Background
Future lunar explorations will require habitats, storage units, and mining operations that must withstand the Moon’s harsh environment. Lunar conditions include exposure to water, oxides, hydroxyl (OH) species, and other volatile compounds such as hydrogen sulfide, carbon dioxide, and carbon monoxide, all of which contribute to corrosion or material degradation over time. This internal research project served as a feasibility study to evaluate those risks. It combined an electron gun for surface ablation and a quadrupole mass spectrometer (QMS) to detect corrosion chemistries in a controlled vacuum environment.
Approach
The IR&D project involved modifying and testing an electron gun prototype and then integrating with an Engine for Automatic Biomechanical Evaluation (ENABLE™) QMS (both were available at SwRI). The combined system was tested in a vacuum chamber to detect aluminum and aluminum oxides under lunar-like conditions.
Accomplishments
A SwRI-owned electron gun was modified for high voltage operation and achieved 30kV. After installation in the vacuum chamber, the gun was operational and successfully ablated material from test surfaces. A QMS detector (also SwRI-owned) was utilized in the vacuum chamber for analysis. During the first test with an Al 6061 target, only a small amount of sodium was detected. Aluminum was detected on an aluminum pellet after repositioning the target. Some gases and Al were also detected on a phosphor screen. No oxides were detected on any of the samples including the aluminum oxide (Al2O3) coupon. However, all scans exhibited background noise. Although the system was able to operate in lunar-like vacuum conditions, the scans took 1-2 hours, rather than the target five minutes. Ultimately, the system operated but not as intended. It demonstrated key lessons learned yet remains limited and not fully operational in its current configuration.
Attempts to improve the signal were performed but did not achieve the goal of detecting oxygen and aluminum on all samples. Possible reasons for the minimal readings include 1) excess residual species in the vacuum chamber that resulted in a large background noise signal, 2) the charge state of the ablated material was not picked up by the QMS detector, and 3) insufficient electron energy density or power to ablate enough material off the surface. A potential improvement would be to replace the QMS detector with an energy dispersive spectroscopy (EDS) detector. EDS (X-ray) detectors can detect oxygen as well as other nonmetals and metals, similar to systems used in scanning electron microscopes. Future studies could integrate an EDS detector while also enhancing the electron gun to reduce weight and power requirements, making the system more efficient for lunar use.