Tuesday, November 14, 2006

Not much work to report I spent the evening cleaning up the shop after the weekend. I do have an idea that sounds crazy.

Mylar is a type of polyester film. According to the article at Google Answers.
"Speaking with Dupont Technical Service this morning,
I found that PET films are virtually industructible
down to -250 degrees C. That is to say, the biaxially
oriented films (such as Mylar, Melinex etc) do lot
lose physically properties significantly as
temperature is reduced. "

Polyester film is closely related to PET soda bottles. It can be readily glued with the proper glue (gorilla glue is one brand) The water rocket people have explored this area extensively.
A gentleman at the 2006 space access had done some experiments with LOX and plastic soda bottles. He found they worked well and remained flexible atLOX Temperatures.

One of the problems of building low temperature composite structures is that they get brittle, and then crack loosing their strength. They also suffer from dissimilar temperature coefficients between their carbon fiber structure and their, usually aluminum, liner.

What if your structure was just a bag inside a mesh support? This is much like a counter pressure space suit instead of a full space suit. One needs to create the mesh out of a fiber that is very light and stiff enough that the liner will yield into the fiber before it fails.

The strongest fiber currently known is spectra 2000, it has a yield of 3.2 Gpa and a young’s modulus of 124 GpaIts also lighter than water. For comparison Titanium has a modulus of 120 Gpa so spectra size for size is stiffer than titanium. It’s also size for size 2X as strong as steel. Spectra is slippery so it’s hard to glue into a matrix, but a woven sleeve of spectra over mylar might make an interesting tank. A high perf tank made of soda bottles and kite line.Yea that is crazy.


Anonymous said...

Is it so crazy that it just might work?

Anonymous said...

I quote Henry Spencer:

LOX compatibility is a major issue for anything like this.
Many organic materials are dangerous explosives in a LOX environment.

Anonymous said...

As I understand it, PET shouldn't explode, it's non miscible with LOX.

But it can burn very quickly if ignited.

Still, just about everything useful burns in LOX. The Shuttle main tank is made of aluminum and that burns real well in LOX- it sometimes fails the hammer test. NASA launch on a waver every time- their argument is that there shouldn't be a 'hammer' at 50,000 ft. This argument sounded better before the Columbia disaster.