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Path: utzoo!henry
From: henry@utzoo.UUCP (Henry Spencer)
Newsgroups: net.columbia
Subject: Re: SRB vs liquid
Message-ID: <6380@utzoo.UUCP>
Date: Sat, 8-Feb-86 20:46:46 EST
Article-I.D.: utzoo.6380
Posted: Sat Feb  8 20:46:46 1986
Date-Received: Sat, 8-Feb-86 20:46:46 EST
References: <615@uwvax.UUCP>, <1759@jhunix.UUCP>
Organization: U of Toronto Zoology
Lines: 36

> ...[Liquid fuels] can be unstable
> at room temperature, require high pressure/low temps to stay liquid,
> and in general are a pain to handle.  Solid fuel, on the other hand, 
> is easy to handle, stable, and generally nontoxic...

Don't forget that liquid fuels can be loaded on the pad.  NASA used to
have an iron-clad rule saying "no fuel in the VAB" [Vertical Assembly
Building, since renamed Vehicle Assembly Building].  They were not happy
about the shuttle SRBs for this reason.  Solid fuel is only *relatively*
stable and easy to handle.  It remains a fire and explosion hazard.  KSC
tours used to include the inside of the VAB, but not any more; in fact
most non-VAB NASA employees aren't allowed in.

> As for the asssertion that SRBs were used because of budget constraints,
> I remember shuttle descriptions included SRBs even in the early 70s
> when the shuttle was being conceived.

Look back a little further and you'll see liquid-fueled boosters.  The
solids have lower performance, are only semi-reusable, and are not nearly
as controllable in flight.  NASA almost used a developed Saturn V first
stage with wings (the "flyback F-1") as the shuttle booster, but its
projected development costs were slightly too high.

> At that time, the Air Force
> was installing solid fueled Minuteman missiles, and their solid fuel
> rockets were considered the state of the propulsion art, making liquid
> fueled Titans obsolete.

For military applications, requiring years of waiting with minimal or no
regular attention, and lightning response to a "launch" command.  This is
very different from space launches!  The USAF wants to keep its ICBMs
fully fueled at all times, which greatly changes the safety tradeoffs, and
the performance penalty was less significant.
-- 
				Henry Spencer @ U of Toronto Zoology
				{allegra,ihnp4,linus,decvax}!utzoo!henry