Path: utzoo!attcan!utgpu!jarvis.csri.toronto.edu!mailrus!ncar!asuvax!enuxha!kluksdah
From: kluksdah@enuxha.eas.asu.edu (Norman C. Kluksdahl)
Newsgroups: sci.space
Subject: Re: Apollo 8, 9, and 10
Summary: hypergolic = restartable
Message-ID: <199@enuxha.eas.asu.edu>
Date: 19 Jul 89 15:51:09 GMT
References: <377@dftsrv.gsfc.nasa.gov> <1989Jul19.005449.3163@utzoo.uucp> <17231@bellcore.bellcore.com>
Organization: Arizona State Univ, Tempe
Lines: 34

In article <17231@bellcore.bellcore.com>, ddavey@grits.ctt.bellcore.com (Doug Davey) writes:
> Does anybody remember whether the ascent or descent engine was used
> during Apollo 10's return from low orbit to rendezvous with the CSM?
> Either option seems difficult.  On the one hand, I would not expect
> the descent engine to be restartable.  On the other, firing the
> ascent engine and getting the ascent stage cleanly separated from the
> descent stage would be tricky since the descent stage was deigned to
> be firmly on the lunar surface during this operation.
> 
The LM used nitrogen tetraoxide and hydrazine (was it UDMH or some other
chemical variant???) as oxidizer and propellant.  These are hypergolic
propellants, which means that you don't need an igniter--the chemicals
hate each other so much that they ignite on contact (paraphrased from
"Chariots for Apollo").  So, if you can control the fuel and oxidizer
valves (simple, since the engines had to have thrust control, so valves
were there), you can re-start the engine repeatedly, until you run out
of fuel.

My memory indicates that the descent stage was cut free, and the ascent
stage was used for the rendezvouz.  Again, the book "Chariots for Apollo"
gives some very human-oriented insight into this process.  Some of the
engineers at Grumman who were responsible for the separation never did
watch or listen to a take-off from the moon.  There were many pyrotechnic
charges for the separation, each of which powered a guilliotine to sever
electrical, water, air, etc, lines between the ascent and descent stages.
Failure of one of the guilliotines would have been catastrophic.  If you
haven't read this book, find it.  It is very good, IMHO.

**********************************************************************
Norman Kluksdahl              Arizona State University
            ..ncar!noao!asuvax!enuxha!kluksdah
alternate:   kluksdah@enuxc1.eas.asu.edu

standard disclaimer implied