Hubble Space Telescope

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Hubble Space Telescope (HST), first general-purpose orbiting observatory. Named after American astronomer Edwin P. Hubble, the Hubble Space Telescope was launched on April 24, 1990. 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 (240 cm), and the optics of the telescope are designed so that, theoretically, when making a visible-light observation, the telescope can resolve astronomical objects that are at an angular distance of 0.05 arcsecond apart. In comparison, traditional large ground-based telescopes, under very good sky conditions, have an image resolution of about 0.5 arcsecond. Originally, the HST was equipped with five detectors: the Wide-Field Planetary Camera, the Faint Object Camera, the Faint Object Spectrograph, the High-Resolution Spectrograph, and the High Speed Photometer (see Spectroscopy). It also has three fine guidance sensors that can be used for precision astronomy measurements such as determining the distances of stars from Earth.

After the HST was launched, scientists discovered that its primary mirror had a systematic aberration, the result of a manufacturing error. A service mission was carried out in December 1993 using the space shuttle Endeavour. A corrective optical device, called the Corrective Optics Space Telescope Axial Replacement (COSTAR), was inserted in the slot for the High Speed Photometer, which had to be removed to make room for COSTAR. The Wide-Field Planetary Camera, which had a different optical path from the other four instruments, was replaced with a second camera, which has a built-in correction for the aberration in the primary mirror. The service mission, which involved numerous intricate procedures, was successful.

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