More than 100 million pieces of orbital debris are circling our planet. NASA has a strategy to cope on the rare occasion when the space junk falls to earth.

Space junk rarely makes the news. It usually stays in space, orbiting the planet, and we only notice when things fall out of the sky.

Recently, for example, there was much scientific hubbub because an uncontrolled Chinese space lab crashed into the earth. If the 8.5-ton Chinese Tiangong had broken apart or run into another orbiting spacecraft, it would have significantly added to the debris in low Earth orbit (LEO)—a place that doesn’t need any more junk. (The Pacific Ocean, where many decommissioned spacecraft are directed, doesn’t need any more junk either.)

Ultimately, the Chinese Tiangong 1 had no impact on Earth or in space. However, it is an important reminder for the critical need for a strategic plan to deal with space junk. Everything floating around up there threatens to damage active communications satellites, the International Space Station (ISS), and other space systems.

The good news is that a lot of work and research is being done to try to address the problem. And a big problem it is: NASA reports more than 100 million pieces of orbital debris measuring smaller than 1 centimeter and more than 21,000 pieces of orbital debris larger than 10 cm. The estimated population of particles between 1 and 10 cm in diameter is approximately 500,000, and the number of particles smaller than 1 cm exceeds 100 million. Most of this junk is in Earth’s LEO, typically defined as at an altitude of between 160 to 2,000 kilometers (or 99 to 1,200 miles) above Earth's surface. Most satellites, the ISS, and the Hubble Space Telescope reside in LEO.

According to NASA, orbital debris is the primary threat to spacecraft, satellites, and astronauts. In the best-case scenario, collisions with orbital debris can pit or damage spacecraft; in the worst case, they can cause catastrophic failures. Averaging speeds of 10 km per second (22,000 mph), a 1-cm paint fleck is capable of inflicting the same damage as a 550-pound object traveling 60 miles per hour on earth. A 10-cm projectile would be comparable to 7 kilograms of TNT. (See NASA's Space debris sensor video for inspiration.)

So where, specifically, is all this debris coming from? NASA's Orbital Debris Program Office says that as of 2016 (the last time it posted a top 10 space junk missions account), by far the source of the greatest amount of orbital debris remains the Fengyun-1C spacecraft, which was the target of a People’s Republic of China anti-satellite test in January 2007. “This satellite alone now accounts for 3,428 cataloged fragments or almost 20 percent of the entire population of catalogued manmade objects in orbit about the planet. Additional debris from this test and other events are currently being tracked by the U.S. Space Surveillance Network (SSN) and are officially cataloged on a routine basis,” NASA states. In 2010, there were 2,841 pieces of junk from this spacecraft.

Top 10 satellite breakups, January 2016







Image credit: NASA, Orbital Debris, Quarterly News. See complete chart here.

Orbital debris can include all manner of space system parts from derelict spacecraft and upper stages of launch vehicles. That includes debris intentionally released during spacecraft separation from its launch vehicle or during mission operations, and tiny flecks of paint from small particle hits on existing spacecraft, NASA says.

The second and fourth most significant satellite debris-makers were the Cosmos 2251 and Iridium 33 spacecraft, which were involved in the first-ever accidental satellite collision in February 2009. More than 68 percent of the Cosmos debris cloud remains on orbit, and only 58 percent of the Iridium cloud is on orbit, due in part to the higher area-to-mass ratio bias of the latter cloud. Because of their relatively high altitude, these clouds will continue to present a hazard for decades to come, according to NASA.

NASA also notes that 10 out of the 5,160 space missions that have launched since 1957 account for approximately one-third of all cataloged objects now in Earth orbit.

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Getting down to earth with solutions

With the potential increase of space debris comes one of the scariest scenarios, say space experts. Known as the Kessler syndrome, after NASA scientist Donald Kessler wrote a paper on the subject in 1978, it defines a scenario in which the density of debris in LEO is high enough that collisions between objects could set off a cascade of disastrous collisions between the debris and orbiting spacecraft or satellites. That would create more debris and kill even more satellites and other spacecraft. If you saw the movie “Gravity,” you witnessed a depiction of the Kessler Syndrome on screen.

According to NASA, “Kessler demonstrated that once the amount of debris in a particular orbit reaches critical mass, collision cascading begins even if no more objects are launched into the orbit. Once collisional cascading begins, the risk to satellites and spacecraft increases until the orbit is no longer usable. Kessler proposed it would take 30 to 40 years for such a threshold to be reached, and today, some experts think we are already at critical mass in LEO.”

NASA says its role in the space debris arena is to ensure that it researches and develops future spacecraft that don’t add to the debris field. "Orbital debris poses a risk to continued reliable use of space-based services and operations and to the safety of persons and property in space and on Earth. The United States shall seek to minimize the creation of orbital debris by government and non-government operations in space in order to preserve the space environment for future generations," the agency wrote.

Other space agencies across the globe have their own orbital debris prevention components, but there is no formal global agreement on how to reduce the debris problem.

There is a ton of ongoing work to discover and perhaps one day remediate the problem. Projects include the following:

SpaceX delivered a University of Surrey experimental system to the ISS to test the idea of casting a net to capture space debris. The mission will comprise a small main satellite platform that, once in orbit, will deploy two CubeSats as artificial debris targets to demonstrate the net capturing capabilities. The debris would be towed to LEO and left to disintegrate in the earth’s atmosphere. Square-shaped CubeSats are typically about 4 inches long, have a volume of about 1 quart, and weigh about 3 pounds

NASA funded work by the University of Maryland in March that looks to spot small pieces of orbital debris in LEO. It uses a fleet of CubeSats equipped with sensors to detect the plasma signature of the debris. “Small debris is currently undetectable and poses a hazard to spacecraft. Recently discovered precursor plasma solitons excited by fast-moving charged debris in plasma could enable mapping of small orbital debris by simple sensors on a fleet of CubeSats. The proposed technology would revolutionize our interaction with small orbital debris by enabling spacecraft placement in less hazardous orbits as well as quantitative evaluation of mitigation efforts,” according to the university.

Earlier this year, NASA attached a Space Debris Sensor (SDS) to the ISS that will monitor debris between 5 millimeters and 0.5 mm in diameter to learn more about their characteristics. Data gathered during the SDS investigation will help researchers map the entire orbital debris population and plan future sensors beyond the space station and LEO, where the risk of damage from orbital debris is even higher to spacecraft. “The orbital debris environment is constantly changing and needs to be continually monitored,” NASA says. “While the upper atmosphere causes debris in low orbits to decay, new launches and new events in space will add to the population.”

Airbus has been working on a harpoon system that would be attached to a spacecraft that would fire a metal harpoon at the desired target, pierce through it, and then drag the target back into Earth’s atmosphere for controlled re-entry. According to Space.com, the harpoon is one of the technologies the European Space Agency (ESA) is considering for tackling Envisat, an 8.8-ton (8 metric tons) monster satellite that died in 2012 after 10 years of service. Envisat is now one of the largest pieces of space junk threatening spacecraft in LEO, experts say. "To capture Envisat, the harpoon would have to be about a meter and a half long and [weigh] 2.5 kilograms [5.5 pounds]," says Alastair Wayman, advanced projects engineer at Airbus Defense and Space. "In comparison to Envisat, it's pretty small.”

Similar in concept to the harpoon idea is a small spacecraft being developed by Astroscale. The company’s End-of-Life Service by Astroscale mission is planned for the first half of 2019. It will demonstrate the company’s capability to conduct end-of-life services for larger satellites. Once “Chaser” finds “Target” (simulated space debris), it will dock with the dead satellite and deorbit it from the congested LEO region and burn up upon atmospheric reentry, the company says.

The ESA says its “Clean Space Initiative is looking at the required technology developments, including advanced image processing, complex guidance, navigation and control and innovative robotics to capture debris. Technologies for a wide range of removal targets will be studied, including real applications. 'e-Deorbit,' to be launched in 2023, will be the first ADR mission conducted by ESA, with the objective of removing a large ESA-owned object from its current orbit and performing a controlled reentry into the atmosphere.”

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