tips on getting light/long items into orbit

[mrklaw]

I'm trying to get a connecting piece for my first space station into orbit

but the rocket keeps spinning out of control. I thought I'd gotten the knack but this is stumping me. It does tend to bend a lot at the docking port joints mainly, also the centre of mass is very low because it is so light. I've tried putting a hitchhiker on top to raise the centre of mass but it doesn't help. I've even tried pulling - putting the load below a bunch of rockets, but that doesn't work either.

any tips?

[scola_p]

First thing I would suggest is a fairing. That looks far to knobbly to be aerodynamic!

[stibbons]

A fairing will probably help. I'd also consider lifting it attached to one of your other modules, with enough struts to maintain some rigidity.

Also, instead of a pure puller approach, I'd try keeping the booster engines below, but putting the fuel tanks above. That'll lift the CoM at least.

[mrklaw]

I had a fairing on it, didn't seem to make much difference. Also I had a terrier/FT400 fuel tank on the end as a pusher so the overall load was longer.

[DeMatt]

I'll second the fairing. This is precisely the type of structure that fairings are supposed to cover.

Additionally, I'll suggest looking at the Z-1k batteries instead of the Z-200's, and maybe swapping the Stratus-V Cylinders for FL-R25 monoprop tanks. Then I'll suggest strutting "around" the floppy docking port joint, connecting from below it on the booster to above it on e.g. the solar panel "arms".

Oh yeah, and a screenie of the module on its booster would probably help with diagnosis. It's not a terribly large module, after all.

[Falkenherz]

I had similar problems with a part consisting of four docked modular girder segments. The fairing did not help at all. I made it with a mix of low speed in the thicker atmosphere until >30km and a no-gravity turn heading, i.e. mostly vertical until >30km.

[Sharpy]

Do you have RCS enabled during launch? Also struts from top to a wider base (edges of the medium-sized fairnig thing?) - four struts on diagonal directions will stabilize it against wobbling; RCS will prevent the whole rocket from flipping over (you may consider the liquid fuel powered RCS thrusters for that).

[Dilli]

I'll second the fairing.

...

Then I'll suggest strutting "around" the floppy docking port joint, connecting from below it on the booster to above it on e.g. the solar panel "arms".

This and use 3/4 way symmetry to place a set of delta wings as a fins at the base of the core of your launcher

[mrklaw]

pic of overall craft I'm trying to use.

[Chaos_Klaus]

I had a fairing on it, didn't seem to make much difference.

You have to eject the fairing after around 20km or 25km. If you bring the fairings all the way up to orbit, they are just too heavy.

[ElWanderer]

That looks like it needs struts, lots of struts. I'd be tempted to replace the second stage with 2.5m parts even though it'll be overpowered - perhaps couple that with a less powerful first stage. If you transition from 2.5m to 1.25m at the docking port on the bottom of your payload, you can put struts inside the fairing (strut upwards).

I've taken to putting (going downwards) payload, docking port, probe core to control rocket once detached from payload, rockomax adaptor type 2, fairing base. Then I strut upwards from the adaptor to the payload. I didn't have much success trying to strut from the fairing base, hence the adaptor.

[Dilli]

Add struts from the base of the 2.5m adapter to the base of fairing. Then from the plane body, goo canisters or solar panel "arms" of the payload to the base of the fairing.

That should stop too much flex in the rocket. Part of the problem may be controlling the rocket from the very tip which is swaying due to flex between joints (particularly in the docking port connections), the sway can also move your center of mass too far off centre.

[mrklaw]

I had similar problems with a part consisting of four docked modular girder segments. The fairing did not help at all. I made it with a mix of low speed in the thicker atmosphere until >30km and a no-gravity turn heading, i.e. mostly vertical until >30km.

this worked, as long as I kept my speed below 200-250m/s, but seems very inefficient. I strutted it up so it wasn't quite so wobbly, but I guess it is too light? Although with the fairing it is about 14t (only 8.5t without a fairing).

How do you guys get light structural elements like this into orbit? Do you use cargo bays? If I used a 2.5m fairing, would that be structurally more sound, or is it still relying on the internal structure and the fairing is just protecting it aerodynamically?

[Harry Rhodan]

Ditch that last stage. it has a laughable amount of fuel and it's only making the lever the drag is pushing you down with longer. Even better would probably be using a real 2.5m upper stage that will keep your CoM from falling too low and a core with a mainsail instead of piling all the stages with all the fuel and mass at the bottom.

[rofltehcat]

Something I once did was using a kinda heavy end stage with the light payload. Then I flipped the payload and the end stage by 180° so the end stage was on top (pointing down). Depending on what ends up being flipped some part of the ascent prograde and retrograde will be mixed up on the navball (and for mechjeb etc.) unless you use two probe cores and switch control during flight.

It looked pretty funky with the decoupler and nose cone on the end stage engine (didn't have farings unlocked yet) but it worked fine. Also had a lot of struts.

If it looks stupid but works it isn't stupid!

[georgTF]

For large, assymetrical, lightweight or otherwise mass-annoying payloads that won't fit into a fairing i just bite the bullet, accept that i can't use an efficient lift and go slow straight up until well clear of aerodynamic interference. Strut the hell out of it for good measure too.

Lower TWR helps in cases where one attachment node is overwhelmed but that can also be taken care of with struts. Aerodynamic effects are far worse and together with the wobbly nature of the beast almost guarantee rocket flippiness. You can avoid them by lifting up above the air, then burning for orbit in a less efficient ascent profile. Very late "gravity turns" may be frowned upon, but they have their uses.

Another enemy is SAS. If you lock SAS, the craft will almost certainly begin to shake itself apart at some point, which is another reason to go slow. I lock it for initial liftoff, then release while the rocket climbs through the "locking SAS will shake it apart" zone, then try to engage in brief periods that help keep the thing pointed up.

But yeah, the solution is to waste fuel. Just waste fuel. But obviously, not for fun, but for profit. Or science! Actually, for orbit!

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In these examples fairings large enough weren't available yet, or i lacked other tech that could help. I did get them up, though they were very annoying.

[Foxster]

I've found fairings to be generally worse than useless. They add more drag than they fix and are very heavy.

All that craft needs is some fins stuck on the bottom.

[mrklaw]

I got it there in the end. Barely. I switched to an X32 + Skipper for the transfer stage, and a jumbo 64+32+mainsail for the launch stage. Went up slow and steady and inefficiently. Just as I got into orbit around the mun, I noticed my orbit was the opposite direction to my space station. Doh. (really, that seems difficult to see what your approach is like using manouvre nodes).

Used up all my fuel switching orbits, but managed to rendevous and dock using just RCS thrusters - lucky I had lots of fuel on board.

Is there a rocket based cargo bay, or are they only for spaceplanes? Something like a tall version of the 2.5m service bay would be great - it forms the structure of the rocket so you can put long/light/flimsy items inside.

[StrandedonEarth]

...noticed my orbit was the opposite direction to my space station. Doh. (really, that seems difficult to see what your approach is like using manouvre nodes).

In map view you can click on the Mun and 'Focus view'. Then you can see what your trajectory will be like during the encounter. You can also use tab to cycle your focus through all the bodies, and backspace to focus back on your ship.

There's a stickied thread at the top of the Tutorials sub forum about keeping silly payloads going up

[mrklaw]

In map view you can click on the Mun and 'Focus view'. Then you can see what your trajectory will be like during the encounter. You can also use tab to cycle your focus through all the bodies, and backspace to focus back on your ship.

There's a stickied thread at the top of the Tutorials sub forum about keeping silly payloads going up

Thanks - and that stickied thread at least shows it can be done

[cybersol]

The main thing you need for the this is low and outside control fins (av-r8). 4 on your middle stage and 4-8 on the boosters should do it. If not, MOAR FINS!

[TheXRuler]

If I may make some recommendations: loose the 1.25 m stage and one set of liquid boosters, add at least one more tank to the centeral stage and use a small 2.5m second stage. While this may seem ridicolously overpowered it will probably be more efficient, especially if you crossfeed fuel from the outer to the innner tanks. If you don't want the additional weight of a larger 2.5 m engine such as the poodle you could try emptying some of the fuel before launch and using a smaller engine covered by an interstage fairing, now that I think of it, why not use interstage fairings to make the rocket smoother without dumping the 1.25m cor for a 2.5m core Also, fins at the bottom will help you fly straight, and winglets will actually provide you with control authority.

In my experience any rocket that get's thinner in the middle will flip if not built and piloted veeeery carefully.

Edited June 3, 2015 by TheXRuler

[Beowolf]

My new rule is, if it has a bulging fairing then it gets fins. Even the starter fins seem to make a big difference, and even when I'm already using gimballed engines. The other thing is to watch your acceleration, particularly while passing through 10k-16k. I limit acceleration to 18 m/s all the way up. Then, at 30k, I eject my fairing, finish bringing the nose down to 0-degrees, and go to full throttle.

Happy flying!

[Geschosskopf]

One of my favorite tricks for such things is to build the rocket backwards. Put the light, long (or heavily winged airplane) on the bottom and build heavy, thrusty rocket above this. That way, the CoM is forward and the CoL is aft like they should be.

For example, a lifter for 2x airplanes going to Laythe, mounted on a transfer tug that's a full orange tank at launch. This is in 1.0.2. The lifter is SSTO and the explosion in the right pic is it exploding after staging in orbit via TAC Self-Destruct so as not to be debris.

[banterlad]

Strut it up, a fairing would be nice as well