sion force we use a diverter valve to switch some of the mass current from the channels in the first tube into the second tube, but going in the opposite direction. The reverse current will cancel some of the gravitomagnetic field inside, which is equivalent to decreasing its strength. The decreasing gravitomagnetic field will make a gravity repulsor field that will keep the lander levitated above Egg."
"What is the hover time?" Cliff-Web asked.
"Only three methturns, so far," the Lander Team Leader replied. "Now that we have the basic design, we are going back and cutting weight. Our goal is six methturns levitation time, which should give us nearly a grethturn for a landing."
"Keep working," said Cliff-Web. "Launcher Team?"
"We had the easy job," another student reported. "The launcher is basically like the gravity catapults on Egg, but bigger. Our real effort has been on making the gravity repulsion field at the center as uniform as possible to minimize strains on the lander during launch. The size became awfully large though, twenty centimeters. I don't think we are going to be able to put it on one of the human compensator masses. We will need the larger deorbiter mass. I think the humans call it 'Otis' after the human that built the first space fountain."
"It wasn't a space fountain, it was an elevator," Cliff-Web explained.
"What is an elevator?" asked the student.
"Never mind. Launch Base Team?"
"While the launcher keeps getting bigger, the base keeps getting smaller," said a third student. "We've formed a joint study team with an astrophysics class taught by Plasma-Sheath, Doctor of Astrophysics. We are learning the realities of particle and plasma physics, while they are learning the fun of being a gravitational engineer. Our team now has the name 'Planet Busters.' We went out in a scout ship and took a look at Otis. The surface is too far down in the fuzz. We are going to have to use monopoles to shrink it and make it denser. Fortunately, the humans kept their monopole factory running, so they have plenty in storage."
"You are all doing good work," said Cliff-Web. "You have 24 more turns to finish your team report, then I think Plasma-Sheath and I had better talk to the humans before we go any further."
10:13:32 GMT TUESDAY 21 JUNE 2050
"We have a call from East Pole Space Station, Pierre," said Jean. "It's Cliff-Web and an astrophysicist named Plasma-Sheath. They are dumping some detailed information through a data channel, but they also want to speak with you."
Pierre stopped his checkout of the ship's computer and switched his screen to the communications channel, where two cheela appeared on the screen. Cliff-Web was the smaller, although large for a male. The other wore badges on her hide with a starburst in the center. Pierre was becoming better at identifying the sexes, although Plasma-Sheath made it easy with her big lower eyeflaps.
"We have found a way to get back down to Egg," Cliff-Web began without preliminaries. "Since we are very short of everything in space, we would have to borrow some mass and monopoles from you. Unfortunately, your ring masses are too small; only the deorbiter mass would do. We would shrink it with monopoles until it turns into a miniature neutron star, then use that as a base to construct the lander and its launcher."
Pierre was puzzled. "I don't see how you can do that. Even if you could shrink it so the surface density equals that of a neutron star, the equation of state is unstable and it will collapse into a miniature black hole."
"We are aware of that," said Plasma-Sheath. "By injecting only one type of monopole into the deorbiter mass, we can increase the center density by the formation of monopolium, but the monopolium atoms will have a tendency to repel each other since they will have the same magnetic charge. It is hoped that in this way we can keep the shrinking of the deorbiter under control and keep it from collapsing into a black hole."
"Sounds risky to me," said Pierre. "Are you sure of your calculations?"
"No," replied Plasma-Sheath. "But it is a risk that we must take."
Suddenly another cheela appeared on the screen. Pierre recognized the two-star clusters on the hide of Admiral Steel-Slicer, leader of the space cheela.
"That is not what concerns us," he said. "We not only want to use the deorbiter mass as a base to build our gravity catapult, but to deliver the catapult to the surface of Egg. We will have to divert it from its normal orbit."
"That's all right," said Pierre. "All we need is its gavitational field, and it makes no difference if it is a degenerate asteroid, a miniature neutron star, or a black hole. The external gravity field is the same. Just make sure you put it back in its elliptical orbit when you are through so we can use it to get back up to St. George. You aren't going to be using it for too long, are you? We only have supplies for a few weeks since this mission was designed for eight days."
"That is the problem." Steel-Slicer was now alone on the screen. "It is possible that the compensator mass will be destroyed in the process of placing the gravity catapult on Egg."
Pierre paused for a few seconds in shock, then quickly realized that he was wasting the equivalent of weeks of time of the cheela whose blinking image indicated he was checking in at the console every fifth of a second.
"Without the deorbiter mass, we would be stuck here.... What are the odds?"
"We are constantly trying to find another way of doing it," Steel-Slicer replied, "but right now the odds are 12 to 1."
"Well," said Pierre. "That's not bad."
"There is an 11 in 12 chance that the deorbiter mass will be tidally disintegrated while delivering the gravity catapult to the surface of Egg and only a one-twelfth chance it will survive. It all depends upon how the orbital and tidal dynamics couple into the interior vibrational modes of the deorbiter mass during the actual transit."
Pierre paused a few seconds again, but this time his brain was not worrying about the cheela.
"There is Oscar, the other large asteroid mass that was used to put the deorbiter mass into its elliptical orbit. Couldn't you use that?"
"With our limited resources, we do not have the power to alter the celestial laws for large, low-density masses," said Steel-Slicer. "That asteroid is well on its way out of the Dragon's Egg system. The best we could do is bring it back in about six months. That is equivalent to eternity for us."
"Hmmm." Pierre considered the options, then said, "I think I'd better talk with Commander Swenson and the rest of the crew."
They gathered in the viewport lounge to discuss the question. Doctor Wong blackened the viewport in the floor as they entered. No one objected. It would be hard enough to make a
decision without having the bright yellow image of Sol flickering through the port.
"Commander Swenson says the decision is up to us," Pierre replied. "Her only conditions were that there be a secret ballot and that the decision to let the cheela use Otis be unanimous."
"It would be a lot easier to say 'Yes' if the chances were better," Jean said. "Eight percent is not very good odds."
"Eight and a third percent," corrected Seiko. "We must also remember the number of intelligent beings involved. By putting our five lives at risk, we prevent the demise of an entire intelligent civilization."
"I just don't like the way we have to go," said Abdul. "Starving to death is not my idea of fun. I'd rather go quickly."
Cesar spoke up. "I would like to remind everyone that just over three hours ago, all of us would have experienced a quick death if it had not been for the efforts of the two cheela, Admiral Steel-Slicer and Engineer Cliff-Web, who now ask for our help."
Pierre waited for more discussion. There was none, so he passed out blank sheets of paper.
"Write 'Yes' if you agree to let the cheela use Otis, and 'No' if you think the risk is too high." Then Pierre collected the ballots and went through them quickly.
"There are four 'Yes' votes and one 'No.' I will inform Admiral Steel-Slicer that they will have to find another way of getting down to Egg. Then I will program the herder rockets to change Otis's orbit so we can go h
ome."
"Just a minute," Abdul spoke up. "I change my mind. Switch my vote to a 'Yes.' It wasn't the fault of the cheela that Amalita was taken away and it's stupid to be mad at a neutron star. It doesn't care."
10:25:02 GMT TUESDAY 21 JUNE 2050
Steel-Slicer and a newly rejuvenated Cliff-Web watched from a scout ship as the cargo ship brought the first batch of north monopoles from the distant monopole factory and dumped them into the human deorbiter mass. The monopoles scattered into a diffuse cloud from their mutual repulsion as they were released from the hold of the cargo ship. The cloud was sucked up by the gravity field from the deorbiter mass and disap-
peared beneath the fuzzy surface of the kilometer-sized ball. Later they would have to shoot the monopoles into the magnetized ball with an electromagnetic accelerator.
"One," said Cliff-Web. "And an infinity more to go." He sucked on a chewy red ball from one of the new food machines.
"It's going to be a long, dull job," Steel-Slicer said. "Forty generations of ferrying monopoles over the same dull stretch of space between the factory and the deorbiter mass. The situation is ripe for boredom, mistakes, and even mutiny. I want plenty of history in the creche-classes, lots of time off from the ferrying job at entertainment centers, and the best and newest of the food machines on the ferry ships."
They watched the second ship dump its cargo of north monopoles.
"Let's go over to the refurbishment facilities at West Pole Space Station," said Cliff-Web. "I want to see how they are coming on the conversion of the Abdul from an exploration ship to a cargo ship."
20:55:45 GMT TUESDAY 21 JUNE 2050
It was many greats later when Steel-Slicer and Cliff-Web visited Otis again. Having recently undergone his 34th rejuvenation, Steel-Slicer was now young looking, while Cliff-Web and the scoutship were old and tired. The black hole at the center of the scout ship was now noticeably less massive, as its rest mass had been used up to operate the inertial drives for the past 1300 greats. They watched as a cargo ship unloaded the last of the north monopoles in the holding tank of a long electromagnetic gun. A stream of high-speed monopoles shot from the tube and penetrated deep into the now solid crust of the deorbiter mass. In the center, the monopoles were held by the strong gravity forces of the ten-meter-diameter ball despite the magnetic repulsion from the rest of the monopoles in the ultra-dense core.
As the last of the stream spluttered out, a continuous combination of 'trumming and dancing for joy rose throughout the communications links. It grew in volume as the image of the last of the monopole stream spread through the space around Egg at a slow crawl of the speed of light.
"We're done!" Cliff-Web's aged tread was trying to keep up with the victory 'trumming of his engineers.
"That's one giant ripple for cheela-kind," said Steel-Slicer calmly, knowing that they still had much to do. "We'll let it cool down for eight to twelve greats, then we can take the next tread-ripple on our long journey home."
"My new class of gravitational engineers will be ready. Will you have a good gravity-well pilot to take us down?" Cliff-Web asked. "Even though the surface gravity and escape velocity of Otis are only a small fraction of that of Egg, it will be a tricky landing for someone used to flying around in space."
"My next class of pilots are already training on the ring masses around the human spacecraft Dragon Slayer," said Steel-Slicer. "In about two greats they will transition to simulated landings 50 meters up from Otis. You'll get the best one from that group, and he or she will be allowed to choose a new name. Everyone in the class agrees that the name they want is 'Otis-Elevator.' "
Landing
21:00:10 GMT TUESDAY 21 JUNE 2050
"Everyone out of the southern hemisphere," Captain Otis-Elevator said into his tread amplifier. The command rippled out from the control deck at the "north pole" of the large cargo hauler and echoed back and forth through the hull underneath the deserted cargo holds on the bottom of the spherical ship. The warning was unnecessary. They were rapidly approaching the surface of Otis, and from the southern hemisphere it looked as if the planetoid were falling directly down upon them.
The inertia drive humming vigorously, the mighty cargo ship approached the planetoid. Otis-Elevator hovered at a point fifty meters from Otis while they watched the asteroid slowly turn. The attraction from Otis was now stronger than the attraction from the black hole in the middle of the cargo ship.
"Feels good being under a little gravity once again," said Cliff-Web.
"I wouldn't know; I've always lived in space." Otis-Elevator slowly descended in a vertical trajectory. As they drew closer, the gravity became stronger and began to approach the gravity on Egg. Choruses of groans could be heard through the deck.
"I can't hold my eyes up," said Otis-Elevator.
Cliff-Web looked at the pilot, who was struggling to keep his eyes elevated in the strong gravity field. The eye-stubs were thin, and wavered as they attempted to balance the heavy eyeball on top of them. Cliff-Web's eye-stubs had automat-
ically thickened into the proper exponential shape. They ached slightly from generations of little use, but at least the automatic balance reflexes kept the eyes steady.
"I didn't realize that you might not be able to function in high gravity," said Cliff-Web. "Shall I take over the controls?"
"No, I can handle it, but I'm going to have to switch to tread-screen control." He pulled his eyes in under his eyeflaps and concentrated on the taste image on the deck beneath his tread.
They dropped quickly down the last few meters, then, very slowly, Otis-Elevator put the cargo ship down on the crust. The hemispherical top flattened noticeably as Otis pulled hard at the black hole at the center of the cargo ship. Squeals and pops could be heard through the deck plates. The stabilizing fields that held the black hole at the center of the spacecraft finally reached their limit and the black hole fell through the bottom of the hull into the center of Otis where it evaporated. The hull rebounded a little, then stabilized.
Cliff-Web had thought they could begin work as soon as they landed, but it took a dozen turns and a lot of food to build up the space-bred cheela to the point where they could function in the strong gravity field. Cliff-Web had returned to normal rapidly and had taken a prospecting trip out on the ten-meter ball while the others were building up their strength.
"The portable analyzer says that the crust has a high percentage of high-strength metals," he said upon returning. "The volcanic regions where we inserted the monopoles have ejecta containing some of the rarer neutron-rich isotopes that we might need for alloying, but other than that, the composition of the crust is pretty much the same everywhere. Let's set up the power generators and start the mass separators and foundries going."
Within half a great, the mass separators were pouring out powdered raw materials that were turned into working stock by the foundries. The first structure they constructed was a simple space fountain. It only had one stream of rings and only went up 50 meters to a crude top platform, but it sufficed as a landing dock for other spacecraft in the fleet. Soon, most of the space cheela were on Otis, working to make the gravity ma-
chines that would enable them to return from their enforced exile from Egg.
Their next task was the construction of a large gravity catapult capable of accelerating the lander at many times Egg gravity so it would reach the escape velocity of Egg after less than 10 centimeters of travel. Unlike the ancient gravity catapults now lying dormant on Egg, which had only to toss small spacecraft into the sky, this gravity catapult had to be big enough to toss a miniature copy of itself to those speeds. It took nearly four greats of turns to fabricate the twenty-centimeter ring with its meters and meters of high-strength tubing full of ultra-dense liquid and the battery of pumps to accelerate the fluid to high velocities rapidly. The uniformity of the resulting gravitational repeller field was important.
"Run it up again," Cliff-Web ordered. He was monitoring the display of the array of
gravity sensors spread across the center of the gravity catapult ring. The ring was large in diameter, but small in thickness. Cliff-Web had pushed every rule of gravitational engineering to make it. It only had to work once, but if it worked, it was worth it. The tests they were doing now were at fractions of its operational power levels. That would do—until the final blink when full power was applied. The machine hummed, and the sensors displayed a contour map of gravitational force levels.
"There is only a difference of a billion gravities across the central centimeter portion," Engineer Push-Pull announced. "Surely the lander can handle that."
Cliff-Web looked carefully at the contours, made minor adjustments to some trim loops and closed down the display.
"The launch ring is ready. Next is the lander," he said. "We have passed apoapsis, so we have only four greats of turns to build it."
"It will be ready long before that," said Push-Pull.
"I'm sure," said Cliff-Web. "But there is someone else we must consult with before it is properly delivered." He reset his tread screen, treaded a brief formal message, then left without waiting for a reply. The reply would come later, much later.
21:02:03 GMT TUESDAY 21 JUNE 2050
The call that Pierre had been dreading came. "Request asteroid O-l be reprogrammed to arrive at space-
time point given by following coordinates," said the image of Cliff-Web. There followed an x,y,z,q,f, l,t listing of coordinates in the Dragon's Egg space-time system. The requested orbit went far down in the gravity well of Egg so that the ten percent time rate and frame drag difference between deep space and the surface of the neutron star was significant.
Cliff-Web was not used to talking to humans. He forgot to always assume the same position each time he checked in at the screen for a reply, so his image flickered every fifth of a second.
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