A First Study of MMA Antenna Offset Performance

For scientific reasons, it must be possible to offset the MMA antenna pointing by 1.5 degrees within 1.5 seconds. To study the feasibility of this, a simple, lumped model of the antennas is set up and cascade controllers for velocity and position loops are added. It is found that the bandwidth of the position loop must be 3-4 Hz to achieve this. To avoid structural oscillations (“ringing”) after the offset, specially shaped input trajectories must be applied. It seems likely that feedforward in combination with such shaped input curves will permit fast offsets in pointing. Further studies to explore this possibility are pending.