STS-31 was the thirty-fifth mission of the American Space Shuttle program, which launched the Hubble Space Telescope astronomical observatory into Earth orbit. The mission used the Space Shuttle Discovery, which lifted off from launchpad 39B on April 24, 1990 from Kennedy Space Center, Florida.
Discovery's crew deployed the telescope on April 25, and spent the rest of the mission tending to various scientific experiments in the shuttle's payload bay and operating a set of IMAX cameras to record the mission. Discovery's launch marked the first time since January 1986 that two Space Shuttles had been on the launch pad at the same time - Discovery on 39B and Columbia on 39A.Launched April 24, 1990, 8:33:51 a.m. EDT. Launch scheduled for April 18, then April 12, then April 10, following Flight Readiness Review (FRR). First time date set at FRR was earlier than that shown on previous planning schedules. Launch April 10 scrubbed at T-4 minutes due to faulty valve in auxiliary power unit (APU) number one. APU replaced and payload batteries recharged. Countdown briefly halted at T-31 seconds when computer software failed to shut down a fuel valve line on ground support equipment. Engineers ordered valve to shut and countdown continued. Launch Weight: 112,994 kilograms (249,110 lb).