Date: 25 Oct 89 02:20:19 GMT
From: cs.utexas.edu!mailrus!jarvis.csri.toronto.edu!utgpu!utzoo!henry@tut.cis.ohio-state.edu  (Henry Spencer)
Subject: Re: Space Shuttle SRB exhaust gas makeup.

In article <1989Oct24.222743.23580@agate.berkeley.edu> gwh@typhoon.Berkeley.EDU (George William Herbert) writes:
>	A _dash_ of aluminum???  The majority of the thrust is achived
>by the aluminum component of the fuel !
>	The actual materials are Ammonium Perchorate, Aluminum powder, PVC
>binder and extra bits to stabilize.  It's about 99% those three.

If we're being picky, the numbers (according to NASA) are 69.83% ammonium
perchlorate, 16% aluminum, 12% rubber (it's not PVC, it's a polybutadiene
acrylic acid acrylonitrile polymer), 2% curing agent, and more or less
0.17% iron oxide catalyst.

And don't sneer at the idea of doing without the aluminum, because the
rubber is also a fuel; similar combinations without aluminum have almost
as high a specific impulse.  (For that matter, ammonium perchlorate by
itself is apparently non-trivial as a monopropellant, although it's not
used that way because its physical properties aren't right.)
-- 
A bit of tolerance is worth a  |     Henry Spencer at U of Toronto Zoology
megabyte of flaming.           | uunet!attcan!utzoo!henry henry@zoo.toronto.edu

Date: 26 Oct 89 05:28:01 GMT
From: mailrus!jarvis.csri.toronto.edu!utgpu!utzoo!henry@tut.cis.ohio-state.edu  (Henry Spencer)
Subject: Re: Space Shuttle SRB exhaust gas makeup.

In article <1989Oct26.025442.17842@agate.berkeley.edu> gwh@typhoon.Berkeley.EDU (George William Herbert) writes:
>>And don't sneer at the idea of doing without the aluminum, because the
>>rubber is also a fuel; similar combinations without aluminum have almost
>>as high a specific impulse...
>
>...	As for the 'no aluminum' bit, it really was described as making
>most of the difference.  There's a whole lot more energy in Al than rubber...

I confess I was a bit surprised myself, but Sutton lists a PVC/AP combination
as having only about 10% less exhaust velocity than PVC/AP/Al.  Aluminum is a
lot more energetic, but it also exacts a price:  aluminum oxide has a very
high molecular weight, and it tends to condense out to complicate things
further.  I'm not up enough on the fine points of solids to really assess
the tradeoffs.
-- 
A bit of tolerance is worth a  |     Henry Spencer at U of Toronto Zoology
megabyte of flaming.           | uunet!attcan!utzoo!henry henry@zoo.toronto.edu