Long wordy explaination/observations about the new 0.21 Attitude Control System

[dlmarti]

Sorry about the yet-another-SAS thread explanation, but I really thought the others were misleading.

About:

1. Forget all the terms from the 0.20 (and before version), wipe the ASAS and SAS terms from memory. TUT!, no just forget them.

2. Every control module contains the ability to do Automatic Attitude Control. What that means is this system can control the forces generated by the control surfaces (like flaps), rocket gimbals, engine vectoring, and the new reaction wheels, in order to maintain your crafts attitude (direction it is pointing).

3. The control modules may also include a reaction wheels of varying strengths. Reaction wheels are NOT attitude control, they are a device that CAN be used for attitude control. When in action (when force is being applied), they consume electricity.

How to build your craft now:

1. Build your craft... done. When you add the control module (manned or remote) you get the Automatic Attitude Control system, and some version of a reaction wheel (sizes vary depending on the control module).

2. If your craft is still unstable, or difficult to control, you will need to add more forces that can be used for attitude control. These can be flaps, engines with vectoring, or additional reaction wheels. You can add some of each, or all of one type. Just remember: flaps only work inside the atmosphere, engine forces require fuel, and reaction wheels require electricity.

Things to remember:

1. The old SAS/ASAS parts are gone, poof. Yes I know they have the same names as before, just ignore that. What they are now is just reaction wheels. They have no smarts, the are just big spinning discs that can be used by the pilot or the Automatic Attitude Control system to exert forces which can be used to point the craft.

2. The old 'T' button, turns on and off the Automatic Attitude Control, it does not turn off the reaction wheels (on or off, the pilot's inputs still can control the reaction wheels).

Gotchas:

The new reaction wheels are very cool, and a welcome addition to KSP. However some crafts do better without them, and some parts of missions do better without them (note: I am talking about the reaction wheels, NOT the Automatic Attitude Control). For example:

1. Rovers in general should have them turn off, at least until they flop on their backs like a turtle and you need to try to right yourself.

2. Vessels docked at space stations should have their reaction wheels turned off (the station should have them turned on), or they can oscillate on their docking nodes.

3. Vessels either being pushed/pulled by another Vessel, and the tug Vessel itself, should all have their reaction wheels turned off. This prevents oscillating on the docking node, and gives you more accurate burns.

Tricks:

1. For every vessel you make, create an action group (I use '0'), that turns off all reaction wheels. Do this for every vessel type, except for Space Stations. Remember turning off the reaction wheels does NOT turn off Automatic Attitude Control. The Automatic Attitude Control can still use the gimbals, flaps, etc to control the craft.

2. Place extra reaction wheels on vessels you expect to use for docking. This will allow you to have a lot of command authority, which is useful for switching between your targets direction and your retrograde.

Scott Manley, video on the subject:

Edited July 28, 2013 by dlmarti

[xclusiv8]

I give you a cyber cookie sir.

[dlmarti]

I give you a cyber cookie sir.

oh, thanks!

[Whackjob]

Can you reconfirm the docked parts needing to have the reaction wheels turned off? I don't believe they still try to rotate as a separate part. I think once they dock in, they're all considered one vessel, and therefore the calculations to torque update with regards to their new distance from the center of mass.

I have not done extensive testing, but in my experience, it actually helps, not hurts.

#EDIT: Ok, running a mental simulation right now. I think it updates, but at the same time, given that there's only a docking port separating them, it puts torque on that docking port, and they're not rigid at all. They wiggle. So corrections ensue, then resonance. Ok, so I can see a plausible way reaction wheels on something could be a problem.

[rodion]

All of these points are sound and intelligent, except that the terms "SAS" and "ASAS" are so tattooed into my brain by now that no amount of merely renaming the parts will ever get the ink out.

[dlmarti]

Can you reconfirm the docked parts needing to have the reaction wheels turned off? I don't believe they still try to rotate as a separate part. I think once they dock in, they're all considered one vessel, and therefore the calculations to torque update with regards to their new distance from the center of mass.

I have not done extensive testing, but in my experience, it actually helps, not hurts.

#EDIT: Ok, running a mental simulation right now. I think it updates, but at the same time, given that there's only a docking port separating them, it puts torque on that docking port, and they're not rigid at all. They wiggle. So corrections ensue, then resonance. Ok, so I can see a plausible way reaction wheels on something could be a problem.

Even if both docked ships were perfectly balanced, the minute ANY force was applied on one, the other would try to compensate. Which would torque the docking node.

Believe me, EVERY mission I run includes docking and towing/pushing. Which is why my attempt at a solution.

[dlmarti]

All of these points are sound and intelligent, except that the terms "SAS" and "ASAS" are so tattooed into my brain by now that no amount of merely renaming the parts will ever get the ink out.

That is simply not possible, because in the very first point I clearly deleted them.

[Tiron]

That is simply not possible, because in the very first point I clearly deleted them.

Except, gasp, the little light on the Navball still says 'SAS'!!!

[AustralianFries]

How to Tutorial section?

Good guide, though. It's still a bit weird calling the AS- I mean... Reaction Wheels something different.

[dlmarti]

Except, gasp, the little light on the Navball still says 'SAS'!!!

Do a google image search for "eeprom label", use that. They are tiny stickers you can write on, place them over the "XXX" on the navball, and right ACS instead.

[purpletarget]

#EDIT: Ok, running a mental simulation right now. I think it updates, but at the same time, given that there's only a docking port separating them, it puts torque on that docking port, and they're not rigid at all. They wiggle. So corrections ensue, then resonance. Ok, so I can see a plausible way reaction wheels on something could be a problem.

That was historically the issue with large space stations, or collections of docked vessels. It wasn't the different ASAS modules that each ship had, but rather all the different pods trying to torque their way around would induce wobbles in the docking ports, and eventually the oscillation would grow to the point of structural failure.

The new SAS behavior is gentle enough with the controls that this should be less of an issue overall, but there is probably still potential for it...indeed have seen some large multi-part ships that have issues just because of the large number of parts playing bumper-boats with each other when there's a reaction wheel on either side.

So, turning off the reaction wheels for docked ships may or may not be needed, depending on your station and SAS...but it's prudent to have the ability to shutdown if it does start to happen.

[manskal]

Is this ACS supposed to hold heading? Because it is not doing it for my rockets (spaceplanes are mostly fine though). I feel it might still be bugged (on my version at least).

Either that or I'm really bad at KSP (which I slightly am) because it seems to work flawlessly for others.

[dlmarti]

Is this ACS supposed to hold heading? Because it is not doing it for my rockets (spaceplanes are mostly fine though). I feel it might still be bugged (on my version at least).

Either that or I'm really bad at KSP (which I slightly am) because it seems to work flawlessly for others.

According to the devs it is supposed to do that.

If it is not, either you did not give it enough control force, or you are experiencing the tiny bit of wander that is still in the code.

What I see on my well balanced designs, is a small amount of wandering around on the burn vector, when I am trying to do a maneuver node burn. If you are seeing something more than that, you are probably having a design issue with your rocket.

[manskal]

According to the devs it is supposed to do that.

If it is not, either you did not give it enough control force, or you are experiencing the tiny bit of wander that is still in the code.

What I see on my well balanced designs, is a small amount of wandering around on the burn vector, when I am trying to do a maneuver node burn. If you are seeing something more than that, you are probably having a design issue with your rocket.

Supposed to do what?

I am going to try it with the stock rocket designs, seeing as those have been tested by Squad.

[DMagic]

Supposed to do what?

I am going to try it with the stock rocket designs, seeing as those have been tested by Squad.

Supposed to hold a heading, I'm guessing.

The stock craft do not work very well and should not be used as a guide for proper design. The Kerbal X works fairly well, but the others are all pretty much junk.

The Z-map satellite especially, doesn't work well because of the winglets they used. In fact I would recommend never using the Delta-deluxe winglets for controlling your rockets, I always use the AV-R8's.

[manskal]

OK, just tried Kerbal X, the flight was pretty much rock solid. No issues at all. I have not tried the Z-map satellite yet.

My craft, on the other hand...

Looks like I have to rethink the way I design stuff now. Thanks to all that helped me, I hope I haven't been a nuisance.

[dlmarti]

OK, just tried Kerbal X, the flight was pretty much rock solid. No issues at all. I have not tried the Z-map satellite yet.

My craft, on the other hand...

Looks like I have to rethink the way I design stuff now. Thanks to all that helped me, I hope I haven't been a nuisance.

Try this craft:

https://www.dropbox.com/s/uovsk0a8jazgcqt/Fueler%20Mk6.craft

Its balanced for launch and docking, you should have no problems with it.

[theflyingfish]

That was historically the issue with large space stations, or collections of docked vessels. It wasn't the different ASAS modules that each ship had, but rather all the different pods trying to torque their way around would induce wobbles in the docking ports, and eventually the oscillation would grow to the point of structural failure.

The new SAS behavior is gentle enough with the controls that this should be less of an issue overall, but there is probably still potential for it...indeed have seen some large multi-part ships that have issues just because of the large number of parts playing bumper-boats with each other when there's a reaction wheel on either side.

So, turning off the reaction wheels for docked ships may or may not be needed, depending on your station and SAS...but it's prudent to have the ability to shutdown if it does start to happen.

On C7's devblog video, I remember him saying something about how the new ASAS doesn't use the root part to determine the orientation, but the center of mass. In the previous system, on large ships you would see oscillation in the root part, which is often why the ASAS would freak out. But I think that this version uses the rotation around the CoM instead, which sees much less oscillation and is much more stable.

[Benie]

Right. Time for me to stop hatin' on the update and actually see if I can make sense of it.

Going by what I skimmed through in the OP, I'm still confused (and enraged they did this, but.... nothing I can do about it). So I can still slap on an ASAS module to my rocket, but it will not work as it did in 0.20. *grumble*

I do want to say I never use winglets on any of my rockets. I see no need for them. Even for my past MechJeb-assisted flights (even when I wasn't cheating at all), I didn't need them. The rocket always did its gravity turn nicely without them. I guess I got lucky.

Attempting to push the still steaming pile of rage aside, let's go with a simple, example rocket to help me understand the SAS' new mode of getting something into space: an SSTO (as an example). It has a single engine used to get out of Kerbin's orbit and where it needs to go.

I put an ASAS, an RCS Fuel Tank, a Fuel Tank, and an engine.

Am I to put a Reaction Wheel ontop of the ASAS, or at the joint between the fuel tank and the engine? And does it matter where, or how many reaction wheels you use to make it fly like it did in 0.20?

Yes, I'm aware that they can turn even with it on (seen videos as proof, even commented in one). But I just want to get this through my thick skull that 0.21 isn't "the end of the world" as I'm thinking.

Now for stress talk of how I feel from what I've seen and heard of the update.

The very thought of adding more parts; more weight to unbalance my already perfectly balanced Rover/Landers, keeps me away from the patch. And lord forbid what it will do to my rovers; especially my Speed Rover that requires ASAS to keep it on a precise heading.

Edited July 28, 2013 by Benie

[dlmarti]

Added the Scott Manley video on the subject.

[Abrexus]

One interesting thing I ran across that may (or may not) play into this. My first rocket was a simple 3 stage probe w/engine, mid stage, and launch stage rocket. I had a severe wobbling problem I wasn't able to resolve until I locked the gimble on the launch stage skipper engine and used 4 of the small side mount engines for their gimble. The wobble disappeared and I was able to steer the rocket without a problem.

[Somerled]

Don't the old SAS parts have the new ACS, just like the pods? If you activate this and then detach the parts, would they continue to stabilize without any manner of player control? Stabilized debris might have its uses, and elsewhere someone mentioned something about command seats.

[DMagic]

Don't the old SAS parts have the new ACS, just like the pods? If you activate this and then detach the parts, would they continue to stabilize without any manner of player control? Stabilized debris might have its uses, and elsewhere someone mentioned something about command seats.

It seems that way. Even without a probe core, a detached rocket with a reaction wheel will hold its heading if you leave SAS activated when you decouple. If you turn off SAS before decoupling the detached rocket will start to tumble.

[littlebattler]

Correct me if I'm wrong but the new system should still attempt to maintain heading right? For some reason it does not properly use the gratuitous amounts of control surfaces I have applied on my spaceplane, causing it to crash right after leaving the ground (the centers of lift, thrust and mass are not perfectly aligned, but within tolerable limits for the old ASAS). And yes I am in 21.1

EDIT: NVM it no longer locks the heading, at least not to the extent of the old ASAS units. My SSTO fleet are pretty much grounded unless they reintroduce the old, aggressive, wobbly ASAS. Rockets still work fine (didn't bother checking before since I don't like rockets)

Edited July 28, 2013 by littlebattler

[dlmarti]

Correct me if I'm wrong but the new system should still attempt to maintain heading right? For some reason it does not properly use the gratuitous amounts of control surfaces I have applied on my spaceplane, causing it to crash right after leaving the ground (the centers of lift, thrust and mass are not perfectly aligned, but within tolerable limits for the old ASAS). And yes I am in 21.1

EDIT: NVM it no longer locks the heading, at least not to the extent of the old ASAS units. My SSTO fleet are pretty much grounded unless they reintroduce the old, aggressive, wobbly ASAS. Rockets still work fine (didn't bother checking before since I don't like rockets)

It does lock the heading if you have it turned on, but yes, it is not as aggressive.