Nuclear Powered Aliens

[Varyon]

Originally Posted by Nereidalbel

The 10% maximum would be for a plant that used all 7 (known) variants of chlorophyll. No reason you can't engineer that in your ships, honestly. Throw in the bacteriochlorophyll that can hit up to 70% efficiency, and your ships can at least hibernate if they need to be abandoned for some reason.

I didn't realize bacteriochlorophyll got to such efficiencies. At Jupiter-equivalent orbit in the human-inhabited systems (I'm not bothering to create the systems inhabited only by malakim, as human technology is currently incapable of reaching those... and the malakim located in such are by far in the minority), solar energy is around 92 W/m^2. A theoretical SM+0 bioship might have around 20 m^2 in exposed surface area with its wings fully spread and angled to catch as much sunlight as possible. That's around 1840 Watts, or just shy of 160 MJ in 24 hours. A GURPS adventurer needs to consume roughly 12.5 MJ (around 3000 kcal) daily, so even 10% efficiency would keep the bioship going, with some left behind. Considering consumption scales roughly with surface area, this relationship would scale up just fine for the actual bioships in question. If the crew members are 4 SM's smaller than the ship, for roughly 1/5th the consumption, the leftover 3.5 MJ would be enough to sustain nearly 1.5 of them, which is appropriate considering an SM+4 bioship would probably be a single seater fighter or similar.

Granted, this is assuming a bioship is going to have similar caloric requirements as a human scaled to the same size. They'll actually have much lower basal metabolic rates (less energy need be spent getting up to temperature, as space is a pretty good insulator, and they don't need to burn energy to sustain oversized brains), but much higher active caloric needs (their "aether flukes" burn through a lot of energy), which will probably work out to overall higher caloric requirements. Additionally, interstellar travel requires them to travel all the way out to the system's termination shock (which in-setting is simply called the helioshock), which is going to be somewhere around 18x further from the sun than the Jupiter-equivalent, and then requires them to travel through hyperspace where there's no solar radiation to rely on, so they'll need radiosynthesis - and/or a very large store of fat or similar - to make it through all that.

...

I think I have my sort-of-rubber-science explanation. In the systems of interest, the primary gas giant has incredibly high radiation levels, resulting in any of its moons that lack atmosphere having high concentrations of radioactive elements - notably, they tend to have an abundance of Plutonium-238. One of the malakim forms, the Lachporim, is a specialized digger and bioconcentrator of a variety of useful elements, including Plutonium-238. It shares this with other malakim, and they use its decay energy to supplement their rations. As Plutonium-238 produces around 0.57 W/g, with 10% efficiency a malakim with a 3000 kcal daily requirement would require somewhere around 2 kg to avoid needing to eat. They'll actually have a good deal less than this, of course, as they do still need to eat. Also, any energy that isn't converted into usable calories is going to be waste heat, which could be problematic with only 10% efficiency. On the bright side, the malakim probably don't need to "waste" any food calories on staying warm, as their internal plutonium reserves handle that for them.

The bioships themselves tend to "park" in a highly-radioactive orbit around the gas giant to store energy (likely as fat or similar) from time to time. This is particularly common following travel through hyperspace, as that tends to deplete their reserves.