How to orient large, heavy ships in orbit.

[Wild Card]

Okay, so I've been doing pretty well with the new large parts.

Gotten a 3-man pod, 1 large full fuel tank, 1 large half-engine, 4-radial engines, and 4 large landing legs landing on the mun and minmus.

The only large issue that I'm having with these extremely large parts is getting them to orient properly in orbit.

I have attached ridiculous amounts of both linear-port and regular RCS thrusters to these things, always at the top and bottom of the craft, and on the areas furthest from center (both of which should exert more leverage).

Fins do nothing in orbit, so I won't bother with those, as while under full-thrust, the large LFE's offer enough control while ascending. The problem comes first when I try to circularize my orbit. I just CAN'T get her to point prograde, or to point pro-grade reliably without giving some throttle on the main engines. Usually, at this point I have my lander stage, and my injection stage (4 full Large fuel tanks, 1 large LFE, and 4 radial engines) up there. The problem with giving throttle to the main engines to maneuver is that it also completely messes up my orbital paths.

Onwards, when it comes time to do an injection burn to either Mun or Minmus, I have the same problem, with the additional problem of timing. By the time I get the craft lined up and ready to fire for injection, I almost always miss my window. I know, I should start earlier, but it seriously is taking 5-10 minutes to wrestle the craft into orienting prograde, and without the main boosters, it's not gonna happen.

I was considering using one of the larger, half-LFE's as my injection engine of choice, due to their more efficient vacuum operation, larger gimball range, and less amount of thrust, but I am still using the injection stage to also circularize my orbit, so I still need a decent amount of thrust for that.

Any thoughts or ideas on this dilemma?

Edited August 10, 2012 by Wild Card
Correct some engine terminology....

[sal_vager]

It's a tricky one that's for certain, I try to get a slight rotation well in advance of when I need it, rather than try to overload the craft with RCS, it's not a perfect method though, the large pod and engines are just so heavy.

Maybe extra SAS would do it but I have not yet experimented with them enough to know, I tend to rely on the capsules SAS which is barely adequate, and a tiny bit of main engine thrust just as you have been doing.

Really, RCS should do the job but it's going to use a lot of gas unless you take it slow.

[MrMadGameplay]

I agree with sal_vager it can be tricky and I usually just use a tiny bit thrust.

[Clouds]

Just one full large fuel tank? The pod's gyro should be able to work that around. Just turn slowly and let ASAS recenter it once you've arrived.

The big parts weigh so much that RCS is mostly useless, I find.

Something I've wanted to play with (and have only tried in proof-of-concept capacity) is to mount pairs of equal gimballing engines facing in opposite directions. This would just "waste" fuel, but it lets you turn a very heavy ship with good responsiveness and no net thrust. You'd have to switch them, and the main boosters, on and off by disabling or enabling fuel tank flow, though, since you can't individually control LFEs.

[Vanamonde]

it lets you turn a very heavy ship

Since they'd always be opposing each other at the same throttle setting, how could that get anything done?

[togfox]

You can turn them on or off individually with right clicks. Need to turn left? Turn off the other one.

That said, you can just put ONE engine on an angle and rotate your craft so it points the right way.

[Paprika]

Do a crazy Ivan!

I, too, have trouble moving them but I guess it's like boats, the bigger ones will always be less nimble.

[Clouds]

Since they'd always be opposing each other at the same throttle setting, how could that get anything done?

That's just how it keeps the net thrust at near-zero. They're swivel-engines, so they turn whichever way will make the ship rotate; that skews some of the thrust to the side but only for turning.

Let me diagram it with text:

>===< :A ship with engines just pushing against one another.

7===L :A ship with those same gimbal engines swiveling for a turn. They'll spin you but not move you...at least not much.

You can turn them on or off individually with right clicks. Need to turn left? Turn off the other one.

Well, that's another way, but not what I meant.

[Vanamonde]

7===L

So they can rotate but not change attitude? As for attitude control, I've been meaning to try two smaller engines angled out from the main one, like on the old Atlas rockets. In ASCII-CAD, that's something like: /I\ with the slash and backslash indicating the angles of the side engines around the main engine represented by I. But I haven't gotten around to trying it.

[Langy]

I think I found a semi-reliable way to make sure your large ship moves where you want it to (albeit slowly of course).

I was playing around last night with launching a large station into orbit and found that pressing W-A-S-D quickly before actually doing any maneuvers, AND before/after enabling or disabling ASAS, seems to 'calibrate' the controls and then they seem to respond properly. I'm quite sure it wasn't pure luck, because I played with it for quite a while and it was dead reliable, whereas before I made this discovery large ships/rockets would just spiral out of control regardless of any control input. Hope it helps!

[MrPwner]

What do you mean exactly by "pressing W-A-S-D quickly before actually doing any maneuvers, AND before/after enabling or disabling ASAS"

Like press them all in short sequence, or all at once? If it helps, this tip will prove invaluable!

[Naiba]

Pretty sure 0.17 is going to have some larger/beefier SAS and RCS systems scaled up to the new larger parts. Could be wrong 'tho.

[Langy]

Just tap them briefly one at a time. Would love to hear if this works for anyone else.

[SpeedDaemon]

The way I've been handling this is to try to keep it from getting so far out of alignment that if I need to use a little throttle, it at least is in the right direction. For your initial orbital circularization (pre-AP), as long as you stay pointing 90o, firing the engine at almost any positive or slightly negative pitch angle will still be pushing you the direction you want to go.

Also, you don't need to fire the engine the whole time. Use the lowest throttle setting to get some rotation started, then shut down and don't burn again until you need to stop the rotation. MechJeb is an incredible help for this, since it will always be pushing in exactly the right direction while you have the engine burning.

Third, anything you do with big rocket is going to be slow, so start early. Heck, if you know you're going to need to fire retro at some point in your orbit, you can get yourself pointing prograde half an orbit early, which will have you pointing the right direction when the time comes.