⟨10egg⟩ For the orbit frame we have:
> The centre of <<A:1>> is fixed.
> The plane of its orbit around <<A:3>> is horizontal.
> The reference frame rotates with the orbit, fixing the direction of <<A:3>>.Currently for the frame of the Lagrange points we have, in the simple (single-secondary) case:
> The centres of <<A:3>> and <<A:1>> are fixed.
> The plane of their orbit is horizontal.
> The reference frame rotates with the orbit and pulsates to keep the <<nom:3>>–<<nom:1>> distance constant.I would like to have the description to be symmetric in that case, so we need to have both centres fixed, and thus we cannot talk about the direction of one (and indeed the third line is mostly redundant). But it makes sense to keep the third line, to make the nature of the motion clear, and because it is related to the orientation of the...
... navball.
How about:
> The centres of <<A:3>> and <<A:1>> are fixed.
> The plane of their orbit is horizontal.
> The reference frame rotates with the orbit, keeping the <<nom:3>>–<<nom:1>> line fixed, and pulsates to keep the <<nom:3>>–<<nom:1>> distance constant.