Four Steps to Global Management of Space Traffic Jamie Morin Sets out the Elements Required to Track Satellites and Avoid Crashes

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A cloud of satellites and space debris orbits Earth, as seen in this artist’s impression. Four steps to global management of space traffic Jamie Morin sets out the elements required to track satellites and avoid crashes.

pace is getting crowded. Today, we can companies and even schools can build one 2012, the crew of the International Space track more than 20,000 artificial objects to photograph Earth for as little as $10,000. Station was forced to shelter in the Soyuz that orbit Earth — including 1,500 work- And constellations of thousands of spacecraft escape capsules when debris from a 2009 Sing satellites and a plethora of expired craft, will increasingly be used for ambitious pro- satellite collision passed close by. used boosters and other debris. That’s just the jects. For example, the company SpaceX in To adapt to a crowded and democratized tip of the iceberg. Later this year, ten times Hawthorne, California, aims to launch nearly space future, we will need some form of as many objects could be revealed when the 12,000 small satellites to form a space-based space traffic management. The US govern- US Air Force switches on its Space Fence internet system by the mid-2020s. ment is seeking to lead global efforts while (see go.nature.com/2dxztu3). This powerful The potential for collisions, accidents, developing policies to manage its satellites radar, located on Kwajalein Atoll in the Pacific misunderstandings and conflicts is grow- more effectively. This would not involve Ocean and costing US$1.6 billion, will make ing. Each crash releases debris that threatens ‘traffic police’ directing satellites left or 1 million observations a day. other space activities. In 2007, China’s test of right, but a system more like the weather Keeping up with space traffic is becom- an apparent anti-satellite weapon created tens service (see go.nature.com/2dtjznn). ing more challenging. Satellites are getting of thousands of shards and raised geopolitical Satellite operators would share information smaller and cheaper to launch. Scientists, concerns (see go.nature.com/2tv2nja). In and receive status reports and collision

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alerts. Companies would develop and sell if they were to hit a satellite. are currently expected to occur each decade2. services and apps based on the data. Placing a greater number of improved But satellite owners need to assess the risks. But space traffic is a global concern, affect- sensors in more locations around the globe Manoeuvring a satellite is not taken lightly ing civil, commercial and national security would increase the frequency and sensitiv- — it consumes fuel, creates other collision activities. China and India are now major ity of measurements. This will become more risks, might interrupt the satellite’s mission players; Australia and New Zealand have both important as satellites manoeuvre more often and can reduce its useful lifespan. Missions created national space agencies in the past to change their orbits. Better still, real-time need to establish thresholds of probability three years. Entrepreneurs and educators are information from on-board sensors and for collision alerts, balancing the frequency eager to expand their foothold. Legally, they communications links can be shared by of manoeuvres with acceptable risks. have every right. The 1967 Outer Space Treaty space operators — as they are for aircraft. Operators also need to be identified. Own- states that no country may restrict another’s Sharing such information will be crucial as ership is much harder to establish today than access to and peaceful use of space. satellite operations become more automated. it was when few nations operated in space. But there are few internationally accepted Finally, fitting satellites with transponders Under the UN Convention on Registration of rules or norms for operating in orbit. Discus- that are designed to transmit position even Objects Launched into Outer Space, govern- sions have occurred intermittently, including after a satellite fails could provide precise ments are obliged to record new space objects. around the European Union’s draft Code of location information and reduce false colli- But this takes weeks or months, and lists are Conduct for Outer Space Activities, and in the sion alarms. incomplete. One rocket can launch dozens United Nations Committee on the Peaceful Ultimately, global sharing of tracking data of satellites, and some satellites carry smaller Uses of Outer Space. But no global framework is desirable, to make the best use of sensors ones inside them3. Responsibility for small exists for coordinating spacecraft movements. around the globe. Within the next few years, pieces of debris that have not been tracked An international regime for managing national systems could complement the US consistently is especially hard to pin down. space traffic could in some ways mirror Space Fence. These could be operated jointly As the numbers of craft and operators that for aviation: multilateral standards and with US programmes through bilateral and grow, precision tracking and manoeuvre practices for safety and communications, multilateral data-sharing agreements, such as information will need to be provided quickly augmented by bilateral agreements cover- those now used by and completely. For example, in-orbit main- ing certain economic activities and safety “Expired the US Air Force’s tenance systems would need near-real-time situations. But there are major differences satellites and Combined Space information to avoid collisions with other between the control of space and of air traf- debris can Operations Center satellites. fic. Unlike most aircraft, satellites are not remain in at Vandenberg Governments and companies such as required to transmit their identification, orbit and go Air Force Base in ExoAnalytic Solutions in Foothill Ranch, speed, direction or altitude. Establishing uncontrolled for California, to share California, and LeoLabs in Menlo Park, Cali- ownership is hard. The positions of craft are centuries.” tracking and colli- fornia, are developing services for reporting uncertain and some of the best data are kept sion-warning infor- potential collisions; currently, the US Air private for commercial or governmental rea- mation with other countries and companies. Force is the primary provider. To be relevant, sons. Expired satellites and debris can remain The private sector should also contrib- these services must be available 24 hours a in orbit and go uncontrolled for centuries. ute. Associations of satellite operators could day and be updated rapidly and regularly. Here, I outline the four main elements of provide tracking data and plans for craft They must also handle contradictory data a global management system for space traf- manoeuvres, and companies that estimate from multiple sources effectively. fic, and the steps needed to make it happen. satellite positions could enable the use of their commercial tracking data. Increasingly, Standards and norms. Data-sharing FOUR ELEMENTS private companies are eager to sell space- protocols, standards and norms for operat- Improved tracking. Aeroplanes are traffic data and value-added services to ing in orbit and mitigating debris need to controlled much more strictly than satellites satellite operators. The prospects for interna- be developed and agreed internationally. are. Air-traffic systems direct aircraft along tional cooperation on tracking and manage- In an April 2018 speech, US vice-president registered flight paths during trips that are ment are constrained by geopolitical risks, in Michael Pence announced that the Depart- measured in hours. Most aircraft broadcast that some countries might not want to rely ment of Commerce will take a lead in estab- their positions continuously. The United on the United States and would seek their lishing common global practices to manage States uses 150 radars to follow 5,000 planes own, independent data. This is analogous to space traffic. However, many more steps are at peak times over its territory1. By contrast, the current situation with global navigation needed for successful implementation4. just a few dozen sites worldwide track tens of and timing data, in which Russia, European To build global consensus, the US gov- thousands of space objects. Satellites can be nations, China and Japan have all developed ernment must consult with commercial left for years to follow orbits that are defined some form of alternative to the US-operated space actors and international partners. For only by the laws of physics. Global Positioning System. example, an industry–government forum Tracking space objects is technically of space experts is being established by the difficult, especially if they are small and fast- Prediction and identification. To fore- Consortium for Execution of Rendezvous moving. Objects can be as small as a fleck cast collisions, orbits need to be predicted and Servicing Operations (CONFERS). of paint or as big as a city bus (see ‘Traffic accurately. Sparse observations make deter- Concerns will need to be ironed out jam’). And most travel many kilometres mining a satellite’s location and velocity regarding handling of proprietary and sen- each second, along orbits from 200 kilo- uncertain. So, too, do limitations in models sitive information, lines of management metres to 40,000 kilometres above Earth’s of gravity and other forces, such as drag from authority, distribution of development surface. Currently, the US military uses a the upper atmosphere. contracts and the potential for liability. website to publish extensive data for objects Possible collisions can be forecast using Voluntary standards and economic incen- that are larger than about 10 centimetres models when ‘bubbles’ of uncertainty over- tives for compliance would be a good first (www.space-track.org). However, for every lap. Because of the large uncertainties, most step. For example, the World Economic tracked object, there are 20–30 times as possible collisions will not result in an actual Forum is building an industry coalition many pieces of debris. Most are too small to crash: given the population of satellites cur- along these lines. It has sought proposals be followed, but many could end a mission rently in orbit, only one or two such collisions for setting up a Space Sustainability Rating

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and economic barriers can be overcome. Altitude The US Federal Communications 2,000 km TRAFFIC JAM Commission, which is charged with Low Earth orbit (out to 2,000 km) is crowded with satellites and space debris, travelling fast with little control. Only the largest objects (3.6%) are tracked. licensing all US commercial communica- Yet even tiny shards could prove fatal or end missions. tions satellites before they are launched, has announced that it will update its JE AE rules on debris mitigation (see go.nature. 1,800 Not tracked, 410,180 total (small, >1 cm) com/2einkjh). Encouraging other nations Planned tracking, 62,006 total (medium, >5 cm) to create or enhance their national rules and Currently tracking, 17,391 total (large, >10 cm) standards will improve the space environment, even without international treaties. EEE A 1,600 Existing WHAT NEXT? Proposed The United States is beginning to take the SOURCES: SPACE-TRACK.ORG/THE AEROSPACE CORPORATION AEROSPACE SPACE-TRACK.ORG/THE SOURCES: Globalstar first steps. The federal government has plans (1,414 km) to move space-tracking data from the military to a civil agency. This could increase 1,400 SpaceX plans to international public trust and willingness launch 12,000 to share data, and could improve space ,5 satellites by the medium objects safety. Relationships remain to be built mid-2020s orbiting at SpaceX across US government agencies, between 860 km (1,325 km)* the public and private sectors, and between 1,200 space-capable countries. Shifting duties to ,226 different federal departments and handing small objects tasks to contractors will not be enough to orbiting at protect valuable space assets. 860 km 1,000 Dozens of data-sharing arrangements between the US government, foreign government agencies and commercial satellite operators need to be linked. Data formats must be ,22 objects orbiting at 860 km compatible, and protocols will be needed for 800 merging streams of data containing proprietary or national-security information. EXOSPHERE (>700 km) National and international norms and standards of operations must be agreed. Hubble Space Discussions have been under way for years; Much of the debris in the Telescope 600 (568 km) as space traffic escalates, now is the time 750–900 km range comes to accelerate progress domestically and from a 2007 Chinese large objects anti-satellite test and a globally. The International Astronauti- orbiting at 2009 accidental collision. International cal Congress meeting in Washington DC 780 km Space Station (408 km) this October will be a key opportunity that ■ 400 should not be missed. Most human space ight SpaceX Jamie Morin is executive director of the (340 km) Center for Space Policy and Strategy at The Aerospace Corporation in Arlington, 200 Virginia, USA, which runs a federally funded research and development centre in support THERMOSPHERE (80–700 km) of the US space enterprise. He is a member of MESOSPHERE (50–80 km) the World Economic Forum’s Global Futures STRATOSPHERE (12–50 km) Council on Space Technology, and previously 0 served in the US Department of Defense. 0 2 4 6 8 10 12 e-mail: [email protected] *Not all will be at 1,325 km; around 7,500 will y at very low Earth orbit (335–346 km) Objects (thousands) per 10 km of altitude EARTH 1. Federal Aviation Administration. Air Traffic by the Numbers (FAA, 2018). 2. Inter-Agency Space Debris Coordination Committee. Stability of the Future LEO Environment system, modelled on the approach used to Space Debris Coordination Committee IADC-12-08, Rev. 1, January 2013 (IADC, 2013). certify green buildings. (IADC), a group of 13 civil space agen- 3. McLeary, P. ‘Space Mystery: Are Russian Doll Sats cies5. For example, the IADC’s ‘25-year a Threat?’ Breaking Defense (16 August 2018). 4. Gleason, M. P. & Cottom, T. U.S. Space Traffic Reduce space debris. Most of the current rule’ calls for satellites in low Earth orbit Management: Best Practices, Guidelines, collision threat to active satellites is from to be removed within 25 years of the end Standards and International Considerations (The debris rather than from other satellites. To of their mission. Eliminating all on-board Aerospace Corporation, 2018). 5. Inter-Agency Space Debris Coordination maintain a sustainable orbital environment energy sources — from fuels to spinning Committee. IADC Space Debris Mitigation for the long term, the creation of further momentum wheels — lowers the risk of Guidelines IADC-02-01, Revision 1, September debris must be limited. International guide- decommissioned satellites exploding. Some 2007 (IADC, 2007). lines on space-debris mitigation should especially hazardous debris objects might J.M. declares competing financial interests; build on those drafted by the Inter-Agency be removed from orbit, if technology, policy see go.nature.com/2tpncjt for details.

CLARIFICATION In the Comment ‘Four steps to global management of space traffic’ (Nature 567, 25–27; 2019), the graphic ‘Traffic jam’ originally implied that all 12,000 SpaceX satellites will orbit at 1,325 km; in fact, around 7,500 of them will fly at very low Earth orbit (340 km).