Cape Canaveral, Fla. Two spacewalking astronauts clamped power equipment onto the international space station on Tuesday and inadvertently added to the collection of junk whizzing around Earth.
A cap for a depressurization valve floated away moments after Bill McArthur emerged from space shuttle Discovery.
The aluminum cover, about the size of a gas cap on a car, bounced against the space station, then against the shuttle robot arm. Then it was gone.
"It was a nice billiard shot," McArthur radioed. "It's become the latest addition to tiny bodies orbiting the Earth."
Mission Control said the lost cap was no reason for concern. Its tether either came loose or broke. Flight controllers expect the cap to plunge through the atmosphere and burn up in a few days.
The main purpose of Tuesday's spacewalk the third in as many days was to mount two power converters on the space station's new aluminum framework, or truss.
Astronaut Leroy Chiao performed the job from the end of Discovery's robot arm. He removed the 175-pound converters one by one from the shuttle cargo bay. From inside the shuttle, Michael Lopez-Alegria used the robot arm to give Chiao a lift.
The converters will be used to regulate power once a pair of solar wings stretching 240 feet from tip to tip are installed during the next construction mission, in December.
Chiao and McArthur clearly enjoyed their 240-mile-high construction work.
"How would you like to live on this thing for a few months?" McArthur asked.
"I think that would be pretty cool," Chiao replied.
By the time the seven-hour spacewalk ended, the two had completed all their cable connections, toolbox work and other chores.
One spacewalk remains. Lopez-Alegria and Jeff Wisoff will go back today out to clean the top of the truss for the arrival of the solar wings, test their mini jetpacks and practice carrying each other. NASA wants to see how hard it would be for a spacewalker to rescue an incapacitated colleague.
When Discovery pulls away Friday, it will leave behind 10 tons of new space station pieces. It will also leave the space station in a slightly higher orbit.