Space-unique fusion engine and flight system design parameters and operational principles permitting the use of fusion energy for space power and propulsion are presented. Solutions that meet those design parameters and operational principles are appropriately addressed during investigations and research on confinement designs for D-3He reactions. Once acceptable solutions have been found, space will then be an alternate customer for fusion energy. Key mission parameters are defined for consideration as advancements occur in design and testing of new confinement concepts. Power levels, thrust, firing duration, and mission quality aspects are presented. The importance of research on maintaining stability during burning while removing plasma for propulsion is considered a significant issue in making magnetic fusion reactors practical for space propulsion. Burning efficiency is important for long-duration missions. Space operation of a fusion reactor offers relief from the vacuum constraint that ground systems are required to meet, but space vehicles are mass sensitive, requiring the use of a fuel such as D-3He that produces charged particles as ash and requiring the use of compact reactors.