Splitting one repair mission into two will cost NASA an extra $125 million or so, Weiler says. But he's quick to point out it's money well spent.
"The scientific community is enamored with Hubble," Weiler says. "I mean, we have enormous rejection ratios. That is, four or five proposals out of every six are rejected. So it's greatly oversubscribed. Any loss in scientific productivity, you're not earning."
Among Hubble's more recent discoveries: a galaxy 13 billion light-years away that's the most distant object ever detected, and dust rings around two remote stars that may have been gravitationally sculpted by planets.
NASA hopes to keep Hubble working until 2010. The last repair mission is slated for 2003.
"Hubble has a limited lifetime. I mean, it's not going to be up there forever," Brown says. "So every day, every month, that it's not operating is a day of lost science that we could have."
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A brief look at the Hubble Space Telescope's past and future:
April 1990: Hubble launched into orbit aboard space shuttle Discovery.
December 1993: Astronauts conduct five spacewalks to correct Hubble's blurred vision and make other repairs.
February 1997: Astronauts conduct five spacewalks to add or replace 11 major Hubble parts, including two new science instruments.
October 1999: Astronauts to conduct three or four spacewalks to replace all six gyroscopes, main computer, radio transmitter, guidance sensor and data recorder, and patch peeling insulation.
Early 2001: Spacewalking astronauts to install new solar panels, advanced camera and cooling unit for idle infrared camera, and finish patching insulation.
2003: Spacewalking astronauts to install new camera and new spectrograph to enhance imaging, and replace all worn-out parts.
2010: Hubble to return to Earth aboard space shuttle.