How does the gravity gradient pointing work?
Any two differential accelerometers will measure slightly different common mode accelerations if they are at slightly different heights in the Earth’s gravity. The difference in their common-mode gravitational acceleration will be A =gDH, where DH = L sin q is the difference in height for two accelerometers separated by L, q is the angle L makes wih the horizontal, and g is the gravity gradient. This acceleration is used as an error signal in much the same way as the mass centering; but the controller uses the angle q, i.e. satellite attitude, as a control input to minimize A, rather than the distance between mass centers. Why is the gravity gradient disturbance at twice the signal frequency? It’s a matter of geometry. The gravity gradient is symmetric about the horizontal plane, while the total gravity is not. So when the experiment rotates, the gravity gradient changes direction twice per rotation, and the total gravity only once. The illustration shows how the total force and differ
Related Questions
- Why is the electrolyte specific gravity in the DYNASTY VRLA battery (1.300) higher than that used in an automotive (SLI) battery (approximately 1.260)?
- If the dirt under the dome is chewed away, would the dome be subject to gravity (a physical force)? Would the sphere and its occupants fall?
- How does the gravity gradient pointing work?
