Thanks to advances in solid-state detectors, the new camera will be "almost an order of magnitude more sensitive" than its predecessor, WFC2, says Jeffrey Hoffman, a professor of astronautics at MIT and a former astronaut who helped install the WFC2 during a Hubble servicing mission in 1993. By increasing the telescope's ability to detect faint objects, Hoffman says, the new camera will open up "a huge unexplored discovery space," with a potential for new discoveries that can't be predicted.

The new repair mission will also include an attempt to fix the Space Telescope Imaging Spectrograph (STIS), one of the instruments delivered during an earlier Hubble servicing mission in 1997. STIS worked successfully until 2004, when it suffered a power failure. Before it failed, though, this instrument made a major breakthrough, providing direct evidence for the first time of supermassive black holes in the center of some galaxies. Astronomers had long believed such black holes existed, but having the proof helped confirm the theoretical predictions.

Astronauts will attempt to repair the instrument during an upcoming mission, which is tentatively scheduled for the spring of 2008. Pursuing the work on black holes, including learning more about how they formed and how they interact when galaxies collide, will be among the instrument's high priorities if the challenging repairs succeed. Unlike replacing entire instruments, which was a capability designed into Hubble from the start, repairing the failed power supply is a much trickier operation that involves getting into the guts of the instrument to swap out components. Hoffman points out that this requires removing 120 bolts that could potentially float around and damage other parts of the telescope.

To prevent this, NASA has developed "a very clever scheme" with a Plexiglas container that will capture all the loose bolts as they are removed, Hoffman says. "If everything goes right, they'll make it look easy."

Wheeler says that one important outcome of keeping the Hubble telescope working longer is that it is now expected to survive long enough to overlap with the next-generation telescope that will ultimately take its place: the James Webb Space Telescope, which is to be launched in 2013. While the Webb telescope will be much larger than Hubble, with a 6.5-meter-diameter main mirror compared with Hubble's 1.8 meters, Webb will not replace all of Hubble's function. Webb is designed primarily for infrared observing, while Hubble is also effective for visible and ultraviolet light.

Having both telescopes functional at the same time, which is not assured but is now likely, is "terribly important," Wheeler says. "It gives you a multispectral capability" for coordinated observations, and thus "you get a lot more information" about a given object.

Until then, the repaired Hubble will continue carrying out a variety of projects that can't be done with any other instrument. "You can't do the science" without Hubble, Wheeler says.