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#2226 Today 16:36:37
- SpaceNut
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- From: New Hampshire
- Registered: 2004-07-22
- Posts: 29,722
Re: Starship is Go...
What is Crunch wrap?
"Crunch wrap" is the informal name for a new material SpaceX is testing on Starship to seal gaps between heat shield tiles during atmospheric reentry. This material, often a ceramic fiber felt, is installed around each tile before it's snapped into place. After installation, the excess material is trimmed, creating a flush and sealed surface that prevents hot plasma from leaking through the gaps and damaging the underlying layers.
Why it's needed
Heat leakage: In previous flights, heat was able to seep through the gaps between the heat shield tiles, causing the underlying ablative material to burn away and creating white deposits on the hull.
Durability: The "crunch wrap" is designed to be quickly trimmed and allows the tiles to be more resistant to damage during reentry and to better withstand the stress of multiple flights without extensive refurbishment.
Rapid reusability: By improving the sealing and reliability of the heat shield, the "crunch wrap" helps SpaceX achieve its goal of making Starship a rapidly reusable vehicle.
How it works
Installation: Before a tile is mechanically attached, the "crunch wrap" material is wrapped around its sides.
Sealing: When the tile is pressed into place, the material is forced into the gaps between the tiles.
Trimming: The excess material that sticks out beyond the surface is then cut off, leaving a neat, flush seal.
Testing: This system was tested and performed well, leading SpaceX to plan on using it more extensively on future flight
Flight 11 Crunch Wrap™ TPS upgrade
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#2227 Today 17:29:45
- GW Johnson
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- From: McGregor, Texas USA
- Registered: 2011-12-04
- Posts: 6,070
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Re: Starship is Go...
In the previous post, the "kaowool" is a low-density ceramic or mineral fiber insulation. That low density means it has a low thermal conductivity, letting the tile get hotter without the tank shell seeing that heat addition so very much. You can only do that if you have a separate means of "tying" the tile in place over the insulation. In SpaceX's case, that is the tile retention pins.
That low density insulation has to be a mineral/ceramic fiber to take the temperatures at the interface with the tile. That way the tile can be a denser and therefore stronger and tougher ceramic (or other material, but apparently not iron-based from Flight 10). Denser is higher thermal conductivity, inherently. Which makes the inner tile face temperature much closer to the outer face temperature. Which is why they need the "kaowool" layer.
The "Pyron" ablative layer is not something I understand yet, except that it is the backup in case the tile is lost. It is related to PICA-X, based on what little there is to be read about it. PICA-X is what the Dragon uses for its ablative heat shield. "PICA" is an acronym for "phenol impregnated carbon ablator". The carbon is likely in a woven fabric form. This was originally a NASA thing, but it was expensive and difficult to fabricate. SpaceX subsequently did a cheaper- and easier-to-fabricate variant, and named it PICA-X. It is still phenolic reinforced with carbon fibers (likely in woven fabric form) and who knows what else, either way. I have seen no material specs for either form, much less "Pyron".
Apparently, the tiles used on Flight 10 were "metallic" in the sense of high iron content in some way. I know NOTHING about the actual material! But apparently it oxidized very fast during the one entry, quite unexpectedly. Whatever Flight 11's tiles were made of, it was something different, likely some kind of firebrick-like material. And those tiles worked a lot better.
Bear in mind that there was no insulation or backup underneath the space shuttle heat shield tiles. Those were a fragile and vulnerable low density ceramic, combining the high temperature resistance of the alumino-sililcate material and the low thermal conductivity of the very low density, into a single material. The new nose and leading edge tiles on X-37B are the first step away from that approach, they being a high-density ceramic locked onto a low-density ceramic underlayer. SpaceX seems to be pioneering yet a different approach. And it would seem to be working.
GW
Last edited by GW Johnson (Today 17:49:36)
GW Johnson
McGregor, Texas
"There is nothing as expensive as a dead crew, especially one dead from a bad management decision"
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