as he was about to step on Astro's hand, he turned and walked quickly
back to the door. "You must be nuts, Charley," the two cadets heard him
say. "There's nobody here."

The door rolled closed and the light was cut off. Tom and Astro rose and
quietly made their way toward the door. They stopped, leaned against the
door, and tried to hear what was going on inside, but were unable to
distinguish more than a vague mumble of voices, because of their masks
and the thickness of the door. Suddenly, however, they were conscious of
footsteps approaching from the other side.

There was no time to hide. Each boy flattened himself against the wall
on opposite sides of the door and held his breath as the door opened
slowly.

* * * * *

"There can be no doubt about it, Steve," said Commander Walters to the
young captain. "What we need are more powerful pumping stations for
oxygen _and_ additional generators for supplying power to the force
field."

"How do you figure that, sir?" asked Strong.

"It's simply this," replied Walters. "The population here has nearly
tripled in the past two years. The force-field screens were set up
originally to accommodate only a minimum number of miners and their
families. With the heavy demand for crystal, and therefore, more
civilians to dig it out, the force field has been overloaded."