The Hubble Space Telescope

[Hubble Space Telescope]The Hubble Space Telescope was launched by NASA in April, 1990. It is the largest astronomical observatory ever built to go into space. Hubble was supposed to be extremely powerful, able to look deep into space (up to 14 billion light years away!).

Because Hubble would look so far into space, scientists hoped that it might be able to see things that could answer questions about the origins of the universe. The distance to stellar phenomena is measured in light years, the amount of time it takes light to travel from there to us. This means that if you look at something 5 light years away, the light of what you're looking at took 5 years to travel to you. So when you look at it now, you're actually seeing what it looked like in the past. The stellar phenomena that Hubble would be studying were so far away that what they would look like to us was what they were like close to the beginning of the universe.

Strangely, soon after its launch, Hubble was not sending back to Earth the types of images that should have come from such a powerful telescope. The mirrors on Hubble, 2.4 meters in diameter, were supposed to be the smoothest large mirrors ever made. Scientists discovered, however, that one of the mirrors (known as the primary mirror) had been ground too flat on one edge. The total size of the error amounted to 1/50 of the width of a human hair, but it was still enough to make Hubble's pictures fuzzy.

Scientists had to fix this problem somehow, so they decided to fit Hubble with a corrective lens, kind of like a pair of glasses. So, during a special shuttle mission, the astronauts took the corrective lens up to space with them, and they fitted it on Hubble.

Currently, Hubble is sending spectactular images of distant galaxies and stellar phenomena that have never been seen before. To make it able to do this, Hubble has many more instruments aboard than just its mirrors. Among these instruments are a Faint Object Camera (FOC), a Space Telescope Imaging Spectrograph (STIS), and a Near Infrared Camera and Multi-Object Spectrometer (NICMOS).

Hubble uses an internal computer system called the Tracking Data Relay Satellite (TDRS) system. The TDRS system sends the data Hubble collects back to Earth for scientists to analyze. The information goes to a station in White Sands, New Mexico where it can be distributed to scientists who need it. The ground station can also send instructions to Hubble's instruments via the TDRS system. Any instruction that the ground station sends to Hubble is translated into a series of commands to be sent to the onboard computers. These commands are then uplinked several times a day to keep the telescope operating efficiently. Up to 24 hours of commands can be stored in the onboard computers of Hubble. Data collected can be broadcast from Hubble to the ground stations immediately or stored and downlinked later.

Although Hubble's operations never stop, not all of its time is spent observing. Each orbit of the earth lasts about 95 minutes, with the time divided between housekeeping functions and observation. Housekeeping functions include turning the telescope towards a new target, or away from the Sun or Moon, switching communications antennas and data transmission modes, receiving command loads and downlinking data, calibrating, and similar activities.

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Last updated on: 8 August 1997.