that," said Logan. "I told Vidac I wanted this
information about Space Academy for Billy. That seemed to satisfy him."

"I don't know," mused Tom. "He's pretty smart."

"What else can we do?" asked Astro.

"Nothing," said Tom bitterly. "Not a space-blasting thing until we get
out of here!"

* * * * *

"We've _got_ to have that triple vacuum tube," declared Roger. "That's
the only thing that will transmit a voice quickly back to Earth from
this fix out in space."

The three boys and Jeff Marshall were back in their quarters after their
first week of active duty again. They had surreptitiously begun
collecting parts for the communicator and were sorting them out on one
of the bunks when Roger mentioned the necessity for the special vacuum
tube.

"How quickly?" asked Astro.

Tom explained. "The equipment we have now is strong enough to talk to
the Academy, but it'll take about six hours for my voice to reach it.
And then another six hours for the Academy's answer to get back to us.
At the end of twelve hours we might not be ready to receive and the
communications officer might pick up their answer. Then we'd be in the
middle of a space hurricane!"

"I see," said Astro. "You've got to be able to talk directly to the
Academy, so that when they answer, you'll be ready!"

"Right," said Tom. "We might only get ten or fifteen minutes of free
time, when the professor would be away from the observatory."

"Where do you think I could get one of those tubes, besides on the radar
bridge, Roger?" asked Jeff. He had been the main source of supply for
the equipment used in the communicator. Since getting out of the brig,
his movements had not been as restricted as the cadets'.

"That's just it," said Roger. "I remember distinctly loading all of them
in the locker near the main scanner on the radar deck."

"Then we have to get it from another ship," said Tom. "The chances of
getting one here, aboard the _Polaris_, are zero."

"Say, Roger," suddenly asked Astro, "do you think you remember enough
about that triple vacuum tube to draw me a blueprint?"

"Sure," said Roger. "And you could probably build it too. But how are
you going to get the inside tube vacuumized, then the second one, and
finally the third. They have to be absolutely clean!"

"How about outside in space?" Astro suggested. "We could take the parts
of the tube with us and assemble it out there. You can't ask for a
better va