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Challenger's challenge includes reliabililty tests

America's five Challenger astronauts, orbiting 184 miles from our planet's surface, face a tough work schedule that is crucial for the timely progress of the shuttle program.

Their first job is to launch India's Insat-1B communications and weather satellite. This is their main commercial mission. But much of their time in orbit is to be spent learning to manipulate major payloads with the shuttle's mechanical arm, and testing communications through the Tracking and Data Relay satellite (TDRS). These operations must be mastered and shown to be reliable for the shuttle system to perform to full capacity.

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The night launch, which produced an artificial ''sunrise'' at Cape Canaveral at 2:32 a.m. Eastern daylight time Tuesday, showed that the shuttle can launch even under mildly unfavorable weather conditions. A moderate overcast following rain caused officials at the cape to delay the launch 17 minutes. Yet, in the end, it went off smoothly. At this writing, the astronauts were preparing for a scheduled eight-hour sleep period prior to the scheduled launch of Insat-1B at 3 :49 a.m. EDT today.

The TDRS tests that lie ahead are especially important for the next mission, when the shuttle Columbia is scheduled to carry the European-built Spacelab into orbit Oct. 28. The TDRS link is needed to handle the massive data flow from Spacelab, a laboratory in which astronaut scientists can work. The European Space Agency, which has funded Spacelab, has said it will run out of project money if that mission, already behind schedule, is further delayed. Yet, until the US National Aeronautics and Space Administration (NASA) has assured itself that the TDRS link is reliable, it cannot guarantee to launch Spacelab on time.

Originally, Spacelab was planned on the assumption that there would be two TDRS available. Located at different points along a shared 22,300-mile-high geosynchronous orbit, these satellites would have provided almost continuous communication between Spacelab and the ground. The satellites move along this orbit at the same rate at which Earth turns. Thus, they hover above a given spot on the globe.

TDRS-1, launched last April, went into the wrong orbit when its Air Force-supplied booster rocket malfunctioned. It took 12 weeks of careful maneuvering with the satellite's own control rockets to put it in its proper orbit. Now TDRS-2 won't be launched until the booster problem is solved, perhaps next spring. This will limit the fruitage of Spacelab somewhat.

Meanwhile, tests with TDRS-1 using the Landsat Earth resource satellite were begun in early August. These suggest the satellite is working properly. But NASA won't know how well it allows communication with the shuttle until this is tested this week.

Testing the manipulator arm with a dummy payload that fills the bay is another operation that must be proved workable. Some 15 hours have been allotted for this. Challenger, then, appears to be well named. Its newest crew, like previous shuttle crews, have a bigger job then just launching a customer's satellite. They still are having to prove the capability of the shuttle system.

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