Tips for docking without RCS on the Center of Mass?

[dryer_lint]

So, almost every docking tutorial I've seen says to put the RCS thrusters on the center of mass. This is very helpful, I personally can't dock at all without it. Unfortunately, I messed up the RCS thrusters on my Mun lander and now I can't dock to the transfer ship, because the freaking lander won't stop rotating (sorry, had to rage a little bit there). Does anyone have any advise?

Edited July 7, 2014 by Nikola7007

[Alshain]

You can still dock with an imbalanced system, that's how stations typically end up getting pieced together since the parts often don't have RCS and it has to rely on the tug or delivery vehicle. It's just harder. There is little you can do once it's launched though. You just have to try your best to get it there.

[WooDzor]

Dock the transfer ship to the lander instead of the other way around?

[Mr Shifty]

So, almost every docking tutorial I've seen says to put the RCS thrusters on the center of mass. This is very helpful, I personally can't dock at all without it. Unfortunately, I messed up the RCS thrusters on my Mun lander and now I can't dock to the transfer ship, because the freaking lander won't stop rotating (sorry, had to rage a little bit there). Does anyone have any advise?

If you've got enough torque generated by the RCS thrusters (i.e. sets at each end of your vessel), they should be able to hold attitude (using SAS) during linear translation even if they're unbalanced. (Note that you don't want RCS thrusters at the center of mass because they can't generate any torque from there. You want them balanced around the center of mass.) Otherwise, as others have said, just dock the transfer ship to the lander instead.

[dryer_lint]

The transfer ship doesn't have any way to control it, it's just a fuel tank and an LV-N.

Maybe I should have thought this out a little more... ah well, I'll try my best, I guess. The ship has enough fuel to get back home but I don't want to repeat the whole mission. Aaaagh.

[Cerberus738]

You can use two hands to control your craft. Set rotation controls to wsad and translation controls to ijkl. So you translate with one hand and fight the rotation with the other hand.

Also putting on precision control (default caps lock I believe) you should get less rotation happening from your thrusters

[RoboRay]

(Note that you don't want RCS thrusters at the center of mass because they can't generate any torque from there. You want them balanced around the center of mass.)

NASA begs to differ.

One set of four quads in a ring around the CoM is all you need for a small to medium-sized craft like a typical lander. They still produce torque based on their distance from the CoM. (The only way they could produce no torque is they were installed at the actual CoM, inside the craft.) In any case, pod torque alone should be sufficient for rotation unless you're building enormous spacecraft.

I demonstrate this type of arrangement in this movie. Note the orientation of the RCS puffs as they produce torque to rotate the spacecraft.

Edited July 7, 2014 by RoboRay

[dryer_lint]

Wait a second... when in (translation) docking mode, will ASAS try to rotate your ship?

I suppose it doesn't matter anyways, I gave up on the docking and returned to Kerbin. Who needs this, I'm just going to make a huge lander

[Mr Shifty]

One set of four quads in a ring around the CoM is all you need for a small to medium-sized craft like a typical lander. They still produce torque based on their distance from the CoM. In any case, pod torque alone should be sufficient unless you're building enormous spacecraft.

Yeah, you're right. You got me there. I didn't consider distance from the CoM introduced by the diameter of the vessel.

EDIT:

Wait a second... when in (translation) docking mode, will ASAS try to rotate your ship?

It will continue to try to hold attitude.

[RoboRay]

Wait a second... when in (translation) docking mode, will ASAS try to rotate your ship?

SAS will attempt to hold your orientation if you turn it on while translating in docking mode. So long as the pod/wheel torque is greater than the opposing torque of an imbalanced RCS system, you'll stay aligned.

[LethalDose]

You can also try activating fine control mode (default key: Caps Lock) and just docking very slowly. The torque from any capsule should be able to arrest any roll or spin created by unbalanced RCS thrust in fine control mode.

And if try this, you probably won't see thrust coming from the RCS ports, but they're still working. The thrusters release so little exhaust in this mode, it usually only renders if you hold the key down.

[Reactordrone]

Blipping the RCS thrusters rather than doing long continuous burns will also help since the SAS will correct orientation in between thruster firings.

[Kryxal]

Blip and turn off RCS ... otherwise, you're going to get counter-thrust.

[Lheim]

Yeah, I thought fine mode was suppose to try to balance the directional thrusts.

However, there's always just getting within ten meters of your target, killing velocity, pointing the docking points very carefully at each other, then firing your engines..