  In the development of space-based large telescope systems, having the
capability to perform active optics correction allows correcting wavefront
aberrations caused by thermal perturbations so as to achieve
diffraction-limited performance with relaxed stability requirements. We present
a method of active optics correction used for current ground-based telescopes
and simulate its effectiveness for a large honeycomb primary mirror in space.
We use a finite-element model of the telescope to predict misalignments of the
optics and primary mirror surface errors due to thermal gradients. These
predicted surface error data are plugged into a Zemax ray trace analysis to
produce wavefront error maps at the image plane. For our analysis, we assume
that tilt, focus and coma in the wavefront error are corrected by adjusting the
pointing of the telescope and moving the secondary mirror. Remaining mid- to
high-order errors are corrected through physically bending the primary mirror
with actuators. The influences of individual actuators are combined to form
bending modes that increase in stiffness from low-order to high-order
correction. The number of modes used is a variable that determines the accuracy
of correction and magnitude of forces. We explore the degree of correction that
can be made within limits on actuator force capacity and stress in the mirror.
While remaining within these physical limits, we are able to demonstrate sub-25
nm RMS surface error over 30 hours of simulated data. The results from this
simulation will be part of an end-to-end simulation of telescope optical
performance that includes dynamic perturbations, wavefront sensing, and active
control of alignment and mirror shape with realistic actuator performance.
