Stages crashing into eachother

[WatchDragon]

When my gargantuan boosters release, they clip my middle stage nozzle and some fuel tanks =(, i am not sure how to fix this, any ideas?

I want my rocket to get into circle orbit with mekjeb and no other addons, and no help from me.

[Foamy]

Maybe if you put winglets on each of them that would produce an even force on the rocket as a whole (due to symmetry) but when released would cause them to be pushed away from the rocket.

[Amoral]

Go for stage separation while they still have a tiny bit of fuel, and are still burning. That should push them up and away from your center stage.

[Ziff]

I\'m having a hard time seeing where the vertical decouplers are for the outer tank separation, are you using addon parts for decouplers? Check their ejection strength. Try using radial couplers instead, they tend to push the empty stage away instead of just pushing it straight down. Mechjeb tends to start turning early at 10-12km, I assume your launch stage is still burning at that point so when it releases its hitting you from the side as its trying to drop straight down. Stack multiple radial decouplers on each other if you have to.

[Creat]

@Ziff: He uses the small ones that come with MechJeb. They are the grey rings that are in there

Well it\'s kinda hard to give you specific tips. I\'ve rebuild your design from your screenshot (as you didn\'t attach it). Also, I have no idea what your settings for the ascend autopilot are. What is the orbit altitude, when is it set to start/end the turn (click \'edit path\' to see those

From some test I can only guess that you the autopilot is still turning when the initial stage (meaning the four \'bosters\') is separated, and that one of them ends up above, so the next stage basically turns into it, clipping the middle engine in the back.

Obviously what 'Amoral' suggested won\'t work as you want mechjeb to be able to do the separation.

What is the tank right at the top (below the capsule) doing? Is it even connected to anything that uses fuel? There isn\'t anything on the screenshot...

There are quite a few solutions to this, it\'s basically a bit of a dangerous design with such a long central stage that isn\'t separated with the surrounding ones.

A) Use different parameters for the ascend autopilot. The default settings turns way too early anyway (try 25 km turn start, 60 turn finish). Target at least 100 km orbit with those settings obviously.

Use radial decouplers. They push away whatever is decoupled, so you\'re less likely to run into the stuff. The TT-38K (ejection force 120) is better than the lighter 'structural pylon' here. I tried this, but as long as stage separation occurs while the vehicle is still turning, it won\'t help.

C) include the five tanks that make up your second stage in the top, meaning you have 8 tanks surrounding the center (well, it\'s one less, but whatever). You\'ll actually have more thrust (4*50 = 200 instead of 175 with the exact same fuel consumption for speed gained, basically 25 thrust for 1 \'fuel usage\' unit). This works of course (also tried it). See screenshot and attached craft. Reached orbit @ 400 KM with about 1.4 tanks per engine remaining (meaning 5.6 total) so about out of the initial 9, 8 surrounding the center one which is drained first with the fuel pipes.

D) remove the central engine, not the tanks though. Connect them to the outer tanks with four fuel lines. Decouple simultaneously. Will use more fuel to reach orbit as your design (or as answer C) as the central tanks will have to push more weight. Keep in mind though that the final vehicle is lighter in comparison to option C, so it can do more with that amount of fuel. In my test it reached the same 400 KM orbit (also same settings for autopilot) with close to 4 tanks remaining.

E) If you want to keep it at three stages, make the stage less long, but wider. Example also attached. will behave exactly like yours in terms of fuel consumption as it\'s the only change that is only arranged differently.

EDIT: forgot to add about option E, it only barely reaches orbit with the middle stage as it\'s a bit low on thrust. It will work as is with a higher 'turn end' though! Otherwise more thrust is needed as the gravity turn isn\'t completed before the initial Apoapsis.

EDIT2: also, the outer tanks apparently explode (due to colliding with each other) when they are dropped, so you either need to reduce the 'stage delay' or combine separation of outer tanks with ignition of middle engine. I\'ve updated the attached file accordingly.

Sidenote: what on earth are you doing with all those RCS tanks? why 5? isn\'t 1 enough? Only turn on RCS once you\'re out of atmosphere, it tends to slow you down (at best) before that... also I only see RCS thrusters at the bottom of the central unit, but not the top part. Intentional?

Sidenote2: you can use all basic engines interchangeable, they have exactly the same fuel efficiency (25 thrust per fuel usage). Bigger will burn fuel faster but give you the same total acceleration per fuel unit. This only applies to flying in space, where you have no drag, of course.