Replacing a circuit breaker in a dark basement is one thing. But what if you had to climb around the outside of a spacecraft orbiting hundreds of miles above the Earth to do it? This kind of dangerous maintenance work has become fairly common for astronauts aboard the International Space Station, where they spend as much time fixing the $100-billion-plus orbiting science lab as they do performing actual research.

For a gallery of Hubble's most incredible images, click "View Photos" at left

The terrific thing about NASA chief Michael Griffin's decision to launch a Hubble servicing mission–the telescope's fifth since 1990–isn't simply that the spacecraft will be able to limp along for another four years. After astronauts visit Hubble on this latest mission (set to launch no earlier than May 2008), the telescope will be more powerful than it has ever been, thanks to some incredible new instruments being tested now.