For 16 years, an orbiting telescope the size of a school bus has given humanity breathtaking views into the universe and deep new insights into its structure and evolution.
But the Hubble Space Telescope is showing undeniable signs of wear. If left untended, the problems could slow Hubble's torrent of discoveries to a trickle. Scientists estimate they would have to close its "eye" for good by 2009 or 2010.
Tuesday, NASA Administrator Michael Griffin directed the agency to book a final repair trip to Hubble, tentatively set for 2008. The decision ends two years of angst over the future of the telescope – by many accounts the US space program's most productive ambassador.
The planned repairs and instrument upgrades are akin to putting a 2005 Saab engine into a used, if still serviceable, 1990 Toyota. The repairs will keep Hubble humming for at least five years after the shuttle visits it, NASA scientists estimate. And the new instruments astronauts will install will dramatically improve the science Hubble can perform.
"Hubble will be at the peak of its powers," says a relieved Malcolm Niendner, deputy senior project scientist for the Hubble program at NASA's Goddard Space Flight Center in Greenbelt, Md.
At a meeting with Goddard employees Tuesday, Dr. Griffin explained that with three shuttle flights behind them since the loss of Columbia in 2003, astronauts had cleared a roadblock to a Hubble mission. They showed that they can repair the shuttle's heat-shielding tiles on orbit in ways that would fix the most likely types of damage and survive a fiery reentry. In addition, the two-week Hubble mission has been designed in a way that would enable the crew to squeeze in all that needs to be done: mandatory in-flight shuttle inspections, four or five spacewalks to make repairs, and time for any contingency spacewalks. NASA will have a second shuttle on an adjacent launch pad to mount a rescue mission, if one is required.
Planning for the Hubble mission was well under way when Columbia was lost – and Sean O'Keefe, NASA's head at the time, canceled the repair mission a year later out of concern that it was too risky.
Many astronomers and key members of Congress challenged Mr. O'Keefe's cancellation. Space-exploration advocacy groups mounted petition drives to save Hubble. Under pressure, O'Keefe turned to the National Research Council for advice. It replied: Scrap any thoughts of a robotic repair mission and plan a shuttle visit.
During the mission, astronauts will swap out Hubble's batteries, which have been slowly losing their ability to hold a full charge from the observatory's solar panels. They will replace elements of the telescope's precision pointing system. They will replace a camera and a spectrograph with better versions. The upgrades are expected to open a window on a period in the universe's early history between 700 million and 1 billion years after the big bang, taking Hubble to the limits of its optical abilities.
Some astronomers hold that NASA's money could be put to more productive use building unique space telescopes rather than operating a rejuvenated Hubble for three or four extra years.
"Hubble has done a great job and earned its place in history. But astronomers made a serious mistake in not undertaking a cold cost-benefit analysis" for a repair mission, says Shri Kulkarni, an astronomer at the California Institute of Technology in Pasadena. Hubble's operating costs run about $350 million a year, he adds – money that could have gone to projects postponed indefinitely after President Bush called on NASA to end the shuttle program by 2010 and return humans to the moon on a new set of rockets by 2020.