According to NASA's Johnson Space Center, there are currently nearly 1.25 billion space debris around the Earth, ranging in size from 1 millimeter to tens of centimeters. These space debris fly at a speed of 7 km to 8 km per second, or even 10 km to 15 km, which is equivalent to more than 10 times the speed of a bullet and poses a certain threat to space vehicles. What few people know is that most of the space debris came from the Anti-Satellite Experiments of the United States and the Soviet Union during the Cold War. When fragments collide with each other, new fragments (this fragment is called secondary fragment).
Dynamic schematic of space debris distribution
At present, the amount of space debris is still increasing rapidly, and at this rate, it will be difficult for humans to find an orbit without space debris. Cleaning up space debris is imperative! To this end, all major space powers have also carried out space debris removal research, and China is no exception.
According to Xinhua News Agency, at 9:27 on October 24, 2021, China successfully launched the Shijian-21 satellite with the Long March 3B carrier rocket at the Xichang Satellite Launch Center. The satellite successfully entered the predetermined orbit and the launch mission was a complete success.
Shijian-21 satellite is mainly used for space debris mitigation technology test verification.
<h1 class="pgc-h-arrow-right" data-track="22" > so what is "space debris mitigation technology"? </h1>
To put it bluntly, it is the technology that will slow down the outer space debris through technical means and thus fall into the earth's atmosphere and burn up.
Specifically, "space debris mitigation technologies" have several approaches:
1, electromagnetic method: electric power rope, magnetic sail with magnetic adsorption to collect space debris, after reaching a certain amount of it pushed into the atmosphere and burned.
2. Capture method: Capture space debris by means of flying nets, flying claws and robotic arms, collect space debris in a centralized manner, and eventually push it into the atmosphere and burn it.
3, momentum exchange method: to the larger space debris installed solar sails, drag increase device, the use of space debris still exists in the extremely thin air to slow down, or with the solar sail to generate micro-power to slow down the space debris, accelerate its orbital descent, thereby falling into the atmosphere and burning.
4, remote method: for example, the use of high-energy laser to generate small power to remove small fragments.
Schematic of high-energy lasers removing space debris
5. Change the material properties or material state: through high-energy microwave heating to vaporize or release oxidant, ignition and burn it.
Among the above five methods, the second and third methods are more suitable for removing large and large space debris. The remaining three methods are suitable for removing small space debris, but the best way is to use high-energy lasers to remove them.
On June 25, 2016, China successfully launched the "Aolong-1" technology test satellite with the first flight of the Long March 7 carrier rocket.
The "Aero-1" space debris actively cleans up the aircraft
Aero-1 is a space debris active debris clean-up vehicle that is unique in its robotic arm: it can grab discarded satellites and space debris and has the ability to take them to the atmosphere and burn them. The robotic arm system of "AeroLong-1" fully integrates multidisciplinary technologies such as biomimicry, mechanics and electronic control, and has the ability to stay at a fixed point and continuously track and orbit the target debris, which can not only allow the front end to maintain the flexibility of grasping, but also the back end to maintain a large moving space during the grasping process.
<h1 class="pgc-h-arrow-right" data-track="20" > which "space debris mitigation technologies" will be verified by the "Shijian-21" technology test satellite? </h1>
After the analysis, there are major discoveries!
According to the information released on the official website of the "China Academy of Launch Vehicle Technology", the "Long March 3B" (CZ-3B) is a kind of high-orbit high-thrust carrier rocket developed by the China Academy of Launch Vehicle Technology (hereinafter referred to as the "Rocket Academy"), which is based on the Core Stage of the Long March 3A Rocket and bundled with four boosters on one of its sub-stages, mainly for launching geosynchronous transfer orbit satellites, and can also carry out a multi-satellite launch or other orbital satellite launch.
"Long March 3B" carrier rocket
In short, this rocket is not designed to launch low-orbit satellites at all, but to launch high-orbit satellites. Therefore, the "Shijian-21" satellite launched this time is obviously a high-orbit satellite!
According to the altitude at which the satellite is operating, the satellite orbit is divided into:
1. Low orbit: the flight altitude of the satellite is less than 1000 km;
2. Medium and high orbit: the satellite flight altitude is between 1000 km and 20000 km;
3, high orbit: satellite flight altitude is greater than 20,000 kilometers.
In response to reporters, the vice president of the China Academy of Space Technology and the chief expert of the space debris action plan once said: "The low Earth orbit below 2,000 kilometers, the medium orbit at an altitude of 20,000 kilometers and the geosynchronous orbit at an altitude of 36,000 kilometers are the concentrated distribution areas of space debris. ”
Among them, space debris located in high orbit is mainly the debris of failed satellites, which belongs to large-volume, massive "space debris". For such large-volume, massive "space debris", the best way to remove it is generally to use the second method mentioned above, the capture method.
This method can collect them together in the form of flynets, claws, or robotic arms, and eventually drag them into the Earth's atmosphere and burn them.
It can be seen that the "Shijian-21" technology test satellite has at least the ability to capture space debris with flynets, claws or robotic arms!
Since the "Aero-1" technology test satellite has already verified the method of capturing space debris by the mechanical arm, the "Practice 21" technology test satellite is unlikely to be used to verify that the mechanical arm captures space debris, and it is more likely to verify the ability of the space flynet to capture space debris!
Flynet captures schematic diagrams of discarded satellites
To do this, the "Shijian-21" technology test satellite is required to have a strong orbit-changing capability, to be able to precisely control, approach any high-orbit "space debris", and eventually capture it.
It is unclear whether the Shijian-21 technology test satellite will also validate the fourth method, the high-energy laser directional removal method, in addition to verifying the second type of space debris removal measure.
Of course, such satellites can be used to capture "space junk" in peacetime, and in wartime, they can also be used to capture controlled "space junk" that is harmful to our country. As a peace-loving country, we hope that such satellites will never be used for military purposes!