"Stand by to reduce thrust on main drive rockets!" The tall, broad-shouldered officer in the uniform of the Solar Guard snapped out the order as he watched the telescanner screen and saw the Western Hemisphere of Earth looming larger and larger.

"Aye, aye, Captain Strong," replied a handsome curly-haired Space Cadet. He turned to the ship's intercom and spoke quickly into the microphone.

"Control deck to power deck. Check in!"

"Power deck, aye," a bull-throated voice bellowed over the loud-speaker.

"Stand by rockets, Astro! We're coming in for a landing."

"Standing by!"

The Solar Guard officer turned away from the telescanner and glanced quickly over the illuminated banks of indicators on the control panel. "Is our orbit to Space Academy clear?" he asked the cadet. "Have we been assigned a landing ramp?"

"I'll check topside, sir," answered the cadet, turning back to the intercom. "Control deck to radar deck. Check in!"

"Radar bridge, aye," drawled a lazy voice over the speaker.

"Are we cleared for landing, Roger?"

"Everything clear as glass ahead, Tom," was the calm reply.

"We're steady on orbit and we touch down on ramp seven. Then"—the voice began to quicken with excitement—"three weeks' liberty coming up!"

The rumbling voice of the power-deck cadet suddenly broke in over the intercom. "Lay off that space gas, Manning. Just see that this space wagon gets on the ground in one piece. Then you can dream about your leave!"

"Plug your jets, you big Venusian ape man," was the reply, "or I'll turn you inside out!"

"Yeah? You and what fleet of spaceships?"

"Just me, buster, with my bare hands!"

The Solar Guard officer on the control deck smiled at the young cadet beside him as the good-natured argument crackled over the intercom speaker overhead. "Looks like those two will never stop battling, Corbett," he commented dryly.

"Guess they'll never learn, sir," sighed the cadet.

"That's all right. It's when they stop battling that I'll start getting worried," answered the officer. He turned back to the controls. "One hundred thousand feet from Earth's surface! Begin landing procedure!"

As Cadet Tom Corbett snapped orders into the intercom and his unit-mates responded by smooth co-ordinated action, the giant rocket cruiser Polaris slowly arched through Earth's atmosphere, first nosing up to lose speed and then settling tailfirst toward its destination—the spaceport at Space Academy, U.S.A.

Far below, on the grounds of the Academy, cadets wearing the green uniforms of first-year Earthworms and the blue of the upper-classmen stopped all activity as they heard the blasting of the braking rockets high in the heavens. They stared enviously into the sky, watching the smooth steel-hulled spaceship drop toward the concrete ramp area of the spaceport, three miles away.

In his office at the top of the gleaming Tower of Galileo, Commander Walters, commandant of Space Academy, paused for a moment from his duties and turned from his desk to watch the touchdown of the great spaceship. And on the grassy quadrangle, Warrant Officer Mike McKenny, short and stubby in his scarlet uniform of the enlisted Solar Guard, stopped his frustrating task of drilling newly arrived cadets to watch the mighty ship come to Earth.

Young and old, the feeling of belonging to the great fleet that patrolled the space lanes across the millions of miles of the solar system was something that never died in a true spaceman. The green-clad cadets dreamed of the future when they would feel the bucking rockets in their backs. And the older men smiled faintly as memories of their own first space flight came to mind.

Aboard the Polaris, the young cadet crew worked swiftly and smoothly to bring their ship to a safe landing. There was Tom Corbett, an average young man in this age of science, who had been selected as the control-deck and command cadet of the Polaris unit after rigid examinations and tests. Topside, on the radar bridge, was Roger Manning, cocky and brash, but a specialist in radar and communications. Below, on the power deck, was Astro, a colonial from Venus, who had been accused of cutting his teeth on an atomic rocket motor, so great was his skill with the mighty "thrust buckets," as he lovingly called the atomic rockets.

Now, returning from a routine training flight that had taken them to the moons of Jupiter, the three cadets, Corbett, Manning, and Astro, and their unit skipper, Captain Steve Strong, completed the delicate task of setting the great ship down on the Academy spaceport.

"Closing in fast, sir," announced Tom, his attention focused on the meters and dials in front of him. "Five hundred feet to touchdown."

"Full braking thrust!" snapped Strong crisply.

Deep inside the Polaris, braking rockets roared with unceasing power, and the mighty spaceship eased itself to the concrete surface of the Academy spaceport.

"Touchdown!" yelled Tom. He quickly closed the master control lever, cutting all power, and sudden silence filled the ship. He stood up and faced Strong, saluting smartly.

"Rocket cruiser Polaris completes mission"—he glanced at the astral chronometer on the panel board—"at fifteen thirty-three, sir."

"Very well, Corbett," replied Strong, returning the salute. "Check the Polaris from radar mast to exhaust ports right away."

"Yes, sir," was Tom's automatic answer, and then he caught himself. "But I thought—"

Strong interrupted him with a wave of his hand. "I know, Corbett, you thought the Polaris would be pulled in for a general overhaul and you three would get liberty."

"Yes, sir," replied Tom.

"I'm not sure you won't get it," said Strong, "but I received a message last night from Commander Walters. I think the Polaris unit might have another assignment coming up!"

"By the rings of Saturn," drawled Roger from the open hatch to the radar bridge, "you might know the old man would have another mission for us! We haven't had a liberty since we were Earthworms!"

"I'm sorry, Manning," said Strong, "but you know if I had my way, you'd certainly get the liberty. If anyone deserves it, you three do."

By this time Astro had joined the group on the control deck.

"But, sir," ventured Tom, "we've all made plans, I mean—well, my folks are expecting me."

"Us, you mean," interrupted Roger. "Astro and I are your guests, remember?"

"Sure, I remember," said Tom, smiling. He turned back to Captain Strong. "We'd appreciate it if you could do something for us, sir. I mean—well, have another unit assigned."

Strong stepped forward and put his arms around the shoulders of Tom and Roger and faced Astro. "I'm afraid you three made a big mistake in becoming the best unit in the Academy. Now every time there's an important assignment to be handed out the name of the Polaris unit sticks out like a hot rocket!"

"Some consolation," said Roger dourly.

Strong smiled. "All right, check this wagon and then report to me in my quarters in the morning. You'll have tonight off at least. Unit dis-missed!"

The three cadets snapped their backs straight, stood rigid, and saluted as their superior officer strode toward the hatch. His foot on the ladder, he turned and faced them again.

"It's been a fine mission. I want to compliment you on the way you've handled yourselves these past few months. You boys are real spacemen!" He saluted and disappeared down the ladder leading to the exit port.

"And that," said Roger, turning to his unit-mates, "is known as the royal come-on for a dirty detail!"

"Ahhh, stop your gassing, Manning," growled Astro. "Just be sure your radar bridge is O.K. If we do have to blast out of here in a hurry, I want to get where we're supposed to be going!"

"You just worry about the power deck, spaceboy, and let little Roger take care of his own department," replied Roger.

Astro eyed him speculatively. "You know the only reason they allowed this space creep in the Academy, Tom?" asked Astro.

"No, why?" asked Tom, playing along with the game.

"Because they knew any time the Polaris ran out of reactant fuel we could just stick Manning in the rocket tubes and have him blow out some of his special brand of space gas!"

"Listen, you Venusian throwback! One more word out of you and—"

"All right, you two!" broke in Tom good-naturedly. "Enough's enough! Come on. We've got just enough time to run up to the mess hall and grab a good meal before we check the ship."

"That's for me," said Astro. "I've been eating those concentrates so long my stomach thinks I've turned into a test tube."

Astro referred to the food taken along on space missions. It was dehydrated and packed in plastic containers to save weight and space. The concentrates never made a satisfactory meal, even though they supplied everything necessary for a healthful diet.

A few moments later the three members of the Polaris stood on the main slidewalk, an endless belt of plastic, powered by giant subsurface rollers, being carried from the spaceport to the main academy administration building, the great gleaming Tower of Galileo.

Space Academy, the university of the planets, was set among the low hills of the western part of the North American continent. Here, in the nest of fledgling spacemen, boys from Earth and the colonies of Venus and Mars learned the complex science that would enable them to reach unlimited heights; to rocket through the endless void of space and visit new worlds on distant planets millions of miles from Earth.

This was the year 2353—the age of space! A time when boys dreamed only of becoming Space Cadets at Space Academy, to learn their trade and later enter the mighty Solar Guard, or join the rapidly expanding merchant space service that sent out great fleets of rocket ships daily to every corner of the solar system.

As the slidewalk carried the three cadets between the buildings that surrounded the grassy quadrangle of the Academy, Tom looked up at the Tower of Galileo dominating the entire area.

"You know," he began haltingly, "every time I go near this place I get a lump in my throat!"

"Yeah," breathed Astro, "me too."

Roger made no comment. His eyes were following the path of the giant telescope reflector that moved in a slow arc, getting into position for the coming night's observations. Tom followed his gaze to the massive domed building, housing the giant one-thousand-inch reflector.

"You think we'll ever go as far into the deep with a rocket ship as we can see with the big eye?" he asked.

"I dunno," replied Roger. "That thing can penetrate other star systems in our galaxy. And that's a long way off!"

"Nearest thing to us is Alpha Centauri in our own galaxy, and that's twenty-three and a half million million miles away," commented Astro.

"That's not so far," argued Tom. "Only a few months ago the Solar Alliance sent out a scientific exploration to take a look at that baby."

"Musta been some hop," commented Roger.

"Hey!" cried Tom suddenly. "There's Alfie Higgins!" He pointed in the direction of another slidewalk moving at right angles to their own. The cadet that he singled out on the slidewalk was so thin and small he looked emaciated. He wore glasses and at the moment was absorbed in a paper he held in his hand.

"Well, what do you know!" cried Astro. "The Brain!"

Roger punched Astro in the mid-section. "If you were as smart as he is, you big grease monkey, you'd be O.K."

"Nah!" replied Astro. "If I was as smart as Alfie, I'd be scared. And besides, what do I need to be smart for? I've got you, haven't I?"

When they drew near the other slidewalk, the three members of the Polaris unit skipped lightly over and jostled their way past other riders to the slightly built cadet.

"Alfie!" Tom yelled and slapped the cadet on the back. Alfie turned, his glasses knocked askew by Tom's blow, and eyed the three Polaris members calmly.

"It gives me great pleasure to view your countenances again, Cadets Corbett, Manning, and Astro," he said solemnly, nodding to each one.

Astro twisted his face into a grimace. "What'd he say, Roger?"

"He's happy to see you," Roger translated.

"Well, in that case," beamed Astro, "I'm happy to see you too, Alfie!"

"What's the latest space dope around the Academy, Alfie?" asked Tom. "What's this?" he indicated the paper in Alfie's hand.

"By the sheerest of coincidences I happen to have a copy of your new assignment!" replied Alfie.

Tom, Roger, and Astro looked at each other in surprise.

"Well, come on, spaceman," urged Roger. "Give us the inside info. Where are we going?"

Alfie tucked the paper in his inside pocket and faced Roger. He cleared his throat and spoke in measured tones. "Manning, I have high regard for your personality, your capabilities, and your knowledge, all of which makes you an outstanding cadet. But even you know that I occupy a position of trust as cadet courier for Commander Walters and the administrative staff. I am not at liberty to mention anything that I would have occasion to observe while in the presence of Commander Walters or the staff. Therefore, you will please refrain from questioning me any further regarding the contents of these papers!"

Roger's jaw dropped. "Why, you human calculator, you were the one who brought it up in the first place! I oughta knock off that big head of yours!"

Tom and Astro laughed.

"Lay off, Roger," said Tom. "You ought to know Alfie couldn't talk if he wanted to! We'll just have to wait until Captain Strong is ready to tell us what our next assignment will be!"

By this time the slidewalk had carried them to the front of the main dormitory, and the wide doors were crowded with members of the Space Academy Corps heading in for the evening meal. From all corners of the quadrangle, the slidewalks carried Earthworms in their green uniforms, upper-class cadets in deep blue, enlisted spacemen in scarlet red, and Solar Guard officers in their striking uniforms of black and gold. Chatting and laughing, they all were entering the great building.

The Polaris unit was well known among other cadet units, and they were greeted heartily from all sides. As Astro and Roger joked with various cadet units, forming up in front of the slidestairs leading down to the mess halls, Alfie turned to take a slidestairs going up. Suddenly he stopped, grabbed Tom by the shoulders, and whispered in his ear. Just as abruptly he turned and raced up the ascending slidestairs.

"What was that about?" asked Roger, as Tom stood staring after the little cadet.

"Roger—he—he said our next assignment would be one of the great experiments in space history. Something to be done that—that hasn't ever been done before!"

"Well, blast my jets!" said Astro. "What do you suppose it is?"

"Ahhh," sneered Roger, "I'll bet it's nothing more than taking some guinea pigs to see how they react to Jovian gravity. That's never been done before either! Why can't we get something exciting for a change?"

Tom laughed. "Come on, you bloodthirsty adventurer, I'm starved!"

But Tom knew that Alfie Higgins didn't get excited easily, and his eyes were wide and his voice trembled when he had whispered his secret to Tom.

The Polaris unit was due to embark on a great new adventure!