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Those who recall the early days of NASA's space program may recall that the Mercury, Gemini, and Apollo capsules had "ablative" heat shields. An ablative material is sacrificial, its surface absorbs heat and a thin layer breaks off, then the newly-exposed surface absorbs more heat and another thin layer
breaks off, etc. A surprisingly small thickness (an inch or two) was sufficient to protect Apollo from the heat of 25,000mph re-entry speeds.
Ablative heat shields were OK for one-shot space capsules, but the Shuttle needed something long-lasting and reusable, so it is covered with special tiles. As you know, however, the tiles are fragile and do tend to
either break or fall off. MOSTLY they do stay on and whole, but "mostly" has proved to be inadequate.
So, what the Shuttle should carry up to the Space Station is a special "patch kit". Inspection of the shuttle via
binoculars from the personnel of the Space Station can
reveal broken/missing tiles, before the Shuttle finds out the hard way. The kit should consist of dissolved/pressurized ablative foam. The holes in the tile shield can be filled in with this stuff, during a spacewalk.
During re-entry, the hardened foam will sacrifice itself in traditional ablation fashion, protecting the Shuttle and mostly disappearing by the time of landing, so that not too much work need be done, to chip away the rest of the foam, to allow replacement tiles to be installed.
Orbital manufacture of replacement tiles
http://www.halfbake...replacement_20tiles
[phoenix, Oct 04 2004]
On orbit inspection
http://books.nap.ed...tml/48.html#pagetop
Committee on Space Shuttle Meteoroid/Debris Risk Management [lurch, Oct 04 2004, last modified Oct 21 2004]
On orbit repair
http://books.nap.ed...059887/html/47.html
"Before the first shuttle flight, NASA developed a spray can foam-in-place ablative material to repair damaged or lost TPS tiles." [lurch, Oct 04 2004, last modified Oct 21 2004]
[link]
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I thought the thing crashed because the damage to the shields was not apparent, except in hindsight, and then only under close scrutiny. I like the idea, but I'm dubious as to whether shield damage that calls for a patch will be evident. I'm also not sure that using binoculars is the best way to assess this damage. |
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I think the tiles on the Shuttle are ablative too. Not that this wouldn't work. In my opinion, though, it best be an interim solution until the 'new shuttle' is built. |
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snarfguy, the idea for using binocs is to avoid a spacewalk for inspection. The shuttle could "stand off' from the Space Station and use its attitute thrusters to present whole exterior for examination. |
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galukalock, the Shuttle tiles are NOT ablative. They are built to take a lot of heat and come through virtually unscathed by it. Nifty material! |
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reensure, while the Shuttle may or may not have suits onboard for a space walk, I thought that the Space Station always has some handy? If not, then such suits should be part of the patch kit, that stays at the Space Station (doesn't need to be carried along on every flight). |
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lurch, if this idea has been baked, then it needs to be baked again, until it actually gets used!!!!! Thanks for the link! |
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Columbia's orbit was nowhere near the ISS on its last journey. Additionally, the idea of spacewalk tile repairs was eliminated due to the possibility of the astronauts damaging more tiles than they fix in the process. |
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Interesting approach but not practical under the circumstances. If you could rig a way to spray the material from the end of the Arm, perhaps it might work, but you couldn't reach all of the surface. |
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The underside of the Shuttle is supposed to be a flush surface. The foam, to be useful, would have to be thicker than the tiles and thus stick out from them; this would very likely cause accellerated heating/burnoff. |
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[waugsqueke] - re: EVA damage to tiles - I find lots of stuff alluding to that decision, but haven't been able to track down source documentation. Do you happen to know where I could find some? |
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Ron Dittemore talked about it during one of the early press conferences after the accident. T'is how I know it. It may be documented somewhere but I would not know where. |
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Biggest problem with orbital repair is: no hand holds on the underside of the shuttle. Columbia was not carrying MMUs (Manned Manuvering Units, the flying armchair), only the SAFER packs. Even if an MMU were avalible, the dificulty in mantaining position on the underside of the shuttle while using any repair equitment may have resulted in colisions with the shuttle by the astronaut, causing more damage. |
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Suction cups! ... er, oh, yeah. Sorry. |
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I would think that candidates for attachment points on the underside would be: fore and aft external tank mounts, external tank fuel/oxidizer intake points, nose and main landing gear. All these are covered by doors; I don't think any of them are currently set up to be cycled open/shut. The majority of these are down the shuttle midline, quite some distance from any critical leading edges. |
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<extensive description of possible handhold apparatus moved to new idea - link added> |
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My thinking would be to use two or three elastic tethers which wrap around the shuttle and are fastened in the cargo bay. Fasten a small somewhat-cushioned weight to one and throw it in such a way that it will loop around the shuttle and return to the cargo bay (cushioning it so that it won't hurt anything if it strikes the shuttle where it shouldn't). |
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// The idea is not to find ways that this will not work, but to find ways that it can. // |
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Huh? In this context that statement makes absolutely no sense. Clearly NASA has asked every question you just did, and based on the answers they rejected this solution. |
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//Prove it// Proof is not going to happen here. You have at your fingertips an incredible amount of material, data, lore, interpretation, bias, and rants. No one can force you to access, read, or believe any of it. |
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From my reading, it looks like they did consider all this and *lots* more. I won't say someone didn't screw up big time. On the other hand, to successfully fly a committee-crafted machine like the shuttle a hundred times has required more than just dumb luck. |
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Basie, if your objections are based on silly governmental cynicism, well we have nothing further to talk about. I maintain that NASA experts have probably thought this issue through far more than you have. Meaning they've asked all the questions you've thought of and another two hundred you haven't. That's what these people do for a living. |
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And, well, if I'm wrong, then you'd better give them a call. Obviously they need people like you. |
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