Human Missions Throughout the Outer Solar System: Requirements and Implementations, APL

"Distance scales and mission times set the top-level engineering requirements for in situ space exploration. To date, the implementation of various planetary gravity assists and long-term mission operations has made for a better cost-trade than technology development to decrease flight times. Similarly, crewed missions to date have not had mission time limits per se as drivers to implementation. However, unconstrained cruise times to the outer solar system are not acceptable for either robotic sample returns or human crews. Galactic cosmic ray fluxes likely provide a human limit for total mission times of ~5 years, and more restrictive limits may be driven by lack of gravity. We consider the implications for taking humans to the Neptune system and back, and, using this example, we deduce the minimum-cost path to realizing human exploration of the entire solar system by 2100."