An example reusable high-altitude balloon system includes a balloon with a first end supporting a payload and a second end with an aperture and an apex fitting that is positioned within the aperture. A clamp applies a pressure to a plurality of pleated folds formed in the perimeter of the aperture around the apex fitting to form an air-tight seal against the balloon at the perimeter of the aperture. The reusable high-altitude balloon system further includes control circuitry that controllably releases the apex fitting from the balloon to initiate a descent sequence.