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Advances in Spectroscopic Characters of Space Objects.

Spectroscopic characters of space objects are basic optical attributes which could stand for the material types of space objects. By comparing actual spectral characteristics with that obtained in the lab, the types of space materials can be identified, which is beneficial for the analysis of working states and compositions of space objects. Aiming at the problems of spectrum measurement and material information retrieval, the spectroscopic theory, retrieval methods and reddening effect of space objects spectrum are analyzed in this paper. The contributions on the spectrum from 350 to 2 500 nm from vibrational spectrum and electrical spectrum are investigated based on solid spectrum characters. Three methods commonly used in space objects material identification based on spectrum characters are studied, which are artificial neural network algorithm, particle swarm optimization algorithm and spectrum unmixing algorithm, and the features including spectrum reflectance and its derivative, center displacement are discussed. Reddening effect in spectrum measurement is studied, and it is shown that the reddening effect is related to the deoxidizing effect when some material access to space environments. The loose chemical bonds are formed due to the separation of oxygen and the combination of contaminations in space, which results in more absorptions of light energy and the higher slope of reflectance at longer wavelength that is named reddening effect. The reflectance of spectrum can be used to analyze material aging problems on the surface of satellite material under the continuous influences of harsh space environment, including chemical or physical changes, which are favorable for repairing existing satellite or launching new satellite.