The Hubble Telescope is named after the American astronomer Edwin P. Hubble.
Hubble is the first general-purpose orbiting observatory . Launched on 24th April, 1990,
Aboard the Space Shuttle Discovery The HST makes observations in the visible, infrared, and ultraviolet regions of the electromagnetic spectrum (see Electromagnetic Radiation). The primary mirror of the HST has a diameter of 94.5 in (2.4 m), and the optics of the telescope are designed so that when making a visible-light observation, the telescope can theoretically resolve astronomical objects that are an angular distance of 0.05 arcsecond apart. For comparison, traditional large ground-based telescopes under very nice sky conditions have an image resolution of about 0.5 arcsecond.
After the HST was placed in orbit, scientists discovered that its primary mirror had a systematic aberration, the result of a manufacturing error. A service mission to repair the problem was carried out in December 1993, using the Space Shuttle Endeavour. A device called the Corrective Optics Space Telescope Axial Replacement (COSTAR) was inserted in place of one of the original instruments, the High-Speed Photometer. The original Wide-Field Planetary Camera, which had a different optical path from the other four instruments, was replaced with the Wide-Field Planetary Camera 2 (WFPC 2), which has a built-in correction for the aberration in the primary mirror. This servicing mission gave HST the ability to conduct the research for which it was intended, including measuring the rate at which the universe is expanding (a figure known as the Hubble constant) from which the age of the universe can be calculated.
A second servicing mission took place in February 1997, when astronauts installed the Near Infrared Camera and Multi-Object Spectrometer (NICMOS) and the Space Telescope Imaging Spectrograph (STIS). NICMOS was used to observe regions of space where stars are born and to study extremely distant objects whose light has been red shifted into the infrared, while STIS took spectra of objects including gas swirling around black holes at the centres of galaxies. NICMOS worked for two years before running out of the nitrogen-ice coolant needed to keep it at sub-zero temperatures. A third servicing mission, in December 1999, replaced HST's ageing gyroscopes and computer. On the fourth servicing mission, in March 2002, astronauts replaced HST's solar panels with smaller yet more efficient ones, providing 20 per cent more electricity so that all HST's instruments can operate at the same time. They also installed the Advanced Camera for Surveys (ACS), which covers twice the area of sky as the WFPC 2 with five times the sensitivity. Among its tasks will be to monitor weather on planets in our own solar system, to search for planets around other stars (see Extrasolar Planets), and to survey the distribution of galaxies in the distant universe. The ACS replaced the Faint Object Camera, the last of HST's original instruments. During this same mission, the astronauts also installed a new radiator for NICMOS, restoring its infrared observational capability.
Among the many achievements of its first decade of operation, the HST provided the best views of the planet Jupiter when fragments of Comet Shoemaker-Levy 9 bombarded it in July 1994. The HST's images of the effects produced by the collisions provided scientists with important data for a spectral analysis of the chemical makeup of Jupiter's atmosphere. In December 1995 the HST took one of its most important images, a composite of exposures made over 10 days and known as the Hubble Deep Field. By pointing the telescope at an area of sky devoid of bright objects for up to 40 minutes at a time, the astronomers were able to detect galaxies fainter (down to magnitude 30) and more distant (up to 12 billion light years away) than any seen before. In October 1998 the telescope was used to take a 36-hour infrared exposure of a small portion of the Deep Field, revealing even fainter, cooler, and more distant galaxies. The HST has also provided evidence for the presence of supermassive black holes at the centres of many galaxies.
A 5th and final HST servicing mission was scheduled for 2006, but this was cancelled in January 2004. The mission would have involved astronauts fitting an entirely new instrument, the Cosmic Origins Spectrograph, which would have taken spectra of hot gas such as in the centres of quasars, plus an improved Wide Field Camera. This final refurbishment would have given HST greater discovery capabilities than ever before. It is now hoped that HST will continue in operation until 2010, when it will be superseded by a much larger telescope, the James Webb Space Telescope.