With a 2.4-meter (7.9 ft) mirror, Hubble's four main instruments observe in the near ultraviolet, visible, and near infrared spectra. Hubble's orbit outside the distortion of Earth's atmosphere allows it to take extremely high-resolution images, with substantially lower background light than ground-based telescopes. Hubble has recorded some of the most detailed visible light images ever, allowing a deep view into space and time. Many Hubble observations have led to breakthroughs in astrophysics, such as accurately determining the rate of expansion of the universe.
The HST was built by the
Space telescopes were proposed as early as 1923. Hubble was funded in the 1970s, with a proposed launch in 1983, but the project was beset by technical delays, budget problems, and the Challenger disaster (1986). When finally launched in 1990, Hubble's main mirror was found to have been ground incorrectly, compromising the telescope's capabilities. The optics were corrected to their intended quality by a servicing mission in 1993.
Hubble is the only telescope designed to be serviced in space by astronauts. After launch by Space Shuttle Discovery in 1990, five subsequent Space Shuttle missions repaired, upgraded, and replaced systems on the telescope, including all five of the main instruments. The fifth mission was initially canceled on safety grounds following the
Hubble accommodates five science instruments at a given time, plus the Fine Guidance Sensors, which are mainly used for aiming the telescope but are occasionally used for science (astrometry). Early instruments were replaced with more advanced ones during the Shuttle servicing missions. COSTAR was strictly a corrective optics device rather than a true science instrument, but occupied one of the five instrument bays.
Since the final servicing mission in 2009, the four active instruments have been ACS,
- Advanced Camera for Surveys (ACS; 2002-present)
- Cosmic Origins Spectrograph (COS; 2009-present)
- Corrective Optics Space Telescope Axial Replacement (COSTAR; 1993-2009)
- Faint Object Camera (FOC; 1990-2002)
- Faint Object Spectrograph (FOS; 1990-1997)
- Fine Guidance Sensor (FGS; 1990-present)
- Goddard High Resolution Spectrograph (GHRS/HRS; 1990-1997)
- High Speed Photometer (HSP; 1990-1993)
- Near Infrared Camera and Multi-Object Spectrometer (NICMOS; 1997-present, hibernating since 2008)
- Space Telescope Imaging Spectrograph (STIS; 1997-present (non-operative 2004-2009)
- Wide Field and Planetary Camera (WFPC; 1990-1993)
- Wide Field and Planetary Camera 2 (WFPC2; 1993-2009)
- Wide Field Camera 3 (WFC3; 2009-present)