The harsh environment in space can be damaging
to the human body. Space radiation is caused from high-energy
charged particles (especially from the sun) that can be life
threatening if the astronaut is not properly protected while
performing experiments outside the ISS (Extra-Vehicular Activity
or EVA). Radiation also affects ISS electronics so proper
shielding is required.
Plasma is the ionized gas that surrounds
the ISS and is the final area of environmental concern. Because
the ISS is negatively grounded with respect to the space
plasma, the ISS will build up electrons on its surface. This
causes an arcing hazard, which could put the astronauts at
risk of electrical shock during EVA. Since simulating this
environment safely on Earth is impossible, analysis and modeling
is being performed using data collected from the PCUs, ground-based
radar, and the floating potential measurement unit. An earlier
instrument, the floating potential probe, provided approximately
four months of data after the activation of the power module
in 2000 and has since been jettisoned to space.
In addition to providing modeling and analysis oversight, Glenn successfully managed the building and testing of the PCU, which is considered the “grounding plug” of the ISS. While astronauts are working outside their spacecraft, the PCU generates an ionized gas that pulls excess electrons off the surface of the ISS and releases them into space. This process prevents the excess build-up of electrons and greatly reduces the risk of electrical shock.
Two PCUs are in operation during all EVAs on the ISS and are expected to last until 2020. Each PCU contains a gas feed system to supply xenon to the HCA. The power electronics unit inside the PCU controls and monitors the PCU. Three Glenn researchers received the “NASA Government Invention of the Year” award in 2001 as well as a patent in 2002 for the invention of cathode technology for the HCA (http://www.grc.nasa.gov/WWW/PAO/pressrel/2002/02-021.html).
Currently, Glenn is analyzing the performance and investigating issues related to the PCUs that have been on the ISS since 2000. This analysis is part of Glenn’s sustaining engineering effort of several hardware components on the ISS to ensure the safety of the crew.