Perilous Snag Develops in Release of Satellite : Space: The shuttle’s craft rises only 570 feet during deployment, apparently by the tether binding on its reel.

As Mission Control watched enthralled, the shuttle Atlantis on Tuesday stepped out on a daunting dance through space with a diminutive partner held on a string as thin as a shoelace.

But the venture, considered perhaps the most exacting exercise ever attempted by the shuttle, struck a possibily devastating snag after the shuttle’s Tethered Satellite had risen only 570 feet.

Progress was suddenly stopped, apparently by the tether somehow binding on its reel. The reel, in the shuttle’s cargo bay, holds more than 13 miles of tether. Like fishermen grappling with a balky line, the astronauts found they could reel the satellite downward, but initial efforts to pull out slack and extend the line failed.

The orbital ballet saw astronauts reeling the 1,000-pound satellite out of the Atlantis cargo bay on a mission hailed as the harbinger of future orbital operations.

With Atlantis flying backward with its nose pointed down at the Pacific Tuesday afternoon, the gleaming white satellite rose from a four-story boom extended from the shuttle’s open cargo bay.

Bathed by the setting sun, the satellite was pushed from its cradle by tiny thrusters shooting bursts of nitrogen gas. At a snail’s pace, the satellite rose from the mother ship.

The beginning of the deployment at 2:50 p.m. PDT came after hours of frustration, including one aborted release when astronauts saw unexpected movement in the tether linking the satellite to the shuttle.

Because of the delays, flight planners scrambled to devise a new plan. The much-anticipated exercise is designed to send the satellite to a distance of 12.5 miles about 5 1/2 hours after its deployment and turn the linked vehicles into a huge electrical generator.

During the early portions of its ascent into the black sky, the satellite rose so steadily that its movement was barely perceptible. Half an hour after its release, it had moved upward 138 feet, its speed had reached one-tenth of a foot per second, and it was accelerating.

Then came the snag, which raised the additional concern that a prolonged problem with an immobile reel would use up maneuvering fuel required for the satellite to carry out several scientific experiments planned as it flies at the end of its line.

If the satellite is successfully reeled out, the tether and the shuttle will form a huge electrical generator in orbit as the combined vehicle flies through the Earth’s magnetic field.

With the satellite collecting electrons as it passes through the Earth’s ionosphere, the system is expected to generate an electrical potential of 5,000 volts, sending a current of about 1 ampere down the tether to the shuttle.

Initial plans had called for the satellite, designed and owned by the Italian Space Agency, to remain at its 12.5-mile distance for about 10 hours, and to be reeled back into its cradle some 30 hours after its release.

But because of the long delay in carrying out the deployment Tuesday, flight controllers tentatively planned to extend the operation by another eight hours so that astronauts could rest before the recovery operation.

Although the satellite rose straight upward on its tether, computer projections were that it would eventually begin to sway from side to side, requiring shuttle commander Loren J. Shriver to move Atlantis about to remain beneath it.

Soon after the satellite began its ascent, shuttle crew members began preparations for their maneuvers to swing and sway with it for about 38 hours.

Several techniques will be used, using computer projections, telemetry data received from the satellite and observations by the astronauts tracking the vehicle with both radar and laser ranging devices.

The operation is sufficiently delicate and mysterious that NASA Administrator Daniel S. Goldin ordered an additional safety review before giving the mission final clearance.

While the plan is to reel the satellite back, recapture it and return it to Earth, officials emphasized that the mission will be successful as long as they carry out the electrical generating exercise and other scientific experiments and gain an understanding of tethered vehicles’ behavior.

The United States’ only experience thus far in flying tethered objects in space came during the Gemini flight program in 1966, but as many as 50 potential applications are foreseen for the technique.

Besides the generation of electricity, they include exploration of altitudes beyond the reach of balloons and conventional aircraft and below safe operating altitudes for orbiting vehicles.

Tuesday’s first delay came when a plug at the end of an umbilical cord carrying communications and electrical power to the satellite from the shuttle failed to disconnect.

Until then, preparations for the exercise had progressed without a hitch. The boom holding the satellite was raised into an upright position in the cargo bay well ahead of schedule and smoothly extended to its full length.

But when astronaut Jeff Hoffman sent a command for a small motor to pull out the electrical plug, nothing happened.

For more than two hours, Mission Control in Houston and the shuttle crew struggled with the problem, first turning the shuttle so the cable remained in the sunlight, hoping that the warmth might encourage it to disconnect.

When that did not work, tension on the tether between the spacecraft and the satellite was released, leaving only the umbilical holding it in its cradle atop the boom.

After 10 fruitless tries, flight controllers produced an elaborate scheme combining everything they had unsuccessfully tried before.

Atlantis flew more more than half an hour with the balky plug and umbilical connection facing the sun, until the temperature reached about 150 degrees. The last bit of tension on the tether line was released, and shuttle commander Shriver was ordered to fire maneuvering thrusters, pushing the vehicle downward.

The plan called for as many as 30 bursts carried out at the same time Hoffman turned the motor driving the withdrawal reel.

Suddenly, the plug came out. In the Mission Control room in Houston, a cheer went up.