To send astronauts back to the moon, NASA is planning to begin by making maximum use of existing U.S. and foreign rockets as launching systems. Vehicles under consideration may use updated propulsion systems that could blast a flotilla of spacecraft from the Earth to the vicinity of the moon. For voyages of longer duration, however — to Mars and possibly even more distant destinations — NASA is designing a whole new system for both space propulsion and space power. If successful, the system could provide future astronauts a swifter means of voyaging far beyond the moon and equip their ships and robotic scouts with far more electrical power than ever has been available to space missions before.