Practical spinning solar sails will be needed for the most demanding and scientifically compelling solar sail missions of the future. The "heliogyro" is potentially the most feasible high-performance spinning architecture, although technology readiness is very low and deployment and flight dynamics are impossible to validate on the ground. A pathway towards an affordable flight demonstration of a practical heliogyro spinning solar sail will be required to realize the full potential of solar sailing for solar system exploration and science missions.
The "HELIOS" heliogyro solar sail concept, developed as part of this project, has a theoretical characteristic acceleration performance 5 to 10 times that achievable with current in-space propulsion technologies. This is sufficient to provide a lower-cost alternative to long-duration solar electric propulsion missions. Missions where practical, heliogyro solar sail technology would be enabling or significantly enhancing include space weather solar storm early warning sentinels, multiple-NEO rendezvous human exploration precursor missions, pole sitters for terrestrial and lunar communications relays, Earth-Mars cargo conveyors for supply prepositioning, and asteroid deflection missions. These "fast" heliogyro solar sails would also enable many space science missions that are impossible to perform with chemical or electric propulsion. These include high-inclination solar polar imaging spacecraft, inner solar system sun-synchronous orbiters, Kuiper belt fly-throughs, and interstellar probes.