Physicists and engineers now realize that just as most car crashes stem from driver error rather than mechanical failure, the same logic applies to nuclear weapons, their platforms, and their potential use. Whether Americans like it or not, humans are in the system and humans are, almost certainly, the weakest link.

Humans are the weakest component in the quantification of margins and uncertainty (QMU) sense. Engineers often test individual components and larger systems of nuclear weapons to a 1-in-1,000 certainty that they will function correctly. There has long been a view that nuclear weapons should always detonate when employed and never when they are not. To achieve this “always/never” goal, systems are engineered to perfection while largely ignoring sources of human error.

Humans design and manufacture the components, assemble the weapons, complete the wiring, and install systems onto delivery platforms (i.e., subs, silos, and bombers). Humans verify satellite signals of potential attacks from US Strategic Command, communicate those findings to the President, and, depending on the response, draft and transmit emergency action messages (EAMs). This is a gross simplification because fragile humans play a much larger role, but it illustrates the embeddedness of the human element in the system.

One example of human fragility that took place in September 2023 at the Pantex Plant is instructive. It appears a worker mistakenly cross-connected color-coded electrical wires inside a nuclear weapon.

Across the world this very task might be performed by a civilian or by an Air Force 2W2X1 Nuclear Weapons Specialist. At first glance, it seems simple; connect the red wire to the red wire and the green wire to the green wire. But around 8 percent of men are born with red-green color vision deficiency (color blindness) that makes it difficult for them to differentiate between red and green (and many other color combinations. The US Air Force correctly requires normal color vision for this role.

Not all color tests are created equal. Some vision tests catch 99 percent of people with colorblindness and others catch 90 or even 50 percent of colorblind individuals. An analogy may be useful in illustrating this point.

If, for example, a worker was testing a component and needed to detect 14MeV neutrons, a detector that simply says “between 2 and 20 MeV neutrons were detected” would be unacceptable. A tester with adequate sensitivity is required to test critical components. Detectors that verify the specific reading may even be required. Sensitive tests for humans who work on nuclear weapons is also required.

The Federal Aviation Administration (FAA) recently updated its standards, rejecting the century-old Ishihara color vision test and the D-15 test due to known shortcomings. The Ishihara test is fairly good at detecting red-green defects but will miss 100 percent of blue (Tritan) defects. Humans have red, green, and blue light sensitive cones in their eyes, and the Ishihara only tests two cones and ignores blue vision entirely. The D-15 test can pass up to half of individuals with color blindness, depending on how its administered (a test commonly used by police departments).

Figure 1. Simulated Color Vision Defects and Wire Color

Even if Pantex adopted one of the FAA’s “best in class” tests, such as the CAD, Rabin, or Waggoner Computerized Color Vision Test (WCCVT), there is still another issue—test frequency. Color vision should be tested periodically, not just once.

While 8 percent of men and 0.5 percent of women) are born with color blindness, it is expected that 15 percent of all people will develop an acquired color vision deficiency during their lifetime, most often affecting blue vision. Most people assume color vision is a static ability, but it is more like hearing loss, which is impacted by age and environmental factors.

Changes in color vision ability can occur rapidly due to medications, diseases, or environmental conditions. For critical roles, annual color vision testing should be a minimum standard.

Finally, different color vision tests examine different axes within the visible spectrum of light, meaning that a person could pass the Rabin but fail the WCCVT based on individual differences and the specific axis tested by each test. This is truer for mild vision defects but mild defects can still cause sub-par performance on real world tasks (i.e., reacting to red traffic lights).

Across the United States, teams are working to quantify this human element in complex, high-consequence systems. These include the Air Force’s 711th Human Performance Wing and the social scientists at Sandia National Laboratories.

The next time you hear about a cognitive psychologist, industrial-organizational psychologist, or human factors researcher at a national lab, do not assume they’re experimenting with LSD and goats to perfect psychic warfare. They’re far more likely to be studying how humans interact with technology—quantifying behavior, limitations, cognition, and the human’s reliability within critical systems.

Organizations should, whenever possible, bring these human-focused professionals into projects. They will identify issues most engineers never consider across a variety of scales, “from neurons to nations.” Factors like color vision, tool slips, (as in the Louis Slotin “demon core” incident), dropped sockets (as in the Titan II missile explosion in Damascus, Arkansas), mismatched job abilities, fatigue, attention lapses, and even intentional sabotage can all impact the nation’s deterrence posture. When processes are optimized to include the human, overall risk is minimized.

In the end, deterrence is not just about weapons. It is about the humans behind the weapons, the fallible, unpredictable, indispensable human element that remains both our greatest strength and our greatest risk.

Rob Kittenger, PhD, is a Senior Fellow at the National Institute for Deterrence Studies. The views expressed are his own.

Meet the Human in Nuclear Deterrence was originally published on Global Security Review.

Recent scientific research at Sandia National Laboratories proves that carefully aimed nuclear detonations in space, early enough in an object’s approach to Earth, can deflect a threatening comet or asteroid by enough to put it on a safe trajectory. The idea is not to try to pulverize the object by a direct hit, which might still shower Earth with debris. Rather, by detonating the warhead at a modest distance from the object, the forceful ablation (evaporation) of one side of its surface, induced by the intense X-ray of a nuclear detonation, would cause the entire object to move away from the detonation.

This would be an example of what has been called a peaceful nuclear explosion (PNE). Back in the early Cold War, the US Atomic Energy Commission looked into potential applications of nuclear detonations for peaceful civil engineering purposes. These included digging canals, creating harbors, and moving mountains. And yes, fallout was expected, which is why these terrestrial applications were abandoned. An underground nuclear blast was also tested as a way to extract natural gas, by creating in some geologically promising area a subterranean cavity that could then be tapped. The test was not a success because the natural gas was radioactive.

Later, India’s first successful nuclear test (1974) was announced as a peaceful nuclear explosion, for oil extraction and mining purposes, not a weapon test. Then, in 1976, the U.S. and the USSR signed the Peaceful Nuclear Explosions Treaty, which permitted such blasts anywhere on Earth if the host country gave permission. Thus, there is some precedent for the use of nuclear devices for peaceful purposes.

Certainly, non-nuclear methods for diverting menacing space objects are possible. For instance, the National Aeronautics and Space Administration’s (NASA) test-demonstration DART high-velocity inert impactor mission was successful. But the object whose orbit was changed slightly was a very small moonlet of a slightly less-small asteroid. Other techniques being studied include attaching rocket motors to a threatening object or moving it aside via space tugs deploying giant nets. Such motors or tugs could be driven by chemical engines, or non-explosive nuclear propulsion, or solar power (either solar panels, or light sails).

These latter techniques are years or decades away from meaningful deployment. Due to their lower specific energy compared to a PNE, they would need for the inbound object to be detected very early and to be comparatively small.

For the largest potential Earth-bound objects, especially those coming from sunward, which can make them hard to detect very early, peaceful nuclear explosions might be an essential diversion method.

Obviously, such use of nuclear devices, well away from any people living on Earth or in space, would be for the benefit of mankind. However, nuclear devices can also be deadly weapons of war. They are indeed being looked at by America’s adversaries for purposes of space-based coercion and blackmail and even warfighting in space. Examples include Russia’s “Sputnuke” and China’s fractional orbital bombardment system. Effective strategic deterrence thus continues to require American preparedness and vigilance, throughout the cislunar and beyond the Moon.

However, nuclear explosives in space are truly a dual-use technology. There are already copious amounts of natural hard radiation throughout the solar system. An asteroid- or comet-moving PNE blast’s fallout would dissipate relatively harmlessly.

PNEs in space raise troubling but pressing questions about the need to rethink and update the Outer Space Treaty, since it prohibits placing any nuclear devices anywhere in space. On the one hand, all nuclear weapons based on-orbit should continue to be forbidden. But on the other hand, the same warheads used to defend Earth against space rocks simply must be allowed.

This might be achieved in one of two ways. One is to create a “Planetary Defense Guard” under the auspices of the UN, with the necessary nuclear devices put under UN Security Council control. However, the UN does not have a record of success regarding cooperative use of nuclear devices. A proposed plan in the early Cold War called for all nuclear arms to be pooled under central UN control. It went nowhere. The modern UN attempt at a treaty banning all nuclear devices everywhere (including PNEs) is also going nowhere, for the same reason. States owning nuclear warheads have no desire to give them up.

The other way to get the protection Earth requires is to recognize that planetary defense is a necessary and unavoidable aspect of the “Scramble for the Skies” now emerging. In this alternate scheme, rival powers compete using nuclear devices in a peaceful way for space-based civil engineering purposes. They vie to develop the best suite of proprietary systems, procedures, and technologies for deflecting Earth impactors via peaceful nuclear explosions. They could then also “race” to launch them whenever actually needed. Such healthy competition might significantly increase the odds of at least one contender making a successful diversion, while letting all contenders participate in this ultimate “space Olympic decathlon.”

Changing the OST out of sheer necessity, to allow PNEs for planetary defense, would have several very significant societal benefits. It would more rapidly and effectively advance humanity’s space defenses. It would urgently accelerate everything needed for the successful commercialization, industrialization, and colonization of space, which advocates say could take pressure off Earth’s endangered environment, too.

Allowing PNEs in space would also give spacefaring nuclear powers a way to stay within Cold War–style safety guardrails against nuclear crises and nuclear war. It would allow them to instead compete to show their culture’s and their government’s superiority through the peaceful, beneficial harnessing of both spaceflight and nuclear energy. Such a grand competitive program would help address three existential threats to the human race at once, three possible extermination events: a large asteroid strike, a climate catastrophe, and a nuclear holocaust.

Joe Buff is a Senior Fellow at the National Institute for Deterrence Studies.

Nuclear Devices in Space was originally published on Global Security Review.