Energia-Polyus/SDLS Style Payloads

[Sauron]

So I'm trying to duplicate Energia/various US shuttle-derived launchers with their payloads mounted on the side of the rocket (without any engines on the payload). However I'm struggling to get a balanced rocket in which the COM and COT stay lined up (especially as it stages).

I realize that the easy answer is to mount a twin payload on the other side of the rocket, but that really isn't my goal here. Does anyone have any suggestions or examples of this type of approach?

Edited January 12, 2014 by Sauron

[Giggleplex777]

I've tried to do this a while ago before we got reaction wheels, but it couldn't get past 50km.

With enough reaction wheels though, this shouldn't be too hard.

Also, I think it's easier to build a Shuttle-style payload rocket than a Energia-style rocket.

^4 tons to orbit.

Edited January 11, 2014 by Giggleplex777

[Sauron]

I've got to 10km as it stands. Because I'm building a bit bigger than your example (my side payload pod is also 2.5m) the amount of reaction wheels and SAS is getting a bit absurd.

Any pointers on tilting engines in such a way that they stay aligned with COM over multiple stages?

[Giggleplex777]

I would recommend building small first.

[jedensuscg]

What we need is some modder to give us some counter weights. Something you can throw on the rocketside to shift the CoM. Or a mod that allows you to vector the thrust statically to counter the CoL (as opposed to vectored thrust built into the game for control.) Say a tweakable on the engine that angles the thrust just a few degrees to counter the roll issues.

Also, you might have to play with your thrust settings. Are you using FAR? Remember as the atmo thins, and the same thrust that got you to 50K can suddenly flip your rocket in a second. If you do not need the thrust, and your speed is good, bring down the thrust just enough to maintain acceleration. Might get you the extra needed altitude. I had a few rockets like this, that where unbalanced or had to much thrust asymmetrically that I could not power through to space, I had to micro manage my thrust thrust once I got to around 40K or so.

[Skorpychan]

Might I suggest a thematic compromise?

http://en.wikipedia.org/wiki/Saturn-Shuttle

Just slap a big booster under it, and/or disable some engines.

[Sauron]

HAHAHA! I DID IT!

Well, sort of.

it flies straight and controllably for most of the (sub-orbital) flight before COM shifts too far.

The trick wasn't turning the engines like most shuttle designs. Instead, mounting them straight but not attached to the node under the tank did it. I also used a bit of a counterweight at the top to bring COM to a more useful place. I think I can work with this. Pics will follow this afternoon.

Edited January 11, 2014 by Sauron

[Sauron]

I've got it to 50000m at this point. Gradually nailing this down. A few lessons:

1: The downwards facing nosecone on my payload was actually causing a lot of control issues. Replaced it with a procedural fuselage. Lol KSP aerodynamics :|

2: Mech Jeb is really bad at launching this thing. I thought it'd be better at holding the heading than me but it's actually not.

3: An inefficient launch profile with an early gravity turn is a lot safer than waiting unil you reach 10km. If you tip in such a way to offset the payload with gravity life gets a lot easier.

And now, as promised, pictures:

[Sauron]

Okay, steady improvements. It's crossed the Karman (Kerman?) Line and started (but not finished) circularizing. A few more lessons:

1: It's actually easier to make heading corrections with your engines throttled down or turned off. It's an inefficient way of doing things, but much safer.

2: On a related note, throttling down to a TWR of around .8 to 1 as soon as you're out of the thickest parts of the atmosphere really helps avoid losing control

Just need to find another 1 km/s of DV in an aesthetically pleasing format.

[Vanamonde]

Stop, people! Think! When Sauron asks for help crafting things, it does not end well!!!

[Sauron]

It's too late!

I've put the payload into a stable orbit already at this point! (I suppose a smaller rocket would've done well enough for a ring. That's what those little Rockomax engine are for, right? )

I've also created a much more attractive, fully FAR-compatible version that can put a 15 ton payload pod on an (Alternis-Kerbol) Laythe trajectory. It flies surprisingly well with FAR. I was expecting the usual 'parts flying everywhere' dealie, but I put it into orbit on the first try with even less fuss than the stock aerodynamic version. Part of that would be the fact that I could just barely downsize from a mainsail to a skipper--much more controllable. And FAR's preference for lower trajectories suits the launch profile really well.

So I suppose this is resolved now. See you in the showcase!