How do you use the "new" big fuel tanks?

[korniton]

Hello everyone, 

 

I´ve been strugling by using the new fuel tanks in KSP. The really big ones that hold like 20k+ LF and OX (The Making history fuel tanks). I´ve seen people use them mostly for the Saturn V. 

 

I´ve been strugling to use them any otehr way as they are really heavy, expensive and I end up with a super huge fuel tank in kerbin orbit witch I dont know what to do with. As much reaction wheels as you have, its always a pain to rotate the craft in space. But on the otehr hand, its really good to have a ton of fuel.

Maybe I should stick with the otehr tanks instead.

[Just Jim]

I already plan on hauling a couple empty ones to use as fuel storage on my ore-processing space stations. A couple of those filled would re-fuel my shuttles a dozen times and more.

[korniton]

3 minutes ago, Just Jim said:

I already plan on hauling a couple empty ones to use as fuel storage on my ore-processing space stations. A couple of those filled would re-fuel my shuttles a dozen times and more.

I see what you mean, build normal rockets with the smaller parts and refuel em in space to advance further. Nice idea. Thank you.

[Tokoshoran]

I haven't seen them yet (I'm kind of rubbish at this game), but I'd assume they're good for refuelling stations. Going alongside the idea of hauling empty ones up, you could do that to carry a load of fuel further and further out--Launch the first one not as far out, then an empty one to grab the fuel and carry it further.

[Aegolius13]

The 5m tanks should be great for mining ships.  Low and wide is the way to go. Large orbital fuel depots also seem like possibilities. 

I agree they are probably got going to be that useful for launches.   For really big rockets, it's usually more economical to build out with TwinBoars, SRBs and the like than to go with just a big core stage. 

[blakemw]

The make good cores for certain kinds of things, especially the shorter ones. Big landers, bases and such.

Also if you have a payload for a 5m fairing, they can make pretty good boosters. It might involve a little clipping but you can pack 3-4 Twin-Boars into a 5m engine plate. Nice for big SSTO, my favorite kind of rocket.

With rotation, the closer something is to a sphere the easier the time reaction wheels have rotating it, so the big dense tanks are actually going to be easiest to rotate (especially the one which is as tall as it is wide). You can just add like 8x 2.5m reaction wheels, that's what I use to rotate Class E asteroids.

[bewing]

RCS has a lot more rotational thrust than reaction wheels, and Vernors have even more thrust than that. And you only have to get those tanks into space once. Yes, it's expensive to launch the things. Which is how space launches really are, y'know?

[korniton]

11 hours ago, bewing said:

RCS has a lot more rotational thrust than reaction wheels, and Vernors have even more thrust than that. And you only have to get those tanks into space once. Yes, it's expensive to launch the things. Which is how space launches really are, y'know?

lol...Nice answer, I agree with you. It would not be fun if it was too easy. 

Also, when I think about it, its probably better to put some mono tanks or more LF tanks than add reaction wheels. 

[blakemw]

4 hours ago, korniton said:

Also, when I think about it, its probably better to put some mono tanks or more LF tanks than add reaction wheels. 

Nah, reaction wheels are more powerful pound-for-pound.

But don't take my word for it, try it out in game.

Make a simple vessel, let's say a big fuel tank with a token probe core. Copy the vessel and couple them. On one of them add 4x Large Reaction Wheels (0.2t each). On the other add 10 Vernor thrusters - 4 for pitch, 4 for yaw, 2 for roll. Both setups involve 0.8t of reaction control hardware. Then cheat the setup into orbit, decouple the two vessels and compare in terms of rotation speed.

What you should find is that the one with Reaction Wheels can do a 180 slightly faster. This is despite not using propellant.

Reaction wheels are more bulky but they're more powerful.

Okay, technically, if you only need one of yaw, pitch or roll, and don't need the others, then RCS thrusters might be able to beat reaction wheels (nor including propellant) since reaction wheels can't be dedicated to one axis of rotation - actually RCS can even allow rotating in only one direction (but how to slow down other than time warp abuse?). But in general reaction wheels are OP and beat the pants off RCS.

[bewing]

Two S4-512 tanks connected end to end. 4 vernors around each end. Total rotation time for a 180 = 45 seconds. Total mass = .64t

Same two tanks, 6 Adv Reaction wheels -- rotation time = 90 seconds, mass = .6t

So I can't confirm your assertion. Vernors were twice as fast. In general, it completely depends on how far from CoM you arrange your RCS thrusters. The farther they are, the more leverage you get. Which doesn't work for the reaction wheels.

[blakemw]

Fair enough, if the vessel is long enough thrusters become more mass-efficient, but even then mainly only if you can discount the propellant consumption. Vernors consume ~0.92 units of LF/Ox per s, and each unit of LF or Ox weighs 5kg, so using 1 thruster for 45s would be 0.21t of propellant consumed, with maximum rotation rate (using both pitch and yaw as SAS modes tend to) 4 thrusters would fire basically the whole time: about 0.84t of propellant, with an economizing strategy it'd be something like  0.21t consumed, though the rotation would be a lot slower. Either way you can *very* quickly afford the mass for more 2.5m reaction wheels - you could probably add 4 more 2.5m reaction wheels for the mass the Vernors consumed and they'd rotate the vessel in the same 45s.

 

I'm aware that there are some cases it makes sense to use Vernors, like I sometimes use them on my heavy landers on the top of booms to resist flipping over on a bad landing (they'll only burn for a few seconds), and they can be mass-efficient on Falcon 9 style boostback boosters since they are only used very briefly. But for purposes like a space station reaction wheels are just insanely powerful and vernors are almost never mass-efficient - for almost any station 4 large reaction wheels is between adequate and overkill and they are about the same weight as a complete set of vernors and don't consume propellant (and also don't have problems with asymmetrical placement or SAS being silly and burning opposing thrusters simultaneously).

Edited March 31, 2018 by blakemw