The astronaut who lost her bag in space has admitted that she did not check to see if the tool-kit was tied down and said it was hard to face her colleagues after the expensive accident

The bag, dropped by Heidemarie Stefanyshyn-Piper during a space walk on Tuesday, was one of the largest items ever lost by an astronaut - and one of the most expensive, valued at $US100,000 by NASA.

Ms Stefanyshyn-Piper, leading a spacewalk to clear a jammed joint on the International Space Station, was trying to clean up grease that had oozed from a grease gun in her bag when she let it slip out of her grasp and was forced to watch it float away.

For a second she thought she could grab it but, she told AP, "I thought, no, that would probably just make things worse and the best thing to do would be to just let it go.

"There's still the psychological thing of knowing that we made a mistake and having to live through that," she added. "During the spacewalk ... it was easy to put it aside because I knew that we still had five hours of spacewalk work to do and the work needed to get done and you can't dwell on a mistake. It was hardest coming back in and having to face everybody else."

She said it was possible the bag had become untethered in the acking and repacking of the tools and sacks, and promised not to make the same mistake again in any of the enxt three space walks planned.

"You're not going to see us lose another bag. We're going to double- and triple-check everything from here on out," she said.

Her spacewalking partner, Stephen Bowen, insisted on sharing the blame for the mishap.

"I didn't go back and triple-check everything. So I'm just as guilty at this as Heide is," he said.

Ginger Kerrick, the flight director, would not apportion blame. He told reporters yesterday: "We don't know that this incident occurred because they forgot to tether something. We don't know if perhaps the hook just came loose inside the bag.

"You've got to remember, we are working with humans here and we are prone to human error. We do the best we can, and we learn from our mistakes."

He said precautions would be taken to help prevent any more leaking grease guns or loose bags.

Ms Stefanyshyn-Piper said some air might have gotten in with the grease and forced the grease out. She said it seeped out in small bits and was all over the inside of the bag.

Meanwhile, the bag that got away was still in the neighborhood of the shuttle-station complex but was expected to fall out of orbit fairly soon.

The gummed-up joint is full of metal shavings, the result of grinding parts. It's been used sparingly for more than a year and, as a result, has hindered energy production at the space station.

Over the course of four spacewalks, astronauts will clean and lubricate the joint and replace the bearings inside, and do a little work on another joint. The first three spacewalks concentrate on the bad joint, the fourth will focus on the good joint.

The joint is supposed to keep the solar wings on the right side of the space station pointed toward the sun. A twin on the left side is operating fine, but the astronauts will squirt on some extra grease as a precaution.

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