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Engineers debate options for coaxing balky array to full retraction BY WILLIAM HARWOOD STORY WRITTEN FOR CBS NEWS "SPACE PLACE" & USED WITH PERMISSION Posted: December 13, 2006 After multiple stop-and-start retractions and extensions, the Discovery astronauts were unable to fully retract a huge solar array. While it eventually retracted enough for another array to start rotating later to track the sun, additional work was needed to coax the balky array into full retraction. The not entirely unexpected problem threw a wrench into Discovery's tightly choreographed space station re-wiring mission, requiring multiple retraction-extension-retraction cycles to coax the array's venetian blind-like slats to smoothly fold into a storage box at the base of its collapsible central mast. After several slats folded the wrong way, astronaut Sunita Williams sent commands to redeploy the mast in hopes they would straighten out. "Going to deploy. Ready, ready, now," Williams called at 2:58 p.m. The blankets then appeared to unfold normally and the kinks smoothed out as engineers hoped. "We like that. We'd like you to abort, abort the deploy now," astronut Terry Virts called from mission control. "OK, aborted." "Just to let you know, while definitely it's a lot better, it still looks like in that center it's bowed out ... and I'm afraid when we retract it we'll see the same thing," commander Mark Polansky radioed. "Are you saying you think we need to deploy some more?" Virts asked. "Our recommendation would be to deploy it a little bit more," Polansky agreed. "We've onely gone one bay so far." "OK, thanks, give us just one sec while we talk about it." A few moments later, Virts told the astronauts to continue the extension. "OK. On three, we're going to deploy," Williams called at 3:01 p.m. "Ready, ready, now." The panels continued extending. And finally, the two slats that had bowed and folded the wrong way appeared to pop back out and into the right positoin. Williams immediately stopped the extension with 27 of the array's 31 40-inch mast bays extended. "OK, copy that, we did see it pop in place," Virts said. After discussing the array's appearence, flight controllers told Williams to attempt another retraction and to collapse the central mast until just two bays remained extended from its storage canister. "Ready, ready, now," Williams called at 3:09 p.m. "And it looks like that spot, that troublesome spot is folding correctly now." "Still with a long way to go, that's still good news from Suni Williams, that redeployment of the array cleared the problem," observed NASA commentator Kyle Herring in mission control. But two minutes later: "Going for an abort," Williams called. "Stand by, we'll get words down to you in a minute. ... We just wanted to check out the tension wires, we saw a little bit of motion. Now that we've stopped everything looks fine. We're happy to continue if you're OK with that." "OK, Suni, that's good news to hear," Virts said, getting laughs in the control center when he repeated lines made famous during the Apollo 11 moon landing: "You've got a bunch of guys about to turn blue down here. ... You're 'go' to proceed with the retract." The retraction then resumed, but was aborted again a few moments later when the forward blanket appeared to bow out somewhat. Polansky suggested another re-extension to clear the problem and flight controllers ultimately agreed. "You know, Terry, I kind of think this is going to be one of those things where we're going to go ahead and retract it for a while, and if there's a problem we're going to have to stop and then extend it for a while until it resolves and then maybe retract it again," he said. "It might be just a back-and-forth thing to get it in." The astronauts then re-extended the array until the blanket slats in question straightened out and then ordered another retraction cycle. "Retracting. Ready, ready, now," Williams called at 3:28 p.m. A moment later, "Aborting!" Two slats on one of the blankets folded the wrong way right at the blanket storage box. The mast was re-extended to 27.5 bays, the slats straightened out and Williams tried again. "Ready, ready, now," she called at 3:33 p.m. Then: "Aborting." "Houston, Discovery, now the problem's over there on that first panel on the forward, the first panel from the blanket box, right smack dab in the middle, it looks like its bowing out against the fold," Polansky reported. "We thought it had popped out, but I guess not." Once again, the mast was extended, this time to nearly its full length of 31 bays. And then another retraction cycle began. "So far, all looks good," Williams radioed as the mast began pulling the blankets back in. A few moments later, "Still looking good..." But at 3:41 p.m., "Going for the abort," Williams called. "We count about 19 bays and the reason we aborted is that the guide wires looked a little slack." "OK, copy, about 19 bays," said Virts. "We're going to take a look at it." He then told Williams to retract one additional bay. There were no folding problems, but the blankets did not appear to be under as much tension as one might expect. In any case, flight controllers told her to resume retraction, saying "Suni, keep on pressing. You're go to retract until you see a problem." But she had to stop again with 17-and-a-half bays still extended. Again, it appeared critical cables used to keep tension on the blankets were not applying enough force. Polansky was not sure if the panel could be extended enough to clear the problem without passing through the 19-bay point, the minimum amount of retraction required to permit engineers to begin rotating the newly installed P4 solar arrays later today. As the shuttle-station complex passed from orbital daylight into darkness, engineers told the astronauts to stand by pending additional discussion about what to do. Our latest story on the situation is available here.
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