Second space station solar array wing deployed
BY WILLIAM HARWOOD
Posted: December 4, 2000
"Houston, Endeavour, we'd like to make this final call: We have two tensioned blankets," astronaut Joe Tanner reported.
"Copy that, great work, gentlemen, you've got a lot of happy folks down here," astronaut Mario Runco replied from mission control. "We think you've earned your solar array wings and we'll be issuing your new uniform insignia upon your return."
"Thank you very much, you're very kind. There was a fair amount of - tension - in the cockpit."
"Needless to say, the room down here was filled with electricity."
Elated at the successful extension of the port wing of the $600 million P6 solar array, engineers are working around the clock to determine the feasibility of having Endeavour's two spacewalkers tighten up the tension in the array's starboard wing, deployed Sunday.
"We are looking at the option," station flight director John Curry said in an interview late this evening. "We have got a team of folks in California looking at the real hardware, prototypes, (to assess) the feasibility of having the crew do it.
Tanner and Carlos Noriega are scheduled to carry out a second spacewalk Tuesday to wire the now operational P6 solar power system into the station's electrical system.
A third, shorter, spacewalk is on tap Thursday to install an instrument to measure the electrical environment around the station. Any attempts to tighten up the slack blankets making up the starboard solar wing likely would be made during this final spacewalk.
"If they come up with something we can implement that's fairly straight forward, then we'll do it on that spacewalk," Curry said.
"One thought we've had here is Carlos gets in an APFR (articulating portable foot restraint) and then holds my feet and we essentially become a stack of two people to get me up high enough to get a tether around the tension bar to pull it down," Tanner said. "It should be exciting if we try it."
In the meantime, flight controllers are busy checking out the newly deployed port solar wing and charging up the P6 array's batteries.
"We're in really good shape now and well on our way," said lead flight director William Reeves. "We've got the power now to press on to the next phase of assembly of the international space station."
The P6 power system features two independent channels, or circuits, one fed by the starboard wing and the other by the port. Curry said channel 2B, fed by the starboard wing, was producing about 25 kilowatts of power. The port wing, supplying channel 4B, should produce a similar amount.
In recent dispatches, this writer has reported the P6 array would produce about 20 kilowatts of useable power. This was based on details presented at a pre-launch NASA news conference. One assumes the NASA briefer was referring to a single wing and not the complete array.
In any case, Curry said today the array's useable power would be less than 50 kilowatts but certainly more than 20.
One of the two flexible solar cells blankets making up the wing appeared to unfurl normally. But the other blanket was not as taut as engineers would like.
During extension of the wing's central mast, the blankets rippled back and forth, oscillating dynamically as blanket panels bunched up and then pulled free. The astronauts said today the behavior of the blankets was alarming enough for them to consider halting the deployment.
"We were thinking about, talking on the flight deck about whether we should stop or not," Tanner told a reporter today. "We can't go any slower, there's only one rate those will deploy unless you do it manually.
"We were watching it closely and the panels were sticking together and as it continued to deploy, the panels would unsticks and it was pretty dynamic there for a while. ... It was like you were loading up a spring and then it would release.
"The tension mechanism is a spring, basically, and as it stretched out it put enough tension on the stuck panels to cause them to break loose," Tanner said. "Then the spring would retract again and the process would keep occurring as the panels broke loose."
Commander Brent Jett said the crew was "a little bit surprised by where the arrays were sticking and how much the tension bar was being pulled out."
After studying closeup video views of the blankets, NASA managers decided today to press ahead with deployment of the port-side wing.
But instead of letting the deployment proceed unchecked at one constant speed from start to finish, they told the crew to turn the wing's mast extension motor off and on to minimize stress on the tension cables and to let any oscillations damp out.
The procedure worked as engineers had hoped, and the wing ended up in a fully deploy, properly taut condition. The extension took one hour and 54 minutes, concluding at 9:46 p.m.
As for the slack panel on the starboard array, Jett told flight controllers early today that Tanner and Noriega would be willing to attempt repairs during one of their remaining spacewalks.
"We were thinking about maybe another way to tension the arrays using PRDs (payload retention devices) to tension it and a long tether to secure it."
Tanner said the main problem with attempting any repairs is that the wings are so high above the shuttle's cargo bay - 90 feet or more - making them difficult to reach.
"There are not too many options because the work site is very high," he said. "One thought we've had here is Carlos gets in an APFR (articulating portable foot restraint) and then holds my feet and we essentially become a stack of two people to get me up high enough to get a tether around the tension bar to pull it down. It should be exciting if we try it."
But the spacewalkers never practiced such a procedure during training.
"Unfortunately, this is not one case we simmed or even dreamed about," Noriega said. "This tension bar one is unfortunately one of those we didn't anticipate. And those are the ones that usually catch you."
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