After getting off the plane, Zhang Xiaogang went straight to the scientific research center. Luo Jinyong was waiting for him, and asked Tong Shaowei to greet him outside the gate.

"How's it going?"

"The professor didn't say anything, let me take you directly."

Zhang Xiaogang quickened his pace, and when he was about to arrive at Luo Jinyong's office, he said to Tong Shaowei: "Go make a pot of coffee, and send someone to my dormitory to get two bottles of Erguotou." ”

"Erguotou?" Tong Shaowei thought he had heard it wrong.

"Yes, send it quickly."

Tong Shaowei didn't ask any more questions, and Zhang Xiaogang also entered Luo Jinyong's office.

"Lao Zhang, you've finally arrived."

"What, miss me?" Zhang Xiaogang smiled and said, "You kid, you're getting more and more clever, you can tell the truth now, right?" ”

"You see that?"

"If I couldn't even see this little trick you're playing, would I be able to get up to today? I told you a long time ago that I know you better than your mother. As soon as you kick your ass, I know if you're going to fart or shit. Zhang Xiaogang took out a cigarette and said, "Time is running out, what did you find?" ”

"It's all here." Luo Jinyong tapped on the computer screen.

Zhang Xiaogang leaned over to see that it was a photo of the 2014X1 asteroid after its disintegration, and it was a partially enlarged photo.

"What is this?"

"Pay attention to the edges."

Zhang Xiaogang looked at it for a while, but he didn't see the fame.

"See these brighter parts?" Luo Jinyong pointed out a bright spot on the photo with a pen. "This is where the debris is facing the sun."

"Reflected sunlight?"

Luo Jinyong nodded and said, "After the light is no longer shining, all we see is the reflection of the asteroid, and the part facing the sun is even brighter. ”

"What does this mean?"

"Haven't seen it yet?"

"If I can see that you can still sit here?"

Luo Jinyong smiled and said, "This is a linear bright spot, right?" ”

Zhang Xiaogang immediately frowned, Luo Jinyong's words were enough for him to figure it out. "You mean, the pieces are thin?"

"It's very thin, about the size of an eggshell."

"This ......"

"Unbelievable?"

Zhang Xiaogang didn't say anything, and after extinguishing the cigarette butt, he lit another one.

Luo Jinyong also lit a cigarette and said: "Although the calculation results have not yet come out, my intuition tells me that the total mass of these fragments is only about 1 500 percent of that of the asteroid." ”

"Are you sure?"

"Intuition."

"Your instincts have always been accurate, as if they never failed."

Luo Jinyong smiled and said, "If the debris is the shell of an asteroid, like an egg shell, and the thickness is uniform, do you know how thick the Dao is?" ”

Zhang Xiaogang shook his head, his mental arithmetic ability is very strong, but he is not a mathematician.

"It won't be more than ten meters."

"What?" Zhang Xiaogang's eyes immediately widened.

"It's about eight meters."

"This ......"

"I analyzed this bright spot, and the width of the reflective area is about eight meters."

"This ...... What does this mean? ”

"At least we won't go to the Netherworld Mansion in more than ten hours to compete for positions with more than eight billion people."

"You mean ......"

"If both of my guesses are true, that the total amount of debris is 1,135, and the total mass of the debris is only about 15000 of the asteroid, the mass of each debris is about 100,000 tons. Because it is very thin, the success rate of intercepting these fragments is greatly increased. ”

"The problem is, if we fail once, we're doomed." When he went to Shanghai, Zhang Xiaogang also had a very important task, which was to understand the progress of the Houyi project. The results were very satisfactory, the fourth Arrow launch vehicle has completed testing, and the nuclear warhead has been deployed.

"It's not that serious."

"Really?"

"Even if you fail a few times, as long as it's this thin shell-like fragment, you can sit back and relax."

"For what?"

"Lao Zhang, don't you often say that Lao Chu is 100,000 for something? Such a simple question, you don't think for yourself? ”

"Come on, there's no time to think about it right now. Besides, you're the real 100,000 why, no matter what others ask, you can answer it, right? ”

Luo Jinyong rolled his eyes and said, "After this thin shell-like fragment falls into the atmosphere, it will rub against the atmosphere and produce extremely high temperatures. According to the results of the spectral analysis, the main component of the fragments is silica, which is rock, so it will completely burn out before it hits the ground. If the angle of penetration into the atmosphere is ideal, the debris will explode and disintegrate at an altitude of about 300 kilometers above the ground. ”

"That is, it doesn't cause harm?"

"It's not that it won't, it's that it's much less harmful. Even if the fragments do not disintegrate, they will completely burn up at an altitude of more than 20 kilometers above the ground, or they will explode at a higher ground. In each case, the damage to the ground caused by the debris was not serious. ”

"How does it compare to the Tunguska explosion?"

"Probably about the same, maybe the scope of the impact will be several times larger, but it will definitely not lead to the extinction of human beings, and the damage to the earth's ecological environment will be minimal. Even in the most extreme case, when all the debris falls into the atmosphere, there will be no global catastrophe that would lead to mass extinction. Luo Jinyong extinguished the cigarette butt and said, "If the debris is intercepted from a million kilometers away, people can see an unprecedented meteor shower." ”

"So, can we really sit back and relax?"

"Overall, but there are some uncertainties."

"What uncertainties?"

"The size of the more than 1,000 fragments varies greatly, and we don't know how much of the asteroid's surface area is made up of the luminous parts of the asteroid."

"This ......"

"That is, there is a possibility that my estimate of the thickness of the fragments will be skewed greatly, and there may be some fragments that are smaller in area but have a lot of thickness."

"These debris will not burn up in the atmosphere?"

Luo Jinyong sighed and said, "Not only will it not burn up in the atmosphere, but it is also very difficult to intercept. ”

Zhang Xiaogang immediately tightened his brows.

"If such debris is produced on the far side of the asteroid, then when the interception is carried out, it will definitely be obscured by a large area of debris."

"Will the pieces be close?"

"Because the asteroid rotates around a central axis that coincides with the orbit, the debris as it approaches the Earth is scattered over a very large cross-section of the orbit, with a radius of almost 6,500 kilometers. The problem is that the asteroid is disintegrating on its own, and all the debris has the same orbital velocity, and the distance in its orbital direction must be very close, around twenty kilometers. Maybe a little bigger, but not too much. ”

"Damn, this is a big problem." Zhang Xiaogang cursed.

Luo Jinyong sighed, of course he knew the reason for Zhang Xiaogang's curse.

When a nuclear warhead explodes in outer space, most of the energy is converted into electromagnetic waves because there is no medium to transmit internal energy and wave energy. If two nuclear warheads are too close together, they cannot be detonated at the same time, because the first nuclear warhead will destroy the other in an instant. The detonation of the two nuclear warheads must be staggered to ensure that the nuclear warheads do not affect each other when they explode.

For a nuclear warhead with a speed of more than 300 kilometers per second, the distance of more than 20 kilometers is only equivalent to a time difference of less than 0.1 second.

By design, the detonation time difference of a super-nuclear warhead is at least 0.2 seconds.

This means that when a super-nuclear warhead intercepts a target, the distance from the explosion point must be controlled at least 70 kilometers or more.

If the debris in front of the larger area is intercepted first, a large number of smaller debris will inevitably be generated, making it impossible to track and lock the debris that is already much smaller in the rear.

"Professor, is there a way to ......?"

"Yes, but it can't be avoided."

"This ......"

"After successfully intercepting the larger fragments, the explosion gives the resulting debris a velocity component. Regardless of the direction of this velocity component, it is bound to change the velocity of the wreckage. As long as there is enough time, it will be possible to find the one from the wreckage that has not changed significantly. ”

"This is the little shard hidden in the back?"

Luo Jinyong nodded, indicating that this was what he meant.

"What if a small debris collides with the wreckage of a large debris?"

"Then everyone will be happy." Luo Jinyong smiled and said, "After the collision, it is very unlikely that the velocity direction of the small fragments will not change. If the interception is carried out at a distance of a million kilometers, there is a high probability that the small fragments will avoid the Earth after the change in the direction of velocity. ”

"So we just need to find the little pieces that haven't changed in velocity."

That being said, it's very difficult to do. With our current technology, it would be very good to be able to intercept again at a distance of 500,000 kilometers from the earth. Luo Jinyong sighed and said, "In addition, if the small fragments have enough thickness and the mass is about 100,000 tons, the size must be very small." If it is a regular spherical shape, the diameter will not exceed 30 meters. Even if the mass of the fragments reaches one million tons, the diameter will not exceed eighty meters. What is the accuracy of the final stage of the Zhilu Dao Divine Arrow launch vehicle? ”

Zhang Xiaogang nodded and lit a third cigarette.

In this case, only the super-nuclear warhead dropped by the Divine Arrow rocket can intercept the fish that slips through the net, and the throwing error of the nuclear warhead will not be less than 50 meters.

"To be honest, if this is going to happen, I want the smaller pieces to be as massive as possible."

"If there are only 100,000 tons, what will be the consequences if the interception fails?" Zhang Xiaogang asked.

"As long as the small fragments are relatively regular, such as spherical, oval or olive-shaped, with a speed of more than 300 kilometers per second, it is very unlikely that it will completely burn before it hits the ground. Even if most of the mass is vaporized in the atmosphere, the speed is reduced, and the rest can be catastrophic enough. ”

"How old?"

"I can't say, it depends on the situation."

"Roughly?"

Luo Jinyong thought for a while and said: "If the remaining mass is 10,000 tons and the speed is 300 kilometers per second, the kinetic energy released by the impact is equivalent to 5 billion tons of TNT equivalent. Depending on the geology of the impact site, the absolute radius of damage to ground facilities and personnel is between 2,000 and 3,000 kilometers. ”