How much reaction wheel leverage do I need?

[MaxwellsDemon]

I have a space telescope that's a tad difficult to train on a target that's far off...  when I maneuver the telescope, there's a bit of drift back and forth as SAS tries to settle it on target.  I was thinking I need to add more reaction wheels to make the training a bit more precise, but perhaps I'm going the wrong direction?   Might I actually be overpowered with my reaction wheels?   (What I have right now is the HECS probe's internal reaction wheels...)

[steuben]

One answer I've gotten in the past is 1kn of torque for each ton of craft.

[Kandréas]

Could you write down the stats of your space telescope (like weight, performance of the reaction wheel, ecc.)?
With that informations it'll be more easy to see if you are overpowered or not.

[natsirt721]

 In general, you are going to want less torque for fine-tuned attitude control such as a telescope requires.  You can achieve that by reducing the wheel authority slider in the HECS's RMB menu.  I would also recommend using fine controls mode (CAPSLOCK).  You also may want to disable SAS altogether and manually train the scope, which should be easier with fine controls.

If you are using the CactEye telescope, IIRC there are some high-precision gyros that you can use to really dial in on a distant target.

[bewing]

SAS is built on a very generic type of negative feedback system. And negative feedback systems do not ever settle down to a precise direction. They are always constantly hunting (it may be very high frequency/low amplitude hunting, but it's still there). The best you can do, I think, is to get your scope pointed in just the right instantaneous direction with SAS in "stability" mode, click timewarp for a second, kill timewarp, and then kill SAS.

 

[MaxwellsDemon]

3 hours ago, Kandréas said:

Could you write down the stats of your space telescope (like weight, performance of the reaction wheel, ecc.)?
With that informations it'll be more easy to see if you are overpowered or not.

0.724t, standard HECS reaction wheel of "0.5".

1 hour ago, bewing said:

SAS is built on a very generic type of negative feedback system. And negative feedback systems do not ever settle down to a precise direction. They are always constantly hunting (it may be very high frequency/low amplitude hunting, but it's still there). The best you can do, I think, is to get your scope pointed in just the right instantaneous direction with SAS in "stability" mode, click timewarp for a second, kill timewarp, and then kill SAS.

 

hmm.    More to think about.

I may have to mount the "repair the telescope again" mission just for the heck of it, though!   Seems the Kerbal thing to do.

[Kandréas]

Just now, MaxwellsDemon said:

0.724t, standard HECS reaction wheel of "0.5".

Well, I think you'll be okay with that.
Control manually the attitude of the telescope and point it where you want, then try to stabilize it the more as you can by yourself and only after that switch on the SAS on stability mode. Use the Precision Mode when doing this.