Shuttle Atlantis tentatively cleared for launch
BY WILLIAM HARWOOD
STORY WRITTEN FOR CBS NEWS "SPACE PLACE" & USED WITH PERMISSION
Posted: January 30, 2008
Exhaustive testing shows the low-level fuel sensor problem that derailed two attempts to launch the shuttle Atlantis in December has been resolved, NASA managers said today, and engineers are confident soldered connectors will prevent a repeat of the open circuits that grounded the ship two months ago. But a decision on whether to press ahead with a third launch try Feb. 7 was put off to Saturday pending results of last-minute troubleshooting to assess the health of a kinked flex hose in the ship's Freon coolant system.
In what engineers thought was an isolated case, a similar kink was noted last year aboard the shuttle Discovery and engineers were somewhat surprised to find another unexpected bend in one of four such hoses aboard Atlantis that leads from the orbiter's fuselage to radiators on the inside of the shuttle's cargo bay doors.
The shuttle's computers and other electronic systems are mounted on cold plates that use circulating water to carry away heat. That heat is then transferred to two Freon coolant loops that, in turn, carry it to the cargo bay radiators for dissipation into space or to an internal system that boils water to accomplish the same goal.
The concern with the kinked line is that launch vibrations, coupled with stress on the line, could cause a leak. That could force the crew to bypass the radiator in question and rely instead on the flash evaporator system, an option that could affect the duration of the mission.
Shuttle Program Manager Wayne Hale told reporters today after an executive-level flight readiness review that he's optimistic the problem will be resolved in time to proceed with launch on Feb. 7, either by agreement to launch Atlantis as is or to simply straighten out the hose before flight.
"I think we'll have a good answer by Saturday," he said. "Since the hose is not leaking now and a sister hose on Discovery did not leak on a number of flights when it was exhibiting this behavior, I'm feeling very positive we'll come to a good conclusion on this. But we have to do our work here and we want to make sure we know what we're doing before we go fly this vehicle."
On a more upbeat note, Hale said engineers are confident the low-level engine cutoff - ECO - sensors at the base of Atlantis' external tank will work properly following replacement of the so-called pass-through wiring connector with a modified design that features soldered pins and sockets.
Launch attempts Dec. 6 and 9 were scrubbed because of open circuits in the ECO sensor system. The ECO sensors serve as a backup to ensure the main engines don't suck a tank dry in the event of some other problem that might cause them to consume hydrogen fuel faster than expected.
Hale said engineers traced the problem to a temperature-induced loss of continuity in the pins and sockets making up the external side of the pass-through connector. By soldering the pins and sockets together, engineers believe they have eliminated the failure mode.
"We had a multi-disciplinary team from a number of NASA centers, as well as a number of contractors, working together in a unified manner and we have come to a root cause, we believe, for our problems that we've been having in those circuits," Hale said. "There is a good solid repair, or fix, technique which has been implemented and we have a lot of testing that's gone on to prove that this fix is a good fix, does not entail any unanticipated consequences and will provide us with a reliable safety system in the low level cutoff protection world.
"The work is complete on the vehicle at the launch pad and we're beginning to implement that fix on subsequent tanks so that we won't ever have to talk about engine cutoff sensors again," he said.
NASA's original ECO sensor launch commit criteria required three of the four circuits to be operational for a launch to proceed. That rule later was changed to four-of-four because of concern about a common component that, should it fail, could take out two circuits. After that issue was addressed, the rule was changed back to requiring three of four operational circuits.
That's the rule that was in place for Atlantis's initial launch try, but it was amended to four of four for the second attempt, primarily because engineers did not yet know what was causing the problem.
Now that testing indicates the problem has been resolved, NASA managers have agreed to go back to the original three-of-four criteria, "which is the design intention for that system," Hale said.
"On this first tanking with the new system in place we're going to watch it very closely to ensure that we really have eliminated the common cause mechanism," he said. "If there are any funnies that happen, they will be scrutinized very carefully. ... I expect when we go tank up the vehicle next Thursday we'll be in good shape to go fly."
Concern about the Freon hose cropped up Tuesday when Atlantis's cargo bay doors were opened for routine payload processing. Engineers noticed one of the two flex hoses leading to the shuttle's right-side radiator had not retracted properly and was bent sharply when it should have been straight.
"This (hose) goes down into a box, it's got some rollers and a spring mechanism to kind of suck this hose down as the payload bay doors close and clearly something is not lining up in that box properly," Hale said. "So we'll figure it out, but today I don't think anybody knows what's causing it."
The hose in question is located under the European Columbus research module bound for the international space station. While engineers may be able to manually straighten the hose, replacing it might not be possible at the launch pad because of access issues and rules governing the release of Freon into the atmosphere. Hale said he is optimistic it won't come to that.
"Right now, that hose is perfectly functional," he said. "We're not leaking, it's in good shape. It's just kind of bending the wrong way. Fortunately, we have the hose we took off the sister ship, Discovery. We now have good knowledge we've flown at least two flights, perhaps more, with this kind of bend in the hose and that hose did not leak. It has been removed from (Discovery) and taken to the Boeing Co.'s laboratories in Huntington Beach, Calif., where we're doing a great deal of work to understand whether or not this is a threat to us. I would repeat again that this hose on Atlantis is not leaking, It's just merely bent the wrong way. So we're trying to understand that."
NASA managers will meet again Saturday to review the troubleshooting and make a decision on whether to press ahead with launch preparations. Liftoff is targeted for 2:45 p.m. on Feb. 7.
"Hopefully, and I'm going to be positive about this, we will come to the conclusion that this is acceptable to fly at least one flight, either exactly like this or potentially, having (to) manually straighten this hose out and then flying it. So that is work ahead of us that we must clear before we go fly."
Otherwise, he said, all systems are go for launch.
"I had a nice discussion with the commander of the flight, Steve Frick, in Houston a few days ago, they're ready to go, all the elements report ready to go and if we didn't have this hose to talk about, it, frankly, would be a little boring."