A Minefield in Earth’s Orbit

How the Space Debris Problem Is Spinning Out of Control

Like many other modern marvels, space exploration has yielded huge technological benefits for humankind, but it can’t help but have the same major side effect as many other advances: It has left a trail of garbage in its groundbreaking wake. The rockets, satellites and probes we have sent into orbit over the decades have created a fast-moving debris field that contains hundreds of thousands of pieces of space junk—even a one-centimeter piece of which can damage or destroy a spacecraft worth millions, or even billions, of dollars. The International Space Station and its crew have had to dodge dangerous debris several times in the past few years.

This threat has doubled in the past few years, thanks to antisatellite weapons testing and space collisions that are producing ever more debris. And scientists say that this space shrapnel is being produced faster than it will burn up in the atmosphere. This means that vehicles in orbit will face an ever-riskier path around the planet unless an international cleanup effort begins soon.

The headlines may focus on large pieces of space debris falling from the sky—even though such debris rarely hits land or causes damage—but the threat that urgently needs our attention, scientists say, is the massive and growing amount of space junk spinning above us. Here is our guide to the increasing dangers of this debris.

Did You Know?

Space Junk 3D, a film intended to raise awareness about orbital debris, opened in IMAX, 2-D and 3-D on January 13.

6 Reasons to Worry about Space Junk

Text by David Wright
  1. 1
  2. 2
  3. 3
  4. 4
  5. 5
  6. 6

Did You Know?

Satellites in low Earth orbit (LEO) travel in various crisscrossing planes. Thus high-speed collisions are much more likely in LEO than in other regions of space.

Nearly half of the world’s roughly 950 active satellites are located in LEO.

The destruction of a single 10-ton satellite could double or triple the amount of debris larger than one centimeter in LEO.

Tiny Pieces, Big Risks

As the chart below shows, even the smallest pieces of space junk can have catastrophic effects on satellites. And these small pieces make up the largest part of the debris field in low Earth orbit. Although NASA does track space debris there are some pieces too small to be counted—but they can still cause damage.

open/closeCategories of Debris

Categories of LEO (Low Earth Orbit) Debris
Physical Size Potential Risk to Satellites Comments Estimated Pieces of Debris in LEO
Larger than 10 centimeters
(about four inches)
Complete Destruction
  • Can be tracked
  • No effective shielding
1-10 centimeters Severe Damage or Complete Destruction
  • Smaller objects in this range cannot yet be tracked
  • No effective shielding
Smaller than 1 centimeter Damage
  • Cannot be tracked
  • Effective shielding exists

open/closeHow Objects Spread

Illustration of debris clouds expanding and orbiting the earth after 15 minutes, 10 days, 6 months, and 3 years.

These images are calculated by taking into account the NASA Breakup Model on the spread of fragments and by the asymmetries of the Earth.

(Source: Dr. Ting Wang, Stanford University)

Bar graph comparing the total conjunctions from January 1, 2006 (1419 total) and July 18, 2009 (3320 total)

Number of conjunctions (close approaches of less than five kilometers) between LEO objects in a 24-hour period. (Collision risk is proportional to the number of conjunctions.) Fragments from a 2007 antisatellite test and from a 2009 collision between two satellites (Iridium and Cosmos) greatly increased the number of conjunctions.

(Calculation by Dr. Ting Wang, Stanford University)

The Cleanup Conundrum

It’s no surprise that the three nations with the most active space programs—Russia (including the former Soviet Union), the United States and China—have the most objects in orbit, including debris.

Whereas Russia leads the orbital field in terms of mass, China has the largest ratio of debris to spacecraft, owing to its antisatellite testing, which has created a large amount of debris.

These nations and others realize that hundreds of billions of dollars in satellites vital to communications, military strategy and environmental monitoring are on the line; the international community is beginning to make plans to clean up debris. Russia and the U.S. have already crafted some debris-removal proposals, and China’s recently unveiled five-year space plan has provisions for monitoring debris. Scientists who say the debris problem has reached a tipping point are urging space agencies to begin cleaning debris as quickly as possible, but legal and technological hurdles could stall such efforts.

open/closeWhich Countries Own the Objects in Space?

An interesting way of looking at who owns objects in space is to consider the percentage of ownership by number of objects (left) and by mass of objects (right).

pie chart showing percentage of total cataloged objects by country
  1. Russia*: 37.8%

    Total Objects: 6,087
  2. USA: 30.1%

    Total Objects: 4,850
  3. China: 22.4%

    Total Objects: 3,615
  4. Others: 9.7%

    Total Objects: 1,565
pie chart showing percentage of total mass of objects by country
  1. Russia*: 53%

  2. Others: 24%

  3. USA: 19%

  4. China: 4%

*(Includes former Soviet Union)
Left: (As of 1/4/12, cataloged by the US Space Surveillance Network; Data from Orbital Debris Quarterly News, 1/12 issue)
Right: (As of 1/12, cataloged by the US Space Surveillance Network)

open/closeHistorical Growth of Space Debris Through 2011

Chart showing debris growth from 0 in 1966 to over 15,000 in 2012.

The creation of space debris has followed a trend line—until very recently, when two events catapulted the amount of debris in space: A 2007 antisatellite test that blew up a one-ton weather satellite (Fengyun), and a 2009 accidental collision between a U.S. (Iridium) and Russian (Cosmos) satellite. China’s test brought international condemnation, and the Chinese government stated it would not conduct further tests. The Iridium-Cosmos accident prompted increased efforts at monitoring and limiting space junk.

Video Resources

Interview with scientist Donald Kessler about the proliferation of space debris

Did You Know?

According to space law attorney Michael J. Listner, abandoned satellites can’t be disposed of or disturbed without the owner’s consent—and under international space law, even fragments of space objects “would require identification to determine the owner and either individual or blanket consent to remove it from orbit.”

On January 17, the U.S. announced it was beginning talks with the European Union focused on limiting space debris.

There have been nine known or suspected accidental collisions of objects in space, beginning in 1991. (pdf)

Image based on objects in low Earth orbit (a region of space within 2,000 kilometers of Earth’s surface) that are currently being tracked by NASA. About 95 percent of these objects are space debris (not functional satellites). The orbital debris dots are not scaled to Earth. Click here for more information and similar images

illustration of debris hitting a satellite

1. Faster than a bullet:

Because of their very large orbital speeds, even small pieces of debris can be deadly. Objects in low Earth orbit (LEO) travel seven times faster than a rifle bullet. At that speed, a one-millimeter piece of debris can damage a satellite if it hits a vulnerable area, and debris larger than about one centimeter can seriously damage or destroy a satellite in a collision.

illustration of debris orbiting the Earth

2. Increased threat of collisions in key regions:

Several debris-creating events in the past five years have greatly increased the amount of dangerous debris in the heavily used region of LEO between 800 and 1,000 kilometers in altitude. The risk of collision between two large pieces of debris in LEO more than doubled during that time. In some parts of space, the risk of a damaging collision may now be several percent over the lifetime of a satellite.

illustration of a missile about to hit a satellite

3. Debris from antisatellite attacks:

Antisatellite weapons that destroy satellites by colliding with them—as was done in a Chinese test in early 2007—can cause a satellite to completely fragment, creating a huge amount of debris. Destruction of a single large satellite, such as a U.S. spy satellite, could by itself double or triple the amount of large debris in LEO.

illustration of debris hitting the International Space Station

4. Threats to the International Space Station:

Debris spiraling down from higher orbits passes through the relatively low altitude of the space station, and the risk posed to the station grows as the amount of debris increases. In the past few years the station has had to maneuver twice a year on average to avoid debris—twice as often as in the previous eight years.

illustration of objects colliding in space

5. The Kessler Syndrome:

The density of debris in LEO has grown so large that accidental collisions now produce additional debris faster than atmospheric drag removes it from orbit. The additional particles further increase the frequency of collisions, which leads to a slow-motion cascade, sometimes called the Kessler Syndrome, that will cause the number of pieces of debris to increase even in the absence of any new rocket launches. So whereas efforts to limit the production of new debris are important, remediation measures, such as removing massive objects from orbit, are also important.

illustration of debris entering the Earth's atmosphere

6. Reentering debris:

Currently, nearly a hundred tons of debris falls from orbit each year. Due to its very high speed, most of this material burns up in the atmosphere. Some pieces, however, do reach Earth but have been slowed considerably while passing through the atmosphere. Most of the surviving pieces fall into the oceans, which make up a large fraction of Earth’s surface. Several are known to have fallen in populated areas but have not caused extensive damage.


Monitoring Space Debris



Space Junk Threatens Future Space Exploration

Hari Sreenivasan sat down with recently with Donald Kessler, former NASA scientist and expert on space junk, to talk about the who’s and what’s of orbital debris: how much is out there, what does it look like, what happens when these objects collide and what danger do they pose for future space travel and for us on Earth.

—PBS NewsHour


David Wright, PhD

David Wright, PhD is a senior scientist and co-director of the Global Security Program at the Union of Concerned Scientists (UCS). He is an expert on the technical aspects of arms control, particularly those related to missile defense, missile proliferation, space weapons, and space debris. Dr. Wright has worked for a number of years on projects to help train technical arms control experts in other countries, especially Russia and China.