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I've built the following ship, which is capable of taking me to the Mun. However, with some careful piloting, I can make it into a stable Mun orbit with a bunch of fuel still left in the second-to-last stage. So if I want to land on the Mun, I have to decouple my lander module from the rest of the ship, and abandon any spare fuel I might have left in the tank.

So, I came up with the idea of using a docking clamp to attach the capsule to the main ship instead, so that I can leave my fuel in orbit when I want to land, and return to it later after returning to orbit from the surface.

Only problem is, I have no idea how docking clamps work. I'll learn how to approach docking maneuvers later, what I'd like to know NOW is how I should build the connection between the two sections to make this possible. I've circled the current decoupler in the image below.

Appalling Lander Mk1

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Parachutes on the SRB's are a nice touch. –  Steven Lu May 19 '13 at 17:27

3 Answers 3

Docking clamps have very little shear strength, so I suspect if we just changed the decoupler into two docking clamps, your cockpit would fall off during the ascent.

It's a bit more complicated to replace decouplers with docking ports; decouplers just fire off of your current stage, and stick to the stage you might want to return to. That doesn't work so well when you want the decoupler to detach from BOTH stages, leaving the docking port free for later use.

So what you want is:

  • A docking port on top of your fuel tanks.
  • A decoupler on it, upside-down, so your lander detaches from your extra fuel.
  • A decoupler on top of the other one, right side up, under your engine, that will fire both decouplers off of your lander, and into space somewhere.
  • A docking port somewhere on your lander. On the nose, if possible. Anywhere else will require you to dock on your side, which will make controlling it more difficult.

Pictures of this will be forthcoming shortly.

This setup will allow you to take it back to Kerbin (if you have enough fuel remaining), and leave it in orbit for future use.

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I've had (at least some) success with attaching ship parts using docking clamps for the ascent. As long as the forces perpendicular to the axis of the clamps are minimal, it should survive launch. However, your idea of using 2 decouplers won't work. I've tried that too. You want the other kind of decoupler (can't remember what it's called ATM). Instead of staying attached to the discarded stage, it simply disappears. –  MBraedley Dec 7 '12 at 15:29
    
Hmm. It doesn't work? Good to know. I'll have to test the various decouplers and see which ones do what is needed. –  Frank Dec 7 '12 at 15:31
    
You're close though. I can't view the images at work, so I don't know what Gnome has set up already, making it a bit harder to make recommendations. –  MBraedley Dec 7 '12 at 15:35
    
@MBraedley: The "other kind of decoupler" is called a separator. But I've also had success doing this without any separators or decouplers. The one on the bottom of your lander should go right side up, the one on the top of your launch vehicle goes upside down (turn it over by pressing W twice). If they snap together and the result looks symmetrical, you got it right. –  Thomas Nov 16 '13 at 0:37

So you're actually really close. That Stack Separator is exactly the part you want. Below it, place your docking port. (Alternatively, you can place them on the outside, doesn't really matter, although doing that won't allow you to take it back to Kerbin.) You'll also need a docking port on your capsule. I would suggest using the shielded docking port, just because it looks nicer. Place it on the nose of the capsule instead of the aero nose cone. However, none of this is strictly necessary. Assuming you achieve Munar orbit with the second stage (it's possible), there's enough fuel in the lander stage to land, take off, and return to Kerbin without topping up the tank.

As a side note, you should probably invest in some parachutes for the capsule. Kerbals don't react well to hitting the surface of Kebin at 360km/h :P

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Wait, if I reattach via the nose cone, won't my capsule be on backwards? That means the engine in the second to last stage and the engines on my capsule will be facing opposite directions. That might not... work. –  ElfSlice Dec 8 '12 at 15:00
    
Technically, yes, but you can disable your lander engine, set the control point to the fuel docking port, and then thrust away. Personally, I would just top up the lander fuel and leave the big tank in orbit of the Mun. –  MBraedley Dec 8 '12 at 15:34
    
Oh, you can do that? Neat! –  ElfSlice Dec 8 '12 at 15:58

There are 2 ways to use docking ports to build a spacecraft that can rendezvous with another in orbit

Non-reattachable method:

Mun Lander payload stack decoupler highlight

First we have a TR-18A Stack Decoupler flipped upside down (you can tell by the red arrow which side will detach), with a Docking Port attached underneath it.

You will notice many EAS-4 Strut connectors used here. Those are for payload stability during takeoff. Don't worry, they disappear when you decouple the node. (let's imagine they have explosive bolts in them like everything else in our rockets)

On top of the lander, we have a Shielded Clamp-o-tron Docking Port. After achieving a parking orbit, the way it works is you decouple the lander, flip it around 180°, (remember to open the shield!) and dock with your fuel tank. Presto! Remember to turn the lander's engines off before trying a burn.

Mun Lander shielded docking port top highlight

This is very similar to the way the Apollo missions did it. (but not on purpose, I didn't know how Apollo worked until after I built my rocket! After a few refinements, mine just turned out like this :)

When building, Shielded docking ports seem to attach very well on TOP of things, while regular ol' docking ports attach well UNDERNEATH things. That seems to be the way the game likes it, and it's best not try to build something unnatural. You will get weird effects on your spacecraft (like uncontrollable spinning) that may force an emergency landing, for Jeb's sake.

Note that when you hit the stage for the stack decoupler of your lander, you will also have to right click the docking port and ask it to "decouple" there as well. Otherwise, they will still be stuck together. One way I found to prevent this is to set up custom action groups.

Custom action group to decouple lander from fuel tank

I set up group 1 (the 1 key on your keyboard) to set off both the stack decoupler AND the "decouple" option on the docking port to ensure separation.

I call this the "Non-reattachable method" because once you decouple the lander, you can't reattach it in the same place again. Which is fine, since we already put another docking port on top!

Re-attachable Method:

Yes, I am making these terms up. Launching this way with two docking ports is only really necessary if you can't fit a Shielded docking port on top, or you want the payload to have two docking ports, top and bottom, as with this orbital Mobile Processing Lab.

orbital Lab dual docking ports

Again, you will notice the liberal use of strut connectors for stability. Because there are no stack decouplers at all here, the only way to detach these is with a right-click decouple command.

Remember when building things should snap into place. The first docking port you have to turn upside down, (rotate parts with WASD keys) and the next docking port should snap onto it immediately.

It may look unstable, but with enough duct tape reinforcements just about anything will fly!

Happy "docking"!

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