Large aperture segmented space telescope (LASST): Can we control a 12 000 segment mirror?

The primary mirror diameter of affordable space telescopes is limited by mass and manufacturing cost. Currently planned optical/near-IR space telescopes use a segmented primary mirror with relatively few segments, and make limited use of real-time position control. However, control can be used as an enabler for a fundamentally different, very highly segmented architecture, leading to a significant reduction in areal density, and hence a significant increase in the realistically achievable diameter of a space telescope. Small segments can be thinner, and overall mirror stiffness provided by control rather than a back-support structure. However, the resulting control problem involves thousands of actuators and sensors, and many lightly damped modes within the bandwidth. A local control approach similar to that previously developed for large deformable mirrors can provide robust performance for this problem. This is illustrated here for a 30 m diameter primary mirror composed of 12 000 0.3 m diameter segments. The areal density might be as low as 3-4kg/m², nearly an order of magnitude lower than current designs.