CAPE CANAVERAL, Fla. (AP) - An ozone-measuring satellite trailing space shuttle Discovery came frighteningly close to a 500-pound piece of space junk that could have smashed it to pieces.
The discarded rocket motor passed within 11/2 miles of the German-built satellite, worth tens of millions of dollars.
Discovery and its crew of six were 51 miles ahead of the satellite at the time Monday night and were in no danger, German mission manager Konrad Moritz said.
If the rocket motor and the 7,700-pound satellite had collided - both are hurtling around Earth at 17,500 mph - it could have been disastrous.
The U.S. Space Command, which tracks junk in orbit, knew the object was out there and kept NASA informed. However, as the piece drew near, engineers variously predicted it would pass as close as a half-mile or 31/2 miles.
Because of that wide margin of uncertainty, scientists nervously watched computer screens when the moment of closest approach came.
"We saw that we are still transmitting, so our spacecraft is fine," Moritz said. "This was a moment of excitement."
Ground controllers were prepared to fire tiny thrusters on the satellite to slowly maneuver it out of harm's way.
There is no danger of the motor coming close to the 184-mile-high satellite again, said NASA spokesman Kyle Herring. The astronauts plan to retrieve the satellite on Saturday, two days before their mission ends.
The spent rocket motor was used in the unsuccessful launch of a communications satellite that was carried up on a space shuttle in 1984. Coincidentally, the platform on which the satellite's ozone-mapping telescopes are flying was on that mission, too.
"Now we are meeting this guy again," Moritz said. "Isn't that the story?"
The rocket motor is among more than 8,500 orbiting objects being tracked by the U.S. Space Command, most of them junk.
Discovery's crew spent Tuesday taking more pictures of the Hale-Bopp comet with an ultraviolet telescope mounted on a shuttle window, and conducted more tests with a laboratory platform designed to withstand vibrations from the spacecraft.