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Shuttle's cargo is key link for future NASA missions

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As NASA Deputy Administrator Dale Myers explains, his agency considers the shuttle's return to service ``the beginning of the future for the space program.'' And, he adds, Discovery's cargo - the TDRS communications satellte - is part of ``the key to that future.''

Once it is fully established, the Tracking and Data Relay Satellite (TDRS) system will enable users to be in almost continuous contact with satellites in low-Earth orbit.

It will let the National Aeronautics and Space Administration work with the planned Hubble Space Telescope and other orbiting observatories as well as with the shuttle and, eventually, a space station. (The Hubble telescope and other observatories are scheduled for launch beginning in 1990.)

Without the TDRS system, these and other major elements of the United States space program's future would be severely handicapped or utterly useless. They would not be able to communicate effectively with the ground.

It is this pivotal role that gives the TDRS satellite the high priority reflected in its status as the first new shuttle payload to fly, notes Richard Truly, NASA's associate administrator.

As of yesterday afternoon, astronauts were scheduled to release the satellite about 6 hours after Discovery's 11:37 a.m. (EDT) takeoff.

Once the new TDRS-3 satellite is on station and working satisfactorily, it will join TDRS-1, now in orbit, to form a complete system. TDRS-2, which was to fill this role, was lost in the Challenger explosion.

The satellites orbit 22,300 miles high, where they travel at the same speed at which Earth rotates. They remain virtually over the same ground location. This is known as geosynchronous orbit.

The satellites also have a far better view than do ground stations of objects in low-Earth orbit (below about 300 miles) where many scientific and manned spacecraft fly.

Ground stations now are in touch with such low-orbiting satellites for only about 15 percent of an orbit. With two TDRS on station, NASA should be in contact with these satellites about 90 percent of the time.

Without this nearly continuous contact and the high-speed communications TDRS provides, users would choke on the data volume the US space program soon will be generating, explains Thomas McGunigal, director of the TDRS program for Contel Federal Systems. Contel owns and operates the TDRS system for NASA.


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