Sepratrons fall off

[Wallace]

I'm having a problem with sepratrons falling off, well, flying off on their own when trying to separate the biggest SRB on a big SLS rocket.

I had the SRBs on the big hydraulic detachment manifold decoupler with 4 sepratrons on each of them and a single strut at the top to stop wobbling, but when I activate the staging I see the sepratrons fly off on their while the SRBs just crash into my rocket and destroy it.

I've even tried adding struts to the sepratrons but they still fly off when they are activated.

I'm using NEAR, so I don't know if that makes any difference, I know some ppl mention drag ripping off parts in FAR, but they are fine until they fire and i'm not going fast enough to cause the re-entry effect.

[Vlk]

Sepratrons have some issues for their original role. If they are in a bad angle, they can fall off before separating anything, their thrust damages other parts, even if it is a little damage, it always causes lag for me.

[Aethon]

Screen shots please..

[rkman]

Some or all lateral decouplers seem to have a bug that make the decoupled booster fall apart upon decoupling, if that booster consist of more than one part. Nosecones separating from SRBs, stacked fuel tanks separate from one another, etc.

[Wallace]

I'm not sure I can get a screen shot of the actual moment of sepratron escape, they fly off pretty quick once they are unattached. I'll give it a try.

rkman, that does sound like it could be the problem, tho I've never had it happen before now. I'll have to see if the nosecone falls off too.

[Kilfio]

I am having the exact same issue. When I put sepratrons on an S1 SRB attached by hydraulic manifold to an orange tank, the sepratrons fly off unexplainedly.

Additional information: When I separate the SRBs shortly after launch (running or not), they separate just fine, and the Sepratrons don't fly off. However, when they're almost out or completely out of fuel, the Sepratrons fly off. Pre-firing them prior to decoupling doesn't help, since as soon as the hydraulic manifold decouples, the Sepratrons decouple.

The problem DOES NOT occur if you use TT-38Ks or TT-70s, so I believe I've narrowed this down to an issue with the hydraulic manifold part itself. My advice would be to just not use that part until Squad fixes this little bug.

I tested this with several rockets, but all used the orange tanks for attachment. Here's the one I did the most testing with:

[Wanderfound]

I'm not sure I can get a screen shot of the actual moment of sepratron escape, they fly off pretty quick once they are unattached. I'll give it a try.

rkman, that does sound like it could be the problem, tho I've never had it happen before now. I'll have to see if the nosecone falls off too.

Even if you can't get action shots, just an image of the setup in the VAB would be useful. It could potentially be a construction issue rather than a bug.

[Kasuha]

There seems to be an issue with radial decouplers in the current release, they seem to stop in space (or gain very high drag coefficient for one frame) when decoupled which introduces all kinds of problems with decoupling. Maybe the impulse with which they shake the part on decoupling also breaks the connection between the stage and its sepatrons?

[DMagic]

I think this is at least partly a construction problem. I don't know why it seems to happen more with the big SRBs, but changing you setup just a little seems to fix it.

I've seen this happen before, if I fire the sepratrons before the SRBs run out of fuel they will separate fine, but if I wait until they are out of fuel disaster follows. I think this is because the rockets get pushed up and away while the SRBs are still firing, but if they aren't the sepratrons damage each other and break off. Pushing the sepratrons closer together and rotating them down a little seemed to fix it.

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Edited August 31, 2014 by DMagic

[Wanderfound]

I think this is a construction problem. I don't know why it seems to happen more with the big SRBs, but changing you setup just a little seems to fix it.

I've seen this happen before, if I fire the sepratrons before the SRBs run out of fuel they will separate fine, but if I wait until they are out of fuel disaster follows. I think this is because the rockets get pushed up and away while the SRBs are still firing, but if they aren't the sepratrons damage each other and break off. Pushing the sepratrons closer together and rotating them down a little seemed to fix it.

http://imgur.com/a/IzcQL

Why push up?

Try this:

Note alignment of Sepratrons. One pair per booster.

Launch:

Decouple:

Spinny:

[Geschosskopf]

I had the SRBs on the big hydraulic detachment manifold decoupler with 4 sepratrons on each of them and a single strut at the top to stop wobbling, but when I activate the staging I see the sepratrons fly off on their while the SRBs just crash into my rocket and destroy it.

I've even tried adding struts to the sepratrons but they still fly off when they are activated.

I'm using NEAR, so I don't know if that makes any difference, I know some ppl mention drag ripping off parts in FAR, but they are fine until they fire and i'm not going fast enough to cause the re-entry effect.

What you're probably seeing is the boosters tipping in at the top and exploding, thereby leaving the Sepratrons to fly free. IOW, Sepratrons on the loose is a symptom, not the cause, of the underlying problem.

As Kasuha says, in 0.24.2 there seems to be a decided lack of separation force in all decouplers but especially with the radial ones. What seems to be happening the radial decoupler's force is absorbed in breaking the struts necessary to keep the booster from wobbling. So then the booster is just sitting there in its original position except not attached to the rocket, so from here on, air and gravity will dictate where it goes. And with NEAR, the top of the booster will tip into the core every single time.

This means you absolutely have to have Septratrons now (you could often do without before). And you have to do them differently than before, too. Nowadays, you have to put a pair of Sepratrons perfectly horizontally at the very top end of the booster to keep its top end from swinging into the core. If the boosters are mounted so their nozzles are at or below the core nozzle, this is usually all you need. The boosters will fall behind and slowly rotate away, and by the time their nozzles swing into where the core used to be, the core will have moved ahead. However, if the boosters are higher than the core nozzle, or for whatever reason aren't mounted vertically, then you need another pair of Sepratrions on the bottom end, too. This will move the booster out straight sideways without it pivoting at all.

[Claw]

As Kasuha says, in 0.24.2 there seems to be a decided lack of separation force in all decouplers but especially with the radial ones. What seems to be happening the radial decoupler's force is absorbed in breaking the struts necessary to keep the booster from wobbling.

It's actually worse than that. In 0.24.2 there was a code change to fix one of the stack decouplers. Something in the way the rocket's velocity is applied to the decouplers was done incorrectly. Basically the decoupler isn't receiving enough velocity when initially separating, even though the rest of the separated part seems to be fine. So while stack decouplers aren't affected to badly, the radial decouplers are more obviously broken. The end result is that a decoupled part appears as if it experiences a sudden "drag" on only the decoupler, causing radially decoupled parts to tip inward upon separation. If NEAR or FAR is installed, this initial tip inward then leads to aerodynamic forces shoving the separated parts back into the core. (This can still happen in stock, but it isn't quite as bad.)

Cheers,

~Claw