It's not tethered to the ground. It's a group of rotating "wings" tethered to each other in the centre, wherein the centrifugal force of the rotation give struc

It's not tethered to the ground. It's a group of rotating "wings" tethered to each other in the centre, wherein the centrifugal force of the rotation give structural stability. That way they get away with using less structural material, which means more of the weight can be batteries or fuel.