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Old 08-12-2011, 07:12 PM   #21
vierasmarius
 
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Default Re: TL9 Spaceships

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Originally Posted by wellspring View Post
BTW, how does a fission reactor work in space in the first place? Do you have to rotate it for gravity, or does it use something other than convection to operate?
I'm not sure what you mean by that. The basic (very basic) operation of a fission reactor is to place sufficient radioactive material in close proximity to get a sustained nuclear reaction. This generates energy (in the form of heat plus other stuff I don't really know much about) which, in current reactors, is used to boil water. None of this is dependent on being in a gravity well - a steam turbine is driven by pressure, not gravity.
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Old 08-12-2011, 07:30 PM   #22
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Default Re: TL9 Spaceships

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Originally Posted by Nyarli View Post
... Magsails are on par with reaction drives on AU1, and outperform then on AU2+ distances, which is quite important, if you plan to travel to Jupiter or Saturn...
Are you dividing magsail acceleration by (1/D)^2? It's not mentioned in the magsail description, but is mentioned on p. 39. Discussions on the forums haven't concluded yet which is more realistic*. If you are dividing acceleration, magsails still have some inner system applications at TL9, but often aren't the best option for outer system travel.

* I believe: non-plasma magsails should divide acceleration; plasma sails maintain constant acceleration but realistically should require "fuel" (additional ionizable materials due to plasma loss) at about 6.8 mps per tank.
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Old 08-12-2011, 07:48 PM   #23
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Default Re: TL9 Spaceships

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Originally Posted by munin View Post
Are you dividing magsail acceleration by (1/D)^2? It's not mentioned in the magsail description, but is mentioned on p. 39. Discussions on the forums haven't concluded yet which is more realistic*. If you are dividing acceleration, magsails still have some inner system applications at TL9, but often aren't the best option for outer system travel.
Realistically, magsails should also get constant acceleration, by reeling out more cable as the stellar wind decreases. This is ultimately limited by the tensile strength of the cable, though.

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Old 08-12-2011, 08:38 PM   #24
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Default Re: TL9 Spaceships

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Realistically, magsails should also get constant acceleration, by reeling out more cable as the stellar wind decreases...
The heliopause is in the neighborhood of 100 AUs from the sun. For a magsail to maintain constant acceleration all the way out to there it would need to increase its loop circumference also by a factor of 100, implying that it only has 1% of its cable spooled out when traveling at 1 AU (it can't spool out more closer to the sun because there's a point where, as you said, the acceleration of a larger loop exceeds the cable's tensile strength). I don't think you would design a magsail that way, you'd have the whole thing spooled out all the time and just get less acceleration as you move further from the sun -- and I think the Spaceships magsail stats are based on having the entire mass of the system devoted to acceleration, and not spooled up. Thus the rule on p. 39 to divide the magsail's acceleration by (1/D)^2 (though it is weird it's not mentioned in the magsail's description, like the light sail).

A plasma sail, on the other hand, doesn't need additional mass to get bigger, the plasma loop just expands automatically. But it leaks plasma, hence the need for "fuel" which will run out after a while.
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Old 08-12-2011, 09:12 PM   #25
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Default Re: TL9 Spaceships

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BTW, how does a fission reactor work in space in the first place? Do you have to rotate it for gravity, or does it use something other than convection to operate?
In most designs the working fluid (water or molten sodium) is pumped through the core and the heat exchanger. Convection is not significant.

And then there is the radioisotope thermoelectric generator, a simple design using thermocouples to generate small current but with immense endurance. A subcritical mass of radioisotope keeps one end of each thermocouple hot, and a radiator keeps the other ends cool. An E.M.F. is produced. No moving parts, no circulating fluid. Heat is removed by conduction to the radiator. Power:mass ratio is not impressive, but energy:mass is pretty good, and endurance is decades. These
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Old 08-13-2011, 03:59 AM   #26
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Default Re: TL9 Spaceships

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Originally Posted by wellspring View Post
BTW, how does a fission reactor work in space in the first place? Do you have to rotate it for gravity, or does it use something other than convection to operate?
You just pump the coolant, same as almost all real-world high-power fission reactors.

AFAIK, reactors that can operate on convection are a recent innovation for submarines, and limited to low power levels - to go fast, the sub has to turn on pumps. Making reactors able to deal with residual heat via convection with no pump once they've been shut down is a desirable feature, but is not always achieved.
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Old 08-13-2011, 06:26 AM   #27
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Default Re: TL9 Spaceships

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Which drives would you allow to be used in Earth atmosphere?
I'm not sure any drive would be used. TL9 makes the miracles of a space elevator possible. on a highly developed planet like the earth it would be very practical to transport all goods to one of a couple elevators and than just haul them into space. The use of a reaction drive would probably be limited to highly sensitive military cargos and to the use of off world colonies where it is uneconomical to construct a space elevator.

My 2 cents
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Old 08-13-2011, 06:50 AM   #28
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Default Re: TL9 Spaceships

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I'm not sure any drive would be used. TL9 makes the miracles of a space elevator possible. on a highly developed planet like the earth it would be very practical to transport all goods to one of a couple elevators and than just haul them into space. The use of a reaction drive would probably be limited to highly sensitive military cargos and to the use of off world colonies where it is uneconomical to construct a space elevator.

My 2 cents
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Anybody remembers rules for space elevator construction? As in, how much it costs? (To compare with a space launch.)
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Old 08-13-2011, 07:02 AM   #29
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Default Re: TL9 Spaceships

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Anybody remembers rules for space elevator construction? As in, how much it costs? (To compare with a space launch.)
$40 Billion per ton per day (Ultratech p.224) on earth gravity. This would be devided by the square ration of gravity. I.e. A lunar beanstalk would cost 1/36th.

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Old 08-13-2011, 07:40 AM   #30
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Default Re: TL9 Spaceships

G:Spaceships 2 gives some estimates on costs (for freight, but i suppose it can double as payload cost), though those are of course setting specific...

At TL9 reaction drives (interface rates) are rated as ~ 50 k$ per st going up and ~ 5k$ per st going down. Beanstalks gives 10 k$ per st either way. All values are in standard gravity.

Elevators are still kinda slow and are rather exposed to radiation especially at low TLs (depends on design, but the heavier it gets the more expensive it gets).
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