Space debris threatens global economy and security

Analysis

The global space industry generated 335 billion dollars in revenue in 2016 and is forecast to grow to 1-3 trillion dollars by the 2040s. It also plays a vital enabling role in other industries (such as shipping, transportation, aviation and agriculture) and national security, as well as in the professional and social lives of billions of individuals.

Debris dangers

Objects in space do not 'float' or 'drift'; they are in constant motion at speeds many times those of bullets. At such speeds, collision with a 1-centimetre object can have the same force as an exploding hand grenade, so collisions even with very small objects can severely damage or destroy satellites.

Moreover, each collision produces a larger number of debris objects, which are smaller and therefore harder or impossible to track.

The worst-case scenario is the 'Kessler syndrome', in which a cascade of collisions produces a debris field that makes low-earth orbit permanently unusable and cuts off access to higher orbits. This process need not occur rapidly; it may already have begun.

In contrast, debris falling on earth is a negligible danger. Usually, it is desirable for debris to enter the atmosphere because it burns up. However, parts of exceptionally massive objects can hit the ground, and not in predictable ways. For example, small parts may have survived when the 8-tonne Chinese space station Tiangong-1 made an uncontrolled descent in April.

Sources of debris

Human-made space debris has various sources:

• Every rocket sent into orbit discards part of its engine casing once the fuel it contains has been used.
• Many redundant satellites are simply left in orbit.
• Debris is created when spacecraft explode due to accidental detonation of unused fuel or batteries. Around 200 are reported to have done so.
• Debris is created when spacecraft or pieces of debris collide. Around 10% of catalogued objects in orbit today were created by a single collision between a US and a Russian satellite in 2009.
• Around 20% of the catalogued objects in orbit were created when China destroyed one of its satellites with a missile in 2007.

Overcrowding

Satellites perform specific functions, and certain orbits are better suited to these than others, making them a scarce resource:

• Low-earth orbit (LEO, up to 2,000 kilometres) is used for most earth-observation satellites and all human spaceflight since the Moon missions. This is the most crowded orbit by far.
• Medium-earth orbit (MEO, 2,000-30,000 kilometres) is used for navigation satellites. It is the least crowded but will become more so as more space agencies launch their systems. In addition to the United States's GPS system, Europe's Galileo constellation and China's BeiDou are currently being assembled. More countries, wanting capabilities for national security reasons, may follow.
• Geostationary earth orbit (GEO, 36,000 kilometres) is used for many telecommunications satellites. Objects in this orbit are stationary relative to the places 'beneath' them on the earth's surface. This orbit is crowded because these satellites are concentrated in a ring around the equator.

The more crowded these orbits become, by satellites and debris, the greater the risk of collisions.

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How much is up there

The US Space Surveillance Network tracked approximately 23,000 pieces of debris in 2016. This excludes roughly 500,000 pieces too small to track, and perhaps millions too small even to detect but still large enough to damage spacecraft.

By contrast, there are only around 1,800 active satellites.

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Objects orbiting above around 600 kilometres remain in orbit for decades, centuries or for practical purposes indefinitely. Therefore the long-term trend is upwards.

Moreover, the rate at which new objects are added is likely to increase.

Around 3,000 more spacecraft are forecast to be launched over the next decade, which could more than double the number of satellites in orbit. The actual number could be even higher as technology advances.

Foreseeable game-changers include reusable rockets such as those pioneered by SpaceX, which could sharply reduce launch costs (see INTERNATIONAL: SpaceX will greatly expand space access - February 14, 2018).

Another is the use of new kinds of small satellite known as 'cubesats', 'smallsats', 'microsatellites' and 'nanosats' (see PROSPECTS 2017-22: Space - December 2, 2016). These are small, cheap and simple, some of them no larger than an iPhone. Large numbers can be carried by a single rocket. Many lack thrusters so they cannot manoeuvre to avoid impacts or de-orbit themselves once they are no longer used.

The introduction of satellite broadband services is another potential gamechanger. These require huge constellations of mass-produced satellites in low-earth orbit. US regulators in March approved SpaceX's constellation of 4,400, half to be launched within six years. Boeing and OneWeb have similar plans.

Technical solutions

Various technical solutions to the debris problem are proposed or already adopted.

Avoidance

Collision-avoidance manoeuvres are already frequent, and are required more and more often.

Avoiding collisions relies on detecting objects and accurately predicting their path, which is not always possible. It also relies on the satellite having enough fuel to conduct the manoeuvre. Currently, all satellites are 'disposable' in that they cannot be refuelled, so expending fuel on avoidance shortens the satellite's life while carrying spare fuel raises the cost of launching it.

Refuelling

Advanced spacecraft could eventually be developed for in-orbit refuelling of satellites designed to be refuelled. NASA plans to test a refuelling satellite (Restore-L) in the mid-2020s.

Retirement

Satellites can be built with the capability to retire themselves after the end of their useful life, by lowering themselves into the atmosphere to burn up or rising to a rarely used 'graveyard' orbit beyond the highest active satellites. They can also be placed in carefully calculated orbits in which the gravitational effects of the Sun and Moon eventually cause them to re-enter the atmosphere.

Durability

Shielding is widely used to make satellites resistant to small impacts but increases their weight and cost. This technology will be improved as impacts become more frequent.

Resilience

Space-based systems can be built with backup satellites that can be launched or redeployed from elsewhere at short notice to minimise disruption to services should a collision damage a critical system.

Using new orbits

Satellites can be designed to use orbits that are not yet overcrowded. However, higher altitude can reduce the quality of service, and lower orbits can increase the fuel needed to adjust for atmospheric drag.

All these measures increase costs. Willingness to pay varies between countries and firms.

Tracking

More accurate detection, identification and tracking of objects in space allows more time for avoidance manoeuvres and reduces the fuel wasted on unnecessary manoeuvres.

However, small or high-altitude objects are difficult to detect. Moreover, orbits in real life are not simple circles but follow diverse and complex paths relative to the earth's surface. They are not always easy to predict and can change over time due to small impacts and complex gravitational effects.

There is no unified international system for tracking and cataloguing. The US military has the most advanced systems and best data and shares much of it, but can be assumed to hold back information it deems to be of military value.

Several other countries with space programmes have or are developing independent systems. Several private firms see commercial opportunity in providing paid-for data to civilian and military clients. Silicon Valley-based LeoLabs yesterday announced an agreement with New Zealand to install a radar system to monitor 250,000 objects in orbit above the Southern Hemisphere, which is comparatively poorly covered.

Removing debris

Actively removing debris from orbit presents enormous technical challenges, but various techniques are proposed or under development.

Magnets, nets or harpoons could be used to capture debris. Last month the United Kingdom's RemoveDebris research satellite successfully used a net to capture a satellite for the first time. It will test a harpoon next year, and also a sail that could be used to pull debris into the atmosphere by increasing atmospheric drag.

Plasma beams could be used to deflect debris into the atmosphere. Japanese and Australian researchers last month reported testing this successfully in a lab.

Lasers could be used to heat part of an object so that its orbit is altered by the force from the material being burned off. Chinese researchers published a numerical simulation demonstrating this possibility earlier this year.

However, on current trends, overcrowding will likely become a serious problem long before active debris removal is possible on any significant scale. Even when it is, the costs of the clean-up will be high and who should pay for it will be fiercely contested.

Military sensitivity

Space tracking systems can be used to track military aircraft, spacecraft and missiles, so countries tend to limit what data and technology they share and seek to reduce their reliance on other countries' systems, leading to inefficiencies and wasteful duplication. Moreover, governments may see it as being in their interest not to reveal the details or even existence of military satellites.

Techniques for capturing or destroying debris, meanwhile, could in principle also be used as weapons against active satellites, so their development will be controversial and could contribute to a space arms race, potentially with a negative net impact on space safety. Transparency over the technology and its operation would reduce this risk but would have consequences for intellectual property protection and arms control.

Governance gap

Some governments have passed binding domestic legislation to limit the creation of new debris, such as France's Space Operations Act (2008).

Internationally, however, all guidelines are voluntary and non-binding.

The 1967 Outer Space Treaty, the basis of international space law, does not address the issue of debris. The UN Committee on the Peaceful Uses of Outer Space, the main international body dealing with space governance, issued Space Debris Mitigation Guidelines in 2007.

Other standards and guidelines have been drawn up by:

• the Inter-Agency Space Debris Coordination Committee, a forum at which the major national space agencies coordinate on the issue;
• the International Organization for Standardization (ISO); and
• the International Telecommunication Union, which oversees the allocation of orbits.

Several European space agencies signed a Code of Conduct for Space Debris Mitigation in 2004.

All international guidelines are voluntary and appear to be breached frequently. A NASA study in 2015 found that 20% of cubesats do not comply with an international orbit disposal guideline that satellites should be placed so that they de-orbit within 25 years of retirement.

Binding global agreements are unlikely, at least until the problem becomes acute. The dominant space powers will prioritise their freedom of action while emerging spacefaring nations will reject as inequitable restrictions that did not fetter the earlier progress of the incumbents.

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