Saturday, July 22, 2017

The Hubble Space Telescope

The Hubble Space Telescope (HST) is a space telescope that was launched into low Earth orbit in 1990 and remains in operation. Although not the first space telescope, Hubble is one of the largest and most versatile, and is well known as both a vital research tool and a public relations boon for astronomy. The HST is named after the astronomer Edwin Hubble, and is one of NASA's Great Observatories, along with the Compton Gamma Ray Observatory, the Chandra X-ray Observatory, and the Spitzer Space Telescope.

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 United States space agency NASA, with contributions from the European Space Agency. The Space Telescope Science Institute (STScI) selects Hubble's targets and processes the resulting data, while the Goddard Space Flight Center controls the spacecraft.

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 Columbia disaster (2003). However, after spirited public discussion, NASA administrator Mike Griffin approved the fifth servicing mission, completed in 2009. The telescope is operating as of 2017, and could last until 2030–2040. Its scientific successor, the James Webb Space Telescope (JWST), is scheduled for launch in 2018.

List of Hubble Instruments

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, COS, STIS and WFC3. NICMOS is kept in hibernation, but may be revived if WFC3 were to fail in the future.

  • 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)

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