The Warshawski sail was a gravitic technology, and a key component to interstellar travel in the Post Diaspora era.
The sail was an adaptation of the usual gravitic node used in the impeller drive. It was an extended force field at the bow and stern of a starship perpendicular to the axis of the ship. It served as a way to control the forces which gravity waves produced in hyperspace and thus greatly increase safety. It extended several hundred of kilometers and coruscated colorfully with the energies it handled. The sail was ineffective in normal space, but invaluable in hyperspace. Additionally, the sail could tap into the large energy fluxes in hyperspace and so provide enough power to essentially run the entire ship during its time in hyperspace. This reduced fuel expense considerably, making star transport, even of large masses, economically feasible.
The gravitic nodes used to produce the sail had to be tuned to work with each other properly, and if sufficiently out of tune, a sail could fail catastrophically. Maintenance was important as the nodes and tuners used for sails endured considerable stress and had to be replaced, at high expense, relatively often compared to the life of a starship.
The sails themselves were invisible to the naked eye, but the energies they handled not only could be seen, but most people thought them beautiful, in the way that planetary auroras are. (HH2)