This paper discusses future electrical power requirements for various possible space missions. Probable time frames are included wherever possible. Three categories of missions are considered: earth orbital operations including communication and weather satellites, manned orbiting laboratories, and scientific satellites; lunar operations in the post-Apollo era; and intrasolar system operations including manned and unmanned planetary missions, solar probes, and out of the ecliptic probes. Power levels necessary to support the missions vary widely; various levels from a fraction of a kilowatt to hundreds of kilowatts are discussed. This paper reaffirms the conclusion reached by a growing number of people that the availability of electrical power may pace future space explorations.