Reliability is one of the most important aspects for any system onboard a satellite. This paper discusses different failure conditions and a fault-tolerant design of an active spherical phased array antenna (SPAA). This SPAA is having a hemispherical scan coverage for transmission of satellite imagery data at high bit rates to the ground station. Different failure conditions are identified and a criticality rank has been assigned based on their effects on the overall performance of the SPAA. Two entirely different configurations of the array are chosen to select the best one considering the failure effects. Based on these analyses, a rational margin is built such that the array can take care of even the most critical failure condition. This paper provides an insight toward the realization of a reliable phased array and thus useful for a practicing antenna engineer involved in designing antennas for the spacecrafts.