SAS questions

[Firedtm]

if i put a advanced S.A.S. Module on my rocket, do i need the other S.A.S. Module

Thank for you any help you may give

[Eric S]

SAS modules are almost useless at this time. All they do is make it harder to turn the ship (intentionally or otherwise) while it is on. It does not help you turn when you want to, and other than trying to bring you to a stop, it won't try to turn the ship back in the direction it was pointed when SAS was turned on. It does this by itself. Note that this isn't magic, it uses gyroscopes/flywheels to do the work.

ASAS modules do nothing by themselves. What they will do is use the other control methods available to it (capsule rotational power, RCS, vectorable engines, and aerodynamic control surfaces) to turn the ship back in the direction that it was pointed when SAS was turned on (SAS and ASAS are both turned on with the same key, and it's called SAS regardless of whether there is any SAS on the ship).

ASAS loves to overcorrect if you're using RCS. Basically, it will always be using RCS to turn towards the right direction, even if you're pointed almost exactly the right direction.

[Designer225]

There are perhaps no answer. In fact adding SAS into ASAS system only makes it to turn slowly, because the SAS is applying torque...

[Tw1]

Only makes you turn slowly if it's on. But both are useful to stop you from spinning, ASAS tends to stop my things from rotating at all when on, which is mostly very useful.

Someone said that ASAS only controls engine gimbals, fins, and (if on) RCS, but not the SAS wheels. But I tend to stick on SAS modules anyway,just in case.

I get the impression they help. Only on larger things though.

[Anglave]

SAS adds torque. More add more torque. Keeping them far from the center of mass amplifies their effect.

ASAS is a control system. It will apply torque effects, vector thrust, and use aerodynamic control surfaces to maintain a heading (locked in with the 'T' key). But it doesn't provide any of those effects itself. One is enough to control all the systems on a ship, and more than one adds no benefit.

[Francesco]

"if i put an advanced S.A.S. Module on my rocket, do i need the other S.A.S. Module?"

maybe.

"if i put an advanced S.A.S. Module on my rocket, and there is a command pod onboard (especially the 3-seat one like in your screenshot) do i need the other S.A.S. Module?"

probably not.

there is not an absolute answer, but in general, you don't need them to pilot your rocket:

one thing I've seen people mentioning though, is that SAS units are useful for space stations, to dampen their movement, instead of using an ASAS module.

[ComradeGoat]

I use the occasional SAS module on asparagus probe rockets with no crew-capable command module, otherwise I find they can get a bit spinny.

[HGGundamReviews]

This is something that has kinda bugged me about SAS and ASAS they don't actually seem to do much of anything other than "Lock Position" once you're pointed in the right direction. The Torque they're supposed to apply seems nonexistent. Same with the probe cores. They say they have the same torque value as the command pods but they sure as hell don't act like it. Any unmanned craft I build I have to slap some RCS on it to make it maneuverable. I don't know if that was Squads intention but it's annoying as hell.

[sporkafife]

The advanced SAS (ASAS) uses other parts of your ship like RCS, thrust vectoring engines and pod torque to try and keep you pointing the direction you were pointing when you turned it on, where as SAS just produces a torque to counteract any rotation your ship was experiencing as you turn in on.

Same with the probe cores. They say they have the same torque value as the command pods but they sure as hell don't act like it. Any unmanned craft I build I have to slap some RCS on it to make it maneuverable. I don't know if that was Squads intention but it's annoying as hell.

I assume this is intentional, and I agree with it. There's absolutely no way a tiny little <0.1 mass probe core should be able to turn a gigantic ship as quickly as a >1 mass command pod. It's kind of annoying, but definitely needed to happen. Realistically, none of the command pods or probe cores should be able to produce any meaningful torque without reaction thrusters. They only produce torque for gameplay reasons as most players don't understand the full implications of Newton's laws when it comes to space.

[ComradeGoat]

SAS provides a small amount of roll resistance. If you're having to use a lot, it may indicate poor rocket design.

ASAS will utilise control surfaces, gimbaling, RCS and reaction wheels in command modules to keep a heading locked. The smaller probe cores do have control wheels, but they are quite small. Probes without the larger command modules will likely need RCS for turning, but if you want to hold a heading under power, make sure you are using gimballed engines with ASAS on.

Gimbals don't seem to work properly if they're placed above the centre of mass, I've noticed.

[DerekL1963]

This is something that has kinda bugged me about SAS and ASAS they don't actually seem to do much of anything other than "Lock Position" once you're pointed in the right direction. The Torque they're supposed to apply seems nonexistent. Same with the probe cores. They say they have the same torque value as the command pods but they sure as hell don't act like it. Any unmanned craft I build I have to slap some RCS on it to make it maneuverable. I don't know if that was Squads intention but it's annoying as hell.

I've built and launched several probes with nothing but probe cores, and have no problem maneuvering with them. The vehicle has to be small though, or you need several of them.

[HGGundamReviews]

That's fine for small probes, but I use a lot of probe driven launchers for orbital construction. It's easier to build under a RSC powered probe tug than it is a command pod. Less parts and less fuel as I don't have to worry about returning a crew to Kerbin.

[Eric S]

SAS adds torque.

It did at one time, it no longer does. I tested it top to bottom in 0.18.1, and additional SAS modules actually slowed down turning a ship even when it was off because they added to the mass that needed to be turned.

They say they have the same torque value as the command pods but they sure as hell don't act like it.

Actually, I'd say that's a display bug in the VAB. If you look at the rotPower stat in the command files, you'll find that the torque values do vary. In fact, the command pods vary between each other. The Mk1-2 pod has four times the rotPower of the Mk1, and 40 times the power of the probe pods (except for the Stayputnik, which has even less rotPower).

[ComradeGoat]

That's fine for small probes, but I use a lot of probe driven launchers for orbital construction. It's easier to build under a RSC powered probe tug than it is a command pod. Less parts and less fuel as I don't have to worry about returning a crew to Kerbin.

You can add command modules to probe designs. They'll take off empty, but still give you the benefit of reaction wheels. They can also be used as lifeboats in an emergency.

[HGGundamReviews]

You can add command modules to probe designs. They'll take off empty, but still give you the benefit of reaction wheels. They can also be used as lifeboats in an emergency.

I have no need for lifeboats. My stations are probe driven unmanned fuel depots. Their designed for as low a part count as I can get away with and do the job I need done. Until the dev team gets multithreaded support for the physics engine large constructions are going to kill me since I use a laptop to play.

[ComradeGoat]

Regardless of whether you need lifeboats or not, if you want any reasonable effect from reaction wheels, you need mass. Whether that comes in the form of a empty command pod or a lump of metal in a future version that is just reaction wheels is somewhat moot.

[joppiesaus]

There is plenty information on this thread, but why you didn't figure it out by yourself?

[Anglave]

It did at one time, it no longer does. I tested it top to bottom in 0.18.1, and additional SAS modules actually slowed down turning a ship even when it was off because they added to the mass that needed to be turned.

So wait, if the SAS isn't essentially "rotPower without adding a whole command pod", what does it do?

[Eric S]

SAS modules have a maxTorque stat instead of a rotPower stat, and I'm pretty sure that the difference is that maxTorque only helps you stop turning, it doesn't help you turn faster. While it's not exactly what it's doing, think of SAS as providing friction to turning. If your rocket starts tumbling end over end and you turn on SAS, eventually the rocket will stop tumbling if the SAS has more force than whatever was causing you to tumble. However, just like spinning a roulette wheel, friction doesn't mean it's going to stop pointing the same direction it was when it started moving.

The rotPower from capsules is actually useful for turning the craft, provided you have enough rotPower. I don't know the correct terms for all these different types of gyroscopes/flywheels, but there are actually real life spacecraft parts that behave like SAS modules, and parts that behave like capule rotPower.