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From: roger@telesoft.UUCP (Roger Arnold @prodigal)
Newsgroups: sci.space
Subject: Re: Solid versus Liquid
Message-ID: <359@telesoft.UUCP>
Date: Mon, 13-Oct-86 21:48:19 EDT
Article-I.D.: telesoft.359
Posted: Mon Oct 13 21:48:19 1986
Date-Received: Thu, 16-Oct-86 19:20:35 EDT
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Organization: TeleSoft, SanDiego CA
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> ...
> Anyone on the net know about hybrids and why they seem to be dead? 
> 

What I can recall about hybrids, off the top of my head, is this:

1) They were being developed and promoted by a private company,
   whose name, I believe, was "Star Struck".  I could be wrong 
   about the name; I may be confusing them with another group;

2) The company that was developing them was a serious outfit.  My
   impression is that it had a number of young, idealistic employees,
   but they were bright and competent.  The largest investor was one
   of the principals in Apple Computers, though I don't recall who.
   Anyway, they conducted a number of successful static test firings
   and pretty well proved that the concept was feasible.  They even
   got to the point of making a test launch of the first stage of the
   orbital rocket that they were trying to develop.  The test launch
   was largely successful; it was marred slightly, as I recall, by a
   malfunction in the guidance system midway through the test, but the
   hybrid rocket itself performed well.

3) Unfortuanately, it took them about twice as long and cost three
   times as much to get to the point of that successful test launch 
   as they had originally planned.  On that basis, their financial
   backer(s?) concluded that they would not have the resources to carry
   the development through to the point of a marketable launch vehicle.  
   So they threw a big party, updated their resumes, and went off to
   seek greener pastures with the established aerospace companies.  
   

Or at least that's how I heard it.  If anyone out there has better
info, I'd be interested in hearing about it.

As to the technical merits of hybrids, I think it's pretty safe to say
that their strong point is safety.  They really can't blow up, even if
they rupture a casing, and they can be shut down or throttled.  They
should even be restartable.

Hybrids should also be cheaper than solids, and perform slightly
better.  The rubber-like fuel cores they employ are cheaper to make 
than solid rocket fuel cores, and don't require expensive safety
precautions for handling.  Liquid oxygen is very cheap, and provides
substantially more energy per pound than the oxidizers encorporated 
into solid rocket fuels.  

Unfortunately, hybrids still requires the same heavy, high pressure
casings that solid rockets require, and their performance alone is not
sufficiently better than solids to send anyone like NASA scrambling 
off to develop them.  It's also possible that there are technical
problems with uneven fuel burning that I didn't hear about, but that 
would make them unusable for something as large as a Shuttle SRB.  
Again, if anyone out there in net land has more info, by all means,
don't keep it to yourself.

- Roger Arnold