Hubble Space Telescope
The $2 billion Edwin P. Hubble Space Telescope (HST) was lifted into orbit by the space shuttle Discovery on April 24, 1990. Weighing approximately 25,500 lb (11,000 kg) and measuring 43 ft (13 m) long by 14 ft (4 m) wide, or roughly the size of a school bus, HST is the most complex and sensitive space observatory ever constructed, and it has become astronomers' principal tool for exploring the universe.
During its lifetime, the space telescope has required intermittent servicing. In June 1990, just two months after HST was launched into orbit, astronomers discovered that there was a spherical aberration in one of the telescope's mirrors. In 1991, two of the craft's six gyroscopes failed, and a third failed on Nov. 18, 1993, causing additional problems. NASA successfully repaired the space telescope during the Dec. 2-13, 1993, mission of the Endeavour.
Crew members of the space shuttle Discovery made fresh repairs to the telescope during an upgrade mission in Feb. 1997 and installed two powerful new scientific instruments-the Near Infrared Camera and Multi-Object Spectrometer (NICMOS)-giving HST still sharper and more distant views of the universe. The Near Infrared Camera can see the universe at near infrared wavelengths more sensitively that any other existing or planned telescope.
The third servicing mission by the crew of Discovery in Dec. 1999 extended the telescope's scientific power with new instruments and repaired its optics, solar arrays, gyros, and other components. A fourth servicing mission was carried out by astronauts aboard the space shuttle Columbia in March 2002. This time, the upgrades to the Hubble included a new power control unit, a powerful new camera, and solar array panels.
A fifth servicing mission, scheduled for July 2003, was canceled after the Columbia space shuttle disaster. Without servicing, Hubble was expected to be out of commission by 2008, but was granted a reprieve with a final servicing mission in May 2009. The telescope's status is now listed as "extended mission in progress."
After NASA announced that the telescope would not be repaired due to the risks to a human crew, outcry from scientists, politicians, and the public forced the agency to consider sending a robotic repair mission. In July 2004, a panel from the National Academy of Sciences urged NASA to save the Hubble, voicing a preference for a staffed mission. The telescope repair mission has been put on the back burner as NASA is leaning toward President George W. Bush's announced desire to see Americans on the Moon and Mars.
Hubble is slated to be replaced by the next-generation James Webb Space Telescope, scheduled to be launched in 2014. The new observatory will have a primary mirror that is 20 ft in diameter, compared to the Hubble's 8-foot reflector.
For more information on the Hubble Telescope, see NASA's Hubble Project: http://hubble.nasa.gov/ .