Commander O'Brine had not exaggerated. The residue of carbon and thorium on the blast tube walls was stubborn, dirty, and penetrating. It was caked on in a solid sheet, but when scraped, it broke up into fine powder.

The Planeteers wore coveralls, gloves, and face masks with respirators, but that didn't prevent the stuff from sifting through onto their bodies. Rip, who directed the work and kept track of the radiation with a gamma-beta ion chamber and an alpha proportional counter, knew they would have to undergo personal decontamination.

He took a reading on the ion chamber. Only a few milliroentgens of beta and gamma radiation. That was the dangerous kind, because both beta particles and gamma rays could penetrate clothing and skin. But the Planeteers wouldn't get enough of a dose to do any harm at all. The alpha count was high, but so long as they didn't breathe any of the dust, it was not dangerous.

The Scorpius had six tubes. Rip divided the Planeteers into two squads, one under his direction and one under Koa's. Each tube took a couple of hours' hard work. Several times during the cleaning, the men would leave the tube and go into the main mixing chamber while the tube was blasted with live steam to throw the stuff they had scraped off out into space.

Each squad was on its last tube when a spaceman arrived. He saluted Rip. "Sir, the safety officer says to secure the tubes."

That could mean only one thing: deceleration. Rip rounded up his men. "We're finished. The safety officer passed the word to secure the tubes, which means we're going to decelerate." He smiled grimly. "You all know they gave us this job just out of pure love for the Planeteers. So remember it when you go through the control room to the decontamination chamber."

The Planeteers nodded enthusiastically.

Rip led the way from the mixing chamber, through the heavy safety door, and into the engine control room. His entrance was met with poorly concealed grins by the spacemen.

Halfway across the room, Rip turned suddenly and bumped into Sergeant Major Koa. Koa fell to the deck, arms flailing for balance—but flailing against his protective clothing. The other Planeteers rushed to pick him up, and somehow all their hands beat against each other.

The protective clothing was saturated with fine dust. It rose from them in a choking cloud and was picked up and dispersed by the ventilating system. It was contaminated dust. The automatic radiation safety equipment filled the ship with an earsplitting buzz of warning. Spacemen clapped emergency respirators to their faces and spoke unkindly of Rip's Planeteers in the saltiest space language possible.

Rip and his men picked up Koa and continued the march to the decontamination room, grinning under their respirators at the consternation around them. There was no danger to the spacemen, since they had clapped on respirators the moment the warning sounded. But even a little contamination meant the whole ship had to be gone over with instruments, and the ventilating system would have to be cleaned.

The deputy commander met Rip at the door of the radiation room. Above the respirator, his face looked furious.

"Lieutenant," he bellowed, "haven't you any more sense than to bring contaminated clothing into the engine control room?"

Rip was sorry the deputy commander couldn't see him grinning under his respirator. He said innocently, "No, sir, I haven't any more sense than that."

The deputy grated, "I'll have you up before the Discipline Board for this."

Rip was enjoying himself thoroughly. "I don't think so, sir. The regulations are very clear. They say, 'It is the responsibility of the safety officer to insure compliance with all safety regulations by both complete instructions to personnel and personal supervision.' Your safety officer didn't instruct us, and he didn't supervise us. You'd better run him up before the Board."

The deputy commander made harsh sounds into his respirator. Rip had him, and he knew it. "He thought even a stupid Planeteer had sense enough to obey radiation safety rules," he yelled.

"He was wrong," Rip said gently. Then, just to make himself perfectly clear, he added, "Commander O'Brine was within his rights when he made us rake radiation. But he forgot one thing. Planeteers know the regulations, too. Excuse me, sir. I have to get my men decontaminated."

Inside the decontamination chamber, the Planeteers took off their masks and faced Rip with admiring grins. For a moment he grinned back, feeling pretty good. He had held his own with the spacemen, and he sensed that his men liked him.

"All right," he said briskly. "Strip down and get into the showers."

In a few moments they were all standing under the chemically treated water, washing off the contaminated dust. Rip paid special attention to his hair, because that was where the dust was most likely to stick. He had it well lathered when the water suddenly cut off. At the same moment, the cruiser shuddered slightly as control blasts stopped its spinning and left them all weightless. Rip saw instantly what had happened. He called, "All right, men. Down on the floor."

The Planeteers instantly slid to the shower deck. In a few seconds the pressure of deceleration pushed at them.

"I like spacemen," Rip said wryly. "They wait until just the right moment before they cut the water and decelerate. Now we're stuck in our birthday suits until we land—wherever that may be."

Corporal Nels Pederson spoke up in a soft Stockholm accent. "Never mind, sir. We'll get back at them. We always do!"

While the Scorpius decelerated and started maneuvering for a landing, Rip did some rapid calculations. He knew the acceleration and deceleration rates of cruisers of this class, measured in terms of time, and part of his daily routine on the space platform had been to examine the daily astroplot, which gave the positions of all planets and other large bodies within the solar system.

There was only one possible destination: Mars.

Rip's pulse quickened. He had always wanted to visit the red planet. Of course, he had seen all the films, audio-mags, and books concerning it, and he had tried to see the weekly spacecast. He had a good idea of what the planet was like, but reading or viewing was not like actually landing and taking a look for himself.

Of course, they would land at Marsport. It was the only landing area equipped to handle nuclear drive cruisers.

The cruiser landed and deceleration cut to zero. At the same moment the water came on.

Rip hurriedly finished cleaning up, dressed, then took his radiation instruments and carefully monitored his men as they came from the shower. Private Dowst had to go back for another try at getting his hair clean, but the rest were all right. Rip handed his instruments to Koa. "You monitor Dowst when he finishes. I want to see what's happening."

He hurried from the chamber and made his way down the corridors toward the engine control room. There was a good possibility he might get a call from O'Brine, with instructions to take his men off the ship. He might finally learn what he was assigned to do!

As he reached the engine control room, Commander O'Brine was giving instructions to his spacemen on the stowage of equipment that evidently was expected aboard. Rip felt a twinge of disappointment. If the Scorpius had landed to take on supplies of some kind, his assignment was probably not on Mars.

He started to approach the commander with a question about his orders, then thought better of it. He stood quietly near the control panel and watched.

The air lock hissed, then slid open. A Martian stood in the entryway, a case on his shoulder. Rip watched him with interest. He had seen Martians before, on the space platform, but he had never gotten used to them. They were human, still....

He tried to figure out, as he had before, what it was that made them strange. It wasn't the blue-whiteness of their skins nor the very large, expressionless eyes. It was something about their bodies. He studied the Martian's figure carefully. He was slightly taller and more slender than the average earthman, but his chest measurements would be about the same. Nor were his legs very much longer.

Suddenly Rip thought he had it. The Martian's legs and arms joined his torso at a slightly different angle, giving him an angular look. That was what made him look like a caricature of a human, although he was human, of course—as human as any of them.

Rip saw that other Martians were in the air lock, all carrying cases of various sizes and shapes. They came through into the control room and put them down, then turned without a word and hurried back into the lock. They were all breathing heavily, Rip noticed. Of course! The artificial atmosphere inside the spaceship must seem very heavy and moist to them, after the thin, dry air of Mars.

The lock worked, and the Martians were replaced by others. They, too, deposited their cases. But these cases were bigger and heavier. It took four Martians to carry one, which meant they weighed close to half a ton each. The Martians could carry more than double an earthman's capacity.

When the lock worked next time, a Planeteer captain came in. He breathed the heavy air appreciatively, fingering the oxygen mask he had to wear outside. He saluted Commander O'Brine and reported, "This is all, sir. We filled the order exactly as Terra sent it. Is there anything else you need?"

O'Brine turned to his deputy. "Find out," he ordered. "This is our last chance. We have plenty of basic supplies, but we may be short of audio-mags and other things for the men." He turned his back on the Planeteer captain and walked away.

The captain grinned at O'Brine's retreating back, then walked over to Rip. They shook hands.

"I'm Southwick, SOS Two. Canadian."

Rip introduced himself and said he was an American. He added, "And aside from my men, you're the first human being I've seen since we made space."

Southwick chuckled. "Trouble with the spacemen? Well, you're not the first."

Talking about assignments wasn't considered good practice, but Rip was burning with curiosity. "You don't by chance know what my assignment is, do you?"

The captain's eyebrows went up. "Don't you?"

Rip shook his head. "O'Brine hasn't told me."

"I don't know a thing," Southwick said. "We got instructions to pack up a pretty strange assortment of supplies for the Scorpius, and that's all I know. The order was in special cipher, though, so we're all wondering about it."

The deputy commander returned, reported to O'Brine, then walked up to Rip and Southwick. "Nothing else needed," he said curtly. "We'll get off at once."

Southwick nodded, shook hands with Rip, and said in a voice the deputy could hear, "Don't let these spacemen bother you. Trouble with them is they all wanted to be Planeteers and couldn't pass the intelligence tests." He winked, then hurried to the air lock.

Spacemen worked quickly to clear the deck of the new supplies, stowing them in a nearby workroom. Within five minutes the engine control room was clear. The safety officer signaled, and the radiation warning sounded. Taking off!

Rip hurried to the squad room and climbed into an acceleration chair. The other Planeteers were already in the room, most of them in their bunks. Koa slid into the chair beside him. "Find out anything, sir?"

"Nothing useful. A bunch of equipment came aboard, but it was in plain crates. I couldn't tell what it was."

Acceleration pressed them against the chairs. Rip sighed, picked up an audio-circuit set, and put it over his ears. Might as well listen to what the circuit had to offer. There was nothing else to do. Music was playing, and it was the kind he liked. He settled back to relax and listen.

Brennschluss came some time later. It woke Rip up from a sound sleep. He blinked, glancing at his chronometer. Great Cosmos! With that length of acceleration they must be high-vacking for Jupiter! He waited until the ship went into the gravity spin, then got out of his chair and stretched. He was hungry. Koa was still sleeping. He decided not to wake him. The sergeant major would see that the men ate when they wanted to.

In the messroom only one table was occupied—by Commander O'Brine.

Rip gave him a civil hello and started to sit alone at another table. To his surprise, O'Brine beckoned to him.

"Sit down," the spaceman invited gruffly.

Rip did and wondered what was coming next.

"We'll start to decelerate in about ten minutes," O'Brine said. "Eat while you can." He signaled, and a spaceman brought Rip the day's ration in an individual plastic carton with thermo-lining. The Planeteer opened it and found a block of mixed vegetables, a slab of space meat, and two units of biscuit. He wrinkled his nose. Space meat he didn't mind. It was chewy but tasty. The mixed vegetable ration was chosen for its food value and not for taste. A good mouthful of Earth grass would be a lot more palatable. He sliced off pieces of the warm stuff and chewed thoughtfully, watching O'Brine's face for a clue as to why the commander had invited him to sit down.

It wasn't long in coming. "Your orders are the strangest things I've ever read," O'Brine stated. "Do you know where we're going?"

Rip figured quickly. They had accelerated for six and a half hours. Now, ten minutes after Brennschluss, they were going to start deceleration. That meant they had really high-vacked it to get somewhere in a hurry. He calculated swiftly.

"I don't know exactly," he admitted. "But from the ship's actions, I'd say we were aiming for the far side of the asteroid belt. Anyway, we'll fall short of Jupiter."

There was a glimmer of respect in O'Brine's glance. "That's right. Know anything about asteroids, Foster?"

Rip considered. He knew what he had been taught in astronomy and astrogation. Between Mars and Jupiter lay a broad belt in which the asteroids swung. They ranged from Ceres, a tiny world only 480 miles in diameter, down to chunks of rock the size of a house. No accurate count of asteroids—or minor planets, as they were called—had been made, but the observatory on Mars had charted the orbits of thousands. A few were more than a mile in diameter, but most were great boulders of irregular shape, from a few feet to several hundred feet at their greatest dimension.

"I know the usual stuff about them," he told O'Brine. "I haven't any special knowledge."

O'Brine blinked. "Then why did they assign you? What's your specialty?"

"Astrophysics."

"That might explain it. Second specialty?"

"Astrogation." He couldn't resist adding, "That's more advanced than the simple space navigation you use, Commander."

O'Brine started to retort, then apparently thought better of it. "I hope you'll be able to carry out your orders, Lieutenant," he said stiffly. "I hope, but not much. I don't think you can."

Rip asked, "What are my orders, sir?"

O'Brine waved in the general direction of the wall. "Out there somewhere in the asteroid belt, Foster, there is a little chunk of matter about one thousand yards in diameter. A very minor planet. We know its approximate coordinates as of two days ago, but we don't know much else. It happens to be a very important minor planet."

Rip waited, intent on the commander's words.

"It's important," O'Brine continued, "because it happens to be pure thorium."

Rip gasped. Thorium! The rare, radioactive element just below uranium in the periodic table of the elements, the element used to power this very ship! "What a find!" he said in a hushed voice. No wonder the job was Federation priority A, with Space Council security! "What do I do about it?" he asked.

O'Brine grinned. "Ride it," he said. "Your orders say you're to capture this asteroid, blast it out of its orbit, and drive it back to Earth!"