Re: starship-design: Re: What is safest?

[Kelly St <KellySt@aol.com>]

In a message dated 12/11/97 5:44:14 AM, TLG.van.der.Linden@tip.nl wrote:

>Kelly,
>
>>> There is however a big advantage of staying in the target system, rather
>>> than "floating" through space another 10 year. In the target system you 
>>> have all the resources you want (including energy), but in space you've 
>>> nothing. Also in the target system you won't need your most critical 
>>> (and likely most deteriorating) part of the ship: The engines.
>>> Kelly continously tells us, that to stay at the target system we need to
be
>>> selfsufficient. But don't we need to be selfsufficient if we stay from
home
>>> 20 years (which is the minimum time for a two-way mission)?
>>
>>No, thats the whole point.  If we can keep the total mission length less
than
>>the time the that ships systems will start needing major repair, and within
>>the amounts of stored food we can carry.  We dramatically cut down on the
>>servicing requirements, and hence needed crew size, repair suplies, and ship
>>size.
>
>Before making the discussion unnecessary long: What kind of repairs do you
>consider to be mayor and to be necessary in 60 years but not within 30?
>
>Timothy


More structural repair due to fatigue and corosion.  Power cables and
distrabution systems, reaction vessels for life support reactions (distilation
of water, air processing and synthasis, etc), plumbing, ductwork, pumps,
bearings for the hab centrafuge, etc.  Also electronics get increasingly
erratic at those ages.   More significant is  that as more and more things
reach and exceed their service lives.  More repairs will be needed, but the
shelf life of the need spare parts would also be exceeded.  So you need to
bring more manufacturing gear to make spares that, years earlier, you could
have replaced from stores.  Stores that themself have broken down while in
storage.  But that leeds to more equip and personel to keep that manufacturing
gear runing.

Food also becomes an issue.  For a 30-40 year round trip mission we found the
weight of stored food was less than that for a close ecology systems with full
food production capacity.  But if the crew has to be cared for for their
projected life span.  (Presumably at least a century by then.)  The ship must
be capable of 70-80 years of support.  That eiather means doubling the weight
in stored food, or going recycled.

Paradoxicly the engines to boost back are fairly safe.  They don't need
complex micro systems, and being unpowered arn't under load or much thermal
stress.  Due to the large scale these engines and reactors must be.  Minor
corosion on metal to metal contact points isn't critical.  To be stable the
engines would have to stick to simple stable alloys (copper vers super
conductors etc.), which would also increase stability.  

Since the decel burn into the system has to end in the systems the thrust has
to stay pretty constant.  But with the boost out of the system you just want
to get to the final speed.  If it takes you 6 months or 2 years, isn't as
crytical.  So if you lose half the engines during the boost.  You just boost
with the others twice as long.  Also if you drop the dead engines, the ship is
lighter and can get to a higher speed with the remaining fuel.  

So a 2 way flight puts most stress on the drive systems, which generally have
only been used for a few months, but least on te general suport systems for
the ship which have alread  been in use for deacades.

Kelly