Heavy payload problems...

[zeppelinmage]

I'm trying to lift a 250t drive section for an interplanetary mothership. It's a cluster of nukes attached to 8 fully fueled jumbo orange tanks.

I have a lifter that should be able to handle it... at launch, it has 5000 DV and 1.5 TWR.

(12 asparagus stages driven by mainsails)

Every time I go to the launch pad though, one fuel tank from my payload always falls off. I can't fathom why. I've strutted the crap out of the whole thing. Funny thing is, it's always a different tank, but also, always only one.

Any suggestions/ideas?

Javascript is disabled. View full album

Edited January 26, 2014 by zeppelinmage

[Alchemist]

Moar struts!

Seriously, it needs more structural integrity in that place.

Alternative solution - launch it half-empty and then refuel.

Also, do you really need so many SAS modules? Mainsails usually provide enough control authority for such launchers on their own. But this bunch is definitely the weak spot.

But if you have a tank just falling off from the side despite all struts, try removing the ones that would push the tank away when pushed down. The same goes for randomly desintegrating heavy lifters - wrongly placed struts just make it worse.

Edited January 25, 2014 by Alchemist

[zeppelinmage]

My god, more? It's already over 850 parts with all those damned struts. LOL.

Yeah, I wasn't sure if the mainsails would be enough to turn this monstrosity, so I added a bunch of SAS towards the payload... if the motors themselves are enough, I'll nix the SAS.

[Initar]

And you wonder why its exploding?...

Better separate the payload in two, and launch them empty.

+1 too many sas

[Alchemist]

And place some struts from side stacks of your launcher to the payload - that provides more integrity while it's needed, but during the last stage you won't have so much load anyway.

Also my rule for such heavy things is addind 3 or 4 struts to any 2.5 m stacking (at least in the launcher and lower part of the payload) - the connection itself has insufficient integrity, especially if these are the orange tanks.

[zeppelinmage]

Nixing SAS did the trick. Successfully got off the lauchpad.

...but as soon as I throttled past 1.2 TWR, the linkages between the asparagus stages and the center stack failed. A little more reinforcement should do the trick.

[Pecan]

"Thrust plate" instead of just struts.

[Mr.Rocket]

I'm going to take a wild guess that this is for the Jool-5 challenge Look at post #300 on this page: http://forum.kerbalspaceprogram.com/threads/57197-The-ultimate-Jool-5-challenge-land-Kerbals-on-all-moons-and-return-in-one-big-misson/page30.

Try building on the side of your ship like a shell so it doesn't end up like a tower, but more like a pancake. That payload was 311 tons!

and for your album take away the http://imgur.com/a/ and you don't need the #0

It should just be [ imgur ] R1pjG [ /imgur ] and then take out the spaces

Edited January 25, 2014 by Mr.Rocket

[zeppelinmage]

"Thrust plate" instead of just struts.

I don't know how to thrust plate yet.

I'm going to take a wild guess that this is for the Jool-5 challenge Look at post #300 on this page: http://forum.kerbalspaceprogram.com/threads/57197-The-ultimate-Jool-5-challenge-land-Kerbals-on-all-moons-and-return-in-one-big-misson/page30.

Try building on the side of your ship like a shell so it doesn't end up like a tower, but more like a pancake. That payload was 311 tons!

Lol, how'd you guess?

Thanks, if this asparagus design doesn't end up working out, I'll certainly try the pancake method.

and for your album take away the http://imgur.com/a/ and you don't need the #0

It should just be [ imgur ] R1pjG [ /imgur ] and then take out the spaces

Ah, most excellent. The Forum FAQ said to use the whole link. The functionality must have changed since then.

[maccollo]

I've found that when I build really large rockets they tend to just fail at random points where they really shouldn't fail, and sometimes adding more struts just make it even more prone to fail. Even the thrust plate tends to randomly fail for me when things get to large. But I've found one way to build really really huge things, by using the strongest and most flexible attachment point, which is this:

http://wiki.kerbalspaceprogram.com/wiki/Structural_Pylon

Look at that impact tolerance!

Look at it!

It's also highly flexible, so you only need struts in key locations, which simply by allowing you to have less parts makes the rocket even more sturdy.

Edited January 25, 2014 by maccollo

[zeppelinmage]

I've found that when I build really large rockets they tend to just fail at random points where they really shouldn't fail, and sometimes adding more struts just make it even more prone to fail. Even the thrust plate tends to randomly fail for me when things get to large. But I've found one way to build really really huge things, by using the strongest and most flexible attachment point, which is this:

http://wiki.kerbalspaceprogram.com/wiki/Structural_Pylon

Look at that impact tolerance!

Look at it!

It's also highly flexible, so you only need struts in key locations, which simply by allowing you to have less parts makes the rocket even more sturdy.

Funnily enough, I had structural pylons, and they were the failure point in my rocket. I have a 4-bank of mainsails in my center stack, so I needed to stand off the asparagus stages more than the radial decouplers did so as to avoid part clipping and potential failure there. I've since replaced the pylons with girders, and will be launching later. As soon as I re-attach all those fuel lines and struts.

[Smidge204]

Protip: If you really need that much control torque, you can place the SAS modules *anywhere* on your craft and they'll always have the same effect. There is no need to place them in the stack and have their extremely poor structural integrity ruin your rocket.

Attach them radially to the sides with trusses like so:

Javascript is disabled. View full album

Same torque, none of the wibbly-wobbly.

=Smidge=

[Kasuha]

My experience: it's better to have things hanging off your lifter than to push them by the lifter from below. In this case I would probably attach six separate lifters, one below or at the side of each tank.

[maccollo]

Funnily enough, I had structural pylons, and they were the failure point in my rocket. I have a 4-bank of mainsails in my center stack, so I needed to stand off the asparagus stages more than the radial decouplers did so as to avoid part clipping and potential failure there. I've since replaced the pylons with girders, and will be launching later. As soon as I re-attach all those fuel lines and struts.

Well... Derp... Could have sworn those were the magic that made my giant 2800 ton Saturn rocket work, altho I also used a particular method of strutting where I used minimal strutting between the stacks.

I may have just been lucky.

[Kasuha]

Just out of curiosity I built a lifter that can get a mockup of your payload to orbit. It has 2100 t on launchpad and 749 parts and when it circularized there was still plenty of fuel in last lifter stage. No torque units were used and I had no problem with stability (doing a proper gravity turn) or structural failures. Only towards end of the lift it started spinnig a bit but I don't consider that a problem.

Craft file

Edit: images

Javascript is disabled. View full album

Edited January 25, 2014 by Kasuha

[zeppelinmage]

Thanks for the input guys! In the end, I made a hybrid asparagus/onion design (7 stages on 6x symmetry) based on Kasuha's and Mr. Rocket's designs.

930 parts, it lagged my little laptop to death. Only 1-2 FPS at launch. LoL. It got a lot better once I was able to shed spent stages.

In the end, I was able to get it into 84x91km orbit, with about 75 m/s of delta-v left over.

Javascript is disabled. View full album

[Pecan]

...In the end, I was able to get it into 84x91km orbit, with about 75 m/s of delta-v left over.

Congratulations. From your posts I think you're consistently one or two steps ahead of me in exploring KSP so no doubt I'll inflict this pain on myself soon too ^^

Thrust plate tutorial -

[thunderstar]

you're exceeding your ship structural capacities, its very common with large payloads, use more struts, or some mods can help you, something like kerbal joint reinforcement, or KW's super strong struts