The $1.5 billion Hubble rocketed to space aboard the space shuttle Discovery on April 24, 1990. It's named after Edwin Hubble, a pioneering American astronomer who furthered our understanding of other galaxies and demonstrated that the universe is continually expanding.

The Hubble's primary mirror, nearly eight feet across. A flaw in the mirror was discovered after the Hubble was in space; thanks to miscalibrated equipment, its glass had been ground slightly too finely at the edges. Though the imperfection measured just one-fiftieth of the thickness of a piece of paper, it distorted the Hubble's images. Astronauts fixed the problem in 1993.

The Hubble orbits at a speed of five miles per second, 353 miles above Earth. At that velocity it can cross the United States in about 10 minutes and circle the globe in an hour and a half.

The Hubble Deep Field, our most detailed view of the universe. The image is composed of 342 different exposures taken over 10 days, and features some 1,500 different galaxies. Other Hubble images have helped scientists better estimate the age of the universe and shed light on a mysterious antigravity force called "dark energy."

Among the mesmerizing images the Hubble has captured are these "elephant trunks," towering columns of interstellar gas photographed in the Serpens constellation, 6,500 light-years from Earth.

The Hubble gets a much clearer view of space than telescopes on the ground. Each week the telescope sends back 120 gigabytes of data. Its findings have formed the basis of more than 6,000 scientific articles.

Atlantis' astronauts will install a new "wide-field planetary camera" during their 11-day maintenance-and-repair mission, the fifth to the telescope. With the 2003 Columbiatragedy in mind, NASA will have the shuttle Endeavour prepared to rescue the Atlantiscrew from space on a week's notice should any mishaps occur.

The Hubble is expected to go out of service some time around 2014, 24 years after its launch. By then a replacement, the James Webb Space Telescope, is scheduled to be in place. The Webb telescope's infrared images will let scientists study regions of the universe more distant than what the Hubble can reach. Once its life is over the Hubble may be retrieved from space, or guided to a final splashdown in the ocean.