"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 finest—the most terrif—"

The officer smiled at Astro's inability to describe his feelings. Jenledge was proud of his power deck, proud of the whole establishment, for that matter. He had conceived it, had drawn the plans, and had constructed this space station.

Throughout the solar system it was considered his baby. And when he had asked for permission to remain on as senior power-deck chief, the Solar Alliance had jumped at the chance to keep such a good man on the job. The station had become a sort of postgraduate course for power-deck cadets and junior Solar Guard officers.

Astro beamed. So, the great Jenledge had actually heard of him—of humble Cadet Astro. He could hardly restrain himself from ripping off his blue uniform and going right to work on a near-by machine that had been torn apart for repairs. Finally he managed to gasp, "I think it's great, sir—just wonderful!"

"Very well, Cadet Astro," said the officer. "There's a pair of coveralls in my locker. You can start right to work." He paused and his eyes twinkled. "If you want to, that is!"

"Want to!" roared Astro, and was off to the locker room.

Jenledge turned to Scott. "Leave him with me, Scotty. I don't think Cadet Astro's going to care much about the rest of the station!"

Scott smiled, saluted, and walked away. Tom and Roger came to attention, saluted, and followed the young officer off the power deck.

"Astro's probably happier now than he'll ever be in his life, Tom," whispered Roger.

"Yeah," agreed Tom. "Did you see the way his eyes lit up when we walked in there? Like a kid with a brand-new toy!"

A moment later Scott, Tom, and Roger, in a vacuum elevator, were being hurtled to the station's upper decks. They got out on the observation deck, and Scott walked directly to a small door at the end of a corridor. A light over the door flashed red and Scott stopped.

"Here's the weather and meteor observation room," he said. "Also radar communications. When the red light's on, it means photographs are being taken. We'll have to wait for them to finish."

As they waited, Tom and Roger talked to Scott. He had graduated from Space Academy seven years before, they learned. He'd been assigned to the Solar Alliance Chamber as liaison between the Chamber and the Solar Guard. After four years, he had requested a transfer to active space operations.

Then, he told them, there'd been an accident. His ship exploded. He'd been badly injured—in fact, both his legs were now artificial.

The cadets, who had thought him a bit stuffy at first, were changing their minds fast. Why hadn't he quit, they wanted to know?

"Leave space?" said Scott. "I'd rather die. I can't blast off any more. But here at the station I'm still a spaceman."

The red light went out, and they opened the door.

In sharp contrast to the bustle and noise on the power deck, the meteor, weather, and radar observation room was filled with only a subdued whisper. All around them huge screens displayed various views of the surface of Venus as it slowly revolved beneath the station. Along one side of the room was a solid bank of four-foot-square teleceiver screens with an enlisted spaceman or junior officer seated in front of each one. These men, at their microphones, were relaying meteor and weather information to all parts of the solar system. Now it was Roger's turn to get excited at seeing the wonderful radar scanners that swept space for hundreds of thousands of miles. They were powerful enough to pick up a spaceship's identifying outline while still two hundred thousand miles away! Farther to one side, a single teleceiver screen, ten feet square, dominated the room. Roger gasped.

Scott smiled. "That's the largest teleceiver screen in the universe," he said. "The most powerful. And it's showing you a picture of the Andromeda Galaxy, thousands of light years away. Most of the lights you see there are no more than that, just light, their stars, or suns, having long ago exploded or burned. But the light continues to travel, taking thousands of years to reach our solar system."

"But—but—" gasped Tom. "How can you be so accurate with this screen? It looks as though we were smack in the center of the galaxy itself!"

"There's a fifty-inch telescope attached to the screen," Scott replied, "which is equal to the big one-thousand-inch 'eye' back at the Academy."

"Why is that, sir?" asked Roger.

"You don't get any distortion from atmosphere up here," replied the young officer.

As Tom and Roger walked silently among the men at the teleceiver screens, Scott continued to explain. "This is where you'll be, Manning," he said, indicating a large radarscope scanner a little to one side and partially hidden from the glow of the huge teleceiver screen. "We need a man on watch here twenty-four hours a day, though there isn't much doing between midnight and eight A.M. on radar watch. A little traffic, but nothing compared to what we get during the regular working day."

"Any particular reason for that, sir?" asked Tom.

"Oh, there just aren't many arrivals and departures during that period. We have night crews to handle light traffic, but by midnight the station is pretty much like any sleepy Middle Western town. Rolls up the sidewalks and goes to bed."

He motioned to Roger to follow him to the radar section and left Tom watching the interesting spectacle on the giant teleceiver. A huge star cluster flashed brilliantly, filling the screen with light, then faded into the endless blackness of space. Tom caught his breath as he remembered what Scott had told him about the light being thousands of years old before reaching the solar system.

"Manning's all set, Corbett," said Scott at Tom's elbow. "Come on. I'll show you the traffic-control deck."

Tom followed the young officer out of the room. As all true spacemen do at one time or another in their lives, he thought about the pitifully small part mankind had played so far in the conquest of the stars. Man had come a long way, Tom was ready to admit, but there was still a lot of work ahead for young, courageous spacemen.

As Scott and Tom climbed the narrow stairs to the traffic-control deck, the Solar Guard officer continued to speak of the man-made satellite. "When the station was first built," he said, "it was expected to be just a way station for refueling and celestial observations. But now we're finding other uses for it, just as though it were a small community on Earth, Mars, or Venus. In fact, they're now planning to build still larger stations." Scott opened the door to the traffic-control room. He motioned to Tom to follow him. This room, Tom was ready to admit, was the busiest place he had ever seen in his life. All around the circular room enlisted Solar Guardsmen sat at small desks, each with a monitoring board in front of him holding three teleceiver screens. As he talked into a mike near by, each man, by shifting from one screen to the next, was able to follow the progress of a spaceship into or out of the landing ports. One thing puzzled Tom. He turned to Scott.

"Sir, how come some of those screens show the station from the outside?" he asked. Tom pointed to a screen in front of him that had a picture of a huge jet liner just entering a landing port.

"Two-way teleceivers, Corbett," said Scott with a smile. "When you arrived on the Polaris, didn't you have a view of the station on your teleceiver?"

"Yes, sir," answered Tom, "of course."

"Well, these monitors picked up your image on the Polaris teleceiver. So the traffic-control chief here could see exactly what you were seeing."

In the center of the circular room Tom noticed a round desk that was raised about eight feet from the floor. This desk dominated all activity in the busy room. Inside it stood a Solar Guard officer, watching the monitoring teleceivers. He wore a throat microphone for sending out messages, and for receiving calls had a thin silver wire running to the vibrating bone in his ear. He moved constantly, turning in a circle, watching the various landing ports on the many screens. Three-thousand-ton rocket liners, Solar Guard cruisers, scout ships, and destroyers all moved about the satellite lazily, waiting for permission to enter or depart. This man was the master traffic-control officer who had first contacted Tom on his approach to the station. He did that for all approaching ships—contacted them, got the recognition signal, found out the ship's destination, its weight, and its cargo or passenger load.

Then the connection was relayed to one of the secondary control officers at the monitoring boards.

"That's Captain Stefens," said Scott in a whisper. "Toughest officer on the station. He has to be. From five hundred to a thousand ships arrive and depart daily. It's his job to see that every arriving ship is properly taken into the landing ports. Besides that, everything you've seen, except the meteor and weather observation rooms, are under his command. If he thinks a ship is overloaded, he won't allow it to enter and disrupt the balance of the station. Instead, he'll order its skipper to dump part of his cargo out in space to be picked up later. He makes hundreds of decisions a day—some of them really hair-raising. Once, when a rocket scout crew was threatened with exploding reactant mass, he calmly told them to blast off into a desolate spot in space and blow up. The crew could have abandoned ship, but they chose to remain with it and were blown to atoms. It could have happened to the station. That night he got a three-day pass from the station and went to Venusport."

Scott shook his head. "I've heard Venusport will never be the same after that three-day pass of Captain Stefens."

The young officer looked at Corbett quizzically. "That's the man you're going to work for."

Scott walked over to the circular desk and spoke rapidly to the officer inside. As Tom approached, Stefens gave him a quick, sharp glance. It sent a shiver down the cadet's spine. Scott waved to him to come over.

"Captain Stefens, this is Cadet Tom Corbett."

Tom came to attention.

"All right, Corbett," said Stefens, speaking like a man who had a lot to do, knew how to do it, liked to do it, and was losing time. "Stand up here with me and keep your mouth shut. Remember any questions you want to ask, and when I have a spare moment, ask them. And by the rings of Saturn, be sure I'm free to answer. Take my attention at the wrong moment and we could have a bad accident."

Stefens gave Scott a fleeting smile and turned back to his constant keen-eyed inspection of the monitors.

The radar watch was reporting the approach of a ship. Stefens began his cold, precise orders.

"Monitor seven, take freighter out of station on port sixty-six; monitor twelve, stand by for identification signal of jet liner coming in from Mars. Watch her closely. The Venusport Space Line is overloading again...." On and on he went, with Tom standing to one side watching with wide-eyed wonder as the many ships were maneuvered into and out of the station.

Suddenly Stefens turned to Tom. "Well, Corbett," he rasped, "what's the first question?"

Tom gulped. He had been so fascinated by the room's sheer magic and by Stefens' sure control of the traffic that he hadn't had a chance to think.

"I—I—don't have one—yet, sir," he managed finally.

"I want five questions within five minutes!" snapped Stefens, "and they better be rocket-blasting good questions!" He turned back to the monitors.

Tom Corbett, while he had gained the respect of many elder spacemen, was discovering that a cadet's life got no easier as time went on. He wondered fleetingly how Roger and Astro were making out, and then he began to think of some questions.

Beside him, oblivious of his presence, Stefens continued to spout directions. "Monitor three, take rocket scout out of landing-port eight. One crew member is remaining aboard the station for medical treatment. He weighs one hundred and fifty-eight pounds. Make balance adjustments accordingly...."

Tom's head was spinning. It was all too much for one young cadet to absorb on such short notice.