On this day in 1985, the 19th flight of the Space Shuttle program, STS-51-F, landed at Edwards Air Force Base. STS-51-F was unique for two reasons: it delivered Spacelab 2 to orbit, and it was the only Space Shuttle mission to have performed an abort after launching, called an abort-to-orbit (ATO):
The launch countdown July 12 halted at T-3 seconds after main engine ignition when a malfunction of the number two space shuttle main engine (SSME) coolant valve caused a shutdown of all three main engines. The launch on July 29 was delayed 1 hour, 37 minutes due to a problem with the table maintenance block update uplink. 5 minutes, 45 seconds into ascent, the number one main engine shutdown prematurely, resulting in an Abort To Orbit (ATO) trajectory.