Very-low altitude parasitic radar distributed on small satellites

This paper presents an original approach for a radar-based distributed system. The novel mission concept foresees a formation of very low altitude parasitic small satellites capturing the signal transmitted by existing LEO SARs in C and X bands. Both orbital analysis and radar performance estimation are performed. In order to increase the number of potential illuminators and achieve limited lifetimes, the receiver is supposed to be in a very LEO (altitudes between 300 and 350 km), below the transmitters that generally orbit around 500–800 km. The analysis of the orbital elements reveals that the loss of the initial configuration is mostly due to variations of RAAN. A reference scenario is thus considered with COSMO-SkyMed as transmitter and a small satellite as receiver. The latter is the reference unit of the receiving cluster that forms the sparse passive antenna. Simulation results show the initial patterns are lost in a few days unless some design strategies are used to preserve the desired acquisition geometry over long times. Furthermore, the analysis focuses on the piece of relative trajectory with the receiver in the proximity of the transmitter when the signal acquisition becomes possible. The impact of acquisition geometry on imaging performance is evaluated and spatial resolutions of 6 m (along the range) and 14 m (along the azimuth) are estimated as the best achievable values. The coverage potential of the radar is then computed in terms of areas acquired with good imaging capabilities, strongly limited to guarantee a near-rectangular shape of the pixels. Finally, power considerations as a function of receiving antenna area are carried out. Results show that good SNR value are achieved by a total antenna area of 10 m2, which can be usefully split over a ten of platforms.