MOMENTUM

Asteroid 1207 came spinning into the auxiliary ship's viewplate like a glittering black mirage. The eight-mile chunk of rock was the last link in a chain of nine asteroid navigational-markers still needing blinker equipment installation. Minutes later, the Minnow lay neatly berthed in the deepest hollow of the asteroid, the shining wires of its drill grapples anchoring it firmly to the jagged rock. The airlock opened and two men in spacesuits stepped out. They climbed to the top of the nearest hill dragging a platform of tools and equipment; the ragged, close horizons of the asteroid made a hostile background for them as they worked in silence.

Ballard leaned far over the rough edge of a circular pit, directing the heat radiation beam that melted the foundation plastic smoothly over the walls. He couldn't spare the time to turn his head and watch Walton, but he could follow the other's progress in welding the framework of the blinker tower by the irregular breathing and clanks and buzzes coming through his earphones. He listened to Walton's motions with an automatic alertness developed over six long weeks of tension—ever since the finding of the rotenite nuggets on the second of the light-marker asteroids. The rotenite represented enough wealth to make them among the richest men in the solar system. Or one of them—the richest. That was what Ballard was afraid of.

Suddenly the clanks and rustles stopped, and Walton's voice muttered: "Must have left the number three flux; better go back for it."

"What?" Ballard caught himself asking rhetorically, apprehension flooding through him.

"I said I left something. Have to go back and get it." There was a faint tremor in Walton's voice.

With a hard calm he wouldn't have recognized six weeks ago, Ballard considered the consequences of making an excuse to go with Walton. But the excuse would destroy the pose of innocence he'd so carefully acted since his first suspicions of Walton's intention. And he could be wrong. No sense in antagonizing Walton, particularly with the frayed condition both their nerves were in. "Ok," he grunted. "Bring back another 5R bit; this one I've been using chitters."

There were the sounds of Walton bounding down towards the ship in the peculiar dancing glide demanded by the low gravity. Methodically, without looking up, Ballard continued his job, following Walton with his earphones. Only when the foundation fill was laid would it seem natural for him to stop working for a moment and go to the ship.

Gradually, layer on layer, the plastic melted, coated the walls and hardened. He heard Walton reach the ship, then there was a slight ringing noise as the man touched his key-magnet to the airlock. As Walton entered the lock, his mike registered the pressure of air by suddenly picking up all the sounds of the ship; the throbbing of the generators, the intermittent rush and sigh of the air conditioner, and the close curved walls echoing back the scrape of his shoes on the locker room floor.

Four minutes to go. Ballard finished melting the plastic onto the walls, resisting the urge to hurry and risk botching the work. Walton had no reason to kill him—except for the rotenite. And since its discovery, Walton had shown nothing but a surface friendship covering a hidden hatred and fear that was growing into surreptitious maneuverings towards murder. But with a pretense at normality, Ballard hoped Walton would get over his obsession and forget it, never knowing that he'd seen anything suspicious. And meanwhile Ballard had only to stay out of the way of accidents without seeming suspiciously careful.

He added the last necessary layer of plastic, switched off the heat beam and stood up. There was no sign of motion around the Minnow. Walton had not come out, but Ballard's earphones continued to pick up Walton's nervous, irregular breathing.

Ballard started down the hill in long, low floating bounds. The Minnow expanded up at him, a ship etched in black and white against a jagged mass of black and grey ores. Just before landing on his second bound, his earphones picked up a sharp metallic ringing note he couldn't identify. Suddenly the ship expanded up directly in front of him; he'd overshot his landing. He thudded into the ship, slid down to the ground and landed facing the lock, his key-magnet in hand.

Again he heard the familiar tuning-fork note, this time ringing faintly up from the magnet in his own hand as he put it against the circle of lighter metal that was the lock. The circle turned, with the magnet rotating out into a handle. He grabbed it and yanked to slide back the airlock panel. The yank pulled him off his feet. For an instant he couldn't orientate; then he realized that he had moved because the panel had not. It was a case of action or reaction. The panel had not budged, seeming to be one with the flawless sweep of the hull.

He tried again, yanking it with the same futile results. Apprehension flooded through him. "Walton!" he called. "Walton, the panel's stuck! Open it from the inside!"

For an instant he was aware of Walton's nervous breathing, then it stopped—there was a low chuckle. "Listen, Ballard! I'd be crazy to let you in. Don't you think I've seen you watching me like a hawk ever since we found the rotenite, just waiting for a chance to catch me off guard! I should have done this weeks ago, but it didn't occur to me how clean and easy it would be until I thought of the airlock jamming with you outside. So—the lock is jammed and you have left little over two hours of suit oxygen. And while you're out there suffocating to death, I'll be waiting in my sleep-tank on a nice euphoriac jag. It's going to be nice being the richest man in the—"

"Wait! Walton, listen! You're all wrong! I—"

Walton had cut his radio. For a moment, Ballard dumbly stood there, his mind racing around like a pin-wheel. Slowly it stopped, as numbing fear coursed through his nervous system. He'd under-concealed his suspicions, after all; Walton had suspected him of the very same thing he'd suspected Walton of.

Suddenly, in spite of his predicament, in spite of death waiting for him only a few hours in the future, Ballard smiled. He really couldn't hate Walton for what he'd done; it was the old cliche again of too much greed and suspicion.

He realized that this didn't alter the fact that he was going to die—unless he could think of something fast. Ballard looked at his chronometer; he now had less than two hours.

In spite of this, his mind suddenly calmed and became clear. First he'd have to think of all the possibilities of getting into the Minnow, then allot only so much time to each possibility. There was the welding torch, the heat-beam, a pneumatic jackhammer, and miscellaneous hand tools. Surely with that assortment he could knock or burn a hole in the ship. All the air would swish out, but there were enough suit cylinders to allow him to take the ship back if he didn't damage it too badly getting in. And Walton would be safe in his sleep-tank; Ballard would see to that by disconnecting the awakener.

Ballard smiled at the stars as he bounded back to the hill where the tools lay. Walton had been a fool to lock him out here with cutting, burning, and pounding equipment—and almost two hours in which to use them. Things weren't so bad after all.

He decided to try the welding torch first. He crossed over to the almost-completed blinker tower and picked up the torch and power-pack, then from a tool box he selected a cutting nozzle.

Carefully, so not to exert himself and waste oxygen, he glided down with his gear to the aft section of the Minnow's hull just forward of the tubes where the skin was thinnest. As he ignited the torch, he was aware of what a temptation it was to drain off all the oxygen contained in the power-pack into his own cylinder. Quickly he went ahead and applied the torch to the skin of the ship. Ballard glanced at his chronometer: An hour and a half to go. Good. Fifteen minutes would be long enough to tell whether the torch would cut through the skin or not. If it would, then he could use the rest of the time in cutting the hole.

After the first five minutes he turned the nozzle away and examined the spot where it had been applied. Not a mark.

Six minutes went by. Then seven, eight, nine—

Again he looked at the skin; still no change.

Three more minutes went by. Ballard felt sweat break out on his face as he pulled the torch away for a third time. For a moment—his eyes still blinded by the glare—he could see nothing. His heart sank. Then he detected a faint red spot with a whitish center. It was working. Three more minutes and the hole would be started. He turned back the nozzle to the glowing spot. Then with dismay he watched the torch sputter and go dead. Frantically he pushed the activator button—

Stunned, he finally noticed that the power-pack read empty. Walton had nearly exhausted it on the blinker tower.

Ballard glanced at his wrist. He still had an hour and fourteen minutes.

He didn't smile at the stars this time as he went back up the hill. Things didn't seem ironic any more, merely dangerous. He loaded the heat-beam with its larger power-pack onto the equipment platform and slowly dragged it behind him down to the ship.

An hour and two minutes left. He went to work adjusting the beam to its maximum intensity; then, moving it as close to the hull as possible, he turned it on full force.

Time seemed to have stopped. Twice in one minute Ballard glanced at his wrist, expecting to see a lapse of ten or fifteen minutes. Only five minutes had dragged by; he now had just fifty-seven left. His spacesuit suddenly began reminding him of a coffin. With superhuman effort he jerked his thoughts away from suffocation and back to the job.

Forty-five minutes to go. The beam wasn't going to work. The sudden realization cut into Ballard like a knife. He should have known that in the first place; a beam meant for plastic wasn't intense enough for the skin of a spaceship.

This time as Ballard once more climbed the hill, the stars seemed to be smiling at him. But not with friendliness. They seemed to smile death.

He got the jackhammer all the way down to the ship before a devastating thought struck him. He'd forgotten that the hammer had a cracked 5R bit; it would fly to pieces on the diamond hardness of the hull.

He sat down, stunned at the fact that he'd run out of things to try. The ship lay before him like some impenetrable fortress. Several precious minutes dragged by before Ballard could again calm his spinning brain. He still had forty minutes. Had he overlooked any other possibility of getting into the ship?

Slowly he walked around the Minnow, concentrating as he'd never concentrated before. Then as he stepped in front of the drive tubes something clicked: The main tube was large enough for him to crawl into. If he could remove the recoil plate and hydraulic mechanism, he might be able to burn a hole through the ordinary steel bulkhead beyond.

Half-bounding and half-running, he returned from the hill with the tool box. After selecting several likely wrench sizes, he grabbed a flashlight and crawled up the tube. He wasted five minutes unscrewing the first bolt holding the plate in place. The second bolt was so corroded he couldn't budge it. Cursing he crawled out and dragged in the jackhammer, hoping the cracked 5R bit would hold until the bolt was knocked out.

It almost held, flying to pieces just as there was a quarter inch to go. Frantically he somehow managed to knock the remainder out with the chuck of the hammer. But it had taken Ballard five more minutes. Only twenty-five left.

He went out and grabbed a crowbar and pried the plate off, recoil cylinder and hydraulic fluid following like a jack-in-the-box. After cleaning out the drive tube he almost lost his reason when he discovered the cable connecting the beam to the power-pack wasn't long enough to reach the bulkhead. Fortunately he found an extension in the bottom of the tool box.

Fifteen minutes to go.

That should be just long enough. He switched on the beam. Now time seemed to race by. At ten minutes to go the bulkhead turned a cherry-red. At five minutes it was almost white. At four, the steel started to buckle. At three—the heat-beam suddenly went dead. The power-pack was empty.

Ballard's reason reeled. He grabbed the crowbar and jabbed at the fast cooling metal.

Too late.

In the one minute he had left to live, Ballard suddenly became calm, reconciling himself to his end. Wearily he crawled out of the tube. At least Walton would be in for a nasty surprise, with the main drive recoil plate gone. And to make sure, he would push it off into space. With one last surge of fury he dragged up the foot thick plate he could never have lifted back on Earth, and started shoving to give it momentum.

Momentum equals velocity times mass. Suddenly he stopped, the plate drifting on ahead of him. Now why had he thought of that? Something from his school days—he tried hard to remember—something about mass....

Mass is a constant. Weight is a variable, but mass is what knocks holes in things—spaceships, for instance.

Just one thing could save him now—momentum. Ballard glanced at his wrist. Twenty seconds to go. Then maybe another twenty from the oxygen in the connecting tube. Not much time—

He bounded off after the still-drifting plate, then began forcing it around in a semi-circle back toward the ship. The recoil plate sluggishly began to move faster as it gained momentum. It started getting ahead of him so he gave it one last push, and it slowly crept away heading straight for the hull. It floated edge-wise into the aft section—and kept on going. A three foot stream of light poured out from the side of the ship.

Ballard started crawling into the hull and the light wavered and brightened. He couldn't understand it. Then it dimmed altogether—

The last of his oxygen was gone.

Dizzily he tried to squeeze through the rip. He kept slipping back ... back. There was a roaring darkness all around him, but he could still crawl.

For ages he seemed to be crawling over polished glass—His head crashed into something that clanged hollowly. Some fading portion of his consciousness told him he was inside the ship—and the clang had been the spacelocker. Automatically, as though by instinct, he reached up and fumbled with the handle—Then he was clumsily trying to fit a new oxygen cylinder into place....

Ballard awoke feeling cramped and tired, as though he'd slept all night in a bird cage. He looked at his chronometer, then at his suit air-gauge. No. He'd been out only a few minutes. He got up and crawled into the sleep-tank compartment and disconnected Walton's awakener. Then he went into the control room and looked up the nearest space-freighter lane in the radio call book, and set up an automatic distress signal. He felt as if he were going to pass out again—this time from sheer fatigue. There was still one thing more he wanted to do.

Out of the nose compartment he hauled a small case containing what had caused all the trouble—

Then he crawled back out through the torn hull skin, opened the case and flung every single one of the rotenite nuggets far out into space.