High powered optical amplifiers (HPOAs) are a key subassembly in free-space optical communication systems. As these free-space optical communications systems are being introduced into space applications, it is critical to assess the impact of the radiation environment present in space on the reliability of these systems. One key component in HPOAs is multimode laser diodes, which are used to pump gain fibers in the HPOA. The reliability of these laser diodes is very dependent on optical output power, with increases in optical power causing dramatic reductions in lifetime. At the same time, radiation darkening is a well-known problem that reduces the efficiency in HPOAs operating in environments with high radiation levels. We use Monte Carlo simulation to evaluate the impact of radiation darkening on the reliability of multimode pump ensembles over time. At radiation fields related to geostationary earth orbits (2 to 5  krad  /  year) radiation effects reduce multimode pump lifetime by a factor of 7-220 under typical use conditions. Use of redundant pumps operating under derated conditions can mitigate the impact of radiation.