Not long ago, people saw a surprising news story. According to reports, Chinese scientists have demonstrated a plan that can use 23 Long March 5 rockets to hit the asteroid, causing the asteroid to change its trajectory and thus protect the earth.
What the? Using rockets to hit planets, which kind of brain-opening science fiction movie plot is this?
No, it's a real subject. The results were published in the scientific journal Icarus under the title Assembled Kinetic Impactor for Deflecting Asteroids by Combining the Spacecraft with the Launch Vehicle Upper Stage.
The Long March 5 series of carrier rockets, nicknamed "Fat Five", is a disposable large-scale cryogenic liquid bundled carrier rocket developed by China in 2006, and is also a series of rockets with a diameter of 5 meters in the core stage of China's new generation of carrier rockets.
Long March 5 carrier rocket
In the 2013 American movie Gravity, the Chinese space station Tiangong-1 became the last straw for astronauts. Earlier, in "2012", the "Noah's Ark" built by China saved the lifeblood of mankind. Western filmmakers have put Chinese technology into the film, reflecting the solid progress of China's cutting-edge technology. In 2021, the "occupancy" of the Chinese space station has attracted the attention of the world.
"Fat Five Hits Asteroids to Save the Planet" is not a movie, but a hypothetical response of scientific research to reality.
<h1 class="pgc-h-arrow-right" Data-track="19" will the tragedy > repeat itself? </h1>
Although the probability of a planet hitting the Earth is extremely low, once it happens, the consequences are immeasurable.
Dinosaurs were the ones who witnessed it, and none of them survived.
65 million years ago, a fragment of a planet about 10 kilometers in diameter struck the location of the Yucatan Peninsula in mexico today, and scientists estimate that its power was equivalent to the explosion of 10 billion atomic bombs in Hiroshima, directly causing the extinction of 95% of the earth's life at that time.
Stills from "The Great Collision of Heaven and Earth"
In fact, the theory of "meteorite impact" started very late, was only proposed in the 1950s, and by the 1980s, scientists had found geological evidence to prove that it was true.
There have been major breakthroughs in the study of paleontology, and at the same time, this has also buried fear in the hearts of human beings.
Will the tragedy repeat itself?
In this regard, artists are always one step ahead. In 1998, the classic science fiction disaster film "The End of the World" was released, in which a huge meteorite came towards the earth, and only 18 days later, it was about to crash into the earth, and mankind faced an existential crisis.
Before it, a small "meteorite rain" came to New York. After the meteorite is squeezed in the atmosphere, it turns into a fireball, which looks no different from a missile, and the city buildings, streets, crowds, vehicles, all are in undifferentiated attacks. As people fled, they shouted, "There's a war again!" ”
Stills from "The End of the World"
Impressively, in the film, the president of the United States asks the team of scientists how much damage they would have if the meteorite hit the earth.
The team of scientists replied, "Loss? No, it's all going to end, Mr. President. ”
In that year, "The End of the World" achieved a good box office, which embodied the "fear of doom" of mankind, but in the second half of the film, it is still a cheesy personal heroism narrative. The real relevance of the film is in a monologue at the beginning:
"What happened on Earth will happen again, and it's only a matter of time."
This line is calm and cruel, but it is not alarmist.
In "Apocalypse", Harry is eventually sacrificed in order to complete the mission of nuclear attack on meteorites
The reality is that there are indeed asteroid trajectories that coincide with or approach the Earth's trajectory and could endanger the safety of the Earth, and they are called "near-Earth asteroids" .
The number of "near-Earth asteroids" is still quite large. As of January 7, 2020, according to the statistics of the US Near-Earth Object Research Center, a total of 21,776 near-Earth asteroids have been found, of which 8946 are larger than 140m in diameter and 905 are asteroids with a diameter of more than 1km.
How powerful are they?
According to scientific estimates, a 100-meter-diameter asteroid hitting the Earth could destroy a large city. If an asteroid with a diameter of more than 10 kilometers hits the Earth, it will cause global destruction.
In fact, the "asteroid impact on Earth" event happens almost every day. According to statistics, an average of 700 meteorites fall into the earth every year, an average of 1.9 per day. However, they are much smaller in size and generally do not cause harm.
The most recent of the impacts that really attracted attention was on February 15, 2013, when an asteroid about 17 meters in diameter crashed into the russian city of Sutka in chelyabinsk oblast at a speed of 30-40 kilometers per second.
This incident is known in history as the "2.15 Chelyabinsk meteorite fall incident". From the video taken by the crowd, it can be seen that this fireball drags a glowing tail, and the brightness exceeds the brightness of the sun. At that time, although Russian officials observed meteorites, there was no way to deal with them.
The meteorite incident injured more than 1,500 people, and this is already a "blessing in disguise". Because the meteorite did not directly hit the ground, but disintegrated and exploded in mid-air, which greatly reduced the harm.
Even afterwards, someone found in the video that a suspected object chased the meteorite from behind and "broke through" the meteorite to explode. Therefore, in the Network, there is a widely circulated saying that mysterious forces are secretly protecting the earth.
But there is one thing that the dinosaurs will certainly not agree to.
"2.15 Chelyabinsk meteorite fall", the meteorite fell into the frozen Chebarkul Lake to form an ice cave
<h1 class="pgc-h-arrow-right" data-track="169" > really "Earth Defense War"</h1>
The fact that the dinosaurs were extinct makes the reason very clear: there has never been a savior, and everything can only be on its own.
Suppose one day, a huge meteorite is really found crashing into the earth, and all humans can do is to try their best to change the trajectory of the asteroid.
It's too sci-fi anyway.
Go back to the sci-fi movie "The End of the World" and see how the movie is made. In the movie, scientists propose to use the power of the nuclear bomb to change the trajectory of the asteroid, specifically, to send a team of people to the meteorite, drill a hole about 850 meters deep in the meteorite, and then bury the nuclear bomb in the hole and detonate it remotely.
In "The End of the World", a hole in the meteorite is carved
The practice of "The End of the World" is called the "nuclear attack method" in reality.
"Nuclear attack method" refers to the use of detectors containing nuclear material along the interception orbit, running at high speed towards the target asteroid, by detonating at a suitable explosive point, or placing nuclear explosives at a certain depth on the surface of the asteroid to detonate, so that the asteroid obtains a speed increment, changes the original orbit, and achieves orbital deflection.
Nuclear bombs are "the heavy weapons of the country" and must deal with a crisis that will erupt at once. The scope of application of the nuclear attack method is when the warning time for a dangerous asteroid collision is very short (for example, the warning time is less than 10 years). Its advantage is that it has high energy and quick response.
However, the nuclear attack method has significant "sequelae". First of all, the amount of nuclear pollution after the explosion of a nuclear bomb cannot be completely controlled. Secondly, after the explosion of the nuclear bomb, the asteroid decomposes into large and small fragments, which still pose a potential risk to the earth, and it is not a hundred.
In addition to the nuclear attack method, another mainstream solution is "kinetic energy impact", and it is currently the only asteroid defense method that has been verified in orbit.
Kinetic energy impact renderings
Kinetic energy impact refers to, based on the principle of momentum transfer, the spacecraft launches one or more kinetic energy impactors, enters the interception orbit and directly collides with the asteroid, or embeds the asteroid at a certain relative speed, and uses its own kinetic energy to affect or even change the orbit of the asteroid.
On July 4, 2005, the "deep impact" project led by NASA in the United States was successful, and the spacecraft released a 372-kilogram steel bomb that hit the nucleus of Comet Temple 1, which can be seen as an on-orbit test of the "kinetic impact" program. It validated the feasibility of the scheme, but the impact reportedly did not alter the comet's orbit.
Kinetic energy impacts are possible, but we know that under Newtonian mechanics, momentum P = m·v, then, the greater the mass and higher the rate of the asteroid, the more kinetic energy is required to change its trajectory.
Therefore, the scheme of kinetic energy impact is applicable to asteroids with a diameter of less than 150 meters. For large-mass or large-diameter asteroids, the effectiveness of the protocol is limited.
But on the other hand, based on the same laws of physics, we want the mass of the "kinetic energy impactor" to be as large as possible. This is the focus of the research topic mentioned at the beginning of the article.
According to reports, several Chinese scientists have "upgraded" the traditional kinetic energy impact, and the upgraded plan is called "final stone strike".
Schematic diagram of the "Last Stone Strike" planetary defense mission plan
"Final stage stone strike" means that after the spacecraft enters the deep space escape orbit, the rocket terminal stage and the spacecraft do not implement the star arrow separation, and the spacecraft controls the terminal stage combination to crash into the dangerous asteroid, so as to make full use of the remaining weight of the rocket stage, increase the momentum of the impact asteroid, and then improve the orbital deflection ability of the asteroid.
What is the effect of the "last level of stone strike"?
According to calculations, compared with the traditional kinetic energy impact scheme, the deflection effect of the single-shot Long March 5 launch "final stage stone striking" mission can be equivalent to the deflection effect of the traditional kinetic energy impact task launched by the three-shot Long March 5.
At the same time, for the orbit of an asteroid with a deflection diameter of 140 meters within ten years, the deflection distance can be increased from less than double the Radius of the Earth to more than double the radius of the Earth.
In this way, under the premise of hitting the same target as kinetic energy, a potentially efficient scheme was born.
<h1 class="pgc-h-arrow-right" data-track="170" > "combo punch" swinging into space</h1>
The nuclear attack method and kinetic energy impact (including the "final level of stone" introduced above) can be classified into the same category: the pulse method. The pulse method refers to the orbital deflection of the asteroid through the instantaneous strong external force.
It can be seen from this that researchers are really not "problem solvers", and when it comes to survival, they still have to rely on their brain holes to save the earth.
In addition to the pulse method, the scientists have also designed a number of other schemes, which can be classified as "slow thrust methods". The brain hole in this is even more brilliant.
As the name suggests, the "slow thrust method" refers to the continuous action on the asteroid by external forces, slowly changing the orbit of the asteroid. It does not have the intensity of the pulse method, takes longer, and is not suitable for critical situations with short warning time.
But in contrast, it is more precise, controllable, and can avoid derivative hazards.
How do you apply an external force to an asteroid?
The first is "gravitational traction", based on the gravitational theorem, so that the gravitational force of the spacecraft drags the asteroid to change the orbit, this method is simple and crude, just let the spacecraft remain hovering relative to the asteroid, but the time consumed is often very long, starting in 10 years.
In "The Vastness of the Firmament", the trajectory of the spacecraft changes the orbit of the asteroid
This is followed by the "laser ablation/ablation method", which emits lasers through the lasers carried by the spacecraft, irradiates the asteroid's surface, causing the plasma on the asteroid's surface to fall off, continuously generating a small reaction force, thus gradually changing the asteroid's orbit.
Similarly, "ion beam guidance" emits highly directivistic, high-precision, high-speed ion beams that continuously irradiate the target asteroid, slowly changing the asteroid's orbit and eventually causing it to deviate.
Various schemes vary, such as the "mass drive method", which launches the spacecraft onto the surface of the asteroid, and then the spacecraft drills the material, ejects at high speed, and uses the resulting reaction force to finally achieve deflection.
The "slow push method" introduced above seems to be less sci-fi than the pulse method, and it is much weaker visually, so it is most likely not to be adapted into a movie. But they have the advantage of being able to "combine" – multiple slow-push schemes can be applied to an asteroid if the warning time is sufficient.
Imagine an asteroid being pulled by gravity in the midst of all the attention, with swarms of spacecraft hovering around it, and it's illuminated by N rays of light in unison. In the direction it left, the ejected material was like a short tail... This picture is also a kind of spectacle.
Of course, I hope this spectacle never appears. Endless starry sky, keep your quiet beauty is enough!
Resources:
1. "Research Status of Potentially Dangerous Asteroid Deflection Methods", Yang Huixin, Ma Shiyu, et al.
2. "Optimization of Pulse Orbit of Kinetic Energy Impact Asteroid Defense Mission Based on Deflection Distance Approximation Model", Wang Yirui, Li Mingtao, etc.
3. "Space Center Proposes 'Last-Level Stone-Striking' Defense Plan to Deal with Potentially Threatening Asteroids", National Space Science Center.
Author | To by
Edit | He Ziwei
Typography | Zhang Xiwen