STS-125 is a planned Space Shuttle mission which will be the fifth and final servicing mission to the Hubble Space Telescope (HST). The mission will be flown by , with another shuttle ready to launch in case a rescue mission is needed. STS-125 is currently awaiting a new target launch date following an anomaly aboard the telescope that occurred on September 27, 2008.
Atlantis will carry two new instruments to the HST, in addition to a replacement Fine Guidance Sensor, six new gyroscopes and batteries to allow the telescope to continue to function at least through 2013. The crew will also install a new thermal blanket layer to provide improved insulation, and a "soft-capture mechanism" to aid in the safe de-orbiting of the spacecraft by an unmanned spacecraft at the end of its operational lifespan.
Otherwise known as Hubble Space Telescope Servicing Mission 4 (HST-SM4), the mission will mark the thirtieth flight of Space Shuttle Atlantis, the last planned manned mission to the space telescope. The mission will be the first flight of Atlantis since STS-122, and the first flight of Atlantis not to visit a space station since STS-66 in 1994. It will be the first Shuttle mission not related to the ISS since STS-107, which ended in the Columbia accident.
Due to the large differences between the orbit of the International Space Station and the HST, Atlantis will be unable to reach the safe haven of the ISS in the event of its heat shield becoming damaged upon launch. Therefore the mission will require another Space Shuttle to be ready on launch pad 39B for immediate flight on the STS-400 Launch On Need (LON) rescue mission throughout Atlantis' mission.
Number in parentheses indicates number of spaceflights by each individual prior to, and including this mission.
The mission will add two new instruments to Hubble: The Cosmic Origins Spectrograph, which will be the most sensitive ultraviolet spectrograph installed on the telescope. Its far-UV channel will be 30 times more sensitive than previous instruments and the near-UV will be twice as sensitive. The second instrument, the Wide Field Camera 3, is a panchromatic wide-field camera that can record a wide range of wavelengths, including infrared, visible, and ultraviolet light.
The infrastructure of the telescope will be maintained and upgraded by replacing a "Fine Guidance Sensor" that controls the telescope's directional system, and installing a set of six new gyroscopes, as well as replacing batteries and installing a new outer blanket layer to provide improved insulation.
The payload bay elements are the Super Lightweight Interchangeable Carrier (SLIC) holding the Wide Field Camera 3, new batteries and a radiator; the ORU Carrier with the Cosmic Origins Spectrograph and FGS-3R instruments; the Flight Support Structure (FSS) for holding the Hubble during repairs, and the Multi-Use Lightweight Equipment Carrier (MULE) holding support equipment.
STS-125 (HST-SM04) was originally assigned to Discovery, with a launch date no earlier than May 2008. This would move the mission ahead of STS-119, ISS Assembly flight 15A. STS-125 will be the first visit to the Hubble Space Telescope for Atlantis, although the telescope has been previously serviced twice by Discovery, and once each by Columbia and Endeavour.
STS-125 was further delayed to October 2008 due to manufacturing delays on external tanks for future space shuttle missions. Lockheed Martin experienced delays during the production changes to make new external tanks with all the enhancements recommended by the Columbia Accident Investigation Board, making it impossible for them to produce two tanks for the STS-125 mission—one for Atlantis, and one for Endeavour for an emergency rescue mission, if necessary—in time for the original August launch date.
STS-125 was originally scheduled to be ISS assembly mission ISS-1J. The mission would have delivered the Kibo Japanese Experiment Module (JEM) and JEM's specialized Remote Manipulator System to the station. Columbia was originally planned to fly the fifth Hubble mission, as Columbia was not the optimum orbiter for ISS assembly due to the weight of the orbiter.
The crew of Atlantis was at Kennedy Space Center for the Crew Equipment Interface Test in early July, 2008. This allowed the STS-125 crew to get familiar with the orbiter and the hardware they will be using during the flight.
On August 22, 2008, after a delay following Tropical Storm Fay, Atlantis was rolled from the Orbiter Processing Facility to the Vehicle Assembly Building, where it was mated to the external fuel tank and solid rocket booster stack. Problems encountered during the mating process, and delays due to Hurricane Hanna delayed rollout to the pad, which is normally done seven days after rollover.
The first rollout to Launch Pad 39A occurred on September 4, 2008. Atlantis is now due to be rolled back to the Vehicle Assembly Building on October 20 where it will await its new launch date.
STS-400 is the flight designation given to the Contingency Shuttle Crew Support mission which would be launched in the event Atlantis becomes disabled during STS-125. To preserve NASA's post-Columbia requirement of having shuttle rescue capability, a second shuttle will be on launch pad 39-B at the time of STS-125's launch. This has imposed a constraint on deactivation and conversion of pad 39B for Ares I flight tests. Due to the inclination and other orbit parameters of Hubble, Atlantis would be unable to use the ISS as a "safe haven" in the event of structural or mechanical failure.
NASA had contingency rescue missions on standby for all nine flights conducted between the fatal Columbia flight and STS-125.