Solar cells are the prime power supply for satellites in space. Space is, however, a hostile environment for electronic devices, such as solar cells: in space the devices are subjected to large temperature cycles, atomic oxygen, space dust, meteorites, and high-energy charged-particle irradiation. In this thesis we present the development of a model with which the EOL-performance of hydrogenated amorphous silicon, solar cells can be predicted for a high-radiation space mission. For this development we have performed light-soaking, electron-beam, and proton-beam irradiation experiments on Hydrogenated amorphous silicon, layers and solar cells in order to study the degradation cell performance under these conditions. Furthermore, we present a procedure for the simulation of solar-cell performance degradation and this method has been applied to our measurement results to study some aspects of the degradation in more detail.