U.S. space shuttle Endeavour astronauts will embark on a spacewalk Sunday to install hardware on the international space station's railroad car. But Mission Control is grappling with the implications of the failure of a major space station positioning component.
One of the space station's four gyroscopes failed Saturday, leaving three to control the orbiter's position. Only two gyros, called CMGs, are required for the task, but the failure means there is only one spare.
Shuttle flight director Paul Hill says that if two more CMSs fail, the Russian module's jet thrusters would have to take over positioning the station, using precious fuel to do so. "Losing a CMG is a big deal," he explains. "This is a major component. But from a risk perspective right now, we're in good shape. We're two failures away still from really having a technical problem that we need to jump through hoops for. But this is a major component that's failed and we are going to do the best we can to get the next CMG ready to fly and into an orbiter and get it changed."
But Mr. Hill says it may be six to nine months before the gyro gets to the space station because the next two shuttle flights are already dedicated to other equipment. That could be advanced, however, if another gyro fails, requiring rescheduling of shuttle payloads.
In the meantime, mission officials are concentrating on the next major task for the current shuttle crew at the station. French astronaut Philippe Perrin and Franklin Chang-Diaz, a Costa Rica native, will don their space suits Sunday to begin installing a new platform on the station's rail flatcar.
The base will enable the station's robot arm to ride a railway the length of the outpost for future assembly tasks.
Two more spacewalks are required Tuesday and Wednesday to complete the installation and replace a faulty joint on the arm.