The StratoSail(R) balloon guidance system (BGS) is designed to alter the flight path of balloons. The StratoSail(R) BGS takes advantage of the natural difference in wind speed at different altitudes in the atmosphere. A wing is suspended several kilometers below the balloon gondola using a long thin tether. The wing is hanging on end, so its "lift" acts sideways rather than upward as in an airplane. This sideways lift force is used to drag the balloon across the wind. This allows the balloon to be maneuvered towards regions of interest and away from unfavorable conditions.
The BGS can drive the balloon to sites of interest to scientists. Some governments do not give permission to fly over their countries. With a StratoSail(R) BGS aboard, the balloon can be directed around these uncooperative regions. Hazardous weather patterns can be avoided. Balloon flights may last many weeks and go around the world several times. At the end of a flight, the balloon can be redirected to land back near its launch site. This makes balloon operations much simpler.