Will it be possible to service the James Webb Space Telescope?
Researchers credit servicing missions involving astronauts with rescuing the Hubble Space Telescope and keeping it alive for the past 17 years. But an idea to create a similar, if simpler, capability for Hubble's successor is raising eyebrows among project scientists, who fear it will be impractical and expensive.
The James Webb Space Telescope (JWST), currently scheduled for launch in 2013, will make infrared observations from a position in space 1.5 million kilometres from Earth. That puts it farther away than Hubble, which sits in low-Earth orbit just 600 kilometres away, within easy reach of the shuttle. So the JWST was designed assuming that it would fly without any servicing — by astronaut or robot — for its five-to-ten-year career.
But Edward Weiler, head of NASA's Goddard Space Flight Center in Greenbelt, Maryland, which manages the JWST, has indicated that there may be scope for a manned mission to service or make simple repairs to the telescope.
“It might be valuable if astronauts could fly to the JWST to do something that was a critical, but easy fix,” says Weiler, “like opening a stuck antenna.” Weiler, who used to be NASA's science chief, floated the idea of attaching a docking port to the telescope to allow a future mission to hook up.
“Wouldn't it make sense to ensure that astronauts could go to the telescope if they could fix it?”
But the concept got a chilly reception last week at the American Astronomical Society's biannual meeting in Honolulu, Hawaii. When the JWST was being developed, it seemed impossible that it would ever receive guests — it will be well beyond the reach of the shuttle. Only the decision to develop the Orion crew exploration vehicle, due to replace the shuttle after its retirement in 2010 and take astronauts back to the Moon, puts the telescope within reach. “If Orion is available, and we have a really simple, but significant problem on the JWST, wouldn't it make sense to ensure that astronauts could go to the JWST if they could fix it?” asks Weiler.
But the harsh radiation environment in deep space would probably make it far too dangerous for astronauts, says John Mather, the JWST's chief project scientist at Goddard. And a robot mission could probably do very little. It might be able to give the satellite a good shake to loosen a stuck solar panel, says Mather, but would be unlikely to cope with more complex tasks. And in its repair efforts, it might dirty the telescope's outer mirrors.
Mather says the JWST's team is now conducting a feasibility study to find out whether a docking port could be added. But given that it is unlikely that a problem so simple it could be fixed by a robot will surface during the mission, Mather says he is not keen to add something to the already grossly over-budget telescope. “If it costs more than a few thousand dollars,” he says, “I'm not interested.”
Repair missions to spacecraft closer to Earth than the JWST have so far been rare, but not unheard of. An orbiting mission to study the Sun was rescued by a service mission carried out by astronauts on the space shuttle Challenger in 1984. The first servicing mission to Hubble in 1993 fixed a critical error, installing a corrective optics system to fix the telescope's blurry vision. It has since been serviced a further three times.
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