Docking - The Last 100m Made Easy(er)

[Clipperride]

As a new player (although I seem to have clocked up a frightening number of flight hours already), one of the harder aspects of the game is mastering docking. There are loads of excellent tutorials and guides telling you how to match orbits and approach your target. Once I had master those skills, I was a little disappointed that those final 100 or so metres could become a frustrating dance around my first orbital refueling station. So much so that my fuel tug that services the station has been fitted with a Claw so it can clamp on any where But, after some trial and much error, here's my tip for those last 100m or so

:

1. Design. When designing a craft for docking in the VAB, detach any lower stages and turn on the "Centre of Mass" indicator (one of 3 buttons to the lower left of your screen). You want to place your RCS thrusters at an equal distance fore and aft of that CoM. You want to be able to move your ship up/down & left/right without its attitude changing (ie nose stays pointing in the same direction and no "wiggle" after firing your thrusters). Two sets of 4 thrusters makes life easier when it's time to dock. I use an extended ladder as a rough "tape measure", placing it on the CoM, counting how many rungs down one set of RCS thrusters are. Then I detached, rotate and reattach the ladder and count the same number of rungs for the matching set.

2. NAV ball. When you are close to your target (~100m), reduce all movement relative to your target to 0.0 m/s. This can be tricky, but the NAV ball can help. Apply about 0.2 m/s forward thrust and you'll see the yellow prograde indicator appear. If it's not right in the middle of the NAV ball, you have some additional motion. Using short taps on the thruster buttons (default H = forward N = backwards K = up I = down J = left and L = right) tweak the prograde indicator until its centred. Then press N to slow down and you should come to a complete stop relative to the target.

3. Precision. It's much better to make adjustments in one plane at a time to begin with. With your thrusters placed evenly, you can drift one way and stop again with ease. If you do find you still have residual movement, repeat 2 above.

4. Line up. Set the docking port you are aiming from as your target and "Control from Here" on the active ships docking port. Once you're about 50m away, stop then turn off your RCS and use the WASD keys to align your ship perpendicular to the target docking port. The reason for turning purely with torque wheels is that, although slower, it doesn't change your velocity. Now you can reinitialize the RCS and line up the target indicator with the centre of the NAV ball. Thrust forward again and cancel out any unwanted motion in either of the other two planes using 2 above.

5. Move in. Once you feel comfortably lined up, click on the target indicator next to the NAV ball to lock on to your intended docking port and again remove any residual movement by using your thrusters to line up the prograde marker. Reduce forward velocity to 0.1 m/s, turn off your SAS and RCS and wait for contact

.

6. Finally. Remember you can use "time warp". It's better to execute your final manoeuvres at a few 10ths of a metre per second and speed up time, than try and rush things by moving faster. Just be careful which key your finger is hovering over. Repeatedly pressing ">" in panic, instead of "<" can completely ruin your encounter!

Hope that helps?

Edited August 17, 2015 by Clipperride
You always spot simple errors after posting

[Clear Air Turbulence]

This is very useful advice. I could never understand where that lateral movement came from.

One thing: when calculating RCS placement, how do you deal with fuel related changes?

If a liquid fuel tank is going to be part of my final stage, then the CoM is going to change as the tank empties.

[obsidian_x]

One thing: when calculating RCS placement, how do you deal with fuel related changes?

Tap Caps lock (toggles fine control) it will help, assuming you've got it mostly balanced - It then tries to balance the relative thrust of the rcs ports to keep it straight(er) during translation.

- - - Updated - - -

Sorry, that's for when you're actually close to docking. For RCS placement, there are mods to show you where the dry COM and wet COM are (eg RCS build aid). If you don't want to use a mod, then you have to manually add/remove fuel and try to find the best spot. On a small ship, I'd probably put 4 or 6 rcs ports as close to the COM (if it shifts a lot after burning fuel, it's pretty tricky) as possible, and use pod/core torque for rotation. Anything bigger than a few tonnes, you need a lot more rcs to have the responsiveness though, so as it says above at least 2 sets at an equal distance above and below COM (when building in the VAB).

[Clipperride]

Thank you for the feedback, Im glad you found it useful.

I don't use Mods and so, in the VAB, I manually tweak the amount of propellant in the stage that docks to see how the CoM changes (right clicking on the tank allows you to change the fuel / oxidiser levels.). Even if the RCS thrusters are a little out, using the NAV ball as suggested should keep things fairly simple.

[Clear Air Turbulence]

The RCS build aid mod is extremely useful, thanks. That's going into my standard toolbox.

[OSUNightfall]

As a new player (although I seem to have clocked up a frightening number of flight hours already), one of the harder aspects of the game is mastering docking. There are loads of excellent tutorials and guides telling you how to match orbits and approach your target. Once I had master those skills, I was a little disappointed that those final 100 or so metres could become a frustrating dance around my first orbital refueling station. So much so that my fuel tug that services the station has been fitted with a Claw so it can clamp on any where But, after some trial and much error, here's my tip for those last 100m or so

:

2. NAV ball. When you are close to your target (~100m), reduce all movement relative to your target to 0.0 m/s. This can be tricky, but the NAV ball can help. Apply about 0.2 m/s forward thrust and you'll see the yellow prograde indicator appear. If it's not right in the middle of the NAV ball, you have some additional motion. Using short taps on the thruster buttons (default H = forward N = backwards K = up I = down J = left and L = right) tweak the prograde indicator until its centred. Then press N to slow down and you should come to a complete stop relative to the target.

Hope that helps?

Actually, if you have the thing you want to dock with set as the target, you can just burn retrograde on the nav ball and this will cancel all relative velocity. Then you can line up as you said using reaction wheels.

[Ripper2900]

Another very useful tip: set your view mode to "chase" or "lock" by pressing the 'v' key.

This makes it much simpler to keep your wits when lining up. Basically it makes sure that the craft attitude stays the same relative to the view as you rotate and twist.

- - - Updated - - -

And when you've done a couple of docking and you're not afraid to use mods, get Docking port alignment indicator. I don't consider this brilliant mod as a cheat. Even the earliest generations of spacecraft had a better indicator than the stock one down at the corner.

I've just checking completed a full grand-tour incorporating scores of dockings. Those would have taken forever without.

[Floker]

Here's one more tip for an fast and easy lineup. However this requires both crafts you want to dock with each other controllable.

1.) align craft (1) with your target (duh)
2.) switch vessels! Select docking port of craft (1) as your target / control from docking port of craft (2). Align craft (2) with your target again
3.) switch vessels once more and repeat 2.) controlling craft (1) lining up with docking port of craft (2) this time.
4.) that's it. You're perfectly aligned most of the time.

[Thorbard]

[quote name='Clear Air Turbulence']This is very useful advice. I could never understand where that lateral movement came from.

One thing: when calculating RCS placement, how do you deal with fuel related changes?

If a liquid fuel tank is going to be part of my final stage, then the CoM is going to change as the tank empties.[/QUOTE]

Firstly, you should have a rough idea of how much fuel you will have left when you get to the docking phase. You can use this fuel quantity to see how the CoM changes.

Secondly, the game actually tries to balance the thrust from different RCS ports to give balanced movement. Try building a ship with them very unbalanced and see how it behaves in orbit. The game will also use the reaction wheels to counteract (or assist, depending) any turning forces imparted by the RCS. If the RCS nozzles are too imbalanced the game can't adequately compensate.

[vixr]

Dont forget to disable SAS when you first contact the target port...this lets the magnetic attraction of the ports work for you, without SAS fighting to keep the original orientation... if you disable too soon you can bounce off and start to tumble, turn SAS back on, recover your alignment and turn it off again, then thrust toward the target port. I disable after the first little bump so I'm rebounding very slowly. Never go faster than you are willing to crash into something... Edited November 19, 2015 by vixr

[SpaceplaneAddict]

It was the rendezvous part that I hated. I teached myself how to dock by myself, the rendezvous was always the hard part

[Clipperride]

Thank you for the additional comments and tips. I intend to rewrite the piece to include the things I've missed out or have discovered since I wrote it. One reason I didn't originally include the "switching between ships" tip is that changing ships prevents you from reverting the flight. As I was a new player when I posted the guide, reverting was an important aspect of my game! :)

[neistridlar]

Really good tips here. For the beginner I think a screenshot series with comments for each step would be really good.

[Val]

[quote name='Clipperride']One reason I didn't originally include the "switching between ships" tip is that changing ships prevents you from reverting the flight. As I was a new player when I posted the guide, reverting was an important aspect of my game! :)[/QUOTE]Switching between ships using [key][[/key] and [key]][/key] does not affect your ability to Revert. But switching in Map Screen or through Space Center and Tracking Station does.

[problemecium]

TBH I generally skip Step 1. Once you've docked one or two times, it's far more efficient to use the old "'pull' the prograde vector and 'push' the retrograde vector" rule of thumb than to fiddle with getting an exact 0.0 m/s when still dozens of meters away from the target and thus subject to tidal forces.
In short, my Step 1 is this: Use the engines (at low thrust in most cases) to make coarse adjustments to the prograde vector until it lines up with the target when still a few kilometers out.
This ends up saving a lot of MonoPropellant, so I can easily get away with what's in the pod for most cases and not have to lug around the extra weight of dedicated RCS tanks.