What are STEPs pointing requirements?
STEP has no pointing requirements in the usual sense of the term. Rather, STEP uses the satellite attitude as a control input to reduce gravitational disturbances from the Earth. It does not matter what the attitude is, so long as the disturbances are minimized. We can use whatever attitude does the job. The correct attitude is found by using the gravity gradient disturbance as an error signal. This disturbance is proportional to the angular deviation from the best attitude. Changing the attitude controls the disturbance, so we implement a feedback loop which corrects the attitude until the disturbance is nearly zero. Then the satellite will automatically be pointing correctly. The “correct” attitude which minimizes the disturbances will be a fraction of an arc second from the instantaneous orbit normal, but this should not be confused with a requirement. Because the error signal is internal we wouldn’t even need to know the attitude, if we didn’t need to know the roll rate and phase o
