A high altitude balloon system includes a dual chamber balloon extending from an upper apex to a lower apex with a circumferential edge between the upper and lower apexes. A deflectable diaphragm is within the dual chamber balloon and coupled along the circumferential edge. The deflectable membrane divides the dual chamber balloon into a lift gas chamber formed by an interior surface of the dual chamber balloon and the deflectable diaphragm, and a ballast chamber formed by the interior surface of the dual chamber balloon and the deflectable diaphragm. Optionally, the dual chamber balloon is constructed by interposing the deflectable diaphragm between an upper and lower balloon panels. Each of the upper and lower balloon panels and the deflectable diaphragm are then coupled together along the circumferential edge to form both the lift gas chamber and the ballast chamber.