The Nineties in America
Hubble Space Telescope
Identification: An orbiting astronomical telescope
Manufacturer: The National Aeronautics and Space Administration and the European Space Agency
Date: Launched April 24, 1990, from the Kennedy Space Center in Cape Canaveral, Florida
The first large telescope to take advantage of the clear and undisturbed environment in outer space, the Hubble Space Telescope revolutionized astronomy. After it was repaired in 1993, the telescope produced images of unprecedented clarity.
The Hubble Space Telescope (HST) consists of a single large tubular enclosure, 13.2 meters (about 43.5 feet) long and 4.2 meters (about 14 feet) wide, and weighs about 12 tons. Inside it is the primary mirror, 2.4 meters (about 7.8 feet) in diameter, and other optics, together with several instruments for detecting and analyzing the images formed by the optics. Initially, there were two cameras with charge-coupled devices (CCD) detectors and two spectrographs for both high-resolution and faint-object spectroscopy. The optical design is what is called a Ritchie-Chretien Cassegrain, which involves a series of curved mirrors: the large primary mirror, which brings the light to a focus; a smaller secondary mirror, which bounces the light back toward the primary, where it passes through a central hole; and a set of 45-degree mirrors that can reflect the image to a choice of cameras and spectrographs.
A thin aluminum shell covers the entire telescope to protect it from solar radiation, and many layers of insulation help to keep temperatures low, as the instruments must be very cold to operate most efficiently. Inside there are four heavy flywheels that are used to orient the telescope toward the place in the sky that is to be observed. The HST is remarkably accurate at pointing at celestial targets: It can hold on a star or galaxy for a few thousandths of an arc second.
The telescope is powered by two 8-foot-long solar panels, which are mounted to the sides of the telescope and rotate to face the Sun for maximum power. Batteries provide backup power during the times when Earth eclipses the Sun. Since the telescope's launch in 1990, the panels have been replaced twice by newer models, which can generate about 5,700 watts of electrical power.
The HST remains in a low orbit, about 610 kilometers (380 miles) above Earth, so that it can be serviced by astronauts, but the result is that the planet blocks about half of the sky during the 180-minute orbit. Therefore, exposures are limited to less than half that time, and targets are usually visited many times. Very long exposures can be built up in this way to allow Hubble scientists to detect extremely faint objects, a hundred times fainter than those objects detectable from ground-based telescopes.
The telescope was designed to be upgraded as needed, and provisions were made for the easy removal and exchange of various instruments by astronauts visiting the space telescope. This feature resulted in keeping the telescope up-to-date with the most recent technological advances throughout the 1990's and in the early twenty-first century. There were three such shuttle missions in the 1990's.
Disaster, Recovery, and Triumph
Shortly after the launch of the Hubble Space Telescope, the worldwide astronomy community, which had waited forty years to have access to the wonders expected to be revealed by the HST, was dismayed to learn that a colossal error had been made by one of the National Aeronautics and Space Administration (NASA) contractors who produced the primary mirror. Instead of sharp images, stars appeared fuzzy and indistinct. The mirror suffered from a defect called spherical aberration: It had the wrong shape.
NASA and the European Space Agency (ESA) immediately appointed a panel of astronomers, engineers, and technicians to design a solution to the problem. It took three years to produce a complicated instrument, the Corrective Optics Space Telescope Axial Replacement (COSTAR), and to have astronauts install it in the HST's interior. This occurred in December, 1993, and the COSTAR worked perfectly. The telescope produced images that were basically as good as the original specifications.
Throughout the rest of the decade, the HST made an astounding number of dramatic discoveries in virtually all fields of astronomy, ranging from the planets and comets of the solar system to remote galaxies. An especially spectacular achievement occurred in December, 1995, when the telescope was pointed to a particular small area of sky over a period of ten days, resulting in 342 exposures. Called the Hubble Deep Field, this penetration into the universe recorded galaxies 10 to 12 billion light-years away, during the universe's infancy. The HST showed a different universe, one made up of fragments of galaxies that had not yet coalesced to form giant spiral galaxies like the Milky Way.
Cosmology was advanced through the 1990's by these and similar HST discoveries, including the demonstration that the quasars are actually galaxies undergoing collisions that have led to the formation of black holes in their centers. Black holes in the nuclei of nearby galaxies were also discovered using HST velocity measurements, showing that black holes are the explanation for a variety of puzzlingly active galaxies, known but not understood for decades.
The Hubble Space Telescope has had an important impact on the world's understanding of the universe. The heyday of its discoveries occurred in the years 1993-1999, when it revolutionized concepts of cosmology and dramatically expanded knowledge of the physics of stars, as well as the solar system and other planetary systems.
Christensen, Lars Lindberg, and Bob Fosbury. Hubble: Fifteen Years of Discovery. New York: Springer, 2006. A richly illustrated look at space through the HST.
Petersen, Carolyn Collins, and John C. Brandt. Hubble Vision: Further Adventures with the Hubble Space Telescope. 2d ed. New York: Cambridge University Press, 1998. Offers a comprehensive discussion of the astronomical discoveries made possible by the HST. Includes attractive illustrations, glossary, bibliography, and index.
Smith, Robert W. The Space Telescope: A Study of NASA, Science, Technology, and Politics. New York: Cambridge University Press, 1993. Provides a detailed chronological account of the construction of the HST from its inception to launch preparation.
Voit, Mark. Hubble Space Telescope: New Views of the Universe. New York: Harry N. Abrams, 2000. A clearly written book on the HST. Concise, but not comprehensive.
Paul HodgeSee Also
Astronomy; Hale-Bopp comet; Inventions; Mars exploration; Science and technology; Shoemaker-Levy comet; Space exploration; Space shuttle program.
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