CBS NEWS STS-122 STATUS REPORT: 31
Posted: 7:45 PM, 1/3/08
By William Harwood
CBS News Space Analyst
SR-31 (01/03/08): Shuttle launch no earlier than Jan. 24 as pursues parallel ECO testing/hardware replacement
7:45 PM, 1/3/08, Update: Shuttle launch no earlier than Jan. 24 as pursues parallel ECO testing/hardware replacement
NASA managers today agreed to press ahead with work to replace suspect engine cutoff - ECO - sensor connectors on the shuttle Atlantis' external tank on the assumption parallel laboratory testing will confirm the root cause of open circuits that derailed two December launch tries. Assuming the replacement work goes smoothly, the weather cooperates and the lab testing goes as engineers hope it will, Atlantis could be ready for a third launch try by Jan. 24.
But John Shannon, deputy manager of the shuttle program at the in , told reporters Jan. 24 is little more than a best-case crew training and planning target and that Feb. 2 is a more realistic launch date given the work required.
And that assumes everything goes smoothly. If the lab testing at the in Huntsville, Ala., does not replicate the December trouble, i.e., if the removed connector hardware works normally under super-cold cryogenic conditions, another on-pad fueling test might be required to collect additional data. In that case, launch could slip to around Feb. 7 at the earliest.
"There's no way we're going to be earlier than Jan. 24," Shannon said. "I would say it is a stretch to think we would make the 24th, that would require the weather to cooperate out at the , it would require no hitches in any of the testing or re-application of (foam insulation on the tank around the connector).
"But I asked the team to go ahead and protect that date as the earliest date that we could possibly go," he said. "I think it is much more likely that we'll be ready to go somewhere in the Feb. 2 to Feb. 7 timeframe, given we don't have any additional findings as we go through our testing."
A wild card in 's planning is the scheduled Feb. 7 launch of a Russian Progress supply ship from the Baikonur Cosmodrome in . Joint U.S.-Russian space station flight rules forbid a Progress docking during a shuttle visit. If the Russians stick with Feb. 7, Atlantis would have to take off by Jan. 27 or the flight would slip to around Feb. 9 to get the Progress docked before the shuttle arrives.
A more realistic launch target is expected in a week to 10 days.
Atlantis was grounded Dec. 6 and 9 when intermittent failures of ECO sensors at the base of the hydrogen tank occurred during fueling and later, draining. A fifth sensor, which indicates when the tank is 5 percent full, also malfunctioned when the tank was drained.
The ECO sensors are part of a backup system intended to make sure the shuttle's main engines don't inadvertently drain a tank dry after some other problem - a leak, for example, or an improper hydrogen-oxygen mixture ratio - used up propellant at faster than normal rates. An engine running out of hydrogen during normal operation likely would suffer a catastrophic failure.
The wires that carry signals from all four ECO sensors and the 5 percent sensor pass through the same connector in the wall of the external tank. The three-part connector features a pass-through fitting with male pins, embedded in glass, on both sides. Wires from the sensors inside the tank terminate in a female connector inside the tank that is plugged into the male pins of the pass-through. A similar female socket plugs into the pass-through on the outside of the tank.
Based on data collected during a fueling test Dec. 18, engineers believe the problem involves gaps in pins and sockets on the external side of the feed-through connector when the system is chilled to ultra-low temperatures. They believe the sensors themselves are healthy.
Engineers have now removed the pass-through pin plate and the external connector, keeping the actual pin-socket interface intact for testing. The internal connector, which cannot be replaced at the pad, was inspected and no obvious problems were seen.
The feed-through plate with the external connector still attached has been shipped to the for additional testing at cryogenic temperatures. Engineers are hopeful they will see the same sort of continuity problems that cropped up during last month's launch tries. If so, managers will have higher confidence the issue is, in fact, understood.
"It's a difficult problem," Shannon said. "I'm not making excuses here, but at liquid hydrogen temperatures is the only time it shows up so you have to set up a test that uses liquid hydrogen. We're very interested (in the results), this is the first time we've removed (this) hardware from a vehicle and had the opportunity to test it without disturbing it before hand. So it will be interesting to find out."
While the testing is going on at Marshall, engineers at Kennedy will replace the pass-through plate and external connector with hardware featuring soldered pins and sockets. A similar design was successfully implemented in the 1990s by to address problems with hydrogen-fueled Centaur rocket stages.
Along with soldered pins and sockets, the replacement hardware will feature what amounts to additional slack to permit temperature-induced motion in the wiring that otherwise might put stress on the connector. The modifications should eliminate any possible electrical continuity problems in the external connector hardware.
"All of those changes, it's fairly simple, it's a fairly elegant change and we feel very confident that if the problem is where we think it is, between the external connector and the feed through, that this will solve that," Shannon said. "Now, if you look at the schedule, we're going to have new external connectors and feed-through assemblies at KSC this weekend and we're going to proceed with installing that on external tank Number 125, which is the one Atlantis is currently mated to. We expect that work to be done by next Thursday.
"We're going to do that change and it will occur before we're finished with all our testing out at . We had some discussions on that. We are taking some schedule risk on the program side that if we go through our testing at Marshall and determine there's a new failure mode or something we didn't expect or we learn something new, we might have to go and take that back out. But we feel very confident we are addressing the real problem."
originally planned to launch the shuttle Endeavour on Feb. 14. But the Atlantis delay will force a corresponding slip for Endeavour. Shannon said typically requires five weeks between launches to complete a given mission and provide time to evaluate in-flight problems before launching the next flight.
Shannon said NASA managers have not yet assessed how subsequent flights might be affected.
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