STS-51-F Challenger Mission Performed Only Abort-to-Orbit in Shuttle Program History

STS-51-F Challenger Mission Overview

STS-51-F, also known as Spacelab 2, was the 19th flight of NASA's Space Shuttle program and the eighth flight of Space Shuttle Challenger. It launched from Kennedy Space Center, Florida, on July 29, 1985, and concluded eight days later on August 6, 1985. The primary payload for the mission was the Spacelab 2 laboratory module, though it also included experiments like the Carbonated Beverage Dispenser Evaluation and a helium-cooled infrared telescope (IRT).

Engine Failure During Ascent

During the ascent phase of the launch, the Challenger experienced multiple sensor failures in its Engine 1 Center SSME. At 3 minutes 31 seconds into the flight, one of the high-pressure fuel turbopump turbine discharge temperature sensors failed. Two minutes and twelve seconds later, a second sensor failed, which caused the center engine to shut down. This incident marked the only in-flight RS-25 engine failure recorded during the entire Space Shuttle program.

Abort to Orbit Procedure Executed

As a direct consequence of the engine shutdown, the Space Shuttle Challenger was forced to execute an "Abort to Orbit" (ATO) emergency procedure. This was the sole instance of an abort after launch in the history of the Space Shuttle program. The ATO trajectory meant that the mission proceeded at a slightly lower orbital altitude than originally planned.

Preventing Further Complications

Approximately eight minutes into the flight, another temperature sensor in the right engine failed, and the remaining sensor showed readings near the redline for engine shutdown. Booster Systems Engineer Jenny M. Howard recommended inhibiting further automatic RS-25 shutdowns based on the remaining sensor readings. This action prevented the potential shutdown of a second engine, which could have led to a more severe abort mode and possible loss of the crew and vehicle.