Multiple Docking ports

[LtKraftKrackers]

Hi!! i need some help with docking ports. i am trying to build a spacecraft on orbit around Kerbin. got the rendezvous, the alignment and everything else. The problem is that, in order to make the craft more stable i went with a two point connection. so i got both docking ports aligned and i go in for final approach aaaand bonk-a-donk-a-donk one of the docking ports doesn't dock properly, leaving the part dangling and just looking derpy. how do i make sure they both dock simultaneously? is it even possible?

Edited November 4, 2013 by LtKraftKrackers

[ChrisMayhew]

They should automatically dock with each other once they are close enough?

I guess I should have read it twice because I'm getting confused.. haha

Edited November 4, 2013 by ChrisMayhew

[700NitroXpress]

First of all, this is possible, but it's a real pain to do right and sometimes this issue will happen and then you have to try again. If one of your docking ports placement is off by even an inch, then it won't work. You just have to keep tweaking and messing with it until it works.

The easiest way to get it to work is to use a ruler of sorts. Make pieces that you can build to measure out the spacing of the docking ports like the metal plates.

Shown here on my docking station, I used this model for a Moho rescue mission and had multi-port docking engines to the four sides of this thing.

Here is the station being used in my Moho rescue mission:

You can see that the engines on the side of this thing have two docking ports that are attached to the two docking ports on the station.

Edited November 4, 2013 by 700NitroXpress

[Kasuha]

Assuming you have the docking ports all the right size and facing the right end out, all you need is to align them really really well, particularly in the roll direction. Because they must snap in at once. As soon as one of them locks, the other will not move anymore.

[Sirrobert]

It sounds like you have 2 docking ports right next to eachother, and want something to do with the same docking ports next to each other. That only works if they are aligned absolutly perfect. That's very dificult to guess.

I'd just go with a single port instead. They are stable enough, unles you put it at a weird angle

[JiWint]

Sometimes small docking ports just don't connect all at once.

If you're bad at building big ships,I'd recommend you to make these modules:

1. Lander/Controlling module.

2. Fuel module.

3. Engine module.

These 3 must be connected with Senior Docking ports (the big ones,they do their job just perfectly).

I used this for my mission to eeloo. On each module there must be a rcs tank,with some rcs thrusters. So when you finish an emty fuel tank,you just disconnect the engines,disconnect the empty tank from full one,and just place the engines back,leaving the empty tank floating around!

[Tidus Klein]

I tried this once to build the craft storage area for my failed interplanetary ship, one normal port in the center, and four jr's on the sides. only on mine I docked and was instantly flung off sending the part I just docked and my station spinning and flying away. I stabilized both and tried again only to learn I broke off a jr. end of story... I gave up.

[Taki117]

The way I built my interplanetary ship using multiple docking ports I used 4x symmetry and angle for the center fuel tank and command pod. (With radial attachments and Sr. docking ports on the side, one on top and one on bottom) Then just swapped out the command pod for remote controlled units. when I docked both Sr.s Docked perfectly on both sides. (This leads to lots of unused docking ports though, and unwanted vessel mass, but I had enough Delta-V to compensate)

[LtKraftKrackers]

First of all, this is possible, but it's a real pain to do right and sometimes this issue will happen and then you have to try again. If one of your docking ports placement is off by even an inch, then it won't work. You just have to keep tweaking and messing with it until it works.

The easiest way to get it to work is to use a ruler of sorts. Make pieces that you can build to measure out the spacing of the docking ports like the metal plates.

Shown here on my docking station, I used this model for a Moho rescue mission and had multi-port docking engines to the four sides of this thing.

Here is the station being used in my Moho rescue mission:

You can see that the engines on the side of this thing have two docking ports that are attached to the two docking ports on the station.

yeah, i'm doing this in career mode, so in only have access to the normal and shielded docking ports. what i did to make the part was: i made a ruler of sorts with the new subassemblies. i placed 2 docking ports on the ones that were already on the main part of my ship and then just placed structural pieces in between them to measure them, then save that as a piece on the subassembly. when i made the piece that was to be docked, i took the measure pieces and placed them next to the tanks to place the docking ports as closely aligned as i could. now, you might be saying "that sounds like it should have worked" the deal i think was that i didn't measure the main piece right.. and well, it just didn't fit thanks to my lack of care. but yeah. THANKYOU so much dude at least i know its possible.

[700NitroXpress]

yeah, i'm doing this in career mode, so in only have access to the normal and shielded docking ports. what i did to make the part was: i made a ruler of sorts with the new subassemblies. i placed 2 docking ports on the ones that were already on the main part of my ship and then just placed structural pieces in between them to measure them, then save that as a piece on the subassembly. when i made the piece that was to be docked, i took the measure pieces and placed them next to the tanks to place the docking ports as closely aligned as i could. now, you might be saying "that sounds like it should have worked" the deal i think was that i didn't measure the main piece right.. and well, it just didn't fit thanks to my lack of care. but yeah. THANKYOU so much dude at least i know its possible.

Yeah, it can be done for sure, and I have the video evidence to prove it. I think that the most effective way of doing it is to first build the ship you want to dock things to. Then build the attachment ship in the same room as the main ship. Separate the ship from the main ship and save it as a subassembly. Then if you make an unmanned ship and load the subassembly into the scene and attach it, you should have the correct spacing required because it should have been built and measured in the same room as the main vessel. I found that attaching ships with large mass to two docking ports is easier than attaching a lighter ship to two docking ports because the magnetic attraction bumping that happens when you go to dock. A heavy ship won't bounce around and should attach as one, while a lighter ship might bounce off slightly and not attach properly.

1. Both docking ports have to attach at the same time in order for this to work.

2. Both docking ports have to be aligned to within a few centimeters or each other in order for them to dock.

3. If both of the docking ports don't dock, then you might have to undock and then fly about 50 - 100 meters away and then try docking again in order to get all of the docking clamps to engage.

Even with my design that worked, some of the docking attempts took 2 - 4 tries before I got both of the docking clamps to work. Now that we have subassemblies, you should be able to make the docking craft and save it as a separate part and not have to fiddle with the alignment like I did with my Moho rescue station.

As a side note: if you're using up to 4 docking ports for a craft, it can be very difficult to dock them all properly because you have to rotate all of the ports to the perfect alignment and the S.A.S. system can cause trouble with this. If you use pure R.C.S. then you have to make sure to align everything perfectly and kill all velocity before moving in for docking otherwise the docking ports will be off and won't dock.

Edited November 5, 2013 by 700NitroXpress

[Vanamonde]

One thing to be aware of: even if multiple sets of rings indicate that they are docked, between two assembles there can only ever be one "official" link at full strength, and the others are significantly weaker and may part under stress, even while continuing to claim (on their right-click interfaces) that they are docked.

[fatcargo]

Hi ! I am new to the forums, but i was playing KSP for a while, thus i too stumbled upon the same problem. I got dual-port docking mastered, problem is that i want to make a (admitedly large) refuelling depot from 9 big orange tanks in 3x3 formation, each tank having 2 levels of 4-symmetry normal size ports. Unaware of this problem, i tried to attach a newly delivered tank by docking 4 ports at once in a L formation

Below was my second docking configuration with 3-on-3, you can see 4 tug "drones" (and 1 large unmanned tug, currently unused). Unfortunately, instead of doing 4-port docking, this configuration meant 6-port docking instead Only two lower ports docked, rest of 4 ports were left undocked and were quite misaligned.

I have theory about this : with whatever ports are close by, game engine will begin timed magnetic attraction (state = Acquire in savegame sfs file) and whatever ports are in their satisfactory positions, they will dock together and lock position. All other ports will soon time-out, left unconnected and misaligned.

I wonder that until this issue is resolved by dev team, if there is a way to work around this by using a plugin that could have write-access to ports in-game. Reading in-game info about ports is possible, look at Docking Port Alignment Indicator .

The plugin would access ports info and alter either the time-out value that game engine manages (best option) or try to alter port states between "Ready", "Acquire" and "Docked" for each docking iteration until all ports show are in docked state. This second idea is that ports will connect, some will fail, plugin then detects this failure, then tries again to undock them all with zero ejection force and retries. After each iteration, ports will align closer and closer until finally all ports are aligned and are in "Docked" state.

Problem with this second approach is how to determine if all needed ports are indeed connected, because what if player creates a geometry that has one intentionally port slightly out of alignement ? The plugin might try indefinitely to connect all ports OR it could give up, failing on some predetermined timeout.

BUT this could be bypassed if player would multi-select all ports (usual alt+rmb) and then clicks on plugin's GUI widget to begin multi-port docking procedure (umm maybe best idea yet ???).

[Kasuha]

I made a few experiments with multiple docking ports between parts.

If you connect two ships using multiple docking ports, one of them is always the "main" port. Once you undock that, all other docking ports (between the two parts) become undocked, too, except they won't deactivate so if the ship or the part is not under acceleration, the remaining ports may clamp together again. This means even after docking, the ship is still just a "tree" and you cannot really introduce cycles even with docking.

I have not found any significant difference in clamping force between docked ports (after docking) and attached ports (attached as clamped together in VAB)

Docking ports put against each other in VAB (as to implement cycles in design) are not guaranteed to clamp together after the ship is put to launchpad. I have found that to guarantee they will clamp, you need to add a strut between them.

If anybody wants to play with my testing contraption, here is the craft file.

Edited November 16, 2013 by Kasuha

[fatcargo]

...

Docking ports put against each other in VAB (as to implement cycles in design) are not guaranteed to clamp together after the ship is put to launchpad. I have found that to guarantee they will clamp, you need to add a strut between them.

Hmmmm... struts. This reminds me of quantum struts used to reinforce docking ports. Though i do avoid using non-stock parts or flight/docking/descent assistive plugins, for as long as i can (still stuck at Kerbin SOI, my free time is limited and i enjoy my slow pace of prepping for "next step").

If i ever get around to doing it, i may even try tweakable parameters to see what can be altered. I still did not go through the docs, i assume plugin will list all available properties of a part, this may include docking timeouts, triggers and forces for ports.

[Deadweasel]

The problem stems from the way the game maintains a ship's hierarchy. It is a straight tree, with branches sticking out for the docks. This makes it possible for the engine to figure out physics effects for every part on the ship.

Trying to couple multiple dock ports from one component to another creates a loop in the logic flow. Now, instead of the docked vessel just being a branch through the one docking port, it tries to create a loop through two or more ports instead, conflicting with the linear nature of the engine's physics logic.

You can sort of get multiple ports to align and "believe" that they're docked sufficiently enough to serve your purpose thanks to the magnetic attraction feature of the ports, and due to their proximity and general alignment at contact, but the reality is that the physics calculations are still doggedly proceeding through only one of the ports. If you have a ship with a very high T/W ratio available on the "top" docked section, you might see the evidence of this for yourself when you fire the engines on it, and it swings wildly away from its connection, along the one dock port that was actually considered to be properly and fully connected.

Best option is to use Docking Port Sr where possible, and quantum or docking struts where not. Otherwise, it might be time to see about refining the entire vessel design somewhat.

[Kasuha]

Physics engine has no problem with connection loops. Otherwise struts wouldn't be possible. I believe there are other reasons. Perhaps staging?

[fatcargo]

@Deadweasel : Ok then. Hm this issue is important enough to make a sticky post warning everyone about multiple docking ports.

@Kasuha : Struts are indeed an exception to the rule. I really have no idea how it's done. Only a memeber of dev team working on game physics would be able to fully and correctly answer this question.

[FreeThinker]

Best option is to use Docking Port Sr where possible, and quantum or docking struts where not. Otherwise, it might be time to see about refining the entire vessel design somewhat.

What about using 3.75m Docking Port for docking heavy modules (like space station). Would it help creating a stronger connection?

[sal_vager]

This is pretty old FreeThinker, it pre-dates the large docking ports

Thanks for the advice but I think you have to go further with stock than just using multiple or larger docking ports, I have been thinking of reinforcing my larger orbit-constructed craft with claw-ended structural beams, jockeyed into place by RCS tugs!

Edited November 18, 2014 by sal_vager

[FreeThinker]

This is pretty old FreeThinker, it pre-dates the large docking ports

Thanks for the advice but I think you have to go further with stock than just using multiple or larger docking ports, I have been thinking of reinforcing my larger orbit-constructed craft with claw-ended structural beams, jockeyed into place by RCS tugs!

Intresting, so you can effectively use claws like quantum struts?

You gave me an idea. What about combining your Claws on stuctural beams with Infernal Robotic Powered Hinges? That way you can litterly grab a spacestation after it is docked for a more secure connection...

Edited November 18, 2014 by FreeThinker

[chrisb2e9]

Quantum struts work just fine for that. I use them on massive ships that I dock together.

[Laie]

Thanks for the advice but I think you have to go further with stock than just using multiple or larger docking ports, I have been thinking of reinforcing my larger orbit-constructed craft with claw-ended structural beams, jockeyed into place by RCS tugs!

Wasn't there something problematic about multiple claws?

However, I can assure you that multiple ports work a treat. Picture below shows an early prototype of my Eve Lander, attached to the Heavy Tug with three standard docking ports. The connection didn't bend noticeably; for rigidity purposes, the craft could as well be of one piece. However, the standard ports sunk into each other when I was applying thrust, so I had to limit the bigger engines or the two parts of the vessel would effectively collide and go BOOM. Later versions used Senior Ports and had no problem whatsoever.

Below, a good view of the ports on the Eve Lander part of the vessel (click for a bigger picture):

Note that the port in the center wasn't even used during transfer.

And here's a gallery of my second mission. Pictures 4-7 show good views of the docking ports and how it came together. It was incredibly stable. You've done interplanetary burns, and know how it can be difficult to get it right down to the last meter, because all the flexing in your vessel makes your trajectory quite jumpy? Not with that one. 1300 tons / 500 parts, and I got the ejection burn down to <0.1m/s. I've had tiny probes that were more difficult to handle.

TL;DR: multi-docking does allow for very stable vessels.

[DrScarlett]

Hey Guys,

I know this is an old thread, but I am trying to build a space cube out of ribs with six-sided docking nodes on each corner. the ribs are exactly the same size so everything should fit perfectly. I manage to build the first square, that clicks into place, but around the time three ports need to come together one often fails. Haven't managed to put the whole cube together I tried using SnapDock to guarantee 90 degree rotation on the connections but that doesn't seem to help.

Anyone ever tried this? Any tips?

Here's a pic:

[Vanamonde]

A while back I made a station like this. 

But I'm sorry, I have no tips because I had the same problem, and could never get the last corner to line up properly.