Reliability, availability are extremely important aspects of the overall performance of a digital controller. The safety, in addition, becomes a vital aspect for the space flight applications. In otherwords, a space-flight controller ought to be fault-secure. The present paper presents an architecture, fault-secure and self-checking for a processor which is mainly intended for space-flight controllers. The fault-secureness of a processor means that it never produces an incorrect output due to a fault unless it simultaneously announces the occurrence of that fault. Different techniques of concurrent fault-detection are applied and self-checking circuits are used, which result in minimizing the mean-time-to-detection (MTTD). The error-indication signals aid the system fault-diagnosis which reduces to minimum the repair time. Thus, the system maintainability and availability are well improved.