FocusGEO II. A telescope with imaging mode based on image overlay for debris at Geosynchronous Earth Orbit

FocusGEO II is a telescope developed by Shanghai Astronomical Observatory for efficient observation of debris at Geosynchronous Earth Orbit (GEO). The telescope consists of an optical lens of 150 mm aperture and a high-frame-rate CMOS detector, forming a wide field of view of 10.5° × 10.5°. The telescope and related components are completely sealed in a 3D printed integrated shell, without an astronomical dome. It is mounted on a one-dimensional equatorial mount, which has the advantages of low cost, miniaturization and unattended. However, the small aperture will lead to a weak detection capability, the influence of stray light will be aggravated in the absence of a dedicated astronomical dome. A new imaging mode based on real-time overlay of high-frame-rate and short-exposure images is proposed, which can effectively increase the dynamic range of the system. The new imaging mode can detect objects 1.1 magnitude fainter than conventional imaging mode. When 20 images are overlaid to extend the effective exposure time to 10 s, the limit magnitude is 14.8 magnitude. The observation precision of GEO objects is about 2″ in azimuth and elevation. FocusGEO II can complete a scanning observation of GEO belt within ±5°of latitude direction in 21 min. 220 GEO objects can be observed per night on average, and the completeness of GEO objects with orbital inclination less than 5° above the station is more than 85% (refer to catalogue published on Space_track.org).