All in a Day’s Work

he Hubble Space Telescope is as large as a school bus and looks like a five-story tower of stacked silver canisters. Each canister houses important telescope equipment: the focusing mirrors, computers, imaging instruments, and pointing and control mechanisms. Extending from the telescope are solar panels for generating electricity and antennas for communicating with operators on the ground.

The 12-ton telescope collects faint starlight with an 8-foot-diameter mirror. The mirror - tucked inside a long, hollow tube that blocks the glare from the sun, Earth, and moon - is slightly curved to focus and magnify light.

Unlike ground-based telescopes, astronomers cannot look through Hubble’s lens to see the universe. Instead, Hubble’s scientific instruments are the astronomers’ electronic eyes. The telescope’s instruments include cameras and spectrographs. The cameras don’t use photographic film, but rather electronic detectors similar to those used in home video cameras. The spectrographs collect data by separating starlight into its rainbow of colors, just as a prism does to sunlight. By closely studying the colors of light from a star, astronomers can decode the star’s temperature, motion, composition, and age.

Hubble must maintain a steady position to take long exposures— sometimes hours— of the same subject to produce images of distant or faint objects. Otherwise the images will be blurred. To accomplish this mission, the telescope must battle such celestial elements as air drag, the sun’s radiation, and the gravitational pull of objects.

For Hubble, maintaining proper direction is similar to a sailor fighting the wind and water to keep his sailboat on course. Hubble is successful because of its sophisticated pointing control system, which includes gyroscopes and Fine Guidance Sensors. Once the telescope locks onto an object, its sensors check for movement 40 times a second. If movement occurs, the wheels, which are constantly rotating, change speeds to smoothly move the telescope back into position.

Once Hubble gathers pictures and data on celestial objects, its computers turn the information into long strings of numbers that are beamed to Earth as radio signals. This information streams through a series of satellite relays to the Goddard Space Flight Center and then by telephone line to the Space Telescope Science Institute, where the numbers are turned back into pictures and data.

The information collected daily by Hubble is stored on optical computer disks. A single day’s worth of observations would fill an encyclopedia. The constantly growing collection of Hubble pictures and data are a unique scientific resource for current and future astronomers.

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