STS-61-B

STS-61-B was the 23rd NASA Space Shuttle mission, and its second using Space Shuttle Atlantis. The shuttle was launched from Kennedy Space Center, Florida, on November 26, 1985. During STS-61-B, the shuttle crew deployed three communications satellites, and tested techniques of constructing structures in orbit. Atlantis landed at Edwards Air Force Base, California, at 16:33:49 EST on December 3, 1985, after 6 days, 21 hours, 4 minutes, and 49 seconds in orbit.

STS-61-B marked the quickest turnaround of a Shuttle orbiter from launch to launch in history – just 54 days elapsed between Atlantis' launch on STS-51-J and launch on STS-61-B. As of August 2022^[update], this is still the record for turn around between two flights of the same orbital space vehicle. The mission was also notable for carrying the first Mexican astronaut, Rodolfo Neri Vela. This was also Atlantis' second and final mission before the Space Shuttle Challenger disaster in 1986. The Challenger disaster would ground the shuttle fleet for two and a half years and Atlantis would not fly again until STS-27, which launched three years later on December 2, 1988.

After landing at the Edwards Air Force Base at the end of STS-51-J on October 7, 1985, Atlantis returned to the Kennedy Space Center on October 12, 1985. The shuttle was moved directly into an Orbiter Processing Facility (OPF), where post-flight de-servicing and pre-flight processing took place simultaneously.

After only 26 days in the OPF, a record fast processing in the history of the Space Shuttle program, the shuttle was rolled to the Vehicle Assembly Building (VAB) on November 7, 1985. Atlantis was mated with the External Tank (ET) and Solid Rocket Booster (SRB) stack and was rolled out to launch LC-39A on November 12, 1985.

Three satellites were deployed during this mission: Aussat-2, Morelos-2, and Satcom-K2. Aussat-2 and Morelos-2 were the second satellites in their series (the first satellites in the series were deployed during STS-51-G and STS-51-I). Both of these were Hughes Space and Communications HS-376 satellites and were equipped with a Payload Assist Module (PAM-D) booster to reach geostationary transfer orbit (GTO). Satcom-K2 was a version of the RCA 4000 series satellites, which were owned and operated by RCA American Communications (RCA). This satellite was deployed using a PAM-D2 booster (which was a larger version of the PAM-D). This was the first flight of the PAM-D2 booster on a Space Shuttle.

All three satellites were successfully deployed, one at a time, and their booster stages fired automatically to lift them to geostationary transfer orbits. Their respective owners assumed charge, and later fired the onboard kick motors at apogee, to circularize the orbits and align them with the equator.

A checkered racing flag was carried on board Atlantis during STS-61-B; the flag is now on display at the Indianapolis Motor Speedway Hall of Fame Museum. This was also the second test flight of the Orbiter Experiments (OEX) advanced autopilot. It ran for approximately 65 hours and demonstrated the ability to fly the orbiter on nose jets only, aft jets only, to automatically stationkeep on another satellite and to fly an orbit with zero aerodynamic drag. The OEX autopilot was also more fuel efficient than the baseline system.

Space Shuttle Atlantis lifted off from Launch Complex 39A at Kennedy Space Center at 19:29:00 p.m. EST on November 26, 1985. The launch marked the second night launch of the Space Shuttle program, and the ninth and final flight of 1985.