Frame reference question.

[valli]

Hi I am new to this forum. I didn't find a way to start new thread. That's why I am posting my question here. Currently I am doing a project on Attitude control. When I am studying literature, some papers using inertial frame as reference frame while some papers using orbit frame as reference frame. My question is when to take Inertial frame as reference frame and when to take orbit frame as reference frame?

[Vanamonde]

Hi valli. I'm one of the forum's moderators, and I have moved your post to its own thread. :D

I'm afraid I'm not clear about the nature of your question, though. I think science labs might be the best place for it, but could you describe the problem in more detail?

[Shpaget]

If no other requirements are present, usually you would pick the one that offers the easiest calculation.

[K^2]

Inertial frame does have a few advantages. The following three come to mind.

1) Old style INS would inherently be locked into inertial frame. This is no longer relevant, since we don't really rely on INS and modern computers can recompute to whatever coordinate system is more convenient, but this was a limitation for Apollo era missions.
2) External forces aside, once you have a hold on a given attitude in inertial frame, you'll stay on that attitude without taxing attitude control. This is not generally true of an arbitrary attitude in orbit frame.
3) It's convenient to do physics in an inertial frame. This is rarely relevant for ship in flight, but it's very convenient in simulation. So if you want to save a conversion step, you might want to stick to inertial frame.