In 1982, President Ronald Reagan was considering what became known as “Star Wars,” a plan to shield America from Soviet missiles by deploying up to thousands of weapons in space. At the same time, as a young science writer, I was reporting on how the rays from a single nuclear detonation in orbit could wipe out whole fleets of battle stations and laser death rays. “Star Wars: Pentagon Lunacy,” read one of the headlines.
Decades later, Mr. Reagan and the Soviet Union are gone, but anxiety over a high-altitude nuclear blast lives on, brought back most recently by the ostensible war aims of the Russian president Vladimir V. Putin. Last month, American spy agencies told Congress, as well as foreign allies, that Mr. Putin might deploy and use an atom bomb in space that could disable thousands of satellites. Not only military and civilian communication links would presumably be at risk, but also satellites that spy, track the weather, beam broadcasts, empower cellphone maps, form internet connections and perform dozens of other modern tasks.
The mere claim of such a deployment may help Mr. Putin frighten his adversaries.
“Its purpose is the same as Star Wars was for us in the ’80s,” said Jonathan McDowell, an astrophysicist who publishes a monthly space report. “It’s to scare the other side.”
But for actually fighting a war, analysts say, the step is hard to imagine — unless Mr. Putin wants some of his most important allies and supporters to face the prospect of unspeakable pain.
Five nuclear experts in a 2010 study explained how astronauts hit by the most powerful rays would experience two to three hours of nausea and vomiting before the radiation sickness left them facing “a 90 percent probability of death.”
The International Space Station typically holds seven astronauts — three Americans, a foreigner and — you guessed it — three Russians. The rays could also turn the space station of Mr. Putin’s top ally, China, into a death trap. Beijing’s shiny new outpost currently holds three Chinese astronauts and is set to expand to accommodate even more.
China’s satellites — 628 by a recent count — would pose an additional vulnerability. Stephen M. Younger, a former director of Sandia National Laboratories, which helps make the nation’s nuclear arms, said in an interview that a Russian space blast could blind China’s reconnaissance satellites and thus end the country’s principal way of tracking the U.S. Navy’s Pacific Fleet.
“That’s not going to go over very well,” Dr. Younger said of Beijing’s wartime loss of its eyes in the sky.
Mr. Putin’s purported bomb move, he added, represented more bluster than a serious war plan. “Putin’s not stupid,” he said.
The whole idea behind nuclear weapons, said David Wright, a nuclear expert at the Massachusetts Institute of Technology, is that “you’re self-deterred in part because the arms would cause significant collateral damage to yourself and other countries.” Such deterrence could apply to a space bomb as well, he added, unless an attacker were desperate and saw the risks as acceptable.
“It would be dangerous for the Russians themselves,” said Richard L. Garwin, a physicist and longtime adviser to the federal government who helped design the world’s first hydrogen bomb.
Ever since Mr. Putin invaded Ukraine, he has made atomic threats that analysts see as central to his strategy of deterring Western intervention. If he stationed an atom bomb in orbit, it would violate two bedrock treaties of the nuclear age — signed in 1963 and 1967 — and signal a major escalation.
On Feb. 20, Mr. Putin denied that he intended to loft a nuclear weapon into orbit. “Our position is clear,” he said. “We have always been categorically against and are now against the deployment of nuclear weapons in space.”
But days later, on Feb. 29, in his annual state-of-the-nation address, he reverted to his usual saber-rattling, warning that the West faced the risk of nuclear war. Mr. Putin singled out states that have helped Kyiv strike Russian territory. The West must understand, he declared, that such assistance risks “the destruction of civilization.”
Nuclear arms in general, and space bombs in particular, are the antithesis of precision. They are indiscriminate — unlike conventional arms, which are typically characterized by pinpoint accuracy. In 1981, when I first wrote about orbital nuclear arms as a reporter for Science magazine, I referred to the mayhem from outer space as the “Chaos Factor.”
The unexpected phenomenon flashed to life in July 1962 when the United States detonated a hydrogen bomb some 250 miles above the Pacific Ocean. Dark skies lit up. In Hawaii, streetlights went out. In orbit, satellites failed.
President John F. Kennedy, unsettled by the technical surprises, worried that lingering radiation from nuclear blasts would endanger astronauts. In September 1962, he canceled a test code-named Urraca. The hydrogen bomb was to have been detonated at an altitude of more than 800 miles — the highest of any test explosion, American or Soviet. The next year, Mr. Kennedy signed a treaty that banned experimental blasts in space.
The scientific world was then making an important distinction about the space detonations that is absent in most current discussions. It is that the atomic blasts have immediate, as well as residual, effects.
The initial repercussions are best known. A bomb’s rays speed across vast distances to produce lightning-like bolts of electricity in satellites and ground networks, frying electrical circuits. Experts call them electromagnetic pulses, or EMP. The pulses turned out the lights in Hawaii.
But what caught Mr. Kennedy’s attention was a longer-term effect — how radioactive debris and charged particles from a nuclear blast pump up the natural, donutlike belts of radiation that encircle the Earth. These belts are intense, but nothing like what they become when amplified by a bomb’s radiation.
The five nuclear experts who authored the 2010 study linked such belt overloading not only to astronaut risks but also, after the July 1962 test, to major damage to at least eight satellites. The most famous casualty was Telstar, the world’s first communications satellite.
Over the years, I grew concerned that the complicated topic was being oversimplified. Fringe groups and hawkish politicians sounded alarms over Russian EMP attacks on the nation’s electrical grid, though they seldom noted the risk to Moscow’s own spacecraft and astronauts.
Peter Vincent Pry, a former C.I.A. officer, warned in a 2017 report that Moscow was prepared for surprise EMP attacks that would paralyze the United States and wipe out its satellites.
In 2019, President Trump ordered the strengthening of the nation’s EMP defenses. Rick Perry, the secretary of energy, said the order “sends a clear message to adversaries that the United States takes this threat seriously.”
National security experts know how weapons of mass destruction become caught up in cycles of fear that come and go with the political winds. After decades of reflecting on the basics of nuclear blasts in space, I have come to see the risks as extremely low to nonexistent because a detonation — as Drs. McDowell, Younger, Wright, Garwin and others have argued — would harm not only the attacked, but also the attacker.
“Maybe the Russians will decide their astronauts have to take one for the homeland,” Dr. McDowell said. “But I think that Putin, crazy as he is, is not going to do that.”
