Two spacewalking astronauts were scheduled to work on a jammed solar wing Monday, while their counterparts inside the international space station and in Mission Control send real-time instructions for the impromptu foray into space.
It was to be the fourth spacewalk of this now 13-day mission. NASA added it to the schedule on Saturday after several attempts to fully fold the solar array were unsuccessful.
It's the first time a single astronaut has done four spacewalks on one mission, reports . U.S. astronaut Robert Curbeam will be assisted by Swedish astronaut Christer Fuglesang, who paired up with Curbeam on two earlier spacewalks, as the two try to free some stuck grommets on the 115-foot array.
NASA began retracting the accordion-like structure on Wednesday to make room for some new solar arrays that were to begin generating electricity by rotating with the sun's movement. The new arrays would kick in after astronauts rewired the station over two spacewalks.
Reconfiguring the orbiting space lab's interim power system to a permanent electricity grid was a primary goal of the Discovery mission. But the old array, part of the interim system, retracted half-way before stalling. That was enough to allow the new arrays to rotate but NASA needs it to fold fully into a box so it can be moved on a later shuttle flight to its permanent position.
On the last scheduled spacewalk, which took place Saturday, Curbeam and Sunita Williams headed over to the array after completing their main tasks, and spent about two hours shaking the array, trying to coax apart the problem grommets. They partially succeeded and other astronauts were able to command the array to retract several degrees more. But more grommets got stuck and the spacewalking duo's time was up. The wing is about 65 percent retracted, reports King.
This time, with several hours on their hands solely for this task, Curbeam and Fuglesang hope to put an end to the array saga, the only glitch on this otherwise successful mission.
Asked by a reporter how important is it to get the arrays retracted, crew member Joan Higginbotham, who will be operating a crane-like robotic arm during the spacewalk, offered this assessment: "It's very important from a personal standpoint," she said. "I think we're all very Type A personalities — I think my crew would agree with me there — so we always like to accomplish the task that we are given."
The array could safely be left in its current configuration for a couple of months, but NASA managers decided to take advantage of the extra hands on deck and the flexibility in their time schedule to try and resolve the problem now.
"Of course it's a little more challenging because we haven't done the training on the ground for it, but we did have a lot of generic training for solar array wing deploy and retract," Curbeam said in an interview Sunday evening. "I have a pretty good feeling that we've got a good chance for success."
The robotic arm will take Curbeam to the trouble spots on the array, and he'll have a variety of tools with which to pry the grommets — and the guidewire that runs through them — free.
Curbeam said he'll treat the spacewalk like any other, but added, "Probably the most important thing is for us to keep in mind that since it's my fourth — and you tend to get more and more comfortable as you go along — just to make sure we don't make any mistakes."
Discovery is set to land on Friday, having left the space station with a 2-ton, $11 million addition installed and a new power system. They'll leave Williams on the space station as its newest resident and bring back her predecessor, German astronaut Thomas Reiter.