He went on with his work. The ship was two hundred eighty miles--plus or minus half a mile--above the surface of the earth. An orbit required a speed and rate of downward curvature just fixed so the ship would go downward as the surface curved down, like a glider coasting down a curving hillside and always being the same distance from solidity. Since the earth was a globe, one could coast forever and be always falling, without ever touching the circled world. That is an orbit. McCauley set the rocket timer and said: "Here we go." The rockets blasted. The ship flung itself forward. Again there was the sensation of falling an uncomfortable distance onto a hard mattress. But a one-second blast was a thousand times more endurable than a one-minute one. The ship had now been aloft for something like thirty minutes, of which ten was airborne flight and twenty free fall in orbit, plus two corrections of course and speed. McCauley had had no time to gaze down at the vastness below him. He knew it only as a huge expanse of mottled tawny-green or blue with many white specks upon it. The specks, which were clouds, were closer together toward the horizon, and at any given moment the rim of the world was a ring of plain white. Now he checked his work once more and then took time to look at Earth below him. At its speed, the ship should complete one revolution of the Earth in ninety minutes, more or less. Its speed was seventeen thousand two hundred and sixty miles per hour relative to the ground. In twenty minutes of free-fall flight it had covered something over five thousand and seven hundred miles, relative to the ground, and crossed eighty degrees of longitude. The local time down below was something more than five hours later than the local time at Quartermain Base. Sunset would be approaching here, as the earth's shadow moved from east to west like the dawn.