É explicado nos primeiros parágrafos. Eles não podem se comunicar diretamente com Speedy por rádio (para dizer a ele que eles estão em perigo ou fortalecer a ordem) já que ele está bem fora da faixa de rádio efetiva em Mercury. O rádio em si parece estar fixo no lugar.
They were in the radio room now - with its already subtly antiquated equipment, untouched for the ten years previous to their arrival....
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Donovan must have felt it. He began: "I tried to locate him by radio, but it was no go. Radio isn't any good on the Mercury Sunside - not past two miles, anyway. That's one of the reasons the First Expedition failed. And we can't put up the ultrawave equipment for weeks yet"
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"I sent Speedy to the nearest, naturally. Seventeen miles away. But what difference does that make?" There was tension in his voice. "There are the penciled dots that mark Speedy's position."