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A nuclear explosion codenamed Bluegill Triple Prime as part of Operation Fishbowl in 1962 (Via nuclearweaponarchive.org)
Technical and communication measures are needed to prevent an arms race in Earth’s orbit.
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Nuclear threats in space demand new diplomacyNuclear threats in space demand new diplomacy
The history of nuclear testing in outer space traces back to the early Cold War era, when the United States and the Soviet Union explored the potential military applications of nuclear weapons beyond Earth’s atmosphere.
The most notable instance was the United States Operation Fishbowl in the early 1960s, which included high-altitude nuclear detonations, including Starfish Prime. Detonated at 400 kilometres above the Pacific Ocean, Starfish Prime caused widespread electromagnetic pulse (EMP) effects, disabling satellites and damaging electrical systems in Hawaii. It also produced a bright artificial aurora visible across the Pacific and injected high-energy electrons into Earth's magnetosphere, forming artificial radiation belts that damaged or destroyed several satellites in the months that followed.
The Soviet Union conducted similar tests during this period, launching nuclear devices on rockets to detonate in the upper atmosphere. These experiments revealed the destabilising potential of space-based nuclear weapons, both through EMP effects and long-lasting radiation belts created by the blasts.
The concern that space could become a new domain for nuclear competition prompted urgent diplomatic efforts to prevent an arms race beyond Earth’s atmosphere. In response, two major international treaties were signed to restrict high-altitude nuclear weapons testing and prevent the militarisation of outer space: The Outer Space Treaty 1967 and the Limited Test Ban Treaty 1963. Together, they laid the initial legal foundation for prohibiting the testing and placement of objects carrying nuclear weapons or any other weapons of mass destruction in orbit, on celestial bodies, or in outer space generally.
It is crucial for the United States and its allies, including Australia, to develop a clear and credible extended nuclear deterrence strategy for outer space.
Recently, apprehension over nuclear weapons in outer space has resurfaced, driven by rising geopolitical tensions and rapid advancements in space and missile technologies. Notably, the launch of Russia’s Cosmos 2553 on 5 February 2022 raised concerns about a potential Russian nuclear anti-satellite program, as it entered an unusual, high-radiation “graveyard” orbit at the outer edge of Low Earth Orbit. According to the CSIS Space Threat Assessment 2025, it is possible that Cosmos 2553 is carrying a “dummy warhead”. A nuclear detonation at this altitude would potentially render parts of LEO unusable for years due to increased radiation. The resulting space debris and environmental hazards could disrupt both civilian and military space operations on a global scale. Recent reports, confirmed by space tracking companies LeoLabs and Slingshot Aerospace, that the satellite Cosmos 2553 is now spinning out of control has escalated concerns.
The Open-Ended Working Group (OEWG) on the Prevention of an Arms Race in Outer Space (PAROS), established by the United Nations General Assembly for the 2024–2028 period, aims to address the growing alarm about the militarisation of space. This OEWG consolidated and replaced the efforts of two prior groups, which had different mandates and views on how to achieve space security governance.
A 35mm photograph of the "Starfish Prime" high altitude nuclear explosion as part of the Operation Fishbowl series of tests in 1962 (US Department of Defence via Wikimedia Commons)
The first substantive session of the OEWG, held in April this year, highlighted the challenges in reconciling these differing strategic approaches. Russia advocates for a legally binding treaty that would explicitly ban the placement of weapons in outer space. Whereas the United States and many Western nations, including Australia, Japan, and the European Union bloc, prefer the development of non-binding norms for “responsible behaviour” in outer space. While discussions have underscored the importance of preventing the placement of weapons in outer space, achieving consensus on the way forward for the development of international governance remains elusive.
As strategic competition in space intensifies, it is crucial for the United States and its allies, including Australia, to develop a clear and credible extended nuclear deterrence strategy for outer space. How do we do this? Here is what we propose:
About the authors
Rebecca Connolly
Dr Rebecca Connolly was the 2023 Thawley Scholar in International Security at the Lowy Institute (Sydney) and the Center for Strategic and International Studies (Washington, DC).
Saadia M. Pekkanen
Saadia M.
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