Hubble Servicing Mission 4

The fifth and final Hubble servicing mission, Shuttle mission STS-125, is set to launch from the Kennedy Space Center’s launch pad 39A on 8 October 2008. The 11-day mission will replace two instruments, hopefully fix two more and replace gyros, batteries and other components crucial for the NASA/ESA Hubble Space Telescope’s continued success through the year 2013.

This mission, named Servicing Mission 4, or SM4, since SM3 was split in two missions, almost failed to materialise. In the wake of the Columbia Space Shuttle tragedy in 2003, NASA officials decided that astronauts had to be able to reach a safe haven in case damages to the Shuttle would make a return to Earth too risky. Hubble’s orbit around the Earth makes it impossible for the seven-member crew to take refuge in the International Space Station if the shuttle is, for instance, damaged during launch. After a re-examination of risks, on 31 October 2006, NASA Administrator Michael Griffin decided, however, that Hubble was such an invaluable tool to astronomers and the public alike that undertaking a last servicing mission was acceptable. A second Shuttle will be ready for launch during the SM4 mission in order to minimize risks to the astronauts.

On launch, Atlantis will enter an orbit inclined at 28.5° to the Earth’s equator on a path that will intercept Hubble approximately three days after launch. Following capture, the mission requires 5 spacewalks, performed by two teams of spacewalkers operating on alternate days, to carry out all the necessary work.

New Instruments: WFC3 & COS

The initial plans for the mission consisted of upgrades to Hubble by installing two new scientific instruments: the Cosmic Origins Spectrograph (COS), replacing the obsolete COSTAR package; and the Wide Field Camera 3 (WFC3), replacing the current WFPC2.  Both instruments have advanced technologies that will dramatically improve Hubble’s potential for discovery and enable observation of faint light from the youngest stars and galaxies in the Universe.

COS will primarily study changes in light emitted from faint and distant quasars that has passed through intergalactic gas clouds.  The changes will reveal details on the nature of the gas, its evolution and its influence on surrounding galaxies.

WFC3 allows Hubble to capture large-scale, detailed images from the near infrared to the far ultraviolet.

Fixing Current Instruments: STIS & ACS

Replacing instruments is complicated enough, but there is an additional twist with the need to fix two failed instruments: the Advanced Camera for Surveys (ACS) and the Space Telescope Imaging Spectrograph (STIS).  The attempt to repair both these instruments is unprecedented as neither instrument is designed for repair, or even maintenance in space and engineers have developed new tools and procedures especially for this mission. Discover more about the unique challenges of these fixes on the STIS repair and ACS repair pages.

All the Tasks of SM4

By completing these upgrades, Hubble will perform at a level previously unmatched in its already long, celebrated history.  For the first time, four instruments will work together to provide both wide and narrow field imaging and spectroscopy from the near infrared through to the far ultraviolet.