The Earth's high-altitude range is large, but there is also a lot of garbage, and up to 500,000 pieces of man-made spacecraft fragments that are still floating in the atmosphere after abandonment can reach a speed of 28,000 kilometers per hour – 10 times the speed of a bullet. Once hit by debris, the spacecraft that is still in use is basically scrapped. In such a dangerous environment, one of the most expensive mechanical devices ever built in human history floats: the International Space Station. How will this 460-ton behemoth survive the "rain of bullets"?
See every "bullet"
To avoid every incoming bullet, you need to see the bullet's way forward so that you can dodge it before it arrives.
The International Space Station does not belong to any country alone, it is a product of international cooperation, and the space agencies of 16 countries and regions, including the United States, the Soviet Union, Canada, Japan, Brazil and the European Space Agency, participate in the development. American and Russian astronauts carried various parts and traveled between heaven and earth nearly a hundred times before they finally assembled a space station like this. Therefore, ensuring the safety and normal operation of the space station is also the common responsibility of all countries, and the US Air Force and the Russian Space Agency are jointly responsible for the monitoring of debris.
At the U.S. Strategic Command air base, a "Cosmic Junk List" is recorded, which records the names of all space junk with a diameter of more than 10 centimeters. Every day, the staff will compare the orbit of these space junks with the orbit of the space station at different times in the morning, middle and evening, and check about 400,000 times in total, which is used to determine how much the risk of the space station being "hit" is. Through comparison and calculation, if it is determined that the debris is about to enter the safe distance of the space station (an area 1.6 kilometers above and below the space station, 24 kilometers long on both sides), the air base will issue an alert to NASA.
Every year, NASA receives dozens to hundreds of collision warnings, but not every warning requires a decision to dodge, and NASA experts further calculate the likelihood of collisions and work with Russian experts to decide whether the space station needs to dodge. If the chance of collision is one in 100,000, the space station must be avoided unless there is a collision with a space mission. Once the collision probability reaches one in 10,000, the space station must move even if the space mission needs to be aborted.
The most thrilling "peek-a-boo"
Anticipating risks in advance is because every dodge action the space station takes at least 30 hours to execute.
The most time-consuming is communication. To calculate the right amount of propulsion, NASA staff need to accurately calculate the mass of the space station, including spacecraft and astronauts docked on the space station. Next, together with Russian ballistic experts, the parameters of the space station's dodge operation are decided. Before moving, NASA checks with debris trackers again to ensure that the station does not hit other debris. Once the programme is finalized, the experts will remotely control the space station from a computer.
Don't look at the space station so heavy, in fact it is a fairly flexible "fat man". The space station is controlled by four control torque gyroscopes to control the direction and size of the force, which can change the orbital height and direction of motion. The space station also has several sets of thrusters that can make tumbling and moving movements. When it comes to dodging, the gyroscope is the primary "steering wheel."
In addition, ballistic experts will use the spacecraft propulsion system attached to the space station to change position. Spacecraft that come to deliver supplies can also help, pushing a space station. In 2015, ballistic experts used the thrusters of the Progress spacecraft to deliver the space station about 1 kilometer, successfully avoiding a rocket fragment. After this series of dodge operations, the space station will move at a speed of 0.5 to 1 meter per second.
All of the above is a response with a few days of warning and sufficient reaction time, what if the experts do not find the debris coming until the last minute? If that happens, they can only initiate a scheme called "Fragment Attack's Scheduled Dodge Stunt", which omits all the communication links in the early stages, starts the thrusters regardless of their disregard, and rushes forward at a speed of 0.5 meters per second to get the space station to another location.
Of course, this solution itself is already a very dangerous method of bottom-up, not only may not work, but may also hit other debris in front of it. Once hit by debris, not only the space station may crash, but also the astronauts inside and the scientists in the experiment will also die. Therefore, when accelerating the implementation of the plan, the personnel on the space station need to hide in the attached "Soyuz" spacecraft and be prepared to flee at any time. In 2011, the "Soyuz" made a great achievement, when the space debris was found too late, and even the final evasion plan did not take effect, and everyone on the space station had to hide inside the "Soyuz". The last fragment skimmed just 725 meters above the space station, and a crisis came to an abrupt end.
"Tiangong" is a new trick to hide and seek
As space becomes more crowded, the Islamic Space Station needs to move more and more to avoid. Between January and September 2020, the station has moved three times, including one in which the astronauts have taken refuge in Soyuz, compared to less than twice, or even once, in previous years. This situation is also a big challenge for the Chinese space station "Tiangong", which will begin construction in 2020.
To deal with space junk, Chinese engineers have come up with ways to do it. Similar to the United States and Russia, China has also established a special early warning mechanism to continuously monitor space debris and be ready to take emergency risks at any time. In case of danger, the technician will issue instructions to the "Tiangong" on the ground, change its flight trajectory and speed, avoid dangerous objects, and then return to the predetermined orbit to continue flying.
In addition, the engineers also created a pair of "steel and iron bones" for the "Tiangong", that is, by optimizing surface materials, changing the structure and increasing the thickness to improve the spacecraft's ability to resist the impact of space debris, and also installed protective plates in the weak parts of the space station, which can block the impact of tiny fragments on it, and place the key components that are fragile and cannot withstand the impact in the central area, under layers of protection. Of course, there are more advanced, such as making a mesh of spacecraft protective screens and coating them with a special layer of materials on the outside of the protective screens. When the debris collides with it, the energy generated by the collision can explode into a chemical reaction with the space junk, prompting the fragment to turn into powder.
Finally, the "Tiangong" series is also equipped with a perfect "suicide" program to ensure that the decommissioned aircraft will not generate new space junk. "Tiangong-1" is China's first space laboratory, in 2018, after the completion of the mission, "Tiangong-1" actively de-orbited, most of the devices decomposed in the air and ablated and destroyed, the remaining wreckage fell in the central Waters of the South Pacific, neither posing any threat to the ground, nor creating space junk.
The sky above The earth is becoming more and more crowded, and the difficulty of "hiding cats" here is also increasing, and it is hoped that scientists can come up with a better way to deal with the problem of space junk as soon as possible.
The reproduced content represents the views of the author only
Does not represent the position of the Institute of Physics, Chinese Academy of Sciences
Source: Big Tech
Edit: Herding fish