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  STS-118: Foam damage to thermal tile (Page 1)

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Author Topic:   STS-118: Foam damage to thermal tile
Lunatiki
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posted 08-10-2007 06:56 PM     Click Here to See the Profile for Lunatiki     Edit/Delete Message   Reply w/Quote
quote:
CAPE CANAVERAL, Fla. (AP) - NASA discovered a worrisome gouge on Endeavour's belly soon after the shuttle docked with the international space station Friday, possibly caused by ice that broke off the fuel tank a minute after liftoff.
NASA Finds Gouge on Endeavour's Belly

Robert Pearlman
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posted 08-10-2007 06:59 PM     Click Here to See the Profile for Robert Pearlman   Click Here to Email Robert Pearlman     Edit/Delete Message   Reply w/Quote
From Bill Harwood (CBS/Spaceflight Now):
quote:
"What does this mean? I don't know at this point," [Mission Management Team chair John Shannon] said. "On flight day five (Sunday), we had preplanned a time in the timeline when we could do a focused inspection and we will do that on this spot. ... They will take the orbiter boom sensor system with the laser on it, they wlll put it underneath the vehicle and get a very high fidelity model of exactly what the damage is. It's too hard to tell from a two-dimensional picture with different shading to tell if this gouge is deep or it's not deep.

Lunatiki
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posted 08-10-2007 07:01 PM     Click Here to See the Profile for Lunatiki     Edit/Delete Message   Reply w/Quote
I didn't think too much about it till I read in the article that the gouge is appearing as white, under the black tiles. Does this mean the gouge goes completely though the heat shield tiles?

Robert Pearlman
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posted 08-10-2007 07:13 PM     Click Here to See the Profile for Robert Pearlman   Click Here to Email Robert Pearlman     Edit/Delete Message   Reply w/Quote
quote:
Originally posted by Lunatiki:
Does this mean the gouge goes completely though the heat shield tiles?
No, all black heat shield tiles have only a thin layer of black coating, under which they are white. Thus the gouge could be shallow or deep.

The reason for some concern is that Shannon said that they could see some "color" where the tile comes up against another tile.

"Potentially, that color is the material on the edge of the tile at the very base of the aluminum structure. It's called filler bar material. We don't know that for a fact, but it's certainly got our attention and we're looking at it."

And that's what needed: a closer look. Right now, there's no way to tell if the divot merits concern or is nothing to worry about. And should it become of concern, if necessary, the crew has the tools aboard to repair it and the time to do so.

Robert Pearlman
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posted 08-10-2007 07:50 PM     Click Here to See the Profile for Robert Pearlman   Click Here to Email Robert Pearlman     Edit/Delete Message   Reply w/Quote
Three views of the possible ice strike:

Main landing gear door

External Tank (ET) door

Close-up of the gouge

Robert Pearlman
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posted 08-10-2007 07:53 PM     Click Here to See the Profile for Robert Pearlman   Click Here to Email Robert Pearlman     Edit/Delete Message   Reply w/Quote
NASA has posted a looped video of the possible debris spray.

Robert Pearlman
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posted 08-11-2007 10:16 PM     Click Here to See the Profile for Robert Pearlman   Click Here to Email Robert Pearlman     Edit/Delete Message   Reply w/Quote
Mission Management Team chair John Shannon briefed the media tonight regarding the tile damage on Endeavour's underside.

"We have significantly more data today, specifically about the cause, the location of the damage and previous flight history. We had left here yesterday not knowing exactly what had occurred to cause that damage and we had a lot of homework to do," said Shannon.

There is a 17-inch diameter liquid oxygen (LOX) feedline that runs down the side of the external tank, which feeds the orbiter main engines. Along that feedline there are several brackets that hold the line in place.

The brackets are designed to allow the feedline to flex with the vibration of the vehicle in flight. If ice builds up between the feedline and a bracket, the line doesn't have anywhere to move, so the ice can then exert pressure on the foam covering the bracket, which in turn can then knock off a piece.

This is what happened on STS-118: one of the brackets on the feedline had a softball-sized piece of foam come off and instead of falling harmlessly away from the vehicle (as had happened on STS-115), the foam hit a strut that connects the orbiter to the external tank. A part of that foam then shot straight up into the belly of the orbiter, causing the damage.

"It was a bad bounce off that external tank strut," said Shannon. "The only reason it hit the vehicle on this flight is that it bounced off that external tank strut."

It is unknown if that foam piece had some ice attached.

"I know that ice is the forcing function to make that piece of foam come off. I don't know if any ice was stuck to it as the foam fell," said Shannon.

The location where the foam hit was directly over a stringer, or a structural member inside the wing.

"We don't know if we'll have any elevated temperatures in that area or not, but if we did though, being under a stringer is extremely good because that provides a much greater heat sink," Shannon explained. "There is nothing in there. There are no wires, hydraulic lines, tanks, computers, really anything. It is a really empty spot so if you had some kind of damage or some kind of flow in there, it would not have any subsystems that it could impact."

Moving forward, the plan stays the same.

"The forward plan is still as I briefed yesterday — that we will do a focused inspection tomorrow, which is where you put the [inspection] boom on the end of the shuttle arm and go look at that area very closely with a laser that can give you a 3-D picture of the damage and then run that through our thermal assessment models," said Shannon.

On their first look, Shannon and his team had thought the gouge was much deeper than they now believe it to be.

"Upon further review, we don't think it really went all the way down to the very bottom [of the tile]. We will know that tomorrow after the focused inspection but for our thermal modeling initially, we just assumed it went all the way down to the base of the tile."

Working under that assumption though, Shannon said that in the case of an emergency, he would clear the vehicle to land as it is now.

"It's a risk versus risk judgment," explained Shannon. "Based on the flight history that we saw, based on this location and based on that thermal analysis, it was a unanimous consensus in the mission management team that if we had an emergency, that we would be okay to deorbit with the vehicle as is."

For similar reasons, Shannon felt the likelihood of sending any astronauts to repair the damage was low.

"I would say that the data we pulled together today on exactly where the location, what is under that location and the flight history data, I would say that [a repair] is much more doubtful than it was yesterday."

Looking beyond just this flight, Shannon said a change was already in the works to prevent such foam pieces from falling off in the future.

"After STS-121 where we had the piece come off pre-launch, the External Tank Project initiated a redesign of those brackets that uses titanium as opposed to a foam-covered metal. That titanium fix will debut on external tank 128, which is the flight before the Hubble Space Telescope [mission]."

Edited by Robert Pearlman

Robert Pearlman
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posted 08-11-2007 10:28 PM     Click Here to See the Profile for Robert Pearlman   Click Here to Email Robert Pearlman     Edit/Delete Message   Reply w/Quote
Three related images:

The above shows a damaged external tank feedline bracket taken by the STS-115 crew after ET separation. It is believed that a similar, softball-sized piece of foam was responsible for the damage to Endeavour.

This graphic shows the actual bracket on Endeavour's external tank taken pre-flight and the damage to the external tank strut as a result of the bracket's foam bouncing off it.

Lastly, this image shows damage to six tiles on shuttle Discovery, photographed after STS-26 safely landed. The damage is believed to be of the same severity as is currently on Endeavour.

mjanovec
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posted 08-12-2007 12:04 AM     Click Here to See the Profile for mjanovec   Click Here to Email mjanovec     Edit/Delete Message   Reply w/Quote
Even if the gouge isn't as deep as they originally thought it was, I would still like to see them attempt a repair in space. If nothing else, such a repair will demonstrate their capabilities if future gouges deeper gouges are discovered.

Robert Pearlman
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posted 08-12-2007 12:16 AM     Click Here to See the Profile for Robert Pearlman   Click Here to Email Robert Pearlman     Edit/Delete Message   Reply w/Quote
quote:
Originally posted by mjanovec:
If nothing else, such a repair will demonstrate their capabilities if future gouges deeper gouges are discovered.
If nothing else, it puts astronauts' lives at increased risk and introduces the possibility of them inadvertently damaging the orbiter further.

Demonstrations of the repair techniques were conducted during STS-114 and STS-121, which led to the repairs being approved for flight use.

Besides, the astronauts have a full slate of scheduled EVA activities that need to completed for the ISS. Diverting them to a task that isn't required is not the best use of their limited time in space.

Lunatiki
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posted 08-12-2007 11:17 AM     Click Here to See the Profile for Lunatiki     Edit/Delete Message   Reply w/Quote
Diverting them to a task that isn't required is not the best use of their limited time in space.

NASA can't afford not to repair it. The stakes are way too high. Engineers said the STS-107 foam strike was not to be worried about. If they thought a spacewalk was needed to remove a small piece of gap filler sticking out, I don't see how they can say this gouge is worth the risk of leaving it alone. I don't think they have a choice.

Edited by Lunatiki

SRB
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posted 08-12-2007 12:11 PM     Click Here to See the Profile for SRB   Click Here to Email SRB     Edit/Delete Message   Reply w/Quote
Since the astronauts are taking close up pictures today, I would wait to see what can be learned from the pictures before deciding for or against trying to repair the tile(s) during this mission

Robert Pearlman
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posted 08-12-2007 12:17 PM     Click Here to See the Profile for Robert Pearlman   Click Here to Email Robert Pearlman     Edit/Delete Message   Reply w/Quote
quote:
Originally posted by Lunatiki:
Engineers said the STS-107 foam strike was not to be worried about.
No, they did not. Engineers asked for a closer look so that they could study any damage and then decide if further action was needed, which describes exactly what NASA is doing as I write this.

Further, damage to tile is not the same as damage to RCC. A hole in the RCC, such as on the wing leading edge during STS-107, leads to structural failure.

A hole in a tile, depending on where it is and what is under it, can be perfectly harmless (as has been demonstrated by practically every shuttle flight in history).

The primary difference between flights prior to and post Columbia is the ability to inspect the orbiter using the OBSS boom. Literally, at this very moment, the crew on Endeavour is using the arm and boom to shine a laser at the damage, collecting enough data to create a 3-D model for thermal analysis.

Should the results they return match what is thought to have happened, then a repair will not be necessary and the shuttle will be at no risk because of it. As explained above, to do a repair for its own sake is to put the astronauts and the vehicle at unnecessary risk.

KSCartist
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posted 08-12-2007 12:28 PM     Click Here to See the Profile for KSCartist   Click Here to Email KSCartist     Edit/Delete Message   Reply w/Quote
I am curious about one thing...

On flight day 2 when they scanned the TPS didn't they see this then? Or was it only discovered during the "back-flip" prior to docking at the ISS?

Tim

Lunatiki
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posted 08-12-2007 12:32 PM     Click Here to See the Profile for Lunatiki     Edit/Delete Message   Reply w/Quote
No, they did not. Engineers asked for a closer look so that they could study any damage and then decide if further action was needed, which describes exactly what NASA is doing as I write this.

Well, if they decided the STS-107 foam strike wasn't cause for worry, what did they decide?
I remember reading some material where an engineer expressed great concern about the foam stike, but his concerns weren't really taken seriously from what I gathered. If they were concerned, why no images for the impact site on the wing from a satellite, which I believe an engineer requested informally. If my memory serves me, I believe one member of NASA said, paraphrasing "this has happened before, its OK". I forget her name, but I do know she is no longer employeed by NASA. In her resignation letter, she tried to defend the lack of concern. I'll try to find the woman's name and letter.

I'm a novice compared to most on this board, but I can't see NASA taking the risk of not repairing it. The whole program and astronauts lives are at risk. Like I said, spacewalk to remove gap filler, but not repair this?

Edited by Lunatiki

Robert Pearlman
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posted 08-12-2007 12:54 PM     Click Here to See the Profile for Robert Pearlman   Click Here to Email Robert Pearlman     Edit/Delete Message   Reply w/Quote
quote:
Originally posted by KSCartist:
On flight day 2 when they scanned the TPS didn't they see this then? Or was it only discovered during the "back-flip" prior to docking at the ISS?
The inspections on flight day 2 only image the top surfaces of the orbiter: the nose cap, wing leading edge and blankets. The rendezvous pitch maneuver (the "back flip") is specifically performed to allow the ISS to image the underbelly of the orbiter.

The damage in question was seen as a result of the RPM.

Robert Pearlman
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posted 08-12-2007 01:16 PM     Click Here to See the Profile for Robert Pearlman   Click Here to Email Robert Pearlman     Edit/Delete Message   Reply w/Quote
quote:
Originally posted by Lunatiki:
I believe one member of NASA said, paraphrasing "this has happened before, its OK". I forget her name, but I do know she is no longer employeed by NASA.
You are referring to former mission management team chair Linda Ham, and you are correct: the decision to not collect additional imagery was made because it was (incorrectly) believed at the time that foam was too light to pose an impact threat to the orbiter.

As they say, 'that was then, this is now'. We now have the capability and mandates to inspect the orbiter like never before. Any guess work is completely removed from the process as they can now definitively say whether an impact is of concern (or not) based upon the data they collect. As such, they can clear damage areas from needing repair, based upon the focused inspections and resulting thermal analysis.

quote:
Like I said, spacewalk to remove gap filler, but not repair this?
During Steve Robinson's STS-114 spacewalk, he never came into contact with the underbelly of the orbiter. He simply plucked the gap filler. For a repair, the STS-118 astronauts would, by definition, need to come in contact with the tiles, which presents an increased risk for further damage.

During STS-114, the data collected about the gap filler suggested that it could cause increased heating as Discovery reentered, necessitating its removal. On STS-118, a protruding shim stock was also spotted (in addition to the tile damage), but given its plastic composition, it will disintegrate early in the reentry, posing no risk to the orbiter, thus not requiring a repair. Each issue is different and it's the data that is collected that drives the decision as to whether to clear the vehicle for reentry or execute a repair.

Lunatiki
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posted 08-12-2007 01:44 PM     Click Here to See the Profile for Lunatiki     Edit/Delete Message   Reply w/Quote
Thanks Robert. A wealth of information as always.


Joel

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posted 08-12-2007 03:08 PM     Click Here to See the Profile for Blackarrow     Edit/Delete Message   Reply w/Quote
quote:
Originally posted by Lunatiki:
Like I said, spacewalk to remove gap filler, but not repair this?

A gap-filler sticks up into the super-heated plasma rushing past the surface of the orbiter during re-entry. This could cause hot-spots. A shallow gouge in a tile (I stress "shallow" - let's see what the detailed tests show) does not protrude into the plasma and is not such a problem.

I also thinks it's worth pointing out that on STS-1, several complete tiles were lost on launch from an OMS pod, in an area where they now consider it necessary to fit high-temperature black tiles.

Robert Pearlman
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Mission Management Team chair John Shannon briefed the media this afternoon regarding the tile damage on Endeavour's underside.

"As you can see, and what we had thought coming out of the flight day 2 might be a possibility, is that it's a fairly deep gouge," explained Shannon. "If you remember, the tile itself is 1.2 inches thick, and the gouge goes pretty much through the entire thickness of the tile. There is a small area of what we call filler bar, which is the material that is on the edge of the tile and is what the tile is mounted to, that is showing. We think that that filler bar area is about 0.2 inches by about 1 inch. And then it impacts the second tile and just kind of took a scoop out of that."

According to Shannon, the focused inspections conducted earlier today collected the data his team needed to move forward.

"Not only did we get really good imagery, but we got a good laser scan of it as well, and the process as I've briefed before is that we will make a point-cloud map of exactly what that damage is and we'll do two things with that map."

"The first is we'll be able to model it and run our thermal analysis models to understand what the actual heating impact during reentry will be for damage of this type. The second is a test method. We have already made up two-foot by two-foot sections of tile that are about this thickness and we'll take that cloud-map and actually mimic the exact same damage on those test articles and we'll put them in the arc jet facility here at Johnson Space Center and simulate reentry conditions. That will be able to ground the analysis models with actual test data, so we feel very comfortable with that."

"I expect that we will have the thermal analysis to discuss tomorrow at the mission management team and the arc jet facility run will either be tomorrow or on Tuesday," said Shannon.

The results of those tests will determine if a repair is necessary.

"If it comes back that a repair is something desirable to do, we have three different methods of doing that. I don't have an idea right now whether a repair will be required or if so, which type of repair will be required," Shannon said. "I have a lot of confidence based on the testing that we have done, if a repair is required that we could go execute it."

NASA would not however, conduct the repair only as a demonstration or test.

"Would I do that as a DTO [demonstration test objective]? No, if I wanted to do a DTO or a test of these materials, I would do it under very controlled conditions in the payload bay itself and not take the risk of putting a crew member on the boom, underneath the vehicle, where potentially more damage could take place," Shannon said.

"If it's required we'll do it, if it's not required we won't do it. As to which way we'll go, we'll see through the analysis over the next 24 to 48 hours."

Jay Chladek
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posted 08-13-2007 12:57 AM     Click Here to See the Profile for Jay Chladek   Click Here to Email Jay Chladek     Edit/Delete Message   Reply w/Quote
quote:
I also thinks it's worth pointing out that on STS-1, several complete tiles were lost on launch from an OMS pod, in an area where they now consider it necessary to fit high-temperature black tiles.
The reason for the black HRSI on the fronts of the OMS pods partly came about due to some OMS pod damage during reentry on STS-9.

During a discussion with Randy Avera last year (former KSC NASA engineer) when we were both at KSC to watch the launch of STS-121, I asked him about the patch as I was conducting research for a book I am working on. If you recall the big icesickle on STS-41D from the water discharge chute, it is believed that STS-9 had something similar, but the crew didn't know about it. During reentry it broke away and slammed the TPS at the front of the left OMS pod. The graphite structure of the OMS pod was pretty close to a burn through on that side and the breach was right in front of one of the hypergolic tanks. If it had breached, well it could have been messy.

Anyway, to make a long story short, the reason for the black tile patches there are due to some wind tunnel test data collected after STS-9. They determined that if there was some plasma flow disruption around the sides of the nose, near the wing leading edges, that there could be some hot spots on the OMS pods that might have been too hot for the white LRSI tile or AFRSI to handle. So they put in the black tile patches right where the hot spots might appear. If there is no disruption of the plasma flow around the nose, then there are no temperature spikes on the fronts of the OMS pods. As such, that is why STS-1 reentered with no damage there, even with tiles missing in a couple spots.

The rest of the leading edges of the OMS pods were covered with LRSI tile there in order to provide a bit more impact damage in case of a similar ice shedding incident, although there hasn't been a similar water discharge chute malfunction since those early flights. The pods used on Columbia made large use of white tile while Challenger's pods utilized more AFRSI and FRSI on the pods. It took a few flights for the TPS pattern on the pods to evolve into what we still see on today's shuttles.

Looking at the images from today's OBSS scan passes, I only see one tile dent that mission managers might consider making a tile repair attempt at. But I don't think they are going to do it since indeed these dents are small and the plasma flow will be well over the dings. There doesn't appear to be a deep hole big enough to allow the hot plasma to dip down into contact with the surface, near as I can see.

Robert Pearlman
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posted 08-13-2007 07:02 PM     Click Here to See the Profile for Robert Pearlman   Click Here to Email Robert Pearlman     Edit/Delete Message   Reply w/Quote
NASA has posted a three-dimensional video of the tile damage based on the data collected by the focused inspections.

Robert Pearlman
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Mission Management Team chair John Shannon briefed the media this evening regarding the tile damage on Endeavour's underside.

"This is not a catastrophic loss of orbiter case at all," stated Shannon. "This is case where you want to do the prudent thing for the vehicle."

"This damage does not meet that criteria we think the astronauts are in jeopardy, that is not true. I don't even know if I have to go fix this at all. If it's questionable one way or the other that I could potentially get some underlying skin damage... I would look at the complexity of the EVA and go do that just because I would spend three or four hours of EVA time to just be sure, so I don't have to spend 12 weeks on the ground just to do some type of inspection, taking a bunch of tiles off to go look at the structure underneath."

Shannon provided an update as to the status of his team's work.

"The team has been working on the tile damage assessment... they have done much more work on characterizing the cavity and characterizing the damage itself and have started modeling that."

"We're running computational fluid dynamics models, CFD models, that will give us a very high fidelity look at what exactly the flow field will be inside that cavity. That will verify the analysis assumptions are correct and then we'll go into the arc-jet test facility and we'll bring up the heat in those areas that the computational fluid dynamics says we'll get the hottest and we'll be able to check the entire cavity," he explained.

"Unfortunately, that takes time. The first arc-jet tests are scheduled for tonight and what we are going to run is undamaged tile to make sure we get the right heat flow across the tile itself. They are machining the test samples to put the exact cavity we have into the test samples and once we verify from the computational fluid dynamics that we understand the heat in that cavity, then we will run the arc-jets tests, to make sure that the heat in the cavity is modeled correctly, and that will give us some good data."

"Like I said, that takes time and I was not comfortable as the MMT chairman in waiting for the final answer from that team before we got started on any type of repair options," said Shannon. "So we kicked off a Team 4, which is a standing team of operators, extravehicular activity-spacewalk experts, crew members, engineering team members, they are standing by on every flight to work any problems like this. They are meeting right now to discuss different types of repair options."

There are three primary repair options for tile: a black, paint-like emmitance wash that keeps heat from building up in the cavity; the T-RAD, a gun that squirts heat resistant caulk-like material into the cavity; or an overlay, a sheet of silica carbide that is attached using drywall-like screws to cover the damage for reentry.

Which option to use, if any, won't be known until mid-week.

"By tomorrow I should have the computational fluid dynamics numbers. I should have the simplified models. I will not have the damaged arc-jet test complete by this time tomorrow," said Shannon.

"I don't think [the decision to repair] will be made before Wednesday. We still have a lot of work to be done on the operations side and engineering test side, but we'll probably decide on Wednesday."

Lunatiki
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posted 08-13-2007 10:48 PM     Click Here to See the Profile for Lunatiki     Edit/Delete Message   Reply w/Quote
I know the Cmdr. will go with what Houston tells him, but, traditionally anyway, wouldn't it be his final call?

Lunar rock nut
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posted 08-14-2007 08:25 AM     Click Here to See the Profile for Lunar rock nut   Click Here to Email Lunar rock nut     Edit/Delete Message   Reply w/Quote
Robert,can you provide more technical data on the three options for repair. From my point of view option one would be like applying a band aid that is not completely water resistant to a cut and going swimming. Option two the T-Rad looks very appealing for this fix. Option three seems risky as far as compromising the integrity of the surrounding tiles as far as penetrating them with screws and requires tampering with a larger surface area risking loosening other tiles. As goldilocks said to little to much and just right!

Terry

Robert Pearlman
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posted 08-14-2007 09:51 AM     Click Here to See the Profile for Robert Pearlman   Click Here to Email Robert Pearlman     Edit/Delete Message   Reply w/Quote
quote:
Originally posted by Lunatiki:
I know the Cmdr. will go with what Houston tells him, but, traditionally anyway, wouldn't it be his final call?
Technically yes, but as the crew doesn't have the ability to conduct the same types of tests and analysis that the ground has during the mission, let alone the time to devise new procedures, the likelihood that the commander would override a suggestion of the MMT would be very, very low.

Robert Pearlman
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posted 08-14-2007 09:57 AM     Click Here to See the Profile for Robert Pearlman   Click Here to Email Robert Pearlman     Edit/Delete Message   Reply w/Quote
quote:
Originally posted by Lunar rock nut:
Robert, can you provide more technical data on the three options for repair.
Here is what was uplinked to the crew this morning:
quote:
If a repair is needed, we would target EVA-4 on FD10 at the earliest, possibly moving it to FD11. We're also working options to take advantage of the cryo margins and add even more docked time to complete TPS repairs. The primary option being looked at for repair will be using the OBSS (with both EVA crewmembers) to do emittance wash followed by an STA-54 underfill of the damaged section using T-RAD. The RMS/OBSS positions are being developed and analyzed, but expectations are that the repair position will have similar stability to what we tested on STS-121. All of this is very preliminary, with lots of forward work ahead. Again, no decision has been made to execute a repair.
To answer your direct concern Terry, the type of repair is chosen based on the expected heating requirements and the nature of the damage. All three options have been tested and proven to be effective for particular scenarios. Team 4's responsibility was to decide which of the three repairs best fit this hole.

Further to the above, based upon what I am hearing this morning, should a repair be necessary, the order in which the planned and repair EVAs are performed will change, and an additional docked day may be added to the mission (beyond the three that were already added). If a repair is necessary, Rick Mastracchio and Dave Williams will perform the spacewalk.

Jay Chladek
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posted 08-14-2007 11:01 AM     Click Here to See the Profile for Jay Chladek   Click Here to Email Jay Chladek     Edit/Delete Message   Reply w/Quote
If you can find the STS-114 and STS-121 press kits in PDF form over at the NASA website, go ahead and download those as they have a rather extensive section covering the TPS tile repair techniques which were tried out on those two flights.

After reading the quotes from Rob, my own gut feeling now is they may indeed do a repair to the one deep gouge area. But the vehicle should be fine on reentry even if they don't touch it.

Robert Pearlman
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posted 08-15-2007 10:48 AM     Click Here to See the Profile for Robert Pearlman   Click Here to Email Robert Pearlman     Edit/Delete Message   Reply w/Quote
The following was uplinked to the crew late last night:
quote:
The Debris Assessment Team provided the preliminary thermal and stress analysis for the largest tile damage along with the final analysis results for the three downstream smaller damage sites. The smaller damage sites were cleared for entry with no more than a 10 degree Fahrenheit increase in structural temperatures for the wing skin beneath these damage sites assuming a Mach 16.5 transition to turbulent flow due to the larger damage site.

The preliminary results for the two bounding cases were reviewed at the MMT today. Case 1 contained a simplified geometry shown in Figure 1 where the void does not extend to the filler bar. This case is thought to represent the heat load expected in the actual cavity. Case 2 shown in Figure 2 contains a simplified geometry with a 0.2” x 0.7” strip of filler bar exposed which is representative of the flight damage. Results for both cases are somewhat encouraging, although QA and peer review of the analysis is still in work.

The preliminary Case 1 analysis shows that structural skin temperatures meet all shuttle requirements. The maximum structural temperature is 268 degrees Fahrenheit with an aluminum limit of 350 degrees. The fact that the damage site is located on a structural rib is beneficial for both structural margins and heat dissipation. Case 2 evaluates the temperature on the exposed filler bar and immediate aluminum structure. Preliminary results are favorable and show that the aluminum gets to about 325 degrees for about three minutes with a temperature limit of 350 degrees. This analysis is thought to be somewhat conservative because previous flight damages have always returned with some filler bar and of course the RTV attached to the filler bar. This analysis was being peer reviewed as well with an independent NESC review of the results underway.

Additionally, CFD analysis has been completed and is still under peer review for flow inside the cavity (See Figure 3). At the end of the cavity (downstream), there is a blunt wall that will see the highest heating at the surface of the impact. This can be seen in the red flow (highest enthalpy relative to free stream enthalpy) and is supported by actual flight damages that were inspected post landing. The upper part of the rear edge of the cavity always sees the highest heating because most of the flow does not dip into the cavity since the lower pressure remains near the surfaces (higher pressure in the bottom of the cavity) The flow inside the cavity is turbulent and follows the streamlines in the figure with minimal flow expected in the very deep part of the cavity.

All of this analysis data will be cross checked with Arc Jet runs. A baseline run to undamaged tile was performed last night and a baseline run to damaged tile is being run tonight. The data from these runs will be compared to the analysis in order to verify the thermal results. In addition, a damaged tile sample will have STA-54 applied in a thermo- vacuum chamber, cured for 24 hours and then available for Arc Jet testing if that becomes necessary. A final decision regarding whether a repair of this damage is required is not expected until the FD8 or FD09 MMT.

As a parallel effort, Team 4 has begun creating EVA and robotics procedures and associated timelines for a repair should that be required on EVA 4. These Team 4 activities include a 1-G session on FD 7 to develop techniques for Emmittance Wash and T-RAD application. The tool setup in the NBL was also completed on FD7 and an NBL run will be performed on FD 8 to integrate the robotics, tool exchanges between EV crewmembers, and other EVA details. A FD 8 glove box run will also be performed using T- RAD.

The preliminary timeline is very flexible and allows for decisions to be made as the analysis matures. The preliminary timeline moves EVA4 to FD11 to allow more time for MCC procedure development and crew review prior to performing the repair with T-RAD and emmittance wash. In the event that the tile repair is required the data package and procedures would be uplinked on FD 9 for your review and preparation.

Moving the EVA to FD 11 would also allow the MMT the option of canceling the tile repair and pressing on with the nominal EVA 4 on FD11, with a final decision on FD 9 for the GO/NO GO for repair or nominal EVA 4. The decision on whether the timeline will be adjusted to move EVA 4 to FD 11 will be made at the FD8 MMT. The prime factor that will drive this decision will be the maturity of the thermal, stress and CFD analysis and arc jet testing and whether this analysis can be used to definitively rule out the repair for the remainder of the mission.


Robert Pearlman
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posted 08-15-2007 06:52 PM     Click Here to See the Profile for Robert Pearlman   Click Here to Email Robert Pearlman     Edit/Delete Message   Reply w/Quote
Mission control has told Endeavour's crew that STS-118’s fourth spacewalk will be moved to Saturday. The decision gives the crew an extra day to prepare for the EVA, which may or may not involve repairing the damaged tile.

A decision as to whether to conduct the repair or to proceed with the mission's fourth spacewalk as planned will be made on Thursday. To be ready for the possibility of a repair on Saturday, the crew will spend tomorrow in space preparing as if the repair will happen, though a decision by the mission management team sometime during the day may cut short that work.

Should a repair be necessary, it is expected that a fifth spacewalk will be added to the mission that will be used to complete the tasks originally intended for EVA #4 (in addition to retrieving the experiment pallet missed during today's third spacewalk due to a damaged glove).

Robert Pearlman
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posted 08-15-2007 09:48 PM     Click Here to See the Profile for Robert Pearlman   Click Here to Email Robert Pearlman     Edit/Delete Message   Reply w/Quote
Mission Management Team chair John Shannon briefed the media tonight regarding the tile damage on Endeavour's underside.

As noted earlier, the decision as to whether to repair the tile or leave it as is will be made on Thursday. Leading up to that decision are two primary concerns: the risks introduced by a repair and the understanding of the thermal analysis.

In regards to the earlier, Shannon explained, "I really tried to identify three areas of risk that we identified from the team's work:

"The first one is that we'd be outside our experience base... we would be outside our experience base in putting a crew member on the boom underneath the vehicle.

"If you remember on STS-114 when we had Steve Robinson go to remove that gap filler, that was at the very nose of the vehicle and he was riding the space station robot arm down to go get that. So this would be a little outside our experience base. We've had crew members on the boom before, doing tests for stability and we're very satisfied with that but it's important to know that we haven't done that particular task yet.

"There were some discussions that you probably would not have the helmet video. The comm we think would be pretty good, but you would be relying on some tools we don't typically rely on an EVA to get good communications with the crew. That was not a show stopper, but it was something to think about.

"The second area of risk we talked about was the hardware and the techniques we're using. The emittance wash, the black paint, we have used in a vacuum microgravity environment when we did the testing on STS-114 and it worked very well. So that hardware has been out in space and we have high confidence in it.

"The tile repair ablative, the T-RAD system, which is the pistol grip gun that puts the STA-54 material out, it has not been dispensed in a microgravity environment. The design is fairly simple, it's a pressurized canister that's pushing a bladder up against a tube and it's pushing that down a hose. The design is not anything that is really extravagant. We feel really comfortable that we'd be able to do that but it's important to note that we have not done that in the flight environment as of yet. We've not done that test.

"And the last area of risk that we kind of talked about was a little bit is the control of the repair. We have a dispense box. We'd use a tool to dispense some in the dispense box to get a good idea of the flow rate but this is kind of like when you epoxy something or caulk something. You put a certain amount in there, and you try to get it in all the right areas and if it's mixed right it will start to cure but it's not a like a mechanical fix. It is something that needs a little bit of practice to get it exactly in the right spot.

"We had a long discussion about could we make the situation worse. If we went out there and we did some type of repair with this STA-54 material, could we get it in a place where the cavity would behave differently. If you were paying attention the last couple of days, we've spent a lot of time and effort to try to understand the damaged site that we have and the cavity that we have. You could potentially get into a case where you had a different cavity that you had not analyzed quite as much and then your one opportunity to fill it passed because you had just done that. While that is not something I think is a big risk, I think the astronauts would do a good job, it is something you have to think about when bouncing about all the different risks.

"The way I would summarize it is, if we were in a critical situation, I think we could pull it off. I think we would have the rational to put all these different things together and come up with a very successful EVA. But you have to recognize there is some additional risk in doing that task."

The risks explained, Shannon addressed the study of the damage itself.

"We have almost finished the thermal analysis. If you remember we did computational fluid dynamics to understand the flow in the cavity and that was done at Ames Research Center. And Langley Research Center is backing us up, doing an independent review of that computational fluid dynamics. That work is still on-going and is not completed yet. We expect to have that tomorrow morning. And we're still performing the peer review, where someone goes in, totally independent, and checks all the math, checks all the physics and makes sure we did everything exactly right. That is 90% done.

"The analysis that we have shows there would be no damage at all to the underlying structure, which was very good news to us. We would not violate any of our certification temperatures.

"Additionally we did the arc-jet tests, where we simulated the exact damage we have on orbit on a tile array and we put it in the arc-jet. Here is a picture of the results:

"What you can see is that we have the initial damage site and it did not change very much. We got some tunneling going on that sharp back wall running into the tile adjacent to it. It did not go through the densified lower layer of the tile and it did not violate any temperature constraints on the underside of that aluminum sheet.

"We had a long discussion about what does this mean? Is this what we would expect to see? Well, we might see some erosion, some ablation of the tile and that back wall. The folks that run our arc-jet test gave us some information that the arc-jet exasperates that behavior. You have a thinner boundary layer so there are hotter gases flowing closer to the tile itself. We have thinner structure on the underside so you get a little bit hotter temperature. The bigger thing is that you're getting fully turbulent flow so not only is the boundary layer closer to the tile — so you have the hottest gas closest to the tile — but it's very turbulent. You're getting a lot of mixing and all that gets down in the cavity and the first place it streams that heat is on that back wall, so you're going to start to ablate that wall fairly quickly. And then an artifact of the arc-jet is how you get the flow to the test sample is through a nozzle and you get shocks, shock waves, and that adds energy to the flow as well. So while we would expect maybe some erosion, we do not expect it to look exactly like that.

"Even with all those things that we had that were somewhat working against us by adding heat to the cavity, we did not violate the requirements, we did not violate our certification, we had a full factor of safety for that.

"So, it would seem like that was enough information to say that we're okay to use as is, but I go back and say we haven't totally finished our thermal analysis and again on the arc-jet testing, we're actually going to do one more test case tonight. We are going to put a model in the arc-jet that is exactly not what the damage is on-board the orbiter, but it's exactly what we did for our simplified thermal analysis. That's going to verify that our analysis can accurately predict what the arc-jet facility would show us, then we can relate that back and say okay, what the arc-jet showed us on the real damage is correct."

So in light of that, I asked Shannon during the briefing if, barring any surprises from tonight's arc-jet test and given the risks of the EVA as explained, if he was leaning toward not doing the repair.

"We're pondering for 24 hours, but my personal feeling is that the data, at the 80-90% level, was that we could use this as is and that the EVA carries sufficient risk to it that we wouldn't just go do it as an additional margin," replied Shannon.

Robert Pearlman
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posted 08-16-2007 01:30 PM     Click Here to See the Profile for Robert Pearlman   Click Here to Email Robert Pearlman     Edit/Delete Message   Reply w/Quote
Capcom Steve Robinson radioed commander Scott Kelly regarding the STS-118 crew's on-going preparations for a possible tile repair spacewalk on Saturday.

"There's a reasonable chance to go with a nominal EVA 4, so you may want to think about delaying the actual hardware of that tool gather as long as you're comfortable," said Robinson, referring to the crew's next slated activity of gathering the equipment needed for the repair. Instead, he suggested that Endeavour's crew focus on the documentation requirements, and just be ready to pull the tools if need be.

The mission management team is scheduled to meet at 3:00 p.m. CDT to discuss the results of the thermal analysis and arc-jet tests conducted over the past several days studying the tile damage. A decision whether to repair the cavity is expected to be made later this evening.

fireflyer21
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posted 08-16-2007 08:01 PM     Click Here to See the Profile for fireflyer21   Click Here to Email fireflyer21     Edit/Delete Message   Reply w/Quote
No repair required per Mission Management Team; just called up to Endeavour

Robert Pearlman
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posted 08-16-2007 08:11 PM     Click Here to See the Profile for Robert Pearlman   Click Here to Email Robert Pearlman     Edit/Delete Message   Reply w/Quote
After a five hour meeting, the mission management team (MMT) has decided not to repair Endeavour's damaged tile.

"The MMT has just broken out of their meeting with a decision. The MMT has made the decision to fly the TPS [thermal protection system, tiles] as is," told Capcom Shane Kimbrough to STS-118 commander Scott Kelly. "No EVA repair is going to be required. MMT is still looking at the cut glove issue and any future EVAs on the flight will be for the nominal content."

"Okay, thanks Shane and please pass along our thanks for all the hard work that certainly the MMT, but everyone is doing down there supporting our flight," replied Kelly from aboard Endeavour.

"Yes, as you might imagine, the imagery folks, the engineering folks, the ops plan folks, and the safety folks have really been working hard on this, so it's great we finally have a decision and we can press forward," answered Kimbrough.

A mission status briefing with MMT chair John Shannon is scheduled for 8:30 p.m. CDT.

Lunatiki
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posted 08-16-2007 08:42 PM     Click Here to See the Profile for Lunatiki     Edit/Delete Message   Reply w/Quote
Well, I was wrong. I'm watching the press update now, and its impressive the lengths they went to in testing/simulating re-entry with the tiles.

Robert Pearlman
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posted 08-16-2007 09:40 PM     Click Here to See the Profile for Robert Pearlman   Click Here to Email Robert Pearlman     Edit/Delete Message   Reply w/Quote
Mission Management Team chair John Shannon briefed the media tonight regarding the tile damage on Endeavour's underside. Shannon gave a summary of why the MMT made the decision it did, not to repair the cavity:
quote:
The MMT made two significant decisions tonight. The first was a unanimous recommendation that the damage that we saw, after reviewing all of the engineering tests and analysis, was not a threat to crew safety. This was not something that the astronauts are in danger about. We had thought that for several days but we were waiting for the final analysis to be complete. We did all of the things that we said we were going to do the last few days: the engineering analysis, we had the computational fluid dynamics of the cavity from both Ames Research Center and Langley Research Center — those were both in agreement, we had those results tonight — we did the thermal analysis and that continued to show good margins, and we also did the two arc-jet tests where we put a reentry heating profile on the damage sites. We went through all of that data and it was unanimous that we were not in a loss of vehicle case.

The discussion then centered on whether we should use as is and return Endeavour in its current condition or if the uncertainties in the analysis could potentially cause some underlying tile damage or structural damage that we would have to deal with at the Kennedy Space Center. So, we had that debate. It was not unanimous but it was pretty overwhelming to go with the use as is condition. In other words, not to do the tile repair.

So, we will not be doing the tile repair on EVA #4.

To characterize the debate a lit bit, we have a very broad cross-cut of the NASA centers and the different engineering directorates at NASA. I polled every one of them. It was almost unanimous to use as is, the dissenting organization was the Johnson Space Center engineering group, who took a look at the potential benefits of doing a repair and said that they could not see a reason why that would cause additional damage to the orbiter and thought that that was something that we should think about as a program. On the other side, there was Marshall engineering, Kennedy Space Center engineering, mission operations, the flight crew office, all of the safety organizations that I had on my panel, they were all in agreement that the use as is was the appropriate way to go.

Some of the rational that was summed up by the team members that I think was fairly consistent across the management team was that we have a cavity in the tile that has been analyzed through computational fluid dynamics, through thermal analysis, through two different arc-jet tests, and we understand that cavity. It does not constitute a risk to the crew. It is not expected to cause any damage to the vehicle structure itself. And it is fairly well understood.

On the other hand, we could potentially do this spacewalk and add some material to the bottom of this cavity. The spacewalk has some risks associated with it and once we do the spacewalk and we put the material at the bottom of that cavity, then we would have a new cavity that we had not analyzed. That was the fairly simple decision is that you have something you know you can live with, why would you take the risk of doing the EVA to change that cavity into what, potentially could be an even better situation but also potentially could be a worse situation.

It was the situation that we knew that we found acceptable and we are going to stay in that configuration.

I would also mention that we had the NASA Engineering and Safety Center, which is our independent technical group that goes and looks at the problems of this type, they followed along with us throughout this entire analysis and they were in concurrence with our approach. And we had the Ames Research Center, Glenn Research Center, Langley Research Center, White Sands, and NASA Headquarters were all participating in the mission management team and were all part of the decision process as well.


Robert Pearlman
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posted 08-21-2007 12:36 PM     Click Here to See the Profile for Robert Pearlman   Click Here to Email Robert Pearlman     Edit/Delete Message   Reply w/Quote
First look at the tile damage post-reentry and landing:

mjanovec
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posted 08-21-2007 01:21 PM     Click Here to See the Profile for mjanovec   Click Here to Email mjanovec     Edit/Delete Message   Reply w/Quote
While I think the amount of brainpower that went into this problem was impressive and that the chances for disaster with that amount of damage were relatively low, I think NASA still lost an opportunity to demonstrate their on-orbit repair capabilities. To the general public, they will view this last mission as another example of NASA "rolling the dice" and taking chances. Granted, that's more of a perception issue with the media. But it's still a lost opportunity.

Think of what a great demonstration of NASA's capabilities it would have been to see that hole patched during an EVA. While I know that tiles tests were patched in the shuttle payload bay on a previous mission and tested back on earth, it doesn't carry the same weight as patching tile underneath the orbiter from the end of the robotic arm. In fact, an on-orbit repair could have been less a test of the effectiveness of the repair and more a test of the astronaut's ability to perfom such a repair from the end of the robotic arm underneath the shuttle. While such a repair does contain risk, the risk does not appear to be significantly higher than that of many other aspects of spaceflight. Plus, I feel the experience that could have been gained from conducting such a repair would have outweighed any risks. If we need experience on the moon to help us go on to Mars, then surely we need experience with on-orbit repairs too...before we encounter a situation where such a repair is critical for a safe return.

Instead, much of the population now the views the safe landing of Endeavour as another case of NASA dodging the bullet. In contrast, a successful demonstration of an on-orbit repair would have been a feather in NASA's cap.

FutureAstronaut
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posted 08-21-2007 01:39 PM     Click Here to See the Profile for FutureAstronaut     Edit/Delete Message   Reply w/Quote
quote:
Originally posted by mjanovec:
...I think NASA still lost an opportunity to demonstrate their on-orbit repair capabilities.
I agree that it would have been a good opportunity to demonstrate repair capabilities, I don't think it was worth the normal EVA risks, as well as the extra risk of causing more damage to the orbiter while trying to fix something that NASA was confident wouldn't be hazard.

Robert Pearlman
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posted 08-21-2007 01:47 PM     Click Here to See the Profile for Robert Pearlman   Click Here to Email Robert Pearlman     Edit/Delete Message   Reply w/Quote
quote:
Originally posted by mjanovec:
Instead, much of the population now the views the safe landing of Endeavour as another case of NASA dodging the bullet.
I disagree with this assessment and based upon the comments I have heard from friends and family who do not follow the program as closely as I do, the anecdotal evidence would suggest otherwise. Instead of "dodging the bullet", they have said they were impressed by the amount of study that went into diagnosing the problem. The knee jerk reaction is to do a repair, but the real skill is to know with certainty that you don't have to... and the results speak for themselves:


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