The Space Exploration Initiative (SEI) calls for a return to the Moon and carrying out human exploration of Mars. Trips to Mars involve considerably more time and more complex operations than trips to the Moon; hence, there is a keen interest in developing better space transportation systems. Nuclear propulsion, either nuclear thermal propulsion (NTP) or nuclear electric propulsion (NEP), offers the potential of reduced trip times and/or reduced mass into low Earth orbit, compared to chemical propulsion systems . In addition, the greater performance benefits of nuclear propulsion can provide the added margin for greater operational flexibility, including mission abort options and increased launch windows. During the 1950\u27s and 1960\u27s, experimental and analytical studies showed the feasibility of nuclear propulsion. NASA, in cooperation with other agencies and organizations, is currently planning a technology development program for nuclear propulsion. The overall objective is to develop at least one NTP concept and one NEP concept for piloted and robotic (e.g., cargo) missions to Mars
