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  STS-120: Fixes to ET (WAS: launch delayed?)

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Author Topic:   STS-120: Fixes to ET (WAS: launch delayed?)
cspg
Member

Posts: 6210
From: Geneva, Switzerland
Registered: May 2006

posted 08-21-2007 01:28 AM     Click Here to See the Profile for cspg   Click Here to Email cspg     Edit/Delete Message   Reply w/Quote
Report from a TV station in Orlando, Fla. says that the next shuttle mission (STS-120 Atlantis) will be delayed due to the External Tank foam problems experienced by STS-118.

Any official confirmation?

Chris.

NavySpaceFan
Member

Posts: 655
From: Norfolk, VA
Registered: May 2007

posted 08-21-2007 05:42 AM     Click Here to See the Profile for NavySpaceFan   Click Here to Email NavySpaceFan     Edit/Delete Message   Reply w/Quote
The Program Manager Press Conference I saw last night made no mention of a delay in STS-120.

Robert Pearlman
Editor

Posts: 42988
From: Houston, TX
Registered: Nov 1999

posted 08-21-2007 06:55 AM     Click Here to See the Profile for Robert Pearlman   Click Here to Email Robert Pearlman     Edit/Delete Message   Reply w/Quote
Per Bill Harwood (CBS/Spaceflight Now):
quote:
...the jury is still out on what sort of near-term fix might be needed to keep shuttles flying until the external tank problem that caused the damage can be eliminated.

"We will expect there will be some readjustment to our schedule as we work through those options," said Program Manager Wayne Hale. "However, I believe that based on the discussions we've had, that our impacts to the next flight, in terms of the actual launch date of Oct. 23, will be small."

...

[Quoting Hale] "Today we had about a two hour telecon with the tank designers and the folks that are working on five different options to improve the situation on the next tank. We will expect there will be some readjustment to our schedule as we work through those options. However, I believe that based on the discussions we've had, that our impacts to the next flight in terms of the actual launch date of Oct. 23 will be small, we think we have plenty of time to evaluate some changes and in fact implement them if we feel that they are well justified.

"We are also looking at the further implications to the next flight because as we take time to prepare this tank it does impact the schedule on the subsequent flight and we would really like to hold that flight to the December launch window if we can do it safely. And I think that's the clue. As we look to the manifest ahead of us, we can expect there will be challenges, whether they're from hurricanes or from equipment that is causing us a problem on board the shuttle. However, we do have an amount of time ahead of us, a skilled work force and a umber of options that will allow us to fly the manifest as it's been laid out and complete the international space station with a significant margin of time before the date that the president and the congress have directed us to retire the space shuttle vehicle."


Robert Pearlman
Editor

Posts: 42988
From: Houston, TX
Registered: Nov 1999

posted 08-24-2007 05:14 PM     Click Here to See the Profile for Robert Pearlman   Click Here to Email Robert Pearlman     Edit/Delete Message   Reply w/Quote
NASA hosted a media teleconference today to discuss a review of the STS-120 external fuel tank. The briefing, provided by Space Shuttle Program Manager Wayne Hale, gave the status of ET-120, the external tank for Discovery's mission, targeted for launch on October 23.

According to Hale, as a result of the lessons learned during STS-118, changes are being made to the external tank's liquid oxygen feedline brackets, but he does not believe they will impact the launch date of either STS-120 or the subsequent flight, STS-122 targeted for a December launch window.

The changes to ET-120 precede an in-progress upgrade to the tank, which will see the foam-covered brackets replaced with titanium fittings that require no foam. The new brackets are scheduled to first fly on STS-124 in April 2008.

"We think that that final solution, which we'll have in four flights, will be a good solution into the problem," said Hale, "but in the interim we felt it was necessary to consider our options and what we might do to improve our risk situation from this sort of event happening again, perhaps incurring worse damage."

Hale explained the situation:

quote:
Part of the review of the video indicates that we potentially lost an underlying thermal protection agent called super lightweight ablative, SLA [pronounced slaw] as it is commonly called, which was added to this fitting of the tank when we felt we were going to fly different trajectories which have a higher heating during ascent. We now know and have known for some time that the super lightweight ablative is not really required. The damage that we saw on STS-118, given the trajectory, the size and speed of the debris could not have been caused, we don't believe by the lightweight foam alone so it must have had a heavier weight component, either the SLA underlying that foam or potentially ice on the foam.

As part of the investigation we decided that the next tank in line to fly, ET number 120, which is down at Kennedy Space Center, should be examined and we in fact X-rayed the five brackets on the liquid oxygen feedline over the last few days and found indication that the underlying SLA thermal protection system had cracks in it. The exact origin of those cracks is still under investigation. We think it is associated with the manufacturing process, but clearly this could lead to a shedding of foam debris along with this heavier weight SLA, which we know now could have a debris transport path to the underside of the orbiter.

Therefore, we have decided this is an unacceptable situation and we are in process today at the Kennedy Space Center of removing all the areas of foam and SLA on those five brackets, or at least four of the five brackets — the last bracket we probably don't have to do that to — but at least the first four brackets [foam and SLA] will be removed and then we will replace that with only the lightweight foam, which will provide us the ice growth inhibiting function and certainly is acceptable for all ascent phases.

We think this work will take about nine days, give or take, in the Vehicle Assembly Building. We have looked at the launch schedule and that will still allow us with the number of days of reserve to launch the next shuttle mission on October the 23rd and we're looking at downstream schedules, but at first review of those schedules, it appears we can still launch the subsequent mission in the December launch window that we have available to us with very little to no contingency time but certainly still within that December window.

Those schedules of course, will need to play out over time while we do this repair work. The work will be done by workers from the Michoud Assembly Facility, who are traveling to Florida to do that work over the weekend, start that work probably Sunday, or certainly no later than Monday.


Jay Chladek
Member

Posts: 2272
From: Bellevue, NE, USA
Registered: Aug 2007

posted 08-24-2007 11:26 PM     Click Here to See the Profile for Jay Chladek   Click Here to Email Jay Chladek     Edit/Delete Message   Reply w/Quote
Great reporting as ever Rob. Only thing is with all these upgrades to the External Tank I am sort of reminded by a line from Star Trek III...

"Very good Mr. Scott, you've fixed the barn door after the horses have come home."

It does seem a little sad that when the shuttle fleet retires in a little over 2 years that they will probably have managed to overcome all (or nearly all) the challenges with foam shedding that the design had when Columbia burned up. Then the reset button will get hit again as it did after Apollo and they will go working on a new system that has a new set of challenges that have yet to be discovered.

BTW, are there any images of the new titanium feedline brackets? The design change does sound interesting.

All times are CT (US)

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