Environmental Analysis of the Bounded Lunar Exosphere (ENABLE)

The last mass spectrometer placed at the lunar surface was the Lunar Atmospheric Composition Experiment (LACE) deployed by the Apollo 17 astronauts in December of 1972. Since that time, numerous investigations have uncovered increasingly unambiguous evidence for significant inventories of trapped volatiles at the lunar surface, with the Lunar Cratering Observation and Sensing Satellite (LCROSS) mission producing evidence of H2O, Hg, CO, and NH3 in that spacecraft’s ejecta plume. What is currently needed to establish “ground truth" for lunar volatiles during exploration and prospecting at the lunar surface is a low-cost, versatile analytical chemistry instrument – a mass spectrometer – with the ability to integrate with mission-specific systems to analyze volatiles released from the regolith during upcoming robotic and human exploration, and in situ resource utilization (ISRU) tasks.

We propose to develop a quadrupole mass spectrometer (QMS) as a prototype diagnostic chemistry tool suitable for mission-specific, multi-platform investigations and probing of the lunar surface and subsurface as volatiles are characterized, prospected, and recovered for ISRU and planetary science of primitive, regolith-laden worlds. The Environmental Analysis of the Bounded Lunar Exosphere (ENABLE) project combines the capabilities of a popular commercial off-the-shelf (COTS) QMS manufactured by Extorr with SwRI’s decades-long heritage as a manufacturer of custom electronics for space missions. The Extorr QMS design incorporates both Pirani and ionization gauges into its operation, thus allowing the versatility of measuring the quantity of volatiles present, even when local pressures observed by the instrument exceed the upper operating limit of its ion sensors.

During characterization and calibration, we will further demonstrate ENABLE’s capabilities and function throughout a broad range of local environmental pressures from atmospheric down to ultrahigh vacuum (UHV) conditions. We will also operate ENABLE in “appearance potential” mode to characterize how ionization energies below the standard 70 eV operation enhances the detection of more easily ionized hydrocarbons and organic molecules closer to their respective ionization energies. This method causes such ions to appear in a given mass channel before being overwhelmed by interfering ions produced at the higher ionization energies needed for other gases.

So long as gas mixtures reach the inlet of ENABLE, their composition can be measured according to their partial pressure. Performance testing under various simulated lunar surface operations will be demonstrated on SwRI’s Lunar Advanced Vacuum Apparatus (LAVA) which contains a column of JSC-1A simulated lunar regolith to 50 cm in depth. Not only can LAVA produce volatiles through mechanical and optical disturbances of its simulant column, but the system also provides for thermal gas calibration and sensitivity measurements of the ENABLE sensor.

Possible robotic and human user applications include: leak checking of spacecraft, spacesuits, and structures; monitoring of spacecraft contamination and rocket engine combustion byproducts; mapping of the composition and quantity of lunar volatiles; and measurement of the variability and composition of the local ambient lunar exosphere. Lunar surface locations showing promise as volatile sources could be immediately sampled in situ for rapid analysis by mining operations, or flagged for subsequent ISRU operations by the appropriate NASA or commercial ventures.

The perceived significance of this work is a low-cost, portable device capable of being operated over the entire lunar surface on a variety of stationary, mobile, or orbital platforms, to provide ground-truth measurements of volatiles as to their “content, form, and distribution” (LEAG NEXT-SAT), and to fill “Strategic Knowledge Gaps” regarding lunar volatiles in anticipation of future robotic and human exploration of the Moon.