The minute of the rocket thrust lasted for centuries. Then the engine cut off, and his head was pure anguish from the blood spurted through it by his still-laboring heart. He was blinded by the pain. But it went away. Slowly, slowly, slowly, his sound-deadened ears regained their sensitiveness. He heard Furness gasping: "--minute rocket-blast ended. Checking course now. Over." McCauley said absorbedly: "There was a goof. A twelve-gee thrust with full fuel tanks is a whale of a lot more when they're nearly empty!" It was true, of course. The ferocity of a rocket thrust that would accelerate a fully loaded ship at three hundred fifty-odd feet per second per second would accelerate much more a ship weighing half as much. Toward the end, McCauley and Furness had taken acceleration that no man could live through for more than a very short time. But a man can endure briefly a stress that would kill him if long-continued. McCauley plunged into the desperately necessary task of this moment. He had to determine his present course and speed. He could not take the time to look out of the ports at the immensity of Earth below him. Men in capsules, orbiting, had been as high as this, but they did not have to compute their height or guide their vehicles. McCauley had to do both. The height was relatively simple. A radar screen, reduced to a vertical slot for economy of space and weight, told him the distance to whatever was below. A Doppler-effect velocity indicator would read off the change in frequency of a crystal-controlled radio signal which his speed produced. This substantially resembled the way an automobile horn changes pitch when two cars pass each other; the pitch drops swiftly at the moment of passing. But there was an observation which was simpler and more direct. He spotted a bright star near the horizon ahead. He read off its angular distance from the world's edge. Looking aft, under the belly of the ship, he read another angle from the world's edge to another star. Minutes later, he repeated the observations. The star ahead was higher, the one behind was lower. If one star rose faster than the other sank, he would be gaining height. If one sank faster than the other rose, he would be falling. If one rose exactly as fast as the other dropped, he would be in a perfect circular orbit, neither rising nor falling. That was too good to be expected. But from even two sets of observations he could tell the line the ship was following, and hence its speed. The ship did not have quite the speed necessary for a complete orbit. It needed more. He could guess how much. He said curtly to Furness: "We've got to have a two-second push, anyhow. Maybe more later. Get set." Furness did not reply, but McCauley heard him reporting. There was singularly little exultation in the small cabin. Furness' face was drawn and colorless behind his helmet plate. McCauley was busy.