[en] This paper describes the Pellet Bed Reactor concepts for both nuclear thermal and nuclear electric propulsion applications. This annular core, fast spectrum reactor offers many desirable design and safety features including high power density, smaller size, full retention of fission products, passive decay heat removal, redundancy in the reactor control system, and the option of fueling on the launch pad, or fueling and refueling in orbit. In addition to these features, the concept for nuclear electric propulsion has no single point failure. The average power density in the reactor for nuclear thermal propulsion ranges from 2.2 to 3.3 MW/liter and for nuclear electric propulsion the total power system specific power is about 3.3 kg/kWe. 29 refs