Circular sails are large, spinning disks supported only by lightweight tension lines to carry loads except at the center, where a structure is needed to carry loads between the payload, control system, and sail. The Jet Propulsion Laboratory studied a solar sail design similar to those shown below in the late 1970's for a rendezvous with Halley's comet.
The pictures below are the original images for this page that were rendered with the Persistance of Vision Ray Tracer (Povray). This sail is controlled by allowing sail panels to move outwards so sunlight pushes off center to turn the sail. Select here for the Povray source.