Interplanetary Travel

An atom bomb rocketed to the moon ought to blast a magnificent crater there. Some of the fragments would almost certainly escape from the moon's weak gravitation and shower down on earth, as rather sluggish meteors. Scientists, analyzing them, could then prove beyond all doubt that they were not green cheese.

The proposal that the moon be bombed was made in dead earnest last week by Meteor-Expert H. H. Nininger.

The stunt might work. Even pre-atom explosives can toss fragments fast enough (1 1/2 miles a second) to free them from the moon's puny pull. Some scientists believe that meteors continually knock chips from the moon's jagged mountains; the chips then head for the center of the earth and fall near the equator as fused, glassy blobs called "tektites."

But Nininger was a comparatively modest rocketeer. Those champion optimists of near-science, the astronauts, were also raring to go. They had been vastly encouraged by radar contact with the moon and by the military's super-stratosphere rockets.

Shooting any sort of projectile beyond the earth's gravitational field would take enormous energy. Prewar energy sources could barely do it, even in theory. One calculation: a 100-ton spaceship would need nearly 8,000 tons of gasoline and liquid oxygen to toss it into space.

But atomic energy changed all that. One pound of fissioning uranium 235, which needs no oxygen, gives off as much energy as several thousand tons of the best non-atomic propellants. A very few pounds would be enough for the most ambitious space-voyage. Uranium 235 is not on the market, of course (or likely to be soon). Neither does anyone know how to harness it as a propellant. But such trifling obstacles do not discourage the space-voyagers. Their energy problem "solved" at last, they can henceforth revel in larger dreams.

The basic rules of interplanetary travel have been fairly well worked out. If a rocket or spaceship zooms off at slightly better than seven miles a second (twelve times as fast as an antiaircraft shell) it will have the force to escape entirely from the earth's gravitational field. Best method is to shoot through the dense lower air rather slowly, to reduce air friction; then shift into high above the atmosphere.

Nearest goal for spaceships is the boundary where the earth's gravitational pull and the moon's are equally strong. This "neutral point" comes closest to the earth (160,000 mi.) when the moon's rather feeble attraction is reinforced by that of the sun directly behind it. So a space-voyage to the moon should be made when the moon is "new" and almost in line with the sun. Voyages to Venus, Mars and other planets have been plotted by similar calculations. They would take more time, not much more energy.

Theoretically, spaceships could be steered (around the moon, for instance) by shooting out side-blasts of gas or radiation. When returning to earth, they could be slowed down gradually by coasting in a lopsided spiral through the outer fringes of the atmosphere. If they should hit the denser air unbraked, they would turn as white-hot as a meteor.

In space itself, the spaceships (if ever constructed) may meet their worst perils. The region outside the atmosphere is not mere emptiness. It is chockfull, among other things, of searing X rays from the sun, electron-streams hot out of sunspots, powerful cosmic rays from the depths of space. These are checked by the atmosphere before they smack the earth's surface. Their possible effect on the crew of a comparatively thin-skinned spaceship is something to dampen the enthusiasm even of astronauts.

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