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RE: starship-design: What is safest?

Hi Lee,

>> 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.

But what is their goal with setting such high standards? Clearly not to use
their equipment longer (which is our SD goal). More likely these higher
standards are a byproduct of needing equipment that works in a wider range
of external variations. (Eg. Their computers should work in freezing polar
conditions but also in a hot and humid jungle.) Such variations are likely
not what most equipment of our starship has to deal with.

>> 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...

While cost is an issue, there may not be such a huge difference in designing
the majority of equipment to last 40 or 80 years.
Anyhow, we started this discussion because Kelly said it was impossible,
which is quite different from expensive.

>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.

Hmmm, I thought he was trying to say that some systems can more easely be
made to last longer.

>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.

Yes, several onboard manufacturing facilities are certainly needed (both for
one and two way missions, but one-way likely needs more). Furthermore most
parts of the ship should be constructed so that they can be repaired/remade
with the manufacturing facilities onboard. The latter may mean that certain
things have to be completely redesigned and that uniformity/compatibility is
a main key. 
Rather than to design for efficiency in large numbers we need to design for
efficiency in small numbers and limited equipment.