"Look at that," breathed Ross. "Look at old Tycho shining out like a searchlight. Boy!"
"I wish we could see the earth," said Art. "This bucket ought to have more than one view port."
"What do you expect for a dollar-six-bits?" asked Ross. "Chimes? The Galileo was a freighter."
"I can show it to you in the scope," Morrie offered, and switched on the piloting radar in the belly. The screen lit up after a few seconds but the picture was disappointing. Art could read it well enough- it was his baby -but esthetically it was unsatisfying. It was no more than a circular plot reading in bearing and distance; the earth was simply a vague mass of light on that edge of the circle which represented the astern direction.
"That's not what I want," Art objected. "I want to see it. I want to see it shape up like a globe and see the continents and the oceans."
"You'll have to wait until tomorrow, then, when we cut the drive and swing ship. Then you can see the earth and the sun, too."
"Okay. How fast are we going? Never mind—I see," he went on, peering at the instrument board. "3,300 miles per hour."
"You're looking at it wrong," Ross corrected him. "It says 14,400 miles per hour."
"You're crazy."
"Like fun. Your eyes have gone bad."
"Easy, boys, easy," Cargraves counseled. "You are looking at different instruments. What kind of speed do you want?"
"I want to know how fast we're going," Art persisted.
"Now, Art, I'm surprised at you. After all you've had every one of these instruments apart. Think what you're saying."
Art stared at the instrument board again, then looked sheepish. "Sure, I forgot. Let's see now—we've gained 14,000 and some, close to 15,000 now, miles per hour in free fall—but we're not falling."
"We're always falling," Morrie put in, smug for the moment in his status as a pilot. "You fall all the time from the second you take off, but you drive to beat the fall."
"Yes, yes, I know," Art cut him off. "I was just mixed up for a moment. Thirty-three hundred is the speed I want -- 3310 flow."
‘Speed' in space is a curiously slippery term, as it is relative to whatever point you select as ‘fixed'—but the points in space are never fixed. The speed Art settled for was the speed of the Galileo along a line from the earth to their meeting place with the moon. This speed was arrived at deep inside Joe the Robot by combining by automatic vector addition three very complicated figures: first was the accumulated acceleration put on the ship by its jet drive, second the motions imposed on the ship by its closeness to the earth—its ‘free fall' speed of which Art had spoken. And lastly, there was the spin of the earth itself, considered both in amount and direction for the time of day of the take-off and the latitude of the camp site in New Mexico. The last was subtracted, rather than added, insofar as the terms of ordinary arithmetic apply to this sort of figuring.
The problem could be made vastly more complicated. The Galileo was riding with the earth and the moon in their yearly journey around the sun at a speed of about 19 miles per second or approximately 70,000 miles per hour as seen from outer space. In addition, the earth-moon line was sweeping around the earth once each month as it followed the moon—but Joe the Robot had compensated for that when he set them on a course to where the moon would be rather than where it was.
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."
"Go ahead and laugh!" Cargraves continued, seeing their expressions, "It strikes you as funny as a The-World-Is-Flat theory. But I heard an aeronautical engineer, as late as 1943, say just that."
"No! Not really!"
"I certainly did. He was a man with twenty-five years of professional experience and he had worked for both Wright Field and the Navy. But he said that in it. Next year the Nazis were bombing London with V-2s. Yet according to him it couldn't be done!"
"I'd think any man who had ever felt the kick of a shotgun would understand how a rocket works," Ross commented.
"It doesn't work out that way. Mostly it has no effect on his brain cells; it just gives him a sore shoulder." He started to lift himself out of his semi-reclining position in his pilot's chair. "Come on. Let's eat. Wow! My foot's gone to sleep. I want to stock up and then get some sleep. Breakfast wasn't much good for me—too many people staring down our necks."