Precession

They were ready bright and early on Sunday morning for Morty's piloting lesson. Arthur did not ask Hana why she was carrying what looked like an old-fashioned hair-dryer or a ray-gun from a science-fiction movie.

Under instruction from Arthur, Morty piloted Tugboat 7 out of the freight dock and into space. The solid rockets for close manoeuvring made a hissing sound, as expanding gas rubbed on the outside skin of the tugboat hull. Soon they were far enough away from the space station to turn on the ion drive. The motor hummed as it spat charged particles at near-light speed behind them. The surge of acceleration was smooth and strong, pushing them into the backs of their seats.

In a few minutes they were fifty miles away from the station and ready to join the guided lanes to a berth in the private vessel dock. Their path took them north, above the great wheel, which spun majestically below them.

Slowing rapidly, they passed the passenger dock a mile above the greet wheel and, another two miles further on, turned toward the private vessel dock.

As they entered the dock, Hana went down to the forward observation bay. The plastiglass hemisphere at the nose of the tugboat contained an optical telescope for manual observations. She got comfortable lying on the floor, pointing her detector through the window.

They went the wrong way in the private vessel dock and flew close to Councillor Mason's luxury cruiser. Morty carefully manoeuvred the tugboat from one end of the luxury cruiser to the other, while Hana scanned the vessel for radiation.

"What are your readings, Hana?" Arthur asked.

"None, so far, Daddy," she said. "Can we circle the fusion unit?"

Arthur helped Morty perform the manoeuvre. They slowly orbited the wide section of the cruiser behind its ion drive. They were so close they could see a heat-haze outside the wire-mesh vents as the hydrogen fuel was expelled as a hot vapour.

A sharp woman's voice over the radio broke the silence.

"Tugboat 7, this is Dockmaster Jess Carson. What are you doing?"

"Hello, Dockmaster, this is Tugboat 7," Arthur responded. "We're having a piloting lesson. We're practising manoeuvring."

"Well you're too damn close to that cruiser for my liking," Dockmaster Carson said. "You can practice manoeuvring from a safe distance. Take it away."

"Yes, Ma'am," Arthur said.

Jess Carson checked her manifest and saw who had booked out the tugboat.

"Is that you, Constable Jeffries?" she asked.

"Yes, Ma'am."

"You know I have to report this?"

"Yes, Ma'am."

"Unless you can give me a good reason not to."

Hana popped her head out of the observation hatch. Arthur glanced a question at her but she shook her head.

"No reason, Ma'am," he said.

"Then take that tugboat out of my dock."

They headed back to the freight dock.

"Did you get any data at all, Hana?" Arthur asked.

"No, Daddy. I detected only normal background radiation."

"Is your detector working properly? Do you need more time?"

"The detector's working properly, Daddy. I don't think more time will help. There's no radiation. I need to think about why not."

"All right. We'll debrief in my office," Arthur said.

Hana was silent all the way to the police station. Her father and Morty waited patiently for her to speak, which she did after considering all the options she knew.

"We know the cruiser is the cause of the precession; and we know it can't be due to it venting fuel. If it was radiation from the nuclear reactor, then I would have detected it. If it's an overheating reactor core, then it would have melted down by now."

"So what is it?" Arthur asked.

"The only reason I can think for why I didn't detect the radiation is that the core is being shielded."

"How can it be shielded?" Arthur asked.

"Either very thick lead plating or magnetic fields," Hana said.

She was silent awhile.

"Is there a problem?" Arthur asked. "Isn't the lack of radiation a good thing?"

"It might be bad, Daddy. I need to double-check everything."

Morty accompanied Hana to the library. She walked in a daze, going over the evidence in her head.

At the library they found out something they had missed before. There were two types of fusion reactor fitted to that model of luxury cruiser: a 'light' reactor, which Hana had first described to Morty, and a 'heavy' reactor with more heavy elements, which worked more efficiently but cost vastly more. Only three heavy reactors had been made. The situation made sense only if Councillor Mason's cruiser had one of them.

Once Hana worked out the difference between the two reactors, she knew why the core had become irradiated so quickly and stayed hot even though it was turned off. Radioactivity from the hot reactor caused the precession. Venting hydrogen fuel through the core kept it cool but did not stop the radiation; so David Mason had contained the core with either lead plating or magnetic shielding. That was why she did not detect any radiation. If it was magnetic fields, then it would trap the radioactive particles inside.

Back home, over dinner, Hana told her parents what she thought must have happened and what it meant for the fusion reactor.

"Are you sure you're right, Hana?" Arthur asked.

"Yes, Daddy."

"What do you think, Mary?"

Mary looked over Hana's working out.

"As far as I can see, she's right. Her maths adds up. ... When will you request a meeting with the governing council?"

"I don't need to request a meeting," Arthur said, showing Mary a message on his communicator. "Councillor Mason has summoned me to a hearing tomorrow morning. He's going to press charges of harassment. Mrs Malkin will be presiding."

"I'm sorry, Daddy."

"It's too late to avoid the hearing, but I might be able save my job if I apologise tomorrow and promise to punish Hana and Morty very severely. What do you say, Mary?"

"I say we tell the governing council to get stuffed, even if you lose your job," she said.

"The bad publicity will end your chance of a seat on the governing council," Arthur cautioned her.

"It probably will, but what if our brilliant daughter is right? What if it is a 'heavy' reactor and magnetic shielding of its core is the danger she believes it is?"

"So: no surrender, no apology?"

"None. I'm sorry I can't be with you at the hearing tomorrow morning, but I know we're doing the right thing."

"We are," Arthur agreed.

He made a call to the Justice of the Peace and, with her agreement, everything was set up.

"Hana, try to get some sleep," he said. "Tomorrow, we face the music."

Hana normally slept only three or four hours a night. That night she had a long refreshing five-hour sleep because, after sitting up in the silent apartment, thinking through the whole case, she could go to sleep satisfied that she could prove her theory.

6 Danger

It was Monday morning and the first day back and school after the holiday, so Hana and Morty wore their school uniforms to court. Hana's knee-length tartan skirt, white blouse and red jumper made her look small and vulnerable standing next to her father, holding his hand tightly. Morty, on her other side, was quiet and pensive. His father, Gareth, sat a few feet behind on the observers' bench. Marty's mother, Linda, like Mary, was at work.

Everyone stood as Mrs Malkin entered the court-room.

As Justice of the Peace, Mrs Malkin was the highest legal authority on the space station. She took her place at a seat on the dais two feet higher than the rows of benches for the plaintiffs, accusers and audience.

Almost the whole membership of the governing council and many of its administrative staff were there, plus others who had come for appointments that were now delayed due to this urgent hearing. Veronica Mason stood next to her husband, David, exuding glamour and poise. On his other side was Charles Debben, the chief engineer of the space station.

"You can all sit," Mrs Malkin said. "This is an extraordinary hearing, not a regular court-case, but its importance is such that I think it should not be in secret. However, there are sensitive matters involved, so I have ordered the doors closed and I ask everyone here not to communicate any detail of the case outside this courtroom until everything is resolved. ... Let's begin. We have two cases to hear. They are connected."

"The first is Councillor Mason's accusation of trespass against Hana Jeffries and Mortimer Bowman, plus his accusation of harassment by Constable Jeffries. Councillor Mason says that Constable Jeffries promised to keep Hana and Mortimer away from his pleasure cruiser, berthed in the private vessel dock, but, instead, he took the children out in a tugboat to spy on the cruiser. Is that correct, Councillor?"

"Yes, Ma'am, it is."

"The second case is more important."

"More important, Ma'am?" David Mason asked.

"It's an accusation against you by Constable Jeffries, that the nuclear reactor of your cruiser is a danger to the space station."

"It is not!"

"That's what we're here to ascertain, Councillor."

"Arthur, is this because you think I was heavy-handed in telling off your daughter?" David Mason asked the constable.

"No, David. It's because I think there may be negligence or even reckless endangerment."

"Reckless endangerment? Then why not come and arrest me, instead of springing an accusation on me at a hearing for something else?"

"That was my decision, Councillor," Mrs Malkin said, "to save time, just in case. ... Are you happy for us to proceed, or would you prefer it to be a formal criminal case?"

"I'm innocent, Ma'am, and my boat is safe. Let's have it out now."

"Constable Jeffries, we'll take your evidence first. Why do you say the Councillor's spaceship is a danger to the space station?"

"Hana and Morty discovered that the space station has a wobble. They investigated and learned that the cause was the nuclear reactor on Councillor Mason's cruiser, which the councillor and the chief engineer say is venting hydrogen fuel into space to keep the reactor core cool. We believe differently."

"You're accusing us of conspiracy?" David Mason was outraged.

"No, Councillor. We think it's an honest mistake, as Hana will explain."

This was Hana's moment. The girl had her mother's forthright determination and her father's simple honesty, but she felt unusually nervous for once. She remembered that this was science and she loved science. Her nerves vanished as soon as she began her explanation.

"The fusion reactor on the luxury cruiser has a fault. It's become radioactive and needs to be cooled. But it's the radiation that causes the space station to precess, not the hydrogen vented through the core. We know this because the precession is constant, whereas venting fuel delivers a variable torque to the station."

"After Morty and I tried to get onboard the cruiser, to test our theory that the nuclear reactor's radioactivity was causing the precession, we believe the reactor was shielded with lead plates or magnetic fields. That's why I couldn't detect any radiation when we were out in the tugboat."

There was a stir on the bench where David Mason sat. He whispered something to his wife, who patted his arm and nodded.

"Councillor Mason, do you have something to say about Hana's analysis?" Mrs Malkin asked.

David stood. A tall, handsome and dignified man, normally self-assured but now subdued. All his bluster had gone and he looked as vulnerable as Hana had done only five minutes before.

"I have a confession to make," he said quietly, "and an apology. The fusion reactor went wrong six months ago. It began to emit radiation and got hot. I know I should have arranged a repair long ago but, er, personal reasons made it impossible. I consulted Charles Debben, who advised me that if we cooled the reactor, it would be safe indefinitely, so we have been venting hydrogen through the core to keep it cool."

"Is that correct, Mr Debben?" Mrs Malkin asked.

"Yes, Ma'am. There's no more radiation from the core than particle wash from an ion drive. It's safe, though due to its position in the private vessel dock, it delivers a small torque to the station."

"Then what happened, Councillor?"

"Last week, after the attempted infiltration by Hana and Mortimer, I asked Charles if we could conceal the fault in the reactor, to avoid spreading panic on the station. He advised putting magnetic shielding around the core, to contain the radiation. Now there are no emissions from the reactor."

"Very well," Mrs Malkin said. "I understand that the shielding confines the particles to the reactor core, so they no longer radiate into space. Constable Jeffries, the radiation leak has been plugged. There's no danger any more."

"It seems that way, Ma'am," Arthur said. "But Hana says it's the magnetic shielding that's causing the danger."

"Hana, will you explain it to me, please," Mrs Malkin said, "remembering that I'm an English teacher with only a modicum of scientific knowledge?"

"I think there are details of the fusion reactor that Councillor Mason and Mr Debben don't know. There are two models of the fusion reactor. The 'light' reactor is 95% iron, 3% hafnium and 2% boron, nitrogen and carbon. The 'heavy' reactor is 92% iron, 1% lead, 1% lanthanum, 1% ruthenium and the other elements. I believe that Councillor Mason's cruiser has the heavy type of reactor."

"I didn't know about the two types of reactor. I bought the more expensive model because I was told it was better," David said. "What's the difference between the two reactors?"

"The elements in the core of the heavy reactor are more easily transmuted into radioactive isotopes than the light reactor. This makes the heavy reactor vulnerable to atomic cascade effects."

"Good God!" Charles exclaimed.

"Do you understand what Hana is saying, Mr Debben?" Mrs Malkin asked.

"Yes, Ma'am."

"Then kindly explain to the court."

"In this case, an 'atomic cascade effect' is when the radioactive decay of one isotope causes the formation of more radioactive isotopes, who subsequently decay as well. By redirecting the emitted particles back into the reactor core, the magnetic shielding increases its radioactivity exponentially. Eventually, it will cause an uncontrollable chain-reaction."

"What's an uncontrollable chain-reaction?"

"An explosion, like an atom bomb," Charles said with absurd calmness.

There was a commotion in the courtroom. Amid the babble was Morty's excited voice shouting:

"I knew it! I said it'd explode, didn't I, Hana? Constable Jeffries, I said it'd explode!"

Mrs Malkin banged her gavel to bring the noise to an end.

"Quiet, please," she said. "Let the official record show that Mortimer Cedric Bowman, age 13, native of Capella Space Station, correctly predicted that the reactor core would explode."

"I did! I knew it!" Morty said again.

David Mason was shocked. He did not speak but stood with his head bowed, his face ashen white.

"Charles, can you tell us when it will explode?" Mrs Malkin asked.

"It depends on how hot it is, how much radiation is being redirected back into the core, how much of the core has already been transmuted into radioisotopes and how reactive the isotopes are."

He tapped away at a computer terminal as he spoke, projecting readings onto the courtroom wall.

"These are the readings from the detectors in the magnetic shields. It will take me some time to work out how long it will be before the core becomes unstable."

He applied the formulas and set the computer to do the calculation. Meanwhile, Hana was silently doing the calculation herself, her eyes shut, her hand still in her father's hand. She opened her eyes and gave Arthur's hand a squeeze, but she remained silent, patiently allowing Charles to give his answer first.

Finally the computer finished its calculation.

"There are nearly ten days from when the shielding was applied to the reactor to when it enters the danger zone," Charles said.

"It's 192 hours, plus or minus 4 hours," Hana said quietly.

"How do you work that out?" Charles asked.

"Sorry, Mr Debben," Hana said, "but the computer program you used has left out a variable. As the core gets hotter, the crystals expand and slow down the particles, which makes them easier to absorb. With the extra energy from the heat, the reactions go faster."

"You're right! The cascade speeds up. The core will be hot enough to explode tomorrow or the day after."

Morty let out a long whistle.

"Yes, Mortimer," Mrs Malkin said. "We know you predicted the catastrophe."

"I wasn't going to say that, Ma'am. I was going to say it's not quite so much fun being right if we all get blown up."

"Very true, Mortimer."

******

When there was silence in the court-room after the latest revelations, Mrs Malkin said:

"Given Charles Debben's official assessment that the reactor core is likely to explode in the next 24 hours, I uphold the accusation of reckless endangerment against Councillor Mason and declare a state of emergency. Councillor Mason, you are relieved of your duties. Legally, the space station is the responsibility of Constable Jeffries. Constable, what are your orders?"

Arthur had no hesitation.

"David, get your damn ship off my station."

David nodded and headed for the door.

"I'll help you," Gareth said.

"Thank you, but I can manage," David said.

"You need two men. One to pilot the cruiser and one to eject the reactor core, in case the automatic mechanism doesn't work."

"I'll go with you," Veronica said.

"My dear, you mustn't take the risk. I won't let you."

"You can't stop me. Besides, it's my ship. You bought it for me."

"I'll follow in a tugboat," Gareth said, "in case I can help."

Morty ran to his father.

"I want to go with you, Dad," he said.

Gareth hugged his son.

"You stay here, son. I won't be long. And we'll have a sorting-out when I'm back because you were right all along."

He kissed Morty on the forehead and followed Veronica and David out of the courtroom.

"Right, that's sorted," Arthur said. "We'll transmit the co-ordinates for where to dump the core once we've decided the best place. ... Charles, Hana?"

Charles looked at a holographic map of the space station in its orbit, among a swarm of solar collectors, gamma stream transmitters and hyperspace beacons. He scratched his head, trying to think of where to eject the nuclear core to do least harm if it explodes.

Hana modestly waited for Charles to make his suggestion but he was still working it out.

"Here, Daddy," she said, pointing to a location on the holographic star-map.

"Why there?"

"Because it will fall toward the north pole of Capella Ab, where there are fewer solar collectors. If it explodes on the way, the debris will mostly vaporise in the gamma streams."

"Any objections to Hana's plan? No? Then we'll go with her coordinates. Transmit them to David and Gareth."

"Is that everything, Constable?" Mrs Malkin asked. "Do we now just pray the core is ejected in time?"

"No, Ma'am. Please will you make a broadcast to the station and tell them the truth. I don't think they'll panic. I've always thought it's wrong to treat the public like they're frightened kids. In fact, here are some of our kids ..." he indicated Hana and Morty, "and they're not frightened at all."

"I'm a little worried, for my Dad's sake," Morty confessed.

"He's perfectly safe, Morty, and so are David and Veronica, aren't they, Hana?"

"Yes, Daddy. Nothing can stop the reactor core melting down now but if they turn off the magnetic shielding, then it will give them another day at least."

Mrs Malkin returned from making her public announcement. Arthur had one more task as temporary governor of the space station.

"Someone go and tell my wife and Linda Bowman that their kids are safe. ... Scratch that, tell them that the saviours of the space station are safe."