By John E. Gruener
Hernandez Engineering

It’s been a little over four months since the Lunar Prospector (LP) spacecraft was targeted into the lunar surface in one last hurrah for lunar science.  It was hoped that the impact into a permanently shadowed crater near the Moon’s south pole (now to be named Shoemaker crater) might produce an observable signal proving that the hydrogen detected earlier by LP’s neutron spectrometer was in water-ice form.  Astronomical observations of the impact were focused primarily on using sensitive spectrometers tuned to look for the ultraviolet emission lines expected from the hydroxyl (OH) molecules that should be a by-product of any water vapor and dust kicked up by the crash of LP into the Moon.  Though given less than a 10% chance of success, LP’s science team, and indeed people all around the world, held their breath at 09:52:02 GMT, July 31, 1999, and waited for some observatory somewhere to say it saw something, anything, but nothing was detected.

So, the question of ice on the Moon is still open and it will be up to future lunar missions to resolve just what form the hydrogen concentrations are in.  However, the assay of the ‘mother lode’ of science data that was collected by Prospector during its 18 months in lunar orbit is only beginning.  On November 1, 1999, the LP science team began the Numerical Reduction and Analysis of Lunar Prospector Data Program.  This NASA-funded program will result in the delivery of numerically reduced, higher level science data products of the LP mission to the Planetary Data System (PDS).  The PDS is then responsible for delivering the data to the National Space Science Data Center (NSSDC).  Unfortunately, however, due to budget shortcomings, not all of the data acquired by LP will be reduced in this program.  No data from the Alpha Particle Spectrometer (APS) will be reduced, and magnetic data from the Magnetometer/Electron Reflectometer (MAG/ER) will be not be reduced beyond level 2 (defined later in this article).  The lunar gravity data collected from LP is being reduced separately at the Jet Propulsion Laboratory (JPL).

Below is a brief discussion of Lunar Prospector’s higher level science data products and their scheduled delivery dates.  A more detailed description can be found in the Lunar Prospector Numerical Reduced Data Management Plan.

The first delivery of higher level science data from the LP mission is scheduled to be delivered to PDS on Sep. 1, 2000.  This will include level 2 data for the Gamma-ray spectrometer (GRS) and Neutron Spectrometer (NS).  For the GRS, equal area (equivalent to 5° latitude by 5° longitude at the equator) maps of the absolute abundances of Th and K, and relative abundances of O, Si, Fe, Ti, Al, Ca, and Mg (mapped as the following ratios: Ti/Fe, Al/Fe, Ca/Fe, Si/Fe, Ca/O, Si/O, and Mg/O) will be delivered.  For the NS, 5° x 5° equal area maps of the thermal, epithermal, and fast neutron fluxes at 100 km altitude will be delivered.  Fast neutron flux energy spectra between 0.5 and 8 MeV will also be generated for each equivalent equatorial-area pixel.

Level 2 MAG/ER data, scheduled to be delivered Oct. 31, 2000 will consist of selected MAG time series lunar magnetic field data in selenocentric east, north, and radial coordinates (spacecraft event time, latitude, longitude, and altitude are included in the data file).  Also included will be ER time series of electron loss cone angles when the Moon is in the geotail (but outside of the current sheet), with an electron reflection coefficient map binned at 5° x 5° resolution, covering as much of the Moon as the sampling allows.

Level 3 data products, scheduled to be delivered June 30, 2001, will consist of 5° x 5° equal area maps of the absolute abundances (along with their 1-sigma uncertainties) for the elements Th, K, U, Fe, Ti, Si, O, Al, Ca, and Mg.  Also included will be 5° x 5° equal area maps of H, Gd, and Sm abundances ( in ppm by weight).

Level 4 data products, scheduled to be delivered Oct. 31, 2001, will consist of 2° x 2° equal area maps of Th, K, and H abundances, as well as the ratio of Ti to Fe abundances.  Also, neutron data measured at all altitudes between about 15 and 150 km will be combined to estimate the subsurface (about 5 cm below the surface) temperature of the Moon in each 5° x 5° equal-area pixel element.

It should be stressed that the Numerical Reduction and Analysis of Lunar Prospector Data Program is quite necessary and has to be done so that LP’s vast amount of data  can be put in a usable form for the lunar science community at large.  Hopefully, additional resources will be found in the future to enable the reduction of the alpha particle spectrometer data and further the analysis of the magnetometer/electron reflectometer data.  It would be an awful waste to spend such an effort and amount of time to collect data important to lunar science and then do nothing with it.