Power efficiency in drive specs

[Starstrider42]

Hello, new player here. I'm loving TI, but I'm confused about the "Power Use Efficiency" rating attached to drives. I'd assumed this is the output (mechanical) power divided by the input (electrical or thermal) power, but that doesn't seem to be the case.

For example, the basic 1× Nerva drive has the following specs in version 0.3.76: required power 198.2 MW (and I double-checked that this is the input power, i.e. it matches the reactor rating), thrust 49 kN, specific impulse 8.09 kps, power use efficiency 70%. From these specs, one can calculate the output power as 0.5 × (49 kN) × (8.09 kps) = 198.2 MW, which is the same as the input power to within rounding errors.

I've done this calculation for several other early-game drives, both nuclear and electric, as well as the alien torch, and the answer is always the same: 100% of the input energy goes into the exhaust. This makes the input power range a handy proxy for how much thrust a given drive family is capable of, but it's odd that the efficiency doesn't have an in-game effect.

Is this a bug? Unfinished feature? Vestigial feature? Or am I completely wrong about what "Power Use Efficiency" is supposed to represent? I've searched the forum and the wiki, but I can't find any mention of this rating at all.

[johnnylump]

Right now efficiency is used to determine waste heat and thus radiator size. But you're correct in that the power plant isn't "charged" that extra amount in its requirements, which I suppose I oughta look at

[Starstrider42]

Thanks for the quick reply! To clarify, are you saying the correct specs for the Nerva should be required power 283.1 MW, waste heat 84.9 MW, thrust 49 kN?