The secondary mirror
is a six-sided pyramidal aluminum mirror located 2.4 m above the
primary mirror. The mirror has a diamond fly cut in itÂ’s reflecting
surface at an angle of 5.15 deg that allows it to split the incoming
laser beam into six sub-beams.
The shape of the
mirror was developed by performing a geometric study of the trace
of the laser beam. A suitable geometry was found that would reflect
the incoming beam from the laser source to a point on the panels.
Furthermore, the returning beam is reflected back to the optical
sensors at the center of the primary mirror.
A series of springs
suspend the secondary from the secondary mirror housing. The secondary
mirror has three degrees of freedom in the form of a tip, a tilt,
and a piston motion.
It is equipped with
3 reluctance actuators to provide 3-axis active control and 3
inductive position sensors that provide information about the
secondary mirror attitude.