One embodiment of the invention provides an airship having an outer tube formed in the shape of a toroid and defining a central opening, a first compartment positioned within the outer tube and containing a first gas, and a second compartment positioned within the outer tube and containing a second gas. The airship may also include top and bottom covers further defining and enclosing the central opening, the central opening containing the second gas, and a controller that controls the flow of the first gas into and out of the first compartment to actively control the ascent and descent of the airship.