Has a nuke been detonated in space?

There has long been speculation about whether any country has tested a nuclear weapon in outer space. The topic gained renewed interest in 2019 when the US Air Force updated its doctrine to prepare for the possibility of nuclear war extending into space. However, there is no definitive proof that any atmospheric or exoatmospheric nuclear tests have been conducted to date by any nation. Thelimited information that is available suggests some consideration of nuclear tests in space by the US and USSR during the Cold War, but an actual test most likely never occurred.

Background on Nuclear Weapons Testing

Nuclear weapons utilize a runaway nuclear fission chain reaction to create an intense burst of energy and radiation. The first nuclear weapons were developed during World War II with the Manhattan Project and initially tested on the ground at sites like Trinity in New Mexico. After the war, the US and Soviet Union began testing and developing increasingly advanced nuclear weapons, including thermonuclear weapons that use a fission reaction to ignite nuclear fusion.

Atmospheric testing refers to nuclear explosions detonated above ground or underwater. Exoatmospheric testing refers to explosions outside Earth’s atmosphere, in outer space. Hundreds of atmospheric nuclear tests were conducted from 1945-1980 before being banned by treaty. No exoatmospheric tests are known to have occurred.

US Nuclear Testing

The United States conducted over 200 atmospheric tests from 1945-1962. Many of these were initial tests of new warhead designs. The largest was the 15 megaton Castle Bravo test at the Pacific Proving Grounds in 1954.

In 1958, the US initiated a test moratorium that lasted until 1961. This was an effort to ease tensions during negotiations of the Limited Test Ban Treaty, which prohibited nuclear testing in the atmosphere, underwater and in space.

The US did consider some exoatmospheric tests during the late 1950s and early 1960s:

– Project 119 proposed a series of scientific exoatmospheric tests to study the effects of high altitude nuclear detonations. It was canceled in favor of a non-nuclear program using sounding rockets.

– Operation Fishbowl involved several high-altitude detonations in the upper atmosphere in 1962, reaching up to 250 miles altitude.

– There was a 1958 plan to detonate a nuclear warhead on the moon visible from Earth, as a display of US weapon capabilities. This was never carried out.

Ultimately, no fully exoatmospheric tests were conducted by the US. The Partial Test Ban Treaty went into effect in 1963, limiting the country to underground testing until the early 1990s.

Soviet Nuclear Testing

The Soviet Union carried out over 200 atmospheric tests from 1949-1962. Their program lagged several years behind the US in producing advanced thermonuclear weapons. The largest Soviet test was the 50 megaton Tsar Bomba in 1961.

During the late 1950s, the Soviets proposed negotiating a ban on nuclear testing in outer space. At the time the US held a advantage there, having already developed smaller, more compact warheads capable of being lofted to high altitudes or orbit. The USSR wanted to forestall any US exoatmospheric tests that could enable advances like nuclear-powered satellites or orbital bombing.

There is some evidence the Soviet Union may have considered conducting clandestine exoatmospheric tests, despite agreeing to ban them:

– In 1957, the Soviets attempted to launch an R-7 rocket carrying a mock nuclear warhead on a test flight into the Kamchatka peninsula. The rocket exploded before leaving the atmosphere. Some dispute whether this was an intended exoatmospheric test.

– On October 27, 1960, the Soviets detonated an unspecified device in the Kura test range at 80-100 km altitude, according to US intelligence reports. Some researchers claim this could have been a low-altitude nuclear test, but there is limited evidence.

Like the US, the USSR never conducted a fully exoatmospheric nuclear detonation before agreeing to the Partial Test Ban Treaty in 1963. All subsequent Soviet tests through 1990 were underground.

The Limited Test Ban Treaty

The Limited Test Ban Treaty (LTBT) entered into force in October 1963. The LTBT prohibits nuclear weapons tests “in the atmosphere, beyond its limits, including outer space, or under water, including territorial waters or high seas.”

The treaty was signed by the US, UK and Soviet Union, and since ratified by over 100 other countries. Major nuclear powers like France and China have also signed and pledged to uphold the LTBT.

The LTBT succeeded in ending the risks posed by radioactive fallout from atmospheric testing. It has prevented nuclear weapons use and testing in Earth orbit, on the Moon, and elsewhere in outer space. The treaty lays the foundation for broader efforts to prevent militarization and limit weapons testing in space.

Monitoring for Violations

Verification measures are limited under the LTBT, but include data sharing among parties and citizen radiation monitoring networks. Violations would also be detectable via radiation signatures and seismic monitoring. For example, a nuclear test on the far side of the Moon might be observable from Earth via electromagnetic signals or as a pattern of seismic tremors through the lunar body.

No credible evidence of LTBT violations through exoatmospheric nuclear testing has been substantiated. The US and Russia both halted atmospheric and underwater testing in 1963. Their adherence to the treaty was mutually reinforcing, as either country cheating would have risked severe geopolitical consequences.

Space Nuclear Weapons Today

While the LTBT bans nuclear testing and explosions in outer space, it does not wholly prohibit the orbiting of nuclear-armed satellites or development of space-based nuclear weapons.

The US and USSR both worked on concepts like Fractional Orbital Bombardment Systems (FOBS) during the Cold War. FOBS would have put nuclear warheads into low altitude orbit, enabling surprise attack against any point on Earth. While Soviet FOBS satellites were tested without live warheads, nuclear-armed systems were never deployed.

The 1967 Outer Space Treaty (OST) did establish space as a peaceful domain and prohibited stationing or testing weapons of mass destruction anywhere in outer space, including celestial bodies like the Moon. The OST bans military bases and weapons testing on terrestrial bodies, but does not limit weapons in orbit like FOBS.

Today the US, Russia, China, and several other nations rely onspy satellites for intelligence and communication. There are concerns about emerging technologies and potential new threats in space:

– Anti-satellite (ASAT) weapons that could attack spacecraft
– Dual-use spaceplanes like the US X-37 that could in theory deploy weapons
– Advances in hypersonic glide vehicles and orbital bombardment systems
– Cyberattacks against space-based assets

However, there is still no conclusive evidence any country has tested or deployed an actual nuclear weapon in outer space since the LTBT entered into force. Developing and flying a modern nuclear-armed satellite would face significant technical and geopolitical challenges.

The Future of Space Nuclear Weapons

Looking ahead, space could become an arena for nuclear conflict in several ways:

1. Attacks against satellites

Satellites vital to communication, surveillance and targeting could be disabled using conventional ASATs or nuclear electromagnetic pulse (EMP) attacks in orbit. This could happen during a major war as an attempt to gain advantage on Earth. However, it would still risk escalation.

2. Orbital nuclear weapons

Countries like the US, Russia and China may reconsider concepts like FOBS for rapid global strike capability. Nuclear-armed spaceplanes have also been proposed. However, any deployment of space-based nuclear weapons would likely spark an escalating new arms race.

3. Lunar or deep space tests

Testing nuclear weapons on the Moon or elsewhere for research or as grand strategic gestures could return if the LTBT weakens. However, this would damage space cooperation and carry environmental risks. Public opposition has so far discouraged these ideas when they’ve been raised.

In summary, the prospect of nuclear conflict extending into space is real, but testing or deploying nuclear weapons beyond Earth’s atmosphere remains a serious taboo. The LTBT has been an effective brake on exoatmospheric weaponization since 1963. With effort and engagement between leading spacefaring nations, its prohibitions can continue holding for the foreseeable future.


There is no definitive evidence that any atmospheric nuclear tests have been conducted in space to date. The United States and Soviet Union considered exoatmospheric tests during the Cold War, but never carried them out before agreeing to the LTBT in 1963. While military space capabilities and potential threats have advanced since then, the LTBT has so far endured as a bulwark against nuclear weapons testing and use in outer space. Maintaining the LTBT will be vital to preventing dangerous escalation as security challenges arise in the space domain going forward. With renewed commitment and proper verification, the LTBT can continue preventing nuclear weaponization beyond Earth’s atmosphere in the decades to come.

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