Captain Yujin's left forearm reacted before the hull's alarm even sounded. A sensation of something tugging beneath the skin. As if drawn by a magnet, her arm tilted slightly toward the hull wall. Yujin pulled it back and looked at the instrument panel. Magnetic shielding output: 37 percent. Twelve hours ago it had been 82. The shield was dying. The survey vessel Garam was 14 months past Jupiter's orbit. 7.8 astronomical units from Earth. Send a distress call and the signal would take 65 minutes to arrive, another 65 for a reply. For all practical purposes, they were alone. Garam's hull was a cylinder 94 meters long. Six crew had been living inside this metal tube for 26 months now. The magnetic shield was a field generated by superconducting coils wrapped around the ship's exterior. That field deflected the solar wind and galactic cosmic rays, protecting the crew. If the shield failed, the hull would lie naked before the radiation. The pull in Yujin's forearm meant the radiation was already getting through. Then the alarm sounded. Level 3 radiation alert. Red emergency lights flared across the whole ship. From the corridor speakers, an automated voice spilled out. 'Shield output below critical threshold. Crew, implement radiation protection procedures.' Yujin walked as she listened to it. Protection procedures. Garam had no radiation shelter. The shield itself was the shelter. Without it, there was no safe place anywhere aboard.
Yujin went to the medical bay. The corridor lighting had switched to emergency mode, only the red guide lights glowing along the floor. When she opened the door, Seha, the medical officer, was sitting at the microscope. The tips of Seha's fingers had turned a violet color. Seha looked up.
"Look at my fingers."
Seha spread out her left hand. The first knuckles of the index and middle fingers were purplish. Beneath the skin, the outline of the bone stood out with abnormal clarity. As if the bone had swelled. Seha bent the fingers, then straightened them. The joints moved stiffly. When the fingers curled, there was a faint sound. A sound like something coming from between bone and cartilage. Not the sound of a healthy joint.
"It's 48 hours since the radiation exposure. My marrow cells are proliferating abnormally. But—"
Seha turned the microscope's monitor toward Yujin. On the screen hung a magnified image of cell tissue. The crystalline structure of the bone tissue had changed. It was no longer the usual hydroxyapatite structure. Iron atoms had wedged themselves into the crystal lattice.
"What is this?"
Yujin asked. Seha answered.
"I don't know. The radiation has altered the mineral metabolism of the marrow cells. The bone is absorbing iron. Blood iron concentration has dropped to an eighth of normal."
Yujin looked at her own forearm. She rolled up her sleeve. Under the skin, the outline of the bone was distinct. Not violet like Seha's fingers, but the bone felt close, as though the skin had thinned. Bring the arm near the hull wall and she could feel the pull. Yujin's bones had begun to turn magnetic. Seha pressed a sensor to Yujin's arm. Figures came up on the screen. Bone density was within normal range, but the iron concentration in the tissue was 17 times normal. Setting the sensor down, Seha said,
"All six of us took the same level of exposure. The only difference is each person's rate of iron metabolism."
Yujin asked,
"Who's showing symptoms fastest?"
Seha looked at her own fingers.
"Me."
The cosmic radiation pouring in as the shield collapsed was rewriting the crystalline structure of their bones.
The shield's condition worsened. When Yujin inspected the shield generator with Taemin, the engineer, 2 of the 3 superconducting coils had lost function to microfractures. Taemin showed her a cross-section of a coil. Across the metal surface, cracks finer than a hair had spread like a spiderweb.
"We need to replace the coil."
Taemin said, setting down his tools.
"There's no spare. This alloy can only be made on Earth. Niobium-tin superconducting alloy. It's not something we can source out here."
Grease and coolant were smeared together across Taemin's hands. The mark of 12 hours working inside the shield apparatus. Beneath Taemin's eyes, too, the violet discoloration was beginning. He'd been exposed to more radiation inside the machine. Yujin touched the cracked coil. The cold metal came through her glove.
"What's the key component of this alloy?"
Taemin answered.
"Niobium, tin, and a magnetic iron-alloy matrix."
Yujin's hand stopped over the coil. Iron-alloy matrix. She looked at her own forearm. Inside her bones, iron was rewriting the crystalline structure.
Yujin went back to the medical bay. She asked Seha,
"Can you extract the mutated tissue from my bones?"
The expression drained from Seha's face. Three seconds of silence.
"What did you say?"
"Mutated bone tissue. A crystalline structure bonded with iron. I need to find out whether it can be extracted and used to repair the coil."
Seha rose from her chair. She stood a head shorter than Yujin, but the angle at which her eyes tilted up was sharp.
"You want to shave off your own bone and graft it onto the hull?"
Yujin didn't answer. Instead she pulled up the shield output reading on a tablet and set it in front of Seha. 28 percent. Down 9 percent from an hour ago.
"In 12 hours the shield goes completely dark. Once it does, the hull takes the radiation raw. All 6 of the crew hit a lethal dose within 72 hours."
Seha looked at the tablet. Looked at the numbers. Looked at the purplish discoloration on her own fingers.
"Extraction is possible. Harvest from the iliac crest and you get about 15 grams at a time. But Yujin — there's no guarantee that tissue can replace a superconducting alloy."
Yujin said,
"I'll check with Taemin."
Taemin's analysis took 4 hours. In that time the shield output dropped to 19 percent. When Taemin brought the results, the sample container in his hand held 0.3 grams of mutated bone tissue harvested from Seha's finger. His voice was lower than usual.
"It's magnetic. Strongly magnetic. Not identical to the superconducting alloy, but as a filler to pack the cracks in the coil, it'll work. The problem is quantity."
Yujin asked,
"How much do we need?"
"To repair 2 coils, 120 grams minimum. If we can harvest 15 grams from one person, that's 8 people's worth — and there are 6 of us."
Yujin ran the numbers. 20 grams from each of 6 people made 120 grams. 15 grams from the iliac crest. The remaining 5 from somewhere else. A rib. Or the tibia.
Yujin gathered the crew. 6 of them sat in the cramped meeting room. Yujin, Seha, Taemin, Doyun the navigator, Jia the comms officer, Haeun the life-support technician. Yujin explained the situation. The collapsing shield. The cracked coil. That bone tissue mutated by radiation exposure could serve as repair material. The room went quiet. Only the sound of the ventilation system carried. The red glow of the emergency lights hung on 6 faces. On someone's hand, on someone's temple, the purplish discoloration had already set in. The mutation was already happening to all of them. Doyun spoke first.
"So you're saying we shave our own bones to fix the hull?"
Yujin nodded. Jia asked,
"It'll hurt, won't it?"
Seha answered,
"Under local anesthesia the pain during the procedure can be kept to a minimum. But after the harvest, the structural strength of the site drops. Take 15 grams from the iliac crest and the pelvis loses 30 percent of its load-bearing capacity. Take another 5 grams from a rib and the ribcage weakens."
Haeun said,
"Does everyone have to give?"
Yujin answered,
"No. I'll go first."
Yujin stood.
"Harvest from me first, and do a test repair with the tissue. If it works, then I'll take volunteers."
It took Seha 47 minutes to harvest the bone tissue from Yujin's iliac crest. There was local anesthesia, but the vibration of the drill meeting bone traveled up her spine. Yujin stared at the ceiling. The medical bay's lights burned white. When the vibration stopped, a smear of red mixed with purple clung to Seha's gloves. The extracted bone tissue went into a sample container. Yujin tried to rise. Pain came up from her left hip. Not sharp. A deep, dull ache. Something like a hollowness rising from the place where bone had been taken. Yujin clenched her teeth and stood.
Taemin packed the extracted tissue into the cracks in the coil. Yujin stood beside him and watched the work. When she put weight on her left leg, pain came from her pelvis. She shifted the weight to her right leg. Taemin heated the filler and melted it into the cracks. The heated bone tissue gave off a smell. The smell of burning bone. The smell of Yujin's bone burning. The smell of protein breaking down under heat was laced with the smell of metal oxidizing. Yujin held her breath. Her mouth went dry. Her throat clenched shut. After cooling it, Taemin measured the coil's conductivity.
"It works."
Taemin said. There was no emotion in his voice.
"Not perfect, but it can bring the shield output up to 63 percent. Repair the second coil too and it's over 80."
63 percent meant below the lethal dose. They could live. Hearing Taemin's report, Yujin turned her head where she lay on the medical bed. Pain climbed from her pelvis up through her lower back. But the numbers were rising. The shield was coming back to life. Yujin's bone was guarding the hull.
The rest of the crew volunteered. Doyun came first. Seha worked, and Doyun made no sound. But leaving the medical bay after the procedure, he braced a hand against the wall. His legs were shaking. Jia wept during hers. Without a sound. Tears ran down her temples and soaked the pillow. Before her turn, Haeun asked Yujin.
"Is this it? Just once and it's over?"
Yujin couldn't answer. There was no guarantee the coils would hold steady. Instead of answering Haeun's question, Yujin looked out the window. Through the small observation port at the end of the corridor, she could see the stars. The stars did not blink. Because there was no atmosphere. The light came in a straight line. No refraction. Cold, exact light. Watching that light, Yujin thought of her last night on Earth. Her daughter had been sitting on her lap. The child's weight had felt light. The weight of a 3-year-old body. Yujin did not know the weight of the daughter who would now be 13. She pushed the memory away and thought again about the fact that inside her own body, bone was turning. Bone was becoming mineral. Human bone was becoming the material of the hull. Yujin pulled her gaze from the window and looked at Haeun.
"I'll do everything I can."
When the second coil repair was finished, the shield output climbed to 78 percent. It was after all 6 crew members had given up bone tissue. Yujin checked the state of her own body. 15 grams from the iliac crest, 7 grams from the 11th rib on the right. In all, 22 grams of bone gone. When she put her weight on the left side of her pelvis, a deep pain rose up, and when she touched the right side of her rib cage, she could feel the caved-in place between the ribs. Seha measured Yujin's bone density. At the extraction sites, the density was 40 percent of normal. A number at which a hard impact could fracture the bone.
3 days later, the shield output began to drop again. The bone tissue used as filler had undergone microscopic contraction in the coils' cryogenic environment. That living tissue would contract at minus 269 degrees was a predictable phenomenon. But there was no reserve material. The cracks were spreading open again. Output 71 percent. 68 percent. Falling 3 percent a day. Taemin ran the numbers.
"In 10 days we're back at the danger level. We need more filler."
Yujin asked.
"How much?"
"60 grams."
Yujin looked at the state of the crew. All 6 were still unrecovered from the first extraction. Doyun was limping on his left leg. Jia took only shallow breaths, because a deep one brought pain to her rib cage. The piece of rib taken from Jia's chest was, right now, holding a magnetic field inside a coil. The reason she winced with every breath was out there beyond the hull, blocking radiation. When Haeun sat down in a chair, she cradled her pelvis and lowered herself slowly.
Yujin went to Seha.
"Take more from me."
Seha looked at her. There were shadows under Seha's eyes.
"From where?"
"Left tibia. And a second extraction from the right iliac crest."
Seha's hand stopped over the instrument.
"If I take from the tibia, you won't be able to walk."
"I know."
"You'll lose the left leg."
"Lose one leg, and 6 people live."
Yujin's voice was level. She had to set her jaw to keep it level. Seha said nothing. She looked at Yujin's face. Yujin's jaw was clenched tight. Seha took out the anesthetic. Lying back on the medical bed, Yujin looked at the ceiling. In the ceiling of the medical bay she could see the grille of the ventilation duct. There was the sound of air circulating. The one sound aboard the hull that never stopped. Yujin rolled up her trouser leg. Her left shin was bared. Beneath the skin, the outline of the tibia was sharp. The purple had already risen. Bone with the mutation underway. Yujin looked at her own leg one last time. It was the last moment she could walk on this leg. Seha disinfected the site. The antiseptic was cold. Yujin began to count the ventilation grilles on the ceiling. 7. Air flowed between the 7 grilles. The system that circulated this air, and the shield that guarded this hull, were both being made from her own bone. Yujin stopped counting and closed her eyes. The anesthetic began to spread. Sensation slowly drained from her left leg.
The tibial extraction took 1 hour and 23 minutes. During the procedure Yujin watched the ceiling lights. They dimmed and brightened. Consciousness came and went. The drill's vibration traveled past her knee and up into her thigh. The sound of bone being ground rang inside her body. Not a sound from outside, but one coming from within her. The vibration climbed all the way to her skull. Yujin opened her eyes. Between the ceiling lights she could see Seha's face. Sweat beaded on Seha's forehead. Above the mask, the eyes were unsteady. Yujin bit down. Her gums bled. The taste of iron spread across her tongue. When it was over, Yujin tried to move her left leg. The toes moved. But below the knee, the support was gone. She could lift the leg, but she could not put any weight on it.
While Taemin applied the additional filler to the coil, Yujin lay on the bed in the medical bay. Her left leg was strapped into a fixation brace. She looked at her own face reflected on the ceiling. It looked different. The shadows under her eyes were deep, her cheekbones jutting out. It was because the iron leaching from her bones had dropped the iron concentration in her blood. Anemia. Yujin's fingernails had gone white. Her lips had lost their color too. The face in the mirror was not the one Yujin knew as her own. Doyun came into the medical bay. He stopped short at the sight of the assistive brace fitted to Yujin's left leg.
“Captain.”
Doyun said. He said nothing more. Yujin said,
“It's fine. It works.”
Doyun turned his head away. The rims of his eyes had gone red. Yujin watched his back. Doyun was limping too. They both walked through the same hull, both limping. Yujin watched Doyun's back grow smaller. His gait was off-balance. A gait tilted to the left. Yujin tilted the same way. People whose bones had dwindled, walking through a hull repaired with bone.
The shielding output climbed to 83 percent. Taemin reported.
“This batch of filler is more stable than the last. Lower contraction rate. It'll hold for 20 days.”
20 days. Yujin did the math. Eleven months to make it back to Earth. If it needed recharging every 20 days, that was 16 times. 60 grams each time. 960 grams total. Split across 6 people, that came to 160 grams per person. Yujin added in what had already been drawn from her own body. 22 grams plus 35 grams. 57 grams. She had 103 more grams to give. Tibia, fibula, ribs, the spinous processes of the vertebrae. Seha had drawn up a list of harvestable sites. A list of the places bone could be pulled from Yujin's body. That list glowed on the tablet beside her bed. Yujin looked at it. It was like looking at the blueprint of her own body. A blueprint weighing which parts could be removed while function held. Seha had annotated the list in the margin. 'Tibia — loss of ambulation.' 'Fibula — ambulation possible, unstable.' 'Ribs 3–6 — thoracic weakening, restricted breathing.' 'Spinous processes — reduced postural support.' Beside each site was the harvestable weight. Yujin added those numbers up. The total still extractable from her own body. 87 grams. After that there was nowhere left to take from. The rest would have to come out of the other crew.
Yujin got up from the bed. She fitted the brace to her left leg and looked in the mirror. The brace's metal frame wrapped the leg. From knee to ankle. The metal sat flush against the skin. The line between where the device ended and the leg began was blurred. Yujin walked the corridor. The leg moved on the strength of the metal device. It didn't feel like her own leg. In the corridor she came upon Haeun. Haeun looked at Yujin's leg, then raised her eyes fast. She looked at Yujin's face.
“Captain, have you eaten?”
Yujin shook her head.
“Later.”
Haeun started to say something more, then closed her mouth. She watched Yujin pass. Each time the metal brace met the floor there was a light sound. Tock. Yujin's footsteps and the sound of the device rang out in alternation.
She went into the comms room and sent a message to Earth. Situation report. Method for the shielding repair. Bone tissue harvesting. The reply would come 130 minutes later. Yujin looked out through the comms room window. Jupiter had already shrunk. Ahead lay the dark beyond the asteroid belt. Earth was behind that dark. Eleven months away. After sending the message, Yujin sat in the comms room. For the 130 minutes she waited for the reply she did nothing. The brace on her left leg made a metallic sound beneath the chair. Every time she shifted her posture there was a small metal note. Yujin spread open her left hand. Blue veins showed in the palm. The skin had thinned. As the iron concentration in her blood fell, the hemoglobin dropped with it. Her blood was thinning. Yujin's blood. The iron leaching from her bones was becoming part of the hull. Yujin closed her hand. The finger joints were stiff. The fist would not fully close. A gap remained between the fingers.
Yujin pulled her gaze from the window and looked at her left hand. The bones on the back of it stood out beneath the skin. A purple tinge had crept up to the wrist. The mutation was spreading. Even after the shielding rose to 83 percent, the radiation was not fully blocked. Through the 17 percent gap it still seeped in. The bone kept changing. The more they harvested, the more new bone regenerated in a mutated state. Magnetized bone grew, that bone was shaved down and set into the hull, and it grew again, and was shaved again. Yujin's body was becoming a parts factory for the hull. Yujin bent her fingers. The joints were stiff. The bone was changing. Where the next part she could give the hull would come from — she already knew.
