AllSky-Camera system for Monitoring of Optical Satellite Downlinks

Kurzfassung

Satellites widely use the Radio Frequency (RF) band for communications. However, the rapid expansion of Low Earth Orbit (LEO) in the last decade, driven by reduce costs, has led to larger volumes of data to be transmitted from these satellites (the same problem appears in deep space communications). Optical communications offer a solution, providing higher throughputs with reduced equipment volume, lower power consumption, all while avoiding of the regulatory restrictions and tariffs associated with RF. The main problem of space-to-ground links is that the need to face multiple loss-effects primarily due to three main factors: pointing-error losses caused by the satellite’s pointing precision; Free-Space Losses (FSL) resulting from the orbit geometry; and atmospheric effects and visibility problems such as atmospheric attenuation, scintillation, and obstruction. This could lead to miss the downlink, being difficult to assess exactly why did that happen. We hypothesized that a validation tool could be developed as a proof of concept to evaluate the failure point of the operation. Based on an Indium Gallium Arsenide (InGaAs) camera, the system can locate the satellite and estimating its elevation, azimuth and the received intensity at the camera compared to the expected intensity based on the link budget, all without requiring mechanical tracking. This tool is a waterproof enclosure capable of being transported anywhere with any issue. The camera is fitted with a wide-angle lens, providing a 140 degrees field of view, capturing most of the relevant hemisphere. We tested the lens to estimate the Field of View FOV, while the intensity calibration was performed using a method involving a Coarse Wavelength Division Multiplexing (CWDM) and a radio tower equipped with a 1550 nm laser. The entire system is controlled by a Python project named ”allsky4oleodl,” composed of eight different scripts. Our findings indicate that the device successfully detected the satellite on occasions when the Optical Ground Station (OGS) did not, proving the proof-of-concept successful. If further developed and tested, this tool could become a critical standard component of Optical Low Earth Orbit Downlink (OLEODL) systems in the future.