Are there billions of pieces of space debris? Shenzhou 19 sets out to install a "golden bell cover" for the space station

At dawn on October 30, Cai Xuzhe, Song Lingdong and Wang Haoze leaped out of the sky on the Shenzhou 19 manned spacecraft, and will complete space rendezvous and docking at noon and enter the Chinese space station 400 kilometers high.

This "Dragon-Horse combination" (Cai Xuzhe is a dragon, Song Lingdong and Wang Haoze are horses) has an important mission on this trip, which is to install space debris protection devices for the space station.

"Manned space flight is a matter of life and death." At the Shenzhou-19 press conference held on the morning of October 29, Lin Xiqiang, spokesperson for China's manned space program, said that in response to threats such as leakage caused by space debris colliding with the space station, emergency response plans are constantly being optimized. Compared with the initial stage of the space station's operation, the time available for emergency response by astronauts has increased by five times, and the safety of the space station and astronauts has been greatly improved.

In extreme cases, astronauts can return early on an in-orbit spacecraft, or launch an emergency spacecraft on standby to carry out rescue.

So, what are extreme cases?

At the beginning of the movie "Gravity" released in 2013, there is a plot like this: two astronauts on the International Space Station were suddenly hit by a "rain of debris" when they went out of the cabin to perform maintenance tasks. Satellite debris flying at high speed like bullets not only smashed the space station and the space shuttle assembly into pieces, but also almost killed the two astronauts in space.

It can be intuitively felt from the big screen that the mission of the Shenzhou 19 crew - to add a "golden bell shield" to the space station to protect it from sudden attacks by space debris - is absolutely life-threatening.

A highway without road scavengers

"Low Earth orbit can be understood as a wide lane relatively close to the Earth. Most of the objects launched into space by humans, including space stations, artificial satellites, probes, and spacecraft, are gathered in low Earth orbit."

Wen Xin, a professor at the School of Astronautics at Nanjing University of Aeronautics and Astronautics, made an analogy: if an accident occurs on the highway, a tow truck will tow the accident vehicle away, but the "highway" of low-Earth orbit has been in use for more than 60 years, but there is no tow truck to clear the lane.

Space debris includes discarded boosters of spacecraft, retired satellites (over 3,000), various parts of spacecraft (screwdrivers, nuts, bolts, etc.), and various smaller types of garbage, such as paint fragments that have fallen off the outside of the spacecraft due to strong ultraviolet rays.

"The amount of debris in low-Earth orbit is growing rapidly." Wen Xin told Chao News reporters that there are about 36,000 pieces of debris larger than 10 centimeters in Earth orbit, millions of pieces of debris between 1 and 10 centimeters in size, and hundreds of millions of pieces of debris smaller than 1 centimeter in size .

Because there is so much debris and it is too small to track, no one knows exactly how much junk is floating in space.

On October 21, the US International Communications Satellite Corporation (Intelsat) issued a warning that the Intelsat 33e high-orbit satellite manufactured by Boeing for it malfunctioned and disintegrated while in orbit. 57 pieces of space debris have been tracked, and other satellite operators have been reminded to pay attention to the potential risk of debris cloud collision.

This is not uncommon. As early as 1996, the French CERISE satellite was hit by a piece of debris from the wreckage of an Ariane rocket in the 1970s, damaging the satellite's main antenna and directly affecting the normal operation of the satellite.

In 2009, the first satellite collision in space history occurred when the US Iridium 33 collided with the Russian abandoned Cosmos 2251 reconnaissance satellite, creating thousands of fragments that are still in orbit today, hurtling at the first cosmic speed.

In early 2022, a space debris numbered 49863 "brushed past" my country's Tsinghua Science Satellite, with the closest distance being only 14.5 meters, which was very thrilling.

Documents submitted by Musk's SpaceX to the Federal Communications Commission claim that Russia conducted an anti-satellite test in 2021, generating more than 1,500 debris clouds. To avoid debris, Starlink satellites made as many as 1,700 avoidances.

Space debris must travel at a speed of 28,000 kilometers per hour (about 7,800 meters per second) to orbit the Earth, while a rifle bullet leaves the gun at about one-tenth of that speed. Even small debris can have the same kinetic energy as a speeding car when it hits a spacecraft at such a high speed, enough to pierce the outer shell of a spacecraft or damage key systems such as solar panels and antennas.

As technology advances and costs fall, it is becoming easier to enter space and satellites are getting smaller.

The solar panels of the Soviet Union's Mir space station were hit by debris and became like this. Image source: Yunnan Astronomical Observatory, Chinese Academy of Sciences

Data shows that before 2012, humans launched no more than 200 spacecraft into space each year. However, by 2020, this number soared to 1,200, and in 2021 it was about 1,800.

In 2021, SpaceX's Falcon 9 rocket set a new world record by launching 143 satellites in one launch. SpaceX's Starlink Internet constellation plans to launch up to 42,000 satellites, and currently has more than 6,000 in orbit.

Scientists estimate that doubling the number of objects increases the chance of a collision fourfold.

In 1978, American scientist Donald Kessler proposed the "Kessler effect": when the density of objects in low-Earth orbit reaches a certain level, collisions between fragments will form more fragments, leading to more collisions. The vicious cycle will eventually cause low-Earth orbit to be completely covered by space debris.

Whether it is manned spacecraft or unmanned satellites, they all face the threat of space debris. Every year, spacecraft must make orbital adjustments several times to avoid collisions with these high-speed flying debris. This adjustment not only consumes fuel, but also affects the normal operation of space missions.

Avoiding debris is not that easy

If you want to avoid space debris, you first have to see it.

On September 21, 2023, in the fourth lesson of the "Tiangong Classroom", Jing Haipeng in the space station answered questions from Inner Mongolia students about space junk and said, "We often look through the windows of the space station and even use telescopes to look for it, but so far, no trace of space junk has been found."

However, just because you can't see it doesn't mean it doesn't exist. Some of the fragments are extremely difficult to discern, as faint as 14th to 15th magnitude stars. When the magnitude drops to 15th, the brightness is about 1/1000 of the stars visible to the naked eye.

Lin Xiqiang revealed at yesterday's press conference that compared with the early stages of the space station's operation, the time astronauts have available for emergency response has increased five times, and the safety of the space station and astronauts has been greatly improved.

That is, we found that the warning time for debris is five times longer than before, which allows us to respond calmly. How is this possible?

This brings us to the satellite launched into orbit by China in April 2021 - Test No. 6 03, which marks that China has built its first space-based space environment detection system with completely independent intellectual property rights .

"The Experiment No. 6 satellite system is mainly used for space environment detection to protect the safety of spacecraft." Hu Haiying, chief designer of Experiment No. 6 and deputy director of the Microsatellite Innovation Institute of the Chinese Academy of Sciences, introduced, "These target fragments are like fish in the ocean. We must first make sure we can see them, distinguish what they are, track their movements, and then calculate and predict their orbits before we can 'manage' them." Wen Xin told Chao News reporters that my country's radar electronic technology has made great strides in recent years, and advanced detection technologies including Experiment No. 6 have been applied, giving China a "security guard" for its space frontier.

"It used to be difficult for us to see clearly the debris of 1-10 cm in size in space, but the destructive power of such debris cannot be underestimated. We try our best to keep the spacecraft away from places with a lot of space debris, just like we try to avoid going out on windy and rainy days." Wen Xin said that now that the forecast accuracy has improved, we are much more assured about the safety of the space station and astronauts.

What will be done if debris threatening the space station is found? Jing Haipeng said in the Tiangong Classroom that active avoidance measures such as orbital maneuvers will be taken.

So how is the task of "installing space debris protection devices" to be carried out on Shenzhou 19? According to Li Xuedong, an expert from the China Aerospace Science and Technology Corporation, there are some key equipment such as cables outside the cabin, which need to be protected by protective plates installed by astronauts.

"The Chinese space station has taken many measures to ensure safety, mainly three methods," Li Xuedong introduced.

One of the methods is passive protection . Some protective devices are installed outside the cabin to resist the impact of tiny debris. This device has been installed before launch. However, in view of the unprecedented density of space debris, the Shenzhou-18 and Shenzhou-19 crews need to reinforce the devices outside the cabin to further ensure the safety of the space station.

Method 2: Active avoidance . Predict and catalog space debris, and use orbit calculations to find out in advance which space debris has the risk of rendezvous with the space station, so that the space station can actively change its orbit to avoid the incoming debris.

Method 3: Emergency response . If the space station really leaks due to debris impact, the astronauts must quickly stop the leak and prevent the air in the sealed cabin from leaking further. This is a severe test for the astronauts' psychological quality and emergency response capabilities.

"Small debris is difficult to predict and observe, so we usually take the hard-to-carry approach. There is a protective layer on the surface of the space station. Some particularly sensitive and important equipment must be reinforced and protected separately." Yang Yuguang, chairman of the International Astronautical Federation's Space Transportation Committee, told Chao News reporters, "Once hit, if the leakage speed is relatively slow, it can be handled calmly; if the leakage speed is relatively fast, emergency evacuation is indeed necessary."

If it is found that the debris cannot be avoided, the astronauts can urgently enter the very sturdy spacecraft return capsule and be ready to return to Earth at any time. This scene has happened on the International Space Station in recent years.

On March 2, the photo taken at the Beijing Aerospace Flight Control Center shows Tang Hongbo, an astronaut of the Shenzhou 17, working outside the space station complex. Source: Xinhua News Agency

How to ensure the safety of astronauts' extravehicular activities? "Before going out of the cabin, we will check for possible meteorites and other debris in orbit. If we find that the orbit overlaps, we will not go out of the cabin during this period." Yang Yuguang explained, "And you can see that the cabin space suit is so heavy, it has already been designed to resist the impact of tiny debris to ensure that the astronauts are not in danger of life."

Cleaning up garbage tests human responsibility

"At this moment, the Long March 2F Yao 20 carrier rocket and the Shenzhou 20 manned spacecraft are on standby in the final assembly building of the Jiuquan Launch Center. If necessary, they can quickly switch to launch status to carry out emergency rescue missions for the space station and ensure the safety of the astronauts' lives." Lin Xiqiang introduced at the press conference on the 29th.

How do rockets and spacecraft stand by? Yang Yuguang told the Chao News reporter that in standby mode, they only need to be assembled and tested simply, and can be launched without significantly sacrificing reliability and safety .

"Rockets and spacecraft are both very complex products. Their reliability and flight safety must be guaranteed by adequate testing. But testing takes time. The coverage, comprehensiveness and thoroughness of the test will affect flight safety, which creates a contradiction," said Yang Yuguang. "Therefore, we can only optimize the test process as much as possible to ensure that the test time is shortened as much as possible without losing reliability, so as to gain time to rescue the astronauts."

How to clean up space debris has become an urgent issue. Many countries have launched related projects to deal with the problem of space debris.

The European Space Agency (ESA) has launched a ClearSpace project to slow down space debris to a speed slower than the first cosmic speed. It will then fall into the atmosphere and burn up due to friction with the atmosphere.

The RemoveDEBRIS project, led by the University of Surrey in the UK, experimented with using "nets and harpoons" to clean up garbage in 2018. Through multiple tests, "nets and harpoons" have been proven to be feasible means of cleaning up.

"I think the coordination mechanism should be strengthened, and countries should strengthen mutual notification of spacecraft orbits during work. Especially after the orbit change, the previous orbit is invalid. The updated orbit should be synchronized with other parties in a timely manner. This is the responsible approach." Yang Yuguang said, "Also, we should jointly strengthen the orbit prediction and monitoring of invalid spacecraft and space debris."

Yang Yuguang also raised an important issue - the removal of space debris is technically very complex and costly, but it is something that one cannot see any direct benefits from.

"Who will do it and who will pay for it? This is a common issue currently faced by all countries in the world. This will not only test our technology and financial resources, but also the sense of responsibility and solidarity of all mankind," said Yang Yuguang.