Microcontrollers form the computational backbone of modern space systems by enabling compact, low power, and real time control for sensing, actuation, communication and autonomous decision making in harsh environments. This paper presents a compara- -tive analysis of microcontrollers used in satellites, space probes, landers, and crewed habitats by examining processor architectures, on chip integration features, and mission driven performance requirements. Radiation hardening approaches including hardening by process, hardening by design, and commercial off the shelf strategies with mitigation are evaluated alongside power efficiency, thermal resilience, and fault tolerance mechanisms such as error correction, watchdog supervisi- -on, and hardware redundancy. The study highlights the trade-offs between radiation tolerance, power consumption, and reliability that govern device selection. Evidence from Mars rover missions and CubeSat deployme- -nts demonstrates the importance of autono- -mous operation, robust error management, and efficient energy use. Results indicate that radiation hardened microcontrollers remain essential for long duration and high criticality missions,while carefully qualified commercial devices enable rapid and cost-effective development for small satellites when supported by shielding and fault tolerant design strategies.