The concept of buoyancy propulsion is investigated for a lighter-than-air platform in the upper- stratosphere. This alternative to conventional thrust propulsion requires a cyclical change in net buoyancy (buoyancy minus weight). Methods have proved efficient in water. ?Underwater Gliders? undertake long missions covering vast distances using little power. High altitude, long endurance craft can perform many functions provided by satellites at potentially much lower cost. Such functions include meteorological monitoring, surveillance, and communications. The proposed craft is a super-pressure, helium- filled, aerodynamic airship. It would use a blower to fill an inner bladder with ambient air thus increasing its weight. The airship can then glide forward as it descends. After a valve is opened to release the ?ballast air,? the airship becomes light enough to ascend while again gliding forward. This process can be repeated indefinitely.