Siheyuan (traditional courtyard house): Starting with the Korean War, returning home to take charge

At three in the morning, Lin Jianguo slammed the filter cartridge onto He Yuzhu's desk. Algae sludge splattered out, leaving a black mark on the documents.

"It's congested again. The oxygen level has dropped to 12%."

He Yuzhu didn't look at the filter. He stared at Lin Jianguo's face—he hadn't shaved for three days, his eyes were dark and swollen, and there was a ring of salt frost around the collar of his work clothes.

"What do you want to do?"

Lin Jianguo paused for a second. He thought He Yuzhu would yell at him or urge him to replace the spare part. But the question, "What do you want to do?" made him swallow back the grumble that was on the tip of his tongue.

"Change it. Use a three-stage filtration system, add backwashing, and change the filter without stopping the machine."

"A few days?"

"Three days."

"Two days." He Yuzhu stood up, pulled a blueprint from a drawer, and drew a few lines on the back. "Old Zhao has two horizontal centrifugal pumps in his warehouse, with twice the flow rate of yours. Take them over and use them first."

Lin Jianguo took the blueprints, glanced at them, and turned to run. His leather shoes clicked on the terrazzo floor of the corridor, the sound fading into the distance.

He Yuzhu sat back down in his chair and picked up the enamel mug. The tea had gone cold, and the bitterness lingered on his tongue. He put the mug down, got up, and went to the monitoring room.

He hadn't been home for three days. Qin Huairu had asked the gatekeeper to pass on a message last night, saying that Nianhua had gotten third place in the grade in math on the midterm exam. He didn't return the call. Not that he didn't want to, but he didn't know how to. Should he say "That's good," or "What's so great about third place?" Nianhua wasn't the kind of child who needed encouragement, nor was he the kind who needed to be disciplined. What he needed wasn't a father, but a running track.

The data on the screen is fluctuating. Oxygen is at 13.5%, and it's still dropping.

He picked up the phone and dialed Lin Jianguo's workstation, but no one answered. He then dialed the on-site duty room, and Old Zhao answered.

Where is Lin Jianguo?

"On the second basement level, the pump is being dismantled."

He Yuzhu hung up the phone and stared at the screen. The oxygen level had dropped to 12.8%. He remembered Zhao Chunjiang looking at the wheat through the observation window a couple of days ago, his glasses fogged up and unwiped. When that ear of wheat sprouted from its leaf sheath, Old Zhao's hands were trembling.

the phone is ringing.

"Dean He, the pump is installed. We're testing it with water." Lin Jianguo's voice was panting, as if he had just run five kilometers.

"How much oxygen?"

"It's recovering—it's already up 13%. And it's still rising."

He Yuzhu hung up the phone. The curve on the screen changed from a downward trend to a flat trend, and then it curved upwards at one corner.

At 5 a.m., the oxygen level returned to 21%.

He didn't close his eyes.

On the eighth day, Lin Jianguo made a second modification. He changed the three-stage filtration system to a five-stage system and added an activated carbon layer. The algae sludge blockage stopped at the second stage, and the subsequent three stages were completely clean. Backwashing is automatically triggered every six hours, and pressure drop fluctuations are controlled within five percent.

He Yuzhu had visited the device. Five filter tanks were lined up in a row, the pipes covered with flow meters and pressure gauges, requiring one to walk sideways. Lin Jianguo was squatting next to the last filter tank, holding a notebook and recording data.

How long did this level take?

"In 48 hours, the pressure drop only increased by 3%."

"How long can it last?"

"Theoretically, it will take thirty days. The actual timeframe is unknown."

He Yuzhu squatted down, turned on the drain valve at the bottom of the filter tank, and a stream of clear water flowed out. There was no algae or sludge, and no suspended matter.

"Okay. Keep running."

On the twenty-first day, Zhao Chunjiang called from the Academy of Agricultural Sciences.

"Dean He, come down and take a look."

When He Yuzhu arrived at the third basement level, Zhao Chunjiang was standing in front of the observation window, his back to him. A piece of white paper was pasted on the glass, with the outline of a wheat ear drawn on it in ballpoint pen, and a line of small print written next to it: "Sixth generation, heading stage six days earlier."

He Yuzhu walked over. Inside the cabin, the wheat ears had already sprouted from their leaf sheaths, nearly twice as long as the first generation. The awns were tender green, and the glumes were swollen, like small pockets stuffed full of things.

Zhao Chunjiang didn't turn around. "The weight of 1000 grains is 19.7 grams. That's 4.5 grams more than the first generation."

He Yuzhu didn't speak. Zhao Chunjiang turned around, his eyes red.

"Dean He, I started working on space breeding in 1964. In fifteen years, this is the first time I've seen wheat sprouting in a simulation chamber."

He Yuzhu wanted to pat him on the shoulder, but lowered his hand halfway through. "Memorize the data."

On the twenty-eighth day, the filter clogged four times, and was salvaged three times by backflushing. The fourth time, the pressure drop reached the red line, and the automatic flush failed to reduce the pressure. Lin Jianguo manually switched to the backup circuit, and it returned to normal after fifteen minutes. In his duty log, he wrote: "The activated carbon in the secondary filter tank failed and needs replacement. Emergency repairs completed. It is recommended that the activated carbon replacement cycle be set at twenty days."

He Yuzhu read the log and wrote a line at the bottom: "Twenty days is too conservative. Test for twenty-five days."

Day 30.

Six hours before the countdown reached zero, He Yuzhu sat in the monitoring room. Lin Jianguo brought him a boxed lunch; he ate one, leaving the other cold on the table. Qian Zhiyuan rushed over from the winding workshop, his work clothes covered in carbon fiber debris, and stood at the door without coming in.

The screen displays an oxygen concentration of 20.7%, a carbon dioxide concentration of 0.33%, a temperature of 23 degrees Celsius, and a humidity of 55%. All the curves are as flat as if they had been cut with a knife.

There was only one hour left. Zhao Chunjiang ran downstairs, holding an envelope containing a photo of the sixth-generation wheat.

"Dean He, look at this." He held up the photo in front of He Yuzhu. In the photo, the husk of the wheat ear was cracked open, revealing the pale yellow wheat grains inside.

"Have they grouted it?"

"The grain filling has started. The grain formation period is three days later than the ground control group, but the grain filling rate is the same."

He Yuzhu turned the photo over. On the back was written the date and a set of data.

He returned the photo to Zhao Chunjiang and turned to look at the screen.

Ten minutes. Five minutes. One minute.

The numbers fluctuated. Then, they returned to zero.

No one spoke in the monitoring room. The printer squeaked and spewed out paper. He Yuzhu stood up, tore off a data sheet, and read it through from beginning to end. Water recovery rate 98.3%, oxygen regeneration rate 94%, wheat heading, sixth-generation grain filling.

He folded the data sheet and put it into his inner jacket pocket.

"The second phase, lasting ninety days, will begin in seven days. Animal experiments will be added, using two rats."

Lin Jianguo opened his mouth as if to say something, then closed it again. Qian Zhiyuan took a step forward from the doorway, then stopped as well.

He Yuzhu looked at them. "Is there a problem?"

Lin Jianguo shook his head. Qian Zhiyuan also shook his head.

"Then go and prepare."

The crowd dispersed. He Yuzhu sat alone in the monitoring room, taking the data sheet out of its inner pocket and reviewing it again. The numbers were correct. Thirty days, no major malfunctions, no deaths—although there was no one in the cabin yet. The two rats wouldn't be released until next week, but the thirty days of continuous operation had indeed been successfully completed.

He put away the data sheet, got up, and turned off the light.

Two motion-activated lights in the corridor were broken, and he slowed his pace as he stepped through that dark section. A picture flashed through his mind—Nianhua standing in front of the observation window, his nose pressed against the glass, saying he wanted to grow vegetables on Mars. The child's backpack strap had slipped down to his elbows, and his school uniform collar was open, making him look like he hadn't grown up yet.

But when he said those words, there was no naivety in his eyes at sixteen.

He Yuzhu walked out of the office building. It wasn't fully light yet; the searchlights in the courtyard had just been turned off, leaving lingering glare on his retina. Standing on the steps, he remembered something—he couldn't recall where he was on the day Nianhua was born. Was he chasing after Pu Zheng, or rummaging through old files in the archives? He couldn't remember.

He stood there, trying to remember. He could only recall Qin Huairu saying "She gave birth" on the phone, her voice very soft, as if afraid of waking someone.

He suppressed the thought, opened the car door, and started the engine. He'd go home for dinner today and come back tomorrow to prepare for the second phase.

As the car drove out of the research institute's gate, the gatekeeper, Old Zhao, poked his head out and called out, "Dean He, your son came again yesterday and left something."

He Yuzhu stepped on the brakes.

Old Zhao jogged over and handed over a manila envelope. Inside was a hand-drawn sketch—a structural diagram of the Mars Greenhouse. It showed an inflatable frame, multiple layers of film, hydroponic pipes, and LED light panels. A line of small writing in the corner read: "Dad, I want to participate in the third phase."

He Yuzhu folded the sketch, put it in the inner bag, and stuck it together with the data paper.

He didn't return the call. He'll wait until the 90-day run is over before we talk about it.