UP, UP and away! High-altitude balloons called Stratollites might soon be giving the US military and NASA permanent and relatively low-cost eyes in the sky over any part of the planet they want. Developed by US firm World View, Stratollites are uncrewed hydrogen or helium-filled balloons that tour the stratosphere at between 10 and 46 kilometres up, with cameras and sensors on board. As the wind in each layer of the stratosphere blows in a different direction, a Stratollite's path can be changed simply by moving to a different height and hitching a ride. The balloons are controlled from the ground.
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