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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 
> 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 
> >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.