How to dock while on a surface?

[Jstone39]

I'm currently working on a full blast mun colony, sadly I only have the core down with one regular docking port on the back: and I cant find a way that guarantees the next ship I land will dock. I have landed a clone of the ship on Kerbin and I've tested and set another docking port on a rover to try to get the height right but I'm worried that if i have a technical difficulty or the slope is wrong they won't dock. Does anyone know how I can set up a docking port that is much more likely to connect?

[Dortmunder]

There pretty much is no guarantee, unless you can find a perfectly flat spot to land on that's the same as your test docking area.

I'd build a crane type vehicle and send that to your base as well, it may help you get those tricky ones to dock a lot easier. You'll need Kerbal Attachment System for that.

[thescientist]

The possible solution are:

1 Rover modules that can reach and dock the central core

2 Pinpoint landing with skycrane and autopilot

3 pinpoint landing and docking with KAS cable (that are very useful also as a crane to lift and move modules)

[Temstar]

You don't need a perfectly flat area and you don't need KAS. Surface base building can be done perfectly fine with stock parts, all it takes is clever engineering:

I'll write up a guide on the engineering tricks behind this (hopefully tonight) and give you a link, stay tuned.

[LeadMagnet]

Welcome to the wonderful world of module docking in KSP! And a harsh world it can be.

Here's my suggestion. Try to build your modules using the same component. So lets say I make the Hitchhicker Storgae Container my base part, and lets say I turn it horizontal and add some wheels. I would also add some LT-2 landing struts in exactly the same place of each module, same with the docking ports. So that no matter what else (or how long) you tack onto the module, the landing struts will help position both modules along the same axis. Wheels "sink" or "raise" on their suspension depending upon the weight, landing struts don't.

Having said that, Dortmunder is right, finding the right spot to get the modules to dock is very important.

The KAS mod can help, but only in some circumstances.

You could also try RCS assited alignment, but this has never worked for me.

[Temstar]

Module base building guide, as promised:

http://forum.kerbalspaceprogram.com/showthread.php/48876-The-art-of-modular-base-building

[Dunbaratu]

The difficulty is that unlike in orbit, on the ground the docking magnets are not strong enough to force the alignment into proper orientation. In orbit a tiny amount of force has a big effect. On the ground where it has to fight gravity and fight friction, it doesn't. If your rover isn't lined up just right, the magnets won't slide the wheels sideways to force alignment - the wheel friction is too strong. So you have to line up just right on your own. Also if the height isn't exactly the same, the magnets won't pull the lower piece up to meet the higher piece because gravity is stronger than the docking magnet.

Docking requires absolute precision and in orbit it's easy to think it doesn't because the magnets help do the alignment for you - as long as you get it close the magnets can finish the job. But until the magnets do make the alignment perfect, docking doesn't happen. On the ground where they can't force the craft to move, they can't correct alignment.

Lateral alignment is easy to deal with yourself. It's just a matter of driving very slowly and precisely. But vertical alignment is hard. Even if you test your modules on Kerbin to make sure they line up you'll find that the height still isn't the same once you get to the Mun. The height depends on where the suspension of the springy wheels or struts naturally rests at, and where the suspension comes to rest at ends up slightly different depending on surface gravity.

One cheezy method I've used to adjust height is to put a teeny tiny amount of fuel and one of those little orange side nozzle rockets on rovers. Then you can fire the engine and give it just a little bit of thrust to adjust height by taking a bit of the weight off the suspension (or putting a bit more weight on the suspension if the rocket is mounted upside down, or better yet have one of each and pick which to activate depending on what you need.) If your rover or component is light enough and you're doing it somewhere where gravity is weak enough you might be able to do it with just RCS thrusters instead.

[blackfire83]

As Steven implied, weight of the craft can make a difference, so even if you get two craft to match perfectly on Kerbin, factors such as emptying fuel tanks, stages being discarded, etc can cause the docking ports to not line up. It's a giant pain in the rear. I'd really like a "stretchy" docking tunnel type of thing to be implemented sometime soon!

[iDan122]

Rune made a modular surface base kit. Btw slope doesnt do any bad things. Yu can land modules, place rovers under them and rove them to the docking position.

[little square dot]

Kosmos APAS-69

(A docking port with locking guide fins. Works every time, and doesn't require a great deal of precision.)

Edited September 5, 2013 by little square dot

[Hallofo]

I'll be trying out a few modifications of these designs this week - excellent guide Temstar!

I'm also going to try it "vanilla", since Mods are The Devil (I kid!). Other than the obvious Kethane, what other mods were you using?