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Buck Gordon

Advanced Docking - Moving Parts Around

Question

I'm building a space station in Kerbal Orbit which is requiring me to move sections from the delivery rocket to their final station position. 

I'm having some difficulty. I can get the initial dock done, but using RCS to move my parts around is giving me fits. Any one have any suggestions or recommended videos?

I have built RCS tugs to move things around. I'm also using the docking port alignment mod, but getting those green lines to align is confusing. 

 

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@Buck Gordon:

If it's a pilot error, that's okay:  that's the easiest thing to fix.

First, stay away from docking mode.  It's honestly not necessary and it confuses the controls.  Second, turn on fine controls; you can do this with the caps-lock key.  You'll know you're in fine-control mode when the pitch, yaw, and roll indicators turn turquoise instead of orange.

Fine-control mode limits the thrust from RCS and the rotation authority from reaction wheels so that you get about ten percent of full power.  More importantly, it also activates a fractional control to balance the torque of the vessel.  This means that if you try to translate in one direction but have an unbalanced craft, the RCS thrusters will thrust to try to keep it pointed correctly.  If you're using a tug, then you need this.

Third, learn the translational controls.  Rotational controls, WASDQE, you already know--or else you wouldn't have gotten this far.  The translational controls are IJKLHN, where I and K move you up and down, J and L move you left and right, and H and N move you forwards and backwards, all without rotation, which is what you need to get alignment.  Imagine carrying a full coffee cup from place to place; you don't want to turn it over and spill coffee, so you keep it upright while you move it from side to side or up and down.  That's translational control.

Fourth, don't forget SAS.  There are times to use it and times that it gets in the way, but either way, don't ignore it.

Fifth, be certain that you set the desired docking port as the target (you can do this by right-clicking on it and selecting Set as Target) and that you also set the port on your vessel (the port doing the docking) as the control point (you can do this by right-clicking on it and selecting Control from Here).  Failure to do this will cause everything to be misaligned.

 

Docking Port Alignment Indicator essentially tells you three useful things in its UI.  First, it tells you your orientation (that's the orange marker) relative to the docking plane.  The important thing here is that the docking plane is not the same as the direction of the other docking port.  Instead, if you imagine the docking port's face as defining a plane, then this marker is telling you whether your port's plane and the target port's plane are parallel.  Put another way, say that you face the sun and I face away from it.  We may not be facing one another or even near one another, but we have parallel 'docking planes' in this respect.  This is important because once you line up the orange marker to the cross-hairs (these are the white lines in the indicator, not the green lines), then you are rotated correctly and should only need to use the translational controls (in fine control mode) to align your ports.  This may require dodging the station, so I recommend that you at least get to the correct side before aligning for docking.  Also, don't forget the rotational indicator at the top, if you need it.

Second, it tells you the location of the target port.  That's what the green lines represent.  If you are aligned to the docking plane and moving to align with the target port, then the lines will move.  Getting them aligned with the cross-hairs (and the orange marker) means getting the two ports to face one another.

Third, it tells you the direction your vessel is moving relative to the target.  This is the yellow marker.

Once you rotate to align the orange marker with the cross-hairs, you want to give enough forward thrust (using the H key, not the throttle) to make the yellow marker look like a prograde marker (:prograde:, but yellow).  However, you don't want a lot of forward thrust:  you need to move your vessel so that the two ports not only face in the correct direction, but also face one another, and if you're closing too quickly, you won't have time to do that.  Give it, at most, a tenth of a metre per second until you accustom yourself to it.  To accomplish the alignment, consider where the green lines cross in terms of quadrants on the display.  Then move the yellow marker (with the translational controls) into that quadrant.  What that means is that if, for example, the orange marker is on the cross-hairs but the green lines cross in the upper right, then you want the yellow marker also to be in the upper right.  Use IJKL as necessary to put it there.  What this accomplishes is to send your vessel moving in the direction of the target port.  I prefer to put the yellow marker about halfway to the green lines, and as the green lines move closer to the centre, I move the yellow marker to keep it at the halfway point until everything converges at the cross-hairs.  Once everything is aligned, I use H (and if necessary, N) to close and dock.

Good luck!

Edited by Zhetaan

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What's the specific problem you are having? The main thing with RCS is to make sure the thrusters are balanced around the center of mass to avoid it skewing about.

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Let's say I'm on the left side of the station and need to place a part on the right side. I'm having trouble getting there. I turn on docking mode and am having trouble moving around. Should I be using the Loc mode (the option on the left) to move the craft?

I'm not sure if it's a piloting skill (player) issue or if I'm doing something wrong?

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Zhetaan gave a really great answer and all his advice is fantastic. I propose here a simpler solution: If you're on the wrong side of the space station, you can just rotate your space station 180° so that the correct side is facing your incoming craft.

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Back off some before rotating, you'll appreciate the extra space if a corner would otherwise clip you.  Maneuvers in close proximity to a station are a pain if you have to go around, but you may not have a choice if the station doesn't turn well.

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7 hours ago, Buck Gordon said:

Let's say I'm on the left side of the station and need to place a part on the right side. I'm having trouble getting there. I turn on docking mode and am having trouble moving around. Should I be using the Loc mode (the option on the left) to move the craft?

I'm not sure if it's a piloting skill (player) issue or if I'm doing something wrong?

I never use docking mode myself, I just select the part's docking port to 'control from here' use RCS thrusters, up/down, left/right, forward/back to move it around. In that case like I mentioned earlier though, you really need to have those thrusters balanced around the center of mass and hopefully you have some kind of reaction wheel on the part in question or it can be difficult to control.

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@Buck Gordon In addition to the other really good advice, I have to say I hate DPAI as well. I never did bother figuring out the green lines.

I used to use this, which is fantastic and simple. Nowadays, I just fly the stock navball to dock:

 

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19 hours ago, Buck Gordon said:

Let's say I'm on the left side of the station and need to place a part on the right side. I'm having trouble getting there. I turn on docking mode and am having trouble moving around. Should I be using the Loc mode (the option on the left) to move the craft?

I'm not sure if it's a piloting skill (player) issue or if I'm doing something wrong?

Definitely follow @Zhetaan's advice: use IJKL/HN translation controls without using "docking mode" which doesn't help. Use SAS stability mode only other than in exceptional cases.

In addition to that, the most natural thing (for me anyway) is to use "Locked" view mode. You really get a feel for exactly what your craft is doing, and it also reinforces the link between your movement and the change in position of the icons on the NavBall.

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Thanks for all the help. I plan to incorporate all the suggestions next time I get a chance to play. I really appreciate your help and the great responses.

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I would also recommend setting the translation controls to the number pad on the right of the keyboard, That made it easier for me to remember the keys and it separates it from the rotational controls even more. also, you can set control from docking port set your target to the other docking port and select target on SAS repeat with the station and the docking ports should be facing one another and you just have to guide it forwards and backward.

Edited by Jaime

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3 hours ago, Jaime said:

I would also recommend setting the translation controls to the number pad on the right of the keyboard

That's a valid approach, though personally, I use the number pad for wheel control for rovers.  This allows me to leave reaction wheels on for purposes of righting flips and tips, but it also allows me to drive the rover without trying to make it flip, as would happen if I used WASD.

3 hours ago, Jaime said:

also, you can set control from docking port set your target to the other docking port and select target on SAS repeat with the station and the docking ports should be facing one another and you just have to guide it forwards and backward.

That is also a valid approach, but in my experience it causes more trouble than it corrects.  For example, a station powered by solar panels is going to have a preferred orientation.  Large stations may not be able to turn well, or would tear themselves apart if they tried.  If you are docking with something unpowered (such as that solar station that you forgot to return to the correct orientation, or to which you are delivering a battery pack because the demand was greater than the power supply), then it isn't even an option.

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29 minutes ago, Zhetaan said:

That is also a valid approach, but in my experience it causes more trouble than it corrects.  For example, a station powered by solar panels is going to have a preferred orientation.  Large stations may not be able to turn well, or would tear themselves apart if they tried.  If you are docking with something unpowered (such as that solar station that you forgot to return to the correct orientation, or to which you are delivering a battery pack because the demand was greater than the power supply), then it isn't even an option.

2

True But I mostly build multi-segment interplanetary ships (eg. xenon propulsion segment and landing segment) so that's usually not a problem for me but I see the issue with larger things.

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