en begun, and
only two were even near completion. Joe's had taken off the instant it
was finished. The second had done the same. The second pair of
spaceships wouldn't be ready for two months or more. The ships that
could be used had to be used.

So, only thirty-six hours after the arrival of the second rocketship at
the Platform, the two of them took off together to return to Earth.
Joe's ship left the airlock first. Sanford was loaded in the cabin of
the other ship as cargo. Lieutenant Commander Brown stayed out at the
Platform to replace him.

Obviously, in order to get back to Earth they headed away from it in
fleet formation. They pointed their rounded noses toward the Milky Way.

The upward course was an application of the principle that made the
screen of tin cans and oddments remain about the Platform. Each of
those small objects had had the Platform's own velocity and orbit.
Thrown away from it, the centers of their orbits changed. In theory,
the center of the Platform's orbit was the center of Earth. But the
centers of the orbits of the thrown-away objects were pushed a few
miles--twenty--fifty--a hundred--away from the center of Earth.

The returning space ships also had the orbit and speed of the Platform.
They wanted to shift the centers of their orbits by very nearly 4,000
miles, so that at one point they would just barely graze Earth's
atmosphere, lose some speed to it, and then bounce out to empty space
again before they melted. Cooled off, they'd make another grazing
bounce. After eight such bounces they'd stay in the air, and the stubby
fins would give them a sort of gliding angle and controllability, while
the landing rockets would let them down to solid ground. Or so it was
hoped.

Meanwhile they headed out instead of in toward Earth. They went out on
their steering-rockets only, using the liquid fuel that had not been
needed for course correction on the way out. At 4,000 miles up, the
force of gravity is just one-fourth of that at the Earth's surface. It
still exists; it is merely canceled out in an orbit. The ships could
move outward at less cost in fuel than they could move in.

So they went out and out on parallel courses, and the Platform dwindled
behind them. Night flowed below until the hull of the artificial
satellite shone brightly against a background of seeming sheer
nothingness.

The twilight zone of Earth's shadow reached the Platform. It glowed
redly, glowed crimson, glowed the