A Deployable Telescope for Sub-Meter Resolutions from MicroSatellite Platforms

摘要

Sub-meter resolution satellite imagery serves a more and more important role in applications ranging from environmental protection, disaster response and precision farming to defence and security. Earth Observation at these resolutions has long been the realm of large and heavy telescopes. The costs of building and launching such systems are enormous, which results in high image costs, limited availability and long revisit times. Using synthetic aperture technology, instruments can now be developed that can reach these resolutions using a substantially smaller launch volume and mass. In this thesis, a conceptual design is presented of a deployable synthetic aperture instrument. The instrument can reach a ground resolution of 25 cm from an orbital altitude of 500 km. In terms of resolution, the system is compliant with current state-of-the-art systems, such GeoEye-2 and Worldview-3. With an estimated mass of 75 kg, the system is significantly lighter than conventional solutions. The thesis covers the optical and mechanical design of the instrument as well as the calibration strategy and required image processing techniques. The optical design of the deployable telescope is based on a Korsch Three Mirror Anastigmat. The entrance pupil of the instrument consists of three rectangular mirror segments that, when deployed, span a pupil diameter of 1.5 meters. To ensure that the telescope can deliver a deliver a diffraction limited performance while operating in a harsh and dynamic space environment, the telescope features a robust thermo-mechanical design, aimed at reducing mechanical uncertainties to a minimum. In addition, the system will feature an in-orbit calibration system. Following the launch, actuators beneath the primary mirror segments will correct the position of the mirror segments to meet the required operating accuracies. During operations, a passive phase diversity system will be used. This system can retrieve residual wavefront errors and use that knowledge to restore the image with a Wiener deconvolution filter. Using this approach, an almost diffraction limited image quality can be achieved in all operating conditions.