get down to ground again. But you'll hardly accept that invitation, feeling as you do. I'll say you declined because you want to get some extra sleep tonight since you intend to watch the fuel-up tomorrow."

McCauley blinked at him in amazement. Furness went out.

When he'd gone, McCauley swore to himself. This was more of the attitude he disliked, expecting him to feel self-important. It was one of the penalties of having done something that got publicity. But there was absolutely nothing he could do about it.

Certainly it had been reasonable to mention the one thing that bothered him! The X-21 would take off on jatos, ride to the limit of the atmosphere on ramjets, and have the rocket motor take over there. To get the exact course and speed he needed, he'd undoubtedly have to use the rocket engine in a series of bursts after the original acceleration run. He'd have to turn it off between times. And while an alcohol-lox rocket motor had been turned off and on in flight, no hydrazine-nitric rocket ever had been. Nobody had ever needed to. McCauley would. And the idea was hair-raising.

Rocket fuel is tricky stuff at best. In the earlier X-series ships, alcohol and lox—liquid oxygen—and in one or two cases ammonia and lox, were used in the engines. They could be jettisoned in case a dead-stick landing was necessary. But nobody in his senses would think of jettisoning nitric and hydrazine as an emergency measure. That was the pair, though, that was being used in the X-21. Their great advantage is that they do not need to be ignited. Their great disadvantage is that they become active when they are combined. McCauley had inspected the fuel delivery system and he was concerned about it. In the static runs of the ship's rocket engine everything had gone well. If all went well in space, everything would be fine. But if something didn't....

McCauley couldn't tell what would happen. His training in the mock-up hadn't included meeting that emergency, because there wasn't any way to meet it.

"If it happens," he muttered, "I'll know it because I'll hear St. Peter say, 'Hello, Ed! Come in!'"

He stirred restlessly. The light on the closed Venetian blinds was ruddy now. He found that he didn't feel hungry, but he ought to. He asked the way to the officer's mess and found that it was nearly empty. Most of the base was on leave until nine o'clock, which might be the base commandant's way of boasting that sending off the first actual spaceship 

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