[Spaceships] Benchmarks for spacecraft cost
 

In GURPS Spaceships spaceship components have the following prices per ton.

Leaving aside GURPS's pervading problem of things not getting cheaper with TL improvement, do those figures seem okay? Is jet fuel really $16 per gallon? Is argon really only 9% the price of hydrogen? Should an external clamp cost only half as much per ton as dumb steel armour?

What benchmarks can we establish for what things ought to cost, eg. how do comm/sensor arrays compare to real life avionics prices? What does a Pratt&Whitney aero jet engine cost per ton? Are airbags really $10,000 per ton?

Re: [Spaceships] Benchmarks for spacecraft cost
 

Hm. I think our first problem would be to establish what kind of dollar we are using. Does 1 USD at current value = 1 GURPS dollar?

And Jet Fuel is apparently currently 3.10 USD/gal.

Also, what are we looking at for price? If we can find something(such as jet fuel) available currently, thats all well and good, but how do we assign value to steel spaceship armor? Current bulk cost of steel? Whats the cost of turning that steel into armor shaped to fit on a craft? I'm sure you've already got some ideas about these questions, I think it's just good to define our assumptions before we attempt this, so we're not working at cross-purposes.

Re: [Spaceships] Benchmarks for spacecraft cost
 

I don't know, but even 'dumb steel' is quite expensive in armour grade alloys, especially when you consider heat treating and working.

Re: [Spaceships] Benchmarks for spacecraft cost
 

Is posting the complete price list from Spaceships strictly necessary here?

I mean it is a copyrighted work...

Re: [Spaceships] Benchmarks for spacecraft cost
 

It's a credited excerpt, it's not nearly enough to build your own spaceships without the book, and I don't think that information is available in that manner in the book, so it's probably all right.

Of the questions he raised, the jet fuel might be overpriced, and the argon seems underpriced in comparison to the hydrogen, so I'd be interested in hearing if those were correct or typos.

Re: [Spaceships] Benchmarks for spacecraft cost
 

Well, for a start it isn't complete. And in the second place prices don't appear in that form in the PDF: except for the fuel and ammunition, I had to calculate them all. So this is neither complete nor a price list from Spaceships. It isn't a breach of copyright because it isn't a copy. Even if it were a copy, it would be a small portion of the work reproduced for the purposes of scholarship or review.

So we can squirt that copyright bogeyman with a water-pistol and get on with what we were doing.

Re: [Spaceships] Benchmarks for spacecraft cost
 

Yeah, but a clamp to hold a spaceship has moving parts, actuators, controls, connectors, and is probably made of high-grade and highly-treated materials itself.

Re: [Spaceships] Benchmarks for spacecraft cost
 

I would guess the intention was that the mass included external cargo, but that somehow didn't make it through to the final version. Clamps are minor items in other Gurps design systems.

Re: [Spaceships] Benchmarks for spacecraft cost
 

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.

Hydrogen and Argon look to be roughly right in comparison, but both about an order of magnitude cheaper than today. If we get much cheaper electricity (fusion, better solar panels) this is semi-plausible.

Re: [Spaceships] Benchmarks for spacecraft cost
 

Now there are explicit rules for diminished acceleration and delta-v when there is something in the clamps.

Re: [Spaceships] Benchmarks for spacecraft cost
 

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.

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.

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. :)

Re: [Spaceships] Benchmarks for spacecraft cost
 

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)

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?

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...

Re: [Spaceships] Benchmarks for spacecraft cost
 

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.