Precession

"That's the power source for the ion drive," Morty said. Like most boys, he knew his spaceships. "I bet that's the bit that's got the leak."

They noted the exact model of the cruiser and went to look up its engineering specifications on the library's computer.

The details they downloaded were very interesting, especially in regard to the ship's power source. It had a nuclear fusion reactor.

Spaceships had multiple power sources. They all used electrical storage batteries charged on a space station or an engineering station. Some had their own solar collectors if they were going to be out in space a long time. Spaceships also used hydrogen fuel cells. Some, like this cruiser, had chemical rockets fed by solid fuel; but only large vessels and very expensive mid-size luxury cruisers had fusion reactors as well.

"It must belong to someone rich and important," Morty said. "Probably a smuggler or a pirate."

"It belongs to Councillor Mason," Hana said, remembering the dockmaster's manifest.

Morty whistled to show how impressed he was.

David Mason, the Chairman of the space station's governing council, was extremely rich, very important and very respectable.

Neither a smuggler nor a pirate, Councillor Mason owned the Excelsior Hotel on the West Causeway. His wife, Veronica, was a society beauty. She ran the jewellery shop on the ground floor of the hotel, but was usually to be found getting pampered in the hotel's spa, lunching with her girlfriends or hosting glittering events in the hotel's ballroom. They were a popular couple, in late middle-age. Elegant and successful, with grown-up children on Earth, they were extremely rich. David Mason's spaceship was the most expensive pleasure-cruiser on the space station. It was probably worth as much as the Excelsior Hotel itself.

"It cannot be a fuel leak," Hana said after a little thought.

"Why not?" Morty asked.

"Because the impulse on the space station is constant. If it were fuel or air, then it would reduce over time as the pressure in the fuel tank or air tank reduced. This cruiser isn't big enough for a long-lasting fuel leak at the same pressure, unless it's being supplied with a new tank of hydrogen every few days."

"So it's the nuclear fusion reactor?"

"It must be. It might have a radiation-leak or it might be emitting heat. A fusion core that's emitting radiation or heat could remain at the same strength for years. We know how much torque is needed to make the station precess, and we know where the reactor is on the cruiser, so we can calculate how powerful the radiation must be."

"I don't want to be the sensible one," Morty said cautiously, "but do you think it's time we reported what we know?"

"We don't know anything, yet," she said. "It's all guesswork. Let's wait until we've learned how the fusion power unit works, to see if it might have gone wrong."

*******

They took the downloaded specifications and engineering diagrams of the cruiser's fusion power unit to their secret room and set out to study them.

After he learned some statistics about the power and efficiency of the fusion reactor, Morty declared his brain full and got out his sketchbook to make imaginative drawings of the spaceship exploding and Councillor Mason with a pirate's eyepatch and a hook hand.

Every so often, Hana would share a finding with him, to which he would nod wisely, as if he understood, and she would return to her studies, occasionally looking up details in physics textbooks which she projected onto the basement room walls.

After some time, Hana was confident she knew how the fusion reactor worked and what might have gone wrong with it.

"You know how stars are powered, by nuclear fusion in their cores, where millions of degrees of heat and billions of tons of pressure force hydrogen nuclei to fuse into helium and helium to fuse into carbon and oxygen?"

"Everyone knows that!" he said with a straight face.

"Well the fusion reactor in the cruiser does the same thing, with much less heat. It uses the special properties of some crystals to squeeze things really hard."

"How does it do that?"

"The reactor core is an iron cube with chemical impurities in its crystal lattice, such as boron nitride and an amalgam of hafnium, nitrogen and carbon. The impurities make the iron block porous to liquid hydrogen, which is a superfluid at very low temperatures. The liquid hydrogen gets trapped in gaps between the crystals and is ionised there into protons and electrons."

Morty's eyes began to glaze over.

"Some crystals change shape under an electric charge. In this case, the electric charge squeezes the crystals together, forcing the protons to fuse together, ending up as helium nuclei. Two protons become neutrons, releasing positrons and neutrinos. The neutrinos are lost but the positrons are annihilated by the loose electrons, making gamma particles. Their energy is transformed into heat, which is flushed out of the block on one side by injecting more liquid hydrogen on the other side. Molten lithium takes the heat to a generator. The whole process repeats hundreds of times a second."

"You understand all that?"

"Don't you?"

"Let's pretend I don't," Morty said cautiously. "Can you explain what's wrong with the reactor?"

"Three main things can go wrong. The lithium will become radioactive over time as it's bombarded with stray particles from the nuclear reactor. That's not the cause of the precession but it's dangerous to people, so maybe that's why Councillor Mason has kept the ship in its berth, waiting a repair."

"Secondly, the reactor can overheat, so the core is sometimes cooled by injecting liquid hydrogen and venting it into space without using the electric charge to ignite the fusion reaction. If overheating happened and hot hydrogen gas was being vented, then the cruiser would deliver a torque to the station; but it wouldn't last six months. The reactor core would cool down in hours. Also, the liquid hydrogen fuel would run out. Even if it was replenished, the torque would not be constant but would reduce as the gas pressure and temperature reduced."

"And the third thing to go wrong?" Morty asked, to prove he was keeping up.

"The elements of the reactor core will gradually be transmuted into radioactive isotopes. It will be a slow process to make the core radioactive, taking decades of constant use, because most of the stray particles are flushed out with the hot helium each cycle. This cruiser is only twenty years old. It shouldn't have happened yet; but if it did, then radioactive decay could keep the reactor core hot. I guess this is what's gone wrong. We could tell if we knew what kind of radiation it was and how intense."

"When will it explode?"

"It won't explode. The worst case is that the reactor core melts down. Then it stops working and becomes safe; but it's broken as a power source and costs a lot of money to replace."

"So what should we do?"

"If we get on-board the cruiser to find out which of the problems it is, then we might be able to save Chancellor Mason a lot of money by telling him what's wrong with the fusion reactor."

******

Morty's father, Gareth Bowman, was a fireman. He worked shifts at various locations on the space station, including the private vessel dock.

That night Morty checked his father's schedule and had a question for him.

"Dad, can I visit you at work tomorrow?"

"Wasn't it 'Annoy your dad at work day' a few months ago? How many times can you be a nuisance to me in one year?"

"Many times. I'm quite inventive."

"Anyway, I know it's school holiday. I've noticed your sister hanging around more at home just now."

"It's school holiday to the end of the week, but this isn't a school event. That's why I'd like to bring Hana with me."

"I haven't said you can come yet. Why can't Hana be a nuisance to Arthur at his work?"

"She says his job's boring. All he does is break up fights between drunken freighter-crews and fill out paperwork. She thinks your job's more interesting, though I told her all you do is take naps and play ping-pong."

"You cheeky devil!"

"Please, Dad? It's for our project."

"All right. It's early shift at the private vessel dock tomorrow, so knock at the inner dock door when you can manage to get up."

******

There was some truth in Morty's joke about firemen not having much to do most days. However, although there were few fires or other dangers for the firemen to attend, they did not spend their downtime napping or playing a strange low-gravity version of ping-pong (with a magnetic table and balls). Instead, they and the other emergency crews had never-ending drills to hone the skills they hoped they would never need, testing the safety equipment they hoped they would never use.

In between disaster rehearsals (and very rare near-disasters), the private vessel dock was a sleepy office for the dockmaster and his crew. There were short bursts of strenuous activity when ships arrived. The rest of the work was routine. They checked out tugboats, with their magnetic grapple beams and powerful rockets. They checked them back in again; checked ships were securely moored to their berths; checked passenger lists and transported luggage.

Hana and Morty arrived at the private vessel dock during a quiet time. They had on magnestrip waistbands and overshoes for the magnetic artificial gravitation on the dock floors and in the dockmaster's office. Gareth met them at the door and showed Hana around the crew station. She pretended it was all new to her. It took only ten minutes.

"Not much happens here on a normal day," Gareth said. "Today's particularly slow. The passenger dock is more interesting. The freight dock is the busiest of all."

"Dad, can you tell Hana about your emergency procedures, like you told me?" Morty asked.

"I can do better than that. I can show her. Come with me."

Gareth took yellow high-visibility jackets from a locker and pinned badges with red, blue and green sensor strips on their chests.

"I'll explain what these badges are for as we go. Follow me," he said.

They climbed down ladders from the dockmaster's office to the dock floor, where the bulkheads fanned out into individual berths with airlock hatches. Here their steps were lighter because the magnetic artificial gravitation was set at 75%.

As they toured a section of the dock, Gareth explained the safety procedures.

"The badges are detectors for different kinds of hazards. The green stripe turns purple when there's gamma radiation. The blue stripe turns white in the presence of carbon monoxide. The red stripe goes black when oxygen is short. There are other hazards and other kinds of radiation. There are detectors on the bulkheads every few metres and on both sides of the doors."

He pointed out the alarms, oxygen bottles, face-masks, radiation suits and fire blankets. There were extinguishers that spat out expanding plastic foam and small backpacks that would expand into entire recovery suits for protection in an emergency. There were dozens of individual escape pods lining the walls, in front of escape hatches with explosive bolts.

"What happens if a ship arrives with a fault or develops one when it's here?" Hana asked.

"We can lock down each berth and close the bulkheads between the sections of the docks. We can do a quick-release of any ship and the tugboats can pull it clear of the station."

They had almost finished touring that section of the dock when Gareth was called to a meeting with the other firemen. He left Hana and Morty on the dock floor with strict instructions to touch nothing. He gave Morty a special warning not to be any trouble.

As soon as Gareth was gone, the investigators headed for the berth where David Mason's luxury cruiser was docked. Hana began to work on cracking the entry-lock system. She had just figured out the code when, by unlucky chance, the dockmaster himself saw them from the window of his office.

"Hey, you kids," he called out over the intercom. "What are you doing? Get away from there. You have no permission to go onboard that ship."

A shamefaced Gareth Bowman was sent to escort them from the dock, while the dockmaster reported the incident to Arthur Jeffries and to the owner of the spaceship, Councillor Mason. A breach of the strict privacy laws on the space station was a serious matter.

Gareth was too angry with Morty to speak to him. It was only because the intrusion was now a legal matter that Morty escaped a quick and severe punishment at the hand of his father.

Arthur Jeffries was also grim-faced, waiting outside the dock to escort the miscreants to the council chamber. On the way, they calmly and concisely told him the whole story, leaving nothing out. Arthur made no comment, not even about the precession of the space station and the faulty fusion reactor.

He left them in the court-room outside the council chamber and went inside to face David Mason alone, who sounded angry.

"Constable, can you tell me why I shouldn't press charges for trespass against your daughter and Mortimer Bowman?"

"It's your right, Councillor, but maybe using the full force of the law against two mischievous children is not the best solution."

"Are you undertaking to discipline them yourself?"

"I will, if I'm satisfied that there's nothing substantial in the story they've told me."

"What story?"

"Hana and Morty believe they discovered a fault in the fusion reactor on your spaceship. They might have been doing us all a favour by learning what kind of radiation it's emitting."

"Do you believe that my cruiser is a danger to the space station?"

"Is it safe?"

"Of course, it's safe. Charles Debben will confirm it."

Charles Debben was the chief engineer of Capella Space Station. He was in his office now and easily contacted by videolink from the council chamber. They made the connection and the chief engineer answered immediately.

"Is it true that the space station has a wobble and that Councillor Mason's spaceship is the cause?" Arthur asked.

"Yes, it's true," Charles Debben said. "We've known about the precession for months. It's caused by liquid hydrogen fuel on the Councillor's pleasure cruiser being vented through the fusion reactor and out of the bottom hatch. The reactor is safe but it needs to be kept cool until it can be properly repaired."

"Are you satisfied now, Constable?" David Mason asked.

"I am, though I don't know why you didn't tell us this before."

"We wanted to avoid unnecessary panic," David said. "If people thought a ship with a fusion reactor had a malfunction, who knows what they might imagine, or what panic might ensue? ... I admit that I've been tardy in getting the problem fixed, but I'll expedite the repair now."

"Very good, Sir," said Arthur.

"Can I leave the matter in your hands regarding your daughter and her friend?"

"Yes, Sir," Arthur said. "I'll be responsible for Hana and Morty's behaviour in future."

"Thank you, Constable. I'm willing to forget the incident; but if either of them trespass again, I will bring charges."

Arthur took Hana and Morty back to the police station in silence.

At the station, he sat them down and told them what the chief engineer had said:

"The ship is safe. It's just hot hydrogen fuel venting into space after cooling the reactor core."

"It can't be the whole story, Daddy," Hana said. "The torque applied to the spindle has been constant over many months, but if it was caused by fuel venting, then the force should lessen as the pressure of liquid hydrogen in the tanks reduces. The precession would vary with time as the tanks empty and are re-filled."

"So what would you say to Charles Debben, Hana?"

"I don't know, Daddy. Could he be mistaken?"

"Maybe he's saying it's fuel venting to cover up the real danger to the space station," Morty said, unable to let go of the idea that the cruiser was liable to blow up.

Arthur had been thinking this himself. He paused for a minute, then said:

"You know those Saturday morning movies you watch, where the plucky kids alert the city to a catastrophe but no one believes them?"

"I like those movies," Morty said.

"I hate them," Hana said.

"There's always a scene where a parent or a policeman tells the kids that they're mistaken, that everything's fine and they're to forget all about it. Also, it's best if they tell no one. They always disobey him, get captured but somehow break free and save the day."

"That's what I hate about those movies," Hana said. "They're so predictable."

"Well, I agreed to tell you that there's no danger, so you're to forget all about it and not worry. Everything's under control. Also, it's best if you don't tell anyone, to avoid spreading panic on the station."

"But if it's a problem with the fusion reactor we might all get blown up," Morty protested.

Arthur gave him a look and Marty quieted down. Arthur repeated:

"You're to forget all about it and not worry. Everything's safe."

"Yes, Daddy," said Hana.

"Yes, Sir," said Morty.

"Councillor Mason has let you off this time and won't press charges for trespass, so long as you don't to try to repeat the nuisance. Go and play now. Keep out of trouble."

******

Left alone, Arthur looked up the legal code of Capella Space Station, checking what laws applied when the space station was in danger. He placed a call to Mrs Malkin, the Headmistress of the school and part-time Justice of the Peace. She was the one to whom the governing council of the space station would defer in any legal question regarding their authority. He spoke for some minutes, explaining the problem and how he was going to investigate it.

Some more calls followed, including one to Gareth Bowman, who had still not spoken to Morty, nor let him explain himself. When Arthur told Gareth the whole story, including his own plans, Gareth said:

"I suppose I have to forgive Morty now, even though the boy's a damned nuisance. All right, I'll take out the fire tender if you want."

"No, a tugboat from the freight dock would be best. No need for you to get in trouble as well. Thanks, Gareth."

There were sixteen tugboats on the space station, most of them in the freight dock, some in the passenger dock. The military dock had its own boats.

Tugboats were small, solid and very manoeuvrable spacecraft, easy to pilot, with powerful rocket motors and magnetic grapples. Their job was to help bring large spacecraft into the docks and help them leave safely. They also pulled in smaller craft that had not matched the rotation of the space station; and they cleared away debris and breakages from the docks.

Arthur called the freight dockmaster and officially secured the use of Tugboat 7 at his convenience.

Next day, he summoned Hana and Morty to his office. They were moping, frustrated by the unsatisfactory end to their project but secretly knowing that the adventure was not over.

They stood politely by his desk, waiting for him to tell them off again. He smiled at their sad little faces.

"Morty, can you pilot a spaceship?" Arthur asked.

"No, Sir."

"Then it's time you were taught. I'll take you for a lesson. Hana, you're to come too."

"Yes, Daddy. Where will we go?"

"Does it matter?"

"Only there are some parts of the space station I'd like to see from space."

"Then we'll take a little flight around the station. Maybe call in on the private vessel dock, to practise berthing manoeuvres. What do you say?"

"Can it be in two days, please?" Hana asked.

"Why in two days?"

"I need to make something tomorrow."

"Okay then, Sunday it is."

Hana and Morty bought a radiation detector from a technical instrument supplier on the South Causeway. It was a standard device, used in laboratories across the galaxy. They bought some other components to modify it, adding a wave guide to make it directional and a filter to narrow the range of radiation detected.