Pico-Sat to Ground Control: Optimizing Download Link via Laser Communication

Abstract

Consider a constellation of over a hundred low Earth orbit satellites that aim to capture every point on Earth at least once a day. Clearly, there is a need to download from each satellite a large set of high-quality images on a daily basis. In this paper, we present a laser communication (lasercom) framework that stands as an alternative solution to existing radio-frequency means of satellite communication. By using lasercom, the suggested solution requires no frequency licensing and therefore allows such satellites to communicate with any optical ground station on Earth. Naturally, in order to allow laser communication from a low Earth orbit satellite to a ground station, accurate aiming and tracking are required. This paper presents a free-space optical communication system designed for a set of ground stations and nano-satellites. A related scheduling model is presented, for optimizing the communication between a ground station and a set of lasercom satellites. Finally, we report on SATLLA-2B, the first 300 g pico-satellite with basic free-space optics capabilities, that was launched on January 2022. We conjecture that the true potential of the presented network can be obtained by using a swarm of few hundreds of such lasercom pico-satellites, which can serve as a global communication infrastructure using existing telescope-based observatories as ground stations.

Deep Learning-Based Small Target Detection for Satellite–Ground Free Space Optical Communications

“…To align the receiving aperture of the GS with the satellite, telescopes equipped with a tracking system can be exploited [11]. Using TLE parameters, the tracking system aims the telescope towards the estimated position of the satellite as it moves across the sky.…”

“…TLE is a standard format for encoding a satellite's orbital information, describing the orbit and position of the satellite at a particular time. Each satellite's TLE can be detected, tracked, and updated by the North American Aerospace Defense Command (NORAD) [11], which tracks and monitors satellites using radar systems and optical sensors to generate the TLE. However, this method only guides the telescope to the expected range of the satellite's position, which is not precise enough to establish the FSO communication link [11].…”

“…Each satellite's TLE can be detected, tracked, and updated by the North American Aerospace Defense Command (NORAD) [11], which tracks and monitors satellites using radar systems and optical sensors to generate the TLE. However, this method only guides the telescope to the expected range of the satellite's position, which is not precise enough to establish the FSO communication link [11]. Note that conventional telescopes equipped with a tracking system at the ground station are more suitable for tracking slow-moving space objects such as stars or planets rather than tracking fast-moving LEO satellites.…”

“…Since the orbit of LEO satellites such as nano-and pico-satellites tend to shift more quickly than those of bigger satellites, their TLE accuracy is very low [10]. Furthermore, GS-based telescopes equipped with a tracking system are more suitable for tracking slow-moving space objects such as stars or planets rather than tracking fast-moving LEO satellites [11]. Due to the narrow FOV and slow tracking, slight changes in the angle of the GS-based telescope can cause LOS connection failures for LEO satellites.…”

“…The LED source can appear as an artificial star, and it can be captured using a wide-FOV camera at a GS. Experiments on the detection of a satellite as an artificial star in an image for visible light communication (VLC) have been addressed in [11,12]. While the LEO satellite transmits the light signal, a camera with a wide FOV at the GS can capture images containing the LEO satellite as a small target.…”