Issue-Parts Without Decouplers Detach Mid-Flight

[william_fengler]

I have a vessel I'm trying to launch and the thoroughbred boosters I'm using will detach from my ship when it reaches ~1000m AGL they are directly attached to the inside boosters and when I first launched it had 3-5 struts on each booster I've since boosted this to about 15 struts per booster and have the same issue. It seems that the game pauses for a second to update and during this time disassociates the boosters from their root parts.

 

I have images/videos for reference but don't know how to put them in this post

 

Anyone else ran into this issue? any thoughts how to remedy it?

 

P.S this is vanilla KSP with breaking ground and making history no mods

 

 

[4x4cheesecake]

Welcome to the forum

Does the flight log (press F3) say anything about this event? Stage separations, crashes, breaking joints, etc are often mentioned there.

I would be curious to see a video about it. Since it is not possible to attach any files directly to any posts here in the forum, you have to upload them somewhere else and share a (download) link for us. Cloud services like dropbox, one drive, etc. usually work very well for any type of file but in case of videos, you can of course also upload them to youtube or any other video plattform. You can even upload them there as "unlisted" (option in the upload menu) if you want the video to be only available for persons who got the link to it.

[william_fengler]

 

 

Here are a couple different videos. The first two are with the boosters throttled to 80% and the third is at 100% as you can see from the 3 crash logs nothing is happening as far as the game is concerned as there is always a different first impact. It also seems that speed and altitude have nothing to do with it as it'll happen at different speeds or altitudes and it will arbitrarily separate 1 to 8 of the outer boosters. It does seem to be some kind of physics issue though as when the boosters are cranked up it consistently happens faster. While the boosters are close together none of them clip each other and I don't see any slop in the parts. Bizarrely enough I managed to get to orbit once in my testing but this is out of 50-100 ish attempts.

Note: I have made these attempts through many game restarts and verified the file integrity through steam none of this seemed to affect anything

I believe if i remounted the outer boosters with clamp-o-trons or some structural piece it would fix this which I may have to do anyway but I'd like to figure out why this is happening as I've never encountered anything like it before

[Spricigo]

Too strong forces overcoming the structural integrity of the rocket basically. It may be exacerbated by glitches related with clipping and lag.

Try to reduce part count, avoid clipping, use struts/auto-struts and go for a more vertical flight profile to avoid high aerodynamic forces. Unfortunately, there is not a single solution that works for every craft, u need to mix an match accordingly to the situation.

[4x4cheesecake]

Well, that looks really weird

I cannot tell for sure what happens there but you probably just added too many struts. I know, it's sooo unkerbal to use less of something but in this case, you may want to use autostruts (set to grandparent) instead of a huge load of regular struts.

I can imagine, that KSP gets a little hiccup while trying to calculate the stress for each strut and probably gets caught in a positive feedback loop which increases the stress until the joints break.

Try to remove all the regular struts and activate autostruts on each part instead. If you cannot see the option for autostruts, you have to enable "advanced tweakables" in the game settings first

[Spricigo]

BTW, it may also be an idea to make a orbital refueling. Since it will be considerable simpler to put tha crat in orbit without the fuel.

[william_fengler]

27 minutes ago, 4x4cheesecake said:

Well, that looks really weird

I cannot tell for sure what happens there but you probably just added too many struts. I know, it's sooo unkerbal to use less of something but in this case, you may want to use autostruts (set to grandparent) instead of a huge load of regular struts.

I can imagine, that KSP gets a little hiccup while trying to calculate the stress for each strut and probably gets caught in a positive feedback loop which increases the stress until the joints break.

Try to remove all the regular struts and activate autostruts on each part instead. If you cannot see the option for autostruts, you have to enable "advanced tweakables" in the game settings first

I'll try this in the morning but I doubt that would be it as I started with just 2 or 3 struts on each booster and added more thinking that it was enough force to overcome the few struts I had and eventually got to this monstrosity.

I'll keep you posted with the results

[william_fengler]

36 minutes ago, Spricigo said:

Too strong forces overcoming the structural integrity of the rocket basically. It may be exacerbated by glitches related with clipping and lag.

Try to reduce part count, avoid clipping, use struts/auto-struts and go for a more vertical flight profile to avoid high aerodynamic forces. Unfortunately, there is not a single solution that works for every craft, u need to mix an match accordingly to the situation.

I highly doubt any of this would be an issue as this is maybe a 2/10 the most ridiculous/complex/huge craft I've ever launched in this game and I've recently upgrade from a 6 y/o laptop to a pretty decent desktop so I've gone away with any calculation errors/glitches and its such an oddly specific error. I'm thinking it more has to do with them being direct attached to other boosters and it doesn't like that as an attachment. I'm going to play around with this some more in the morning when I have energy and keep this thread posted with what I find.

 

Also yes I know I can orbital refuel but that isn't as fun and I see no reason why I shouldn't be able to launch the 3,000 part 50,000 tonne mechazorb rocket if I feel so inclined to turn my computer into a space heater

[Spricigo]

1 hour ago, william_fengler said:

I'm thinking it more has to do with them being direct attached to other boosters and it doesn't like that as an attachment.

In my experience neither the Thorougbred or the Clydesdale  like radial attachment in general to a certain degree. I always associated it with the high thrust and the resulting flexing. Being direct attached or through decouplers (or structural parts) don't seem to make that much a difference.

You are correct that the issue can be avoided (or at least remediated) for even bigger crafts but you may have hit some kind of bitter spot.

What I can think is that shaking boosters attached to other shaking boosters may have  triggered a feedback loop due to resonant effect. If that is the case, small adjustment to the boosters position or mass could be just enough to beak the resonant effect (off course, high speculative).

2 hours ago, william_fengler said:

Also yes I know I can orbital refuel but that isn't as fun and I see no reason why I shouldn't be able to launch the 3,000 part 50,000 tonne mechazorb rocket if I feel so inclined to turn my computer into a space heater

Can't argue with style. 

[4x4cheesecake]

I've build a few test crafts and can agree partially. These boosters really don't like to be surfaced attached to each other. In some configuration it works fine but others don't seem to create a proper joint between the parts. Sometimes, a few booster never even left the launchpad and the remaining craft turned into a effervescent tablet...

7 hours ago, Spricigo said:

Being direct attached or through decouplers (or structural parts) don't seem to make that much a difference.

I have to disagree though. Adding a "small hardpoint" between the boosters allowed me to add as many as I wanted:

Spoiler

These are roughly 190 boosters and they are holding together perfectly fine. At a smaller, more realistic scale, I was also able to change a previously unstable design to become stable by using this method.

[william_fengler]

1 hour ago, 4x4cheesecake said:

I've build a few test crafts and can agree partially. These boosters really don't like to be surfaced attached to each other. In some configuration it works fine but others don't seem to create a proper joint between the parts. Sometimes, a few booster never even left the launchpad and the remaining craft turned into a effervescent tablet...

I have to disagree though. Adding a "small hardpoint" between the boosters allowed me to add as many as I wanted:

  Reveal hidden contents

These are roughly 190 boosters and they are holding together perfectly fine. At a smaller, more realistic scale, I was also able to change a previously unstable design to become stable by using this method.

After way too much testing I'm coming to the same conclusion something with the thoroughbreds doesn't like to be direct attached and the simple solution is adding any kind of hardpoint between them. Even just a smaller booster or Rockomax fuel tanks had success. So I'd say the issue here is don't direct attach thoroughbred -> thoroughbred or I would assume the clydesdales as someone else had mentioned I didn't do much testing with them however.

[18Watt]

You may need to enable advanced tweakables for this:  In the right-click part action window activate ‘Rigid Attachment’.   That feature has helped me with the large boosters.

As others have mentioned, I suspect the force those large boosters generate is on the edge of the force at which the game releases parts.  Even a slight amount of oscillation or flexing causes problems.

Another suggestion is look at where you are using struts.  The base attach point for boosters seems to be at or near the middle- so any struts I add are at the top and bottom, to keep the booster from wobbling in/outward.

I would also suggest trying hardpoints for mounting.  Honestly, with ships that large and those large boosters the game just plain acts unpredictably.   What works for one ship might not work for the next, so keep trying different approaches until something works.

[Spricigo]

9 hours ago, 4x4cheesecake said:

I have to disagree though. Adding a "small hardpoint" between the boosters allowed me to add as many as I wanted:

Sorry If I was not clear.

By the seat of my pants, parts seems to make little diference but the spacing (offset) helps. 

In either case, more often than not I can use something else, circumventing the issue altogether. So it fair to assume that other may tun into situation where my solution don't work but something else does.