Batterie relatively useless on space stations?

[Anton P. Nym]

lots of points favouring solar+batteries

lots of points favouring RTGs alone

From which I conclude that Squad has done a good job balancing the two, and wander off in search of snacks. (I am attuned to my inner Kerbal.)

-- Steve

[Tiron]

But there's more to it than that. RTGs never run completely dry. Because they always provide at least a little bit of juice, you can get by with fewer of them than you might think. For example, built a small rover and put 1 RTG on it as its only source of electricity. You start out with your electric charge bar on the resource tab 100%. Now hold down W. The rover will accelerate to a high speed and will maintain this speed as long as there's anything showing in the resource bar. But the bar goes down fairly rapidly until it gets to zero. Still, if you keep holding down W, the rover will merely slow down to a lower speed, but will never stop. You'll see a tiny amount of bar flickering just above zero. This is providing the wheels with less juice than their full-power draw so they don't turn as fast as possible, but they still turn. And if you release the W key the charge bar will shoot back up to 100% and you can go fast again. Meanwhile, the lights never even flicker.

It's the same thing with reaction wheels. Maybe on paper using them would suck the charge down very quickly, but because the charge level is effectively never zero, they keep on spinning, although perhaps slower. But with rockets, you're not holding the control over constantly during a turn, you're just tapping it in the direction you want to go, releasing and drifting to where you want to be, then tapping again to stop the swing. Between these taps, the charge bar will refill entirely so each tap has the full power available. And for whatever reason, SAS never seems to lack for power when using reaction wheels to keep the rocket stable. This is probably also due to the fact that it's not using them constantly, but just doing a series of gentle taps, none of which use much juice and are far enough apart for the charge to rebuild anyway.

So, at the bottom line, 2 RTGs are enough, all by themselves, to keep probe brains alive forever, run however many lights 24/7 with no flickering, control the vehicle with reaction wheels, and keep it stable with SAS, all at the same time. No matter what the numbers say on paper, this is how it actually works. Could be this is an exploit, but I think it's really that reaction wheels and SAS don't need to draw their full load most of the time, and when they do it's only for very brief periods allowing recovery in between.

For the normal domestic electrical needs (probe brain, lights, SAS, and torque) of an airplane, a station module, or a rocket, therefore, all you need is 2 RTGs and could probably survive on 1. Thus, your argument of needing as many as 5 RTGs for such purposes is moot. It's only when you start doing things that impose high electrical loads for long periods (rovers going fast over long distances, messing with Kethane, using ion or electrical airplane/helicopter engines, etc.) that RTGs become inadequate.

Now I should note that solar panels without batteries can do the same thing as RTGs, always providing some non-zero amount of juice even if the momentary demand exceeds their output. But only while the sun's on them. So, if your only source of power is solar, you'll need enough batteries to meet the station's domestic needs all night long. Figuring out the number of batteries can be a chore because it depends on which planet your station's at and how you're orbiting it, and some combinations entail very long nights. You also have to remember to open the solar panels as soon as possible after launch, and retract them before aerobraking and such.

Sure, 2 RTGs weigh more than solar panels and batteries making the same juice, but for domestic needs the total of either is very small and the difference is just a fraction of a ton. This isn't enough to change the size of the rocket needed to move the station module wherever you're going with it so is a non-factor. But RTGs are low-polygon models with small, simple textures and no animations, and you generally need fewer parts with them than with panels and batteries. Plus they require zero intervention on your part. So for simplicity and less load on the computer, RTGs (for domestic use), seem the best bet. In which case there's no need for batteries.

In most cases, 'enough' batteries isn't going to be very many. If you're orbiting a body, you're very likely not going to be in eclipse all that long, unless in a high inclination orbit. That means unless you're trying to do EXTREMELY high power draw things like use ion engines or rotate 12 reaction wheels on all three axes at once the entire time, you're not going to need more than a few batteries, particularly now that the inline 1m batteries hold 1k for the same weight as before. There's now even a large size battery with a capacity of 4000 units of charge,(at the same mass per capacity as the other batteries, even) so battery partcount isn't nearly the problem it once was.

As for rovers, I'm all for nuclear rovers as I've mentioned several times. On the surface, on many worlds you spend a very long time in eclipse, so long that the needed weight of batteries to keep you running during the night is far, FAR higher than the weight of RTGs just to run it all the time. Not to mention that on worlds with any kind of atmosphere, the drag you experience as you roll across the surface is frequently enough to break solar panel arrays off, meaning you're stuck using OX-STATs. OX-STATs have the heightest power to weight ratio of any generation source, but they don't track the sun (meaning they're almost always at a suboptimal angle), and their base output is the same as an RTG's, so you end up needing a LOT of them.

Thus why my rover is nuclear, even though my ships are not(I may investigate the weight requirements of taking my mapping probe nuclear though, the kethane mapper uses a lot of juice, and high inclination orbits give it longer eclipse periods than normal).

From which I conclude that Squad has done a good job balancing the two, and wander off in search of snacks. (I am attuned to my inner Kerbal.)

-- Steve

Yeah, they pretty much did. Solar Panels and batteries save weight, RTGs are more convenient and sometimes have lower partcounts.

It's going to get even better at some point, when we get planets beyond Jool. (Eeloo is allegedly going to be a moon of one of them when it happens.) Get far enough out, and the power reduction on solar panels will swing things sharply in favor of RTGs. Trick being is that there really isn't anything out that far just yet.

[Geschosskopf]

In most cases, 'enough' batteries isn't going to be very many. If you're orbiting a body, you're very likely not going to be in eclipse all that long, unless in a high inclination orbit. That means unless you're trying to do EXTREMELY high power draw things like use ion engines or rotate 12 reaction wheels on all three axes at once the entire time, you're not going to need more than a few batteries, particularly now that the inline 1m batteries hold 1k for the same weight as before. There's now even a large size battery with a capacity of 4000 units of charge,(at the same mass per capacity as the other batteries, even) so battery partcount isn't nearly the problem it once was.

Everybody harps about part count but I think it's not the parts per se, it's the footprint they have. Solar panels have some of the biggest footprints per non-IVA part in the game, what with their complex deploy/retract animations, their sun-tracking, and their rather large textures.

As for reaction wheels, every module I launch for a station or multi-part ship has a probe core, one of the old ASAS units for extra torque, a bunch of lights, and 2 RTGs. None of them individually ever lack for power so all of them combined never lack for power.

As for rovers, I'm all for nuclear rovers as I've mentioned several times.

Agreed.

It's going to get even better at some point, when we get planets beyond Jool. (Eeloo is allegedly going to be a moon of one of them when it happens.) Get far enough out, and the power reduction on solar panels will swing things sharply in favor of RTGs. Trick being is that there really isn't anything out that far just yet.

But if you use RTGs by default, you don't have to worry about this. You know your stuff will work the same at Moho or Eeloo, and you don't have to lift a finger to make it so.

[AstroRick]

Actually, on a few shuttle I have going to LKO, I find that one RTG and One battery works perfectly. Lighter than two RTGs, the RTG charges the battery and the battery keeps those reaction wheels spinning.