Although it was midsummer, the wind on the rooftop was much stronger than down below. Gao Jian's hair was blown into disarray. Director Dan stood at the edge of the rooftop with his hands behind his back, gazing north.
There was nothing in the northern sky but a brilliant blue expanse and a few thin clouds scattered by the wind in the distance.
Most of the people on the rooftop had already raised their phones and were randomly snapping pictures of the horizon. Gao Jian glanced around. Aside from the shifty-looking Song Yaozu, no one was paying attention to their corner.
Gao Jian quietly waited for the two leaders to give him an answer.
"Old Li, he's your man. You explain," Director Dan said.
Old Li frowned. He really hadn't expected Gao Jian to learn so much from one trip to the United States.
"Gao, who did you say told you this?" Old Li asked.
"Elon Musk!" Gao Jian declared the name without hesitation.
"He certainly could know. He got his start in rockets, after all. The higher-ups probably briefed one another," Director Dan said pensively.
Deputy Director Bian cursed. "Why does Elon Musk blab about everything?"
"What good does cursing him do? Outsiders were bound to find out sooner or later." Old Li shot a glare over.
Deputy Director Bian was the most practical. After taking half a step forward and shifting their group slightly away from the rooftop corner, the deputy director began, "Gao, this is complicated, but it isn't as mysterious as you think. The country did notice orbital anomalies very early on.
"The earliest instance was when Comrade Yang Liwei first went into space. The George W. Bush administration had just taken office then. Before our crewed mission, we notified them as a courtesy, but the Bush administration took it very seriously and immediately sent people to contact us. They told us that above Low Earth Orbit, starting at roughly 499 kilometers, localized gravitational anomalies would occur."
Gao Jian sighed inwardly.
The higher-ups really did know about this. That made sense.
"And then?"
Deputy Director Bian continued, "At first, we didn't believe it either. We privately approached Russia to verify it, and they handed over a set of Soviet-era data that confirmed what the United States had said.
"Above Low Earth Orbit, localized gravity failure really does occur. There's absolutely no pattern to it. Sometimes it occurs between 700 and 10,000 kilometers, sometimes between 20,000 and 150,000 kilometers. But its overall range remains between 499 and 200,000 kilometers."
Gao Jian understood. "So there's a limit to its range..."
"Right. Without that limit, the Moon would have been flung away long ago and become a planet in the solar system," Deputy Director Bian explained.
Gao Jian was puzzled again. "Why did we only learn about this after the Americans shared it with us? Hadn't we noticed the gravitational anomalies before? We'd already conducted plenty of space missions."
Old Li reminded him, "Gao, the gravitational anomalies start at around 500 kilometers. Think carefully. Before Shenzhou 5, what altitudes did our space missions reach?"
Before Gao Jian could answer, Old Li rattled them off from memory.
"Starting from my work on the Dongfanghong 1 satellite when I was young, not a single mission had an orbital altitude above 500 kilometers. Dongfanghong 1 orbited at 439 kilometers, Shenzhou 1 at 349, Shenzhou 2 at 340, Shenzhou 3 at 341, and Shenzhou 4 at 343. Others, such as the Long March series, were all around 200 kilometers. Even the recoverable remote-sensing satellite in 1975 reached a maximum altitude of only 483 kilometers."
Gao Jian felt as though he had woken from a dream. "So that's why."
Old Li continued, "About thirty years ago, Dongfanghong 1 drifted out of its orbit and went above 500 kilometers. Then a gravitational anomaly flung it above 2,000 kilometers. It encountered several more gravitational anomalies afterward, and now it's been flung more than 200,000 kilometers away..."
Deputy Director Bian added, "For Shenzhou 5, our originally planned altitude was 543 kilometers. We only changed it to 343 after receiving the Bush administration's warning. Otherwise, Comrade Yang Liwei might never have made it back..."
Gao Jian felt his scalp prickle.
"Why did President Bush tell us all this?"
"Humanitarian considerations, probably," Deputy Director Bian said with a soft sigh.
Director Dan also said, "Back then, the Americans were always exporting their so-called universal values, but the good thing was that some of them actually believed in those values themselves. So they could occasionally show a glimmer of humanity. These days... heh."
Talking about the United States in its golden age, then thinking of the United States today, left both directors rather wistful.
The thought that they would witness the fall of a second global empire made them even more so.
Gao Jian thought for a moment. "These days, most countries' space activities are confined to within 500 kilometers. The International Space Station and our own space station are also at an altitude of 400 kilometers. Is this the reason?"
Deputy Director Bian said, "Not entirely. The vast majority of countries don't even know about this. Remember, even today, in 2028, only China, the United States, and Russia can launch crewed orbital spacecraft. European countries hitch rides on American rockets. Countries like Japan and India haven't conducted crewed space missions."
Director Dan added, "If it hadn't been a crewed mission back then, but an uncrewed one, I'm sure Bush still wouldn't have warned us."
Gao Jian asked again, "What about high-orbit satellites?"
Standard high-orbit satellites generally operated at an altitude of around 36,000 kilometers, primarily serving communications, radio and television broadcasting, weather monitoring, early warning, and other purposes. In theory, these satellites were also within the failure zone between 500 and 200,000 kilometers.
"There are safe spots," Director Dan explained.
"Safe spots are...?" Gao Jian pressed.
"Regions where gravity remains normal. Like bubbles in water, they're fixed above the synchronous orbit and rotate along with the Earth. These safe spots are generally around 100 kilometers in diameter. Out in high orbit, they're individual safety bubbles. Inside the bubbles, gravity always remains normal.
"Those high-orbit satellites are launched into these safe spots while gravity is normal. Examples include the BeiDou system you're familiar with, as well as GPS, Galileo, and GLONASS."
"What's the principle behind these safe spots?"
Director Dan chuckled. "If I knew the principle, the only place you'd see me would be onstage accepting the Nobel Prize in Physics."
Old Li also said, "The entire scientific community is exploring the mechanism behind gravity failure and studying these safe spots, but it'll be difficult to figure it out anytime soon. After all, we still aren't even sure what gravity is. According to general relativity, gravity is merely the curvature of spacetime. According to quantum field theory, gravity is quantized... but who knows whether Einstein or Planck was right?"
Gao Jian was just a lousy immortal cultivator. What did he know about Einstein or Planck?
This was a clash of fundamental paths in the physics community, a struggle between schools of thought that concerned the ultimate ownership of unified field theory. No one could offer a definitive explanation.
Gao Jian looked miserable. He felt he might never get an answer to this.
"But there is one thing we can be sure of," Director Dan said.
"What?"
"The frequency of gravitational anomalies has gradually increased in recent years. Before the 1980s, gravitational anomalies were practically nonexistent."
Gao Jian sank into thought.
"None of the other countries know?"
"No."
Deputy Director Bian explained, "India, Japan, South Korea-when they launch high-orbit satellites, they don't know where the safe spots are. Usually, within a few years of launch, a sudden gravity failure flings them away. But those countries only assume it was a technical error. No matter how hard they rack their brains, they'd never imagine that gravity failure was the cause."
Gao Jian sighed. "So only we, Russia, and the United States know about this?"
Deputy Director Bian nodded. "Right. Russia only knows because of the data left behind by the Soviet Union. We also discovered the safe spots through the records the Soviet Union left behind. Unfortunately, it's been almost forty years since the Soviet Union collapsed, and Russia has more or less exhausted that inheritance. The space race today is mainly between us and the United States."
"To be precise, it's a competition between CNSA and NASA. Aside from them, SpaceX, the European Space Agency, and the like are just extras along for the ride," Director Dan added.
Gao Jian asked many more questions, including about patterns in the gravitational anomalies, the situation aboard the Chinese Space Station, anomalies in the Van Allen Radiation Belt, and so on.
Director Dan and Deputy Director Bian stopped withholding information and told him everything truthfully.
"There's no obvious pattern to the gravitational anomalies. The Yutu Rover, Lunar Probe, and other things you just asked about were all launched while gravity was normal. Over the past ten years, gravity has been normal more than ninety percent of the time."
"Surely launches can't just be gambles on luck?" Recalling the failure of the SLS rocket, Gao Jian still felt a lingering dread.
"Of course not. Gravity can be detected using lasers. Whether it's abnormal can be determined simply by shining a laser through it. If gravity hasn't failed, we launch as usual. If it has, we suspend the launch."
Gao Jian asked, "How exactly does that work?"
Deputy Director Bian explained:
"During the Apollo Crewed Moon Landing and the Soviet uncrewed Moon landings, the American Apollo missions and the Soviet Lunar Rover placed several Corner Reflectors on the Moon. Ground stations fire lasers at them to measure the Earth-Moon distance precisely. If gravity is abnormal in a region of space between Earth and the Moon, the laser's path is slightly disturbed. It's very easy to spot."
Gao Jian exclaimed, "The Apollo Crewed Moon Landing was real?"
Deputy Director Li, Director Dan, and Old Li all looked at him as though he were an idiot.
Gao Jian: "..."
Before you continue