CAPE CANAVERAL - Spacewalking astronauts have lost an important piece of shielding needed for the International Space Station.

The cloth bundle floated away Thursday midway through a spacewalk by Peggy Whitson and Shane Kimbrough. Whitson immediately reported the mishap to Mission Control, which tracked the item as it drifted away.

NASA said the shield will be monitored to make sure it doesn't come back and hit the station. The shielding protects against micrometeorite debris. It was one of four shield pieces to be installed in the hole left by a newly relocated docking port.

It was a disappointing turn of events in a record-setting spacewalk for Whitson, the world's oldest and most experienced spacewoman. It was the eighth spacewalk of her career, the most ever performed by a woman.