This chapter unveils the technology and design options for space reactor power systems and presented design and system integration choices to enhance the safety and reliability of these systems. It is also defined here that the use of these systems should not result in undue radiation exposure to people and astronauts, or damage to property, equipment or space assets. The information provided is offered to stimulate future discussion of the challenging subject of developing safety standards and guidelines for the launch and future peaceful uses of space reactor power and propulsion systems. These include the deployed-in earth orbits and their use for deep space exploration and surface power on the Moon, Mars, and other celestial bodies. Besides these, a number of space reactor designs and power system combinations, for enhancing safety and operation reliability, are presented and discussed. Various factors such as passive operation, decay heat removal, and the absence of single-point failures in the reactor design and the integration of space reactor power systems are desirable characteristics for enhancing safety and operation reliability. Additionally, the use and implementation of autonomous operation schemes and adaptive control capabilities would greatly improve safety and ensure mission success, particularly in deep space exploration. © 2010 Elsevier Ltd All rights reserved.