BioEd Online

NASA administrator Michael Griffin announced today that the agency will mount a manned mission to extend the life of the Hubble Space Telescope.

"We are going to add a shuttle servicing mission to the Hubble Space Telescope," Griffin told employees at the Goddard Space Flight Center in Greenbelt, Maryland, which carries out daily operations of the Hubble.

The mission, scheduled for May 2008, should see the space shuttle Discovery take a team of astronauts to the orbiting space telescope. Once there, the crew will boost the satellite into a higher orbit, replace its ageing batteries and gyroscopes, and install some new instruments.

Taken together, the repairs should leave the telescope in fine form until its replacement, the James Webb Space Telescope, can be launched in 2013.

Ups and downs

The decision is the latest turn of fortune for Hubble, which, in recent years, has seen its repair plan approved, replaced, cancelled and reconsidered. The mission, the fifth to the telescope, was originally scheduled for 2006, but was cancelled in the wake of the 2003 Columbia disaster.

Then NASA administrator Sean O'Keefe proposed a robotic mission, but a study by the National Academies, an independent US scientific advisory group, determined that robotic technology was not yet advanced enough to be used for such a complex task. O'Keefe cancelled the mission in 2004, but in 2005 Griffin vowed to revisit the idea of a shuttle flight after the Discovery's successful return to orbit.

In the meantime, the health of Hubble has steadily declined. Two of the telescope's six gyroscopes, which keep it oriented in space, have failed, and one of its cameras recently went offline temporarily, for an unknown reason. Planners say that the telescope is unlikely to last much beyond 2010 without repairs.

The mission once again seems feasible, Griffin told the staff at Goddard. "I'm fully confident that this fifth mission will go as flawlessly as any of us can imagine." Over the course of 11 days, the crew will install two new scientific instruments: a camera that will give Hubble a wide-angle, high-resolution view of the sky, and an ultraviolet spectrograph that will study objects only visible from space.

They will also install a fine guidance sensor to improve Hubble's pointing system and replace the satellite's six gyroscopes and batteries. Finally, the team will replace insulation that has degraded in space with a new thermal protection blanket. The work is expected to take a total of five spacewalks.

Hubble lovers

Many astronomers applauded the decision to service the Hubble, noting its long and distinguished history. Since its launch in 1990, the Hubble has led to more than 3,500 scientific publications, including several major discoveries.

In 1995, for example, a 'deep field' image uncovered more than a thousand distant, early galaxies. And in 1998, the telescope aided in the discovery of a mysterious force known as 'dark energy', which cosmologists think is pushing the Universe apart, says Adam Riess, an astronomer at the Space Telescope Science Institute in Baltimore, Maryland. "It has literally rewritten the textbooks," he says.

But it comes at a cost. The total price tag for the instruments and flight is some US$900 million, according to NASA spokesperson Allard Beutel. Beutel notes, however, that this cost includes the new instruments, which have already been built.

The mission is probably worth the risk, adds Louis Lanzerotti, a space scientist at the New Jersey Institute of Technology, Newark, who oversaw the academies report on Hubble. "There was a general belief among the committee members that the scientific return warranted servicing," he says, adding that the risk factor is not "substantially different" from that of travelling to the International Space Station, where the rest of the shuttle's missions will take it.

Safety first

NASA will have to be careful as it plans its return to the telescope, according to Keith Cowing, who runs nasawatch.com, an independent website that follows the agency.

If the shuttle were damaged on assent by falling foam or other debris, then mission planners would have a maximum of three weeks to get a second shuttle into orbit a relatively short period of time. The crew would then have to conduct short spacewalks to transfer between shuttles.

It's the sort of mission that the agency would never have bothered planning before the 2003 accident, but in the wake of the disaster, Cowing says, such contingency work has become almost routine: "NASA has come a great distance in accepting the real risk of what they are doing," he says.

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