ESA GNC Conference Papers Repository

High accuracy line-of-sight stabilization for geo high-resolution earth observation missions with onboard optical correlator: imaging performances estimation
V. Chernykh, K. Janschek, B. Harnisch
Presented at:
Salzburg 2017
Full paper:

High-resolution GEO observations require an ultra-high Line of Sight (LoS) stability to avoid motion blur and Modulation Transfer Function (MTF) degradation. Traditional solution based on the satellite attitude measurements with the star sensors can be insufficient due to the accuracy/bandwidth limitations and non - rigidity of the satellite structure. This paper presents the results of the analysis of an alternative solution for pointing instability compensation based on the precise real time measuring of pointing vector during integration time directly in the focal plane (visual feedback) with on-board optical correlator: for each scene a sequence of short-exposed sub images is taken, sub-images are mutually registered and stacked; thus the relative pointing error is compensated. The optical correlator is capable of extremely fast determination of the images misalignment with subpixel accuracy, even with low SNR and poor image contrast. With customized optoelectronic components it is also suitable for compact realization with low power consumption. This solution makes it possible to significantly relax the requirements for the attitude stability of the high-resolution GEO observations satellite and to minimize motion blur and MTF degradation. The paper provides the imaging performances estimation made for two telescope apertures (4.1 and 1.5 m) and two attitude instabilities scenarios ('normal' satellite and 'quiet' platform with vibration isolator). The performances have been estimated as a result of the tests performed with simulated images and a real time testbed with a breadboard model of the optical correlator. The paper also describes the results of the vacuum compatibility and radiation tolerance (TiD) tests of the key optoelectronic components as well as the vibration tests of the optical system of the optical correlator. As a result of the tests, limitations of the basic approach due to the interpolation effects and LoS instability during the sub-images exposure have been observed. The paper also addresses the perspective of further performance improvements by the active LoS stabilization during frame integration with a steerable mirror, a high frames rate image detector and the optical correlator in the control loop. Challenges of the practical realization of visual feedback in this case (fast processing of extremely dark and noisy images) are addressed as well as the advantages of the optical correlator - based solution. Acknowledgements: This work was supported by ESA Contract No. 4000107477/12/NL/CP (Optical Correlator Testbed for High Resolution Imaging from Geostationary Orbit)