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Post by hplasm on Mar 1, 2007 19:36:40 GMT -4
Went home and bought a desktop machine- Babbage or something...Boy you must have a big desk. Needed to have big drawers to keep my digital wristwatch in!
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Post by Grand Lunar on Mar 1, 2007 21:30:46 GMT -4
I profusely apologize in advance for what I'm about to say, but I couldn't help it... it just popped in there... ET foam hone I can smell the cheese from here!
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Post by Grand Lunar on Mar 1, 2007 21:31:43 GMT -4
ET insulation damage is a problem only because the orbiter is side-strapped. Every launch vehicle sheds insulation, ice, paint, and other kinds of debris. But since conventional launch vehicles are top-stacked, the payload is safe. When we recycle the ET design for the new program, the top-stacking arrangement will relax the weather constraint. The ET can shed all it wants and we won't care. That sounds like good news for the Ares 1 as well, I assume. Or will hail damage the BPC on the Orion (I would assume a BPC is stronger than insulation foam on the ET)?
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Bob B.
Bob the Excel Guru?
Posts: 3,072
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Post by Bob B. on Mar 1, 2007 22:27:19 GMT -4
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Post by gillianren on Mar 2, 2007 1:19:22 GMT -4
Okay, that's more ancient than mine.
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Post by Jason Thompson on Mar 2, 2007 5:53:34 GMT -4
The BPC is unlikely to be made of foam. One of the functions of the BPC on the original Apollo was to protect the command module (and especially the windows and optical systems) from the exhast of the launch escape tower when it was jettisoned. Assuming the same function on Orion, we could surmise that it is unlikely to suffer damage from weather, and that even if it did it would be unlikely to cause any damage to the spacecraft since debris will be directed away from the payload.
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Post by JayUtah on Mar 2, 2007 10:19:54 GMT -4
I would assume a BPC is stronger than insulation foam on the ET...
It will be made so.
The primary purpose of the ET outer layer is thermal insulation. So when selecting a material for it, thermal properties lead the way. But since you need a lot of it to cover the ET's vast outer surface area, you need low density material in order to keep the total mass down. Once you start down that path, you arrive rather quickly at the various types of foam that are laid up as a semi-plastic liquid which then expands and hardens. It has excellent thermal properties, and good density properties.
But it has poor fracture tolerance and tensile strength. That means it's easily damaged by things that hit it, and the damage -- once started -- tends to progress. It's also porous; that's a side-effect of the means by which it achieves thermal insulation. But porous materials are susceptible to damage by wetting and subsequent temperature fluctuations.
A BPC, on the other hand, is essentially a sacrificial layer. It is meant to withstand impacts, so the choice of material must be led by mechanical strength concerns.
If an Apollo-style launch-escape system is planned, it will also need to protect against LES plume damage, but only to the extent necessary to safeguard the crew during an aborted launch. Since that is a contingency role, your requirements for preserving the spacecraft are more relaxed than if you had to keep the contained spacecraft viable for its full mission. You're allowed to let the ship get scorched as long as the crew is still okay.
And since the ship in this case is much smaller than the ET, mass and density aren't as much of a problem. We'll probably see a laminated BPC with layers designed for various requirements.
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Post by Grand Lunar on Mar 2, 2007 12:08:26 GMT -4
Thanks for the info, guys.
I think I read somewhere that the Apollo BPC was made of a fiberglass material (that, or I'm thinking of the simulated panels on the shuttle Enterprise). True? Or was it something else?
Also, in the photo of the Apollo CM during the Apollo/Soyuz test, it seems the BPC was left on. True?
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Post by Jason Thompson on Mar 2, 2007 12:14:37 GMT -4
Which photo in particular makes you think the BPC was left on? It had to be removed in order for the Apollo spacecraft to link to the docking module.
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Post by Grand Lunar on Mar 2, 2007 12:34:33 GMT -4
The closest I found was this: euve.gsfc.nasa.gov/Images/apollo-soyuz/apollo_1.gifIt wasn't the one that made me think it was, though. After seeing similar photos, it seems that it was just reflecting something white. Now that you mention it, was the docking module kept in the S-IVB where the LM used to go?
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Bob B.
Bob the Excel Guru?
Posts: 3,072
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Post by Bob B. on Mar 2, 2007 12:35:29 GMT -4
I think I read somewhere that the Apollo BPC was made of a fiberglass material (that, or I'm thinking of the simulated panels on the shuttle Enterprise). True? Or was it something else? " Boost Protective Cover - It is made of layers of impregnated fiberglass, honeycomb cored-laminated fiberglass, and cork. It has 12 "blow-out" ports for reaction control motors, vents, and an 8-inch diameter window in front of the commander's forward viewing window. It completely covers the command module to prevent charring of external surfaces during boost out of the earth's atmosphere. It is jettisoned with the launch escape tower assembly." Source: www.adboo.com/cmnr/launchescape.htm
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Post by Jason Thompson on Mar 2, 2007 12:38:15 GMT -4
Now that you mention it, was the docking module kept in the S-IVB where the LM used to go? Yes. The transposition and docking manoeuvre was exactly the same as for extraction of the LM during the lunar flights.
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Post by Grand Lunar on Mar 2, 2007 12:40:55 GMT -4
Thanks for the info, Bob B. Good to see I wasn't mis-remembering.
Ditto for you, JT. I often wondered where that module was kept. Now I know!
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Post by JayUtah on Mar 2, 2007 14:16:34 GMT -4
In Apollo the BPC and LES were an integrated assembly. The cork is meant to cushion the boundary between the inside of the BPC and the CM skin. The BPC/LES assembly connected to the docking probe, IIRC. Apollo 14's docking difficulties were caused in part by the docking assembly's additional role as the BPC interface.
Aerodynamic heating on the ascent is also substantial and must be accommodated by any protective cover.
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Al Johnston
"Cheer up!" they said, "It could be worse!" So I did, and it was.
Posts: 1,453
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Post by Al Johnston on Mar 2, 2007 16:10:04 GMT -4
Looking it up in Virtual Apollo the LES legs were attached to the forward bulkhead of the CM with explosive frangible nuts. In addition, there was a tensile tie between the BPC and the docking probe: this was to carry the probe away with the BPC when the LES was jettisoned during an abort. (In that event, the docking ring was explosively separated from the CM; during a normal launch the docking probe remained firmly attached, the force applied by the LES engines being enough to snap the tie.)
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