Flight Engine Mount/Fairing/Decoupler not Releasing

[Kilo523]

I've been working on an Saturn V replica since launch and I've consistently run into this issue of the CSM remaining "attached" to the final stage and LM assembly. Sound like others have run into similar problems but I can't find a solution. Please help me before I uninstall again.

Edit: After some troubleshooting...

- Removing the docking port on the LM does nothing

- Exchanging the decoupler for a separator does nothing

- Removing the decoupler altogether and having the fairing attach to the cargo bay does nothing

- Jettisoning the fairing first then activating the decoupler *does* release the CSM, but the decoupler remains "attached" to the CSM

 

Edited March 17, 2023 by Kilo523

[Poppa Wheelie]

I think I have the workaround for this.

Bottom Line:  Use two decouplers - one at the bottom of the fairing facing the Engine Mount, and one below that facing away from the Engine Mount.

I tried separators here, no luck.  It only worked for me with two decouplers.

We have situations where a single decoupler below, and facing, the Engine Mount works fine.  The stock K2 rocket, for example, uses this configuration to get to the stage 3 engines.  My guess is that we introduce the problem when we have control nodes on both sides of the decoupler.  Do you have a probe core under your decoupler?

I reproduced the problem with a test rig on the runway.  This test rig is to demonstrate that my exact scenario could be reproduced, and fixed.  I needed the exact parts you see here, in this order, and I needed to start with 2 kerbals on the right side and move 1 to the left side before decoupling.  I didn't know what was breaking, so I reproduced the sequence of events.  Even so, I think this is the same problem as you are having, and I think the solution demonstrated below should work for you.

Spoiler

Engine Mount test rig

Fire engines to be in Landed state, then turn them off

One vehicle, Landed state

Move a kerbal

After decoupling we still have one vehicle, made of the vehicle half on the right, the one on the left, and the decoupler and fairing that are flying into the air

As the decoupler and fairing fall to the ground and explode, however, we suddenly have the two separate vehicles we want

Here's a demonstration of the solution, using the same test rig on the runway

Spoiler

"Solution" test rig, with two decouplers

Fire and stop engines to enter Landed state

Move 1 kerbal

Decouple the one facing away from the Engine Mount, resulting in two vehicles

Control the vehicle on the right and move it away

Take control of the vehicle on the left and decouple the remaining decoupler, the one facing the Engine Mount

The decoupler flies quickly behind the vehicle and explodes.  We are now "controlling" the decoupler.

Take control of the second vehicle and move it away

Finally, I put a ship in orbit and tested the same solution there.  It worked fine.  I wanted to make sure that it would work for the In Orbit state just as it did in the Landed state.  No screenshots of that, but it worked.

[Poppa Wheelie]

On 4/18/2023 at 4:48 PM, Poppa Wheelie said:

Finally, I put a ship in orbit and tested the same solution there.  It worked fine.

Nope, sorry.  It doesn't work fine.  In the "solution" I showed above, it worked because the decoupler and fairing blew up and were destroyed when they hit the runway behind the vehicle.  If I look at the Tracking Station after they've blown up, I see 3 objects:  Test Rig-1, Default Name-2 (the second ship), and Default Name-3 (the decoupler facing Test Rig-1.  In orbit, the fairing and decoupler continued flying behind the second ship (Default Name-2).  Since they never blew up, I don't get a Default Name-3 for the first decoupler which is sitting there.  I also have no control over the second ship.

So, back to square one.  I don't know how to work around this.

[RaccoonTOF]

Just a guess here, as I've had similar issues previously - make sure you have a decoupler between the upper docking port and the LES, and stick a small probe core on top of the decoupler as well.  Then make sure that the LES probe core is the root part before launching.  Currently, it appears that ANY docking ports above the root part can cause issues, as can control parts below engine plates.  Not sure exactly which part of the "fix" actually fixes the issue, but this is the approach I've been taking lately and since doing so, haven't run into this issue further (though still plenty of issues docking/undocking once you get to space...but at least it launches and stages correctly now!)