14 April 2021
Author: Romain Buchs
As the pace of space activities accelerates and societies become more reliant on space-based systems, the associated risks deserve more attention. Satellites form a critical infrastructure on which military, civil and commercial entities rely. The services they provide are increasingly used in everyday life, raising the prominence of space safety, security and sustainability, and making the development of strategies to address the associated risks more necessary. In this article, we highlight the complexity of the risks inherent to human-made objects in space, noting in particular the pressing issue of space debris in low Earth orbit.
Since the launch of the first human-made satellite, Sputnik I, in 1957, over 6,000 rocket launches have brought about 10,700 satellites into space. As of today, more than 3,400 operational satellites revolve above our heads. While approximately 150 satellites per year were launched into orbit between the 1960s and the 2000s, this number has significantly increased in recent years, reaching 1,200 satellites launched in 2020. The number of spacecraft in orbit will keep increasing in the coming years, with plans to launch up to 40,000 satellites in the next decade. Behind this trend lies a shift from state-sponsored space programs to a dynamic private space economy. Commercial launch activities and technological developments have drastically reduced the cost of launching satellites. These drivers have resulted in a burgeoning set of space companies—generally known as New Space—and opened the way for alternative applications and business models. While the size of the space economy was estimated at $366 billion in 2019, recent reports by Goldman Sachs, Morgan Stanley and Bank of America Merrill Lynch project a $1–2.7 trillion space economy by the 2040s. However, these forecasts are subject to large uncertainties. Addressing the risks associated with space activities is instrumental in the realisation of a thriving space economy and in ensuring the long-term availability of critical space infrastructure.
A growing reliance on space infrastructure
Our dependence on space-based services has grown commensurately with the deployment of satellite systems. Three regions of near-Earth orbital space are commonly used: low Earth orbit (LEO), medium Earth orbit (MEO) and geostationary Earth orbit (GEO). LEO is the spherical shell that extends from the upper atmosphere to an altitude of 2,000 km. It hosts Earth observation satellites, which are instrumental in climate and environment monitoring, weather forecasts, resource management, and land stewardship. This orbital region is increasingly used for communications with the deployment of satellite constellations for the Internet of things and broadband internet. The majority of planned launches in the next decade are part of LEO satellite internet constellations. GEO is a circular orbit at an altitude of 35,786 km above the equator. A satellite in GEO remains above the same point on the Earth’s surface. Due to this particular feature, this orbit is used by television and radio broadcasting satellites, as well as communication satellites. MEO is the region between LEO and GEO. It hosts different systems for position, navigation and timing (PNT), on which critical infrastructures on Earth, such as transportation and banking systems, rely. Across these orbits, satellites are also launched for space science, technology development and military activities. Currently, the vast majority of the revenue from the satellite industry comes from activities taking place in GEO and MEO, as TV broadcasting and PNT services are the dominating segments. However, this is bound to change with the advent of LEO satellite internet constellations.
As space-based services become ubiquitous, increased scrutiny of the risks space assets face or generate is required. Space is a harsh and remote environment where assets cannot be easily refuelled, repaired, inspected or upgraded, although new technologies are being developed to enable on-orbit satellite servicing. Operational spacecraft face numerous threats in orbit. They can become non-functional due to technical failures, collisions with other human-made objects and meteoroids, or due to charged particles from geomagnetic storms.
Space risk landscape
The causal loop diagram below highlights the complexity of the risk landscape inherent to human activities in near-Earth space (excluding risks particular to human spaceflight and related to the exploration and exploitation of other celestial bodies). As the International Risk Governance Center (IRGC)’s earlier work has shown, this pattern of complex interconnections is characteristic of systemic risks, suggesting that a systems approach is needed to address risk in space. Four elements of the diagram are worth highlighting: the volume and variety of objects in space, the sources of risk, the types of harm that can be caused, and the mechanisms for risk reduction.
Anthropogenic space objects (grey boxes in the diagram) all originate from launch activities. Based on the functionality of these objects, a distinction between operational satellites (or active payloads) and space debris can be established. The space environment is marked by debris: while there are about 3,400 operational satellites, more than 26,000 pieces of space debris approximately larger than 10 cm in LEO and larger than 80 cm in GEO are tracked and catalogued. The population of catalogued objects has grown steadily over time, with two major step increases due to a Chinese anti-satellite (ASAT) test in 2007 and a collision between two satellites, Iridium-33 and Cosmos-2251, in 2009. The population of objects in the 1 to 10 cm size range is estimated through modelling at 900,000. Space debris are categorised depending on the mechanism that produced them. Mission-related objects, such as lens covers, bolts, fairings, multi-layer insulation and rocket bodies, are a direct by-product of space missions. Inactive payloads are former active payloads that can no longer be controlled. This category includes satellites that have reached their end-of-life and cannot be de-orbited because they do not have any propellant remaining or propulsion capabilities, and satellites for which their operator has lost control. There are about 2,850 such objects in orbit. Fragmentation debris are the result of explosions and collisions. Inactive payloads and rocket bodies that have remaining fuel or batteries can explode. Pieces of space debris can collide with one another and with active spacecraft. To date, explosion has been the most common break-up mechanism. However, collision is predicted to become the dominant break-up mechanism in the future, as newly formed debris collide with one another, creating more debris and causing more collisions. Due to this feedback loop, the long-term danger is a cascade of collisions that threatens the safety of future space operations. If an operational satellite is involved in a collision, it can result in a loss of functionality or the complete loss of the spacecraft. Collisions can also result in casualties when human spaceflights are involved. Not only can the loss of spacecraft affect the space economy and cause disruptions on Earth, but the mere presence of debris can reduce the attractiveness of space activities by increasing their costs.
Risk reduction mechanisms (blue boxes) can be technical or behavioural. Measures can address the risk on the source side (black boxes) by reducing the probability of occurrence. For example, actively removing large derelict objects can prevent collisions, which create fragmentation debris that could drastically increase the risk of collision for operational satellites. Measures can also address the risk on the impact side by reducing the exposure or vulnerability of the risk absorbing system (red boxes). Spacecraft shielding is an example of a method to reduce the vulnerability of a spacecraft to collisions with small debris and meteoroids.
In near-Earth space, residual atmosphere drags objects down. As altitude increases, this effect decreases. While objects at orbits below 500 km fall back to Earth in several years, objects above 1,000 km can stay centuries before naturally returning to Earth. When re-entering the atmosphere, objects do not always fully disintegrate-depending on their size, shape and materials-and can hit the ground. Re-entries are either controlled or uncontrolled, depending on an operator’s ability to determine the location and trajectory of an object’s re-entry. Uncontrolled re-entries have the greatest risk of harming people or resulting in property damage, as highly populated areas of the planet cannot be avoided. The environmental impact of the burnt materials in the atmosphere is largely unknown due to lack of research, but they could potentially warm Earth’s atmosphere and contribute to ozone depletion.
Among the many other space risks, those worth mentioning here are the effect of launches on the atmosphere, light pollution from large satellite constellations, and space weather:
- Rocket engine exhaust emitted during launch activities impact the atmosphere. Emissions of chlorine, alumina and black carbon directly into the stratosphere are the most concerning, as they result in ozone depletion and radiative forcing. It is generally assumed that these impacts are small components of human influence on the atmosphere, but the overall understanding of the impact of rocket emissions is weak. Moreover, the planned increase of rocket launches could raise the impact of these emissions to a significant level.
- Sunlight reflecting off satellites can have adverse consequences on astronomical research and stargazing. The advent of numerous large satellite constellations has raised concerns from astronomers that a significant share of images taken during the first and last hours of the night could be compromised, especially in the case of very wide-field imaging observations on large telescopes. In addition, communications between large internet satellite constellations and receivers on the ground can adversely impact observations by radio telescopes.
- Space weather denotes the dynamic conditions in the space environment caused by solar activity. Solar wind—the stream of charged particles coming from the sun—can damage or disable spacecraft. Processes in the sun can lead to more dramatic events called geomagnetic storms, which can not only affect spacecraft, but also critical infrastructures on Earth. The economic and societal costs attributable to impacts of a future severe geomagnetic storm could be as high as $2 trillion in the first year following the event.
Space debris collision risk must be addressed now
The fast-growing space economy and our increasing reliance on space-based infrastructure call for heightened attention regarding the associated risks. While there are numerous important risks related to launch and re-entry of objects, light pollution, and space weather, the risk of space debris collision is especially concerning as the number of debris can grow exponentially due to the reinforcing feedback loop of collisions. Space debris is undoubtedly a complex and pressing issue, which requires attention now because of recent decisions and future plans to expand significantly the space economy. This has led IRGC to undertake project work aimed at bringing new perspectives to improve the governance of space debris related risks. There is much uncertainty about the behaviour of the space ecosystems, which demands caution. Space debris collision risk may be dealt with using measures that target it as an individual risk, but because it develops in a complex adaptive system, there are feedback effects that require addressing it as a systemic risk.
Acknowledgements: The author would like to thank Emmanuelle David (EPFL Space Center), Volker Gass (EPFL Space Innovation), Jean-Paul Kneib (EPFL Space Center) and Tim Maclay (ClearSpace) for their reviews of this article, and Marie-Valentine Florin (IRGC) for her valuable inputs.
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