Hypersonic drone aircraft that could bomb any target in the world from a base in America recently grabbed headlines in the Guardian and other newspapers. But fast and flashy is no substitute for slow and steady. UAVS (unmanned aerial vehicles) that can loiter over the same spot for months are likely to be of more lasting military and commercial significance. They are also hard to build. The most advanced prototype of such a UAV, a solar-powered craft called Helios, was destroyed on June 26th when it crashed into the Pacific. The cause of the crash is still unknown, although turbulence is thought to have been a factor.
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