his Rock."

"You mean," gasped Roger, "that the men on this asteroid deliberately
chose to remain criminals?"

"Yes, Manning," said Strong. "Rather than become healthy citizens of the
system, they prefer to stay here and waste their lives in isolation with
no hope of ever returning to society."

"Can they change their minds after they get here?" asked Tom.

"Any time. But when they get this far, they usually stay here. The men
on Prison Rock didn't surrender easily. They are the toughest, most
ruthless men in the universe."

"Attention! Freighter _Dog Star_! Attention!" the audioceiver rasped
into life again. "You have been given temporary clearance. A space
launch will ferry you to the asteroid. You are warned that any weapons
discovered on your person, or acts that may be construed as providing
aid and comfort to the inmates of this prison, will be considered
treason against the Solar Alliance and you will be subject to immediate
disciplinary action."

Tom and Roger glanced at each other, a worried look in their eyes.
Strong just smiled. "Don't worry, boys. That little speech is read to
every visitor to the asteroid."

"Just the same, sir," said Roger huskily, "I would prefer to remain
aboard the _Dog Star_ and give you, Tom, and Astro the pleasure of the
visit."

Strong laughed. "They won't let you, Roger. They'll send up a crew of
guards to search the ship. And the way these boys search makes a customs
inspection look like a casual glance."

"Attention _Dog Star_!" A younger voice suddenly came in on the
audioceiver. "This is Lieutenant Williams aboard the space launch. We
are approaching your starboard catapult deck. Please open the air lock
and take us aboard."

"They sure don't waste any time," commented Tom as he turned to the
audioceiver. "Freighter _Dog Star_, Cadet Tom Corbett to Lieutenant
Williams," he called, "the air lock is open and the catapult deck is
ready to receive you." At the same time, the young cadet turned the
valve that would open the outer air lock to the jet-boat deck.

Five minutes later, the ship was swarming with tight-lipped enlisted
Solar Guardsmen, who spoke to Strong and the cadets with cool courtesy.
These were men who signed up for two years as guards on the Rock after
competing with thousands of other enlisted men. A guard on the Rock was
mid triple wages for the two-year isolation. But more than anything else
the right to wear the bright white patch with a paralo-ray