Astronauts gear up for Thursday spacewalk
BY WILLIAM HARWOOD
STORY WRITTEN FOR CBS NEWS "SPACE PLACE" & USED WITH PERMISSION
Posted: December 13, 2006
Space station flight controllers, faced with an unruly solar panel and an increasingly tight schedule, put array troubleshooting on hold late today and pressed ahead with work to ready the lab complex for a critical re-wiring spacewalk Thursday.
In a first for the orbital outpost, flight controllers fired up a massive gear-driven joint on the left side of the station's main solar power truss to begin slowly rotating a new set of arrays like a giant paddle wheel, allowing the panels to track the sun as the station circled the globe.
Engineers then began work to pressurize one of two untried cooling systems in the main truss. If all goes well, a massive pump will begin active cooling Thursday during a spacewalk by Robert Curbeam and Christer Fuglesang to activate one of the station's two main electrical circuits.
Up until now, the U.S. segment of the station has drawn power from an interim system that provided electricity during the initial stages of construction. NASA now needs to switch the station over to its permanent power system to provide the electricity needed by current and future research modules.
The first step in that process was to retract the left wing of the P6 solar array, the one providing interim power, to clear the way for newly installed arrays on the left side of the main truss to begin rotating as required.
But after more than six-and-a-half hours and repeated attempts to coax the P6 array's two left-side solar blankets to fold up smoothly like pleated window shades, the astronauts were only able to retract the central mast about half way, or 17 of 31 40-inch bays.
Some 45 commands were sent to retract and extend the mast in stop-and-start fashion, but the blankets would not fold neatly. Rather than spend any more time on additional cycles, lead flight director John Curry decided to put troubleshooting on hold and to press ahead instead with preparations for Thursday's long-planned spacewalk.
While not an ideal situation, P6 was retracted enough to provide more than 10 feet of clearance between the end of the stalled array wing and the newly installed P4 arrays. That cleared the way for flight controllers to power up the solar alpha rotary joint, or SARJ, to begin rotating the new arrays.
Engineers then began work to pressurize one of two coolant loops on the main power truss with ammonia. Cooling is required to keep big electrical switching units and transformers in the power system from overheating once activated Thursday and drawing power from the P4 arrays and the still-extended right wing of P6.
Another spacewalk is planned Saturday, by Curbeam and new station crew member Sunita "Suni" Williams, to wire in the station's other main circuit and to activate a second ammonia coolant loop.
"The big picture is very simple," astronaut Stephen Robinson radioed the astronauts from Houston. "Flight day 6 (Thursday) will be executed as planned, including EVA-2. We've been practicing a long time, we're ready to do it exactly as written. The solar array is obviously safe for SARJ rotation because it's rotating. The port (cooling system radiator) is on its way to minus 30 degrees and after that, we'll start filling the ETCS (external thermal control system) loops.
"In the background, we're going to call up Team 4 to assemble an EVA plan that would aid in solar array retraction. Now this would be done no earlier than EVA-3 but it could also be EVA-4 or a stage EVA (by the station astronauts). That's what Team 4 will help us work out."
Robinson said even though P6 is not fully retracted, "we are go to execute the rest of the mission as planned, that includes undocking, the Progress (supply ship) docking coming up in a few weeks. So we're actually in a very good config. We appreciate all your hard work today and we're looking forward to a day tomorrow that should be unlike no other on space station."
"We're trying to figure out what 'unlike no other' means," quipped station commander Michael Lopez-Alegria. "In the meantime, we copy everything else you said and we look forward to working with you guys, Team 4's plan. I'm sure that whatever it is we'll be ready to handle it and we'll just stand by for further words."
"Roger that," Robinson replied. "We'll certainly let you know. ... Thanks again for all the hard work on the solar array today."
"Thanks, Steve, we appreciate you taking our participation into account and you know, we all tried as much up here as you guys did on the ground and it just wasn't going to work for us today. But that stuff happens and I'm sure we'll get through it."
"Well Mike, actually we consider it a success," Robinson said. "We're looking at the SARJ rotating on the big screen up there and people are darn happy about that."
"Yeah, Steve, the glass is definitely at least half full," joked the station commander.