Space Tug by Murray Leinster

There was bright sunshine at the Shed, not a single cloud in all the sky. The radar bowls atop the roof -- they seemed almost invisibly small compared with its vastness -- wavered and shifted and quivered. Completely invisible beams of microwaves lanced upward. Atop the Shed, in the communication room, there was the busy quiet of absolute intentness. Signals came down and were translated into visible records which fed instantly into computers. Then the computers clicked and hummed and performed incomprehensible integrations, and out of their slot-mouths poured billowing ribbons of printed tape. Men read those tapes and talked crisply into microphones, and their words went swiftly aloft again.

Down by the open eastern door of the Shed at the desert's edge, Sally Holt and Joe's father waited together, watching the sky. Sally was white and scared. Joe's father patted her shoulder reassuringly.