STS-51-B

STS 51-B was the seventeenth flight of NASA's Space Shuttle program, and the seventh flight of Space Shuttle Challenger. The launch of Challenger on April 29, 1985 was delayed by 2 minutes and 18 seconds, due to a launch processing failure. Challenger was initially rolled out to the pad to launch on the STS-51-E mission. The shuttle was rolled back when a timing issue emerged with the TDRS-B satellite. When STS-51-E was canceled, Challenger was remanifested with the STS-51-B payloads. The shuttle landed successfully on May 6, 1985, after a week-long mission.

Mission summary
Challenger lifted off from Kennedy Space Center (KSC)'s launch pad 39A at 12:02 pm EDT on April 29, 1985. The crew members included Robert F. Overmyer, commander; Frederick D. Gregory, pilot; Don L. Lind, Norman E. Thagard and William E. Thornton, mission specialists; and Lodewijk van den Berg, of EG&G Energy Management, Inc., and Taylor G. Wang, of the Jet Propulsion Laboratory, both payload specialists. Similar to the previous Spacelab mission, the crew was divided roughly in half to cover 12-hour shifts, with Overmyer, Lind, Thornton and Wang forming the Gold team, and Gregory, Thagard and van den Berg as the Silver team.

STS-51-B was the second flight of the European Space Agency's Spacelab, and the first with the Spacelab module in a fully operational configuration. Spacelab's capabilities for multi-disciplinary research in microgravity were successfully demonstrated. The gravity gradient attitude of the orbiter proved quite stable, allowing the delicate experiments in materials processing and fluid mechanics to proceed normally. The crew operated around the clock in two 12-hour shifts. Two squirrel monkeys and 24 rats were flown in special cages, the second time American astronauts flew live non-human mammals aboard the shuttle. The crew members in orbit were supported 24 hours a day by a temporary Payload Operations Control Center, located at the Johnson Space Center.

On the mission, Spacelab carried 15 primary experiments, of which 14 were successfully performed. Two Getaway Special experiments required that they be deployed from their canisters, a first for the program. These were NUSAT (Northern Utah Satellite) and GLOMR (Global Low Orbiting Message Relay Satellite). NUSAT deployed successfully, but GLOMR did not deploy, and was returned to Earth.

Challenger landed safely at Edwards Air Force Base at 12:11 pm EDT on May 6, 1985, after a mission lasting 7 days, 8 minutes and 46 seconds.

Connection to the Challenger disaster
While participating in the investigation into the destruction of Challenger during STS-51-L in 1986, Overmyer discovered that a problem with the shuttle's O-rings, similar to that which led to the disaster, had emerged during the launch of STS-51-B. Morton Thiokol engineers told Lind after the mission that "you came within three-tenths of one second of dying." It was the problem with the O-rings on the left solid rocket motor on this launch (SRM 16A) that prompted Roger Boisjoly to write his famous memo to Bob Lund about the potential for the O-rings to cause catastrophic failure. (See )