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I am working on building a Minmus orbiting base, where I would use ore from Minmus to make fuel, and basically make this my base of operations for any long range missions. I created a "space mover" ship that has a grabbing claw (because there are parts that aren't feasible to add docking ports in various locations). In this case, I sent up a vessel that has a mostly empty fuel tank with docking ports to be attached to the station, and along with it, a docking port with a large solar panel array. I can grab the array with the claw, (and decouple from the fuel tank, so I'm only trying to move the structure beams with solar panels) but the problem is that once I do that, the movement logistics of the space mover change dramatically. (the CoM shifts outside of my ship) I tried grabbing the array in the middle, but it wasn't much better, I had a really hard time trying to make it to my orbiting base, let alone dock the thing.

I'm basically wondering what else can I do to build this base piece-by-piece in space?

Here are some screenshots of the array (connected to the fuel tank) and the space mover ship.

KSP fuel tank and solar array

KSP the space mover ship

How do people usually connect parts in space? Attach extraneous separators/etc with RCS tanks that move autonomously?

Here is the base I'm trying to connect to, the docking ports in the middle of the ship. I can't even manage to get close to the base with the solar array in the claw.

KSP space base

Update: I finally managed to get a connection on the end of the solar array with the claw, so my CoM would be inside the ship and easier to navigate. (Granted it seems to be on the end, but I don't think I can grab it in the exact center -- I had to grab one of the solar panels). While this was true for forward motion and turning, getting the thing aligned with RCS only at one end was also a challenge:

KSP - claw grabbing one end of solar array

That basically gave me issues in moving the thing around. I positioned the base so that a port was in the correct position, and was able to get the mover ship there, but it quickly went bad when I can't easily translate (due to RCS being on one end of the CoM) and the angle just kept getting worse and worse. I would back off and try again, but after several tries, I'm not getting any closer.

Here's what the end result was:

enter image description here

Update 2: So I had an idea for a more stable mover ship, although I'd have to potentially make different ones of various sizes, would this kind of design be more stable, with RCS on every corner?

enter image description here

  • Instead of making such a mover ship, I'd just make sure to slap RCS ports on anything that you need to move. A few ports at both ends of the solar array would go a long way towards fixing your problem, though I realize it's a little late for that now. Alternatively, putting a second mover opposite of the first one should give you the stability you want. This is really turning into a different question at this point, so I wouldn't continue editing this one. – Wrigglenite Sep 21 '16 at 15:29
  • That was going to be my last edit, I saw the scope creep myself... thanks for the feedback. I'll add RCS going forward to movable parts, that seems a much simpler solution. If only there was a way to add them in space :) – Tim S. Sep 21 '16 at 15:31
  • The simplest solution for you right now is probably to launch a second mover as I said. Good luck! – Wrigglenite Sep 21 '16 at 15:37
  • It does not answer your question but after trying to do what you are doing, I decided to create a refinery ship with 6000dV. I got so frustrated about having to dock and undock things in ground and space (and those take A LOT of time), that I decided to just create a ship that would travel to Minmus, refill the tanks and move on... The idea works! I traveled from Kerbin to Ike, from Ike to Dres and from Dres to Jool moons with that single ship only stopping to refuel and collect experiment results. If I had time, I would be able to land on Duna too. – vianna77 Sep 30 '16 at 18:36
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When connecting two any parts, you want the connection point to be between the two pieces' centers of mass, and them to be aligned in roughly the direction you'll be moving in, so the new center of mass should be in a good position relative to all your engines and RCS ports.

If I'm understanding this right, you're trying to move the solar array by grabbing it from the side, like this:

sketch of my understanding

but then that would require you to translate your mover sideways, using only your puny RCS ports, which create a torque that is not balanced by anything on the other side, causing your ship to mostly rotate around its center of mass.

The main problem is that the solar array has no RCS ports to balance your mover, so if you try to rotate, you'll probably run into trouble. Ideally you want to have RCS ports on the array, but you can try something like this:

alternative method

The idea would be to grab the array, decouple from the fuel tank, then move away only slightly, and instead of moving the array to your base, move your base in position behind the solar array, after which you can dock the parts together.

  • I finally got a connection from the end like that, and have screenshots and new challenges, let me update my question... Nice drawings! – Tim S. Sep 21 '16 at 15:07
  • I overlooked the part about moving the base to meet with the array... while that may work, I'd prefer not to mess around with the orbit of the base -- I am trying to get this done in the traditional sense... – Tim S. Sep 21 '16 at 15:16
  • @TimS. You can try and move the whole thing closer, such distances shouldn't affect the orbit in a big way, and it's probably easier to fix that than try to move the solar array in another way. In the end, the only thing you can safely do with the mover is pull the solar array back and forth. – Wrigglenite Sep 21 '16 at 15:22
  • If you don't mind, can you take a look at my latest edit and let me know what you think? I think this new kind of design would cause much more stability and give the ability to rotate with RCS much easier, even for something as big as an orange fuel tank. – Tim S. Sep 21 '16 at 15:27
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The best way to do this is to use self docking modules. Then you don't even need your docking tug.

But if it's impractical to use a self docking module, there's a few things you can do. The first is to not use the claw, but just a docking port instead. This allows you to properly align the center of mass of your tug with the module. If you still need to use a claw, make it detachable with a docking port, and just store it some place on your station.

The second thing you can do is add RCS thrusters to your modules. When docked, the RCS thrusters on the module will do a lot of the work for you.

Finally, if the above doesn't work for you, there are some other things you can do to improve your tug. Use two sets of 4 RCS blocks (i.e. 8 in total, or more), and fine thruster control, as well as SAS. To also help with keeping your tug pointed in the right direction, add some gyros as well.

  • Just to make sure I understand what you're saying... when you say "self docking", are you talking about putting a docking station on the far end of a part, so I can dock directly from the delivering ship without removing the piece first? – Tim S. Sep 22 '16 at 1:48
  • No, I'm saying the piece should dock itself. Sometimes, that's not a viable option, but when it is, it should be preferred. – MBraedley Sep 22 '16 at 1:50
  • @TimS: I think I know what MBradley means. The solar array being a self-sufficient craft with own RCS and probe core. The 'craft' parts can be decoupled once docking is completed. – SF. Oct 13 '16 at 10:38
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Been there, done that, it's a world of pain ;)

Two things help: - an appropriate reaction wheel on your 'claw' (not too strong, not too weak; the small RW should be okay for the task at hand), and disabling RCS rotation controls (Actuation Toggles, disable 'Yaw, Pitch, Roll' on all RCS thrusters) - switching 'fine control' on - press capslock, the 'needles' on the controls turn from orange to cyan.

enter image description here

With fine control, RCS actuates not to 'full power' but enough to perform translation without rotation. It's also much more gentle - if weaker.

It's still a tricky work, but with these two helps possible.

You may also want to perform the assembly in a relatively high orbit, so that the motion of the craft relative to each other resulting from different orbits doesn't get into your way all the time.

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