Momentum by Charles Dye - Just because an event "has to" happen, some people think that, of course, it will happen. It ain't necessarily so! Ballard had but a few hours to solve the problem, and he knew that the answer was there, before his eyes—if he could see it in time!

Asteroid 1207 came spinning into the auxiliary ship's viewplate like a glittering black mirage. The eight-mile chunk of rock was the last link in a chain of nine asteroid navigational-markers still needing blinker equipment installation. Minutes later, the Minnow lay neatly berthed in the deepest hollow of the asteroid, the shining wires of its drill grapples anchoring it firmly to the jagged rock. The airlock opened and two men in spacesuits stepped out. They climbed to the top of the nearest hill dragging a platform of tools and equipment; the ragged, close horizons of the asteroid made a hostile background for them as they worked in silence.

Ballard leaned far over the rough edge of a circular pit, directing the heat radiation beam that melted the foundation plastic smoothly over the walls. He couldn't spare the time to turn his head and watch Walton, but he could follow the other's progress in welding the framework of the blinker tower by the irregular breathing and clanks and buzzes coming through his earphones. He listened to Walton's motions with an automatic alertness developed over six long weeks of tension—ever since the finding of the rotenite nuggets on the second of the light-marker asteroids. The rotenite represented enough wealth to make them among the richest men in the solar system. Or one of them—the richest. That was what Ballard was afraid of.