Design of Nano-satellite Cluster Formations for Bi-Directional Reflectance Distribution Function (BRDF) Estimations

The bidirectional reflectance distribution function (BRDF) of the Earth’s surface describes the directional and spectral variation of reflectance of a surface element. It is required for precise determination of important geophysical parameters such as albedo. BRDF can be estimated using reflectance data acquired at large 3D angular spread of solar illumination and detector directions and visible/near infrared (VNIR) spectral bands. This paper proposes and evaluates the use of nanosatellite clusters in formation flight to achieve large angular spreads for cheaper, faster and better estimations that will complement existing BRDF data products. In this paper, the technical feasibility of this concept is assessed in terms of various formation flight geometries available to achieve BRDF requirements and multiple tradespaces of solutions proposed at three levels of fidelity – Hill’s equations, full sky spherical relative motion and global orbit propagation. Preliminary attitude control requirements, as constrained by cluster geometry, are shown to be achievable using CubeSat reaction wheels.