The asteroid 101955 Bennu is just a pile of rubble, weakly held together by its own gravity, the remnants of a catastrophic event that occurred a billion years ago. But Bennu is also a bearer of both life and death, containing clues about the origins of life on Earth while, at the same time, having the potential to destroy humanity. For over time, the agencies of physics and chance have brought the 500-metre-wide asteroid onto an orbit very near to Earth.

Until recently, those wanting to escape the effects of terrestrial light pollution could leave cities and travel to the countryside to observe the night sky. But increasingly there is nowhere, and therefore no way, to escape the pollution from the thousands of satellites being launched each year. ‘Mega-constellations’ composed of thousands or even tens of thousands of satellites are designed to provide low-cost, low-latency, high-bandwidth Internet around the world. This chapter outlines how the application of the ‘consumer electronic product model’ to satellites could lead to multiple tragedies of the commons, from the loss of access to certain orbits because of space debris, to changes to the chemistry of Earth’s upper atmosphere, to increased dangers on Earth’s surface from re-entered satellite components. Mega-constellations require a shift in perspectives and policies. Instead of looking at single satellites, we need to evaluate systems of thousands of satellites, launched by multiple states and companies, all operating within a shared ecosystem.

Space tourism began in 2001 when an American investment manager paid the Russian space agency US$20 million to travel to the International Space Station on a Soyuz rocket. In 2021, three US-based companies began launching tourists on their own rockets: Virgin Galactic, Blue Origin and SpaceX. The emergence of Space tourism raises difficult issues. One such issue is the environmental effects of launches on the atmosphere and the corresponding implications for climate change. Space tourism also raises difficult questions of international law, including, where does space begin? Who gets to call themselves an ‘astronaut’? Do states have a duty to rescue tourists stranded in space?

The rapid development of mega-constellations raises difficult issues of international law, including liability for collisions involving satellites. Establishing ‘causation’ – that the actions of one satellite operator caused a specific collision with another space object and resulted in damage – could be a challenge, especially in the context of knock-on collisions where debris from an initial collision later collides with one or more spacecraft, including satellites. A further challenge is determining, in the absence of binding international rules on the design and operation of satellites, what is ‘reasonable’ behaviour and therefore what constitutes ‘negligence’. This chapter also addresses the interference to astronomy that is increasingly resulting from light and radio spectrum pollution from satellites. A full interpretation of the Outer Space Treaty leads to the conclusion that states are already required to take certain steps, including conducting an environmental impact assessment, before licensing mega-constellations, because of the obligation of ‘due regard to the corresponding interests of all other States Parties to the Treaty’.

Anti-satellite weapons that rely on violent impacts and create space debris are regarded as a major threat to the exploration and use of space, including the use of space assets for communications and Earth imaging. This chapter examines two ways in which the testing of such ‘kinetic’ weapons might already have become illegal. First, the accepted interpretation of Article I of the Outer Space Treaty may be evolving as a result of the changing practice of the parties to that treaty. In short, many states are behaving as if tests of anti-satellite weapons that create debris are contrary to the ‘freedom of exploration and use of space’. Second, the same practice and an accompanying opinio juris may be contributing to the development of a parallel rule of customary international law. This chapter also examines the legality of the use of kinetic anti-satellite weapons, as opposed to their testing. Two additional, separate bodies of international law are relevant here: the jus ad bellum governing the recourse to armed force, which includes the right of self-defence, and the jus in bello governing the conduct of armed conflict. A close analysis leads to the conclusion that any use of a kinetic anti-satellite weapon would be illegal today because of the growing crisis of space debris.

More than six decades after Sputnik, most rocket bodies used for space launches are still abandoned in orbit. In 2020, over 60 per cent of all launches to low Earth orbit resulted in at least one rocket body being abandoned in orbit. If that orbit has a sufficiently low perigee, drag from gas in the tenuous, uppermost regions of the atmosphere will gradually reduce the rocket body’s altitude and cause it to re-enter the denser, lower atmosphere in an uncontrolled way. This can occur at any point under its flight path, creating dangers for people on the surface and in aeroplanes. Moreover, many uncontrolled re-entries occur near the equator due to the trajectories of many of the abandoned rocket bodies. As a result, the cumulative risk from rocket body re-entries is higher in the states of the global South, as compared to the major spacefaring states. Yet launch providers have access to technologies and mission designs today that could eliminate the need for most uncontrolled re-entries, albeit at increased financial cost.

At least 14 space agencies have identified ‘in situ resource utilization’ as a necessary capability for long-duration missions, including crewed missions to the Moon, Mars and deep space. Attention is focused on the potential production of rocket fuel from ice and water-bearing minerals. If fuel can be sourced in space, it will not need to be lifted, at great expense, from Earth’s surface. But while the mining of asteroids and other celestial bodies offers benefits, it will also create risks. Mining that is motivated purely by resource extraction could overlook or even destroy important scientific information, while physical interactions with an asteroid could alter its trajectory and, in some circumstances, potentially create a human-caused Earth impact risk. There are presently two competing efforts to develop widely agreed rules on space mining. The first is an industry-friendly effort in which the United States is engaging in bilateral negotiations with dozens of states, encouraging them to sign the non-binding Artemis Accords. The second is a multilateral effort that fully considers the interests of non-spacefaring states and is taking place in the United Nations Committee on the Peaceful Uses of Outer Space.

The global governance regime for space is grounded in six decades of co-operation between the Soviet Union and then Russia on the one hand, and the United States and its allies on the other.

But continued co-operation is not guaranteed. Following the Russian invasion of Ukraine, some elements of international space co-operation broke down immediately. Other elements, such as the International Space Station, notably continued. More worrying, perhaps, is the heavy reliance of Russian and Ukrainian forces on satellites, including, in the case of Ukraine, satellites owned and operated by private companies. This raises challenging issues of international law, including whether these private satellites are legal targets. It also raises the question of how far Russia might go in this regard. What if it decided to target SpaceX’s Starlink mega-constellation?

Humanity’s ascent into space began in 1929 when the German Army tested its first rocket, the A-1. But while militaries have always accounted for a large portion of human space activity, their use of the space environment has been constrained by a mutual self-interest in preserving access to it for communications, navigation, reconnaissance, weather forecasting, arms control verification and early warning. In 1962, the ‘Starfish Prime’ nuclear test demonstrated that nuclear explosions in space pose a major and indiscriminate threat to satellites. This prompted the United States and the Soviet Union to negotiate the 1963 Limited Test Ban Treaty, which prohibits nuclear tests in space. This chapter addresses such tensions between the expansion of military capabilities in space and the need to keep space free of direct conflict. The chapter highlights the growing need for a treaty to ban the testing of ‘kinetic’ anti-satellite weapons, i.e. weapons that rely on violent impacts to destroy a satellite and thus create space debris. Although Russia tested such a weapon in November 2021, the very next month the United Nations General Assembly created an ‘Open Ended Working Group on Reducing Space Threats through Norms, Rules and Principles of Responsible Behaviours’. The chapter concludes with an examination of the potentially destabilising effects of an imminent extension of military activities to cis-lunar space, the region between Earth and the Moon, including special Moon–Earth orbits.

Some 66 billion years ago, a cataclysmic collision between the Earth and an asteroid ten to 15 kilometres in diameter caused the extinction of the non-avian dinosaurs. In 1908, an asteroid 50 to 70 metres in diameter levelled over 2,000 square kilometres of forest in Siberia, while in 2013 an asteroid 19 metres in diameter produced a shockwave over Chelyabinsk, Russia, sending over a thousand people to the hospital. The field of ‘planetary defence’ involves the detection, characterisation, risk assessment and, if necessary, deflection of asteroids and comets that have the potential to strike Earth. Yet there has been a lack of high-level diplomacy on this issue. In particular, the low probability of a major Earth impact happening in our lifetime makes planetary defence a low priority for political leaders, despite the existential consequences of impacts and their eventual certainty of occurring. There is also a shortage of widely agreed international law, including on the potential use of nuclear explosive devices for deflecting asteroids. Most importantly, there is a lack of agreement on who is responsible for vetting the science, assessing the risks and making decisions if Earth were faced with an actual impact threat. Is it the United Nations Security Council that decides? What if a Security Council decision is blocked by one of its veto-holding permanent members? Would a state that acted unilaterally be excused any illegality because of the necessity of its actions, according to the international law on ‘state responsibility’?