Heavy part breaking off on launch.

[MrUberGr]

So, I'm trying to get a fuel module up to my space station. It has to be pretty complex, rather than a simple barrel, because I don't want to be booping the station , and, it's also going to be the point where a potential inline docking port would connect. So, now, I'm facing the problem of the whole module breaking off during liftoff. I know the clamp-o-tron isn't supposed to hold much, but even after I added a bunch of struts it wouldn't work.

Here are some pictures in case you can help me. (removed most struts so you can understand what's going on.)

*Edit: It's actually un-answered in case a moderator can fix it.

Edited December 3, 2013 by MrUberGr

[Tank Buddy]

I think that's still too much of a payload for the 1.25 meter parts, I would suggest maybe adding fuel tanks or I beams/strut beams to add more support with normal struts. You can change the answered to unanswered by editing your post and going to advanced options.

[SSSPutnik]

Strut the plate to the SAS(?) Underneath.

In fact you could strut all the parts to each other. Having same issue where I go from a wide to narrow to wide point.

In the mission log, which bit breaks first? You may also want to strut from the top of the outer tanks to a long way up your stack.

It is very tall.... Maybe too tall and not wide enough...

[MrUberGr]

I think that's still too much of a payload for the 1.25 meter parts, I would suggest maybe adding fuel tanks or I beams/strut beams to add more support with normal struts.

Didn't quite understand what you mean with the extra tanks... Plus, the I beams can't connect to two parts. Or can they?

Strut the plate to the SAS(?) Underneath.

In fact you could strut all the parts to each other. Having same issue where I go from a wide to narrow to wide point.

In the mission log, which bit breaks first? You may also want to strut from the top of the outer tanks to a long way up your stack.

It is very tall.... Maybe too tall and not wide enough...

The lifter is just about fine in my opinion (the part before the large stack decoupler). Then it's only 1 fuel tank and the engine. Then I have the module. I could make it smaller, but then it wouldn't serve it's purpose cause I'd have to refuel it a bit way too often, and since I suck at docking, I wouldn't want to have to do that oftenly ^^.

[MrUberGr]

What does work is to dump the liquid fuel and oxidizer from the top parts. But then I'd have to go again to fuel it.

[antbin]

Look at your flight log. First failure is between the ASAS and the RC-L01. So strut that connection with 3-way symmetry. Fly again. If another connection breaks, strut that.

Ideally you want to strut from your Poodle's fuel tank to the payload's fuel tanks. But that will be tough/impossible.

Generally I find that putting huge payloads on the rocket nose makes it quite difficult to control in the upper ascent.

[SSSPutnik]

Yeah you could shrink the upper stage to a small tank with side mounted nukes. I've used a similar setup to rescue a stuck Mun orbiter. Had enough spare fuel to refuel the orbiter and get both back.

Another SAS unit on the upper may help stability as well. But your design is very long, it will turn like a pig.

[kurja]

Put some small cubic trusses on your payload and then some more on your middle stage tank and strut those to each other, that's how I've solved problems like this. Your current strutting does not help at all because the first failure is between your sas and rc modules, I suspect from compressing into each other during acceleration. That happens with heavy payloads.

[Smidge204]

I've found that the ASAS modules are *extremely* fragile, and I try to avoid them at all cost.

As others suggested, a "Truss and strut" reinforcement will help to some degree. Here's an example:

What I would do is ditch the fragile ASAS and replcae it with two inline reaction wheels (the small ones) at the ends of the trusses. You'll get better control and stability for just a little bit more mass.

=Smidge=

[blizzy78]

You should try a zig-zag pattern instead of strutting straight down. Triangles are an engineer's best friend.

[MrUberGr]

I got a question about struts and part count. I've read that space stations over 200-250 parts may get laggy How do the struts count when they get cut? I believe that the base part is the one that counts, meaning that if I start all struts from the engine towards the module, when I undock they won't count as space station parts?

It works like this, but with no extra ASAS. 1.5 from the engine is deffinately not enough. What do you suggest?

And another question. Even though I have rcs ports on the top of the whole thing, they don't seem to work, and it starts tiping over.

Edited December 3, 2013 by MrUberGr

[allmhuran]

I've found that the ASAS modules are *extremely* fragile, and I try to avoid them at all cost.

Even more than that, the large RCS containers seem to have incredibly weak connections. I have never been able to construct a large rocket that included a large RCS container anywhere other than at or near the very, very top of the stack.

Additionally, docking ports are much more flexible than decouplers.

The combination of a docking-port-based connection and a large RCS container below the heavy payload essentially guarantees that this rocket will, unfortunately, disassemble itself.

I'm sure you want to keep the docking port if you can, so replacing that with a decoupler might not be a possibility. But first and foremost, you should definitely move the large RCS container further towards the top of the rocket. If you can find another way to have the docking port, that would be the second thing I'd be looking at.

Regarding struts: Yes, the origin part "keeps" the strut stub when you separate components. So if you strut from the bottom up, the top section will be nub-free when decoupled.

[kurja]

You should try a zig-zag pattern instead of strutting straight down. Triangles are an engineer's best friend.

perhaps, but that wouldn't help because that's not where his rocket is breaking apart

[DrMonte]

I got a question about struts and part count. I've read that space stations over 200-250 parts may get laggy How do the struts count when they get cut? I believe that the base part is the one that counts, meaning that if I start all struts from the engine towards the module, when I undock they won't count as space station parts?

It works like this, but with no extra ASAS. 1.5 from the engine is deffinately not enough. What do you suggest?

And another question. Even though I have rcs ports on the top of the whole thing, they don't seem to work, and it starts tiping over.

Don't overdo the struts. "More struts" is a nice Kerbal way but it doesn't actually help.

This design will do fine with four struts from the lower fuel tank (+Cubic Octagonal Strut) to the adapter.

[MrUberGr]

Actually it's in orbit this very moment. The struts did their job just fine! I removed the big ASAS and added inline reaction wheels as someone suggested, Cause the ASAS was being the weak point.

I added wings at the top with a decoupler to help going through atmo and everything went fine!

[blizzy78]

perhaps, but that wouldn't help because that's not where his rocket is breaking apart

ok sorry, misread his post then

[700NitroXpress]

Easy fix: Just mount it horizontally instead of vertically. Boom, problem solved.

[Starwhip]

Or just use the Clamp-O-Tron Sr. port on the bottom. Or a large Stack Decoupler with the port on top.

[Hodo]

Several things.

-docking ports are great for, docking.... not for holding loads of launch. They don't take more than about 1.5Gs before they snap.

-SAS modules, ASAS Modules, batteries, and Science lab Jr modules. All are extremely weak and should never be part of the load bearing structure. I place mine at top of most of my craft where the force of the thrust is the least.

If you want that type of setup where it gets narrow in the middle, I HIGHLY suggest adding I-beams or something else that is MUCH stronger. Or your other option is to reduce the thrust on take off and keep the TWR during take off under 1.5 the whole time.

[DrMonte]

Don't underestimate docking ports. One can hold up to three orange tanks at 1g.

[Elmun]

What you could do is instead of having your lift stages directly under the payload, move them so you have 3 or 4 mounted laterally around the fuel tank above the RCS, and stage them down that way. You avoid having issues with the docking port being the weak point in the vehicle, just don't forget the strut the lifting stages together to keep everything rigid.

[Moar Boosters]

What's going on with the top of the rocket?

Is there any reason you couldn't flip the payload over, have it attached with a large decoupler and then have the small docking port acting as the nose cone? If you want it to look nice you can always used the shielded docking port.

[allmhuran]

The problem with the docking ports is not so much that they will break, it's that they will flex and sag much more than decouplers. This puts additional stress on other parts of the structure.

[hammyhamm]

Why don't you put your reinforcement strut/truss structure on top of some radial decouplers and set up an action group or stage to remove them when you want to decouple that point? otherwise you should have enough force to break the struts with some sepratrons.

You can also put less bending stress upon the docking port by having the heaviest section of the upper payload as close to it as possible (think of that mass as a "lever" on the docking node when it swings about)