June 30 is International Asteroid Day. What is an asteroid? How did it come to be? How does it relate to our lives? Next, let's take a look at the "past and present lives" of asteroids.
If the formation of the solar system is compared to the construction of a building, the sun and the eight planets are the main structure of the building, and after completion, there are still some building materials left on the "construction site" of the solar system, and the asteroid is like these remaining bricks.
Asteroids have solid rock surfaces in different shapes, some like snowmen, some like peanuts, some like Saturn with "their own rings", some more than a few hundred kilometers in diameter, and the small ones may be the size of a refrigerator.
One group of asteroids that frequently pass by the Earth, and may even break into the atmosphere and fall on the surface, is the near-Earth asteroid – the closest to the Sun is less than 1.3 astronomical units (AU), about 195 million kilometers.
So far, more than 35,000 near-Earth asteroids have been discovered. They are the "time capsules" of the solar system, some of which contain valuable resources, and some of which contain the codes of species replacement, waiting to be explored after billions of years of watch.
However, these near-Earth asteroids sometimes come into "close contact" with Earth. We need to lock on asteroids before they hit the earth, obtain their orbits, materials, structures and other information in as much detail as possible, select defense means according to the characteristics of the target, formulate emergency plans, and prepare for disaster rescue according to the results of different ground disaster assessments.
Although the probability of an asteroid hitting the Earth is extremely low, the damage is very large, and the goal of asteroid on-orbit disposal is to destroy or deflect the asteroid in order to eliminate or mitigate the impact threat to the Earth.
According to the way the spacecraft interacts with the asteroid, it can be divided into instantaneous and continuous action disposal technology. Instantaneous action processing technology means that the time for the spacecraft to interact with the asteroid is extremely short, or even instantaneous, such as a nuclear explosion or kinetic impact; Continuous-action disposal technology refers to the continuous application of force to an asteroid by a spacecraft on a long time scale, thereby slowly changing the asteroid's orbit, such as gravitational traction, ion beam shift, laser ablation, etc.
A nuclear explosion can be simply understood as "explosion", which uses the enormous energy of a nuclear device to destroy an asteroid structure or deflect its orbit. However, the safety risks of nuclear explosions in the development, testing, and launch are relatively large, and there are uncertainties in the disposal effect.
Kinetic impact can be simply understood as "collision", the spacecraft hits the asteroid at a certain angle at high speed, causing the asteroid's orbit to deflect and move away from the Earth. This is a relatively simple, mature method with a wide range of scenarios, but if you want to hit a larger asteroid, you need super carrying capacity and more and larger impactors.
Gravitational traction can be simply understood as "pulling", using a heavier spacecraft to hover in front of or behind an asteroid, and changing the asteroid's orbit through the gravitational pull between the asteroid and the spacecraft. However, due to the limited weight of the towed spacecraft, it often takes ten years or even longer to achieve effective deflection, and the precise control of the spacecraft is required.
Ion beam offset can be simply understood as "spraying", which is sprayed by the spacecraft ion propulsion system to the surface of the asteroid at high speed, pushing the asteroid to change its orbit. It is necessary to turn on the ion thrusters at both ends of the spacecraft at the same time to maintain the distance from the asteroid, and also need ultra-high spacecraft control accuracy and a long implementation period.
Laser ablation can be simply understood as "burning", through the high-energy laser carried by the spacecraft, the ablation of the asteroid surface material produces thrust, pushing the asteroid to change its orbit, and the unique energy transfer process of the laser will not change the spacecraft's own orbit.
Tug disposal refers to the capture or attachment of an asteroid to the surface of an asteroid by a spacecraft, directly exerting force on the asteroid and pushing to change the asteroid's orbit. This method is suitable for dragging small size asteroids. "Dragging asteroids" is a contact disposal method, and there are great technical challenges in order to grasp the asteroid firmly and effectively control the direction in the asteroid rotation state.
Mass drive refers to attaching to the surface of the asteroid through the spacecraft, using the excavation mechanism to obtain the stones and other materials on the surface of the asteroid, and ejecting them at high speed to promote the change of the asteroid orbit.
Surface spraying is to spray materials with different albedo on the surface of the asteroid or use lasers to modify the surface material of the asteroid, so as to change the absorption and reflection of sunlight, and change its orbit by regulating the thermal radiation pressure of the asteroid, which also requires a long action time.
In addition, there are new on-orbit disposal technologies, such as enhanced gravitational traction, "stone-to-stone", "last-stage stone-to-stone" and "penetrating rod" and other disposal technologies that scientists and engineers are eager to try on their drawings, ready to show their skills.
In order to jointly respond to the global threat of planetary impacts, the 68th session of the United Nations General Assembly in 2013 approved the establishment of the International Asteroid Monitoring and Early Warning Network (IAWN) and the Space Mission Planning Advisory Group (SMPAG) to coordinate global resources, strengthen monitoring and early warning, and find "moves" to deal with asteroids.
China is also actively carrying out asteroid-related research and defense demonstrations, contributing "Chinese wisdom" and "Chinese strength" to protect the security of the earth and mankind. It is believed that in the future, with the cooperation of scientists and engineers around the world, a "shield" against near-Earth asteroids will be gradually built to defend the earth's homeland.
Source: Xinhua News Agency