(London Telegraph) It arrived back at a California air base after dark. Only the eagle-eyed would have spotted the snub-nosed spacecraft gliding out of the black sky.
Officially, the unmanned Boeing-built X-37B Orbital Test Vehicle had just completed its longest ever mission, spending almost two years circling the Earth, conducting experiments.
But its secretive history has sparked countless theories about what the computer controlled craft was really doing in space.
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