Rocket Translation

[cueceleches]

Hello!

I´ve been playing KSP for a couple of mopnths already...I´ve managed to land on quite a few planets and moons, but now almost all my contracts are focused on the Jool system. So, I´ve built a quite heavy rocket, which gives me some near 12.000Dv to reach Jool and its moons and be able to land and return form there. The problem is that while in LKO, the rocket translates way too slowly, and it gets frustrating. 

Which is the best way to make it more maneuverable? Should I place some RCS thrusters, and in this case, do they need some propellant tanks? Which would be the best place for those thrusters?

I post an image of the rocket in order to get an idea of what I have...

 

Thanks a lot for the help!

 

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[Leeman]

I do quite smaller rockets than you are.. But I use Reactionwheels. They help me if the rocket is quite long and would take a while to turn

[Plusck]

For a rocket that size, Vernors are the only reasonable solution. They use (minimal amounts of) LF+Ox, so you don't need to add tanks, but they operate using RCS commands and they provide much more thrust than RCS thrusters.

The only thing about Vernors is that they produce thrust only perpendicular to the surface, so some thought is needed if you need roll control (although if you have reaction wheels already, roll control might well be manageable as it is).

So I'd put two rings of 4x symmetry at the top and bottom of your main stack to give good pitch+yaw control, then maybe one on each side of your innermost pair of side stacks (assuming they've been placed in pairs... if you've used 8x symmetry, you'll be stuck with either placing them manually or placing one on each side of every booster, which would be overkill) for roll control.

Rotation will still be slow - normally for very big ships I deactivate SAS, press the desired direction for a few seconds then use physics warp to let it rotate slowly. As long as there is no control input or other forces on the ship, physics warp is fine even for huge ships. However, trying to use controls or SAS while on physics warp can destroy a large ship quite easily.

If you really want to move it faster, use double rings of Vernors top and bottom...

[Plusck]

btw, just to be a stickler for terminology, "translation" is sideways movement (which is absolutely impossible without RCS thrusters of some sort, whether standard monoprop ones or Vernors). What you're talking about here is "rotation" (which can be done using torque wheels or RCS). : )

[mrclucks]

I'd add one of the large reaction wheels on top of the second to last fuel tank in the middle.  That should give you some more noticeable rotation when you have the large boosters and engines attached while being in a relatively good center of mass for most of your stages.  Once you get down to the second to last stage, as far as tanks and engines are concerned, you'll have good enough rotation from the command pod to rotate without having to wait hours to do a 180.  

You could also clip some monopropellant tanks into that large middle stack and add some RCS thrusters on the bottom.  Be warned that you may run our of RCS so you may just want to use it for the initial rotation and then quickly time warp to stop rotation when you're on or near the desired heading.  

The closer reaction wheels are to the center of mass the better they work, and the further RCS thrusters are from the center mass the better they work.  

[Plusck]

55 minutes ago, mrclucks said:

I'd add one of the large reaction wheels on top of the second to last fuel tank in the middle.  That should give you some more noticeable rotation when you have the large boosters and engines attached while being in a relatively good center of mass for most of your stages.  Once you get down to the second to last stage, as far as tanks and engines are concerned, you'll have good enough rotation from the command pod to rotate without having to wait hours to do a 180.  

You could also clip some monopropellant tanks into that large middle stack and add some RCS thrusters on the bottom.  Be warned that you may run our of RCS so you may just want to use it for the initial rotation and then quickly time warp to stop rotation when you're on or near the desired heading.  

The closer reaction wheels are to the center of mass the better they work, and the further RCS thrusters are from the center mass the better they work.  

Two slight comments about this:

- it doesn't matter where you place reaction wheels compared to your centre of mass, they have exactly the same effect. However (and this is vital for large rockets) they have weak joints so you do not want to put them where they'll weaken the structure. Between two long fuel tanks is the worst place to put them as far as structure-weakening is concerned

- clipping tanks into other tanks has no real benefit other than aesthetics: unless they are in a service bay or cargo bay, the game doesn't look to see whether or not they are exposed to the airflow but merely adds their drag to the drag of the part they are connected to.

Edited April 13, 2016 by Plusck

[cueceleches]

Thank you all for the help... I´ve tried both Vernors and simple RCS thrusters and those ones do the trick quite nicely, though I had to add a couple of monopropellant tanks. In fact I had quite a bunch of reaction wheels on top of the big fuel tanks, but they weren´t able to rotate my ship fast or acurately enough.

[MaxL_1023]

I would also recommend dropping your near-empty stage early - you would likely lose more delta-v putting in the gear to turn the whole thing than you would sacrifice by staging. (Considering vernors, monoprop, large wheels, etc)

Another option which I find works quite well is putting large reaction wheels in large radial stages. They are often the right size (2.5m), and you ditch them when you stage and no longer have enough mass to justify their use. You only haul them for as long as you need them. 0.2 tons is nothing to a 100 ton radial throwaway booster but means a lot when attached to your final payload.