Astronauts aboard the International Space Station readied for a fourth spacewalk on Monday to unstick a jammed solar array in an extra excursion that extended the space shuttle Discovery‘s mission at the orbiting outpost by a day.
Astronauts Robert Curbeam and Christer Fuglesang will try to clear snarled guidewires that are preventing the 33m panel from retracting into a 50cm-high storage box at its base.
The array is supposed to fold like a Venetian blind. It has already retracted enough to allow the crew to successfully complete its primary mission of rewiring the space station.
Construction on the station is due to be completed in 2010 but was halted for over two years by the 2003 shuttle Columbia disaster.
To meet that deadline before the aging shuttle fleet is retired, Nasa expects to fly 13 more shuttle missions.
The fourth spacewalk starts at 7.12pm GMT and is expected to last four to six hours.
The station’s robotic arm will boost Curbeam close to the panel where he can inspect and free grommets that are snagging on guidewires as the panel is reeled into the box. He will use tools wrapped in insulating tape to pluck at the guidewires, push on panel hinges and flip the grommets to try to unstick them as mission controllers slowly retract the panel by remote command. A grommet is a protective eyelet in a hole that a rope or cable passes through.
Fuglesang, posted at the base of the array, will take photos and, if necessary, shake the array by hand to ease bunching in the solar blanket and free the stuck grommets.
That technique succeeded on Saturday for Curbeam and fellow spacewalker Sunita Williams, but it was painstakingly slow.
About a third of the panel remains outside the box. The array must be fully retracted so it can be relocated in future space station construction.
Curbeam, who will make a record-setting fourth spacewalk, said the excursion is ”a little more challenging because we haven’t done the training on the ground for it”.
”The ground has done a great job of putting together a plan that we can follow and I have a really good feeling that we have a good chance of success,” he added.
The ground and space crews will be collecting data and photos about the solar panel fix to help with a mission next year to retract the opposite side of the array.
The fourth spacewalk adds an extra day at the station for the Discovery astronauts. Discovery is set to undock on Tuesday.
The shuttle’s landing is now targeted for Friday at Kennedy Space Centre in Florida, but the craft could be diverted to landing sites in California or New Mexico. – Reuters