In November 1999, White Sands Test Facility (WSTF) was informed of damage to a space shuttle oxygen system component that could release small metal particles into the gaseous oxygen (GOX) pressurization ystem of the external tank (ET). The WSTF oxygen hazards analysis group was requested by the NASA Johnson Space Center Propulsion and Fluids Systems Branch to evaluate the possible particle impact ignition hazards in the ET GOX pressurization system.
The ET GOX pressurization system uses high pressure bled from the oxygen urbopumps to provide ullage pressure for the liquid oxygen (LOX) tank. GOX enters the LOX tank through a diffuser attached to the interior of the LOX tank. The calculated GOX velocity at the diffuser outlet screen was approximately 51 m/s. According to published particle impact data, ignition often occurs at velocities of 45 m/s . Therefore, NASA would have to either fly with a legitimate particle impact ignition risk or dismantle and clean the entire ET pressurization system before a subsequent flight.
Fortunately, WSTF located previously unpublished particle impact data that indicated the particulate potentially trapped in the ET pressurization system did not pose a legitimate ignition hazard. Based on these data, WSTF was able to assure JSC that there was not a legitimate particle impact ignition risk in this case. Therefore, this shuttle mission was safely accomplished without the delay or costs associated with disassembling the entire ET pressurization system.
In addition to presenting the rationale used to safely proceed with the shuttle mission, this paper also presents the previously unpublished data used to make these decisions.