Written by Paul Rincon and Jonathan Amos BBC News

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Russia conducted a missile test and destroyed one of its satellites. Since debris may threaten the International Space Station (ISS) and satellites in low-Earth orbit, this action has caused international outrage.

Russia's test of the anti-satellite (A-Sat) missile system is not the first of its kind.

As early as 2007, China tested its missile system against one of its own meteorological satellites in orbit. The explosion produced more than 3,000 pieces of golf ball size or larger-and more than 100,000 pieces of much smaller pieces.

About one-third of the orbital debris considered to pose a threat to the International Space Station came from this Chinese test. At the speed at which these objects move in orbit, even small debris can threaten the destruction of spacecraft.

The A-Sat test is applicable to the wider space debris problem, and our continued activities in space make this problem worse.

There is now a jungle of garbage all over your head—from old rocket stages that continued to orbit the earth decades after launch, to paint spots that once shining spacecraft lifted off and floated into the distance.

This is the legacy of 64 years of space activities.

It is estimated that there are close to 10,000 tons of hardware in orbit-most of which are still active and useful, but too many have failed and are aimless.

Nearly 30,000 pieces of debris are tracked every day. However, these are just large, easy-to-view items.

Below the scale of 1 cm (0.39 inch), objects will move around more or less untracked. There may be 300 million of them.

All of these things travel at speeds of a few kilometers per second—if they have any, they are fast enough to be destructive projectiles, and if there are any, they are performing space missions.

In 2009, a current communications satellite operated by the US Iridium Corporation collided with an abandoned military communications satellite in the Soviet era, destroying this threat.

Now consider the threat to spacecraft carrying humans.

On Monday, Russia conducted an A-Sat test at the Plesetsk Cosmodrome, about 800 kilometers (500 miles) north of Moscow. The missile destroyed an old Soviet spy satellite named Kosmos 1408, which was once part of Russia's Tselina radio signal surveillance program.

US State Department spokesperson Ned Price said that the destruction of Kosmos 1408 produced approximately 1,500 larger orbiting objects, and civilian sources can obtain tracking information for these objects. But it also created hundreds of thousands of smaller fragments.

Some of these smaller objects may be tracked, although we do not know, because the US military does not want to disclose information about its sensor capabilities. But other debris may be too small to be detected from the ground.

The debris field tested by A-Sat is located at an altitude of 440 kilometers to 520 kilometers above the earth, posing a threat to spacecraft such as the International Space Station and China's Tiangong Space Station.

When the International Space Station approached the debris cloud on Monday, the crew was told to hide in the Soyuz and Crew Dragon spacecraft connected to the orbital outpost. In this way, if the space station is damaged by satellite debris, the crew can leave and return to Earth.

Although space shuttles and other aircraft were hit by smaller debris, a collision with any large object at orbital speed could be catastrophic for the International Space Station.

Russia's actions have been condemned by other countries including the United States and Britain.

The Russian military stated that it is implementing planned activities to strengthen its defense capabilities, but denies that the test is dangerous.

"The United States knows with certainty that in terms of test time and orbital parameters, the resulting debris does not and does not pose a threat to orbital stations, spacecraft and space activities," it said.

Many countries now have their own A-Sat systems; the United States and Russia (and before the Soviet Union) have been developing such weapons since the 1950s. In 1985, the United States destroyed the Solwind scientific satellite with missiles launched by F-15 fighter jets.

After the Chinese anti-satellite incident in 2007, the U.S. military once again used ship-based missiles to shoot down one of its own satellites—the height of which was lower than that of China or Russia. The low altitude above the earth is designed to ensure that any debris will burn rapidly in the atmosphere, rather than staying at high altitudes to threaten space assets.

Then in 2019, India tested its weapons in an operation codenamed Mission Shakti. The missile hit a test satellite whose orbit was lower than the target in Moscow or Beijing, producing more than 200 traceable debris.

Because modern armies rely on satellites for intelligence collection, navigation, and communication, A-Sat technology can be used to disrupt the opponent's command and control system during conflict.

Gravity ensures that everything that rises will eventually fall back-but currently the bathtub fills faster than the plug hole, and the overflow pipe can empty it.

Some materials from the A-Sat test will fall to the earth without being harmed, but a large part will go to high altitude areas, where they will remain dangerous for years to come.

Humans and nature are also conspiring to make the situation worse in unexpected ways. Over the years, the extra carbon dioxide pumped into the atmosphere has cooled its highest layer, the thermal layer.

This-coupled with low levels of solar activity-shrinks the atmosphere and limits the amount of drag on orbiting objects that usually help pull debris out of the sky. In other words, the garbage stays longer.

Leaving aside the increase in debris caused by collisions, the number of satellites sent into space is also rapidly increasing.

Back in the 2000s, the average number of satellites launched per year was around 100. In this decade, the popularity of small satellite technology is likely to rise to an average of more than 1,000 per year.

In general, everyone in orbit now follows the international mitigation guidelines. Or try.

These include ensuring that there is enough propellant at the end of the satellite's life so that it can be pulled out of the sky or at least pushed into cemetery orbit.

Hardware that cannot be ordered out of orbit should vent its fuel tank and disconnect its battery to reduce the possibility of explosion (the main source of debris there now).

The goal is to ensure that all low-orbit material is removed within 25 years after launch.

However, even with well-intentioned actors, compliance has historically been poor.

There are many ideas to clear the space. Many of them seem far-fetched and completely unrealistic. Some more sensible proposals have entered the argumentation stage.

The Japanese-British company Astroscale is currently on track showing how it can approach and acquire redundant and uncooperative hardware.

It is likely that this procedure will have to be actually performed on a broadband satellite belonging to the British operator OneWeb soon.

One spacecraft in its fleet failed at an altitude of more than 1,000 kilometers. At that altitude, it will take several centuries for the satellite to land on its own.

According to calculations, only a few key abandoned rocket stages or damaged satellites need to be removed each year to greatly reduce the possibility of collisions and limit the growth of space debris in the coming decades.

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