"Go on, Astro," shouted the young Space Cadet. "Boot that screwy ball with everything you've got!"

The three cadets of the Polaris unit raced down the Academy field toward the mercuryball, a plastic sphere with a vial of mercury inside. At the opposite end of the field, three members of the Arcturus unit ran headlong in a desperate effort to reach the ball first.

Astro, the giant Space Cadet from Venus, charged toward the ball like a blazing rocket, while his two unit mates flanked him, ready to block out their opponents and give Astro a clear shot at the ball.

On the left wing, Tom Corbett, curly-haired and snub-nosed, ran lightly down the field, while on the opposite wing, Roger Manning, his blond hair cut crew style, kept pace with him easily. The two teams closed. Roger threw a perfect block on his opposing wingman and the two boys went down in a heap. Tom side-stepped the Arcturus cadet on his side and sent him sprawling to the ground. He quickly cut across the field and threw his body headlong at the last remaining member of the opposition. Astro was free to kick the ball perfectly for a fifty-yard goal.

Jogging back toward their own goal line, the three Polaris cadets congratulated each other. Astro's kick had tied the score, two-all.

"That was some feint you pulled on Richards, Tom," said Roger. "You sucked him in beautifully. I thought he was going to tear up the field with his nose!"

Tom grinned. Compliments from Roger were few and far between.

Astro clapped his hands together and roared, "All right, fellas, let's see if we can't take these space bums again! Another shot at the goal—that's all I need!"

Lining up at the end of the field again, the cadets kept their eyes on the cadet referee on the side lines. They saw him hold up his hand and then drop it suddenly. Once again the teams raced toward the ball in the middle of the field. When they met, Roger tried to duplicate Tom's feat and feint his opponent, but the other cadet was ready for the maneuver and stopped dead in his tracks. Roger was forced to break stride just long enough for the Arcturus cadet to dump him to the ground and then race for Astro. Tom, covering Astro on the left wing, saw the cadet sweeping in and lunged in a desperate attempt to stop him. But he missed, leaving Astro unprotected against the three members of the Arcturus unit. With his defense gone, Astro kicked at the ball frantically but just grazed the side of it. The mercury inside the ball began to play its role in the game, and as though it had a brain of its own, the ball spun, stopped, bounced, and spiraled in every direction, with the cadets kicking, lunging, and scrambling for a clean shot. Finally Astro reached the tumbling sphere and booted it away from the group. There was a roar of laughter from the Arcturus unit and a low groan from Tom and Roger. Astro saw that he had kicked the ball over his own goal line.

"Why, you clobber-headed Venusian hick!" yelled Roger. "Can't you tell the difference between our goal and theirs?"

Astro grinned sheepishly as the three jogged back to their own goal to line up once more.

"Lay off, Roger," said Tom. "How come you didn't get Richards on that play?"

"I slipped," replied the blond cadet.

"Yeah, you slipped all right," growled Astro good-naturedly, "with a great big assist from Richards."

"Ah, go blast your jets," grumbled Roger. "Come on! Let's show those space crawlers what this game is all about!"

But before the cadet referee could drop his hand, a powerful, low-slung jet car, its exhaust howling, pulled to a screeching stop at the edge of the field and a scarlet-clad enlisted Solar Guardsman jumped out and spoke to him. Sensing that it was something important, the two teams jogged over to surround the messenger.

"What's up, Joe?" asked Roger.

The enlisted spaceman, an Earthworm cadet who had washed out of the Academy but had re-enlisted in the Solar Guard, smiled. "Orders for the Polaris unit," he said, "from Captain Strong."

"What about?" asked Roger.

"Report on the double for new assignments," replied the guardsman.

"Yeeeeooooow!" Astro roared in jubilation. "At last we can get out of here. I've been doing so blamed much classroom work, I've forgotten what space looks like."

"Know where we're going, Joe?" asked Tom.

"Uh-uh." Joe shook his head. He turned away, then stopped, and called back, "Want a lift back to the Tower?"

Before Tom could answer, Richards, the captain of the Arcturus unit spoke up. "How about finishing the game, Tom? It's been so long since we've had such good competition we hate to lose you. Come on. Only a few more minutes."

Tom hesitated. It had been a long time since the two units had played together, but orders were orders. He looked at Roger and Astro. "Well, what about it?"

"Sure," said Roger. "We'll wipe up these space jokers in nothing flat! Come on!"

There was a mock yell of anger from the Arcturus unit and the two teams raced back to their starting positions. In the remaining minutes of play, the cadets played hard and rough. First one team would score and then the other. A sizable crowd of cadets had gathered to watch the game and cheered lustily as the players tore up and down the field. Finally, when both teams were nearly exhausted, the game was over and the score was eight to seven in favor of the Polaris unit. Roger had made the final point after Tony Richards had left the game with a badly bruised hip. A substitute called in from the bystanders, an Earthworm cadet, had eagerly joined the Arcturus team for the last minutes of play but had been hopelessly outclassed by the teamwork of the Polaris unit.

Promising a return match soon, Roger, Tom, and Astro hurried to their lockers, showered, and dressed in their senior cadet uniforms of vivid blue, then raced to the nearest slidewalk to head toward the main group of buildings that made up Space Academy.

Whisked along on the moving belt of plastic that formed the principle method of transportation in and around the Academy grounds, Tom turned to his unit mates. "What do you think it'll be?" he asked.

"You mean the assignment?" asked Roger, answering his own question in the next breath. "I don't know. But anything to get out of here. I've been on Earth so long that I'm getting gravity-itis!"

Tom smiled. "It'll sure be nice to get up in the wide, high, and deep again," he said, glancing up at the cloudless sky.

"Say it again, spaceman," breathed Astro. "One more lesson on the differential potential between chemical-burning rocket fuels and reactant energy and I'll blast off without a spaceship!"

Roger and Tom laughed. They both sympathized with the big cadet's inability to cope with the theory of atomic energy and fuel conservation in spaceships. In charge of the power deck on the Polaris, Astro earlier had gained firsthand experience in commercial rocket ships as an able spaceman and later had been accepted in the Academy for cadet training. The son of colonists on Venus, the misty planet, his formal education was limited, and though he had no equal while on the power deck of a rocket ship, in theory and classroom study he had to depend on Roger and Tom to help him get passing grades.

The slidewalk moved smoothly and easily toward the gleaming Tower of Galileo, the largest and most imposing of the structures of Space Academy. Made entirely of clear crystal mined on Titan, satellite of Saturn, the Tower rose over the smaller buildings like a giant shimmering jewel. Housing the administration offices of the Solar Guard and the Space Academy staff, it also contained Galaxy Hall, the museum of space, which attracted thousands of visitors from every part of the Solar Alliance.

Tom Corbett, his eyes caressing the magnificent gleaming Tower, remembered the first time he had seen it. While it hadn't been so long in months or years since becoming a Space Cadet, it seemed as though he had been at the Academy all of his life and that it was his home. In the struggle to develop into a well-knit dependable rocket team, composed of an astrogator, power-deck cadet, and a command cadet, Tom had assumed the leadership of the unit, and the relationship between Astro, Roger Manning, and himself had ripened until they were more like brothers than three young men who had grown up millions of miles apart.

As they rode toward the Tower, the three cadets could see the green-clad first-year Earthworms getting their first taste of cadet life--hours of close-order formations and drills. The nearer they came to the Tower, the more intense and colorful became the activity as the crisscrossing slidewalks carried enlisted guardsmen in their red uniforms, and the officers of the Solar Guard in magnificent black and gold, across the quadrangle to the various dormitories, laboratories, lecture rooms, mess halls, and research rooms. Space Academy was a beehive of activity, with the education of thousands of cadets and the operational mechanics of the Solar Guard going on incessantly, day and night, never stopping in its avowed task of defending the liberties of the planets, safeguarding the freedom of space, and upholding the cause of peace throughout the universe.

As their slidewalk glided over the quadrangle, Roger suddenly turned to his unit mates. "Think we might get assigned to that radar project they're setting up on the Moon?" he asked. "I have a few ideas—"

Tom laughed. "He can't wait until he gets his hands on that new scanner Dr. Dale just finished, Astro," he said with a wink.

The big Venusian snorted. "Can you imagine the ego of that guy? Dr. Dale spends almost a year building that thing, with the help of the leading electronic scientists in the Alliance, and he can't wait to tell them about a few of his ideas!"

"I didn't mean that," complained Roger. "All I said was—"

"You don't have to say a word, hot-shot," interrupted Astro. "I can read your thoughts as though they were flashed on a stereo screen!"

"Oh, yeah!" growled Roger. "You should be that telepathic for your exams. Why didn't you read my thoughts when I beat my brains out trying to explain that thrust problem the other night?" He turned to Tom, shrugging his shoulders in mock despair. "Honestly, Tom, if I didn't know that he was the best power jockey in the Academy, I'd say he was the dumbest thing to leave Venus, including the dinosaurs in the Academy Zoo!"

With a hamlike hand Astro suddenly grabbed for Roger's neck, but the wiry cadet dashed along the slidewalk out of reach and the big Venusian rumbled after him. Tom roared with laughter.

As he started to follow his unit mates, one of the passengers on the slidewalk grabbed Tom by the arm and he turned to see Mike McKenny, Chief Warrant Officer in the enlisted Solar Guard and the first instructor the Polaris unit had met on their arrival at the Academy.

"Corbett!" demanded McKenny. "Are those two space crawlers still acting like monkeys out of their cages?"

Tom laughed and shook hands with the elderly spaceman. "Yes, sir," he said. "But you could hardly call Astro a monkey!"

"More along the lines of a Venusian gorilla, if you ask me!" snorted McKenny. The short, squat spaceman's eyes twinkled. "I've been hearing some mighty fine things about you three space bongos, Tommy. It's a wonder the Solar Guard didn't give you a unit citation for aiding in the capture of Coxine, the pirate!"

"Thanks, Mike. Coming from you that compliment really means something!"

"Just be sure you keep those two space lunatics in their proper cages," said Mike, indicating Roger and Astro, who at the moment were racing back and forth along the slidewalk bumping passengers left and right, "and you'll all be heroes someday."

"Yes, sir," said Tom. He glanced up, and noticing that he was in front of the Tower building, hopped to the walkway, waving a cheery good-by to Mike. "Blast over to our mess and have dinner with us some night, Mike!" he yelled to the departing figure.

"And interrupt the happiest hours in Astro's life?" bawled Mike. "No thank you!"

Tom laughed and turned to the huge open doorway of the Tower where Roger and Astro waited for him impatiently. In a few moments the three were being carried to the upper floors of the crystal structure by a spiraling band of moving plastic that stretched from the top of the Tower to the many floors below surface level. Tom glanced at his wrist chronograph as they stepped off the slidestairs and headed for Captain Strong's quarters.

"We're about twenty minutes late," he said to Roger and Astro. "Hope Captain Strong's in good spirits!"

"If he isn't," said Roger, "we can—"

"Don't say it," protested Astro. "I only just finished working off my last bunch of galley demerits."

They stopped in front of a door, straightened their uniforms, and then slid the door to one side and stepped smartly into the room. They came to rigid attention before a massive desk, flanked by two wall windows of clear sheet crystal reaching from ceiling to floor. Standing at the window, Captain Steve Strong, Polaris unit cadet supervisor, his broad shoulders stretching under his black-and-gold uniform, turned to face them, his features set in grim lines of trouble.

"Polaris unit reporting for orders, sir," said Tom. The three cadets saluted crisply.

Strong snapped a return salute and walked to the front of his desk. "Getting pretty big for your britches, aren't you?" he growled. "I've been watching you from this window. I saw the messenger deliver my orders to you, and then, I saw you return to your game and finish it, apparently deciding that the business of the Solar Guard can wait!"

"But, sir—" Roger started to say.

"Close your exhaust, Manning!" snapped Strong. "I'm doing the talking!"

"Yes, sir," stammered the blond-haired cadet.

"Well, Cadets," asked Strong in a silken voice, "if I sent you to Commander Walters' office on the double, do you think I could trust you to get there on the double?"

"Oh, yes, sir," replied Tom. "Yes, sir!" The other two boys nodded violently.

"Then blast out of here and report to Commander Walters for your assignments. Tell him I'll be there in a few minutes."

"Yes, sir!" said Tom, and the three cadets saluted sharply.

"Unit—" bawled Strong, "dis—missed!"

Outside in the hall once more, the three cadets wiped their faces.

"Captain Strong definitely was not in a good mood!" commented Roger.

"I've never seen him so angry!" said Tom. "Wonder why."

"Think it might be something to do with our assignments?" asked Astro.

"Never can tell, Astro," said Tom. "And there's only one way to find out. That's to get to Commander Walters' office on the double!"

Without another word the cadets hurried to the slide-stairs, each of them hungry for excitement. Already having participated in three outstanding adventures, the cadet members of the Polaris unit were eager to begin a fourth.