By Demian McLean
Aug. 13 (Bloomberg) — Astronauts replaced a broken gyroscope outside the space station today as NASA considered another spacewalk to repair damaged heat tiles on the visiting shuttle Endeavour.
The 600-pound (270-kilogram) gyroscope, installed by U.S. astronaut Rick Mastracchio and Canadian Dave Williams, is one of four that control the station's orientation, NASA said. The device helps keep the outpost level as it orbits the Earth and cuts the need for energy-draining stabilization jets.
A decision on the Endeavour's heat shields is expected this evening or tomorrow, spokeswoman Brandie Dean said. Astronauts spotted a playing card-size gouge under the shuttle's right wing after docking at the International Space Station on Aug. 10.
The thermal tiles, about an inch thick, protect the spacecraft as it returns through Earth's atmosphere, withstanding temperatures high enough to melt iron.
On the ground, the National Aeronautics and Space Administration is testing similarly damaged tiles in a blast furnace. The agency may ask astronauts to patch the gouge, which was opened by a piece of falling insulation foam during launch.
Four years ago, a briefcase-size piece of foam punctured the shuttle Columbia's wing during liftoff, dooming the craft and its seven astronauts during re-entry.
While spacewalkers practiced in-orbit fixes last year, NASA has yet to subject a real repair to the stress of re-entry. Astronauts have three options: apply a heat-resistant paint, patch the gouge with putty or affix a metal shield.
"We have really prepared for exactly this case, since Columbia," mission management chief John Shannon said last night in a briefing on NASA TV.
NASA may be able to avoid a repair altogether. In 1998, the ground crews discovered an even larger gouge in the shuttle Discovery when it returned safely to Earth, NASA said.
Since the Columbia accident of 2003, the agency has watched closely for falling foam during liftoff, and astronauts inspect the bottom of the shuttle with cameras and lasers when it docks at the space station.
To contact the reporter on this story: Demian McLean in Washington at dmclean8@bloomberg.net.
Last Updated: August 13, 2007 16:03 EDT