Strongest coupling between parts of a mothership (using docking ports)

[Magzimum]

I'm playing a career game, and the next mission should (hopefully) take some Kerbals to Duna. I would like to build a large mothership with a few extra modules in orbit, but experience has taught me that it's a bad idea to just couple a number of sections together with docking ports. The Space Kraken will wobble the ship apart when under acceleration.

I have been experimenting with stronger bonds between the sections of the ship, using multiple docking ports, but results have been rather poor.

I tried something like this, but when coupling two of these together in orbit, only 2 of the 4 docking ports seem to line up. Common sense and maths tells me that when 2 of these line up, all 4 should line up, but a right-click on the docking ports suggests that only 2 out of 4 are coupled.

Any tips and tricks to make a strong mothership with a bunch of fancy modules, and being able to accelerate it? Launching in 1 piece is the obvious solution, but I haven't unlocked the really big engines yet, so was hoping for an alternative. (Also, I play Kerbalism, which means my ships need greenhouses, huge storages of food and water, and a bunch more life support stuff, and most importantly a lot of living space for the Kerbals).

 

 

[Palaceviking]

3 hours ago, Magzimum said:

I'm playing a career game, and the next mission should (hopefully) take some Kerbals to Duna. I would like to build a large mothership with a few extra modules in orbit, but experience has taught me that it's a bad idea to just couple a number of sections together with docking ports. The Space Kraken will wobble the ship apart when under acceleration.

I have been experimenting with stronger bonds between the sections of the ship, using multiple docking ports, but results have been rather poor.

I tried something like this, but when coupling two of these together in orbit, only 2 of the 4 docking ports seem to line up. Common sense and maths tells me that when 2 of these line up, all 4 should line up, but a right-click on the docking ports suggests that only 2 out of 4 are coupled.

Any tips and tricks to make a strong mothership with a bunch of fancy modules, and being able to accelerate it? Launching in 1 piece is the obvious solution, but I haven't unlocked the really big engines yet, so was hoping for an alternative. (Also, I play Kerbalism, which means my ships need greenhouses, huge storages of food and water, and a bunch more life support stuff, and most importantly a lot of living space for the Kerbals).

 

 

Do you build the whole thing completely in the vab then separate into subassemblies? You should because then the ports are guaranteed to line up.

Getting the hang of rerooting your contraptions and using sub-assemblies is a major leap in ksp motherships and general modular design. 

Edited September 25, 2017 by Palaceviking
Moar tips

[Jas0n]

If you are not against using mods, you can use Konstruction, which add welding ports. Or you can use KAS to add struts between the two modules.

 

[Spricigo]

You may try a small flotilla, something like three vessels: 

-one to delivery the stuff you want to use at the derstination (landers/rovers/satellites/etc)

-one supply ship (fuel/life support)

-a crew transfer vehicle.  This can be sent later in a faster trajectory to save ob life support supply.

Even if you dock later, the vessels will probably be smaller by then.

The drawbacks are pretty obvious: doing the transfer/capture maneuvers multiple times, the need for rendezvous and part redundancy. OTOH you don't need the bigger stuff and have better chance to avoid ridiculous long burns and woobling issues.

 

[Vanamonde]

Docking ports are plenty strong enough, as long as you don't get wild with the accelerations. I fly monstrosities like this all the time. 

[Tyko]

You can use autostruts.

Another way to increase rigidity is to use KAS struts this is a bit less "magic" feeling than autostrutting. You attach the strut endpoints in the VAB and then once the modules are docked you send a Kerbal out on EVA to connect the endpoints together. You can even attach new endpoints if you want to.

[Jas0n]

11 minutes ago, Tyko said:

You can use autostruts.

Beware when using autostruts. If you have set to heaviest part, and the heaviest part of the craft changes due to fuel drain or docking/undocking, it could result in some pretty spectacular RUD.

[Magzimum]

14 hours ago, Vanamonde said:

Docking ports are plenty strong enough, as long as you don't get wild with the accelerations. I fly monstrosities like this all the time.

Nice ship! I noticed that it uses the much stronger Sr. docking ports. My ship has only the regular ones, which are more wobbly (I haven't even upgraded the R&D center to level 3).

Frankly, I am opting to just launch in 1 piece after all, and only do some refueling in orbit to reduce the mass at lift-off. As soon as my ship is back from Duna, I should have enough Science points and cash unlock new parts and solve part of my problem.

[Hotaru]

12 hours ago, Jas0n said:

Beware when using autostruts. If you have set to heaviest part, and the heaviest part of the craft changes due to fuel drain or docking/undocking, it could result in some pretty spectacular RUD.

Personally, I find autostrutting a couple of the most distant parts of the ship to the root is often enough to minimize wobble. I've never had kraken attacks due to autostruts except times when I went completely overboard and autostrutted basically every part of a very complex vehicle. 

So unless you think they're cheating (I disagree, but I can see the argument for it since there are no restrictions on using them) or for some reason they're more kraken-inducing for you than for me (always possible given differences in hardware), there's not much reason not to use autostruts as long as you don't go too crazy with them. 

 

PS. @Magzimum It's possible that the multi-port connector in the image is itself a bit flexible, which could account for the failure of the ports to line up properly. Maybe try a bi- or tri-coupler with docking ports attached, that might be sturdier and therefore more likely to have all the ports connect up properly. (Or just unlock the Sr. ports, that works too.)

Edited September 26, 2017 by Hotaru

[Helmetman]

@MagzimumWhat's also very important to know is whether you push or tow the ship?

Depending on how modules are decoupled on the actual mothership you could eyeball whether it's better for towing or pushing. Multiple docking ports means more connections so less wobble. So I would push the craft in that case rather then towing it. If the craft has few connections it will wobble a lot when pushed, but not when towed (with engines on the front)

Another way to reduce wobble is to make sure that each modules has it's own engine, and that it has the same TWR as all the other individual modules.

This makes sure that all the modules are propelled under the same acceleration, and things won't be ripping of so easily.
Also understand that docking ports in real life aren't meant for heavy stresses.
I'm sure your KSP styled mother ship will have a TWR of 0.30 to 1+, right?

I wouldn't put the ISS under such acceleration and expect all the compartments to stay intact without leaking atmosphere or other chemicals and stuff.
The fact that you can accelerate KSP docked modules at 'decent' acceleration (i.e. TWR 0.30) is already quite awesome and unrealistic.
If you accelerate much faster then that up to 1 G or more and you have multiple docked modules, then you can expect some unintended things to happen, all the way up to RUD.

I also want you to post a picture of the mothership in Orbit as you've tried assembling it earlier on. Seeing how your being thrusted and how the docking port connections are laid out could give any of us some clues.
 

 

[Magzimum]

@Helmetman, You make good points about the TWR of the mothership in comparison to the ISS. However, my mothership needs to get to Duna, while the ISS at best needs to increase its Ap and Pe by a few kilometer.

I cannot post a picture, since it's all under development. I am not trying to solve a very particular problem, but was rather trying to get help already in the conceptual stage of the design.

[Helmetman]

@MagzimumThe ISS under said acceleration was a hypothesis. I didn't mention this so I understand your confusion. It was only to illustrate the fundamental similarities of real world docking ports and ksp ones.
They are not made to handle stress. On that bases I only intend to say that you shouldn't expect miracles using docking ports as connections in KSP. That said, the allowable stresses in ksp are already OP, but balanced and acceptable and nothing worth changing though.

And if it is designs you need I would just watch some interesting playthroughs on youtube. Many guys assemble stuff and put heavy engines at it and make it work without disassembling itself. That's probably the best thing you can do to learn yourself and get some design inspiration. Sometimes it's just better to see things then people trying to explain things to you. Maybe I'll link such a playthrough if I find a proper channel. Haven't got any on hand though that would be a good example. Maybe I'll find something later on.

[Palaceviking]

I may have to make a small speech on the pendulum fallacy,  in other news,- multiple docking ports do work excellently but you have to build it like that,  then launch it separately. 

Edited September 26, 2017 by Palaceviking
Emphasis

[Vanamonde]

14 hours ago, Magzimum said:

Nice ship! I noticed that it uses the much stronger Sr. docking ports. My ship has only the regular ones, which are more wobbly (I haven't even upgraded the R&D center to level 3).

The rovers on the sponsons and the satellites near the front are attached using regular-sized docking rings. And on older versions of the ship, I would hang things on there perpendicularly, and the rings still held during accelerations and aerobraking. 

[overkill13]

Just a quick question:

Is the OP checking BOTH ports in each connection for an undock option?  When multidocking, the ports tend to alternate which vessel is considered the docker and the dockee.  That is to say if you have a ship docking with a station using a double port arrangement, one of the ports will likely show an undock option on the ship and the other on the station once docked.  If this continues for a four port setup I would expect two on one side and two on the other.  I've never used more than two ports at a time so cannot confirm.

[Magzimum]

2 hours ago, overkill13 said:

Just a quick question:

Is the OP checking BOTH ports in each connection for an undock option?  When multidocking, the ports tend to alternate which vessel is considered the docker and the dockee.  That is to say if you have a ship docking with a station using a double port arrangement, one of the ports will likely show an undock option on the ship and the other on the station once docked.  If this continues for a four port setup I would expect two on one side and two on the other.  I've never used more than two ports at a time so cannot confirm.

Good point, but yes, I checked both. You're absolutely right that they alternate.