Catastrophic Rapid Unplanned Deconstruction - C.R.U.D.

[NewtSoup]

Hi, Can anyone help me with my launcher?  It's a 45 ton payload being launched by a lifter of suitable dV.  The takeoff and ascent are smooth, easily controlled and uneventful until ap reaches ~73,000m and alt reaches ~ 55,000.

At this point the rocket simply falls apart with no warning, no explosion, no flexing, it's just like the Kraken reaches in and snaps it in two.

 

What's odd is that it's not breaking where you might expect, at the docking ports or at a decoupler but at the junction between the FL-R1 RCS tank and the Rockomax X200 as shown by this picture.

 

I have autostrutted everything in an attempt to solve this and added actual struts between what i thought were the weaker parts and indeed the soft junctions don't spilt.  Just the one between the two tanks.

I have even put 4 struts between the two tanks and it still suddenly snaps. Though I have noticed on the last attempt that it goes into a very tiny but rapid vibration about a second prior to breaking.

Does anyone have any suggestions?

Edit: Curiouser - it happens when the AP reaches just over 73,000 meters each time, this last failure the alt was 69km but still failed at the point the AP reaches  ~73,000

Edited August 3, 2017 by NewtSoup

[Foxster]

Is it stock? If so, could you post the craft file?

[NewtSoup]

Added more struts in an attempt to strengthen that junction, Same result .

6 minutes ago, Foxster said:

Is it stock? If so, could you post the craft file?

Yes it's stock.  I will post the craft file shortly.

 

here's a link to the craft file:

https://drive.google.com/file/d/0B5NgotHMtCRVNHNuQ0JYRUJ5X2s/view?usp=sharing

[Foxster]

Ahead of looking at the craft file...I'd say it is snapping in the middle because it's a long and skinny craft with heavy front and rear ends that has a number of reduced size couplings. 

You could try getting the whole craft the same diameter and also reduce the height by building out the booster stage from the X200 tank, rather than joining it to the bottom of that tank. 

[ThreePounds]

You shouldn't just blindly strut and especially not auto-strut. While struts make vessels more rigid, they also make them ... brittle. Often joints are suspected to high frequency oscillations that instantly destroy them if you have a particularly unfortunate strut combination. Allow your vessels to flex and bend in certain areas to reduce stress on the structure.

[NewtSoup]

1 minute ago, Three_Pounds said:

You shouldn't just blindly strut and especially not auto-strut. While struts make vessels more rigid, they also make them ... brittle. Often joints are suspected to high frequency oscillations that instantly destroy them if you have a particularly unfortunate strut combination. Allow your vessels to flex and bend in certain areas to reduce stress on the structure.

Quite, the struts and autostruts were added to try and combat the snapping.

@Foxster yep, thing is though I need those docking ports as the tanks are going to become part of minmus station. And anyway it's not snapping at the couplings but at the joint between two same size tanks. However taking on board what you've said I may try adding an extra stage to shorten the craft before burning for orbit and circularisation.

[Foxster]

2 minutes ago, NewtSoup said:

... it's not snapping at the couplings but at the joint between two same size tanks. 

That might be a red herring. The flexibility and movement of the other joints might be leading to failure at this less flexible joint. 

[Cpt Kerbalkrunch]

@NewtSoup, the large RCS tanks are extremely flexible. When I put them on asteroid miners, that's always the place where it's most likely to flop around under acceleration. It's tough with the fairing directly above, so I would suggest maybe trying this: place the smallest Rockomax fuel tank (360, I think?) between the RCS tank and the fairing base. Then, place struts in 4x symmetry (or even 6 or 8 if you want) on both Rockomax tanks surrounding the RCS tank. Use strut connectors to connect the struts. This should make it a lot more stable. Usually does the trick for me. I despise autostruts, which is part of the reason I never use fairings.

One last thing: have you tried cheating it to orbit to see if it starts going nuts? This might give a bit more insight into what's happening.

Edited August 3, 2017 by Cpt Kerbalkrunch

[NewtSoup]

@Cpt Kerbalkrunch @Foxster  I added an extra stage and actually got to 77km but it went nuts while lifting the PE which got to 5km before the Kraken woke.   So close!

 I am going to keep the extra stage as it's an improvement.  And I will rearrange the tanks as suggested.

 What looks like a smaller rocko tank is just the shrouding around a poodle engine but what I've done is got rid of the X200-32 put in 2 X200-16's sandwiched the RCS tank between them and strutted as suggested.

If I can just get to a stable orbit LOL.

I've not cheated to orbit ( very much considered it though ) but seeing as my last attempt exploded at 77km and most definitely in space I'm guessing the results of using set orbit would be about the same.

[NewtSoup]

Tank rearrangement didn't help .  But this time I had the foresight to record it.  So for your delight and delectation, I proudly present:  The Kraken Woke! ( A Short by NewtSoup Kerman )
 

 

I apologise for the 720p.  I need a better Linux recoreder, it doesn't record sound and it didn't record at native screen ( I am using "record my desktop" ) 

[Cpt Kerbalkrunch]

Wow. I've had ships shake to pieces, but that one just broke in half. Looks like the direction change caused too much stress. Have you tried killing the engine before hitting the prograde hold, then reigniting? It might hold together if you keep it in a straight-line profile. And I know this isn't a solution you want to hear, but I think if you split the four modules into two rockets with two modules each, it would eliminate the problem. Still pretty odd, though. It looked like they had no real connection at all, and just came apart with a slight turn. Haven't seen that before.

Edited August 3, 2017 by Cpt Kerbalkrunch

[NewtSoup]

I would agree with you but I'd already done a few direction changes with no issues.  Yes I tried killing the engine on a previous one - throttle up fine.. throttled down bang!.  That was without a direction change.  Glad I was able to show you exactly what happens.  You can better understand my consternation now haha.  By the way that break was again at the junction between the RCS Tank and the Fuel Tank,

Yeah I think that rocket is just fundamentally flawed.  Must be using Kraken scales in some of the plating.    

[bewing]

The problem seems to be that you have a lot of stuff in this ship autostrutted to the heaviest part. As a general rule, it's dangerous to autostrut more than about 5 things to the same part.

However, the key in this case is that the heaviest part is your orange tank ... until it runs nearly dry. Then every single autostrut in the whole ship suddenly tries to attach to a new heaviest part. And that's when you get your CRUD -- at that moment when all the autostruts switch their anchor point (because that can be a violent process, actually).

So, you should be able to get rid of almost all your struts on your core stack. Turn off all autostruts on all the parts -- especially everything inside the fairing (they don't need it at all). Then try just autostrutting your core stack together with connections to the grandparent part. Maybe 2 or 3 to the root part. But don't use the heaviest part for autostrutting on this ship.

 

Here's your ship with the autostrutting redone:

https://pastebin.com/raw/tTSFURJb

(I took the KER Engineer chip off to make it stock. You'll have to put it back on.)

 

Edited August 3, 2017 by bewing

[Cpt Kerbalkrunch]

I thought this was occurring with and without autostruts? I may have been reading it wrong.

[NewtSoup]

It made it into orbit.  Turned off the auto struts on almost all the pieces and what I kept stayed at "grandparent".  Now I understand better how autostrut works and why it fell over on my ship.

It was ocurring without autostruts.  Then it was occuring with autostruts because I added too many in the wrong fashion and the rapid restructuring was causing the issue, at roughly the same AP each time because that's when the fuel ran dry in the main tank.  All makes sense now.  The advice on bracing the RCS tank helped the original problem of Kraken without struts.

Big thanks to everyone who chipped in with their help

@bewing
@Cpt Kerbalkrunch
@Foxster
@Three_Pounds
 

Edited August 3, 2017 by NewtSoup

[swjr-swis]

4 hours ago, NewtSoup said:

Hi, Can anyone help me with my launcher?

I grabbed the craft file you posted, retouched it a bit, and did a few launches up to LKO and to low Minmus orbit; no unplanned disassemblies happened.

https://www.dropbox.com/s/8j76z896t3y5de6/MimusHabitat-Launcher.craft?dl=0

Changes made:

• I had to hand-edit the craft file to delete the KER module, or I couldn't load it in my stock game.
• First removed all struts and all autostruts, to remove any random elements.
• Redid the fuel lines for a bit neater placement (not really needed but OCD kicked in).
• Reoriented the 8 east/west docking ports so their tops were properly aligned (again, just an OCD thing).
• Placed regular struts in 2x symmetry to stabilize the SF/LF boosters.
• Placed regular struts in 4x symmetry between the RCS tank and the bottom 'docking arms' of the payload, to better hold the bottom of the payload.
• Placed regular struts in 2x symmetry between the top Jr docking port and the fairing, to dampen the payload swinging. (1)
• Placed regular struts in 4x symmetry in the two gaps of the center stack, to undo the weakness of your chosen links there. (2)
• Enabled autostruts on a few parts, but made them point to 'root' instead of 'heaviest', for maximum leverage and to stay where they are from beginning to end of the ascent. (3)

 

1. Needs a bit of trickery. I used two cubic struts attached at the bottom of the fairing and offset to a bit above the top of the docking port, then the struts from port to the cubic struts, offset the cubic struts to outside the fairing top, then grabbing the fairing bottom to pull it off the rocket and simply replacing it in the same place - struts get reconnected to the inside of the fairing shell. Deleted the now unnecessary cubic struts.
2. I don't understand these gaps, they severely weaken your rocket. Why not use regular 2.5m decouplers there to use the much stronger 2.5m nodes for the entire stack?
3. Since you don't have designated 'heaviest' parts that remain the heaviest throughout all stages of the rocket, the autostruts get pointed elsewhere with every staging/decoupling event. This will cause problems. So to avoid this, I pointed them at root, which stays the same all the way. Also, there were too many of them; just enable them at the ends of stages/stacks.

 

P.S.: It is still unclear to me how the payload is supposed to work. There's propulsion enough to get it to Minmus orbit and even to descend to the surface. I can also see it's meant to be 4 separate modules, to get on the surface with their wheels and probably docked to each other 'sideways'... but I can't see how you plan to actually land each of them safely and properly oriented on the surface - they have no propulsion of their own, not even RCS.

 

Edited August 3, 2017 by swjr-swis
Went for a bit to eat before writing this up and posting... already solved. Oh well.

[NewtSoup]

@swjr-swis  Thank you so much for your hard work there.   Your changes are more or less the same ones I made to finally get it into orbit.  To answer your question on how the payload works and the reason for not using the 2.5 decouplers.

Looking at the picture above you will see there is an orange tank - this will be discarded along with it's skipper engine.  That will open up the poodle under the shroud.  The poodle is held on by docking ports so that the tanks supplying it ( along with surplus fuel ) can be added to my Minmus space station and the poodle ( possibly ) discarded.  

That leaves the stack of 4 modules.   At minmus station I have a "Sky Crane" with a docking port jr on the bottom can take the stack of modules down to the surface of minmus and drop them one by one.  

Each module has a battery, small solar panels and an OKTO so that they can drive themselves several hundred meters, if needed, to join onto the main base (Rura Penthe).  The main base will consist of a command tower, the four habitat modules, a drilling module, an ore processing module, Ore tank modules LfOx tank modules, RCS tank modules, some solar modules and some fuel cell modules ( for the minman night time).  

Every module is based on that cross shaped support with wheels and docking ports and they interlock in a grid pattern ( which I tested first on Kerbin to make sure they do interlock properly )

Eventually the habitat modules will be populated by labourers ( low paying tourists who just wanted a flight around Kerbin )  This is all the first stage in Empress Valentina's Kerbal Empire Expansion program.

Edited August 3, 2017 by NewtSoup

[swjr-swis]

51 minutes ago, NewtSoup said:

At minmus station I have a "Sky Crane" with a docking port jr on the bottom can take the stack of modules down to the surface of minmus and drop them one by one.

Ok that makes sense, I had not considered something already waiting in Minmus orbit.

 

52 minutes ago, NewtSoup said:

The poodle is held on by docking ports so that the tanks supplying it ( along with surplus fuel ) can be added to my Minmus space station and the poodle ( possibly ) discarded.

Tip: those docking ports can be surface attached to the RCS/LF tanks, leaving the 2.5m stack nodes on top and bottom of that section 'free' to be used for 2.5m decouplers. Best of both worlds: you still get to use the strongest joints over the whole length of the stack, and you get the docking ports to reuse the RCS/LF tank module. I uploaded a 'B' version of the craft with those changes.

https://www.dropbox.com/s/lyons0lbumfj0ux/MimusHabitat-Launcher B.craft?dl=0

 

[NewtSoup]

Thanks again to everyone here.  The results are recorded in my "Going To Minmus " Thread.