Death's End

by Cixin Liu

  After she told Vadimov what had happened, Vadimov laughed. “That’s just a line that used to be popular in our … trade. I heard it started back during the Second World War. Veterans would use it as a joke on novices. The point is: Our profession is the only one on Earth where lies and betrayal are at the very heart of what we do. We have to be … flexible when it comes to commonly accepted ethical norms. PIA is formed from two groups of people: Some are technical experts like you; others are veterans of the various intelligence agencies in the world. These two groups have different ways of thinking and acting. It’s a good thing that I’m familiar with both and can help you adjust to the other.”

  “But our enemy is Trisolaris. This is nothing like traditional intelligence.”

  “Some things are constant.”

  * * *

  Over the next few days, other new PIA staff members reported for duty. Most of them came from countries that were permanent members of the PDC.

  They were polite to each other, but there was no trust. The technical experts kept to themselves and acted as if they were on guard against theft every minute. The intelligence veterans were gregarious and friendly—but they were constantly on the lookout for something to steal.

  It was just like Vadimov had predicted: These people were far more interested in spying on each other than gathering intelligence on Trisolaris.

  Two days after Cheng Xin’s arrival, PIA held its first all-hands meeting, even though not everyone had shown up yet. Other than PIA Chief Wade, there were three assistant chiefs: one from China, one from France, and one from the United Kingdom.

  Assistant Chief Yu Weiming spoke first. Cheng Xin had no idea what kind of work he had done in China—and he had the sort of face that took multiple meetings to remember what he looked like. Fortunately, he didn’t engage in the habit—common among Chinese bureaucrats—of giving long, meandering speeches. Though he was just repeating platitudes about the PIA’s mission, at least he spoke succinctly.

  Assistant Chief Yu said that he understood that everyone in the PIA was sent by their own country, and so they had dual loyalties. PIA didn’t demand, and didn’t even hope, that they would place their loyalty to the agency above their duties to their own nations. However, since the PIA’s task was the protection of the entire human race, he hoped that everyone present would at least try to balance the two appropriately. Considering that the PIA was going to work directly against the Trisolaran threat, they ought to become the most united of the new agencies.

  While Assistant Chief Yu was giving this speech, Cheng Xin noticed that Wade was kicking the table legs and slowly maneuvering his chair away from the conference table as though he didn’t want to be there. Later, whenever anyone asked him to say a few words, he shook his head and refused.

  Finally, after everyone who wanted to make a speech had done so, he spoke. Pointing at the pile of boxes and fresh office supplies in the meeting room, he said, “I’d like the rest of you to take care of these matters on your own.” Apparently, he was referring to the administrative details of getting the agency up and running. “Please don’t take up my time or theirs”—here he pointed at Vadimov and his staff. “I need everyone in the Technology Planning Center with experience in spaceflight engineering to stay. The rest of you are dismissed.”

  About a dozen people remained in the now much less crowded conference room. As soon as the heavy oak doors closed, Wade dropped his bomb. “The PIA must launch a spy probe at the Trisolaran Fleet.”

  The stunned staff members looked at each other. Cheng Xin was surprised as well. She had certainly hoped to get to substantive technical work quickly, but she hadn’t expected such directness or speed. Considering that the PIA had just been formed and there were, as yet, no national or regional branches, it seemed ill-equipped to take on big projects. But the real shocker was the boldness of Wade’s proposal: The technical challenges and other barriers seemed insurmountable.

  “What are the specific requirements?” asked Vadimov. He was the only one who seemed to take Wade’s announcement in stride.

  “I’ve consulted with the delegates of the permanent members of the PDC in private, but the idea hasn’t yet been formally presented. Based on what I know, the PDC members are most interested in one specific requirement—and this is something that they won’t compromise on: The probe must achieve one percent of lightspeed. The permanent members of the PDC have different ideas about other parameters, but I’m sure they’ll come to some compromise during formal discussions.”

  An expert from NASA spoke up. “Let me get this straight. Given those mission parameters, and supposing we only worry about acceleration and provide no way for the probe to decelerate, the probe will take two to three centuries to reach the Oort Cloud. There, it will intercept and examine the decelerating Trisolaran Fleet. Forgive me, but this seems a project better reserved for the future.”

  Wade shook his head. “With those sophons zipping about at lightspeed, spying on us constantly, and completely blocking all fundamental physics research, it’s no longer certain that we’ll make significant technological progress in the future. If humanity is doomed to crawl at a snail’s pace through space, we’d better get started as soon as possible.”

  Cheng Xin suspected that Wade’s plan was at least partly motivated by politics. The first effort by humanity to make active contact with an extraterrestrial civilization would enhance the PIA’s status.

  “But given the current state of spaceflight technology, it will take twenty, maybe thirty thousand years to reach the Oort Cloud. Even if we launch the probe right now, we won’t have gotten very far from Earth’s front door by the time the Trisolaran Fleet arrives in four hundred years.”

  “That is precisely why the probe must achieve one percent of lightspeed.”

  “You’re talking about boosting our current maximum speed a hundredfold! That requires a brand-new form of propulsion. We can’t achieve that kind of acceleration with current technology, and there’s no reason to expect a technical breakthrough within the foreseeable future. This proposal is fundamentally impossible.”

  Wade slammed his fist down on the table. “You forget that we now have resources! Before, spaceflight was merely a luxury, but now it’s an absolute necessity. We can ask for resources that far exceed what was imaginable before. We can throw resources at this problem until the laws of physics bend. Rely on brute force if you have to, but we must accelerate the probe to one percent of lightspeed!”

  Vadimov instinctively looked around the room. Wade glanced at him. “Don’t worry. There are no reporters or outsiders anywhere near here.”

  Vadimov laughed. “Please don’t take offense. But saying we want to throw resources at the problem until the laws of physics bend is going to make our agency the laughingstock of the world. Please don’t repeat it in front of the PDC.”

  “I already know you’re all laughing at me.”

  Everyone held their tongue. The staff just wanted the meeting to be over. Wade looked at everyone in turn, then returned his gaze to Cheng Xin. “No, not everyone. She’s not laughing.” He pointed at her. “Cheng, what do you think?”

  Under Wade’s keen gaze, Cheng Xin felt as if he were pointing a sword at her, not a finger. She looked around helplessly. Who was she to talk?

  “We need to implement MD here,” said Wade.

  Cheng Xin was even more baffled. MD? McDonald’s? Doctor of medicine?

  “But you’re Chinese! How can you not know MD?”

  Cheng Xin looked at the other five Chinese in the room; they looked just as confused.

  “During the Korean War, the Americans discovered that even common Chinese soldiers taken as prisoners seemed to know a lot about their own field strategies. It turned out that your commanders had presented the battle plans to the troops for mass discussion, hoping thereby to find ways to improve them. Of course, if you become Trisolaran prisoners of war in the future, we don’t want you to know that much.”

 
A few of those present laughed. Cheng Xin finally understood that MD meant “military democracy.” The others in the conference room enthusiastically supported Wade’s proposal. Of course, these elite experts didn’t expect a mere technical aide to have any brilliant ideas, but they were mostly men, and they thought that by giving her a chance to talk, they would have a perfect excuse to appreciate her physical attributes. Cheng Xin had always made an effort to dress conservatively, but this sort of harassment was something she had to deal with constantly.

  Cheng Xin began: “I do have an idea—”

  “An idea for bending the laws of physics?” The speaker was an older Frenchwoman named Camille, a highly respected and experienced consultant from the European Space Agency. She looked at Cheng Xin contemptuously, as though she didn’t belong in the room.

  “Well, more like getting around the laws of physics.” Cheng Xin smiled at Camille politely. “The most promising resource at our disposal is the stockpile of nuclear weapons from around the world. Without some technical breakthrough, these represent the most powerful sources of energy we can launch into space. Imagine a spaceship or probe equipped with a radiation sail, similar to a solar sail: a thin film capable of being propelled by radiation. If we set off nuclear bombs behind the sail periodically—”

  A few titters. Camille laughed the loudest. “My dear, you have sketched for us a scene out of a cartoon. Your spaceship is filled with a pile of nuclear bombs, and there’s a giant sail. On the ship is a hero who bears more than a passing resemblance to Arnold Schwarzenegger. He tosses the bombs behind the ship, where they explode to push the ship forward. Oh, it’s so cool!” As the rest of the staff joined in the mirth, she continued. “You may want to review your homework from freshman year in college and tell me: one, how many nuclear bombs your ship will have to carry; and, two, with that kind of thrust-to-weight ratio, what sort of acceleration you can achieve.”

  “She didn’t manage to bend the laws of physics, but she did fulfill the other aspect of the chief’s demand,” another consulting expert said. “I’m just sorry to see such a pretty girl fall under the spell of brute force.” The wave of laughter reached a crescendo.

  “The bombs will not be on the ship,” Cheng Xin replied calmly. The laughter ceased abruptly; it was as if she had put her hand on the surface of a struck cymbal. “The probe itself will be a tiny core equipped with sensors attached to a large sail, but the total mass will be light as a feather. It will be easy to propel it with the radiation from extravehicular nuclear detonations.”

  The conference room became very quiet. Everyone was trying to think where the bombs would be. While the others were mocking Cheng Xin, Wade’s mien had remained chilly and unmoved. But now, that smile, like water seeping from a crack in the ice, gradually reappeared on his face.

  Cheng Xin retrieved a stack of paper cups from the drinking water dispenser behind her and laid them out on the conference table in a line. “We can use traditional chemical rockets to launch the nuclear bombs in advance, and distribute them along the first segment of the probe’s route.” She took a pencil and moved its tip along the line, from one cup to the next. “As the probe passes each bomb, we detonate it right behind the sail, accelerating it faster and faster.”

  The men now moved their gazes away from Cheng Xin’s body. They were finally willing to take her proposal seriously. Only Camille continued to stare at her, as though at a stranger.

  “We can call this technique ‘en-route propulsion.’ This initial segment is the acceleration leg, and it takes up only a tiny fraction of the overall course. As a very rough estimate, if we use one thousand nuclear bombs, they can be distributed along a path of about five astronomical units stretching from the Earth to Jupiter’s orbit. Or we could even compress it further and distribute the bombs within Mars’s orbit. That’s definitely achievable with our current technology.”

  The silence was broken by a few whispers. Gradually, the voices grew louder and more excited, like a drizzle turning into a rainstorm.

  “You didn’t just come up with this idea, did you?” asked Wade. He had been listening to the discussion intently.

  Cheng Xin smiled at him. “It’s based on an old idea in aerospace circles. Stanislaw Ulam first proposed something like it back in 1946. It’s called nuclear pulse propulsion.”

  “Dr. Cheng,” Camille said, “we all know about nuclear pulse propulsion. But those previous proposals all required the fuel to be carried aboard the ship. The idea of distributing the fuel along the spacecraft’s route is indeed your invention. At least, I’ve never heard the suggestion before.”

  The discussion grew heated. The assembled experts tore into the idea like a pack of hungry wolves presented with a piece of fresh meat.

  Wade slammed the table again. “Enough! Don’t get bogged down on details right now. We’re not evaluating feasibility; rather, we’re trying to figure out if it’s worthwhile to study the idea’s feasibility. Focus on big-picture barriers.”

  After a brief silence, Vadimov said, “The best thing about this proposal is that it’s easy to get started.”

  Everyone immediately caught on to Vadimov’s meaning. The first step in Cheng Xin’s plan involved launching a large number of nuclear bombs into orbit around the Earth. Not only did humanity possess such technology, the bombs were already on launch vehicles: the ICBMs in service could easily be repurposed for this use. American Peacekeepers, Russian Topols, and Chinese Dongfengs could all directly launch their payloads into near-Earth orbits. Even intermediate-range ballistic missiles, if retrofitted with booster rockets, could do the job. Compared to the post-Crisis nuclear disarmament plans that required destroying the missiles, this plan would be far cheaper.

  “Excellent. For now, let’s pause our discussion of Cheng Xin’s en-route propulsion idea. Any other proposals?” Wade looked around the room.

  A few seemed to want to speak up, but finally decided to remain quiet. None of them thought their own ideas could compete with Cheng Xin’s. Eventually, everyone’s eyes focused on her again, but this time, the meaning was completely different.

  “We’ll meet twice more to brainstorm and see if we can come up with a few more options. But we might as well get started on the feasibility study for en-route propulsion. We’ll need a code name.”

  “Since the probe’s velocity would go up a level each time a bomb explodes, it’s a bit like climbing a flight of stairs,” Vadimov said. “I suggest we call it the Staircase Program. Besides the requirement of a final velocity exceeding one percent of lightspeed, another parameter to keep in mind is the mass of the probe.”

  “A radiation sail can be made very thin and light. Based on the current state of material sciences, we can make a sail of about fifty square kilometers and limit the mass to about fifty kilograms. That should be big enough.” The speaker was a Russian expert who had once directed a failed solar sail experiment.

  “Then the key will be the mass of the probe itself.”

  Everyone’s eyes turned to another man in the room, the chief designer of the Cassini-Huygens probe.

  “If we include some basic sensors and take into account the necessary antenna and radioisotope power source to transmit information back from the Oort Cloud, about two to three thousand kilograms ought to do it.”

  “No!” Vadimov shook his head. “It has to be like Cheng Xin said: light as a feather.”

  “If we stick with the most basic sensors, maybe one thousand kilograms would be enough. I can’t guarantee that’s going to succeed—you’re giving me almost nothing to work with.”

  “You’re going to have to make it work,” said Wade. “Including the sail, the entire probe cannot exceed one metric ton in mass. We’ll devote the strength of the entire human race to propel one thousand kilograms. Let’s hope that’s light enough.”

  * * *

  During the next week, Cheng Xin slept only on airplanes. As part of a task force led by Vadimov, she shuttled back and forth between th
e space agencies of the US, China, Russia, and Europe to coordinate the feasibility study of the Staircase Program. During that week, Cheng Xin got to travel to more places than she had in her life up to that point, but she didn’t get to do any sightseeing except through the windows of cars and conference rooms.

  At first, they had thought they could get all the space agencies to do a combined feasibility study, but that turned out to be an impossible political exercise. In the end, each space agency performed an independent analysis. The advantage of this approach was that the four studies could be compared to get a more accurate result, but it also meant that the PIA had to do a lot more work. Cheng Xin worked harder on this project than anything in her professional career—it was her baby, after all.

  The four feasibility studies quickly reached preliminary conclusions, which were very similar to each other. The good news was that the area of the radiation sail could be shrunk to twenty-five square kilometers, and with even more advanced materials, the mass of the sail could be reduced to twenty kilograms.

  Then came some very bad news: In order to reach the required speed of 1 percent of lightspeed, the mass for the entire probe assembly had to be reduced by 80 percent—to only 200 kilograms. Subtracting the mass reserved for the sail left only 180 kilograms for sensors and communication devices.

  Wade’s expression didn’t change. “Don’t be sad. I have even worse news: At the last session of the PDC, the resolution proposing the Staircase Program was voted down.”

  Of the seven permanent members of the PDC, four voted no. Their reasons were surprisingly similar. In contrast to the technical staff of the PIA with background in spaceflight, the delegates were not interested in the propulsion technology. They objected that the probe’s intelligence value was too limited—in the words of the American representative, “practically nil.”