STS-125: Hubble’s Final Crewed Servicing Mission in 2009

Since entering orbit in 1990, Hubble had received four Space Shuttle servicing visits. STS-125 was to deliver new equipment, including Wide Field Camera 3 (WFC3) and the Cosmic Origins Spectrograph (COS), repair the Space Telescope Imaging Spectrograph (STIS) and Advanced Camera for Surveys (ACS), and replace gyroscope assemblies, batteries and a Fine Guidance Sensor. Its objectives combined increased observing capabilities with restored reliability in pointing, power and data handling.

In September 2008, one side of Hubble’s Science Instrument Command and Data Handling unit failed. The mission, originally planned for that October, was postponed while engineers prepared to replace the unit as well. Johnson Space Center was responsible for the shuttle and crew, while Goddard Space Flight Center controlled the telescope. The Space Telescope Science Institute and contractors participated in instrument development, functional testing and scientific verification.

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The flight went to Hubble rather than the International Space Station. Their orbits differ, and if Atlantis’s thermal protection system were damaged, its remaining propellant would not allow a diversion to the station for refuge. NASA therefore also prepared the STS-400 launch-on-need rescue mission, positioning a backup shuttle on another launch pad and developing procedures for the two shuttles to rendezvous and transfer crew members.

Hubble also lacked a full set of relative-navigation aids designed specifically for rendezvous. The approach had to limit contamination and mechanical effects from attitude-control thruster plumes on its mirrors and structure, and allow the robotic arm to capture the telescope safely. Drawing on earlier servicing missions, orbital-design, robotic-arm, thermal-control, structures and spacewalk teams coordinated normal and contingency operations.

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Atlantis lifted off from Kennedy Space Center’s Launch Pad 39A at 18:01 UTC on May 11, 2009. Scott Altman commanded the mission, with Gregory C. Johnson as pilot. The mission specialists were Megan McArthur, John Grunsfeld, Michael Massimino, Andrew Feustel and Michael Good.

As the shuttle approached Hubble on May 13, the telescope switched from its relay-satellite link to the shuttle link, temporarily leaving ground controllers without a command channel. Its data-management communications module had not changed from the 1-megabit-per-second science format to the 32-kilobit-per-second rate required by the shuttle link. After reconfiguration, the crew manually flew around the telescope to obtain a suitable orientation. The robotic arm captured Hubble and secured it to a support in the payload bay, providing a platform for the servicing work.

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From May 14 to 18, four astronauts working in two pairs completed five spacewalks totaling 36 hours and 56 minutes. Grunsfeld and Feustel first replaced Wide Field and Planetary Camera 2 with WFC3 and installed a new Science Instrument Command and Data Handling unit. The crew also installed a soft-capture mechanism to provide an interface for future spacecraft approaching and disposing of the telescope.

During the second spacewalk, Massimino and Good replaced three gyroscope assemblies and one battery module. One gyroscope assembly proved difficult to install, requiring a spare. The third spacewalk replaced COSTAR, the earlier corrective-optics assembly, with COS. Later work replaced the other battery module, a Fine Guidance Sensor and external insulation blankets. Unexpected difficulties changed the work sequence, with unfinished tasks moved to subsequent spacewalks.

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Repairs to ACS and STIS reached the level of electronic circuit boards. Goddard engineers developed special tools for this work. During the third spacewalk, the crew installed new wide-field-channel electronics and a power supply in ACS. The fourth replaced the failed low-voltage power-supply board inside STIS’s main electronics box. One bolt on an obstructing handrail could not be removed. After repeated attempts, Massimino broke the retaining bolt and moved the handrail, allowing the repair to continue.

Functional tests after the repairs restored STIS and the ACS wide-field channel; the ACS high-resolution channel was not recovered. The annual technical report also records that replacement control electronics reduced the ACS wide-field CCD read noise from approximately five electrons to four.

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The robotic arm released Hubble at 12:58 UTC on May 19. Atlantis then moved away and completed preparations for return. Poor weather in Florida diverted the landing to Edwards Air Force Base, California. The main landing gear touched down on Runway 22 at 15:39 UTC on May 24, after a flight of approximately 12 days, 21 hours and 37 minutes.

After servicing, Hubble underwent roughly four months of orbital verification, including focusing, alignment, calibration and performance tests of new and repaired instruments. The first observing results were announced on September 9. The COS team’s 2010 technical paper reported ultraviolet coverage extending to approximately 900–3,200 angstroms and a peak effective area approaching 3,000 square centimeters. Broadening of the actual line profile gave some far-ultraviolet modes a full-width-at-half-maximum resolving power of approximately 16,000–21,000. Installation in flight, subsequent instrument acceptance and long-term astronomical observation formed successive, distinct stages.

References: [1] [3] [4]