[solved] My ship explodes at 2590m altitude.

[Darbin Giesorg]

Edit: The problem was apparently a corrupted craft file, although it'd still be interesting to know what makes it splode internally, change of air density, new biome, whatnot.

My ship consistently explodes at ~2590m altitude, regardless of speed. I have tried flying up to 2580m and then inching forward with the thrust controls and it always and reliably explodes at a specific height.

This has never happened with any other ship so far, so at first I thought I had pitched too hard, then I thought it needs more struts, then I thought I was too fast, but even at 5m/s, once the ship reaches that altitude, it immediately detonates.

Here's my attempt at posting screenshots for visualization:

Here's my blueprint, not sure if sharing works.

https://www.dropbox.com/s/602dxqhhe7jxnrh/BugShipThatExplodes.7z?dl=0

How to reproduce the explosion:

- Launch the ship.

- Get above 2590m.

- It should detonate there. I mean it shouldn't but that's what happens for me.

 

As for the ship itself, it is not very well designed. It has structural weakpoints (attached booster under docking port) of which I'm unsure how to overcome them without compromising the look of the final craft. I used plenty of struts. This is my biggest ship so far. It is supposed to get a transit station in Low Kerbin Orbit with plenty of room for crew and temporary fuel tanks that can return on their own, return capsules and a rescue ship. It is not streamlined yet.

This seems to be a bug. Maybe it relates to my settings somehow but I wouldn't know what exactly. Tell me what I can tell you, post, upload and I will, but I don't even know where to start.

A workaround will be splitting the payload into different ships and I will certainly try that. But it seems like there is some physics issue where the game... transitions to a new layer and there is an internal collision or something. I have no idea and I shouldn't speculate.

Edited April 5, 2020 by Darbin Giesorg
Solved.

[4x4cheesecake]

I've loaded your craft into my game and it's the same for me, the craft explodes at ~2590m ASL but I couldn't find anything interesting in the flight log. After playing around with the craft in the editor, I've noticed a few things though:

If you remove the fairings on the left and right, a single RCS thruster will remain in mid air, which isn't attached to anything (it's not highlighted if you hover over the root part of the craft) and if you try to launch it then, you'll get an error message: "part 4294373202 is missing", so if opened your craft file in a text editor to look up, which part it is. Apparently, it's one of the medium sized reaction wheels down in the service bay of the center stack. Coincidentally, if you move the whole craft by grabbing the root part, one of these reaction wheels will stay there in mid air, like the RCS thruster (which also dosn't move).
Even though you can pick up these floating parts, you cannot delete them or do anything at all with them and at some point, you will just get the error message about the missing part again.

I've tried a few things to remove these parts from the craft file via text editor but I always ended up crashing my game or 80% of the craft just disappeared.

So I have to come to the conclusion, that your craft file is corrupted and maybe, someone more skilled comes around who can fix the file for you or maybe there is even a tool for this somewhere in the "Tools and Applications" subforum but I think, the easiest way is to rebuild the whole craft from scratch.
Unfortunately, I cannot tell you why this happened to your craft, so maybe it happens again or maybe not

[StrandedonEarth]

After reading @4x4cheesecake's post, it sounds like an issue I had a long time ago, except my craft exploded as soon as I pressed the space bar to launch it. I have no idea why yours doesn't explode until a certain altitude, unless it has something to do with air density/pressure *shrug*. If you were doing a lot of work with symmetry, sometimes a part gets "stuck," which this issue sounds like. The best solution, now that you have your design hopefully figured out, is to rebuild it from scratch. And I mean scratch. Reboot your computer (or console as the case may be), launch KSP, go to the VAB, and build it again from a clean slate. With all the symmetry going on, it may be best to build up one of your side boosters and save it as a subassembly, to add it (in symmetry) to your core later. 

Pro tip: I see you have a lot of docking ports (too many open ports can contribute to lag, but you should be okay). Your design lends itself to one of my favorite tricks. Place your radial decouplers closer to the top or bottom, and align your docking ports closer to the other end so they are almost touching in the VAB. When you take it to the pad, the ports will stick together, eliminating the need to strut the side boosters to the core. By opening the PAW for the ports by rt-clicking them, you can enable staging for the ports, so they will undock when you stage off the radial decouplers.

Here's an example....

Edited April 1, 2020 by StrandedonEarth

[Darbin Giesorg]

The secondary docking connection is a fantastic trick I will use from now on.

Also thanks for finding the problem. If it's just a corrupted file, I will simply build the thing again from scratch. I was worried there was a fundamental problem with big ships with wonky connections going up but I am relieved.

By the by, does anyone know how I can keep a lower-end docking port on the payload and still firmly attach a decoupler beneath it (see lower booster) without this becoming the rocket's weak point?

[jimmymcgoochie]

On 4/2/2020 at 3:16 PM, Darbin Giesorg said:

By the by, does anyone know how I can keep a lower-end docking port on the payload and still firmly attach a decoupler beneath it (see lower booster) without this becoming the rocket's weak point?

If you enable 'advanced tweakables' in the settings, you'll get the option to add autostruts which will create invisible but fully functional struts between that part and either a) the heaviest part on the rocket, b) the root part or c) the grandparent part- each part is attached to another part, which is its parent, so in the rocket StrandedOnEarth posted, the twin boar engines on the sides are attached to the radial decouplers (parent) which are attached to the central orange fuel tank (their parent, and the parent of a parent is a grandparent).

When you're building rockets with radially attached boosters, it's a good idea to fix the booster part (I usually use SRBs like the Thumper) to the heaviest part for maximum stability, with any fuel tanks on top of that fixed to their grandparent which greatly improves rigidity and the nosecone on the top fixed to the root, which in total makes the boosters stay pretty much exactly where they are in flight instead of wobbling around and occasionally ending up pointing backwards. The same applies in a stack- strut some of the higher parts in later stages to the heaviest part and some of the lower stage parts to either root or grandparent parts, and this works with docking ports in the stack too.

That original rocket of yours looks really strange to me- why are you using a solid rocket as the main stage and twin boars as radial boosters? It's better to do it the other way round and set the booster decouplers to 'enable crossfeed' so that the fuel tanks on top of the boosters can feed the core stage and drain first before being discarded.

[Darbin Giesorg]

The idea of the rocket was to have the fuel rockets be reusable. Behind the fairing is a drone core with batteries and RCS. I didn't know how much I'd spend getting the station up there, so I ballparked it, gave it a little extra and planned on sending one stage back after emptying its contents into the other in LKO by detaching it and using RCS to re-enter the atmosphere. The rockets have a ton of parachutes on them. The Twin Boars provide better economy and power than a tank with Mainsail and I just land them at KSC for money. The big booster in the middle is just there because the Twins didn't have enough power at sea level and it's the only part that won't be reused.

The station itself does not need a big engine. It's supposed to stay where it is and correct with RCS or via helper ship if necessary.

So if the center bit had been a Twin Boar as well, I would have to fit it with parachutes and a drone core with RCS, too. Possible but since I had problems getting anything attached to the docking port in the first place (probably haven't found a proper autostrut configuration yet but I'll try strutting to various parts like you suggested), putting even more in between didn't feel good. I wanted the booster for extra punch and then to be discarded with the two carrier rockets transporting the Kerbal Space Station into orbit.

Turns out, I'm almost using up all the fuel just getting that thing up there. Still, a little is left and it's going to be my future stop for ships to refuel. Currently building a leviathan of a fuel rocket so I can store large amounts of fuel on the station, or its current appended fuel tank, whether that's the second rocket or a new one with more capacity and less fins.

Thanks for the pointers.

Edit: If anyone ever uses two docking ports per rocket instead of one and the game doesn't give you the option to undock, I found that making a docking port the "main docking port" allows me to undock again, which is better than sifting through the savegame file and fixing the docking port bug manually. Related to the docking port suggestion, not to OT, but I didn't find anything about it.

Edited April 5, 2020 by Darbin Giesorg