ip and
listened to the distant throb of a pump, rising and falling, pumping
free air throughout the station.

"Well," sighed Tom, "I always did want to know how a space station
worked. Now I guess I'll learn firsthand."

"Me, too," said Astro. He propped his big feet up on a delicate
instrument panel of the control board.

"Me, too!" sneered Roger, his voice filled with a bitterness that
surprised Tom and Astro. "But I didn't think I would find out like this!
How in the universe has that--that tyrant managed to stay alive this
long!"

CHAPTER 5

"The space station's biggest headache," said Terry Scott, a young Solar
Guard officer assigned the job of showing the _Polaris_ crew around, "is
to maintain perfect balance at all times."

"How do you achieve that, sir?" asked Tom.

"We create our own gravity by means of a giant gyroscope in the heart of
the station. When more weight is taken aboard, or weight leaves the
station, we have to adjust the gyro's speed."

They entered the power deck of the great ball-like satellite. Astro's
eyes glowed with pleasure as he glanced approvingly from one massive
machine to another. The fuel tanks were made of thin durable aluminite;
a huge cylinder, covered with heat-resistant paint, was the air
conditioner; power came from a bank of atomic dynamos and generators;
while those massive pumps kept the station's artificial air and water
supply circulating.

Dials, gauges, meters, were arrayed in seemingly endless rows--but each
one of them actually played its part in keeping the station in balance.

Astro's face was one big, delighted grin.

"Well," said Roger with a sly wink at Tom, "you can't tell me that
Connel has made our Venusian unhappy. Even if he had given us liberty,
I'll bet Astro would have spent it down here with the grease monkeys!"

Astro didn't rise to the bait. His attention was riveted on a huge
dynamo, which he watched with appreciative eyes. But then Terry Scott
introduced the _Polaris_ unit to an older Solar Guard officer.

"Cadets, meet Captain Jenledge," said Scott. "And, sir, this is Cadet
Astro. Major Connel would like him to work with you while he's here."

"Glad to know you, boys," said Jenledge, "and particularly you, Cadet
Astro. I've heard about your handiness with the thrust buckets on the
cruisers. What do you think of our layout?"

The officer turned and waved his hand to indicate the power-deck
equipment.

"This is just about the