WCSAR-TR-AR3-9311-1 Remote Sensing of Astrofuel [Prepared for Space 94, The 4th International Conference and Exposition on Engineering, Construction and Operations in Space, and The Conference and Exposition/Demonstration on Robotics for Challenging Environments, February 26 - March 3, 1994, Albuquerque NM]

A direct, high-resolution measurement from lunar orbit of the location of high concentrations of 3He in the lunar regolith is needed for the initiation of cost-effective mining operations on the moon. Gamma-ray spectroscopy has been successfully used to map the abundances and distributions of certain elements present in planetary regoliths. Helium-3 is unique among these elements since the gamma-rays produced in the 3He(n, γ)4He reaction are 20.6 MeV or above. Thus, detection of the gammaray flux from 3He should be free of interference from the gamma-rays of any other neutron capture reaction. Since 3He is present in the relatively small concentration of about 10 30 parts per billion by weight, the gamma-ray flux resulting from the 3He(n, γ)4He reaction using galactic cosmic-ray (GCR)-induced neutrons will be extremely small. We propose to map the 20.6 MeV gamma-ray from 3He during very large solar proton flares (VLSPF) to take advantage of the increased flux of solar cosmic-ray (SCR)-induced neutrons. The neutron production spectrum in the lunar regolith has been calculated from GOES-7 satellite observations of the October 1989 VLSPF using the BRYNTRN charged-particle transport code. This spectrum is used as input for the ONEDANT neutron/gamma-ray transport code. The production of SCR-induced neutrons during a VLSPF is thus calculated to be several orders of magnitude greater than the production expected for GCR-induced neutrons. The production of 20.6 MeV gamma-rays is also calculated to be several orders of magnitude greater during a VLSPF. This method of mapping the 20.6 MeV gamma ray from the 3He(n, γ)4He reaction would also provide increased sensitivity for mapping other elements in the lunar regolith, and may allow the detection of previously unmapped elements in the lunar regolith as well as trace elements in the Earth's upper atmosphere. _____________________________ Fusion Technology Institute, Nuclear Engineering and Engineering Physics Department and Wisconsin Center for Space Automation and Robotics, University of Wisconsin-Madison, Madison, WI 53706-1687