The Tissue Equivalent Proportional Counter (TEPC) is a major component of the radiation detector onboard the satellite. It is a radiation detector filled with a tissue equivalent propane gas that will enable us to determine how radiation would interact with human cells. In order to keep the gas inside the cavity at the appropriate pressure, the TEPC housing must be kept under vacuum.

To test to see whether the TEPC housing remains under vacuum, the sealed TEPC housing is connected to a vacuum pump, pictured right. This process will reveal any leaking in the housing unit.