Don't know how SAS works exactly

[Llorx]

Hi,

I have a question. Everywhere I read that you must add a SAS module so when you press T key SAS is enabled and working, but I've done some testings and only with a pod, RCS fuel and some RCS thrusters, when I press T while the pod is unbalanced on the launchpad seems that the pod tries to balance itself, and if I activate the RCS system, the pod automatically balances itself using them.

I was testing this because I read the SAS will add torque and ASAS will use RCS and wings and I find this useful because when I'm docking I want my ship stay quiet with SAS and without using RCS, so I can use RCS only for maneuvers, the bad thing is, as I told before, when I press T seems that SAS will use RCS altough I don't added any SAS/ASAS module.

Why I need to add a SAS/ASAS module if seems that the pod already comes with ASAS? And, how can I enable only SAS so RCS fuel is not depleted?

PD: Tested in a plugin-and-non-stock-part-free game.

Edited July 31, 2013 by Llorx

[dlmarti]

http://forum.kerbalspaceprogram.com/showthread.php/42825-Long-wordy-explaination-observations-about-the-new-0-21-Attitude-Control-System

[Lheim]

Hi,

I have a question. Everywhere I read that you must add a SAS module so when you press T key SAS is enabled and working, but I've done some testings and only with a pod, RCS fuel and some RCS thrusters, when I press T while the pod is unbalanced on the launchpad seems that the pod tries to balance itself, and if I activate the RCS system, the pod automatically balances itself using them.

I was testing this because I read the SAS will add torque and ASAS will use RCS and wings and I find this useful because when I'm docking I want my ship stay quiet with SAS and without using RCS, so I can use RCS only for maneuvers, the bad thing is, as I told before, when I press T seems that SAS will use RCS altough I don't added any SAS/ASAS module.

Why I need to add a SAS/ASAS module if seems that the pod already comes with ASAS? And, how can I enable only SAS so RCS fuel is not depleted?

PD: Tested in a plugin-and-non-stock-part-free game.

It has very recently changed. A lot of the advice you'll see on the net predates the changes.

So nowadays, every command pod or probe core comes with 'ASAS', which is just really a kind of automatic pilot.. when you put sas on it'll use what means it has at it's disposal to maintain the heading you put in; that's rcs, control surfaces, engine gimballing, and reaction wheel torque.

SAS modules are in a weird place.. there's some that are still called sas, some just called inline reaction wheels. They are now basically things that give you reaction wheel torque, at the cost of electricity. Most command pods come with some amount of torque power, but some don't.

You can toggle RCS off by hitting R; then it won't be used.

Edited July 31, 2013 by Lheim

[Llorx]

I know that I can toggle off RCS, but I don't want to, I just want ASAS to stop using it while I use it. Seems that I have to add more RCS fuel tanks.

Going to read the link dlmarti posted.

Thank you for your replies!

EDIT: Really nice explanation in your thread dlmarti, thanx again.

Edited July 31, 2013 by Llorx

[Diche Bach]

I've noticed some very strange behavior with my multi-stage ship that I was using to try to setup a geosynchronous space station.

After the launch boosters the final vessel is basically two stages. Lower one is the orbital placement vehicle, top one is the actual station (cupola) but with a small engine and 720 tank. Both stages have smaller engines (the Poodles I think) and 720 Rockomax tanks, plus some RCS (and the large Rockomax size tanks) and battery disks. The lower stage has one of those unmanned 'pods' and the upper one also has some solar panels.

I noticed that the stock space station has two 'reaction wheels' when I took it apart so I copied this sort of (not knowing if those where there because of the multi-directional docking thing). The top of the cupola has a docking port and then one of the multi-directional docking hubs. In between the cupola and its docking port are the two reaction wheels (exact ones used in the stock space station and same order of stacking).

When I get close to 2868 km altitude and I am fine tuning my orbit to get it circularized, I start to notice some very strange behavior with the SAS on versus off.

As seems to be common, when you get to a very close to perfect circular orbit the periapsis and apoapsis markers start to quiver and waver, and this seems to relate to everything in the Navball and map view being a bit shaky. However, here is the part that seemed really weird and maybe it had to do with having too many SAS units in the vessel?

When I would set a maneuver and then time warp to get to it, both my maneuver trajectory marker and my prograde (and retrograde) markers would wobble and shuffle around the navball very erratically with SAS on, whereas turn it off and they were relatively smooth (only as shaky as I typically notice when doing the circular orbit adjustments).

Edited August 1, 2013 by Diche Bach

[DMagic]

As seems to be common, when you get to a very close to perfect circular orbit the periapsis and apoapsis markers start to quiver and waver, and this seems to relate to everything in the Navball and map view being a bit shaky. However, here is the part that seemed really weird and maybe it had to do with having too many SAS units in the vessel?

When I would set a maneuver and then time warp to get to it, both my maneuver trajectory marker and my prograde (and retrograde) markers would wobble and shuffle around the navball very erratically with SAS on, whereas turn it off and they were relatively smooth (only as shaky as I typically notice when doing the circular orbit adjustments).

That shakiness of the periapsis and apoapsis markers when you get close to circular always happens. When the two values get really close together the errors in the game will eventually get larger than the difference, so the markers bounce around a lot.

And having too much torque can definitely make you start shaking with SAS on. It's easy to see with just the 1-man command pod by itself. With SAS on it starts shaking a lot; if you decrease the torque in the .cfg file it goes away. But that thing about the prograde and retrograde markers moving is weird. The maneuver node marker can move around a lot when you have a very small maneuver (<1m/s), but I don't think I've ever seen the velocity vectors do that.

You can right-click on individual reaction wheel parts and command pods and toggle the torque on and off for that part. Try turning off torque in a few of the wheels (but leave SAS on) and see what happens.

[Diche Bach]

Ah DMagic. I will try that. I hadn't thought of turning off some of the reaction wheels