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Anthropogenic Space Object attitude and material characterisation through multi-colour light curve inversion
Authors: Gonçalves, L.F.P.; Simone, N.; de Almeida, A.K.; Barbosa, D.; Jah, M.; Vaillant, T.; Coelho, B.; Correia, ACM;
Ref.: Acta Astronaut. 241, 378-408 (2026)
Abstract: Light-curve inversion for anthropogenic space objects (ASOs) is ill-posed when performed in a single band, which leads to non-unique combinations of attitude and material parameters. We present a physically grounded forward model based on a Cook-Torrance bidirectional reflectance distribution function, explicit shadowing by Earth and self-occlusion, and a satellite-centred geometry. We cast attitude-material retrieval as a constrained optimisation problem and use multi-colour light curves (Johnson-Cousins B, V, R) to regularise the inversion by coupling wavelength-invariant parameters. On four space objects of distinct morphology, the multi-colour constraint improves fit quality and narrows the admissible solution set relative to panchromatic inversions. We report parameter uncertainties from multi-start annealing and provide sensitivity of the fit to key BRDF and attitude parameters. Results support multi-colour optical surveys as an efficient path to unambiguous ASO characterisation from a single site.
