As chairman of the House Permanent Select Committee on Intelligence, Turner later added that he was “was concerned that it appeared that the administration was sleepwalking into an international crisis.” In the weeks and months that followed, the Biden administration largely confirmed Turner’s characterization of the threat, and at a CSIS event in May of 2024, assistant secretary of state for arms control Mallory Stewart seemed to identify a specific Russian satellite that was part of the Russian program, although the information provided did not clearly support the assessment or give insight into Russia’s true intentions.

Regardless of the confidence level of the intelligence, the stakes involved are too high to ignore. Any use of a nuclear weapon in space would have broad, severe, and indiscriminate effects for every nation that relies on space. Moreover, this kind of attack could undermine the very foundation of U.S. military power projection capabilities. Rather than panic or cower before the threat, the next administration must rebuild deterrence against this type of threat using history as its guide.

While the Turner memo may have been a wake-up call for some in Washington, the threat of a nuclear attack in space is not new. The Soviet Union tested this capability four times in the early 1960s at altitudes above 100 kilometers (km), which is generally regarded as the lower bound of space. Two of these tests occurred during the Cuban Missile Crisis. The United States also detonated nuclear weapons in space in the early 1960s, which is why we know just how terrible the consequences would be. In the Starfish Prime test on July 9, 1962, the United States detonated a 1.4 megaton warhead at an altitude of 400 km over the Pacific—that is nearly five times the size of the largest Soviet tests and a factor of 100 larger than the bomb dropped on Hiroshima.

The effects from the Starfish Prime experiment were stronger and more extensive than expected. Rather than merely producing a large electromagnetic pulse, the blast left a high level of radiation in low Earth orbit that lasted for several months. This radiation degraded the electrical components of satellites, such as solar cells and radios, causing some of them to fail prematurely. David Larson at Lawrence Livermore Nation Laboratory estimated that the Starfish Prime test caused at least one-third of satellites in space at the time to malfunction in the weeks and months following the test.

What the United States and the Soviet Union learned from these tests is that using or even testing nuclear weapons in space is in no one’s interest because the effects are broad and indiscriminate. In August 1963, the United States, the Soviet Union, and the United Kingdom (which lost its first satellite to the Starfish Prime test) signed the Partial Test Ban Treaty, which prohibited any further testing or use of nuclear weapons in space. The Outer Space Treaty of 1967 further extended this prohibition, banning the stationing of nuclear weapons in orbit.

Despite these treaties, the nuclear-armed nations of the world retained their ability to use nuclear weapons in space. This is because the intercontinental ballistic missiles used to launch nuclear warheads against targets on Earth can also be used to loft and detonate nuclear weapons in space. This latent capability is not banned by treaty as long as it is not tested in this manner. And it is arguably easier for less-developed nuclear powers, such as North Korea, to launch and detonate a nuclear weapon in space than trying to hit a target on Earth because the warhead does not need to survive the heat and guidance challenges of reentry.

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