increased every second.

The ship could swing to right or left on steering rockets, but the war
rocket could swerve also. It was controlled from the ground. It did not
need to crash the small ship from space. Within a limited number of
miles the blast of its atomic warhead would vaporize any substance that
could exist. And of course the ship could not turn back. Even the
expenditure of all its landing-rockets could not bring twenty tons of
ship to a halt. They could speed it up, so it would pass the calculated
meeting place ahead of the war rocket. But the bomb would simply follow
in a stern chase. In any case, the ship could not stop.

But neither could the rocket.

Joe never knew how he saw the significance of that fact. On land or sea,
of course, an automobile or a ship moves in the direction in which it is
pointed. Even an airplane needs to make only minor corrections for air
currents which affect it. But an object in space moves on a course which
is the sum of all its previous speeds and courses. Joe's ship was moving
eastward above the Earth at so many miles per second. If he drove
north--at a right angle to his present course--the ship would not cease
to move to the east. It would simply move northward in addition to
moving east. If the rocket from Earth turned north or east it would
continue to move up and merely add the other motion to its vertical
rise.

Joe stared at the uncoiling thread of vapor which was the murder
rocket's trail. He hated it so fiercely that he wanted to escape it
even at the cost of destruction, merely to foil its makers. At one
moment, he was hardly aware of anything but his own fury and the frantic