Currently in orbit satellite electrical power system demands are doubling every five years, forcing the spacecraft designer to look for options to solve the power availability problem. The need for high performance solar arrays for space applications continues to increase, as the energy budget of satellites becomes ever higher, and power systems become constrained by either total mass or stowed volume. Solar cells industries have stepped up to this challenge by developing new innovative designs that will increase efficiency and decrease cells weight. Two approaches are being pursued to enable higher power levels on satellites systems. The first approach is to increase the efficiency of the solar cells used on state-of-the-art flat panel solar arrays thereby  increasing the total power delivered to the payload for a given array size. The second approach is to utilize thin film solar cells that can be efficiently stowed, possess greater radiation hardness, and are lightweight and less costly. Solar cell efficiency is the most significant parameter to optimize in order to achieve minimum mass and volume of the solar cell and therefore the power system. Due to the extreme nature of the low earth orbit environment, solar cells are subject to possible damage; most commonly, a radiation damage, which affects all the cells similarly. Radiation causes a constant slow degradation of a solar cell performance. The probability of damage increases with increased mission time, therefore most of these effects can be discounted for short mission times. In order to use the GaAs/Ge or the InGaP/GaAs/Ge solar cells for space applications more efficiently, it is essential to predict their tolerance to irradiation by high energy electrons or protons. This paper reports on the electron or proton irradiation effects on GaAs/Ge and InGaP/GaAs/Ge space solar cells. The paper compares the electrical properties of GaAs/Ge and InGaP/GaAs/Ge space solar cells regarding electron and proton irradiation. The results for the effects were produced by simulation for different energies over a range of 0.5 to 12MeV and fluences ranging from (109,1010, 1011 to 1012 cm-2).