From: Henry Spencer <henry@zoo.toronto.edu>
Newsgroups: sci.space.tech
Subject: Re: micromachined rockets
Date: Wed, 27 Mar 1996 17:51:08 GMT

In article <4is8jb$f5s@newnews.iafrica.com> mithril@iafrica.com (Grantland) writes:
>>The inner walls of most major rocket engines are made of copper...
>>(The reason copper is used is because its heat conductivity is very
>>high, which is crucial to getting the heat out of the wall and into the
>>coolant.)  
>
>  What about  an inner wall coated with monocrystalline diamond?  High
>melting (sublimation?) point, excellent conductivity, strength
>characteristics...

The very high heat conductivity is good.  Brittleness would be a concern,
especially since the chamber necessarily expands slightly due to the high
internal pressure.  Strength is a secondary issue for the inner wall, as
witness the use of copper -- it's the outer wall that needs to be strong.

The real question is whether a diamond coating really helps much.  If you
could make the entire inner wall out of it, the high heat conductivity
would be quite an asset, as would the ability to inspect the cooling 
passages through a transparent wall, but a thin coating is no help in
this department.  The tougher surface is of no great importance in an
environment where copper survives just fine.
-- 
Americans proved to be more bureaucratic           |       Henry Spencer
than I ever thought.  --Valery Ryumin, RKK Energia |   henry@zoo.toronto.edu


From: Henry Spencer <henry@zoo.toronto.edu>
Newsgroups: sci.space.tech
Subject: Re: micromachined rockets
Date: Mon, 18 Mar 1996 16:31:56 GMT

In article <4icevn$8jd@news.uncc.edu> john@uncc.edu writes:
>>...working on development of rocket motors micromachined from
>>polysilicon;  "rocket on a chip"...
>
>Silicon has a serious problem as a rocket engine, it melts at about 1400C.

The inner walls of most major rocket engines are made of copper, which
melts at under 1100C.  The secret is to keep the heat away from the walls
as much as possible, and circulate fuel through them to get rid of the
rest.  (The reason copper is used is because its heat conductivity is very
high, which is crucial to getting the heat out of the wall and into the
coolant.)  Micromachining might well permit effective use of methods like
transpiration cooling, where the walls are porous and fuel is injected
through them -- a very effective strategy, little used because suitable
walls are hard to make.

Now, I agree with John in one respect -- I don't see the point of making
tiny silicon rocket engines -- but silicon's melting point isn't the issue.
-- 
Americans proved to be more bureaucratic           |       Henry Spencer
than I ever thought.  --Valery Ryumin, RKK Energia |   henry@zoo.toronto.edu

From: ederd@bcstec.ca.boeing.com (Dani Eder)
Subject: Re: No-holds-barred dirt cheap launch vehicles
Date: Jul 19 1995
Newsgroups: sci.space.policy

hvanderbilt@BIX.com (hvanderbilt on BIX) writes:

>rogerw@cisco.com (Roger M. Wilcox) writes:

>>   So, it sounds like my best cost-saving measure would be to somehow either
>>increase the temperature resistance of the reaction chamber itself, or cut
>>costs on how the rocket motor is kept cool.  Any ideas?


>For a one-shot throwaway rocket like the one under discussion, an ablatively
>cooled combustion chamber might do the job.  
>				Henry Vanderbilt  hvanderbilt@bix.com

Since the Chinese demonstrated the ability of oak to withstand re-entry
heating as an ablative, you might consider a wooden combustion chamber.
You want the grain radially inward so the char doesn't flake off, and
you want the wood wet, so the water vapor steaming out of the grain
provides transpiration cooling.  Since wood is weak when assembled this
way, it would have to be re-inforced with steel bands to hold it's shape.

For those of you who think I'm kidding about oak barrel technology, 
cork impregnated with phenolic plastic is a standard heat sheild material.

Dani Eder