Hubble is the only telescope designed to be maintained in space by astronauts. Five Space Shuttle missions have repaired, upgraded, and replaced systems on the telescope, including all five of the main instruments. The fifth mission was initially canceled on safety grounds following the "Columbia" disaster (2003), but NASA administrator Michael D. Griffin approved the fifth servicing mission which was completed in 2009. The telescope completed 30 years in operation in April 2020 and could last until 2030–2040. One successor to the Hubble telescope is the James Webb Space Telescope (JWST) which is tentatively scheduled to be launched in late 2021.