Assessment of Contamination Ionization Due to Interaction with the Natural Environment for Gateway

NASA’s proposed Gateway is a space station that will orbit Earth’s moon. Outgassed contamination can cause degradation of Gateway components such as solar arrays, thermal control surfaces and science instruments. Interaction between outgassed material and the natural environment can lead to contamination ionization which can be driven back to Gateway by electric fields. The plasma in the Gateway lunar orbit has a density of 105 to 106 m-3 and the electron temperature is in the 10 to 30 eV range. Short duration high energy excursions with electron temperatures of 150 eV or greater and plasma densities 104 to 105 m-3 occur at the Gateway location. The sheath dimensions are on the order of 10 meters or larger at Gateway. Analysis was performed by solving the plasma sheath equations for Gateway. The expected contamination outgassing rate was used to estimate contamination ionizations rates within the sheath. The ionization rates were integrated throughout the sheath to determine the flux of ionized contaminates returning to Gateway. The susceptibility of various Gateway components to the ionized contamination flux can then be assessed to determine what if any mitigations are needed. The design is still evolving but mitigations can include materials selection to minimize outgassing and providing shielding or reorienting contamination sensitive surfaces.