NASA officials decided today to ease the space shuttle Discovery toward a stranded Navy communications satellite for a risky close-up inspection, but said that any salvage operation will not include a spacewalk by the astronauts.
The operation will add two days to the planned five-day mission, with the shuttle returning to Earth on Friday, the National Aeronautics and Space Administration said.
The Leasat satellite, whose engine failed to fire after it was deployed on Saturday, remained in the shuttle's orbit, about 60 miles ahead of it. Officials planned to maintain that distance through Monday out of concern that the satellite's onboard engine could ignite or its fuel-laden tanks explode if overheated by the sun or jarred.
Shuttle managers said the most likely option for a rescue operation is to attach an extension to the shuttle's mechanical arm to snag the satellite's arming lever, in hopes of restarting the timer to ignite the rocket engine and send the satellite into the proper orbit.
That operation could take place on Wednesday, with the astronauts going into the cargo bay on Tuesday to attach the extension device, a spokesman said.
NASA rejected an earlier option to tether an astronaut to the end of the mechanical arm to release the lever with a hand-held tool.
"When you add a crewman at the end of the arm two feet away, you're adding a new level of risk," said flight director Randy Stone. "We believe these risks are not something we ought to take on in this mission. The crew is not trained for these risks."
In the planned "photo and inspection" maneuver, Discovery's crew would fly within a few hundred feet of the drum-shaped satellite. The astronauts would then have a chance to look it over to determine how it is spinning and whether the arming switch, suspected as the cause of its engine's failure to fire, is jammed in a closed position.
"We think that trip lever may be partly deployed, so that maybe we can flip it over by attaching some device to the end of the arm," astronaut Jerry Ross said from the Johnson Space Center in Houston. "But we don't want an astronaut out there."
Despite the dangers in working next to a spinning satellite whose engine might fire at any time, the crew was acting tonight as if it wanted to consider an operation to rescue the satellite.
"If there's any opportunity of salvaging this guy," Discovery pilot Donald E. Williams said, "we'd sure like to give our best try."
Said Discovery commander Karol J. Bobko: "We're more than ready to attempt a rendezvous. Obviously, we want to get as close to that satellite as we can."
Even the inspection rendezvous involves risk. Discovery's crew has not rehearsed a Leasat rendezvous and no rendezvous maneuver is programmed into its navigating computer. A rendezvous plan was teleprinted to the crew tonight, but there was no guarantee that it will work with precision or that Leasat's engine will not suddenly ignite, as it was supposed to do 45 minutes after being deployed from the shuttle.
"We have to better understand the safety issues involved here," flight director John Cox said. "We're going to come at this success-oriented, but we have one report that says that if we're at a distance of 12 miles and that motor ignites, we can get exhaust all over the windows and we won't be able to see anything."
The satellite's arming switch activates a timing device that deploys its antennas, sends it into a faster spin and then fires the engine to lift it into geostationary orbit.
Working around the clock on Saturday and well into today, engineers from Johnson Space Center and Hughes Aircraft Corp. apparently concluded that the six-inch-long arming switch was at least partly deployed and that it posed more of a danger in that position than if stuck completely closed. This apparently was the reason that a spacewalk, with an astronaut working alongside the satellite at the end of the shuttle's robot arm, was considered so risky.
Arming the satellite activates its timing mechanism, which orders the satellite's antennas to be deployed in 90 seconds, starts spinning the satellite 50 revolutions per minute six minutes later and then orders its engine to fire in less than 40 minutes.
The salvage operation, if successful, would mark the third time astronauts have rescued satellites built by Hughes Aircraft Corp. Two errant satellites retrieved by shuttle crews in 1984 are now being refurbished by Hughes for reuse by other customers.
Rescue also would please underwriters, who reportedly have insured the satellite for between $80 million and $85 million.
Failure, on the other hand, might further tarnish NASA's reputation in its competition for the lucrative space delivery business with Arianespace Inc., which manages the French Ariane booster.
The Leasat satellite is a new type of communications satellite designed to be carried only by the space shuttle. Drum-shaped and squat, it takes up less room in the shuttle's cargo bay than other communications satellites and is less expensive to deploy into orbit.
The satellite stranded in orbit now is the third of this type. The other two are in geostationary orbit where they are working under lease for the Navy.