Flexure-based pointing mechanism with sub-microradian resolution for the Laser Interferometer Space Antenna

The Point Ahead Angle Mechanism (PAAM) for ESA’s Laser Interferometer Space Antenna (LISA) mission will compensate the out-of-plane point-ahead angle between three satellites flying 5 million kilometres apart. The PAAM consists of a mirror supported by flexures allowing the mirror to rotate with a maximum stroke of ± 412 rad. The mirror is actuated in 0.14 μrad steps by two redundant linear Piezo LEGS® actuators driving a sine-bar. Since the actuators are self-locking, a special lever performing the role of a linear mechanical differential is used to provide redundancy. The angle is driven in closed loop using two capacitive sensors.