The quest to study extra-solar planets and search for extra-terrestrial life becomes stronger and stronger as we learn more about our solar system. However, the resolution of any optical instrument is ultimately limited by diffraction at its entrance pupil. Higher spatial resolution in astronomical imaging thus requires telescopes with extremely large apertures. This presents a particularly difficult challenge for space telescopes because rockets for launching these telescopes will always have limited dimensions.
The only solution to deploy a telescope with a mirror of more than 10 m in diameter is to unfold a segmented mirror in space or to assemble a mirror in space from several pieces. However, this will invariably lead to optical aberrations because it will not be practical to achieve a sufficiently accurate surface across the full diameter of a segmented mirror. In addition, temperature gradients have a strong influence on large mirrors and will warp their surface. Correcting the aberrations of the large segmented primary mirror of a space telescope by an adaptive deformable mirror is therefore required. A deformable mirror that can operate in space is thus a prerequisite of any meaningful effort to study large segmented space telescopes.
We are currently developing and testing a novel deformable mirror that can withstand the harsh space environment. This work is performed in the framework of a large contract for the European Space Agency. The mirror has to endure temperature changes from 100 K to 300 K, strong ionizing radiation, and severe vibrations during launch.