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Space debris - litter in Earth orbit

Dr Lucy Rogers
Feb 8, 2012, 0:00 UTC

Sen—Vanguard 1, the world’s third satellite, is one of millions of pieces of man-made debris polluting space, 54 years after it was launched. In the early days of space exploration little thought was given to all the flotsam and jetsam left in orbit. After all, space is big. However, just as pollution of the oceans has become an international problem, pollution of space is also becoming an international problem.

Although the danger of debris falling back to Earth has been in the news recently, the greater danger is to all the satellites and spacecraft still in space.

The most obvious risks are to manned spacecraft, such as the International Space Station (ISS). If debris were to puncture the craft and cause loss of pressure in the life-supporting module or damage critical components, the astronauts might have to evacuate. The ISS performs collision avoidance manoeuvres to reduce the risk of this happening. These manoeuvres are becoming more frequent.

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The image shows damage to a window of the Space Shuttle caused by space debris during STS-7. Image credit: NASA

All spacecraft are at risk of possible catastrophic damage. The effect of broken satellites to our everyday lives is not immediately apparent. Satellite navigation in our cars and live sport on our TVs are a couple of the more obvious benefits. But search and rescue, weather data, pollution mapping, timing on the railway signals and financial transactions are other examples. Some aircraft use satellite radio communications, without which they cannot fly over over large remote areas such as oceans or the Arctic.

On October 6th, 2011 Telesat's Anik F2 satellite suddenly ceased operating. This caused many Canadians, especially those in remote areas of the Far North, to lose all communications and First Air airline to cancel flights. This particular satellite anomaly was not the result of space debris, but due to a software error. As such, it was easily repairable and the satellite continues to operate normally. However, it could have caused a lot more disruption.

Space debris ranges in size from flecks of paint to the third stage of Apollo 12’s Saturn V launch vehicle - at over 11,000 kg. The majority of debris is wreckage from satellite collisions and explosions.

In February 2009 a working Iridium communications satellite and a defunct Russian Cosmos satellite collided. The resulting debris trail included over 2,000 separate pieces - and probably many too small to be tracked. This left two rings of destruction around the Earth, as the pieces spread out around their original orbits.

Other space debris includes decommissioned satellites, rocket bodies, mission related debris such as discarded lens caps and items dropped by astronauts on space walks.

At orbital speeds of around 17,500 mph, something the size of a grain of sand can cause damage. A number of windows in the Space Shuttles had to be replaced due to impacts by flecks of paint.

Something the size of a cherry can be equivalent to exploding a hand grenade next to a satellite.

Getting a new satellite built and into space is an expensive and time-consuming process. A “simple” communications satellite can cost around £120 million. The more sophisticated satellites with on-board processors can cost up to £300 million. They then often undergo months of extensive testing. Launch costs to geostationary orbit are also high at about £60 million, including an insurance premium of around 20%. This premium will go up if there are claims made for satellite and debris collisions.

Spacecraft can be protected from space debris smaller than a cherry (about 1 cm) by bumpers called Whipple shields. These cause the debris to disintegrate before it hits the actual spacecraft. However, this increases the weight of the satellite, so they are generally only used on manned spacecraft.

There are probably over half a million pieces of debris that are smaller than a melon (about 10 cm) and larger than a cherry. These we cannot shield against, and they are too small to track. It is these that cause the greatest risk to space missions.

Items larger than a melon are tracked by systems referred to as Space Situational Awareness (SSA). In most countries, this is usually done by the military, for security purposes. For example, the USA’s department of Defense Space Surveillance Network tracks some objects as small as 5 cm in diameter that are in low Earth orbit - less than 2,000 km above the surface of the Earth. It also tracks items that are about 1 meter across in geosynchronous orbit (35,880 km above Earth).

Much of this information is shared with other nations and with satellite operators, so working satellites are often warned if they are likely to be hit by debris, and can dodge out of harm’s way if required. However, like forecasting the weather, the predictions of where a certain piece of debris will be in the future, is subject to inaccuracies.

The European Space Agency (ESA) also has an SSA capability, which increases Europe’s capabilities to detect, predict and assess the risk to life and property for human-made space objects, re-entries and on-orbit collisions. It also investigates potential impacts of Near-Earth Objects and the effects of space weather.

So whose fault is all this debris? The majority of the pieces that can be attributed belong to the USA, Russia and China.

But there are thousands of pieces where we cannot be sure where they came from. And nobody is taking responsibility for cleaning up space. There is no financial incentive for any commercial company to do so.

In the 2007 the General Assembly of the United Nations adopted mitigation guidelines which aim to limit the production of more space debris. These include limiting the potential for break-up by venting fuel at the satellite’s end of life and limiting the long-term presence or interference of spacecraft at the end of their mission, either by de-orbiting or by moving to a “Graveyard orbit”.

However, mitigation and SSA can only help reduce the problem, they do not solve it.

There are tools and techniques being developed for space debris removal, though currently the technology still needs testing. But the technology is more advanced than the political and legal situation. For example, an Earth-based laser that can remove a piece of space debris can also remove a working satellite - which means it could be used as a weapon.

What happens if a piece of debris is moved, and then hits someone else’s working satellite? Who’s to blame? Unlike the maritime law, a spacecraft remains the property of the launching country forever. So if one country tries to move a decommissioned satellite belonging to another country, it could be seen as an act of war.

Some progress has been made on an International Code of Conduct for Outer Space Activities, which builds on the 1967 Outer Space Treaty.

The main purpose of this code would be to mitigate debris and help establish traffic management procedures. It will “help maintain the long-term sustainability, safety, stability, and security of space by establishing guidelines for the responsible use of space”.

The European Union and the governments of Japan, Canada and Australia have already expressed support for an initiative along these lines. On January 17, 2012, the USA’s Secretary of State Hillary Clinton also showed her country’s support, although there are still political and military issues to be addressed.

She said “The United States has made clear to our partners that we will not enter into a code of conduct that in any way constrains our national security-related activities in space or our ability to protect the United States and our allies. We are, however, committed to working together to reverse the troubling trends that are damaging our space environment and to preserve the limitless benefits and promise of space for future generations.”

A sustainable solution to litter in space requires three things: political will, a legal framework and technology. Without these, debris collisions will cascade - producing more debris and increasing the likelihood of further collisions - until space becomes too dangerous to access.

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