The space shuttle mission that launched Hubble was designated STS-31. NASA’s Space Shuttle Discovery lifted off from Kennedy Space Center on April 24, 1990, carrying the Hubble Space Telescope in its payload bay. The crew deployed Hubble the next day into low Earth orbit, beginning the observatory’s landmark mission above Earth’s atmosphere.
STS stands for Space Transportation System, the formal designation used for shuttle missions. STS-31 was the 35th flight in the Space Shuttle program and Discovery’s tenth spaceflight. Its primary objective was not to service Hubble, but to place the newly built telescope into orbit.
A common mix-up is STS-61, which was the first Hubble servicing mission in December 1993. That flight used Space Shuttle Endeavour and installed corrective optics after engineers discovered that Hubble’s primary mirror had spherical aberration. STS-82 and STS-103 were later servicing missions. Discovery’s STS-31 flight therefore marks Hubble’s deployment, while those other designations refer to subsequent repairs or upgrades.