Attitude control and SAS - Tutorial Orbiting 101

[Mondriaan]

Hello i just started playing Kerbal and i like it very much, i am trying to follow the tutorials and i stumble on Orbiting 101.

When the craft is out of control you get two options to stabilize it, through Pitch-Roll and yaw and by using SAS, now i would like to do it official because there was once an astronaut (or cosmonaut) that had this uncontrolled movement in his craft, this was i believe before they invented this stability controls.

He managed it to get safe back to Earth.

I also would like to handle this manually but when browsing for example youtube i cant find a real good explanation, they managed it to stabilize but i dont believe that they can do it again.

I think i need more info input outside the navball to view pitch-roll and yaw.

Can somebody help because SAS works very good but...... When SAS would fail (it can happen in real spaceflight).

 

Thank you, stay healthy and safe flights.

Mondriaan

[Wobbly Av8r]

Not sure if this information is what you're looking for, but stabilizing a tumbling vessel is a matter of technique, and good technique is a matter of understanding both what your instruments are indicating and having a mental process by which you analyze and make control inputs to correct the situation. With that concept established, controlling a wildly out-of-control vessel is relatively straight-forward: Slow down rotational movement first (yaw/z-axis) using Q & E keys, then choose to slow horizontal (A & D keys) or vertical movement (W & S keys) finally followed by slowing the movement you ignored at the second step. Identifying the direction of rotational motion is straight-forward by observing the direction the horizon line 'twists' on the navball even if the horizon line is only moving around wildly.

The reasoning for this is that as long as you are rotating about the z-axis, your x- and y-axes are swapping with each other every 90 defrees of rotation; thus it is important to slow/stop it first followed by focusing on ONE of the remaining axes to bring the situation under control most efficiently.

If I'm not mistaken, the incident you referred to was Gemni 8, a reminder that good old 'stick & rudder' skills are always good to have on standby!

Good luck!

Edited November 9, 2020 by Wobbly Av8r

[Mondriaan]

Oke i totally accept your explanation and i will keep on practising your way, thank you very much.

[king of nowhere]

yep. actually, the main skill there is being able to focus on the navball. if you will just look at the tumbling spacecraft, it will be hopeless. look at the navball, and try to figure out just one motion at a time. ok, the ship is wildly out of control, but let's ignore that and focus on seeing if it's actually spinning on its axis. let's fix that, then continue with another axis. if you can focus on one movement at a time, you'll do it

[Spricigo]

15 hours ago, Mondriaan said:

Can somebody help because SAS works very good but...... When SAS would fail (it can happen in real spaceflight).

Well, in stock KSP it wouldn't fail. As "step zero" you need to deliberately ignore the option is available (either by refraining to use it or adding  a mod that include failures to the game.) Even you don't have SAS avlable, just a brief activation of time warp makes all rotation goes away. It works even better than SAS for this particular purpose. 

It may also be useful (step .1, I guess) to have Advanced Tweakables enabled to limit reaction wheel's authority and/or thrust of RCS  (maybe tied to an Axis Group you are not using otherwise)

 

 

[RoninFrog]

1 hour ago, Spricigo said:

Well, in stock KSP it wouldn't fail.

There are some times when it can: for example, landing on Duna in career with a scientist and a probe core, and the probe loses connection.

[Spricigo]

@RoninFrogMaybe I'm arguing semantics here. But,  if SAS turn off because the craft is not setup to have SAS in the current situation, I don't call it  'SAS fail". 

[king of nowhere]

i've done challenges where i had to launch stuff without sas because i could not afford a module and i had to prioritize other things than sending a pilot. including doing mun landings without sas, keeping manually aligned retrograde.

so, i can testify that managing without sas is indeed something that may turn out useful

[vv3k70r]

On 11/9/2020 at 1:45 PM, Mondriaan said:

He managed it to get safe back to Earth.

Atmosphere helps capsule to align corectly. So if You touch the atmosphere with LEO speed falling down is guaranted. Vector in the atmosphere from such an orbit and such engines have chance to not be significant to orbital velocity to cause suicide angle. It kill speed in low dense atm before it burns.

Whatever direction You burn the engines there is slighty chance to higher Your orbital velocity on LEO so You get to touch with atmosphere anyway in some point of the not enough circular orbit.

On 11/9/2020 at 1:45 PM, Mondriaan said:

Can somebody help because SAS works very good but...... When SAS would fail (it can happen in real spaceflight).

When You dock to many spacecrafts (for example very long chain of refueling ship to get asigment on fuel number done) together SAS would not help - it will only makie it wobling so You gonna do all this corections and manouvers by hand. Good design = You can control spacecraft manualy and kind of stabile it by shifting COM and trust.

It comes with practice. Then You gonna realize that orbital drift of such a monstrosity is a significant factor.

Navball is all You need to navigate - kill rotationQE, than other factors. After some practice there is no need an SAS to fly.

 

 

 

 

 

Edited November 11, 2020 by vv3k70r