Control step length

[fe-de]

Control step length

[ericstoneking]

Hi Fede,

1. Look in your SC_foo.txt file, line 6 for your FSW sample time.
2. I'm guessing your installation is more than three weeks old :-) By request, I recently made a clear distinction between PULSED and PROPORTIONAL thrusters. See Docs/Thruster Modes.pdf for more.
3. What does RTN signify?

Regards,
-Eric

[fe-de]

Hi Eric,

thank you very much for your answers. I totally missed those two points...

Regarding the third point, I'd like to align the body axis of the S/C with the radial, along-track, cross-track frame (that is the LVLH frame). However, the torque commands needed to control the attitude are not provided by my external controller. If it's possible, I'd like to use one of the controllers already implemented in 42 on top of my orbit controller, but I'm not sure on how to do that. I'd like to call the function AcFsw(&S->AC) together with my controller, is there a standard way to do that?

Thanks,
Fede

[ericstoneking]

Hi Fede,

Radial/Track/Normal. Makes sense, I'd just never run across the acronym before. So in 42, the "L" frame is a permutation of it, so that part is easy enough.

There is no "standard" way, but I think you can cobble one together without too much trouble. Look in 42fsw.c:AdHocFSW(). It happens to be controlling to a permutation of L.

I'm a little unclear about your external controller, but if you're talking to it over a socket, then the call to it is in 42fsw.c:FlightSoftWare() in the CFS_FSW case. You can add a call near there to call your attitude controller, either AdHocFSW or something similar. Or you can add code to your external controller, either way.

Refer back to Docs/42 Overview.pdf and Docs/Nomenclature.pdf if you need to decypher reference frame notation.

Regards,
-Eric

[fe-de]

Hi Eric,

thank you very much for your helpful answer. I still have a doubt though. What if I need to operate the two controllers at different frequencies? It appears to me that I can call the AdHocFSW at each simulation step (instead of only at each FSW step) to enforce a higher frequency for the attitude control, but is it a good practice? I have some trouble in understanding the best approach to decouple attitude and orbit controls.

Thanks
-Fede

[ericstoneking]

Hi Fede,

Study the code. If you can understand how the FSW and sensors run at different sample times than the sim timestep, then you can figure out how to make your controller(s) run at the sample rate of your choosing.

Regards,
-Eric