Can you imagine shutting down the Hubble Space Telescope even if it were still working perfectly? Six months ago NASA was thinking of doing just that in 2010. Such a move would save up to $200 million dollars a year, enabling the cash-strapped agency to keep Hubble's successor, the James Webb Space Telescope, on track for a planned launch in 2011. NASA has since stopped threatening to turn off the world's most famous telescope, but Hubble is far from out of danger of coming to a premature end.
Anne Kinney, director of NASA's Astronomy and Physics Division, tells Sky & Telescope that her office is following the recommendations of an advisory panel, which suggested that NASA keep Hubble alive as long as it continues to produce cutting-edge science. Ideally this will involve at least one more visit by Space Shuttle astronauts to replace worn-out parts — especially the gyroscopes used to aim the observatory — and to install new, more powerful scientific instruments.
The servicing mission originally planned for 2004 has slipped to mid-2006 at the earliest. This in itself is not a problem. "Four years after the last gyro replacement, we still have four out of six operating gyros," says Kinney, "and we need only three to point the telescope." What is a problem is that NASA, still reeling from last February's Columbia disaster, may yet decide that it's too risky to send astronauts anywhere but to the International Space Station, where they can find a haven if something goes wrong with the shuttle.
Whether or not astronauts visit Hubble again, and however long the observatory lasts, NASA has already determined that the massive telescope cannot be brought back to Earth safely in the shuttle's cargo bay, as once envisioned. Left alone, Hubble — which has no onboard propulsion system — will lose altitude and burn up in the atmosphere sometime after 2013, possibly endangering people and property on the ground. NASA has therefore begun a $300 million effort to develop a robot that will lift off on an expendable rocket, grapple Hubble, and use its own retrorocket to steer the observatory to a fiery reentry over an unpopulated area. "We call it 'the Claw,'" says Kinney, after the mechanical hand of a character in the 1973 James Bond movie Live and Let Die.
Space Shuttles will start flying again no sooner than September 2004. By then we should know if Hubble will get a new lease on life in 2006. If it does, the upgrade will include a new camera and spectrograph, six redesigned and longer-lasting gyros, and a boost to a higher orbit. The telescope should then be able to operate well past 2010, even with no further servicing. That would certainly make astronomers happy. They'd like to have Hubble and Webb in orbit at the same time, at least for a few years, because the former works mainly at visible and ultraviolet wavelengths, while the latter is an infrared telescope. Operating in tandem would maximize their combined scientific return. "I'm really optimistic," says Kinney. "Time is on our side."