The Space Shuttle is used to introduce instruments into low Earth orbit. Satellites like the Hubble Space Telescope orbit about 600 kilometers above Earth's surface. This is a low Earth orbit and accessible to the Shuttle. To put satellites into high Earth orbit, an upper stage must be carried in the Shuttle's payload bay or the satellite is lofted with one of several different kinds of uncrewed launch vehicles. For example, the Geostationary Operational Environmental Satellite (GOES) orbits about 40,000 kilometers above EarthUs surface. A Delta rocket was used to put GOES into high orbit. The choice of altitude--high Earth orbit or low Earth orbit--depends on the data to be measured.

Recent Astronomy Missions

In May 1989, the crew of the Space Shuttle Atlantis (flight 30) released the satellite called Magellan on its way to orbit Venus. The atmosphere of Venus is unfriendly to humans. It has thick sulfuric acid clouds, high pressures, and high temperatures. Magellan used radar to penetrate Venus's dense atmosphere and map the planet's surface.

In October of that same year, the crew of the Shuttle Atlantis launched another planetary satellite--Galileo--on its way to visit the planet Jupiter. On its way out to Jupiter, Galileo (named after Galileo Galilei, an Italian astronomer of the 17th century) took pictures of several asteroids.

Just a month later, in November, the Cosmic Background Explorer (COBE) was launched from a Delta rocket. This satellite surveyed the entire sky in microwave wavelengths and provided the first precise measurement of the background radiation of the universe. The distribution of this radiation exactly matches the predictions of the Big Bang Theory.

In April 1990, the crew of the Space Shuttle Discovery launched the HST. This telescope combines ultraviolet and optical imaging with spectroscopy to provide high quality data of a variety of astronomical objects. However, the primary mirror aboard the satellite was later discovered to be slightly flawed. Astronomers,

however, were able to partially compensate for the slightly out-of-focus images through computer processing. In December, 1993 the Hubble servicing mission permitted astronauts to add compensating devices to the flawed mirror, to readjust its focus, and to replace or repair other instruments and solar arrays. The servicing mission has led to images of unprecedented light sensitivity and clarity.

In October 1990, the crew of the Space Shuttle Discovery released the spacecraft Ulysses (named after the famous voyager of the Trojan War) to travel out of the plane of the solar system on a long loop around the Sun's south and north poles. It will collect and send back data about conditions in the solar system out of the plane of Earth's orbit.

In December 1990, the crew of the Space Shuttle Columbia conducted two experiments during their flight. The Astro-1 instrument platform and the Broad-Band X-ray Telescope (BBXRT) both study the x-ray and ultraviolet emissions of astronomical objects.

A few months later, in April 1991, the crew of the Space Shuttle Atlantis launched the Compton Gamma Ray Observatory (CGRO). This satellite carried four experiments to study high

The Hubble Space Telescope attached to the Space Shuttle Endeavour during the 1993 servicing mission

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