STS-31 was the 35th mission of the NASA Space Shuttle program. The primary purpose of this mission was the deployment of the Hubble Space Telescope (HST) into low Earth orbit. The mission used the Space Shuttle Discovery (the tenth mission for this orbiter), which lifted off from Launch Complex 39B on 24 April 1990 from Kennedy Space Center, Florida.

Discovery's crew deployed the Hubble Space Telescope on 25 April 1990, and then spent the rest of the mission tending to various scientific experiments in the Shuttle's payload bay as well as 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.