Space Platform by Murray Leinster

It was not, however, the crack of doom. When Joe stared out the window by the head of his cot, he saw gray-red dawn breaking over the landing field. There were low, featureless structures silhouetted against the sunrise. As the crimson light grew brighter, Joe realized that the angular shapes were hangars. Improbable crane poles loomed above them. One was in motion, handling something he could not make out, but the noise that had awakened him was less, now. It seemed to circle overhead, and it had an angry, droning, buzzing quality that was not natural in any motor he had ever heard before.

Joe shivered, standing at the window. It was cold and dank in the dawn light at this altitude, but he wanted to know what that completely unbelievable roar had been. A crane beam by the hangars tilted down, slowly, and then lifted as if released of a great weight. The light was growing slowly brighter. Joe saw something on the ground. Rather, it was not quite on the ground. It rested on something on the ground.