Flight controllers optimistic about successful repair
BY WILLIAM HARWOOD
STORY WRITTEN FOR CBS NEWS "SPACE PLACE" & USED WITH PERMISSION
Posted: November 2, 2007
The Discovery astronauts today reviewed plans for a dramatic solar array repair spacewalk early Saturday and appeared confident they have a good shot at fixing the mangled panel to keep space station assembly on track. Lead flight director Derek Hassmann said concern that spacewalker Scott Parazynski could get zapped by an unexpected electrical discharge while working near the charged array was misplaced and that the additional risk was minimal.
Said lead spacewalk officer Dina Contella: "Having the extra day to prepare for this spacewalk has really been a good thing for the EVA team, we've really hammered flat a lot of the details. ... It's really been a huge, coordinated effort. The big picture really hasn't changed. it's just a matter of the details, really, getting (figured) out in the extra day that we had."
A successful repair is critical to NASA's plans for continuing space station assembly. At the Kennedy Space Center in Florida on Saturday, engineers are scheduled to move the shuttle Atlantis from its hangar to the Vehicle Assembly Building for attachment to a set of boosters and an external tank. Launch on the next space station assembly mission, a high-profile flight to deliver Europe's Columbus research module, is targeted for Dec. 6.
Because of problems with the station's right-side solar array rotary joint, NASA needs to get the P6 array repaired and fully extended to provide the power necessary to support the attachment of Columbus next month as well as Japanese research modules scheduled for launch early next year.
"At this point, we've got problems on both ends of the truss, unfortunately," Hassmann said. "We've got the issues with the starboard truss, with the starboard solar array rotary joint, and now we've got this issue on the port side of the truss with the 4B solar array. ... We need to address one of these two problems before we proceed.
"Based on the discussions I've been involved in, we need to get the solar array addressed and fixed, fully deployed, structurally stable, available for power before we would proceed with 1E (the Columbus mission)."
Parazynski and astronaut Doug Wheelock plan to begin the dramatic spacewalk around 6:30 a.m., floating out of the station's Quest airlock module and making their way up onto the lab's main solar power truss. Parazynski will attach a foot restraint to a 50-foot boom carried by the station's robot arm and then lock his boots in place for a slow but spectacular 45-minute ride to the damaged array.
Wheelock, meanwhile, will make his way to the base of the P6-4B solar array on the far left end of the main power truss and provide verbal guidance cues for arm operators Stephanie Wilson and Dan Tani, working inside the Destiny laboratory module.
The P6-4B solar array is mounted on the far left end of the space station's main power truss, half a football field from the space station's pressurized modules. The robot arm alone cannot reach the damage site, even when positioned at a work site on the end of the power truss. But using the shuttle's heat shield inspection boom as an extension, the space crane can just barely get Parazynski into position.
On Thursday, mission managers said it would take Parazynski more than 30 minutes to reach the safety of the station's airlock in the event of a major spacesuit malfunction, primarily because of time needed to maneuver the robot arm. All NASA suits are equipped with a 30-minute supply of emergency oxygen and NASA has never before planned a station spacewalk that could put an astronaut in a position where he or she couldn't reach the airlock in a half hour.
But Contella said Friday engineers had refined their plans and that she believed Parazynski could get back to the Quest module before running out of air in any credible failure scenario.
After reaching the damage site, Parazynski, one of NASA's most experienced spacewalkers, first will inspect the mangled section of the 4B solar blanket to determine what might be needed to release an apparently snarled guidewire believed to have ripped open two blanket panel hinges during deployment Tuesday.
Before addressing the presumed snarl, the spacewalker will attach a homemade clip dubbed a cufflink, threading clasps on each end through reinforced holes above and below the rips in the blanket. That way, if the tension on the blanket changes because of work to free the snarl, it will not worsen the tears that are already there. Five such cufflinks will be installed across the 15-foot width of the blanket before any attempt is made to complete its extension.
"The problem would come is if we get there and we realize the snag either can't be cleared or maybe the snag has altered the guidewire, for example, in some way that we don't really want to do the deploy with the guide wire in that particular state, we don't think it's a good idea to have the damage as is for a deploy," Contella said.
"So if we get in either of those two cases, then we will cut the guidewire. So the idea is, Wheels would get ready at the bottom of the array. Remember, there's the take-up reel mechanism at the bottom and Wheels will have needle-nose pliers at the base and he'll get ready and basically grip the bottom part of the wire. And this is because we want to have a controlled intake as opposed to something that would accelerate and potentially end up with a big snarl at the base."
The spacewalk is timelined to last up to six hours and 30 minutes. But Hassmann and Contella said if Parazynski doesn't run into any major problems, the actual repair work could be completed in as little as a half hour. The astronauts inside the space station will attempt to redploy the repair panel as soon as Parazynski can be moved out of the way.
NASA expects to have good video coverage of the repair work, using cameras mounted on the space station and in the helmets of both spacewalkers. But Hassmann said video was not required. It will be up to Parazynski, the man on the scene, to determine the best course of action.
"We don't have fantastic photography of this area, we just don't have the capability to see exactly what's happening," Contella said. "So at that point, Scott's going to have to use his best judgment on what he thinks we're going to do."
In the end, she said, "it's a snag clear; it's not rocket science. So you want him to probably tell you what he thinks would be the best thing and then we'll just discuss it on the ground and make sure everybody sort of agrees that yeah, the solar array's not going to have some sort of adverse dynamics because of the way he wants to clear it, something like that."
During a news briefing Thursday, astronaut Dave Wolf downplayed the threat of a shock hazard, but told reporters it was possible, in theory, for an astronaut to get electrocuted in a worst-case short. Today, Hassmann downplayed those concerns saying "a number of things have to happen all at once for there even to be a small risk of any kind of electrical problem or shock hazard while Scott's out there doing his work."
"The thing to remember," he said, "is a pristine solar array, an undamaged solar array is completely isolated. The suit itself, obviously, is completely isolated. ... A spacewalking astronaut could put his hand on that solar array and there would be no risk of any kind of shock of any kind.
"What we do is, we think about the worse case scenarios and any possible way a shock hazard, any kind of electricity incident, could occur. And really what you have to do in your mind to make that happen is to find a metal piece on the suit, which in general is the rings around the gloves, the ring around the waist, the ring around the boots, and you'd have to take one of those metal rings and apply that to a hot part of the solar array. And in order to find a hot part of the solar array, you'd have to find a damaged portion.
"So if you could find that hot wire, a crew could put a metal portion of his suit, which is very limited, on the hot part and then he'd have to complete the circuit. So he'd have to find another part of his suit, the boot ring, for example, or the waist ring, and he'd have to apply that to another part of the solar array in order to complete that circuit in order to come anywhere close to any kind of shock hazard."
Playing it safe, Parazynski's tools were wrapped in non-conducting tape, as were the glove, boot and waist rings on his spacesuit.
The 17-ton P6 solar array truss segment was launched in 2000 to provide power during the initial stages of assembly. The lab's main power truss is now built and equipped with huge sets of solar panels on each end: starboard 4 (S4) on the right side and port 4 (P4) on the left. The outermost right side S6 arrays, scheduled for launch next fall, will be attached to a short spacer segment known as S5.
During two recent shuttle flights, astronauts retracted the two wings of the P6 array and disconnected it from the station's power system. Spacewalkers had problems retracting the 4B panel, however, encountering a frayed guidewire that repeatedly hung up on grommets during the retraction process.
On Tuesday, P6 was unbolted from its initial mounting point and moved to the far left end of the power truss and bolted to the P5 spacer segment. The first of its two solar array wings, known as P6-2B, extended a full 110 feet as required, but the crew aborted deployment of the 4B wing when one section of hinged blanket slats hung up, presumably due to a guide wire snag. Two seams between adjacent slats pulled open, resulting in separate tears, and the edges of several nearby slats were crumpled. The largest rip measured some two-and-a-half feet long.
Eighty percent deployed, the P6-4B array can generate 97 percent of the electricity of a fully extended wing. The station is not yet using power from the torn array, but engineers say tests confirm no major damage to its internal wiring.
The immediate concern is figuring out a way to fully extend the P6-4B wing to provide the necessary structural rigidity. With a partially deployed panel, none of the arrays on the left side of the main power truss can be rotated as required to track the sun without risking additional damage. As a result, the station's left-side solar alpha rotary joint, or SARJ, is locked in place until the damage is fixed.
Adding to NASA's problems, the station's right-side arrays also are locked in place because of unexpected metallic contamination inside the starboard SARJ. Parazynski and Doug Wheelock were in the process of gearing up Wednesday for a spacewalk to inspect the starboard SARJ Thursday when NASA managers decided to focus instead on fixing the P6-4B solar blanket.
Engineers initially held out hope for a repair spacewalk Friday, but NASA managers decided early Thursday to wait until Saturday, giving engineers more time to fine-tune the plan.