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Old 08-12-2011, 12:50 PM   #1
Nyarli
 
Join Date: Jun 2011
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Default TL9 Spaceships

I am reading Starship books, and i have some questions about drives:
1) I have made some calculations, and it's looks like magsails are Just Better for interplanetary transportation inside of Solar system at TL9( without superscience) than everything else, especially if you don't want more than 10 systems dedicated to propulsion. 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. They are not the most expensive of all drives, they don't require fuel and their only drawback is inability to start from planet. Am i right, or i have missed something?
2)Related question: Which drives would you allow to be used in Earth atmosphere? It is obvious that Orion drive is off-limits, but what about other drives?
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Old 08-12-2011, 01:02 PM   #2
sir_pudding
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Default Re: TL9 Spaceships

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Originally Posted by Nyarli View Post
Am i right, or i have missed something?
Other options might be cheaper in some applications if you are more worried about expense over velocity, but otherwise they seem like a pretty good choice in real-life too.
Quote:
2)Related question: Which drives would you allow to be used in Earth atmosphere? It is obvious that Orion drive is off-limits, but what about other drives?
Would who allow? Me personally? A likely near-future Earth (with a still active anti-nuke contingent)? A hypothetical space-faring civilization that's less conservative?
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Old 08-12-2011, 05:09 PM   #3
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Default Re: TL9 Spaceships

Re: magsails:

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Originally Posted by sir_pudding View Post
Other options might be cheaper in some applications if you are more worried about expense over velocity, but otherwise they seem like a pretty good choice in real-life too.
They are pretty much the best real-life choice, for suitably broad definitions of "real life". We have yet to demonstrate superconductors that can operate at the required temperatures, but if you take modern high-T superconductors and say "like that only up to 350K" then you get very impressive performance.

Plasma sails, OTOH, require consumables, and I would wager that the concept proposals likely err on the side of optimistic specific impulses.

TeV
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Old 08-12-2011, 05:24 PM   #4
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Default Re: TL9 Spaceships

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?
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Old 08-12-2011, 07:12 PM   #5
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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?
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, 09:12 PM   #6
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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   #7
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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 08-12-2011, 01:08 PM   #8
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Default Re: TL9 Spaceships

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Originally Posted by Nyarli View Post
2)Related question: Which drives would you allow to be used in Earth atmosphere? It is obvious that Orion drive is off-limits, but what about other drives?
Do you mean "Which drives do you believe are capable of functioning in Earth atmosphere?" or "Which drives would you, as a GM, have be legal to use in Earth's atmosphere?"
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Old 08-12-2011, 01:22 PM   #9
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Default Re: TL9 Spaceships

I asked about legality( and yes it is future of our Earth, not abstract space-faring civilization) but I would be glad to hear if some drive s from Spaceships are unable to function in atmosphere, by your opinion.
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Old 08-12-2011, 01:32 PM   #10
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Default Re: TL9 Spaceships

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I asked about legality( and yes it is future of our Earth, not abstract space-faring civilization)
Then any kind of nuclear or antimatter propulsion is almost certainly right out.
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