I have a docking puzzle.

[Saltpeter]

(I'm new to the forum, but I did enough reading to realize that there are many many threads here about docking. I hope it's apparent by this thread and the picture that this isn't just an inquiry into basic docking. All the tutorials I've found only go into the basics.)

So I am assembling a space station comprised of 26 large orange tanks arranged in a hexagonal trefoil. Each tank has a large port on each end and nine small ports in sets of three on the sides. I am having difficulty getting them all to connect properly. Here is an illustration of the situation:

I am not sure how to approach this problem. I'm trying to resolve it by detaching the bottom half and then trying to get all the small ports resolved before reattaching the entire thing to the top half, and this is the closest I've gotten. If this is the best way to do it, then by the time the station is done, the final docking maneuver will involve matching up 13 pairs of large ports, and that sounds dreadful. Is there a better way?

Alternately, I am willing to install mods that facilitate docking so that maneuvers like this aren't as finicky. I'd rather not have to, but if you know of one that would make this project easier, I'm open to trying it.

Edited March 13, 2014 by Saltpeter

[kahlzun]

You have to be very exact with the placement of the docking ports. Mechjeb helps a bit with its PAR+/- feature (lines the ship automatically) but you've picked a big & complicated mission there... not much anyone can do to make it much easier

[Saltpeter]

I've never tried MechJeb because all the stuff that comes with it is intimidating, but I'll try the tool you suggested. Will report here with results.

[Lohan2008]

Ksp tries to line up each of those docking ports seperately, use a structural fuselage (with clamp-o-tron each end) to connect port to port.

[How2FoldSoup]

Perhaps try the docking port indicator mod so that you know when you are perfectly aligned?

[Kasuha]

The question is, what do you mean under "not connected properly"? Is it that the two docking ports don't seem to be aligned correctly, or that there is no physical strength in the connection.

The matter is, when you dock two ships using multiple docking ports, only one of them is the "primary" one, i.e. the one through which one ship becomes part of the other. The rest of docking ports act as struts, they provide physical connection but often are not perfectly aligned.

Note that under certain circumstances you may even achieve the "primary" docking port to come out unaligned.

The problem with multidocking is that it is very hard to do and it does not guarantee you that the two parts will align perfectly.

[Saltpeter]

What I mean is that they're not connected at all. When I right click on them, the option to undock is not there, on either side of the connection. I haven't had trouble with multidocking until this part. All of the ports on the front end of the station are completely connected. I already know that what I am trying to do is possible, I'm just looking for ways to make it easier.

I tried the Docking Port Indicator. It helps big time with the small ports. I haven't tried MechJeb yet, since I'll need to launch one up there. I like to use Lazor Docking Cam, but I can't seem to get it to work.

Will report when I launch a MechJeb.

[Saltpeter]

Alright, MechJeb is awesome. Hohmann transfers are great and all, but I no longer have anything to prove with them, so automating rendezvouses is nice. The docking AP isn't quite working. I've gotten two, but not all three of the ports to connect. There is apparently a mod that allows you to turn off the dock magnets, but I can't get it to work. I think that would help the situation.

[Saltpeter]

I may give up on this two-tank-long venture after all. I suppose 13 tanks will be enough for my project. At the very least, I can get the front tanks lined up entirely first. The structure will be strong enough if the rear tanks don't have the radial ports, right?

[Kasuha]

You have plenty of docking ports docked there, you may not need all of them to be docked.

[Saltpeter]

Two tanks will tear each other apart if only one of the three ports are connected. I'll be satisfied as long as every large port is docked properly. I've been unable to get all three large ports to dock so far, but that appears to be mostly due to the small ports not completely lining up.

Here is the present situation. As you can see, with 1/3 small ports, there is too much error to get the large ports lined up. I will continue to try and get at least two small ports of that last tank lined up. I PREDICT that if I can get two of the three small ones (preferably the top and bottom ones), I'll be able to dock all three large ports. Alternately, I can take a up a 4th tank, might make rotating the entire construct easier.

I actually had to do a refueling run because of all the monoprop I've been using getting these tanks together.

[Saltpeter]

So I launched a 4th tank. Of course this one manages to get all three small ports docked on the first try. But the Senior didn't connect. I am hoping that that'll remedy itself once I finally get that last blasted tank connected up.

I think I can take it from here. Thanks for all the help!

[Aphobius]

Or you could just launch all of them at once.

Space carrier with 21 orange fuel tanks

Anyway, docking things like that is not a good idea, if I use multiple docking ports I try to keep them in the same direction and if some of them do not connect, I just undock all of them, move a little back and dock again ... until eventually all of them connect.

[juanml82]

How about using a different approach and using the KAS mod to build struts in orbit. I haven't tried that part but, basically, you put radial parts which act as strut ends in both the ships you want to connect to each other and, with a kerbonaut on EVA close by, you build the struts in orbit

[Saltpeter]

Anyway, docking things like that is not a good idea, if I use multiple docking ports I try to keep them in the same direction and if some of them do not connect, I just undock all of them, move a little back and dock again ... until eventually all of them connect.

That is what I do, but I separate the entire rear section first to prevent interference from the Senior ports. For some reason, on that last tank, only one of the small ports exhibits any magnetism no matter how far away I pull it before redocking. I'm going to replace that tank.

If I can't get the next tank to work, I will give the KAS mod a trial run.

[Sirrobert]

Alright, MechJeb is awesome. Hohmann transfers are great and all, but I no longer have anything to prove with them, so automating rendezvouses is nice. The docking AP isn't quite working. I've gotten two, but not all three of the ports to connect. There is apparently a mod that allows you to turn off the dock magnets, but I can't get it to work. I think that would help the situation.

Use the Smart ASS.

Set it to target, and than fiddle with the buttons. They will instruct Mechjeb to hold perfect allignment relative to the target (so you can get them to allign perfectly parralel)

[celem]

If you can turn off some port magnets or cut down the number of lateral ports that should help. As Kasuha mentions on the first page the game will only consider 1 to be a proper full-on dock, the others will dock if aligned just right but are softer docks. It all still boosts the rigidity. What I suspect may be the issue is that the magnetic forces are tugging things out of alignment. If your fuel tank is hard-docked with the 3 small lateral ports then the senior cant pull closed, theres no give in the module since its anchored, it might only want 1mm, but theres nothing to get. Even if you have everything aligned spot on in the VAB and are sure they are all in exactly the right spot...floating point math means no position is ever quite spot-on certain and with multiple contact points that situation exacerbates.

[Saltpeter]

I've been unable to get the mod that can turn off the magnets to work, but with MechJeb I don't think it'll be that effective. The dock autopilot offsets the magnetic force well enough. Smart A.S.S. is definitely helping with the alignment, but I still can't get more than two seniors to dock at once.

I am tempted to redesign the entire station with the Core unit being the same length from senior to senior as the Outer units. Even if I can't get every small port to dock, the seniors MUST all dock up.

I will also take the opportunity to use KAS to strengthen the station in orbit.

[Saltpeter]

I have discovered part of the problem One of the tanks, despite being fully connected, is terribly aligned.

Now that I know this is causing the issue with the seniors, I might be able to get this to work without a complete relaunch.

[celem]

If the seniors are all already placed then releasing some of the laterals may cause it to click into place yes. I also agree with your backup plan, if all else fails, just get all the seniors locked in, the laterals dont do so much for the design rigidity as the big boys on the ends

[Saltpeter]

This is killing me. x.x I wish I could get that mod with the magnetism toggle to work, because it just caused this nightmare:

Poor alignment of the small ports prevented the senior from docking, but all three small ports are docked. The alignment error was caused by the magnetism.

The mod that has the magnetism toggle has two folders, GameData and "Sources", which doesn't seem to have a vanilla analogue. I extracted it to the main KSP folder. The comments for this mod indicate that I'm not the only one unable to install it.

I believe getting this mod to work is the key to solving this issue once and for all.

[celem]

That mod should install by pasting GameData into your Kerbal Space Program so that it merges with the existing GameData folder. Whether it works or not of course I cant say. Source is the code that made it, you dont need it, its just part of the open source transparency that pervades here. You can always check what your plugins are doing, assuming you can understand what you read.

Its always possible that you could force dock this. Release the clamps all up the sides and give the tanks a push from the back with a reasonably firm engine. With all clamps loose its gonna be free-floating in a magnetic storm, you just gotta get the senior to bite first, whichever laterals can then make a dock will do so and the rest can go cry. Big structures are pretty resilient, I often keep up 1-2ms of push with RCS while the magnets do their thing, hammer it shut.

Edited March 11, 2014 by celem

[Saltpeter]

If the seniors are all already placed then releasing some of the laterals may cause it to click into place yes. I also agree with your backup plan, if all else fails, just get all the seniors locked in, the laterals dont do so much for the design rigidity as the big boys on the ends

I've tried a dozen times just now to just get the senior to click into place, and it refuses to. x___x I've gotten all three laterals to connect three times in a row, but not that blasted senior. I KNOW I can get all four ports to click, I did it on the first try with the last tank I launched up. It just seems to be really hard to do after the first outer tank.

[Saltpeter]

In my attempt to debug the issue, I find that it is impossible to connect the seniors, even when I rotate the tank so that the laterals are not facing each other and are not magnetized. How far away do I have to make the seniors before the magnetism comes back?

Edit: I pulled the tank an entire tank's length away and the senior still refused to connect. I'm increasingly leaning towards a relaunch of this tank.

Edited March 11, 2014 by Saltpeter

[Vice-roy]

Just an Idea, but I had some problems with docking on senior ports. The problem finaly was, i had attached the port the wrong way around. Like docking side inwards. The senior port looks pretty simillar on both sides..

With thad constellation i had the effect of the magnetic force missing