Spaceships--how much IS a power point

[YankeeGamer]

A power point clearly scales with the size of a ship, but is there any decent way to covert a plant's output into megawatts?
I'm using Spaceships as a rough outline for building some craft for a story, and that would help a lot. It is also useful if a ship's plant is going to power a city for a time.
Thanks to any with ideas--don't need exact numbers.

[Diomedes]

Ages ago, I did some math on the subject, extrapolating the value of a power point from the weapons.

[ericbsmith]

Spaceships, like other GURPS 4th Edition books, is purposefully vague about how much power is produced by a power plant or power cell. The closest you could get would be to take the mass of a power plant and divide its weight by the weight per kw from GURPS Vehicles 3rd Edition.

Using that method we get approximately:
Fission 2MW/ton 1 Power Point
Fusion 10MW/ton 2 Power Point
Antimatter 40MW/ton 4 Power Point
Total Conversion 200MW/ton 5 Power Point

This scales roughly correctly for Fission, Fusion, and Antimatter, but Total Conversion was considerably more efficient. Other power plants from other books are going to be even further off from these figures.

Still, if we assume that the conversion rate is correct, this means that a SM+5 Fission, Fusion, and Antimatter plant, which mass 1.5 tons, provides 3MW per Power Point. This number could be high, since that 1.5 tons of mass includes hull and frame, so it could be more like 2MW per Power Point.


Given that a SM+6 Power Point would be roughly 3.33x this, or 7-10MW per Power Point, SM+7 would be 10x that of a SM+5, or 20-30MW per Power Point.

These figures are wholly non-canonical estimates, of course.

[ericbsmith]

Originally Posted by Diomedes

Ages ago, I did some math on the subject, extrapolating the value of a power point from the weapons.

Interestingly, the numbers I just calculated are in the same ballpark as yours, even if coming from a a different source, suggesting that David Pulver may have had some real numbers behind the scene that were close(ish) to the Vehicles 2e numbers.

[AlexanderHowl]

I generally use ([Main Battery Output × 4] ÷ 20) for electricity generation. The electricity generation assumes a 25% efficiency on the TL that a beam weapon first appears and a 50% efficiency one TL higher. A SM+10 Power Point is the equivalent of 600 MW of electricity.

[YankeeGamer]

HUGE amounts of power. That would put my SM +13, 300,000 ton fusion-powered land behemoth (2 power points) could easily have an output of 40,000 megawatts. YIKES!
Park on solid ground, lest radiated heat start melting the oxygen and nitrogen ice beneath the tracks.

[Anthony]

Remember that Spaceships assumes an RoF of 1/10. I recall working out (based on performance of electrical drives) that one pp is in the 50-100 kW/ton (of vehicle, not of power plant) range.

[Pomphis]

Originally Posted by YankeeGamer

HUGE amounts of power. That would put my SM +13, 300,000 ton fusion-powered land behemoth (2 power points) could easily have an output of 40,000 megawatts. YIKES!
Park on solid ground, lest radiated heat start melting the oxygen and nitrogen ice beneath the tracks.

My GURPS Traveller TL11 CB Overlord with 200,000 tons (27,000 dt, J-4, 2G) has a bit over 281,000 MW. It is a beam weapon heavy design.

[Johnny1A.2]

Originally Posted by YankeeGamer

HUGE amounts of power. That would put my SM +13, 300,000 ton fusion-powered land behemoth (2 power points) could easily have an output of 40,000 megawatts. YIKES!
Park on solid ground, lest radiated heat start melting the oxygen and nitrogen ice beneath the tracks.

Yeah, that's the kind of power serious spacecraft have to have. Depending on how you measure it, a Saturn V first stage generated somewhere between 60,000 and 200,000 megawatts (for a few minutes, granted). The thrust power of some hypothetical engine designs could easily get into terawatt levels.

Now 40 gigawatts is an awful lot for a land vehicle. For comparison again, a Nimitz class aircraft carrier has a power plant that runs in the range of 200 megawatts.

[cptbutton]

Originally Posted by Johnny1A.2

Yeah, that's the kind of power serious spacecraft have to have. Depending on how you measure it, a Saturn V first stage generated somewhere between 60,000 and 200,000 megawatts (for a few minutes, granted).

I heard once that just the sound was 10,000 megawatts.