STS-31 was the 35th mission of NASA's Space Shuttle program and the tenth flight of the Space Shuttle Discovery. The primary purpose of this mission was the deployment of the Hubble Space Telescope (HST) into low Earth orbit. Discovery lifted off from Launch Complex 39B on April 24, 1990, from Kennedy Space Center, Florida.
Following the Challenger accident clarification was required on mission numbering. As STS-51-L was also designated STS-33, future flights with the previous STS-26 through STS-33 designators would require the R in their documentation to avoid conflicts in tracking data from one mission to another.
Discoverys crew deployed the Hubble Space Telescope on April 25, 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. Discoverys 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.
Crew
Crew seat assignments
{| class="wikitable" style="text-align:center"
! Seat
! Launch
! Landing
|rowspan=8| 150px<br />Seats 1–4 are on the flight deck.<br />Seats 5–7 are on the mid-deck.
|-
! 1
|colspan=2| Shriver
|-
! 2
|colspan=2| Bolden
|-
! 3
| McCandless
| Sullivan
|-
! 4
|colspan=2| Hawley
|-
! 5
| Sullivan
| McCandless
|-
! 6
|colspan=2 style="background-color:lightgray"| Unused
|-
! 7
|colspan=2 style="background-color:lightgray"| Unused
|}
Crew notes
This mission was originally to be flown in August 1986 as STS-61-J using Atlantis, but was postponed due to the Challenger disaster. John W. Young was originally assigned to command this mission, which would have been his seventh spaceflight, but was reassigned to an administrative position and was replaced by Loren J. Shriver in 1988.
Mission highlights
thumb|upright=1.3|Space Shuttle Discovery launches from LC-39B for STS-31 with Columbia on LC-39A in preparation for [[STS-35.]]
upright=1.3|thumb|Hubble Space Telescope in the cargo bay of Discovery
STS-31 was launched on April 24, 1990, at 12:33:51UTC (8:33:51amEDT, local time at the launch site). A launch attempt on April 10, 1990, was scrubbed at T−4 minutes for a faulty valve in auxiliary power unit (APU) number one. The APU was eventually replaced, and the Hubble Space Telescope's batteries were recharged. On launch day, the countdown was briefly halted at T−31 seconds when Discoverys computers failed to shut down a fuel valve line on ground support equipment. Engineers manually commanded the valve to close and the countdown continued.
The main purpose of this mission was to deploy Hubble. It was designed to operate above the Earth's turbulent and obscuring atmosphere to observe celestial objects at ultraviolet, visible and near-infrared wavelengths. The Hubble mission was a joint NASA-ESA (European Space Agency) effort going back to the late 1970s. The rest of the mission was devoted to photography and onboard experiments. To launch HST into an orbit that guaranteed longevity, Discovery entered an orbit of around . At one point during the mission, Discovery briefly reached an apogee of , the highest altitude ever reached by a Shuttle orbiter. The record height also permitted the crew to photograph Earth's large-scale geographic features not apparent from lower orbits. Motion pictures were recorded by two IMAX cameras, and the results appeared in the 1994 IMAX film Destiny in Space. Experiments on the mission included a biomedical technology study, advanced materials research, particle contamination and ionizing radiation measurements, and a student science project studying zero-gravity effects on electronic arcs. Discoverys reentry from its higher-than-usual orbit required a deorbit burn of 4 minutes and 58 seconds, the longest in Shuttle history up to that time. Discovery orbited the Earth 80 times during the mission.
Secondary payloads included the IMAX Cargo Bay Camera (ICBC) to document operations outside the crew cabin and a handheld IMAX camera for use inside the orbiter. Also included were the Ascent Particle Monitor (APM) to detect particulate matter in the payload bay; a Protein Crystal Growth (PCG) experiment to provide data on growing protein crystals in microgravity, Radiation Monitoring Equipment III (RME III) to measure gamma ray levels in the crew cabin; Investigations into Polymer Membrane Processing (IPMP) to determine porosity control in the microgravity environment, and an Air Force Maui Optical Site (AMOS) experiment.
Discovery landed on Runway 22 at Edwards Air Force Base in California on April 29, 1990, at 13:49:57UTC (6:49:57amPDT, local time at the landing site). The landing had a rollout distance of , took 61 seconds, and marked the first use of carbon brakes on a shuttle. Discovery was returned to Kennedy Space Center after STS-31 on May 7, 1990.