Imaging Space Debris and Small Targets with Space-Based Radars and Dynamic Satellite Constellations – First Tests

The risks caused by space debris are steadily increasing: objects large enough to be tracked from the ground exceed 18,000; small (1 – 10 cm) objects are conservatively estimated at 670,000; and many more, smaller, objects are thought to be present in LEO. Millimeter-size debris pose the highest penetration risks at these altitudes, although there is a dearth of direct measurements. In 2017 alone, NASA assisted in 21 collision avoidance maneuvers by uncrewed spacecraft, and cumulative impacts from small objects were mapped in different key areas of the International Space Station. Recent missions show promising approaches to remove the largest debris, but they also rely on knowing where they are and their physical surroundings.
To detect and characterize debris clouds and individual targets, we leverage recent developments in subsea acoustic imaging and radio-interferometry (Blondel et al., RISpace 2017). Detailed in UK Patent # GB2561238 (10/2018), they are based on the concept of a dynamic satellite constellation with multiple EM receivers and several potential transmitters, enabling multi-aspect of small targets like space debris, through bespoke signal processing (beamsteering, synthesis of virtual apertures and dynamic beamforming to create virtual pencil beams to interrogate
volumes of interest). Our presentation will present the first steps toward embodiment of this answer solution to derisk future space activities. Taking advantage of the adaptive and modular architecture of the proposed system, we are building the first experimental stage toward a scaled demonstrator, using different radar transceivers and adaptive processing of echoes from moving targets. The algorithms developed aim to be used on-board satellite nodes, with potential distribution of the most demanding tasks amongst neighboring nodes. This laboratory work is
supplemented with analyses of US and European orbital debris databases, to identify the LEO portions most at risk from collisions, and to match the expected orbits and velocities of debris with the detection capabilities of the satellite constellation (ranges, fields of view, reaction times afforded by different configurations). These calculations inform the types of radars needed (frequencies, powers), whether in space and part of the constellations, or groundbased
and used as sources of opportunities. Orbital constraints are used to match the number of nodes in the dynamic constellations with their respective positions, depending on propulsion modes and other considerations (general situational awareness).
This enabling technology will lead to accurate mapping of debris clouds and small debris causing risks to space assets, and greatly assist future debris removal missions. Although focused on Near-Earth application, this method is also suitable for activities beyond Earth’s orbit; the ASIME-2016 White Paper on meeting the needs of the space mining industry clearly showed the risks caused by small asteroids and dust, for prospecting spacecraft and during actual mining. By demonstrating in practice (but at scale) what can be achieved in space, we aim to make future
missions more affordable and more responsive, assisting future partners by de-risking their space activities, protecting their assets and delivering adherence to potential future regulations.