Active optics for space telescopes

Active optics has been used on new, ground-based telescopes since the 1980s. It is used to maintain telescope alignment and generally operates at a much lower temporal frequency than adaptive optics. It can allow lighter optics for space telescopes and has been under development for this application since the 1960s. It has been spectacularly successful in the case of the 6 m JWST, thus paving the way for future, even larger segmented space telescopes. Approaches to active optics for monolithic space telescopes have also been developed, either actuating directly on the telescope mirrors or using a small deformable mirror at a relayed pupil image. Several different types of active mirrors have been developed for this purpose. Finally, picometer-level wavefront control will be necessary for the detection of exo-Earths using space telescopes, and this requires precise wavefront sensing and correction.