Shuttle boss 'optimistic' about three flights in '06
BY WILLIAM HARWOOD
STORY WRITTEN FOR CBS NEWS "SPACE PLACE" & USED WITH PERMISSION
Posted: February 28, 2006
If NASA can get the shuttle Discovery off the ground on the second post-Columbia mission this spring or summer, the agency will have a realistic shot at launching three flights this year, program manager Wayne Hale told reporters today.
But the shuttle program faces a wide variety of complex technical challenges as it readies Discovery for launch as early as May 10, including critical wind tunnel tests to prove external tank modifications will work as expected; engineering studies to determine whether additional changes are needed; resolution of main engine seal and contamination concerns; and a success-oriented processing schedule that assumes no major problems develop between now and then.
Even so, Hale said he remains "very optimistic that if we can fly in May or July, that we'll get three flights, three shuttle flights, up in this calendar year."
That assumes, of course, that no large pieces of foam insulation break away from shuttle fuel tanks during launch and that whatever debris does fall off doesn't cause any serious damage.
"It does depend on what happens with those flights because when we get back from a mission, we have to review what happened and see if there's anything that affects the next flight," Hale said.
"We have been holding a series of management meetings to make sure we have the right resources staged to be able to look at any in-flight anomalies and come a resolution on them in the 10 or so weeks we'd have between flights. That is going to be a challenge to change from this kind of interregnum period, where we've had lots and lots of time to work on anything and everything to the maximum extent possible down to something that says well, we need to kind of turn the crank here and do what is reasonable and proper, surely, but probably not guild the lily. ... I remain optimistic that if we fly this summer, we'll be able to get three flights off this calendar year. But time will tell."
"The real tough question is, will we come to a reasonable consensus that we have done enough to mitigate foam loss once again," he said. "And there are probably a dozen other issues that we're looking at on a daily basis. One of those could turn out to be a speed bump. But as of today, I see no reason to say anything other than we are progressing toward May. I remain optimistic. There's a lot of work to be done. I will commit to you and to the team and to the crew that we won't proceed until we have done the work that we need to do to prove it's safe to fly."
Hale will chair a program requirements control board - PRCB - meeting Thursday that will consider making the following dates "no-earlier-than" launch targets:
Because of photo-documentation requirements to launch the next flight in daylight, and to ensure external tank separation in daylight half a world away, NASA has to deal with limited launch windows. The next three useable windows are May 3-22; July 1-19; and Aug. 29-Sept. 14. NASA would give up the daylight launch constraint for an emergency mission and may give it up for flights after May if the upcoming mission suffers no major foam loss and if ongoing analysis shows new cameras and radar systems could detect debris shedding in darkness.
As it now stands, NASA will be extremely hard pressed to make May 10. Launch director Mike Leinbach said the processing schedule has no built-in contingency time to handle unexpected problems.
"External tanks typically are not in the critical path for a launch," he said. "That's not the case this time. This time, when the tank shows up it is in the critical path to get to a May launch attempt. ... We used to provide on the order of 25 to 30 days of contingency in the whole processing flow, from the tank, through the SRBs, the orbiter processing and the vertical flow out at the launch pad. What we've done this time is, we've put together a schedule that has no contingency in it.
"Some people could call that an aggressive schedule. I like to call it an exciting schedule. It has a reasonable chance of success. If we run into a significant technical issue, we don't have much time to resolve it, obviously. But barring the big 'gotcha' in the processing, we feel pretty good about making that schedule."
An official launch date will not be set until much later in the processing flow and "we will run right down to the wire to whatever the launch date turns out to be," Hale said of the ongoing work and analyses. "Right now, I have asked, we've put in a request for the team to evaluate a May 10 launch date. We're going to review the response to that request on Thursday. I expect, and already have been given some hints, that there are going to be some poke outs. The question is not are there poke outs, the question is how many and can we mitigate them. ... We're going to have a very interesting discussion Thursday."
The major change to the shuttle's external fuel tank is removal of two protuberance air-load - PAL - ramps that ran up the lower hydrogen section of the tank and the upper oxygen section. The ramps were in place to shield two external pressurization lines and a critical cable tray from potentially damaging aerodynamic buffeting as the shuttle rockets through the sound barrier shortly after launch.
But during Discovery's launch on the first post-Columbia mission last July, a large piece of the hydrogen PAL ramp broke off. In the wake of that incident, NASA managers decided to re-evaluate the engineering justification for the PAL ramps and tentatively concluded, based on computer modeling, that the design was overly conservative and that the ramps weren't needed.
The ramps were then removed from ET-119 and the huge tank was shipped to Florida on the assumption upcoming high-speed wind tunnel tests using mock ups of tank hardware will confirm computational fluid dynamics modeling. If they don't, all bets are off.
"The computer simulations and the paper analysis indicates that the structure should be able to take the aerodynamic loads that we generate on the cable tray, particularly after we removed the PAL ramp. But the proof is in the wind tunnel testing. We've got a series of wind tunnel tests, the first kicks off in just a couple of weeks at the Glenn Research Center, and we hope to get the data that will confirm what we hope is conservative engineering analysis on paper. If we find a surprise in the wind tunnel ... then we'll go deal with that.
"When we look forward to the launch date, the thing that is going to pace getting Discovery off the ground is not the work that we're doing at the Kennedy Space Center, because we believe we have that well in hand and know what to do, but it is the engineering analysis and tests that go toward proving that what we have assembled on the launch pad is safe to fly."
Overall, NASA engineers believe changes to the tank in the wake of Discovery's last mission will limit the size of any foam debris to small one-ounce chunks the size of a matchbox or smaller. The chunk of foam that came off during the July mission weighed more than a pound. Other areas of foam loss also have been addressed.
"Just to make it perfectly clear to you, foam will still come off the tank after we have done all of these mitigation efforts," Hale said. "What we have done is worked off all the large pieces and we believe the pieces that come off will be small. ... Our task ahead of us is to ensure that all of these very small pieces of foam, most of them less than an ounce, will be of a size that they cannot have enough energy to do damage if they strike the orbiter. So that is work ahead of us.
"I wanted to make sure everyone understands we are trying to eliminate critical foam loss, but we will expect to see foam coming off this next tank. As we go forward in the manifest for the next several flights, we'll continue to make improvements so we can eliminate even smaller and smaller pieces of foam loss."
Along with final tank modifications, the wind tunnel testing and on-going analysis of the launch debris environment, NASA also faces additional work to complete servicing of Discovery's heat shield tiles and resolution of concern about out-of-specification main engine seals and metallic debris trapped in a main propulsion system oxygen propellant line.
Hale said he is optimistic the seal issue will not hold up the launch even though at least some of the six seals in question do not meet printed specifications. The propulsion system has passed a helium signature leak test and engineers currently are evaluating whether the fact that some of the seals are slightly too thin could cause any problems. If worse comes to worse, the current seals can be replaced - even at the launch pad - but it's not clear if such work could be done in time to support a May 10 launch attempt.
The other propulsion system issue - debris trapped in a main engine liquid oxygen inlet filter - is less clear cut. At issue is the nature of the debris. If it is made of titanium, it could pose an ignition threat during engine operation. There is no titanium in the liquid oxygen system and engineers say it's probably a metal that poses no threat. But they can't prove it. The debris cannot be removed without breaking open the propulsion system, which engineers don't want to do out of fear the fix might cause additional problems.
"We can't get it out," said Leinbach. "To open up the system, to clean the screen, is an extensive job. It still fits the processing flow, but it's an extensive job, one that we don't want to do. But if the program decides it's a risk to flying and we need to pull it out, we'll do it."