Compact Wide-Field Space Telescope with Freeform Optics: A ZEMAX based Kepler Space Telescope

Future space based observatories have to adhere to stringent SWaP (Size, Weight, and Power) limitations while maintaining high sensitivity and ultra wide fields. The rotationally symmetric Schmidt corrector of the traditional Kepler space telescope caused field dependent aberrations close to the edge of its large focus plane, despite the telescope's success in finding exoplanets. This study reimagines a small freeform Kepler Space Telescope utilizing ZEMAX Opticstudio. A new freeform surfaces is added with a Zernike Fringe Sag freeform surface to correct non-rotationally symmetric aberrations while maintaining throughput and compactness. During optimization, a modified merit function minimizes RMS Wavefront Error and enforces SWaP restrictions. MTF and field curvature data demonstrate better off-axis performance and image uniformity as compared to the conventional design. While Tolerance analysis and Monte Carlo simulations validate manufacturability under practical slope restrictions. This work demonstrates how historical telescopes such as Kepler Space Telescope can be transformed into more high performance platforms for future exoplanet and wide field photometry missions. It also highlights the broader potential of freeform optics to improve upcoming small satellite and CubeSat observatories.