Nuclear power is still a genuinely new domain with respect to space exploration. The field is still in its infancy, despite of over 60 years of peaceful exploitation of nuclear power on Earth, and many successful applications in space. Nuclear power sources are very compact and may be used for local power generation or as a source for propulsion in advanced thrusters. Fission batteries experience drastic limitations with respect to the energy that might be stored on board a spacecraft, due to criticality issues. Fusion batteries remove this impediment, but fusion energy is in an early stage of technological research. Today, the best propulsion systems are inertial, jet based electric thrusters, providing a owerful source of efficient propulsive energy, but even with the development of these thrusters, travel throughout the solar system within reasonable time scales is unattainable. In the absence of other superior, physics-based propulsion concepts, nuclear-energy-powered jet propulsion may take us to the limits of our solar system, but no further.