Velocity control?

[drbitboy]

So what is controlling the velocity from millisecond to millisecond?

It would start with an ongoing re-calculation of the desired inertial angular velocity dΘ/dt = dThDtTDI - vFb cos²Θ / deltaY, then be offset for any measured inertial rotational velocity (in the trajectory plane), of the spacecraft and/or instrument pointing platform, and then converted from angular velocity to step rate in Hz. So it's more bookkeeping than complicated.


However, final conversion is what brings up this second statement.

The trick is being able to follow a velocity profile as you show in your document where the angular velocity of the mirror is changing very slowly. At slow speeds the encode[r] must have very high resolution or be geared down a lot so the velocity doesn't change in steps determined by the encoder resolution.

That's a good point. The observation could possibly be designed so that the expected range of Hz does not get into such a region.