The A.20 was a two-step rocket. It had to be, for it was using chemical fuels. The upper component, with its tiny cabin, its folded aerofoils and flaps, weighed just under twenty tons when fully fuelled. It was to be lifted by a lower two-hundred-ton booster which would take it up to fifty kilometres, after which it could carry on quite happily under its own power. The big fellow would then drop back to Earth by parachute: it would not weigh much when its fuel was burnt. Meanwhile the upper step would have built up enough speed to reach the six-hundred-kilometre level before falling back and
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