Space Shuttle Discovery Launch Delayed Again
More Work Required To Review Data, Perform Tests, Before Experts Will Be Comfortable With Flight Safety
Another Flight Readiness Review May Be Held; No Liftoff Seen During March 13-April 6; 2009 Launch Manifest Retained
The launch of Space Shuttle Discovery on the STS-119 Mission to the International Space Station has been delayed yet again, with no new date set for liftoff, senior NASA officials said in a news conference.
Perhaps by Wednesday, enough unknowns will be clarified and answered that a new launch date can be set.
At issue is a hairline crack that can develop in any of three flow control valves in the fuel lines feeding from the external fuel tank to the shuttle main engines, with fears that the crack might enlarge and a tiny piece of the valve might break off and cause dangerous damage in the fuel lines. (Please see Space & Missile Defense Report, Monday, Feb. 9, 2009.)
Discovery was to lift off Feb. 12, and recently was set for a Feb. 29 launch.
Announcing the further delay of the mission, Bill Gerstenmaier, associate NASA administrator for space operations said, "I’m not even picking a target launch date this time," preferring to let experts take their time to further assess the flow control valve problem.
He and John Shannon, the shuttle program manager, and Mike Leinbach, the shuttle launch director, explained the situation to space journalists after a marathon 13-hour shuttle flight readiness review meeting at Kennedy Space Center.
They each portrayed the shuttle as very nearly ready to fly, with all open items now closed as the shuttle awaits preparation for flight.
"We still need to do a little bit more work" in evaluating "the consequences if a piece [of the flow control valve] breaks off," Gerstenmaier said.
"We were really close to having the entire team" sign off and clear the shuttle to fly, Shannon said. But there were "small errors" in some assumptions, and "we did not have the rigor" usually seen in presentations at shuttle flight readiness reviews. There was, Shannon said, "a sense of unease," with not enough time to review and mull over data, and a desire to repeat some tests and gain more peer reviews. And as the flight readiness review dragged on for hours, it was getting late into the night Friday, he added.
Although "we were extremely close to" giving a green light for flight, Shannon said, even so Gerstenmaier "did exactly the right thing" in deciding to delay the mission and not set a new launch date. That delay helpfully "didn’t put any schedule pressure on the" flight readiness review team of experts.
The worries here are that if a piece of the flow control valve breaks off, suddenly the flow of fuel increases greatly, and the piece of shrapnel would be accelerated rapidly, possibly hitting part of the fuel flow plumbing to cause a disaster.
Investigators have concluded that no serious damage would occur in the external fuel tank, but there is a possibility of a damage problem in the orbiter vehicle where the crew sits.
But the irony is that every shuttle that has flown, since the first shuttle liftoff in the 1980s, has flown with those flow control valves, including a shuttle where a part of the valve did break off, and there were no untoward results. "It’s a problem that’s been there all along," Gerstenmaier said.
Shannon expects that early this week, solid information will give reviewers confidence that they know what can go wrong, and that it wouldn’t cause any serous problem or if it does, they know how to prevent it, so a new launch date can be set.
Once a launch date is established, it would take about five days to prepare Discovery for flight, unless there are delays such as installing new valves, Leinbach said.
Discovery won’t be able to launch between March 13 and April 6, though that no-fly period is flexible, because a Russian Soyuz flight will be headed for the space station, Gerstenmaier and Shannon said.
If Discovery launches after that, it is unclear what impact it might have on the timing of succeeding shuttle flights and other missions. For now, the planned order of missions likely will remain the same, Gerstenmaier said.
Questions for experts to answer before a new Discovery launch date is set include an examination of two factors with the flow control valves: how "high cycle fatigue" can cause cracks to appear initially, and then how an overload might cause the crack to enlarge and a piece of the valve to break off and zip through the plumbing.
This is "a really tough problem to solve," Shannon said, involving imponderables such as how large a piece would have to break off before some serious damage would occur.
The tiny fracture cracks are caused by flowing fuel in the system producing harmonic resonance in the valves, which produces vibrations causing the cracks.
Ultimately, NASA is looking for a permanent fix for the problem, which might involve changing the shape of the valves to eliminate the resonance, or a new material better able to withstand the resonance, or both, briefers indicated.
In the near future, there are many short term fixes being discussed.
The Discovery flight, at this point, shouldn’t be affected by debris caused when an Iridium satellite was hit by a defunct Russian satellite, Gerstenmaier said. (Please see Space & Missile Defense Report, Monday, Feb. 16, 2009.)
But perhaps the debris field of 200 pieces being tracked might affect the STS-125 Mission of Space Shuttle Atlantis to repair and refurbish the Hubble Space Telescope, he said.
Ultimately, the question that must be answered — after more than 100 shuttle flights where the valves caused no problem — comes to this:
Do all those flights where the valves caused no problem mean the valves are safe, Shannon asked, "or did we just get lucky," with the incident where a valve broke and a piece of it went flying through the plumbing serving as "a warning to us?"