Goals NASA should undertake before establishing a lunar base A. Lunar mapping from orbit
B. Exploration of the lunar surface
1. Oxygen-rich soil 2. Hydrogen 3. Helium-3 4. Water With the exception of water, all of these are found in varying concentrations in the lunar regolith
Uses of Lunar Resources A. Oxygen 1. Life support 2. Oxidizer for rocket propellants B. Hydrogen 1. Rocket propellant C. Helium-3 1. Implanted by the solar wind 2. Nuclear fusion 3. However, other possible sources D. Water 1. Life support 2. Rocket proellant
Most likely location of lunar water A. Water in the form of ICE may exist deep under the lunar regolith in permanent COLD traps at the lunar poles
B. Arecibo S-band (radar) observations indicate possible water ice at Mercury's poles. But, other possible explanations exist (e.g. young lava flows) C. Area on lunar surface that is permanently shaded from the Sun is approximately 0.5 percent Possible sources of water on the Moon A. Meteoritic impacts 1. About 1 tonne per day 2. Most is cometary in nature 3. For low-velocity impacts, this source is a steady one B. Massive comets 1. Contain large amounts of water 2. Individual masses about 10E16 grams (Tycho and Copernicus)
3. Short-period comets impact the Moon with low velocities (about 20 km/s) 4. Long-period comets have velocities that are too high (> 30 km/s) a. Decomposition b. Escape 5. Uncertainties in water source a. Mass distribution b. Impact rate c. Physical models 6. Wetherhill (1976) estimates that about 10 percent of lunar impacts were active comets a. About 1/3 occurred when the comets were in short- period orbits 7. Five comets worth of water have been liberated into the lunar atmosphere in about 2 billion years (from comets > 1 km), yielding about 10E16 to 10E17 grams of water 8. May also be a source of lunar carbon dioxide since comets contain significant amounts C. Apollo Asteroids 
1. Probably account for remaining 90 percent of large lunar craters 2. May be extinct comet nuclei 3. May liberate large amounts of water and carbon dioxide on impact Destructive Processes A. Photodissociation 1. Mean life of about 20 hours is close to the time required to reach permanent cold traps. Thus, may be responsible for the loss of the order of one half of the atmospheric molecules 2. Very difficult to analyze B. Solar wind 1. Sputtering 2. Chemical decomposition by radiation damage 3. Flux is lower at high lunar latitudes 4. When the Moon is in the Earth's magnetotail for 3 to 4 days each month, solar wind particles have larger angular dispersions a. Increase in sputtering rates may present problems C. Other minor mechanisms 1. Electrostatic transport of fine particles out of cold traps 2. Radiation damage from lunar radioactivity 3. Sudden release of stored energy on impact 4. Catastrophic events (e.g. supernovae) Conclusion A. The discovery of significant amounts of water on the Moon would have profound consequences for science and future habitats B. Recent observations by a neutron detector on the Lunar Prospector spacecraft indicate what appears to be water ice (in the form of hydrogen) at the lunar poles in permanently shaded craters. The dip in the signal (blue and purple regions) on the neutron data maps shown below is consistent with the signature of water ice
C. Lunar Prospector and other polar orbiting spacecraft will: 1. Provide a sensitive measure of hydrogen in the regolith 2. Helium-3 neutron counting instruments to measure water content in regolith 3. Map mature regolith as identified by its relatively high hydrogen content (about 100 ppm H over each 100 km by 100 km surface resolution element in one year of observation)