SRB separation always blows my ship up

[Talavar]

Anyone else having this frustrating issue? the giant SRB's attached to the side of the Largest fueltank.. when they separate, it ALWAYS destroys the main tank. I've tried everything. Sepratrons out the wazoo, chutes to pull them away.. nothing works.... EDIT: Added video

Edited August 31, 2014 by Talavar
added video

[TYRT]

Anyone else having this frustrating issue? the giant SRB's attached to the side of the Largest fueltank.. when they separate, it ALWAYS destroys the main tank. I've tried everything. Sepratrons out the wazoo, chutes to pull them away.. nothing works....

Try to activate sepatrons before seperation stage.

[Liowen]

Anyone else having this frustrating issue? the giant SRB's attached to the side of the Largest fueltank.. when they separate, it ALWAYS destroys the main tank. I've tried everything. Sepratrons out the wazoo, chutes to pull them away.. nothing works....

Pictures would help as to see what might the problem. It could be as simple as the radial decouplers are too low (or the SRB is off center on the decoupler) and kicking them inwards, or they are moving when you separate them from the craft.

[Talavar]

Try to activate sepatrons before seperation stage.

no-go.. still blows them.. Ill post a video so everyone can see my set-up.. need to grab some capture software real quick.

[Speeding Mullet]

Have you tried mounting the sepatrons on the central fuel tank pointing out at the boosters. Sounds strange but it works.

[Talavar]

OK, here is the Video.. take a look.. nothing touches the tank.. it just blows up.. I even tried using mechjeb to ensure it was done "right" (i guess)..

[Whackjob]

When in doubt...

... make your own seperatrons.

[Talavar]

When in doubt...

http://i.imgur.com/YccwWbO.png

... make your own seperatrons.

LOL.. not exactly what I had in mind.. haha

[Talavar]

Have you tried mounting the sepatrons on the central fuel tank pointing out at the boosters. Sounds strange but it works.

I'll give this a try. Thanks for the info, Speedy.

[magico13]

Try reducing the amount of fuel in them. I had that happen to me with a rocket and had to cut the fuel in half or so, that way it couldn't overheat my fuel tank. Still got enough force to make a clean separation.

[SkyRender]

You need to install your boosters lower on the decouplers, and put the decouplers lower on the rocket. It's very hard to keep them from bowing inwards when separating when they've got most of their mass near the top like that. Ideally you want the radial decoupler installation relative to the SRB to be as close to the center of mass of the SRB as possible, tending so that slightly more of the mass of the SRB is below the decoupler. That prevents the issue that's taking out your fuel tank.

[Talavar]

Seperatrons overheating Main fuel tank as Magico said... Almost makes them useless.

[Lunaran]

From the video I can see the boosters aren't colliding with the tank. Your decouplers are fine.

Your sepratrons are pointed straight in at the main tank, however. They're like tiny guns. Roll them around the outside of the boosters a little bit so they point inward in a v-shape. The thrust will still be straight away from the tank but no single sepratron will be pointed straight at it.

[TrooperCooper]

Not sure if its your sepratrons firing into the tank and blowing it up (might want to try repositioning them so their exhaust doesnt hit the tank) or if it is a collision problem...

The Kerbodine liquid booster engine you are using in the center is actually a little wider than 2.5 meters iirc. I havent used it for a while, but when I did, I had similar problems. A few things to avoid those collisions...

1.) Make sure you are going straight up when decoupling the SRBs. Else you will clip into the SRBs which are not accelerated into the same direction as your craft anymore. Sepratrons can help with this, but even with them in effect, tilting increases the chance of a collision, since the distance between the SRB and the sticking out engine is very narrow.

2.) Using the TT-70 Radial Decoupler, which mounts the SRB further away from your craft can reduce the problem as well, but I see you are using those already.

3.) Ultimately, what I considered as mandatory when using that main engine plus radial SRBs was to mount the boosters higher up. By making sure the bottom end of your SRB is about half a tank length away from the top end of the engine, it gives the sepratrons more time to accelerate the booster radially away while it is travelling downwards relative to your craft at the same time before it passes the engine. I usually just had a small tank between engine and bottom end of SRBs. See the two pics below...

[Whackjob]

I managed to sneak a peek at the vid while at office. The separation looks clean. The danger area was the top of the SRBs as they tip inwards from the bottoms being blasted out via decoupler force. I did not see the top of the SRBs strike the central stack. I believe the problem, oddly enough, is the loss of weight causing the central stack to pogo-stick. Uh... hard to explain... the weight of the SRBs suddenly releasing means there's less to push against with the main engine block. And the jump in force each component feels is shared by the center bottom fuel stack. So it crumples like an empty beer can.

My suggestion for fix: Reinforce the bottom a bit more, specifically between center bottom engine block and center bottom fuel tank, and center bottom fuel tank and the item directly above it.

SOURCE: I've put absurd thrust under small stacks and huge weights on top and dealt with all the engineering problems they present.

Edited August 31, 2014 by Whackjob

[TimberWolffe]

Y'all completely wrong. I know exactly what OP is talking about. Apparently it's a bug in 0.24.2 where SRBs, no matter where mounted our what measures taken, always gravitate inwards. My solution for this is to get into 0 air orbit, then dump SRBs and blast away, as their velocity will be relatively constant and I'll be much faster, too fast for them to gravitate inwards and blow up my tank.

[Wanderfound]

Y'all completely wrong. I know exactly what OP is talking about. Apparently it's a bug in 0.24.2 where SRBs, no matter where mounted our what measures taken, always gravitate inwards. My solution for this is to get into 0 air orbit, then dump SRBs and blast away, as their velocity will be relatively constant and I'll be much faster, too fast for them to gravitate inwards and blow up my tank.

The bug has the SRBs rotating top-in a bit more than they should, but it's easy to compensate for. Just mount your Sepratrons a little bit higher than you would otherwise.

[TimberWolffe]

The bug has the SRBs rotating top-in a bit more than they should, but it's easy to compensate for. Just mount your Sepratrons a little bit higher than you would otherwise.

I tried that. With 3 separatrons at the very top, still did it. I know the bug is atmospheric, as in it only happens with an atmosphere, because once I'm in a place with no air the separation couldn't be cleaner.

[Wanderfound]

I tried that. With 3 separatrons at the very top, still did it. I know the bug is atmospheric, as in it only happens with an atmosphere, because once I'm in a place with no air the separation couldn't be cleaner.

Give me a few hours and I'll post a demo. They do work when used right.

[TimberWolffe]

aight, because I'm hanging for an atmospheric fix so I can stop launching interstellar rockets with wimpy little spaceplanes

[SkyRender]

Here's a useful little tip for you: drop your throttle to zero just before you decouple (this is easily done by hitting X). If your rocket is running solely on inertia when the SRBs decouple, they will come off far more smoothly. You can throttle back up right after decoupling safely, too.

[DavidHunter]

When in doubt...

http://i.imgur.com/YccwWbO.png

... make your own seperatrons.

Procedural Parts' tiny SRBs with high-thrust are 'da ....'.

[magnemoe]

From the video its pretty obvious to me that the the problem is the top of the SRB moves inward and destroy the tank.

You want more force on the top of the booster than the bottom, I rarely uses bottom seperators and then only on large an long liquid fuel boosters where the center of mas is low because its an huge engine and 2-3 empty tanks.

On the large SRB I only use one, I often reduce seperator trust to 1/2 too, another idea is to point it 30-45 degree upward, it will then brake faster.

As you are under trust you can afford that the bottom of the booster move inward a bit as you have moved past then it happens.

Often just adding an fin on the outside of the SRB solve this, it would increase drag on the outside bottom and tilt the top out, you don't need much force here, just enough to avoid hitting the rocket.

Last issue, mechjeb start gravity turn at 6.7 Km, around the same time the huge SRB run out. Might be an idea to increase the start to 8 km

[Wanderfound]

Okay: Sepratron demo as promised.

Note alignment of Sepratrons. One pair per booster.

Launch:

Decouple:

Spinny:

Same rocket decoupling while pitched over:

You’ll want a few more Sepratrons if you're shifting huge things like LFBs, or if you’re planning on decoupling while pitched horizontally, but in either case: they work just fine if you set them up right.

Edited August 31, 2014 by Wanderfound

[TimberWolffe]

Yeah, I tried the same but with one also pointing vertically, thruting downwards. It may have been due to FAR but from what I can tell it's impossible for me to separate in surface atmospheres