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Just for completeness I’ve thought of one other scenario to add to my initial list. Since the Shuttle was a spacehab mission, the payload is likely to have been well forward. If the payload tie downs to the longerons were to have broken during the reentry, the payload would have slammed into the back and the payload doors. The vehicle would then break up as in the other scenarios.
I rate this idea as extremely unlikely but worth tossing out for the sake of completeness.
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Upon re-entry the G forces would be in a forward direction
Off of Instapundit:
I’M WATCHING THE NEWS CONFERENCE, and it looks like a zipper effect followed by burnthrough and structural damage, leading to the loss of the left wing. They’re reporting anomalous heat sensor readings, loss of tire pressure in the main gear on that side, and so on.
The shuttle can tolerate the loss of a tile or two. But when the integrity of the tile cover is breached, tiles can be pulled off one after another — hence the term “zipper effect.” Then enough heat can penetrate through in sufficient quantity to destroy or weaken what’s underneath. This is a well-understood possibility, so expect a quick resolution (by the standards of these kinds of things) if the evidence continues to point this way.
Best NASA line from the press conference so far: “We’ll find it and we’ll fix it.”
Off of Instapundit:
I’M WATCHING THE NEWS CONFERENCE, and it looks like a zipper effect followed by burnthrough and structural damage, leading to the loss of the left wing. They’re reporting anomalous heat sensor readings, loss of tire pressure in the main gear on that side, and so on.
The shuttle can tolerate the loss of a tile or two. But when the integrity of the tile cover is breached, tiles can be pulled off one after another — hence the term “zipper effect.” Then enough heat can penetrate through in sufficient quantity to destroy or weaken what’s underneath. This is a well-understood possibility, so expect a quick resolution (by the standards of these kinds of things) if the evidence continues to point this way.
Best NASA line from the press conference so far: “We’ll find it and we’ll fix it.”
Reading the AP reports, it was mentioned the left wing was slightly damaged during liftoff. Debris from the main tank apparently hit it. NASA apparently thought it didn’t do any real damage. But based on the fact that the problem causing this seems to have been the left wing (from what they said in the news conference), I guess they were wrong.
Keith: Think again. The deceleration vector is pushing the astronauts into their seats. The vector, with respect to the shuttle’s own X-axis, is backwards and slightly upwards due to the raised nose attitude used to ensure the TPS takes the brunt of the re-entry heat. Highest thermal loads are around the nose and the leading edges of the wings, which is why they have special material. If anything breaks lose, it goes tailwards. Believe me, the astronauts are not in an eyeballs out re-entry with the straps holding them down on their seats.
Sandy: Yes, that is what I would expect. I believe the port side wing is also the one which was impacted by ET insulation during boost.
It’s amazing to look back at the posts regarding this disaster by Dale Amon!
I’m in Florida and was in my car and just after 9am heard there’d been no communication. My husband and I had a sinking feeling immediately and were watching our partly clouded skies wishing to hear our usual 2 sonic booms as the time drew closer to 9:16.
The problems leading up to this will be detected and resolved. There are a lot of people who contract work for NASA and I’m sure everyone is working hard already collecting and sharing data.
-Elizabeth
Just a note on payload positioning in the payload bay. Due to center of gravity concerns, payloads are almost always placed as far back as possible. I’m sure this mission was no exception.
Instapundit’s scenario is possible, but it’s at least as likely that there was heavy ice build-up on the liquid fuel tank during ascent, so the piece of light foam insulation that struck the left wing was heavily weighted with ice and either did structural damage or knocked enough tiles off the leading edge of the left wing to allow a burn through leading to catastrophic failure.
It also wouldn’t be surprising if there was a combination failure of the left wing: minor damage to the tiles and structure at ascent, plus structural fatigue in the oldest shuttle in the fleet plus the heat and stress of reentry . . . . . . .
Dale,
If the left wing’s TPS unzipped and blew out the left main landing gear tire, which is what the initial sensor readings NASA talked about leads me to believe is true.
The break up of that wing at mach 20.9 would have hit the crew and payload with 40+ gees of instantanious acceleration. They would have been knocked out immediately, if not had their necks broken. And that same shock most certainly have shaken loose the payload to assist in the break up of the Columbia.
Trent: As you can see if you scroll down I agree they died instantly.
As to when the payload broke free or whether the hull split first, we may never know, but as I said, I put it very far down the list as a potential first cause.
Everything I’ve seen still falls in line behind my immediate gut feel for what happened.
Anarchus: The ice mostly comes off at launch, but it could have been a cause for the delamination of some of the ET insulation. I doubt very much it was anywhere near sufficient to cause actual structural damage as the impact velocity (relative velocity) would not be that great nor the weight particularly large. The problem is TPS is fragile. It may not have even knocked tiles off, it may only have cracked an area of them. I can’t say what precise level of damage was caused. But anything near the leading edges is crucial, and a couple shattered tiles there could easily give enough purchase for the unzipping to occur. It’s both the heat and the slipstream working together on re-entry.
Ross: but the Spacehab will not be full aft, and if it was one of the small ones, it is full forward. I have not yet researched exactly what unit they were flying. And it is getting late here and I am getting quite fatigued both physically and emotionally as it slips on towards 2am over here.
Most of which is moot anyway, as I would be extremely surprised if the attachments failed before the ship began disentegrating anyway.
Dale: I was a third class cadet majoring in astronautical engineering at the Air Force Academy when the shuttle was in final development in the 1970s. I clearly remember a Aeronautical engineering prof telling us that it only took a few lost tiles to turn the shuttle into a giant heat sink on reentry . . . . . and then of course there were lots of lost tiles on the early orbital flights and there were no problems. Of course, most of the lost tiles were on the top of the orbiter vehicle and not on the front-bottom or leading edge of the wings.
I have always wondered why the orbiters weren’t more vulnerable to lost tiles though, and apparently tiles have been lost on all or most missions.
this is worth watching:
launchvideo
I think it is a function of how much damage and where it occurs. The leading edges are particularly bad. Damaging several contiguous tiles could have a rather bad effect as well.
I’ve been looking over the animated gif, time after time and I can’t really tell where the strike is occuring.
Whatever happened, it seems fairly clear there was a burn through that got into the wheel wells just seconds before failure. The wells are pretty close to the where the wing and hull meet FWIW.
I recognize of course, that as we get into the details of what happened and move beyond generalizations. I’ll have to wait for the reports from the investigators. My level of knowledge on the shuttle is “good” but not in the class of people who work on it at HMSFC or KSC.
Of course that won’t stop me from stating opinions and making a fool of myself 🙂