Atlantis Crew Ready to Try Gemini XI’s Old Rope Trick : Space: It’s been 25 years since NASA tested tethered vehicles. Astronauts hope to learn more about linked motion and even make electricity.

It’s been a quarter of a century since American astronauts tried flying space vehicles linked together by a tether--an experience they found as promising as it was trying.

Then, with their Gemini XI spacecraft tied to an Agena rocket with a 100-foot strap, astronauts Charles Conrad Jr. and Richard F. Gordon Jr. traveled through space for three hours. The conclusion was that vehicles roped together in space could be successfully maneuvered.

They were bedeviled by snaking motions that they could neither understand nor control. But before they cut the rocket stage loose, they had pulled the tether taut, and the combined vehicle slowly rotated, creating artificial gravity as it traveled through space.

The experiment, officials said after it was over, revealed a potentially efficient way for a manned spacecraft to remain on station with an orbiting laboratory.

Today, the shuttle Atlantis is due to pick up where Gemini XI left off, beginning a vastly more ambitious effort to assess the engineering and scientific potential of tethered space vehicles.

At 11:30 a.m. PDT, astronauts were to begin reeling out a 1,000-pound, five-foot diameter satellite on its way to a distance of 12.5 miles from the shuttle.

Atlantis flight director Ron Dittemore conceded Monday that mission control does not fully know what to expect when the satellite is released from a 40-foot boom that will raise it from the shuttle’s cargo bay.

But he added: “We are as ready as we are ever going to be . . . we are looking toward nothing but a successful operation.”

The satellite is to fly at the end of a shoe-lace-sized cord for more than 10 hours while shuttle commander Loren J. Shriver and his crew maneuver the shuttle to maintain control over any swaying and bobbing motions that were predicted by computer simulations.

Besides gaining a better understanding of handling tethered objects in space, the exercise will generate electricity--perhaps as much as 5,000 volts--as the shuttle, tether and satellite function as a generator by cutting across the Earth’s magnetic field.

An electrical circuit will be created when electron generators in the rear of the cargo bay receive the current traveling down the tether from the satellite and beam it into magnetic field lines, which will conduct it back to the satellite.

In preparation for the climactic hours of the weeklong Atlantis mission, the astronauts lowered their orbit by 70 miles Monday.

They spent the day checking scientific experiments associated with the operation and calibrating equipment that will monitor it.

If all goes as planned, the satellite will be slowly reeled back into the shuttle bay about 4 p.m. PDT on Wednesday.

Because the main shuttle antenna will be used to track the satellite’s movement away from the shuttle and back, there will be little television coverage of the drama. Pictures will be available only when Atlantis passes within close range of Earth stations.

As the astronauts worked through preparations for the tether operation, the European Space Agency postponed until today an attempt to boost its EURECA research laboratory into a higher orbit, where it can safely operate for several months.

Released from the shuttle Sunday, EURECA was left 55 miles lower than its proposed operating orbit when controllers abruptly ended a transfer maneuver, fearing that the satellite was not on the proper course.

ESA officials had earlier expected to try to boost the satellite again early Monday, but decided to use the day for further evaluation of the spacecraft and its command and communication systems.

The new plan, a spokesman for the agency said, was to attempt the first of two boosting maneuvers early today, with a final adjustment 24 hours later.

For their own part, flight controllers at the National Aeronautics and Space Administration delayed a decision on extending the Atlantis mission by one day to compensate for the 24-hour delay in releasing the EURECA satellite.

The question of whether Atlantis will land at the Kennedy Space Center Friday morning or Saturday will be determined by how much propellant the shuttle has to use in its 30-hour dance with the tethered satellite today and Wednesday.