Lunar orbital science

Summary Orbital science has, to the present, concentrated on studies of force fields, particles, and visible photography. Cameras have been the major scientific instrument (it could be debated that for geodesy and gravity the entire spacecraft represents an instrument), and geology has been the principle benefactor. Photography has also been essential for the manned landing program, which would not have been possible on the schedule followed without the detailed Lunar Orbiter pictures.Orbital tracking data indicates that the Moon is almost homogeneous with perhaps a slight increase in density with depth. Significant analysis of the higher gravity harmonics have identified localized, near surface gravity highs that appear to be associated with circular maria. The Moon does not have a significant magnetic field of its own, and the solar wind appears to impinge directly on the surface. Russian and United States evidence on micrometeorite fluxes near the Moon is conflicting, but probably there is a decrease in flux compared to that near the Earth.Photographic evidence indicates that both impact and volcanic action has shaped the lunar surface. Mass movements of surface material and surface erosional effects are clearly evident. Surface water in the past, or near surface permafrost now, are definite possibilities to explain the sinuous rills. Faulting, both regional and local, is evident, as is probably horizontal layering near the surface.The United States space program is embarking on a broad program of orbital science including nearly the entire spectra of remote sensing. Approved orbital missions extend through 1972 and will be carried out in conjunction with manned landings. Emphasis will be placed on determining the extent and degree of surface variations between and within lunar provinces and the nature and strength of the lunar spectrum. Information obtained from the surface missions and the returned lunar samples will be invaluable in helping us to design orbital instruments and interpret the results.Missions after 1972 undoubtedly will carry more sophisticated instruments that will give us definitive information on the geochemical nature of the lunar surface and interior.Copies of NASA-issued documents may be obtained by writing to the Superintendent of Documents, U.S. Government Printing Office, Washington, D.C. 20402. Information about, and data from, U.S. space missions, including photographs, can be obtained from the National Space Science Data Center, Code 601, Goddard Space Flight Center, Greenbelt, Maryland 20771.