“Five-fifteen-fifteen, Wilson!”
He must get used to his name—Wilson, that was his name. “Ready!”
“Fifteen-twenty!”
Five hours, fifteen minutes, twenty seconds. In another thirty seconds, sunrise. Or blast-off! For it was the same thing when you calculated orbits for an outbound ship. At sunrise a spaceship would add its own speed to Earth’s orbital velocity of eighteen and a half miles per second. In other words, the ship, going too fast to be maintained in Earth’s orbit by the sun, would drift out in space toward Mars, or the asteroids, or the Jovian moons. After that, it was up to the ship’s astrogator.
Blasting off for Venus, or for the outer planets when they were not in opposition, a ship followed the setting sun. Then it would subtract its own speed from Earth’s orbital velocity,
