RCS makes stages spin out of control

[Akkapama]

Good day everybody,

I've been trying to do an Apollo style Lunar mission where eventually once I'm in an orbit around Luna I'll have two stages left: A lander and a stage that will remain in Lunar orbit, with which I'll meet up again later and which will bring the lander pod back to earth.

In order to couple the the two stages back together after my visit to Luna I have RCS on both stages (with mono-propellant on each vehicle) and a command chip on the stage without command pod so I can control it independently. So basically what I'm trying to do is the good old Kerbal Space Program way of coupling where you set the targets of both vehicles to eachother and then use RCS to actually bring them together.

But for some reason RCS on both stages make them completely spin out whenever I set "lock to target". Actually, even if I just try to move the stages using the orange and blue circle things, RCS makes the stages spin out of control beyond recover because I won't have enough mono propellant left.

What can I do to stop this? How can I make the RCS actually work so that they can bring the two stages back together? It's so frustrating because I've successfully done the landing, take-off and re-orbitting Luna so many times now and every time I try to hook the two stages back together RCS screws it up and I can start over again..

[ΗΞΧATαηταlνs]

Hmm... I think the developers of SR2 can better answer this as I'm still learning the systems of the game. However, you might have to change the activation group of the RCS nozzles on the lunar-orbiting craft to place them into a separate activation group from the RCS nozzles on the lander. This way, when flying the lander and lifting it off from the moon to intercept the lunar orbiter above, you'll need to deactivate the activation stage of the RCS nozzles on the orbiter by clicking the icon on the bottom screen menu bar with the two long but narrow white ellipses with white filled-in circles inside, one circle in the left ellipse is in the upper portion of its ellipse, and the other white filled-in circle is in the bottom of the right ellipse. This icon is the right-most button on the bottom menu bar while in flight mode.

This dual-ellipse button will open a sub-menu in the bottom-right of the screen in flight mode, inside it will be a list of activation stages, you can enable or disable any activation stage of your crafts. So, in this instance to prevent the orbiter from maneuvering out of position while attempting to send the lander to rendezvous with it, deactivate the orbiter's RCS nozzles by deactivating their activation stage, and turn on the activation stage that contains the lander's RCS nozzles.

By default, all RCS nozzles on all stages of your whole rocket are in the "RCS Activation Stage" and it is enabled as soon as your game loads the launch pad scene. When you first launch the entire rocket on the starting launch pad, before first stage ignition on the Earth you'll want to disable all RCS nozzle activation stages except the RCS nozzles on your first stages (the nozzles that are on your main rocket and needed for attitude control of the main rocket and its first stages as it escapes Earth's atmosphere). There might also be a way to control which RCS nozzles are activated and start thrusting on each stage by making each set of nozzles part of "sub-assemblies", but I have no idea how sub-assemblies work. Good luck!

[Akkapama]

Thanks Yopo but unfortunately your tip didn't fix it. The problem as well isn't that when I try to use RCS on one, that the other one starts moving as well. That bit works fine. It's that when I try to control for example the orbiter, I want it to turn left slightly and it just seems to overshoot massively, even on auto control and does not recover.

[Akkapama]

Alright, I fixed it by not using the RCS Nozzle rather than the Multi Directional RCS. Those really don't work at all unless I've been using them wrong. I also found out that you need to place the command chip pointing upwards as otherwise it will place your vehicle in a different angle than you want it to.

[ΗΞΧATαηταlνs]

Oh yes, I forgot to recommend the multi-directional RCS. Also, make sure you turn part mirroring on for each row of multi-directional RCS nozzles. I like to place 2 to 6 rows of symmetrically aligned multi-directional RCS nozzles near the very top of my crafts (to increase lever-arm force, torque). Each RCS nozzle row is made up of a x6 mirrored single multi-directional RCS. The rows of nozzles are placed symmetrically on a small to large fuel tank containing monopropellant. with fuel line enabled. Doing this has never caused me problems with attitude control or spin in my crafts (even extremely large many-stage rockets (with nested inner stages to each stage like a Russian nesting doll)). If you need directional/attitude/spin control on very very large/heavy crafts, I recommend using many rows of 6x-mirrored multi-directional RCS nozzles on a larger monopropellant fuel tank as close to the top of each stage as possible. Then, make sure you add separate RCS activation groups (in increasing order from bottom-to-top stages), so any lander crafts packaged inside the main body of the main stage rocket (inside a fairing) don't waste their monopropellant before they get launched later in the mission. Hope that helps and I'm glad you got your problem fixed with a simple correction. :)

[ryansw989]

Hi, I too have been trying to master the RCS for similar reasons, some things I have learnt are :-
* To limit the power of the thrusters in the side panel.
* Placement is absolutely everything as per CoM
* If your creating a thruster block to save as a sub section using a squared off fuel tank as a base, be aware of the x2 connection nodes, and leave one of these free from a thruster. Do this so you can actually connect the part on any side directly. Also helps using the small part in the utils designed for connecting multiple engines.
* As mentioned above by Yopo, it can also help having another set of single thrusters below the CoM and above depending on the position of the CoM / Sive of craft. I've been placing them not directly inline below/ above the main set but half way between, if that makes sense.

Hope you can use some of this info to help in some ways.

[JundrooGames]

@EvaJoer I've been looking into the multi-directional RCS today trying to address some of these issues. Do you still happen to have a sandbox that has a craft that is suffering from poor attitude control from the multi-directional RCS? If so, could you please upload it as a sandbox to SimpleRockets.com and give me the link so I could investigate it?