Prelude to Space by Arthur C. Clarke Read Free Book Online Page A

landing.”
    There was a breathtaking sequence, obviously speeded up many times, showing almost
     the whole Earth spinning below at an enormous rate. It made Dirk quite dizzy for a
     moment, and when he had recovered the narrator was talking about the force of gravity.
     He explained how it held everything to the Earth, and how it weakened with distance
     but never vanished completely. More animated diagrams showed how a body could be given
     such a speed that it would circle the world forever, balancing gravity against centrifugal
     force just as the Moon does in its own orbit. This was illustrated by a man whirling
     a stone around his head at the end of a piece of string. Slowly he lengthened the
     string, but still kept the stone circling, more and more slowly.
    “Near the Earth,” explained the voice, “bodies have to travel at five miles a second
     to remain in stable orbits—but the Moon, a quarter of a million miles away in a much
     weaker gravitational field, need move at only a tenth of this speed.
    “But what happens if a body, such as a rocket, leaves the Earth at
more
than five miles a second? Watch…”
    A model of the Earth appeared, floating in space. Above the equator a tiny point was
     moving, tracing out a circular path.
    “Here is a rocket, traveling at five miles a second just outside the atmosphere. You
     will see that its path is a perfect circle. Now, if we increase its speed to
six
miles a second the rocket still travels round the Earth in a closed orbit, but its
     path has become an ellipse. As the speed increases still further, the ellipse becomes
     longer and longer and the rocket goes far out into space. But it always returns.
    “However, if we increase the rocket’s initial speed to seven miles a second the ellipse
     becomes a parabola—so—and the rocket has escaped for ever. Earth’s gravity can never
     recapture it: it is now traveling through space like a tiny, man-made comet. If the
     Moon were in the right position, our rocket would crash into it like the ‘Orphan Annie.’”
    That, of course, was the last thing one wanted a spaceship to do. There was a long
     explanation then, showing all the stages of a hypothetical lunar voyage. The commentator
     showed how much fuel must be carried for a safe landing, and how much more was needed
     for a safe return. He touched lightly on the problems of navigation in space, and
     explained how provision could be made for the safety of the crew. Finally he ended:
    “With chemically propelled rockets we have achieved much, but to conquer space, and
     not merely to make short-lived raids into it, we must harness the limitless forces
     of atomic energy. At present, atomically driven rockets are still in their infancy:
     they are dangerous and uncertain. But within a few years we shall have perfected them,
     and mankind will have taken its first great stride along the Road to Space.”
    The voice had grown louder; there was a throbbing background of music. Then Dirk seemed
     to be suspended motionless in space, a few hundred feet from the ground. There was
     just time for him to pick out a few scattered buildings and to realize that he was
     in a rocket that had just been launched. Then the sense of time returned: the desert
     began to drop away, with accelerating speed. A range of low hills came into view and
     was instantly foreshortened into flatness. The picture was slowly rotating, and abruptly
     a coastline cut across his field of vision. The scale contracted remorselessly, and
     with a sudden shock he realized that he was now seeing the whole coast of Southern
     Australia.
    The rocket was no longer accelerating, but was sweeping away from Earth at a speed
     not far short of escape velocity. The twin islands of New Zealand swam into view—and
     then, at the edge of the picture, appeared a line of whiteness which for a moment
     he thought was a cloud.
    Something seemed to catch at Dirk’s throat when he realized that he was looking