Extremely aggravating SAS

[Bob's Guardian Angel]

Today I decided to launch a simple probe to Duna. While the rocket was large, I added several reaction wheels and generous RCS thrusters, like I had been advised to do for a large rocket.

Then I launched it.

It decided to flip itself over while the SAS did absolutely squat to keep it from spinning to the right. The SAS didn't apply any torque at all until it was about 45 degrees over, at which point the mission was unsalvageable.

Any help?

[Platofan2]

The RCS Can Make It Wobble If There Is To Many Thrusters

[Ali_J_101]

I only activate the RCS when I've left the atmosphere. Fins tend to work better at lower altitudes.

[Bob's Guardian Angel]

It didn't wobble. And the biggest problem was that the SAS did nothing. Can I make it more sensitive?

[Platofan2]

If There Is More Than One Reaction Wheel I Think They Cancel Each other Out

[annallia]

If There Is More Than One Reaction Wheel I Think They Cancel Each other Out

I've never experienced them cancelling eachother out.

I have however experienced having too much torque. There seems to be a point where too many SAS modules make you spin rather than keep you steady. Though I have never had that problem while using just one.

[SRV Ron]

Use only thrusters at the probe for flight control. You can use fuel from a RCS tank on the booster if you disable the tank on the probe to save its fuel for later. Make sure that you have stitch all the stages and tanks together as unseen wobble will cause major control issues on such long rockets. One RCS at the probe should be enough with possibly a second one at the bigger booster.

Most of all, do the gravity turn gradually to avoid the risk of such long rockets swapping ends in powered flight.

Edit;

Upon further study of your flight, you have two engines that have shut down. If the shutdown is not symmetrical the uneven thrust will flip your rocket regardless of how much SAS or RCS is applied.

Edited August 17, 2013 by SRV Ron

[DMagic]

RCS doesn't do much in a dense atmosphere with a large craft, so you would be better off just getting rid of them. You probably don't even need them for the probe on the upper stage either.

Multiple reaction wheels don't counteract each other, they just add to the total amount of torque available. You can always add more, but keep in mind that doing so just adds mass and size to your craft. You can also try to add fins. The AV-R8's work well for me, just put a set of four near the bottom.

Is this happening while you are trying to fly straight up? Is your craft properly balanced? I noticed the odd engine arrangements in your stage list too. I can't see where the two shut down engines are, but if you have unbalanced thrust, or fuel, it will throw off your craft.

And about SAS, it won't lock onto your orientation if you are constantly touching the controls. Any manual input keeps SAS in damping mode, and it will never switch to locking mode if you don't let it stop for a few seconds.

[nhnifong]

Ise imgur or your photo will disappear. Welcome to the Internet.

[Johnno]

Today I decided to launch a simple probe to Duna. While the rocket was large' date=' I added several reaction wheels and generous RCS thrusters, like I had been advised to do for a large rocket.[/quote']

Neither is really necessary if the rocket is well designed, you can do most of the controlling in atmosphere with winglets + gimballed engines and in space with just engines. One or two reaction wheels should be enough to give a probe rocket enough torque to turn before circulization.

It decided to flip itself over while the SAS did absolutely squat to keep it from spinning to the right. The SAS didn't apply any torque at all until it was about 45 degrees over, at which point the mission was unsalvageable.

Any help?

Can we see a screenshot before launch, or even better a craft file? I suspect that adding winglets would help a lot. Might as well remove the RCS too. Also having the reaction wheels on the centercore would probably help, rather than dropping them with the boosters. Asparagus staging can in itself introduce spinning, the reaction wheels probably simply weren't enough for the SAS to control the rocket. Again, winglets should help.

[Frederf]

Certain craft are not stable within the control authority available to either the player or the SAS. In such cases it's not the computer's fault that it's impossible. However the SAS is quite weak and reactionary. Often corrections build too late since the disruptive forces increase with the steering error. I find the SAS only suitable in less dynamic situations like orbit or airplane flight.

[ZenithRising]

It sounds like your craft is unbalanced, either in thrust or mass. Everytime SAS has failed to keep one of my rockets going straight up, there has been a balance issue.

For control, use fins in atmo, A few RCS for large payloads in the vacuum, and a control wheel for smaller payloads. Loading up on everything isn't a solution to your problem. Balance is.