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Old 03-13-2008, 07:51 PM   #11
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Default Re: [Spaceships] Benchmarks for spacecraft cost

Quote:
Originally Posted by thtraveller
I make it closer to $12, in any case I think it a fair assumption that the price of oil based jet fuel will rise considerably.
if it does, then it might not be a fair assumption that the jets will be fueled with petroleum, rather than ethanol, methanol, oil from bioengineered plants, hydrogen-hydrogen slurry, or the compressed atmosphere of Titan.
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Old 03-14-2008, 02:18 AM   #12
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Default Re: [Spaceships] Benchmarks for spacecraft cost

There does seem to be a bias that these fuels for space craft are cheaper and fuel for aircraft are more expensive. Not only that but these spacecraft fuels have to be available in orbit and are bulky and/or difficult to store. Earth based prices an space based prices are likely to be significantly different.

If it's a problem just run it trough your groups reality filter and come up with a good number for each.
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Old 03-14-2008, 06:49 AM   #13
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Default Re: [Spaceships] Benchmarks for spacecraft cost

BTW, you missed out empty fuel tanks at $6,000 per ton of capacity, though as they seem to be weight/massless themselves, I suppose they won't fit very well. :)
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Old 03-14-2008, 12:44 PM   #14
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Default Re: [Spaceships] Benchmarks for spacecraft cost

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Originally Posted by Rupert
BTW, you missed out empty fuel tanks at $6,000 per ton of capacity, though as they seem to be weight/massless themselves, I suppose they won't fit very well. :)
In VE2 they were typically 0.5 lb and $20 per gallon (light self sealing tank) or 0.1 lb and $50 per gallon (ultralight self sealing).

Having the same price for water tanks as for liquid hydrogen tanks has always been an issue with design systems.

(EDITED)
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Last edited by thtraveller; 03-15-2008 at 11:20 AM. Reason: Extra information
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Old 05-03-2013, 04:31 PM   #15
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Default Re: [Spaceships] Benchmarks for spacecraft cost

In researching spaceship drives, I've found the following tidbids of information.

Liquid Hydrogen = $4.5 per kilogram
Thruster-grade Argon = $40 per kg
Thruster-grade Xenon = $5000 per kg
Liquid Oxygen = $0.08 per kg

Using the GURPS baseline of $2000 for a ton of LH2, converting to GURPS $ gives (2 significant figures):
Argon = $18000 per ton
Xenon = $2200000 per ton
LOX = $36 per ton

The GURPS price for "ionizable reaction mass", realistically, seems to be off by several orders of magnitude. An MPD Arcjet can use hydrogen, though.

Here's some thruster stats:

NEXT Ion Thruster: Impulse 4190, 0.236 N thrust @ 6.9 kW, 58.2 kg
In GURPS: Delta-v of 1.4 mps, thrust 0.0002 G, requires 0.12 MW / ton, uses Xenon

VASMIR Magnetoplasma rocket: Impulse 12000, @ 2.5 MW, 1900 kg; 5 N thrust @ 0.2 MW (estimates from proposed design and the VX-200 prototype)
In GURPS: Delta-v of 4 mps, thrust 0.0016 G, requires 1.3 MW / ton, uses Argon

RD-0410 Nuclear Thermal Engine: Impulse 910, 2000 kg, 35300 N thrust
In GURPS: Delta-v of 0.3 mps, thrust 0.88 G, uses LH2

Vulcain 2: Impulse 429, 1800 kg, thrust 1359000 N
In GURPS: Delta-v of 0.143 mps, thrust 4G, uses LH2/LOX

I'm trying to get thrust-to-weight ratios for MPD Arcjets and the lithium-fueled LiLFA thruster. Also, the cost-per-ton of thruster-grade lithium.

Power
I read about a power unit's "alpha" on Winchell D. Chung's excellent site, and derived these power outputs for a 1.5 ton module in a 30-ton hull (all TL8 I guess)
Radioisotope Thermoelectric Generator = 0.015 MW
Fuel Cell = 0.115 MW
Fission Plant = 0.083 MW
Nuclear Power Unit (design proposed by Otis Peters @ Los Alamos) = 0.1 MW


Do any of the above figures look wrong?
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Old 05-04-2013, 07:31 AM   #16
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Default Re: [Spaceships] Benchmarks for spacecraft cost

I highly doubt that an external clamp necessarily takes up 1/20th of a ship's total mass. That and quite a few of the other things that pop out of spaceships come about, I think, because of the abstractions the book makes. For example, the guns don't make a lot of sense to (why would barrel size be necessarily tied to gun tonnage?)

This is one of the reasons I eagerly await GURPS VDS. GURPS Spaceships is fine for approximations or very large, space-opera-y ships (though the combat system doesn't support them well), but if you want more detail and specifics...
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Old 05-04-2013, 07:44 AM   #17
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Default Re: [Spaceships] Benchmarks for spacecraft cost

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Originally Posted by Mailanka View Post
I highly doubt that an external clamp necessarily takes up 1/20th of a ship's total mass. That and quite a few of the other things that pop out of spaceships come about, I think, because of the abstractions the book makes. For example, the guns don't make a lot of sense to (why would barrel size be necessarily tied to gun tonnage?)
External clamps taking less than 1/20 are of course allowed under Smaller Systems. But they cost the same per ton and also have somewhat limited functionality.

Gun barrel size tying in to tonnage is a completely unsurprising simplification to allow guns to inhabit a 1-dimensional spectrum. It might be reasonable in many cases...I can't really see lower-velocity 'sawed-off' cannon being attractive considering the issues, except maybe as a bombardment weapon due to bombs being strictly 'dropped' rather than thrown. And a higher velocity cannon variant might be technically infeasible.
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