by James Dona
Rick Kirby wasn't sure his son was ready for a trip into space. There would always be hazards, but Jeremy had wanted to make this trip since he was ten. Besides, engineer Kirby had made the trip several times before, and the risk factor was so low it was statistically the safest way to travel. Not like the early days, when ships were blasted into orbit by controlled explosions.
They sped along the Bayshore Guideway, toward the Peninsula Levport. Rick was relaxed as the car slowed to enter the Lev exit. He had to admit that there was just a little tensing of his muscles as the car pulled into the parking area and threaded its way to an assigned slot.
Jeremy hoisted his own travel bag onto the manrail. It only took a minute for them to arrive at the check-in station. From here they viewed the ship that would take them into space and down to Australia. Even Rick marveled at the great levitation rings, spinning in opposite directions so fast they needed almost total vacuum to keep from burning up. They were so large that the far side of their vacuum housing disappeared in the lingering fog.
Jeremy blurted out, "The rings must be a mile in circumference. But Dad, why is the cabin so small?"
"It isn't that small, when you get close to it. It just looks small at this distance, compared to the levrings. We're working on ways to make the system more efficient. At this stage of development we need an enormous ratio of rotating mass to payload."
"So how many tons of rotating mass does it take to lift my weight?"
"Quite a few. Let's get aboard, so we can see the control room before we take off." He was glad Jeremy was too interested in the mechanics of the ship to think scary thoughts of going into space and back.
Jeremy said,"Wow!"when he saw the flight deck, with many screens around the room full of technical data and views of all parts of the ship. He was bursting with questions, but they would have to wait. They settled into their assigned recliners and strapped themselves in for the trip. Overhead screens showed a view from the control room, looking out over the levport. One screen showed the passengers, as an attendant scanned the cabin to verify that everyone was properly secured.
The pilot announced liftoff, and Rick felt a slight pressure from the recliner as their ship accelerated upward at about one G. He had made similar flights before, but was still thrilled by pictures on the screens, showing a widening panorama as they rose above the bay. He had also flown in airplanes many times, and the smoothness of this climb was still amazing. The great mass of the levrings was immune to the air currents that made airplanes shudder and bounce.
Jeremy was lost in study of all the screens showing details of the operation."We're going straight up now. Shouldn't we be heading for Australia, Dad?"
"Not yet, Son. We need to clear Bay Area airspace first. Look at that screen showing the inertial thrusters. They're pointed straight up to assist in the ascent. When we get a little higher you'll see them start to rotate to begin the flight toward Australia. The auto-pilot will control the thrust so we don't exceed Temp-One until we are clear of the atmosphere."
Jermy's eyes lit up. "Yeah. Temp-One is the maximum safe outer skin temperature."
"It also isn't efficient. Once we are out of the atmosphere we can accelerate much faster. We don't have to carry all that streamlining material. Shape doesn't matter in the vacuum of space."
Rick watched the altimeter climb to fifty miles, and the thrusters start to tilt. At seventy miles he watched the thrusters tilt to horizontal, propelling the ship toward Australia. The horizontal velocity increased above 1000 miles per hour, as the acceleration pushed them back against their now-vertical recliners. He watched the screen showing the Pacific Ocean below, with an occasional surface ship that seemed to speed across the water toward San Francisco, no matter which direction it might be sailing.
Jeremy watched the thruster. "Dad, I still don't think I really understand how thrusters operate."
"Well, go back to the original rocket operation. They accelerated hot gasses out the tail of the rocket. Remember the equation, F equals MA."
Jeremy's forehead wrinkled. "Force equals mass times acceleration. And for every action there is a reaction. The acceleration of hot gas in one direction provides the force to accelerate the rocket in the opposite direction. Those rockets burned a lot of fuel, and out in space they needed to carry oxygen in some form to make the fuel burn. Sometimes the rockets exploded. It was like riding on a bomb. I'm glad we have thrusters instead, but how do they work?"
"Well, you understand your third grade physics. In order to accelerate the rocket in one direction you need to accelerate mass in the opposite direction. Now suppose you could use a linear motor to accelerate a heavy steel rail out the back of the rocket instead of the hot gas."
Jeremy laughed at the thought. "You'd run out of rail pretty quick. Then what would you do?"
"Preposterous of course. But for a second there it would work. To keep the process going you would have to make the rail into a hoop, and accelerate it in a circle."
"Great! Now you've got a big iron hoop hanging out the side of a rocket. That would never fly."
"Of course not. But it illustrates a fundamental principle. The linear motor driving the hoop propels the rocket by converting linear thrust into rotary acceleration. In practice the hoops are made small enough to fit inside the rocket."
"But Dad. The hoop has to keep accelerating to provide the thrust force. What do you do when the hoop is going fast enough to fly apart?"
"Well, fortunately a linear generator on the opposite side of the hoop can decelerate it while producing a thrust in the same direction as the accelerating motor did. So the hoop accelerates to a maximum safe speed, then the accelerating motor turns off and the decelerator generator brings the hoop back to a lower speed. The hoop oscillates between the two speeds, providing continuous thrust."
"But wouldn't the ship rotate in the direction opposite to the hoop rotation?"
"That's why there are a pair of hoops, in line, with their rotation in the opposite direction. The motors are reversed in position, and synchronized so they cancel the ship's rotation."
"And there are two more hoops, set at right angles. They keep the thrust even in that plane, right?"
"Yes, and the generators are individually controlled to provide some rotation of the thrusters. That is necessary to keep the levitation hoops level. The thrusters are mounted on gimbals to provide additional lift or horizontal travel for the ship."
"So, why do they need the big levitation hoops, when they could just use thrusters?"
"We haven't been able to produce thrusters strong enough without needing too much power. The generator cycle of thrusters in one plane are synchronized with the motors in the other plane, so some power is recovered. But the losses are so high it takes a lot of power to supply the system. On the other hand, the levitation rings have little loss once brought up to speed. So the initial lift uses very little power. The rings are accelerated on external power at the levport, and the ship's internal power only needs to supply power to compensate for the losses."
Jeremy was silent for a few minutes. When he spoke, he said, "And the internal power from the atomic fusion generator can't be made a lot bigger because it would be too heavy for the levitation rings."
"That's right. We still don't know how to build fusion generators without a heavy magnetic Tokomak. It took almost a century to develop a Tokomak small enough to power this ship. It may take another century to discover how to build a smaller and lighter power source."
The pressure holding them against their recliners slackened. The voice of the pilot came over the speakers. "We are nearing the midpoint of our flight, and our recliners will now be rotated to begin the deceleration phase."
The recliners began the slow rotation, to face in the opposite direction. The feeling of weightlessness came and went, as the ship's deceleration pressed them again into the recliner cushions. Rick said, "We should be sitting on the Sydney levport in about half an hour. I know you will enjoy Australia."
Before Jeremy could answer, a sudden shudder rattled the ship. Rick tensed, wondering what could have caused this unexpected event.
"What was that Dad?"
"It may have been a collision with space junk or a small meteor. We'll just have to wait for the pilot to tell us. I'm sure the crew is checking to see what happened."
The pilot's calm voice came on the speakers. "We've been hit by something. It has damaged the shell of the levitation rings. No immediate problem, since the vacuum of space is as good as we are able to achieve on the ground. The levitation rings are at normal speed now. But we must restore the integrity of the vacuum system before we can reenter the atmosphere. We are diverting to Pago Pago in American Samoa as a precaution."
"What do we do now, Dad?"
"We just wait. The ships emergency procedures call for an attempt to patch the hole in the vacuum chamber around the levitation rings. One of the crew is always suited up for a space walk. We should be able to watch it on the outer-ring cameras."
One of the outside screens showed a section of the vacuum ring, where a small hole was easily seen. As the image moved in closer, the jagged tear in the housing loomed larger. They saw a rip in the metal that went from the hole to the outer edge of the housing and disappeared out of sight beyond the camera image. Rick looked in horror at this tear. He knew it was beyond space repair. He tried not to give away his feeling to his son.
One of the cameras now turned to the cabin exit port, where a space-suited crewman scooted out and moved off toward the site of the damage. When he arrived there he stopped to communicate with the Captain. Then he came back to reenter the cabin.
The Captain came on the screen. "We are near American Samoa. The vacuum ring can't be patched in space. We will detach the cabin and drop the levitation ring into the sea where it can be recovered later. The thrusters will be used to power the cabin to a landing at Pago Pago. If the thrust is not sufficient to slow our descent, the cabin will be detached from the thruster and power module. We will land the cabin inside the harbor using the emergency parachute. Remain in your recliners until we make a water landing in the harbor."
"Why can't we land using the levitation rings, Dad?"
"Without vacuum the rotating rings will burn up in the atmosphere. Nobody has jettisoned levitation rings, and we don't know what will happen. They could explode, or start a fire in the cabin. We hope the thrusters will slow our descent enough to get us down."
The recliners moved to their horizontal position. The Captain came on the screen again. "We are still able to use the levitation rings to slow our descent until we start to enter the atmosphere. When we start to lose vacuum out there, we will fire the separation bolt charges and the emergency retro-rockets. The levitation rings will continue to descend until they start to burn up. Whatever is left of them will drop into the sea near Rose Island. We will go to emergency power on the thrusters to slow our descent, and to steer us toward the airport at Pago Pago."
Rick felt the sudden jolt from the separation. The emergency retro-rockets fired at the same time to push him down into the recliner. One of the screens showed the great levitation rings fall away from them. It seemed in no hurry in its departure. He suddenly realized he was holding his breath, hoping it got far enough away before it hit the atmosphere. It suddenly dropped away faster, as the pilot followed emergency procedure and slowed the ring's rotation to speed their descent.
The instrument screen showed the rate of cabin descent. It was slow enough to avoid burning the cabin, but not slow enough for a safe landing. The image of the levitation assembly was getting smaller, but now glowed red from the atmosphere's friction on the internal rings. It was soon just a glowing light in the distance.
The Captain's image came back on the screen. "We have successfully jettisoned the levitation assembly, and are entering the atmosphere at a safe speed. The thrusters are not able to slow us enough for a safe landing, even on water. We will jettison the thrusters and the main power module. Then we will deploy the parachutes and aim for a landing in the harbor."
Rick suddenly felt a sense of loss. He had worked on the design of those thrusters, and this was the first time a set had to be jettisoned. But never mind that. He hoped the steering system for the parachutes would set them down inside the harbor. The seas outside would be pretty rough this time of year.
The cabin shook and the sound of exploding bolts signaled the separation of the cabin from the thrusters. The heavy thruster module dropped away quickly as it was shut down at separation, and the cabin's fall was arrested by the emergency parachute. The outside screen now showed a view of the harbor, and they were drifting toward it.
There was still one more anxiety. They must steer the parachute into the harbor so they could land on its calm waters. All the screens went blank, as power was shut down for the landing. Rick regretted that they couldn't watch the rest of the descent, but knew this was a part of the emergency procedure. At least he was here to experience the first emergency landing of a Levitation Ship. He hoped he survived to recount the story to the many people who participated in its development. Jeremy showed no sign of concern.
During the boat ride to shore, Jeremy called his cousin on his satellite phone. "Hi, Chuck. We just landed in Pago Pago, and Dad says we can tour the island before we leave for Sydney tomorrow."