It's new because it is being done in the atmosphere. I work with Autonomous Underwater Vehicles (AUV) which have employed this method of propulsion for at lea

It's new because it is being done in the atmosphere. I work with Autonomous Underwater Vehicles (AUV) which have employed this method of propulsion for at least a decade. For AUVs the variable buoyancy is achieved by having an expandable bladder of fluid which can be contacted to allow ballast to enter or expanded to expel ballast. Check out Slocum gliders if you are curios