HUBBLESPACETELESCOPE

HUBBLE SPACE TELESCOPE

(HST), space-based observatory named for the American astronomer Edwin Powell Hubble. The spacecraft is a cooperative program of the National Aeronautics and Space Administration (NASA) and the European Space Agency. The heart of the HST is a 94-in. (2.4-m) reflecting telescope capable of making observations in the visible, near-ultraviolet, and near-infrared portions of the spectrum. Onboard scientific instruments include the wide field and planetary camera, intended to provide digital imaging over a wide field of view; the faint object camera, designed to provide high-resolution images of small fields; a near-infrared camera and multi-object spectrometer; and a high resolution imaging spectrograph.

Roughly cylindrical in shape, the body of the HST is 13.1 m (43 ft) long and 4.3 m (14 ft) in diameter at its widest point. Flanking the cylinder are two replaceable solar panels which, supplemented by nickel-hydrogen batteries, provide electrical power to the spacecraft. Commands to the HST originate from the Space Telescope Operations Control Center of NASA's Goddard Space Flight Center in Greenbelt, Md., and are transmitted to the spacecraft via the Tracking and Data Relay Satellite (TDRS) system. Data downloaded from the spacecraft follow the opposite path and are then transmitted from the control center to the Space Telescope Science Institute at Johns Hopkins University in Baltimore, Md.

The idea for an orbiting observatory originated in the realization that no ground telescope, no matter how large, could overcome the effects of atmospheric distortion. In addition, astronomers recognized that a space-based telescope could observe infrared and ultraviolet emissions that cannot penetrate the earth's atmosphere. Developed and built in the late 1970s and the 80's at a cost of more than $1.5 billion, the Hubble Space Telescope was deployed by the crew of the space shuttle Discovery in April 1990. Although the first images transmitted from the HST were superior to those available from any ground-based telescope, their resolution was not as fine as had been expected; investigators subsequently found flaws in the manufacture and testing of the primary mirror. To compensate for the mirror's spherical aberration, a redesigned wide field and planetary camera and a package of corrective mirrors (COSTAR) were installed on the HST during a servicing mission by the space shuttle Endeavour in December 1993. By 1996 the orbiting observatory had taken and transmitted more than 100,000 exposures. These images offered unprecedented evidence for the existence of black holes and quasars, and revealed primeval galaxies 4 billion times fainter than those that can be seen with the naked eye.

During an 8-day repair mission by the space shuttle Discovery in December 1999, astronauts replaced all six gyroscopes, which had caused the telescope to stop working a month earlier. They also fitted the telescope with voltage regulators to prevent batteries from overheating and installed two steel panels to shield it from damage from solar rays. The equipment included a new radio transmitter, guidance unit, and data recorder; and a more powerful computer, 20 times faster than the original one.