Engineers will make a decision late Thursday on whether to raise the International Space Station's orbit slightly to avoid a piece of debris from a European rocket, NASA managers said Wednesday.

The debris, catalog number 29274, apparently is part of the dual-payload "SYLDA" adaptor used by an Ariane 5 rocket that launched Japanese and French communications satellites on Aug. 11, 2006. Such adaptors typically weigh around 1,000 pounds, but it's not known if the debris in question is intact. It is in a highly elliptical orbit, with a high point of about 20,000 miles and a low point of around 200 miles.

Tracking data indicates the debris will pass within about two miles of the space station at 11:06 a.m. EDT Friday. NASA managers are developing plans to change the station's orbit slightly to widen the miss distance if continued tracking shows more than a 1-in-10,000 chance of a collision.

John McCullough, chief of the flight directors office at the Johnson Space Center in Houston, said a preliminary analysis indicates no such maneuver will be needed. But he cautioned that more accurate tracking data will be available Thursday and that a final decision will be made Thursday evening.

"Right now, it's looking very positive, it's looking like we probably won't have to do that," he said. "But we are building a plan to allow us to make that decision as late as possible."

If a reboost maneuver is required, the shuttle Discovery's primary maneuvering thrusters would be used to impart a 1.1 mph change in velocity over a two-hour period.

"It's called a config-1 reboost," McCullough said. "It's a tail and forward alternating firing of the primary jets. It's about a two-hour maneuver to get a half meter per second, so it's not exactly efficient, but it's a predefined (procedure)."

The station's Russian thrusters can be used for orbit adjustments, but mission managers want to conserve the lab's on-board fuel if possible. McCullough said using the shuttle to do a reboost would have no impact on Discovery's mission.

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