See the word 'glider' and the chances are you'll picture a humble-looking aircraft flying lazily a few thousand feet above the countryside on a summer afternoon. You might not automatically think an engineless aircraft could climb into the stratosphere to 60,000-70,000ft (18,288-21,336m) or higher, far above commercial airways where the only manned types to operate are the US Air Force U-2 and NASA ER-2.
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