tain time and
then crumble away. Crumbling, the refractory particles would be hurled
astern and so serve as reaction mass. When the steel outer tubes were
exposed, they would melt and be additional reaction mass.

In effect, as the rocket fuel was exhausted, the tubes that contained it
dissolved into their own blast and added to the accelerating thrust,
even as they diminished the amount of mass to be accelerated. Then the
quantity of fuel burned could diminish--the tubes could grow smaller--so
the rate of speed gain would remain constant. Under the highly special
conditions of this particular occasion, there was a notable gain in
efficiency over a liquid-fuel rocket design. For one item, the Platform
would certainly have no use for fuel pumps and fuel tanks once it was in
its orbit. In this way, it wouldn't have them. Their equivalent in mass
would have been used to gain velocity. And when the Platform finally
rode in space, it would have expended every ounce of the driving
apparatus used to get it there.

Now the rocket tubes were being lined and loaded. The time to take-off
was growing short indeed.

Joe watched a while and turned away. He felt very good because he'd
finished his job and lived up to the responsibility he'd had. But he
felt very bad because he'd had an outside chance to be one of the first
men ever to make a real space journey--and now it was gone. He couldn't
resent the decision against him. If it had been put up to him, he'd
probably have made the same hard decision himself. But it hurt to have
had even a crazy hope taken away.

Sally said, trying hard to interest him, "These rockets hold an awful
lot of fuel, Joe! And it's better than scientists thought a chemical
fuel could ever be!"

"Yes," said Joe.

"Fluorine-beryllium," said Sally urgently. "It fits in with the
pushpots' having pressurized cockpits. Rockets like that couldn't be
used on the ground! The fumes would be poisonous!"

But Joe only nodded in agreement. He was apathetic. He was uninterested.
He was still thinking of that lost trip in space. He realized that Sally
was watching his face.

"Joe," she said unhappily, "I wish you wouldn't look like that!"

"I'm all right," he told her.

"You act as if you didn't care about anything," she protested, "and you
do!"

"I'm all right," he repeated.

"I'd like to go outside somewhere," she said abruptly, "but after what
happened up at the lake, I mustn't. Would you like to go up