Getting a space station into orbit (with a wibbly launcher)

[Clear Air Turbulence]

... Or, eventually, I hope, a non-wibbly one.

The Kerbonauts have built their first space station: just a crew pod, some solar panels and some docking ports.

The thing is to now try to get it into orbit.

I have designed a simple launcher with enough d-v. But the thing gets the conniptions and looks very unsteady in flight. When I start ye "gravitye turne" it starts tumbling in a way that does not make for a good orbital insertion.

I just have a stack of rockomaxes & a mainsail & some fins.

Pic below

Clearly the thing is top heavy. But anything with a 5 ton space station on the end is going to be top heavy

What am I doing wrong?

Edited September 26, 2015 by Clear Air Turbulence

[Reactordrone]

The size transition will make it a little bendy in the middle. If you have the rockomax adaptor you could consider consider attaching the station upside down with the LV-909 pointing upwards and just flip the ship around for orbital insertion. That will give you a much stronger stack that will be less inclined to bend resulting in less control oscillations.

[Clear Air Turbulence]

That's a great suggestion, thanks!

[Harry Rhodan]

Clearly the thing is top heavy. But anything with a 5 ton space station on the end is going to be top heavy

But top heavy is good. Adding a wasp waist is bad. You could try don't seem to play career mode so you could swap that 1.25m second stage with a 2.5m stage with a Poodle and maybe shift some of the fuel from the first to the second stage. And then you add a fairing from the aerodynamics selection to shield that unwieldy station from the attacking wind.

[SpeedDaemon]

That's overbuilt by a rather large margin, I'm afraid... For only a 5t payload, you can even squeak by with 1.25m parts. Also a fairing is pretty much required for a payload like that.

This gets a 2.5m, 5.2t payload to 100x100, with 400dV to spare, for half the price, better TWR, and 100% less wobble (that's a Poodle on the 2nd stage):

[Clipperride]

As others have said, a lighter capsule and launcher is probably the way to go on this flight. But wobble can become a problem when launching large payloads. The way I got around it to launch this mining rover:-

was by;

Enclosing the payload in a fairing - worth doing if you already have them. I also used a landing section that had 4 radial propellant tanks attached to a central tank. I added a separator to the top of them and a modular girder (rotated so it was vertical) to the separators. I then used a load of struts to connect the payload to the girders and hold it in place. It adds a little weight, but I found it made a big difference to the wobble. I've read you can also "cheat" and strut across to the fairing although I haven't tried it out myself yet.

Pay careful attention to your RCS thrusters making sure they all fire in the same directions and don't "fight" each other.

For oversized loads I fly vertically to 10km and then start turning to the East. The turn can often induce wobble, but I've found it helpful to turn off the SAS, tap "D" to start a turn then stop that turn every 5°-10° with the "A" key and reengage the SAS. Repeat until horizontal. It's not the most efficient flight profile, but does allow awkward loads to be launched a lot more easily. I find that turning with the SAS engaged can set up a kind of harmonic wobble as each end of the rocket tries to keep to the desired heading. Once out of the atmosphere, life gets much easier.

One last tip, try a test launch and keep a close eye to see where and why the wobble starts and work on that area back in the VAB. Sometimes the problem isn't where you'd expect.

[Clear Air Turbulence]

I actually eventually got the rocket into orbit as built, just by flying carefully & not engaging SAS as suggested.

But a second attempt to launch a fuel tank with the same launcher got the problem returning much worse... My launcher started behaving like a cross between a bucking bronco and a thrashing serpent. Not pretty.

There is clearly a problem at the decoupler. I am using a small stack decoupler.

Also: @SPeedDaemon - wow. I need to figure out how to get payloads into space without ridiculous amount of fuel. I am just trying to get a 7 ton rockomax tank plus docking port into orbit to the space station.

Edited September 26, 2015 by Clear Air Turbulence

[Gaarst]

Struts ! Y u no struts ?

[Clipperride]

I bet an explosion followed shortly after that screen shot?

Further ways to strengthen your rocket are;

You can use struts across stages to make them more rigid. Just add a group of 3 or 4 modular girder segments to each stage and then attach struts. If you connect them at opposite corners of the girders, so they cross, you add quite a bit of rigidity.

Another method to consider is to build "out" rather than "up" in the VAB. If you have a set of radial tanks, you can add a decoupler to each engine (or tank) and use the decouplers as an anchor point for more struts (again adding modular girder segments to the lower stage if you need the clearance).

If you add decouplers and leave the other end clear, its better to have the "separate" and "start engines" in two different stage commands. If you combine them into one, you get a good sized explosion behind your ship. It doesn't seem to do any damage to the remaining rocket, but does produce a lot of debris.

[Clear Air Turbulence]

OK, I see what you mean. That Poodle is seriously efficient. That plus a couple of Kickbacks is all it will take. Thanks!

- - - Updated - - -

I bet an explosion followed shortly after that screen shot?

[Kryxal]

Even if it's already answered, I'd like to second the idea of flipping the final part ... put a nose cone on a reversed decoupler and eject it once you're well up in the atmosphere.

[Clear Air Turbulence]

? I don't quite understand about the reversed decoupler?

[MarvinKitFox]

... and looks very unsteady in flight. When I start ye "gravitye turne" it starts tumbling in a way that does not make for a good orbital insertion.

So your rocket starts tumbling at about 500 meters altitude?

1) use a smoother turn.

2) consider wrapping a fairing around that

3) use struts to reinforce your jello.

[Vectura]

? I don't quite understand about the reversed decoupler?

The 'bottom' of the decoupler will stick to whatever it is attached to, so if you put one upside-down on the top with a nose cone attached, it will get ejected along with the nosecone.

[Superfluous J]

? I don't quite understand about the reversed decoupler?

The 'bottom' of the decoupler will stick to whatever it is attached to, so if you put one upside-down on the top with a nose cone attached, it will get ejected along with the nosecone.

Yeah the arrows point at what will detach, so just make sure when you put on the decoupler, the arrows are pointing down.

[Clear Air Turbulence]

OK, I see. I just have a fairing covering a port. I assume the port will be available once the fairing has been jettisoned...

[Clipperride]

OK, I see. I just have a fairing covering a port. I assume the port will be available once the fairing has been jettisoned...

That's right.

It's just that if you cover a docking port with a decoupler and nose cone for lift off, you need to make sure the decoupler stays attached to the nose cone when you jettison them. You could also use a separator, which detaches from both ends when fired. As long as the port is clear before you try docking, all should be goods.