.01 nT accuracy and thus provides the directions of the lunar fields. ER magnetometry is a remote sensing technique to map the surface magnetic field strength with high spatial resolution (down to about 3 km) and very high sensitivity (about 0.01 nT at the surface averaged over the resolution element). Data from the magnetic experiments will also address the issues of magnetic anomalies on the lunar surface and the existence of a lunar core. Finally, the Doppler shift of Prospector's communications signal will be used to map the global lunar gravity field, which is known to be non-uniform as a result of mass concentrations distributed below the surface of the Moon. The Doppler data will have a surface resolution of 200 km from the nominal 100 km mapping orbit.

If all goes well during the primary mapping mission, an extended mission will have Prospector lowering its orbit to get better spatial resolution for the science instruments. One possibility would be to put the spacecraft into an elliptical orbit with periselene altitudes down to 10 km. This would greatly enhance locating any ice deposits detected in the polar regions or correlating gas release events or magnetic anomalies with specific surface features.

You can follow the Lunar Prospector mission or lunar exploration in general at these websites: