THE MOON IS A HARSH MISTRESS by Robert A. Heinlein

“A higher mountain would be better?”

“Oh, yes, sir!” I assured him. “A higher mountain would be preferred over one nearer the equator. The catapult can be designed to make up for loss in free ride from Earth’s rotation. The difficult thing is to avoid so far as possible this pesky thick atmosphere. Excuse me, Doctor; I did not mean to criticize your planet.”

“There are higher mountains. Colonel, tell me about this proposed catapult.”

I started to. “The length of an escape-speed catapult is determined by the acceleration. We think–or the computer calculates–that an acceleration of twenty gravities is about optimum. For Earth’s escape speed this requires a catapult three hundred twenty-three kilometers in length. Therefore—”

“Stop, please! Colonel, are you seriously proposing to bore a hole over three hundred kilometers deep?”

“Oh, no! Construction has to be above ground to permit shock waves to expand. The stator would stretch nearly horizontally, rising perhaps four kilometers in three hundred and in a straight line–almost straight, as Coriolis acceleration and other minor variables make it a gentle curve. The Lunar catapult is straight so far as the eye can see and so nearly horizontal that the barges just miss some peaks beyond it.”

“Oh. I thought that you were overestimating the capacity of present-day engineering. We drill deeply today. Not that deeply. Go on.”

“Doctor, it may be that common misconception which caused you to check me is why such a catapult has not been constructed before this. I’ve seen those earlier studies. Most assumed that a catapult would be vertical, or that it would have to tilt up at the end to toss the spacecraft into the sky–and neither is feasible nor necessary. I suppose the asswnption arose from the fact that your spaceships do boost straight up, or nearly.”

I went on: “But they do that to get above atmosphere, not to get into orbit. Escape speed is not a vector quantity; it is scalar. A load bursting from a catapult at escape speed will not return to Earth no matter what its direction. Uh. . . two corrections: it must not be headed toward the Earth itself but at some part of the sky hemisphere, and it must have enough added velocity to punch through whatever atmosphere it still traverses. If it is headed in the right direction it will wind up at Luna.”

“Ah, yes. Then this catapult could be used but once each lunar month?”

“No, sir. On the basis on which you were thinking it would be once every day, picking the time to fit where Luna will be in her orbit. But in fact–or so the computer says; I’m not an astronautics expert–in fact this catapult could be used almost any time, simply by varying ejection speed, and the orbits could still wind up at Luna.”

“I don’t visualize that.”

“Neither do I, Doctor, but– Excuse me but isn’t there an exceptionally fine computer at Peiping University?”

“And if there is?” (Did I detect an increase in bland inscrutability? A Cyborg-computer– Pickled brains? Or live ones, aware? Horrible, either way.)

“Why not ask a topnotch computer for all possible ejection times for such a catapult as I have described? Some orbits go far outside Luna’s orbit before returning to where they can be captured by Luna, taking a fantastically long time. Others hook around Terra and then go quite directly. Some are as simple as the ones we use from Luna. There are periods each day when short orbits may be selected. But a load is in the catapult less than one minute; the limitation is how fast the beds can be made ready. It is even possible to have more than one load going up the catapult at a time if the power is sufficient and computer control is versatile. The only thing that worries me is– These high mountains they are covered with snow?”

“Usually,” he answered. “Ice and snow and bare rock.”

“Well, sir, being born in Luna I don t know anything about snow. The stator would not only have to be rigid under the heavy gravity of this planet but would have to withstand dynamic thrusts at twenty gravities. I don t suppose it could be anchored to ice or snow. Or could it be?”

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