Complex sentence: Pyke realized that the answer was ice, which could be manufactured for only 1% of the energy needed to make an equivalent mass of steel and proposed that an iceberg, natural or artificial, be levelled to provide a runway and hollowed out to shelter aircraft.
Split into simpler sentences: Pyke realized that the answer was ice, which could be manufactured for only 1% of the energy needed to make an equivalent mass of steel. He proposed that an iceberg, natural or artificial, be levelled to provide a runway and hollowed out to shelter aircraft.