Intelsat rescue saga may alter training.

Last week, three astronauts emerged from the space shuttle Endeavour, placed themselves just below a wayward, 9,000-pound satellite and reached out with gloved hands to snare the massive communications craft. That feat, a last-ditch effort to rescue the errant Intelsat-6 and place it in its proper orbit, marked the first time that so many astronauts had ever ventured out in space together. But the successful maneuver, which came after two failed attempts, also spotlighted the differences between ground training and the challenge of working in space.

Astronauts need "better ways to train, so when we get up there the learning curve isn't quite so steep," noted mission commander Daniel C. Brandenstein from orbit. During two days of the flight, which ended May 16, astronaut Pierre J. Thuot tried to manipulate the pincer-like claws of a tool called a capture bar in order to grasp a ring on the satellite's bottom. But he managed only to jar the spinning craft so that it began to wobble.

"The satellite was much more responsive [to touch] than indicated on the ground," says engineer Calvin Seaman at the Johnson Space Center in Houston. He notes that on Earth, crew members attached the capture bar to a stand-in for Intelsat-6 that floated on cushions of air above a laboratory floor, simulating weightlessness in space. But unlike the vacuum of space, air has resistance, or friction, which slows the motion of objects when they are pushed. (Astronauts also rehearsed tasks while immersed in a tank of water, another medium that has resistance.) In orbit, the satellite reacted to even small forces exerted by crew members as they tried to grab the craft.

NASA's W. Michael Hawes cites another limitation: air cushions permit motion along the plane of the floor, but not up and down. "In space, it's a three-dimensional problem," he notes.

A key challenge in orbit, says Seaman, was the interaction among several bodies: the satellite, the astronauts, the capture bar, a robot arm extending from the space shuttle and the shuttle itself. "The dynamics of all those bodies was not what we expected," he says, adding that no simulation on the ground could completely mimic the complex interplay. Due to Earth's atmosphere, notes Seaman, the spacesuits worn during ground training can't easily simulate the stiff, highly pressurized suits that astronauts must wear during space walks. Those suits make it difficult to bend arms or elbows--movements vital for many routine tasks.

Seaman says the problems in space could modify training for construction of the Freedom space station, as well as a mission to repair the Hubble Space Telescope. But last week's activities had an important difference, he notes: The smooth surface of Intelsat-6--unlike Hubble--lacks hooks that equipment can grab onto.

"This satellite was never designed to be touched by humans," Seaman says.

Some researchers say sophisticated computer simulations that invoke the concept of virtual reality can better mimic orbital conditions. But Stephen Ellis of NASA's Ames Research Center in Mountain View, Calif., warns that this technique, though promising, could mislead astronauts because it creates a highly specific environment, parts of which may differ from space.