scope:

Description of Driving Event:

On August 22, 1992 an Atlas/Centaur Launch Vehicle (Atlas 1, Launch AC-71) carrying a Hughes Galaxy I-R Spacecraft was destroyed in flight. The Centaur C-1 engine had failed to achieve full thrust, resulting in an uncontrolled tumble of the vehicle. The guidance system, sensing that the vehicle had not achieved proper acceleration, shutdown both engines and instituted a restart sequence. Once again the C-1 engine failed. Full thrust was achieved by the C-2 engine both times. In lieu of the C-1 thrust failure the vehicle was destroyed by the range safety officer.

To start reliably, the RL10 engine requires proper fuel and oxidizer pressure at its pump inlets and the fuel and oxidizer pumps to be at the proper cryogenic temperature. The engine temperature results from a two-stage chilldown process. The prelaunch chilldown is provided by ground dewars supplying pressurized helium. Each RL10 engine receives the flow of helium through a check valve. These valves should close when the flow is terminated to prevent further flow of any gas through the engine via the chilldown ducts exiting the vehicle. The state of the chilldown check valve was not monitored. As a result, the check valve of the C-1 engine was not closed and an ingestion of air occurred which eventually caused the engine to fail.

The investigation team also concluded that AC-70's failure is due to the same cause as AC-71. For more information on AC-70, see AC-70 Anomaly Investigation Summary Report. Further details on the AC-71 failure are found in the AC-71 Anomaly Investigation Summary Report.