STS-31

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,^[2] which would have been his seventh spaceflight, but was reassigned to an administrative position and was replaced by Loren J. Shriver in 1988.^[3]

STS-31 was launched on April 24, 1990, at 8:33:51 a.m. EDT. 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 Discovery's computers failed to shut down a fuel valve line on ground support equipment. Engineers ordered the valve closed and the countdown continued.^[4]

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.^[5] 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 613 × 615 km (381 × 382 mi). At one point during the mission, Discovery briefly reached an apogee of 621 km (386 mi), the highest altitude ever reached by a Shuttle orbiter.^[6] 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.^[7] 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. Discovery's 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.^[8] Discovery also orbited the Earth 80 times during the mission.^[8]

During the deployment of Hubble, one of the observatory's solar arrays stopped as it unfurled. While ground controllers searched for a way to command HST to unreel the solar array, Mission Specialists McCandless and Sullivan began preparing for a contingency spacewalk in the event that the array could not be deployed through ground control. The array eventually came free and unfurled through ground control, while McCandless and Sullivan were pre-breathing inside the partially depressurized airlock.^[9]

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 crystalsinmicrogravity, 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.^[8]

The mission marked the flight of an 5 kg (11 lb) human skull, which served as the primary element of "Detailed Secondary Objective 469", also known as the In-flight Radiation Dose Distribution (IDRD) experiment. This joint NASA/DoD experiment was designed to examine the penetration of radiation into the human cranium during spaceflight. The female skull was seated in a plastic matrix, representative of tissue, and sliced into ten layers. Hundreds of thermo-luminescent dosimeters were mounted in the skull's layers to record radiation levels at multiple depths. This experiment, which also flew on STS-28 and STS-36, was located in the shuttle's mid-deck lockers on all three flights, recording radiation levels at different orbital inclinations.^[10]

Discovery landed on Runway 22 at Edwards Air Force BaseinCalifornia April 29, 1990, at 6:49:57 a.m. PDT. The landing had a rollout distance of 2,705 m (8,875 ft) 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.^[11]

NASA began a tradition of playing music to astronauts during the Project Gemini, which was first used to wake up a flight crew during Apollo 15. Each track is specially chosen, often by their families, and usually has a special meaning to an individual member of the crew, or is applicable to their daily activities.^[12]

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  Hubble at the pad
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  Liftoff of Discovery with the Hubble Space Telescope on board
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  Low hover position
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  High over Cuba
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  Solar array deployment
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  Hubble drifts away over Peru.
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  Florida and The Bahamas
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  Discovery returns home.

• List of human spaceflights
• List of Space Shuttle missions
• Outline of space science
• Space Shuttle

• NASA mission summary Archived August 15, 2011, at the Wayback Machine
• STS-31 Post Flight Crew Presentation
• STS-31 Post Flight Conference
• STS-31 Mission Highlights