Splitting rocket into 3 LV-Ns

[lumpman2]

I am currently designing my Eve lander, and the lander stage works fine, but I can't recombine the 3 LV-Ns I have for my IP transfer, because I don't think you can attach a tri-adapter to all of the nodes. The rocket flexes and compresses and eventually breaks because a small stack decoupler can't hold up against a mainsail.

How am I supposed to actually attach all of the decouplers to the adapter?

[blizzy78]

Docking ports. It has been discussed quite a few times in the Questions forum in the last days.

[Ampere]

The basic problem arises from how KSP describes rockets. It uses a tree data structure; all parts have a single 'parent' part which is the part you clipped the new part onto. Basically you've got 3 engines whose parent is the tri-coupler, and the lower one can only have one 'parent', so the other two connections are not connected, physically, as far as the game is concerned, so you have off-axis forces which causes problems.

There's a couple solutions you could try. My personal preference for interplanetary stages with LV-N's is to use sidepods- there's a number of ways to connect them, and you'll need to ensure you include a fuel hose if you want to pull fuel from the center tank.

Alternatively, you can leave the setup you have now, but augment the connection with a web of struts. You may need to do this anyways as rockets of that size tend to have rigidity problems already. Struts bypass the whole tree idea a bit and create physical links between any two parts.

Your third option is to use docking adapters on the bottom of the engines, on the other side of the decouplers (so you can remove them when the engines are ready to fire). Docking ports, I'm told, can create multi-joins at least as far as forces are concerned. I've never attempted it myself since in the past it didn't work.

If you go with struts, you can use trusses or I-beams on the side of the tanks to clear the lip of the couples/engines.

[capi3101]

Yep. Screwed up this one myself recently...

Here's what you do:

1) Before you go putting the adapter on for your rockets, you want to build the bottom first. Stick a tri-adapter on your stack, then attach three Clamp-O-Trons on that.

2) Pull the adapter off the stack, flip it over and set it aside for the time being.

3) Stick another tri-adapter on the stack. Add your engines (you're working with LV-Ns, so watch how you line them up!), stick decouplers on the bottom of them, then docking ports on the bottom of the decouplers.

4) Pick up the bottom piece you built earlier and attach it via the docking ports.

It's the old "extra rigidity through multiple docking ports" trick. When you get out to the pad, the game will only count one of the ports as attached, but as soon as the physics engine releases it the other ports will suck each other in and lock down. The addition of the decouplers allows you to jettison the whole thing as a normal stage when the time comes.

Edited August 29, 2013 by capi3101

[chaos_forge]

Another option is to side-mount your LVNs. KSP uses a tree structure for ships, so when you try to put an upside down n-coupler, it only attaches at one point. Apart from using docking ports, which bypass this by docking to each other once physics kicks in, there's really no solution.

EDIT: capi3101's post is much better than mine xD

[lumpman2]

Yep. Screwed up this one myself recently...

Here's what you do:

1) Before you go putting the adapter on for your rockets, you want to build the bottom first. Stick a tri-adapter on your stack, then attach three Clamp-O-Trons on that.

2) Pull the adapter off the stack, flip it over and set it aside for the time being.

3) Stick another tri-adapter on the stack. Add your engines (you're working with LV-Ns, so watch how you line them up!), stick decouplers on the bottom of them, then docking ports on the bottom of the decouplers.

4) Pick up the bottom piece you built earlier and attach it via the docking ports.

It's the old "extra rigidity through multiple docking ports" trick. When you get out to the pad, the game will only count one of the ports as attached, but as soon as the physics engine releases it the other ports will suck each other in and lock down. The addition of the decouplers allows you to jettison the whole thing as a normal stage when the time comes.

I never thought that docking ports were that rigid (looking at all the flexing that happens with interplanetary drives), and then I realized they're actually strong when there are 3 of them together

[lumpman2]

Yep. Screwed up this one myself recently...

Here's what you do:

1) Before you go putting the adapter on for your rockets, you want to build the bottom first. Stick a tri-adapter on your stack, then attach three Clamp-O-Trons on that.

2) Pull the adapter off the stack, flip it over and set it aside for the time being.

3) Stick another tri-adapter on the stack. Add your engines (you're working with LV-Ns, so watch how you line them up!), stick decouplers on the bottom of them, then docking ports on the bottom of the decouplers.

4) Pick up the bottom piece you built earlier and attach it via the docking ports.

It's the old "extra rigidity through multiple docking ports" trick. When you get out to the pad, the game will only count one of the ports as attached, but as soon as the physics engine releases it the other ports will suck each other in and lock down. The addition of the decouplers allows you to jettison the whole thing as a normal stage when the time comes.

I never thought that docking ports were that rigid (looking at all the flexing that happens with interplanetary drives), and then I realized they're actually strong when there are 3 of them together

[capi3101]

A single one by itself isn't terribly strong, true. That's why in pre-0.21 you had folks with docking ports mounted on tri-couplers all the time. Of course, the tri-coupler came with its own set of headaches (namely the fact that it wouldn't sit flush with a big fuel tank on the narrow end, necessitating additional struts - and the additional headaches associated with docking more than one port at once), but at the time it was still the best option. The n-adapters that came with 0.21 go a long way towards fixing the extra strut issue. And then there are Seniors - I'm not entirely sold on them, to be honest, but then again it's been a while since I've launched a proper interplanetary mission.

[lumpman2]

Ok, well, I tried it out, and the whole upper stage flipped over every single time I tried to launch it. I made a second adapter, put 3 docking ports on it, and then when I went to put the upside down adapter under the ports on the decouplers, there was no node on the adapter's ports so I just put 3 upside down ports under the others and stuck a tri-adapter on that.

Can't post pictures right now because I really don't feel like restarting KSP every single time I have to open the internet (I have 2gb ram.)

[M4ck]

Ok, well, I tried it out, and the whole upper stage flipped over every single time I tried to launch it. I made a second adapter, put 3 docking ports on it, and then when I went to put the upside down adapter under the ports on the decouplers, there was no node on the adapter's ports so I just put 3 upside down ports under the others and stuck a tri-adapter on that.

That's the exact way to do this wrong. This way you have three stacks of engine/port/port, and when you add the tri-coupler, it gets attached to one pair of docking ports. the way to do this is to make a rocket/tri-coupler/3x engine/3x decoupler or separator(whichever you prefer)/ 3x docking port facing down. Then, you take 1x symmetry, not 3x, and place a single docking port(let's name it X) so it "connects" to one of your already placed. Then, take a tricoupler and orient it so it faces the right way; hold it under the one docking port and when it looks like it's oriented right, click Q or E twice to make it rotate. NOW place it. Take two more docking ports and put them on the two available nodes on the tri-coupler. Now pick up the X port, hit Q or E twice and place it under any of the ports(if the thing is rotated, use Q, E or shift+Q/E to fit it). Works fine for me all the time

[lumpman2]

Still doesn't work, it continues to flip over. I don't really see any difference other than the way I installed the docking ports. I zoomed, and I saw that two of them were compressing while the upper stage tipped and fell.

[lumpman2]

Still doesn't work, it continues to flip over. I don't see any difference, other than the way I installed the ports. Two of them compress while one appears to stay docked, which causes the upper stage to tip towards the 2 disconnected ports.

NOTE: Sorry, I have no idea why my computer keeps double posting these.

Edited August 30, 2013 by lumpman2

[Whirligig Girl]

Your biggest problem is that when the LV-Ns destach the fairings will disintegrate eachother and the LV-Ns.