STS-51-C was the first shuttle mission dedicated to the United States Department of Defense (DoD), and consequently many details remain classified.

STS-51-C launched from Kennedy Space Center (KSC) on January 24, 1985, at 19:50:00 UTC, and was the first of nine shuttle missions in 1985.

[4] The U.S. Air Force only stated that the shuttle successfully launched its payload with an Inertial Upper Stage (IUS) on the mission's seventh orbit.

[7] Also, according to Aviation Week, the shuttle initially entered a 204 × 519 km (127 × 322 mi) orbit, at an inclination of 28.45° to the equator.

Almost exactly a year after STS-51-C, Space Shuttle Challenger was destroyed with all hands on board during the STS-51-L 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-51-C, the worst Space Shuttle Solid Rocket Booster (SRB) blow-by effects of any mission prior to STS-51-L occurred, indicating conclusively that the Viton O-rings were not sufficiently sealing the hot gases inside the combustion chambers of the SRBs while firing.