— An astronaut removes the High Resolution Spectrograph to make way for the Space Telescope Imaging Spectrograph during the second servicing mission in 1997. The telescope can hold four telephone-booth sized instruments and four piano-sized instruments (Image: NASA)
NASA's most famous observatory, the Hubble Space Telescope, will get a much anticipated life extension after all. NASA Administrator Michael Griffin announced on Tuesday that a space shuttle will be sent to upgrade Hubble and add a few years to the lifetime of the venerable queen of the sky.
"We are going to add a shuttle servicing mission to the Hubble Space Telescope to the shuttle's manifest to be flown before it retires [in 2010]," Griffin said to applause at NASA's Goddard Space Flight Center in Greenbelt, Maryland, US.
The move, though not unexpected, still had astronomers on the edge of their seats. The telescope is enormously popular and has brought back a wealth of data since its launch aboard a space shuttle in 1990.
A fifth shuttle mission to service the Hubble telescope was cancelled by former NASA chief Sean O'Keefe in 2004, following the Columbia accident (see Hubble condemned to slow death). Robotic missions to fix the telescope were considered but dropped because of the time and difficulty involved in mounting them.
Then Griffin replaced O'Keefe and said NASA would study whether it could reduce the risk of sending astronauts back to Hubble if anything went wrong there, the astronauts could not take refuge aboard the International Space Station.
The Hubble mission will be the only shuttle flight to a destination other than the International Space Station. As many as 16 shuttle flights will be sent to service and complete construction of the ISS by 2010, when the shuttles are retired.
On those missions, if in-flight inspections of an orbiter's heat shield reveal significant damage, the problem that felled Columbia, the crew could wait on the ISS for another shuttle to come and pick them up at the station. The station usually has about 70 to 80 days' worth of supplies for a large crew.
If the same situation occurred during a Hubble mission, the astronauts could not take refuge on the ISS, because the telescope and the station are in very different orbits. They would have only two to four weeks' worth of supplies in the cramped shuttle quarters, depending on how supplies were rationed.
Sending a rescue flight would also require a lot of work on the ground. Because of the need to save the stranded crew, NASA would have to start the launch countdown for the rescue flight even before the launch of the initial vehicle, according to NASA's own return-to-flight implementation plan. Also, there would not be time for significant design changes between flights, so the rescue shuttle could run the same risk of being damaged as the Hubble flight.
A rescue flight would rendezvous in the vicinity of the damaged shuttle, and a tether would connect the two vehicles. Astronauts would make spacewalks to move to the new shuttle.
Since the Columbia disaster, the heat shields of shuttles are inspected in-orbit using the crafts robotic arm.
If inspections revealed something amiss with the heat shield, before automatically mounting a rescue flight, the astronauts could make a spacewalk to examine and possibly repair the damaged site. The past three shuttle flights have tested these new repair methods, which include putties, patches and paint-like material to patch holes or cracks in the thermal protection system.
During Discovery's flight in July 2006, astronauts also tested the stability of working on the end of an extra-long robotic arm. It wobbled slightly, but not as much as they had expected, giving hope for a stable work platform should a repair be needed under the shuttle (see Shuttle's robot arm performs well during spacewalk).
One of the challenges for NASA will be cramming another shuttle flight into an already tight launch schedule. The shuttles will be retired in 2010. With a servicing mission, that would give NASA a total of at least 15 shuttle missions with the possibility of two extra ISS supply missions before they are forever grounded. The next shuttle, Discovery, is scheduled to begin its construction mission to the ISS in December 2006.
Batteries and gyroscopes
The servicing mission, if successful, could keep Hubble operational until at least 2013. Without a shuttle flight, Hubble's instruments would have eventually started to shut down. The gyroscopes that point Hubble and keep it steady could last until 2008 and the batteries until 2010.
The servicing mission will add six new batteries, six gyroscopes, a flight guidance sensor, the Cosmic Origins Spectrograph and the Wide Field Camera 3. They will be by far the best instruments ever sent to Hubble (see New Hubble instruments would illuminate early universe).
Astronauts might also try to fix the Space Telescope Imaging Spectrograph by replacing an electronics board. Astronauts will attach handles on the back end of Hubble to make it easier to grab later, in preparation for its de-orbit, probably after 2020.
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