Spaceflight mission report: STS-51C

Launch from Cape Canaveral (KSC) and landing at Cape Canaveral (KSC), Runway 15.

The launch was scheduled for January 23, 1985 but was delayed because of freezing weather conditions. Orbiter Challenger had been scheduled for this flight, but Discovery was substituted when thermal tile problems were encountered with Challenger.

Gary Payton became the first military astronaut in space.

This was the first Shuttle mission dedicated to Department of Defense, and most information about it remains classified. For the first time, NASA did not provide pre-launch commentary to the public until nine minutes before liftoff. The U.S. Air Force Inertial Upper Stage (IUS/ELINT) booster was deployed and met mission objectives. It is believed that the payload was a Magnum/ORION ELINT satellite into geosynchronous orbit, and that STS-33 and STS-38 launched others. Gary Payton stated in 2009 that STS-51C's payload is "still up there, and still operating".

Also, according to Aviation Week, the shuttle initially entered a 204-kilometer (127 mi) x 519-kilometer (322 mi) orbit, at an inclination of 28.45 degrees to the equator. It then executed three Orbital Maneuvering System (OMS) burns, the last being executed on the fourth orbit. The first burn was conducted to circularize the shuttle's orbit at 519 kilometers (322 mi).

Almost exactly a year after STS-51C, Space Shuttle Challenger was destroyed with all hands on-board during the STS-51L mission including Ellison Onizuka, a crew member on both flights. As part of the investigation into the disaster, it was reported to the Rogers Commission that during the launch of STS-51C, the worst solid rocket booster (SRB) blow-by effects of any mission prior to STS-51L occurred, indicating conclusively that the Viton O-rings were not sufficiently sealing the hot gases inside the combustion chambers of the SRBs while firing. After they were recovered post-flight, the O-rings in both the right and left SRBs showed some degree of charring, but analysis of the center field joint of the right SRB showed an unprecedented penetration of the primary O-ring and heavy charring on the secondary O-ring.