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RE: starship-design: What is safest?
On Wednesday, December 17, 1997 11:04 AM, Timothy van der Linden
[SMTP:TLG.van.der.Linden@tip.nl] wrote:
> What areas and why would they do that? What if a 2 times longer life
means
> a
> 3 times higher price? From an economical view, the latter would likely
> make
> little sense, so I wonder if the military did research in that direction.
All flight and nuclear rated systems and some ground and naval combat
hardware, all propulsion and computational hardware, and even some common
handtools have strict reliability and lifecycle criteria in military
procurements. These criteria are typically at the leading edge of what is
available. As a quick comparison, try jet engines - some commercial
airlines fly cargo aircraft that are basically similar to some military
cargo aircraft, they even use nominally the same engines. However, the
military's version of the engine is rated for more hours between
maintenance and a generally longer total life cycle. This isn't even combat
hardware, so that excuse doesn't apply. Because of these requirements
military hardware generally costs more (sometimes a lot more) than similar
civilian hardware.
>
> >To a degree, but the drive is only run a few months, rather then
decades,
> >and
> >has to be rated for full operation for those months under any condition.
> > So
> >it would need a lot of reserve toughness built in.
>
> Reserve toughness? So one can build in more than enough reserve (double?)
> toughness for engines, but not for micro objects that have much less
> stress...
> This argument doesn't fully convince me.
>
Sure you can, and we probably will, but oh the cost...but what I think
Kelly is trying to say is that some systems are not as easy to replace or
carry spares for as others. For instance, if you get a break in a fiber
optic control run, you take some out of spares and replace it. The same
fiber optic can be used to repair any fiber optic, not just a particular
one. Structural members of the ship on the other hand are both less likely
to fail and impossible to carry spares for.
Since MTBF doesn't mean that ALL the parts will fail just that some will,
we obviously wouldn't want to plan on replacing EVERYTHING, but some things
like spare computer parts, switches, bearings and such that can be
interchanged between a lot of different systems we could include enough of
to make a difference. For others, some modest on-board manufacturing
capability should be included.
Lee