[Spaceships] How many types of power plant in your universe?

[Ulzgoroth]

Originally Posted by Varyon

For my Harpyias setting, I intend for the ships to use superscience capacitors, without any sort of proper power plant on board. Many will have small retractable solar panel arrays to augment the capacitors, but those really just serve to reduce the rate of energy consumption (or to slowly recharge in the case of an emergency). Power generation in space is in the form of solar "fueling stations" that vessels can dock with to recharge (most are likely to have various supplies available for purchase, at a premium) - chemical fuels don't have enough energy density to compete with the capacitors, fission (and RTG) is outlawed, and fusion/antimatter/total conversion simply aren't available. Planetside, the same superscience that protects spacecraft with shielding can be exploited to generate energy, but that's not really feasible in the vacuum of space (it draws power from subspace, and heats up while in operation; this lets you setup a heat engine powered by subspace, provided you've got somewhere to dump the heat).

What makes that not viable in space?