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Re: starship-design: Mean Time Between Failure

L. Parker wrote:

>So you see, the system as a whole is much more fragile than any single one 
>of its parts, which is what makes it so terribly difficult to build 
>something like Voyager or Mariner and expect them to not only survive for 
>long, but do so in a hostile environment. Using the argument that we don't 
>build them to last longer because we don't have to won't wash. Even the 
>military and NASA, both of whom go to extreme lengths and pay outrageous 
>sums for reliable parts are still plagued with what they describe as "low 
>operability" or "mission capable rate".

NASA and the military don't build things to last centuries, and have
no incentive to do so.  (The former because nothing they build will
be used so long and the latter because anything built today will
be obsolete soon enough.)

Building things to last is an engineering problem, and it can be done.
Ask an engineer to design something that will last 100 or 1000 years,
and he'll go and do it.

The question is--why?  Why would you build something designed to last
1000 years without maintainance?  Well, Hoover Dam's massive turbines
are an example of this.  There simply isn't any practical way to
perform maintainance on them, so they and their bearings were designed
to last 1000 years (this is undoubtably optimistic, and extrapolating
far beyond any reasonable bounds, but at least they've done well for
the larger part of a century).

There really isn't a big secret to making things last--you keep them
simple and big and heavy rather than miniaturized and pared down to
minimum tolerances.  My dad's old Sony turntable and amplifier works
perfectly after 3 decades because they just plain overengineered the
things back then.  Advances in technology allowed miniaturizing,
reducing wasted space, and paring down the thicknesses of the case
walls to a minimum, so today's Sony amplifiers are more sophisticated,
smaller, and lighter.  But I wouldn't be on them lasting as long.

For today's space missions and military applications, of course, it's
anathema to bulk up components without good reason.  Making them last
more than a few decades isn't a good reason for a mission which lasts
only a few years.
    _____     Isaac Kuo kuo@bit.csc.lsu.edu http://www.csc.lsu.edu/~kuo
/___________\ "Mari-san...  Yokatta...
\=\)-----(/=/  ...Yokatta go-buji de..." - Karigari Hiroshi