How to build launch vehicles capable of lifting heavy payloads.

[MmPMSFmM]

Whenever I want to launch heavy payloads of over 50 tons, trying to make the launchers it takes up my whole midday, and when I try to launch them, it disintegrates in mid-air. And if it doesn't disintegrate it doesn't respond to the ASAS once I turn it off for my gravity turn.

This really bothers me, as I cannot launch 2m modules for my space station without sending every part separately, and eventually making my station twice as big thanks to the ASASs, the Probes and the RCS required for every docking.

[Flixxbeatz]

any screenshots of your lifter design?

[MmPMSFmM]

Sure! My failed heavy lifter: unfortunately, something happened and made it .jpg, hence the poor quality.

And my successful medium lifter: . Please note the lack of Asparagus staging on both craft. I did this purely because they both had enough Delta-Vs. Normally I use Asparagus staging when making an launch vehicle.

[Godot]

Disintegrating vehicles always sound like a case for "moar struts"

(what happpens is, IMHO, that you steer your rocket with gimbal engines and, upon executing a maneuvre, your rocket, due to its length, bends and this causes too much stress on some of the connections between modules, causing them to break)

[Flixxbeatz]

Hmm, tall and heavy launchers needs RCS when maneuvering even if you have a command pod on-board.

As for in-flight disintegration, I've found out that six-booster assembly tends to wobble uncontrollably without any reason at all no matter how much struts you put on it(and it gets worse until your rocket undergoes spontaneous assembly) when I tried making one. Are those fuel tanks (the one with docking ports) you're carrying on the first screenie? If so, then use your 4-booster assembly (turn gimbals off for strap-ons) and either drain the fuel of the payload before launching or transfer all the fuel at the middle stack of the first stage (don't transfer on straps, else your rocket will tumble out of control) while on the way to orbit, and just refuel it later.

[rpayne88]

More struts, more SAS at the bottom of the rocket, and RCS. If your getting collisions while jettisoning stages, I suggest sepratrons or ullage motors pointed away from your rocket.

[Jeakle]

To copy everyone else, "MORE STRUTS!"

Err...ok, maybe not more, but better placement will help a lot. Two struts connecting each rocket on the the lowest stage, one connecting top-to-top & one connecting bottom-to-bottom.

All of those higher struts are, IMO, are pretty poorly placed. I suggest, removing those I-beams and just placing one strut connecting the top of each tank to the mid-to-top of the higher one. You can do a similar setup to stabilize the cargo if need be. Struts from the middle of the mid-stage to the base of the cargo.

Also, disable the gimble on the outside rockets, use the central one to steer with. You lose turning power, but gain stability. As the ASAS can cause some pretty crazy wobble if it has too much turning capability.

[MmPMSFmM]

The problem is not wobbling and I never had problems with that. My rockets fly straight and don't wobble at all. The problem is when I try to launch big payloads, I build high rockets. They don't wobble and fly perfectly stable and in mid air, things disassemble, don't get logged and everything explodes. Or at least, that's my main problem.

[stupid_chris]

Basic question but, are you disabling the gimbal on all the asparagus boosters?

[Fyzzi]

Yeah, this happens to me quite a lot when I try to launch heavy things using heavy lifters... as far as I can tell, it's caused by a lot of force being put on the weakspot, which is mostly the decoupler... the really heavy part (the payload) is being pushed up with some heavy force from the main engine and THAT'S when it starts to disassembly quite a lot...

The only thing that can and WILL help is adding more struts... they do not only cancel out the wobbling issue (they are not like ropes) but they also hold the ship firm... they are much more like girders or so

[rodion_herrera]

Disable the gimbals on first stage--you don't need to do gravity turns on the early part of the flight, so gimballing will not be needed. Unless your stack is somehow badly imbalanced (thus it will tip over considering gimballing would be off), disabling the gimbals on the 1st stage will prevent the swaying/pogo-ing effects.

[Talisar]

Also, ensure that you pay particular attention to strengthening the points where you have docking rings or decouplers... if one of those shakes loose, you lose all your struts that span that point at once, which would lead to that instant disintegration you mentioned

[Superfish57]

In timeless kerbal knowledge this is time for the saying, "MOAR STRUTS!"

[sturmstiger]

I would disagree with all those "moar struts". You need to first figure out WHY your rocket disintegrates. To do this take a look at the flight event log and check exactly which part / connection broke first. Think about what forces (gravity / thrust / "shear") are acting on it, and how you can either reduce these forces (for example by distributing it to other parts), or strengthen the part / connection (by replacing it with higher strength parts or adding a few struts to appropriate places). This way you actually learn how to build better and better rockets, rather than those ugly strut-fests which seem popular on the forum these days.

As an example, take a look at the Modular Medium / Heavy Lift ELV Family. The 76 ton-to-LKO variant has only 31 parts while the 42 ton-to-LKO variant has 17 parts. If I remember correctly these vehicles uses only 2 pairs of struts. Remove a pair and see how they wobble / disintegrates, and you'll see why the struts are placed where they are. Reverse that process and you'll see when and where you need (or do not need) struts for your design.

Edited June 4, 2013 by sturmstiger

[triffid_hunter]

if wobble is not evident, what causes this is parts being pushed through each other vertically by the thrust and becoming clipped. this is fixed by MOAR STRUTS!

can lift ~50T last time I checked and I don't even need to disable the gimbals

[chrischambers]

I also have been having issues in getting a reliably Heavy lifter to work, can someone please post a example or list the parts, as so far every time I try and lift something I get one of two things happen.

one: it lifts off, and around 10,000m, it turns and nose dive for the ground, or

Two: it run short of getting into orbit, and crash landing on the other side of the plant.

[Temstar]

Part of the problem is everyone have different definition on what is considered "heavy lift". I personally define it as:

Light lift: <10ton

Medium lift: 10-36 tons

Heavy lift: 36 -100 tons

Super heavy Lift: 100-200 tons

Ultra heavy lift: >200 tons

For people who don't care for building booster rockets and only interested in payloads I designed this rocket family for reliable payload lofting:

Zenith rocket family

[triffid_hunter]

I also have been having issues in getting a reliably Heavy lifter to work, can someone please post a example or list the parts, as so far every time I try and lift something I get one of two things happen.

have a play with Fuel Tanker no MechJeb.craft - if you want mechjeb, just stick the AR202 on the central orange below the stackable probe core. Feel free to ditch the upper orange tank which is just payload and substitute your own.

if you need to lift bigger payloads, feel free to add another ring of orange tanks with appropriate strutting

[zalzane]

This design reliably lifts 50 tons to any planet's SOI.

I've been able to use it to launch >130 ton loads to minimus, havent bothered to find the upper limit yet. However, the latest patch did something with the physics engine, so it's been having issues with breaking up halfway through the atmosphere despite how many struts i use.

Edited June 4, 2013 by zalzane

[info600]

in lull of all those "moar struts" jokes, is it wise to insert approximately 4 struts to connect the sections being connected by a seperatron for reinforcements?

(I saw a few rockets on youtube having something like that...)

[zalzane]

in lull of all those "moar struts" jokes, is it wise to insert approximately 4 struts to connect the sections being connected by a seperatron for reinforcements?

(I saw a few rockets on youtube having something like that...)

yes, this is standard for almost all of my tank->tank / tank->sepatron connections

you can even see it on the big rocket above if you look closely

[Sephta]

One thing, that happend to me: too much struts (go ahead an laugh... )

I made the experience, if you build your rockets too rigid, the stress on one part can get way to high and it explodes (mostly on connection points from tanks). After that, your stage desintegrates bit by bit.

If you have a problem of this kind (stress to high on one part) try to get some load off of it, hold the stage/part above it with struts or reduce weight there. Best way I found are the quantum struts: they can take quite a lot of load, but they're nor too rigid and thy don't break things. And most of all, they don't clip (another problem rockets can have...)

[Flixxbeatz]

in lull of all those "moar struts" jokes, is it wise to insert approximately 4 struts to connect the sections being connected by a seperatron for reinforcements?

(I saw a few rockets on youtube having something like that...)

I go for a standard 2-strut rule. Each strap is taped to the main booster by 2 struts, and each component of the core booster and the payload is connected by two struts on the component above/below it. For extra-tall rockets, I'm going for steel girder method.

[birrhan]

Well, it looks like you're using KSPX or KW Rocketry parts, and what I've found (especially with the 3.75 m parts) is that those engines provide almost twice the force of a mainsail, acting on parts that weight up to 3x an orange tank. That's a lot of horsepower acting on a lot of mass, and your poor payload is getting pushed around like whoa. Two things will help:

1) Get rid of your current 7x boosters, and instead mount them 6x radially around your payload; keep the payload engine off until your second stage.

2) I normally cringe when people say "moar struts", because stock parts need 3-5 struts at most--a tripod to mount radially, and two more if you're stacking stuff on top of it (to prevent vertical clipping)--that said, KW/KSPX requires a lot more struts for the forces involved. One of those mods will have super-strength struts--use them. Or else treble (3x) your normal struts. Your boosters will also require 6-10 decoupling rockets because your fuel tanks are very heavy, even when empty, and they get off center and collide into stuff really easily once decoupled.

Best of luck. I also recommend using Kerbal Engineer Redux in the VAB, just get your TWR over 1.2 or so and your ascent stage(s) dv over 4500 and you're golden.

[SixthFall]

i used kw parts to build a simple, five engine 2 stage to orbit rockets that can lift a 130 tonne payload to a 70 km orbit. Ill post a pic so you can see it.

Here is a link to the photo:

http://s1307.photobucket.com/user/RKirz/media/screenshot1_zps28e5cf21.png.html

basically, out of the five engines on the main stage, two engines on opposing sides are droppable liquid boosters that feed fuel asparagus style to the fixed boster next to it, as well as the center tank. (this allows all five engines to run off only 2 fuel tanks, so once the strap on boosters are empty, you drop them, and continue on with the three remaining engines with full tanks of fuel *this happens at about 5-6000 meters up*) Asparagus staging is def. something to try, it will help alot. Also, don't be afraid to use struts with kw parts. All the tanks on the rocket i posted are cross braced and laterally braced to the center tank, while also being braced to the stage above. Also, try to set up triangular bracing across the interstages, as they are very wobbly (use the small cubic trusses as anchor points, as they will make sure the struts don't clip through the rocket)

Also, if you want, pm me, and ill send you a download link for my .craft file if you want to check it out.

Good luck!