The dawning of the Space Age marked the start of an ongoing relationship between the professional astronomical community and both state and non-state actors that launch and operate spacecraft in near-Earth orbital space. While the Cold War heated up in the late 1950s, military uses of outer space quickly came into conflict with the priorities of astronomers then building ever-bigger ground-based telescopes and envisioning the first generation of space telescopes. As the threat of global thermonuclear war loomed, the United States carried out Project West Ford, which tested an “artificial ionosphere” for microwave radio propagation by placing several hundred million tiny copper dipoles into a belt orbiting the Earth. While the test was ultimately successful, it ignited a firestorm of concern and criticism among astronomers and ultimately influenced the framing of the United Nations Outer Space Treaty. Here we examine the history of Project West Ford as it prompted astronomers to react, comparing it with the ongoing problem of the potential impact of large satellite constellations on astronomical research.

The rising population of artificial satellites and associated debris in low-altitude orbits is increasing the overall brightness of the night sky, threatening ground-based astronomy as well as a diversity of stakeholders and ecosystems reliant on dark skies. We present calculations of the potentially large rise in global sky brightness from space objects in low Earth orbit, including qualitative and quantitative assessments of how professional astronomy may be affected. Debris proliferation is of special concern: we calculate that all log-decades in debris size contribute approximately the same amount of night sky radiance, so debris-generating events are expected to lead to a rapid rise in night sky brightness along with serious collision risks for satellites from centimetre-sized objects. This increase in low-Earth-orbit traffic will lead to loss of astronomical data and diminish opportunities for ground-based discoveries as faint astrophysical signals become increasingly lost in the noise. Lastly, we discuss the broader consequences of brighter skies for a range of sky constituencies, equity/inclusion and accessibility for Earth- and space-based science, and cultural sky traditions. Space and dark skies represent an intangible heritage that deserves intentional preservation and safeguarding for future generations.

Our planet and our species are at an existential crossroads. In the long term, climate change threatens to upend life as we know it, while the ongoing COVID-19 pandemic revealed that the world is unprepared and ill-equipped to handle acute shocks to its many systems. These shocks exacerbate the inequities and challenges already present prior to COVID. As weary nations look toward a post-COVID world, we draw attention to both the injustice and many impacts of the quiet occupation of outer space near the Earth, which has rapidly escalated during this time of global crisis. The communities most impacted by climate change, the ongoing pandemic, and systemic racism are those whose voices are missing as stakeholders both on the ground and in space. We argue that significant domestic and international changes to the use of near-Earth space are urgently needed to preserve access to, and the future utility of, the valuable natural resources of space and our shared skies. After examining the failure of the United States and international space policy status quo to address these issues, we make specific recommendations in support of safer and more equitable uses of near-Earth space.

The population of artificial satellites and space debris orbiting the Earth imposes non-negligible constraints on both space operations and ground-based optical and radio astronomy. The ongoing deployment of several satellite ‘mega-constellations’ in the 2020s represents an additional threat that raises significant concerns. The expected severity of its unwanted consequences is still under study, including radio interference and information loss by satellite streaks appearing in science images. In this Letter, we report a new skyglow effect produced by space objects: increased night sky brightness caused by sunlight reflected and scattered by that large set of orbiting bodies whose direct radiance is a diffuse component when observed with the naked eye or with low angular resolution photometric instruments. According to our preliminary estimates, the zenith luminance of this additional light pollution source may have already reached ∼20 μcd m−2, which amounts to an approximately 10 per cent increase over the brightness of the night sky determined by natural sources of light. This is the critical limit adopted in 1979 by the International Astronomical Union for the light pollution level not to be exceeded at the sites of astronomical observatories.