Space Shuttle Main Engines (SSME) discharge a significant quantity of unburned hydrogen during normal start and shutdown operations. At Vandenberg Air Force Base (VAFB), a Flight Readiness Firing (FRF) or launch abort could introduce this unburned hydrogen into the enclosed SSME exhaust duct. This hydrogen in a closed duct creates a risk of detonation which could result in significant overpressure at the aft heat shield thereby causing damage to the Space Shuttle Vehicle (SSV).
To mitigate the detonation hazard the Air Force (AF) initiated a Hydrogen Disposal System (HDS) program. Extensive analyses and feasibility testing were conducted on possible solutions. In December 1986 the AF Shuttle Test Group (STG) selected the Steam Inerting System (SIS) concept as the most technically feasible resolution to the unburned hydrogen issue. The following January, STG directed the Shuttle Processing Contractor (SPC) to complete the development and design of a SIS for the VAFB SSV launch pad (Refs. A & B)
