Possible interference sources and their effects on Korea Multi-purpose Satellite (KOMPSAT) missions are investigated in this paper. Limited frequency resources allocated in space communications make many space programs share the frequency bands allocated to other programs. Interference sources can be divided into two categories-space and ground oriented sources. Both interference sources can degrade KOMPSAT mission performance when the sources are in the main and the first side lobe of the KOMPSAT ground antenna and the satellite antenna. Degradation is a function of interference source Effective Isotropic Radiated Power (EIRP), KOMPSAT EIRP, and the antenna-viewing angle. Possible interference situations are analyzed and the results are shown as normalized graphs relative to KOMPSAT EIRP.