The U. S. Navy's Space Scan Radar Station No. 5 picked up the new rocket before it was fairly into space. It clung to it with an electromagnetic train, bleeding it of data. The information was fed into computers, digested, analyzed and transferred to Alpine Base, and thence telemetered to the Aztec where it appeared as a pip on the analog display. The grid had automatically adjusted to a 500-mile scale with the positions of the intruder and Aztec separated by almost the width of the instrument face. The Aztec seemed to have a clear edge in the race for the moon. Prochaska became aware of the newcomer but refrained from questions, nor did Crag volunteer any information. Just now he wasn't worrying about the East World rocket. Not at this point. With Drone Able riding to starboard, the Aztec was moving at an ever slower rate of speed. It would continue to decelerate, slowed by the earth's pull as it moved outward, traveling on inertial force since the silencing of its engines. By the time it reached the neutral zone where the moon and earth gravispheres canceled each other, the Aztec would have just enough speed left to coast into the moon's field of influence. Then it would accelerate again, picking up speed until slowed by its braking rockets. That was the hour that occupied his thoughts--a time when he would be called upon for split-second decisions coming in waves. He tried to anticipate every contingency. The mass ratio necessary to inject the Aztec into its moon trajectory had precluded fuel beyond the absolute minimum needed. The rocket would approach the moon in an elliptical path, correct its heading to a north-south line relative to the planet and decelerate in a tight spiral. At a precise point in space he would have to start using the braking rockets, slow the ship until they occupied an exact point in the infinite space-time continuum, then let down into cliff-brimmed Arzachel, a bleak, airless, utterly alien wasteland with but one virtue: Uranium. That and the fact that it represented the gateway to the Solar System. He mentally reviewed the scene a hundred times. He would do this and this and that. He rehearsed each step, each operation, each fleeting second in which all the long years of planning would summate in victory or disaster. He was the X in the equation in which the Y-scale was represented by the radar altimeter. He would juggle speed, deceleration, altitude, mass and a dozen other variables, keeping them in delicate balance. Nor could he forget for one second the hostile architecture of their destination. For all practical purposes Arzachel was a huge hole sunk in the moon--a vast depression undoubtedly broken by rocks, rills, rough lava outcrops. The task struck him as similar to trying to land a high-speed jet in a well shaft. Well, almost as bad.