STS-51-F - Launch

Launch

STS-51-F's first launch attempt on 12 July 1985 was halted with the countdown at T-3 seconds after main engine ignition, when a malfunction of the number two Space Shuttle Main Engine (SSME) coolant valve caused the shutdown of all three main engines.

Challenger launched successfully on its second attempt at 29 July 1985, 17:00 EDT, after a delay of one hour and 37 minutes due to a problem with the table maintenance block update uplink.

Three minutes and 31 seconds into the ascent, one of the center engine's two high pressure fuel turbopump turbine discharge temperature sensors failed. Two minutes and 12 seconds later, the second sensor failed, causing the shutdown of the center engine. This was the only in-flight main engine failure of the shuttle program. Approximately 8 minutes into the flight, one of the same temperature sensors in the right engine failed, and the remaining right engine temperature sensor displayed readings near the redline for engine shutdown. Booster Systems Engineer Jenny M. Howard acted quickly to command the crew to inhibit any further automatic SSME shutdowns based on readings from the remaining sensors, preventing the potential shutdown of a second engine and a possible abort mode that may have resulted in the loss of the vehicle and crew.

The failed SSME resulted in an Abort To Orbit (ATO) trajectory, whereby the shuttle achieved a lower-than-planned orbital altitude.