The old man was beaming, proud of it. He didn't know it wasn't skill but the built-in safety factor, all the stabilizing mechanisms coming into play at once. Demarest, the chief of construction, had seen to it that the ships were well designed. Marlowe would have to commend him when he got here. A thought occurred to the training director. If the stabilizing mechanisms were there, why not use them always? Of course, it wasn't that simple. Interplanetary ship stabilizers weren't effective at high speed. Another thought crowded in. Why such high speed? That was something over which there was no choice. The protective atmosphere had to be left swiftly. The speed was added to at every opportunity. It was possible to slow down only at the last moment. Otherwise.... Otherwise what? There was no escape from the conclusion--otherwise heredity was altered and mutations would result. Marlowe sat back. This was true without exception. It was the biggest factor that controlled the conditions of interplanetary flight. But-- _They'd had their children!_ Marlowe's pulse increased. As training director, he'd learned not to leap at things that merely looked good. He had to examine them carefully. But--well, it was a new approach, though he couldn't really expect anything from it. There was more to a crew than a pilot, more to space flight than one incredible lucky voyage, for angels took vacations, too. "You weren't on duty at all times," Marlowe pointed out. "Then there's navigation." "Don't sleep much," said Ethan. "Catnap once in a while." He thought it over. "When I did sleep, 'Mantha helped out." He looked at her. "I'm not the expert on navigation. You'd better ask her." "_No!_" cried Marlowe. "Why not? Just because I'm a woman?" Her eyes were bright. "But who taught you navigation?" Amantha sniffed. "Look here, young man, don't tell me what I can learn." She closed her eyes and imagination carried her back to the ship. "Lots of dials and gadgets--but I used to have near as many in my kitchen before they said I was too old to cook. Anyway, you don't have to figure it out on paper. If you look at things just right, you sort of know where you are." * * * * * Amantha folded her hands. "First, you take a big handful of the Sun's attraction and mix it with a bigger scoop of the gravitation of the planet you happen to be on. For us, that was Mars. Then you add a pinch of acceleration. That's what makes you rise. When you get out a ways, you decrease Mars and add more Earth and another pinch of Sun, stirring it around in your mind each day until it feels just right." She smiled. "I never did hold with too much measuring."