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From: rfc@calmasd.UUCP (Robert Clayton)
Newsgroups: net.columbia
Subject: Re: Columbia's Tiled Damaged by Rain
Message-ID: <542@calmasd.UUCP>
Date: Thu, 15-Aug-85 17:28:15 EDT
Article-I.D.: calmasd.542
Posted: Thu Aug 15 17:28:15 1985
Date-Received: Mon, 19-Aug-85 23:07:15 EDT
References: <4010@alice.UUCP> <199@mot.UUCP> <521@calmasd.UUCP> <47@darwin.UUCP> <1400@cbosgd.UUCP>
Organization: Calma Company, San Diego, CA
Lines: 57

> In article <47@darwin.UUCP> ian@darwin.UUCP writes:
> >>> how interesting!  Columbia's tiles survive atmosphere re-entry only to get
> >>> beat up by a rainstorm (which you'd think would be gentle) coming at it at
> >>> a couple hundred mph.
> >
> >>A several hundred mph blast of water is extremely destructive.
> >>Fortunately in a storm the water is dispersed, but I suspect it compares
> >>to a sand blaster in terms of destructive potential.
> 
> 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.

The original posting was in regard to the tiles.  Metal routinely
endures sandblasting - it is a common method of preparing metal for
priming and painting.  I haven't held these tiles, but pictures I've
seen give me the impression they could not endure extended exposure
to a sand blast effect.  The tiles, as I understand it were chosen
for their lightweight insulation characteristic.  Strength and wear
resistance were limitations the designers were forced to accept.  They
allowed for this by making them replacable.

Getting this discussion back to shuttle-related matters,  The reason
the tiles were chosen was that designers were trying to make a structure
cheaper than Titanium.  In the early '70s, welded all-Titanium structures
were reserved for exotic craft such as the SR-71 Blackbird.  The
shuttle's goal was to find low cost structures that would lend
themselves to production line fabrication.  For the few shuttles made,
a Titanium craft probably would have been cheaper, but that is not the
point.  The project was intended to research designs that could
eventually lead to assembly line production of shuttle craft.

I would be interested in knowing if this structure is indeed less
expensive.  Ignoring the intial year or so when tiles were dropping
like flies but studying the later years when the shuttle operations
arrived at steady state, have the operating costs imposed by these
tiles been low enough to compete with Titanium structures?

Recognise as well that Titanium structures are probably less expensive
now due to improved fabrication techniques.  Since the early '70s, there
have been improvements in welding, adhesive bonding and Numerical
Control Machining.  In addition, there have been great reductions in
the cost of Finite Element analysis and CAD/CAM.  This greatly reduces
the prototype stage of design and its high costs.  This would
significantly reduce costs in the low volume production of shuttles.

I suspect that a second generation shuttle, designed for a production
run of perhaps as many as 25 craft, might re-evaluate the problem
and choose a Titanium structure that would not require (so much)
insulation.

Bob Clayton
GE Calma
San Diego, Ca.