Kessler syndrome facts for kids

Space junk around Earth. The two main areas are the ring of objects in geosynchronous orbit (GSO) and the cloud in low Earth orbit (LEO).

The Kessler syndrome is a scary idea about what could happen to space around Earth. It was first suggested by NASA scientist Donald J. Kessler in 1978. It describes a situation where there's so much space junk (or "debris") in low Earth orbit (LEO) that collisions between objects become very likely. Each crash creates even more junk, which then causes more crashes, like a chain reaction. This could make it very hard or even impossible to use satellites and travel in certain parts of space for a long, long time.

History of Space Junk Concerns

Early Warnings and Tracking

Gabbard diagram showing almost 300 pieces of debris from a Chinese rocket stage that broke apart in 2000.

Even back in 1960, a scientist named Willy Ley thought that too many objects might build up in space. After the first satellite, Sputnik 1, was launched in 1957, the North American Aerospace Defense Command (NORAD) started keeping a list of everything in orbit. This included satellites, rocket parts, and protective shields.

Scientists noticed that many objects in orbit were from explosions. Some were from tests of "anti-satellite weapons" (ASATs) in the 1960s. Others happened when leftover fuel in rocket stages exploded. A NORAD employee named John Gabbard created a special way to track these exploding objects. His "Gabbard diagrams" are still used today to predict where debris will go.

Kessler's Discovery

In the 1970s, NASA scientist Donald J. Kessler used these tracking methods. He and Burton Cour-Palais wrote a paper in 1978. They showed that space junk in LEO could cause a chain reaction of collisions in just a few decades. Before this, many thought that Earth's upper atmosphere would pull debris down faster than it could build up. But Kessler and Gabbard realized this wasn't true for all types of debris.

John Gabbard was the one who first used the term Kessler syndrome. This name became well-known after an article in Popular Science magazine in 1982.

Learning More About Space Debris

Baker–Nunn cameras were used to study space debris.

Because there wasn't much clear information about space junk, NASA gave Kessler money to study it more. Scientists used telescopes and radar to find out how many objects were in space and how big they were. They found that the official lists were missing at least half of the objects! Many small pieces of debris from exploding rockets and ASAT tests were not being tracked.

They also looked closely at parts of spacecraft that had returned to Earth, like Skylab. These parts had tiny dents and pits from hitting small pieces of debris. All these studies showed that there was much more space junk than expected. They also found that this junk was the main danger to spacecraft, not natural space dust.

In 1978, Kessler found that almost half of the tracked debris came from just 19 events, mostly rockets exploding after their mission. This led NASA to start its Orbital Debris Program. They realized they could prevent many explosions by getting rid of unused fuel in rocket stages.

A New Kind of Kessler Syndrome

In the 1980s, the United States Air Force studied what happens when debris hits satellites. They found that these collisions create large chunks of new debris, which are very dangerous.

In 1991, Kessler published more findings. He explained that even though most debris pieces are tiny (like paint flakes), most of the mass of debris is in larger pieces (about 1 kilogram or more). A 1-kilogram object hitting a satellite at high speed could completely destroy it. This would create many more large pieces of dangerous debris.

Kessler explained that if there's too much debris, new collisions will happen faster than old debris falls out of orbit. This leads to a "chain reaction" where more and more debris is created. This chain reaction is what we call the Kessler syndrome.

Kessler warned that certain space activities could make this problem much worse. These include launching many satellites at once (like large groups of satellites) or using anti-satellite weapons.

Anti-Satellite Missile Tests

Anti-satellite (ASAT) missile tests are a big concern because they create a lot of space junk.

• In 1985, the United States tested an ASAT missile. It hit a satellite at an altitude of 555 kilometers. NASA predicted that the debris would stay in orbit for many years and would require future space stations to have better shielding.
• On January 11, 2007, China destroyed one of its own weather satellites with an ASAT missile. This happened at 865 kilometers altitude. The crash created a huge amount of debris that will likely stay in orbit for decades or even centuries.
• On November 15, 2021, Russia destroyed its Kosmos 1408 satellite with an ASAT missile. This created over 1,500 pieces of trackable debris and many more tiny pieces. This debris spreads out and could hit any satellite in low Earth orbit, including the International Space Station and the Chinese Space Station (Tiangong).

How Debris is Made and Destroyed

Every satellite, space probe, and human space mission can create space debris. The more satellites we have, the more likely the Kessler syndrome becomes. In 2014, there were about 2,000 satellites orbiting Earth. By 2021, there were over 4,000!

Scientists estimate there are:

• 600,000 pieces of space junk between 1 and 10 centimeters in size.
• 23,000 pieces larger than that.

On average, one satellite is destroyed by hitting space junk each year.

Space junk eventually falls out of orbit because of tiny amounts of drag from Earth's atmosphere. The Sun's energy and the Moon's gravity also play a small role. But at very high altitudes, this process can take thousands of years.

Why the Kessler Syndrome is a Problem

This image shows models used to track debris in Earth orbit in July 2009.

The Kessler syndrome is worrying because it's like a domino effect. When objects crash, they break into many pieces. These pieces then hit other objects, making even more space junk. If a big crash or explosion happened, it could create so much debris that it would be extremely difficult to use satellites in certain low Earth orbits.

However, even a very bad Kessler scenario in low Earth orbit would not stop launches that go past LEO. It also wouldn't affect satellites in medium Earth orbit (MEO) or geosynchronous orbit (GEO) as much. The worst predictions suggest more collisions each year, not a complete barrier to space travel.

Avoiding and Reducing Space Junk

To prevent the Kessler syndrome, space agencies and companies are trying to reduce space junk.

• New satellites are often designed to be safely removed from orbit at the end of their life. This can be done by making them fall back into Earth's atmosphere to burn up, or by moving them to a "graveyard orbit" far away from active satellites.
• In the United States, the Federal Communications Commission (FCC) requires new geostationary satellites to move to a graveyard orbit when they are done.
• The US government also requires a plan for satellites to either re-enter the atmosphere, move to a storage orbit, or be brought back to Earth.

Scientists are also looking at new technologies to deal with existing debris. One idea is a "laser broom." This would be a powerful laser on Earth that could zap small pieces of debris. The laser would heat one side of the debris, creating a tiny push that would make it fall out of orbit and burn up safely in the atmosphere.

Possible Triggers

• The Envisat satellite is a large, inactive satellite that weighs about 8,211 kilograms. It orbits at 785 kilometers, which is an area with a lot of debris. Scientists like Don Kessler predicted in 2012 that Envisat could easily cause a major debris event if it collides with something in the next 150 years.
• SpaceX's Starlink program plans to launch thousands of satellites into low Earth orbit. Many experts worry this could greatly increase the risk of the Kessler syndrome. SpaceX says that most Starlink satellites are launched at a lower altitude (550 kilometers). This means that if a satellite fails, it will fall out of orbit and burn up within five years, even without power, due to atmospheric drag.

In Fiction

• The 2013 movie Gravity starts with a Kessler syndrome disaster. In the film, Russia shoots down an old satellite, causing a chain reaction of debris.
• Neal Stephenson's 2015 novel Seveneves begins with the Moon exploding. This leads to a cloud of debris from the Kessler syndrome, which then causes meteoroids to hit Earth.
• Planetes is a Japanese comic book series about a crew whose job is to remove space debris from around Earth and the Moon in the near future.
• The 2019 video game Ace Combat 7: Skies Unknown features a Kessler syndrome scenario. It is caused by two countries using anti-satellite weapons against each other.

See also

In Spanish: Síndrome de Kessler para niños