Proton and electron irradiations induce the degradation of space solar cells. The rate of the degradation depends on the current regime in the junction; it is four times lower when the cell is in the diffusion current regime than in the recombination regime. The analysis of the current regime shows that the diffusion regime is predominant for voltages larger than a critical value, which reduces with large values of the surface recombination velocity, small-base doping levels and increasing concentration of recombination centres. We examine the conditions for which we can keep as minimum the degradation rate under irradiation. (c) 2005 Elsevier B.V. All rights reserved.