JAXA is currently carrying out development of lightweight and flexible thin-film solar cells for space application. The cells are thin-film III–V multi-junction solar cells with high efficiency and CuInGaSe2 solar cells with super radiation tolerance. The electrical performances of InGaP/GaAs dual-junction solar cells and CIGS solar cells in space have been demonstrated by JAXA's small satellite, which flew in a Low-Earth Orbit since January 2009. This flight demonstration is the first experiment for a thin-film III–V multi-junction solar cell in the world. Thin-film solar cells were laminated using transparent polymer film in place of conventional coverglass for protection of solar cell's surface. The film-laminated cells were observed for short-circuit current degradation. The ground tests in which atomic oxygen, charged particles and ultraviolet rays were irradiated to the cells and films indicated that the cause of the degradation was attributed to the film coloring by obliquely incident UV rays. This is because the lamination film has UV-reflective multilayer coating on its surface and the optical properties vary depending on the UV incident angle. The flight degradation trend of short-circuit current was, therefore, predicted using the ground test results taking into account the incident angle dependence. The flight data and the predicted results were in reasonable agreement with each other. Thus, we could verify the validity of the ground tests and prediction methodology for film-laminated solar cell in this study. Copyright © 2010 John Wiley & Sons, Ltd.