Undocking two vessels destroys them.

[RabidSmurf]

My quite simple Mun lander and Mun command module (apollo style where I stack separated them, turned 180 degrees and docked while in transit to Mun) are now unable to undock without exploding randomly. Note the lander is a two stage vessel with descent and ascent (like the real apollo lander). If I first jettison the descent stage I am then able to undock them, but then ofc there is no landing legs or enough deltaV to land.

I initially thought it was some of the struts from inside my jettisoned fairing, that had bugged/flipped around and attached themselves to the docked lander, so I tried deleting all struts from the save file, but this did not fix the problem.

I submitted the quicksave to a PD support ticket #47551 it should be easy to reproduce.

 

 

Edited February 26, 2023 by RabidSmurf

[LizardEnterprises]

I had an identical issue yesterday using the same mission architecture, and have spent most of today working on tracking this down. I don't yet have a solution or workaround, but I can at least narrow it down somewhat. Here's what I've got:

Like you, I built an apollo-style Mun mission, with a LES on top, then Apollo-style CSM assembly, then Munar-lander with separate ascent/decent stages, and then three stages underneath that. Several things bugged out and im not sure which of them are separate bugs, and which of them are the same bug manifesting multiple symptoms. In order of appearance:

Fuel drained from the decent stage of my lander when the third-stage engine of my burned, even though they were separated by a decouple. 
After CSM separation for the Lem+Transfer stage assembly, while controlling  the CSM, right clicking on the Lem's docking port did not give me an option to set it as target. Quicksaving and quickloading at that point Does  restore the option to target, but Does Not Prevent any and of the other bugs, which appear regardless of whether I quicksave/quickload or dock without targeting and continue the mission.

Roll and Pitch control authority on the reaction wheels is lost sometime between the munar transfer burn and arriving in the muns SOI. Yaw continues to work, and RCS and Engine gimbaling still have full freedom of movement on all axes.

After munar capture, undocking the craft while not under timewarp results in a vessel destroyed message. Despite this, going to the tracking station shows that the vessel is still there and can be controlled, however the docking ports no longer function at all.
If instead, I try undocking *while* under time warp, one or both new craft get a prograde acceleration of about 500 m/s.

My first thought was that this was a rare bug involving all docking ports but only affecting me and a small handful of others, so to test this I spent most of this morning building a small orbital station. The docking ports were a little... imprecise? sometimes registering connection when the craft were at very wide angles, or very far apart, but docking and undocking worked without destroying anything, I can therefore rule out a general docking port bug. 

Im currently testing the lander legs. The feul flow issues with those are pretty bizarre, and seem like an obvious place to test next; Ive read elsewhere in the forum that putting the legs on radial decouples prevents the feul flow issues, so I did that. If it works, I'll see if I still bug out when trying to undock.
If I do, I'll build a lander that lands on struts - no legs at all - and see what effect that has.
If the bug persists I'll build a CSM version with radial engines so I don't need to flip it around for its transfer burn, and see if its the flipping or the redocking to the same craft you launched on that causes it.
Depending how that goes, I'll probably have more station testing to do.

[Talisar]

I have encountered a similar situation with undocking causing immediate mission failure, and was able to recreate the issue on the launch pad.    What I was experiencing appears to be specifically caused by docked cargo being secured with struts.   If struts were not used (frankly not an option), then the cargo was able to undock successfully.    If stuts were connected, then the mission immediately failed, with the cargo remaining held in place by those struts. 

As a workaround with limited useablity,  if I used a decoupler instead of a docking port, I was able to release the cargo without issue, 

I reported this via the launcher feedback option as well, but due to the limited amount of picture upload available, I'm adding them here too  (Lots of pics incoming, apologies)

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Lol, I even had to go recover the password for the imgur account I used when actually trying to make mods for KSP1  :)

[LizardEnterprises]

Added decouplers to the landing legs. 
Feul flow problem was fixed.
Loss of control problem was fixed.
Craft being destroyed on undock was not fixed.

Struts are a promising lead. I'll look into it tomorrow, its too late tonight for another test.
We might be able to get around this by attaching radial decouplers to both halves of the vessel, and attaching the struts to those? I guess that would depend on how they changed the behavior of struts - they're clearly very different in 2 than they were in 1.
Either way, thank you for the heads up, you probably saved me about 10 hours of trial and error :-)

[LizardEnterprises]

So I tried removing the first set of struts and adding struts attached to radial decouplers. I could dock and undock freely in Kerbin orbit, but trying to undock in Munar orbit still caused vessel destruction message. I'll look into another workaround. 

[RabidSmurf]

Interesting bit on the fuel flow and landing legs, I ran into that as well. With my 3rd stage drawing from the lander descent stage despite being separated by a decoupler with fuel crossfeed OFF. I used the  awesome new resource manager to transfer fuel back before I jettisoned my upper stage that still some fuel remaining, and didn't think much of it besides that it was kind of odd. It sounds like there are some general fuel flow and fuel prioritization bugs as I read in another thread that asparagus staging does not work. So that's possibly related, and hopefully will get resolved quickly.

For the undocking issue I do not think it's the struts, although that was my first thought. I removed them all manually via the save file and still had the same problem.

Unfortunately due to another bug, my Mun mission crashed into the surface due to some mysterious orbital decay (it was a stable orbit at 32km when I left it). I believe it was caused by some kind of continuity bug where activating engines on a completely separate craft on kerbin somehow activated the engines on the craft orbiting Mun, so I'll need to refly that mission, but I am going to wait for the first round of bug fixes I think. 

I've hit just about every bug listed in the forums, which I suppose is a good sign as they are easy to reproduce and thus should be easy to fix.

[schlosrat]

@LizardEnterprises Can you elaborate on how you fixed the fuel flow problem? I’ve seen this slow where my first stage drains from tanks in stages 4 and 6.

@Talisar Why are struts the only option? Have you looked at using engine mounts to simulate a faring interstage? I posted an example craft in the vessel exchange which uses engine mounts, docking clamps, and decouplers to release three stacked probes which are carried up inside a faring. No struts used at all.

@RabidSmurfAspergas staging is working fine for me, thoughI’ve only got a few rockets that need that. Where is this new resource manager! I could really use that!

[RabidSmurf]

1 hour ago, schlosrat said:

@RabidSmurfAspergas staging is working fine for me, thoughI’ve only got a few rockets that need that. Where is this new resource manager! I could really use that!

My understanding is the fuel flow issue is caused by the landing legs, and attaching them to radial decouplers instead of directly to the fuel tank resolves it, although I have not tried it.

The resource manager is opened from the far right button on the app bar (the row of buttons just left of the staging/launch button).

 

 

[LizardEnterprises]

1 hour ago, schlosrat said:

@LizardEnterprises Can you elaborate on how you fixed the fuel flow problem? I’ve seen this slow where my first stage drains from tanks in stages 4 and 6.

Sure thing. The problem occurs for me due to a bug with lander legs; if you attach lander legs to a fuel tank, that fuel tank will drain into other stages, regardless of what any decouplers have to say about it. The solution is to separate the lander legs from that stage. Adding radial decouplers where you want your landing legs to attach, and then bolting the landing legs onto those decouplers prevents the bug, you just need to remember to check your staging to make sure you don't accidently decouple your landing legs. 

Someone doing a proper investigation of this bug might want to try using other radial parts like struts, and/or radial parts with toggleable fuel flow toggled on and off, but I have like 3 other bugs I'm trying to figure out before I have time for that. Anywho I hope that helps :-)

3 hours ago, RabidSmurf said:

Unfortunately due to another bug, my Mun mission crashed into the surface due to some mysterious orbital decay (it was a stable orbit at 32km when I left it). I believe it was caused by some kind of continuity bug where activating engines on a completely separate craft on kerbin somehow activated the engines on the craft orbiting Mun, so I'll need to refly that mission, but I am going to wait for the first round of bug fixes I think. 

At the risk of further derailing this thread, I might have a lead for this one. Ive had a few instances where unselected craft in orbit refuse to update any of their orbital characteristics when not-selected. The craft just hangs there in its same position forever, not actually orbiting, just hovering, even though its orbital path is shown. Switching to the stuck craft will usually fix it, but sometimes the fix is incomplete; the craft will update its position and begin moving again, but keep its old orbital velocity... including relative direction of movement to the body its orbiting. This can result in some serious orbital shenanigans as the angle of the orbit no longer matches  the crafts position, and a previously circular orbit can suddenly partially, or completely, radially out or in from the planet instead. 

[schlosrat]

@RabidSmurf Thanks! Found it. I also noticed that opening it does nothing if you're under thrust, but with resources static it opens just fine. Also thanks to both of you guys for the tip on the fuel flow issue with the legs! I think this explains what I've been seeing.