Difficulty attaching boosters radially (beginner)

[MiddleC]

I have a straight-up liquid fuel rocket. I want to attach big long solid boosters () to the side, staged with radial decouplers (trying TT-70 decoupler). I have only been able to attach a booster to a decoupler at the booster's midpoint. The long boosters then flop around in flight. I want to have decouplers at the top and bottom of the booster, but I can't get the UI to do that.

My experience of the UI is, while moving the booster, if I point the mouse right at the decoupler, it attaches the booster midpoint, no matter where I "grabbed" the booster. If I do not point at the decoupler, the booster gets attached to the hull, instead. If I have two, vertically aligned decouplers, the booster only gets attached to the one I point at.

All of that makes some sense, but I just can't figure out how to do a 2-point, decoupling attachment.

P.S. I am able to ride this garbage into orbit, with the thrust vector moving all over as the boosters flop about. (Sometimes.) I'm bad.

Edited September 8, 2014 by MiddleC

[deepspacecreeper]

Actually it is ok to only attach the booster to 1 decoupler. to solve the floppy problem, strut the top and bottom of the boosters to the main hull. (eas 4 strut connector). the connection of struts between the booster and the hull will be automatically severed when the booster decoupler is fired.

[MiddleC]

Interesting. I thought about struts, but assumed it would make a mess when they were still attached on decouple. Will do.

Funny, I learned about KSP from XKCD, where he joked about "more struts".

[SRV Ron]

As you can only mount a SRB to a single radical decoupler, do so at its center. Use braces if necessary to stabilize. They should drop straight off so long as you are not turning.

The extra long ones will need to be braced like this design.

[cantab]

Whenever you attach a part, other than a strut connector or fuel line, you can only attach it to one other part. That's a limitation in the way the game handles ships, as a "tree" of parts. So you cannot fit an SRB to a pair of decouplers.

[MiddleC]

Actually it is ok to only attach the booster to 1 decoupler. to solve the floppy problem, strut the top and bottom of the boosters to the main hull. (eas 4 strut connector). the connection of struts between the booster and the hull will be automatically severed when the booster decoupler is fired.

That was it! Thanks, and the other answers were right, too.