Booster separation question

[Kerbal Productions]

I saw some videos that when the booster is jettisoned, it kinda has an additional burn on the side making it roll. What is this? How can I do this?

[RealKerbal3x]

@Helvica_Ring_Scientist You can use Sepratrons to push boosters away after separation, if that's what you mean. There's also a fuel tank in Making History which has a small solid-fuel separation thruster built in.

[jimmymcgoochie]

Most (all?) real rockets with side boosters use separation motors to push them away once they’re out of fuel. These are usually mounted on the nose of the booster to let aerodynamics push the boosters away from the core and avoid the risk of collisions.  The Sepratron rocket is provided in the game for that reason, although you only really need it for making your rockets ‘more realistic’ or when using very big boosters; the Making History DLC includes a fuel tank that has its own separation rocket built in to replicate the R7/Soyuz rocket’s boosters.

You can get a similar effect in KSP just by moving your boosters so they’re attached to their decouplers near the top of the booster- when the decoupler fires it provides an impulse to the part attached to it, and since this force is acting above the centre of mass it will push the booster away at the front.

Just be careful that you don’t accidentally hit anything at the back of your core stage when the boosters decouple, which is possible if you make the boosters pivot without moving away (making the back of the boosters hit the back of the core) or if you add too many separator motors (I’ve done this with the MH tanks, they separated but spun around and crashed point-first into the main engines because the separation motors were too powerful and burned for too long).