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In the movie Gravity, there is a plot like this:

While two astronauts were on a mission in space, they were suddenly hit by a "debris rain".

The space debris flying at high speed like a bullet not only crashed the spacecraft into pieces, but also nearly killed two astronauts in space.

▲ Photo Source: the movie Gravity

Don't think that this is just a fictional plot of a science fiction film.

In fact, space debris has gradually become a major threat to the space industry.

In February 2009, a private communications satellite from the United States collided with a Russian military satellite at a speed of 11.7 kilometers per second, both of which were destroyed. NASA estimates that the collision produced at least 1000 pieces of debris of more than 10 centimeters.

In March 2021, China's Yunhai-1-02 satellite disintegrated after being collided by a piece of space debris, and in May 2021, a robotic arm of the International Space Station was hit with a hole by space debris.

A hole in the ▲ International Space Station that was hit by debris. Photo Source: NASA

These space collisions all took place in low-Earth orbit.

Low-Earth orbit can be understood as a wide driveway closer to the earth.

Most of the objects launched by human beings into space, including space stations, man-made satellites, probes, spacecraft and so on, are gathered in low-Earth orbit. The resulting garbage is also basically distributed on this track.

However, no matter how wide the driveway is, once it becomes crowded, collision accidents are inevitable.

Schematic diagram of ▲ space collision. Photo Source: best documentary

In recent years, due to technological development and falling costs, it has become easier and easier to enter space.

In the past, traditional radar satellites were huge, weighed several tons, and cost hundreds of millions of dollars at a time, so only the government could afford it.

Today's satellite launches are becoming more and more commercial, and the satellites are getting smaller and smaller. The cube satellite jointly developed by Stanford University is only 10 centimeters square, and the super homing pigeon satellite developed by an American company is only the size of a shoebox.

▲ Cube Satellite. Photo Source: Wikipedia

At the same time, more and more satellites can be carried by rockets.

In 2021, the SpaceX rocket operated by Musk could launch 143satellites, setting a new world record. SpaceX currently costs only $1 million to launch a satellite, which greatly reduces costs.

As a result, the number of man-made objects in space also began to blow out.

Before 2012, no more than 200 objects were launched into space each year. By 2020, however, that number would soar to 1200 and about 1800 in 2021.

At present, there are more than 10,000 satellites orbiting the earth in low-earth orbit.

The number of ▲ launches began to blow out after 2015. Photo Source: our world in data

In the future, there will be no fewer satellites planned to be launched, only more and more.

SpaceX is deploying satellites on a large scale, with plans to expand the 24 orbital planes scattered in low-Earth orbit to 72, and to launch 12000 star chain satellites in the future.

Low-Earth orbit is becoming more and more crowded, and the resulting amount of space junk is not to be underestimated.

The so-called space junk covers abandoned boosters of spaceships, retired satellites (more than 3000), various parts of spacecraft (screwdrivers, nuts, bolts, etc.), as well as all kinds of smaller rubbish, such as paint fragments that fall off from the exterior of the spacecraft due to intense ultraviolet radiation.

Because the debris is so large and so small that it is untraceable, no one can know exactly how much rubbish is floating in space.

▲ space junk schematic map. Photo Source: MIT News

Scientists estimate that in low-Earth orbit, there are about 750000 pieces of debris between 1cm and 10cm, 30,000 pieces of debris larger than 10cm, and more than 100m pieces of debris less than 1cm.

"We have been surrounded by something like a junkyard." Said Megan Donahue, a professor of astrophysics at Michigan State University.

The increase in space junk will first increase the probability of collision.

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

And debris travels very fast, reaching 28000 kilometers per hour. Even a small piece of debris can destroy a much larger satellite or spacecraft, causing a large-scale disaster.

The main source of ▲ space junk. Photo Source: BBC

What is more frightening is that the collision between the fragments will have a cascade reaction, which is called the "Kessler effect".

This was first put forward by American scientist Donald Kessler in 1978. It means that in low-Earth orbit, when the density of the object reaches a certain degree, the debris collides to form more fragments, which leads to more impacts, eventually causing the low-Earth orbit to be completely covered by space junk.

In addition, space junk may pass through the atmosphere and fall back to Earth.

When a ▲ satellite passes through the atmosphere, it may burn out due to friction, or it may not burn completely, and debris may still fall to the earth. Photo Source: space news

In the 1970s, a rocket fragment of NASA fell in western Australia. Australian authorities fined the United States $400 for "littering", which has not been paid.

In recent years, the news that space debris has fallen to the earth is not uncommon.

In July, China's long March 5B carrier rocket was successfully launched, with some wreckage falling into the Indian Ocean, and in August, several pieces of space debris, each about 3 meters high, were found on a farm in New South Wales, Australia, which was later confirmed to have been dropped by a SpaceX rocket.

Debris from ▲ falling on a farm in Australia. Photo Source: the guardian

But only one person has really been hit by space debris in history. She is Lottie Williams, a resident of Oklahoma, USA.

One night in January 1997, when she was walking in the park, she saw something like a meteor passing by. Then she suddenly felt a pat on the shoulder and looked back to see that a charred piece of net had fallen.

She later learned that the rubbish came from the Delta II rocket that crashed to earth that day.

An article in the science magazine Nature predicts that humans have a 10% chance of being hit by falling space debris within 10 years.

▲ this lucky lady with the fragments that hit her. Photo Source: fox news

Cause collisions, may fall to the earth, hinder cosmic observation. The harm of space junk is expanding.

How to clean up space junk has become extremely urgent.

Many countries have launched projects to deal with the problem of space junk. The RemoveDEBRIS project, led by the University of Surrey in the UK, experimented with the use of nets and harpoons to clean up garbage in 2018.

In the test of the net, the spacecraft launches several objects, pulls out the vertices of the net, unfolds the net to catch garbage, while in the test of harpoon, the harpoon is launched at a speed of 20 meters per second, successfully hitting and penetrating the target.

After many experiments, nets and harpoons have been proved to be feasible cleaning methods.

▲ 's vision of using a net to capture space junk. Photo Source: ESA

The Stork cargo ship launched by Japan in 2016 uses a metal rope to adsorb space junk to the surface and then discharge it through the rope to slow it down.

When the speed of space debris is lower than the speed needed to revolve around the earth, it will fall into the atmosphere and burn up against the atmosphere.

ESA (European Space Agency) has also launched a ClearSpace project, also aimed at cleaning up space junk, which is expected to be launched in 2025-26.

▲ 's vision of cleaning up space junk. Photo Source: ESA

In spite of this, the speed of cleaning up space garbage is far from keeping up with the speed of production.

Some people say that the low-earth track is like a highway that has been used for more than 60 years without a trailer.

Collisions will be the dominant space problem in the future. If there is no intervention, it is only a matter of time before low-Earth orbit is occupied by garbage. However, this point has not been paid enough attention by countries all over the world.

An airline consultant expressed his concern: "I hate to say this, but only when the disaster really happens to humans will we act."

Referenc

[1] "Photos Suggest Spacex, NASA, And China Space Junk Struck Land. There's A 10% Chance A Person Will Be Hit This Decade.". 2022. Business Insider.

[2] About space debris-The European Space Agency

[3] Heavy Space Traffic Ahead-The European Space Agency

[4] Space debris is coming down more frequently. What are the chances it could hit someone or damage property?-The Conversation

[5] Where Falling Satellite Lands Is Anyone's Guess: NPR

[6] Space Debris and Human Spacecraft | NASA

[7] How many satellites orbit Earth? | Live Science

[8] Space junk: The cluttered frontier | MIT News | Massachusetts Institute of Technology

[9] Why space debris cleanup might be a national security threat-The Conversation

[10] What is space junk and why is it a problem? | Natural History Museum

[11] Solving the space junk problem | CU Boulder Today | University of Colorado Boulder

[12] Falling Space Junk From SpaceX, NASA, China Risk Life, Property. Business Insider.

[13] SpaceX capsule confirmed as source of space debris that crashed on farm in Australia | The Guardian

[14] SpaceX and our space junk problem-Vox

[15] the problem of removing debris from Earth's orbit and space junk-BBC News

[16] Japan launches cargo spacecraft to test removal of space junk-BBC News

[17] take stock of several potential clean-up schemes for space garbage flooding-BBC News

[18] SpaceX rocket launches 143satellites at a single time, setting a new world record of "multiple satellites with one arrow"-BBC News

[19] Sputnik is becoming an obstacle to exploring the universe-BBC News

[20] there are more and more near-Earth satellites, and scientists are worried about affecting the planetary defense plan _ NetEase science and technology.

[21] can low-Earth orbit hold tens of billions of satellites? This boast hardly makes a draft _ Sina Finance _ Sina

[22] how many satellites will orbit the earth in 2021? _ NetEase subscription

This article comes from the official Wechat account: bring Science Home (ID:steamforkids), written by: Greye revision: Han Jingjing

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