Extravehicular Activity Micrometeoroid and Orbital Debris Risk Assessment Methodology

A well-known hazard associated with exposure to the space environment is the risk of vehicle failure due to an impact from a micrometeoroid and orbital debris (MMOD) particle. Among the vehicles of importance to NASA is the extravehicular mobility unit (EMU) “spacesuit” used while performing a US extravehicular activity (EVA). An EMU impact is of great concern as a large leak could prevent an astronaut from safely reaching the airlock in time resulting in a loss of life. For this reason, a risk assessment is provided to the EVA office at the Johnson Space Center (JSC) prior to certification of readiness for each US EVA. This paper will detail the methodology for an ISS EVA risk assessment. The soft goods regions (multilayer fabric over a pressurized bladder) are the highest contributors of risk for an ISS EVA. The gloves, due to reduced fabric layers to allow for improved dexterity, carry the highest risk per area. ISS EVA risk can be reduced by minimizing the exposure of the front of the suit and gloves to the orbital debris flux.