Why do my crafts keep falling apart during take-off?

[Ozzah]

Hello everyone, I'm new to the forums and only about a week into the game so please be nice.

I've been trying to build increasingly larger, multi-stage rockets for interplanetary travel and return. My bottom stage (the bit that gets me most of the way into orbit) is usually 12-16x radially symmetric Rockomax Jumbo64 fuel tanks (the 1440L ones) in asparagus configuration in two or so concentric layers with the Mainsail engines. The tanks are held on by the TT-70 radial decouplers that have a bit of extra space. I've also tried the Structural Pylon for attachment/decoupling.

The problem is, they always break before I can even get into orbit. One or more of the tanks come loose and fly up into the higher sections of my craft and blow it to pieces. Different tanks come off at different times. Sometimes they come off quite early, sometimes they come off late.

I usually end up trying to re-enforce the design with several EAS-4 struts. As I keep experimenting, and rockets inevitably keep coming off, I add more and more strut connectors. In the end, I have a giant web (read: mess) of struts going every which way, but it doesn't make the rocket any more structurally stable.

I once even saw a Jumbo 64 tank just fall off while the craft was docked, before I'd engaged the engines. It was one of the outer ones, so no extra weight on it, and there were several struts connected between it and the inner tanks.

Another on-going problem is with TR-XL Stack Separators dropping the connection between the upper modules (with my command pod) and the lower modules with the engines. I add struts to try and hold the two sections steady, but this only works sometimes.

I absolutely love this game. I am a little obsessed with it. However, the fun part is up in space; not necessarily spending days and days trying to get my rocket up into orbit. I'm starting to get quite frustrated. I don't know if it's a bug or if it's a problem with my designs.

I'm running the latest version at this moment via Steam: 0.20.2.

[stupid_chris]

Picture would help a lot. But your problem probably lies in a mix of over-engineering and not enough struts.

[Tw1]

Perhaps you need to be smarter with your strut placement? I find a pattern like this works best:

Also, make sure you add more struts down low near the engines. They tend to vibrate a lot. Are you using launch clamps? Larger rockets don't sit on their engines safely.

Nhnfong's humours guide to strut placement may help you.

http://forum.kerbalspaceprogram.com/showthread.php/20773-Tutorial-Six-places-you-should-be-using-more-struts%

Welcome to the KSP forums!

Edited July 15, 2013 by Tw1

[kinnison]

have the gimbals off? on the outer boosters of your lifter?

[Ozzah]

Here is an example:

[Gargamel]

As mentioned.... need more struts.

I usually put 4-8 struts between each tank section, keeping them from wobbling.

The KW pack has stronger struts if you can only get one or two between parts, but at the expensive of weight, IMO not a good trade off.

Edited July 15, 2013 by gargamel

[Ozzah]

(There are lots of struts you can't see behind the tanks)

[Turd]

They work better when going side to side between tanks, going inwards only does so much.

[arq]

I commonly experience the same issue (actually, I was wrestling with it last night for a 1-launch land-on-everything-but-eve trip, haven't finished working it out yet). Usually I can make it launch after several hours of tweaking, but I agree it's a pain. Also, all the struts jack up the partcount. I'm contemplating adding the welded-parts mod to drop the partcount, but I'm not sure that it will fix the problem.

A few notes from my experience...

Sometimes removing a strut is better than adding one, especially when your ship gets above the 1500t mark. If a part is strutted-out-the-wazoo and still breaking, it's possible that your struts are directing too much force through that part. In this situation, if you can 'route' some of the force through other parts it may help. I find tanks at the top of stacks (especially on asparagus stages) to be especially prone to this, and often I leave them nearly or completely without struts.

As a means to redirect force, one effective technique I've found here is to replace upper rockomax tanks on boosters with t800 tanks, stacked much higher to keep the same fuel load (1 x32 == 4 t800's). Of course, this only works on outer boosters where there is nothing above them. These taller stacks make fantastic supports to strut to your payload, moving more force to the top of your rocket in addition to stabilizing it against wobble.

[Tw1]

Looks like you need more between tanks. Strut them together with this kind of pattern.

Constructing a ring of struts between the tanks should hold it.

Also, you may want to add grey tanks below the orange ones, that reduces the overheating.

[Leveller]

Also below 10k meters the air is VERY thick, going in high speeds below 10k (and depending on craft etc) even higher causes drag that tear the pieces.

[Mr Shifty]

You also may not need so many tanks. I use 5 stacks of 2 orange tanks each + mainsail in 2 asparagus stages with a central booster. It's very simple, and can lift 50-60 tons into orbit.

Here's an image after the first stage has dropped.

[stupid_chris]

You only have four launch clamps holding all of that? That must stress your connections to the breaking point probably, try adding more launch clamps, that will help prevent breaking on the launchpad. Doesn't mean it won'T break after liftoff, however most people have given good tips and I think they got everything covered.

[Ozzah]

Thanks for tips and suggestions!

I've put together a monster ship with plenty of orange tanks and it didn't fall apart at all, even at full throttle in atmosphere with gimbals enabled.

I did have a lot of struts before. The problem wasn't the quantity of struts, it was the placement. I've got a lot more criss-cross struts and that seems to make all the difference.

[Ozzah]

In general, I have good success recently with tanks not falling off during take-off. Here and there, I have a failure, and I can either fix it by adding or removing struts.

I'm having a really, really weird problem with this craft I put together today. The A-SAS module separates from the orange fuel tank just below it. The only weight above it is the command module, mechjeb, protractor, and the sensors. I've even added struts to the A-SAS module (not that I believe I should have to), but it still has a structural failure. In fact, the ship doesn't even need to be moving! Just sitting on the launch pad, about 10 seconds after the model is fully initialised, it has a structural failure and I lose all ability to launch.

What is going on here?

Edit: When I remove the A-SAS module, I get the same structural failure between the command pod and the fuel tank blow. Even when I limit my acceleration to about 15m/s^2, I still have a structural failure.

Edited July 23, 2013 by Ozzah

[mellojoe]

Also, look up stitching with struts. It basically joins the tanks in a single stack together.

[lammatt]

too much thrust => the ship gets torn part

to combat this... the easiest way is to limit your TWR to ~1.5-2.5

so that you ship would experience too much stress/strain

if it's not because of the thrust being too high

you should then proceed to add MORE STRUTS!

[Ozzah]

too much thrust => the ship gets torn part

if it's not because of the thrust being too high

you should then proceed to add MORE STRUTS!

Thanks for taking the time to reply.

I really don't think the issue is "too much thrust". With respect, I've built a few dozen crafts now and I know that certain joins are significantly weaker than others. Thanks to some of the tips in this thread I've learnt a lot about specific ways of using struts that overcome the "tanks flying off the others" problem. This problem seems to be something entirely different, and I'm seriously leaning towards either a bug or a problem with my craft file.

The craft sits on the launchpad stationary, without any wobble, and after about 10-20 seconds, the A-SAS module (or just the command module if there is no A-SAS) has a structural failure from the tank below. This makes no sense. There is no thrust to speak of as I haven't even engaged my engines yet.

Despite all previous evidence suggesting that struts are not needed between the command module and the tank underneath, I added a bunch of struts. I "stitched" the A-SAS module to the orange tank underneath. Something that I still believe to be unnecessary. Even with the struts and stitching, the module experiences a structural failure with the tank below, while the craft is stationary on the launchpad or even when taking off with low acceleration.

I really think there is something wrong with the game or with my craft file.