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From: eder@ssc-vax.UUCP (Dani Eder)
Newsgroups: net.columbia
Subject: Re: Columbia's Tiled Damaged by Rain
Message-ID: <130@ssc-vax.UUCP>
Date: Sat, 17-Aug-85 01:32:29 EDT
Article-I.D.: ssc-vax.130
Posted: Sat Aug 17 01:32:29 1985
Date-Received: Tue, 20-Aug-85 06:14:36 EDT
References: <4010@alice.UUCP> <199@mot.UUCP> <521@calmasd.UUCP> <47@darwin.UUCP> <1400@cbosgd.UUCP> <1095@cbdkc1.UUCP>
Organization: Boeing Aerospace Co., Seattle, WA
Lines: 40

> >Regular airliners manage to fly at several hundred miles per hour
> >and fly through clouds and rainstorms without much trouble.  They
> >seem to have metal skins designed to not hit the air/water head on,
> >but rather deflect it over them.  Aerodynamics, right?
> >
> >I would think the same property would apply to the shuttle.
> 
> I once saw a sample of the shuttle's tile skin. It looked like the kind of
> brick you see inside a ceramic kiln. It looked very soft and absorbant. 
> While the shuttle *is* aerodynamic to some extent, it is still very close to
> a flying rock. It does not have the very sharp features that an airliner 
> possesses.

     Back when the design of the Shuttle was being decided, NASA decided
that developing the Space Shuttle Main Engines was enough of a technical
challenge.  If there were another difficult piece of technology, the risk
of the program failing because the technology was not working would have
been too high.  At that time there were two candidate thermal protection
systems: metallic and ceramic.  The metallic technology was not in hand,
the ceramic was.  The ceramic was therefore chosen.

     Another area where the technology did not exist at that time (early
1970's) was structure that could stand high temperatures.  The basic
structure of the Shuttle is aluminum, just like most commerical airplanes.
Aluminum, while light, cannot stand high temperatures.  The thermal
protection had to keep the structure cool, but it couldn't weigh too
much.

     The solution worked out was to tailor the thermal protection to the
temperatures it was exposed to, using the lightest materials available.
Unfortunately, these materials, which are cermics, are brittle, and hence
chip easily and fracture in a way metals do not.

     Yes, the Orbiter is a kludge, but the best kludge that could be
devised at the time.  The next generation vehicle will have the benefit
of 15 more years of technology development, and will therefore be better
in many respects, but it too will be a compromise of available technologies
needed to do the job.

Dani Eder / Advanced Space Transportation / Boeing Co / ssc-vax!eder