Neutral Mass Spectrometer Under Development for the Lunar Atmosphere and Dust Environment Explorer (LADEE) Mission

Introduction: The objectives of the LADEE Mission given in the March 21, 2008 Request for Information (RFI) from the Lunar Science Program of NASA’s Science Mission Directorate [1] were: • Determine the global density, composition, and time variability of the fragile lunar atmosphere before it is perturbed by further human activity; • Determine if the Apollo astronaut sightings of diffuse emission at 10s of km above the surface were Na glow or dust and; • Document the dust impactor environment (size-frequency) to help guide design engineering for the outpost and also future robotic missions. These objectives were derived most immediately from the report of the LADEE Science Definition Team [2] and are consistent with the National Research Council’s report, “Scientific Context for the Exploration of the Moon” [3]. NASA selected for the LADEE payload an Ultraviolet Spectrometer, a Neutral Mass Spectrometer, and a Dust Detector. The core science mission to be implemented in the 2012 time frame is 90 days to allow measurements to be made over a period of one or more lunations and examine the lunar exosphere in different space environments from an orbital altitude of 50 km or lower. In addition to the science mission NASA plans to use this mission to demonstrate optical communication technology away from low Earth orbit. Species in Lunar Exosphere: To date, the four constituents He, Ar, K, and Na have been firmly identified [4, 5] in the lunar exosphere by mass spectrometers accommodated by the Apollo program and by ground based spectroscopy. The source of the species in the lunar exosphere can be from (1) the solar wind, (2) from the lunar regolith, and (3) from the lunar interior. He, both K and Na, and Ar are expected to be predominantly from these three sources respectively. Nevertheless, upper limits have been set for a large number of other atomic and molecular species. These upper limits vary widely [5] from greater than 1,000 particles/cc predicted at 50 km above the surface for Mg, Al, Kr, Xe, CO, H4, H2, and OH to tens to hundreds of particles/cc for Si, Al, Fe, CO2, H, N, C, N2, O, and S. The LADEE measurements are designed to measure the abundance of several of these species and substantially lower the upper limits for others.