There were also the complicated motions of the sun and its planets with reference to the giddily whirling ‘fixed’ stars, speeds which could be nearly anything you wanted, depending on which types of stars you selected for your reference points, but all of which speeds are measured in many miles per second.
But Joe cared nothing for these matters. His cam and his many circuits told him how to get them from the earth to the moon; he knew how to do that and Doctor Einstein’s notions of relativity worried him not. The mass of machinery and wiring which made up his being did not have worry built into it. It was, however, capable of combining the data that came to it to show that the Galileo was now moving somewhat more than 3300 miles per hour along an imaginary line which joined earth to the point where the moon would be when they arrived.
Morrie could check this figure by radar observations for distance, plus a little arithmetic. If the positions as observed did not match what Joe computed them to be, Morrie could feed Joe the corrections and Joe would accept them and work them into his future calculations as placidly and as automatically as a well-behaved stomach changes starch into sugar.
“Thirty-three hundred miles per hour,” said Art. “That’s not so much. The V-2 rockets in the war made more than that. Let’s open her up wide and see what she’ll do. How about it, Doc?”
“Sure,” agreed Ross, “we’ve got a clear road and plenty of room. Let’s bust some space.”
Cargraves sighed. “See here,” he answered, “I did not try to keep you darned young speed demons from risking your necks in that pile of bailing wire you call an automobile, even when I jeopardized my own life by keeping quiet. But I’m going to run this rocket my way. I’m in no hurry.”
“Okay, okay, just a suggestion,” Ross assured him. He was quiet for a moment, then added, “But there’s one thing that bothers me . . .”
“What?”
“Well, if I’ve read it once, I’ve read it a thousand times, that you have to go seven miles per second to get away from the earth. Yet here we are going only 3300 miles per hour.”
“We’re moving, aren’t we?”
“Yeah, but-”
“As a matter of fact we are going to build up a lot more speed before we start to coast. We’ll make the first part of the trip much faster than the last part. But suppose we just held our present speed — how long would it take to get to the moon?”
Ross did a little fast mental arithmetic concerning the distance of the moon from the earth, rounding the figure off to 240,000 miles. “About three days.”
“What’s wrong with that? Never mind,” Cargraves went on. “I’m not trying to be a smart-Aleck. The misconception is one of the oldest in the book, and it keeps showing up again, every time some non-technical man decides to do a feature story on the future of space travel. It comes from mixing up shooting with rocketry. If you wanted to fire a shot at the moon, the way Jules Verne proposed, it would have to go seven miles per second when it left the gun or it would fall back. But with a rocket you could make the crossing at a slow walk if you had enough power and enough fuel to keep on driving just hard enough to keep from falling back. Of course it would raise Cain with your mass-ratio. But we’re doing something of that sort right now. We’ve got tower to spare; I don’t see why we should knock ourselves out with higher acceleration than we have to just to get there a little sooner. The moon will wait. It’s waited a long time.
“Anyhow,” he added, “no matter what you say and no matter how many physics textbooks are written and studied, people still keep mixing up gunnery and rocketry. It reminds me of that other old chestnut — about how a rocket can’t work out in empty space, because it wouldn’t have anything to push on.”