Re: Re: starship-design: One way (again...)

[kuo@bit.csc.lsu.edu (Isaac Kuo)]

Kelly St wrote:

>If you are for some reason assuming a 2 way trip without refueling, I'm not
>sure mearly halving the cruse speed would allow you to stay withing the same
>total fuel mass ratio.

One possible reason is that there are no resources in the target system
with which to refuel.

Another reason is that this mission is the first manned mission, and
that because of this there isn't enough information about the target
system to refuel.

And halving the cruise speed is very obviously adequeate to keep the
same fuel mass ratio, because the example I pose is one of a rocket.
In a rocket design, the maneuvers it can perform are determined by
its delta-v (in this case, .4c).  A one way trip can have a cruise
speed of .2c.  A two way trip can have a cruise speed of .1c.

[...]
>>Hence, the two-way mission will need approximately the same
>>amount (and duration needs) of the equipment.
>>But two-way will be much more demanding from the fuel/engine
>>point of view (as Isaac correctly remarked, not simply two times
>>more, but possibly orders of magnitude more).

>This makes no sence.  If your assuming the same total fuel ration on the ship
>for a one or two way mission.  You need the same total thrust from the engines
>(but of course on the return leg you can stand dropout with less mission
>impact).  So how could the demands on the engines be orders of magnitude more,
>or realisticly even twice as much?  At most the engines firing time is twice
>as much, but thats separated by years to do check out and servicing.

No, he is assuming the same cruise speed, but with different fuel
ratios (no refueling).  You're the one assuming refueling.

Because the fuel ratio goes up so much (e.g. in the case of a
10,000-1 ratio for the one way trip, it goes up by 10,000), the
total costs can be many orders of magnitude more.

>>Or "leaving them to die" during the long and quite boring 
>>return flight (of old age/sickness or in a catastrophic accident,
>>much more probable during the return flight due to engine wear)?

>The return flight would certainly be no more boring then being parked in the
>target system.  Eaither way you still stuck in the ship with no where to go.
>But at least your going back somewhere at the end.

It sure would be more boring to me, and anyone else I could imagine
going on the first interstellar manned missions!  The people on the
first manned missions will all be astronomers (even if you send up
someone who isn't, by the time he arrives at the target he's an
astronomer).

It should go without saying that studying another star (let alone
two) is a lifetime endeavor.  Even if the only sensor available
left is the Mk 1 Eyeball and dark sunglasses, it's at least possible
to study the stars.

(I seriously doubt your assertion that all the sensors and backups
fail within a few decades, and find your assertion that telescopes
back home can outperform those on site utterly ludicrous.  At the
very least, we can expect the starship to have a baseline of 1km
for LBI telescopes.  At 1 light minute away, a telescope back
home would need to be 2 million km wide just to compete with the
_resolution_; there isn't any atmosphere-less body big enough to
anchor all those elements onto.  At frequencies where VLBI is
practical, the starship can expect a baseline of perhaps 1 light
minute, which would require a telescope back home 4 light years
wide.)
-- 
    _____     Isaac Kuo kuo@bit.csc.lsu.edu http://www.csc.lsu.edu/~kuo
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