“Though Russia’s pursuit of this particular capability is troubling, there is no immediate threat to anyone’s safety,” Kirby said. “We are not talking about a weapon that can be used to attack human beings or cause physical destruction here on Earth. That said, we’ve been closely monitoring this Russian activity, and we will continue to take it very seriously.”

The capability is a nuclear-armed — not a nuclear-powered — weapon, said two U.S. officials, who like others familiar with the intelligence spoke on the condition of anonymity to discuss sensitive information. ABC News first reported that Russia was seeking to deploy a nuclear weapon.

Revelations that Russia is developing a new kind of space weapon have brought back fears about the use of nuclear weapons in space that go back to the Cold War and the dawn of the Space Age.

Space today is nothing like it was in 1957, when the Soviet Union’s launch of Sputnik triggered a years-long space race that culminated with the United States’ moon landing in 1969. Now, there are thousands of satellites whizzing in orbit at dizzying speeds that enable everything from the blue-dot GPS signal on your phone to the image on your television. And a conflict in space that affected those satellites would have wide-ranging implications, not just for the world’s militaries but for civilians around the globe.

Deploying such a weapon would be highly escalatory and “mark a crossing of the nuclear threshold,” said Ankit Panda, a nuclear policy fellow at the Carnegie Endowment for International Peace.

“It would irreparably damage the low Earth orbit environment,” Panda said. “We would potentially be looking at a cascade of collisions of defunct satellites that would render large bands of low Earth orbit effectively unusable for all of humanity.”

Since the start of the war with Ukraine, the use of commercial satellites to track Russian troop movements, provide internet and communication links to the ground, and detect missile firings and guide precision munitions has heightened concerns that Russia might target those systems as well as official U.S. military and intelligence satellites.

Commercial satellites test the rules of war in Russia-Ukraine conflict

For years, Pentagon officials have warned that their satellites are vulnerable to attack, and Russia, China and others have proved them right. In 2007, China fired a missile that destroyed a dead weather satellite. In 2021, Russia hit another dead satellite.

Exactly what the new Russia weapon is remains unclear, but the system is a “serious national security threat,” said Rep. Michael R. Turner (R-Ohio), chairman of the House Intelligence Committee.

“I am requesting that President Biden declassify all information relating to this threat so that Congress, the Administration, and our allies can openly discuss the actions necessary to respond to this threat,” Turner wrote in a statement Wednesday.

In his briefing to reporters Thursday, Kirby said only that the system is “an antisatellite capability that Russia is developing.”

He said that the administration intended eventually to declassify information about the Russian system but that the information was prematurely made public, following Turner’s cryptic public statement. “The intelligence community has serious concerns about a broad declassification of this intelligence,” Kirby said, in a not-so-subtle criticism of Turner for getting ahead of the administration’s process and setting off a media frenzy about the Russian system.

Many national security space experts believe that a nuclear-powered weapon is more plausible than a warhead. But if the weapons system Turner warned about is, in fact, a nuclear bomb, its use would amount to a “suicide kamikaze attack,” said Todd Harrison, a senior fellow at the American Enterprise Institute. Russia has a host of its own military and intelligence satellites in orbit that also would be affected by a nuclear detonation.

“You destroy yourself but hurt the other guy in the process,” he said. “If Russia tried to use a nuclear weapon in space, it would be sloppy and reckless. It would affect satellites indiscriminately, including their own.”

The installation of a nuclear weapon in space also would be a violation of the 1967 Outer Space Treaty.

“The one inviolable law and consensus agreed to in international space law is: Do not place nuclear weapons in orbit, on the moon or on celestial bodies,” said Brian Weeden, director of program planning at the Secure World Foundation, a think tank. Given the strict nature of the treaty and its widespread adoption, detonating a nuclear warhead in space “doesn’t make sense politically,” he said. “It completely destroys any credibility they have with the United Nations, and with the Chinese.”

According to a report by the Center for Strategic and International Studies, a “nuclear detonation in space would immediately affect satellites within range of its EMP [electromagnetic pulse], and it would also create a high-radiation environment that would accelerate the degradation of satellite components over the long term for unshielded satellites in the affected orbital regime.”

That could include China’s satellites as well as the inhabited space station China has assembled in low Earth orbit.

“It would turn the whole world against them, and I mean including China and Latin American countries, and India as well,” Harrison said. “They would screw everyone if they used a nuclear EMP weapon in space.”

The International Space Station, which is run jointly by the space agencies of the United States, Russia, Europe, Japan and Canada, would also be affected by a nuclear detonation. But that hasn’t stopped Russia’s aggressive tactics in space before.

In 2021, when Russia blew up the dead satellite, it created a debris field so large it threatened the ISS and forced its occupants, including Russian cosmonauts, to prepare for an emergency evacuation.

“As space gets more and more crowded, you would not be eager to cause widespread destruction in orbit,” said Jack Beard, director of the space, cyber and national security law program at the University of Nebraska College of Law. “The Russians have shown their recklessness with their antisatellite mission. It was an irresponsible move that hurt everyone, including them. So they’re not beyond doing reckless saber rattling.”

During the Cold War, the United States looked into nuclear-armed antisatellite weapons, Panda said. “But we don’t have such a capability anymore,” he said. No country does, though U.S. officials say Russia is apparently developing one. “Militaries don’t tend to value space weapons with indiscriminate effects,” he said.

Last year, in unveiling a new strategy for the U.S. Space Force, Gen. Chance Saltzman, chief of space operations, said its “counterspace activities may be necessary to prevent adversaries from leveraging space-enabled targeting to attack our forces. But we will balance our counterspace efforts with our need to maintain stability and sustainability of the orbits we are required to use.”

The United States has led an international moratorium on destructive antisatellite attacks, which generate dangerous debris fields in space, and probably would not fire a missile in response, Weeden said. Still, the Pentagon has a “whole list of capabilities” at its disposal to thwart an attack, he said, including electronic warfare and cyberattacks on ground stations. But defending against attacks in space is complicated and depends on what the threats are, he said.

In a contingency, depending on the altitude at which such a weapon was deployed, it may be possible for the United States to repurpose a missile defense interceptor to take something like this out in low Earth orbit, Panda said.

A nuclear weapon has been detonated in space before, by the United States, in 1962. Called Starfish Prime, the 1.4 megaton bomb, more powerful than the atomic bomb dropped on Hiroshima in World War II, detonated at an altitude of about 250 miles and knocked out about “one-third of the satellites on orbit,” Harrison said. “It affected our satellites. It even destroyed the U.K.’s first-ever satellite that was only launched a few months earlier.”

The effects of such a blast “are going to be felt for weeks and months,” Weeden said, because of the lingering radiation it would create.

Russia has grown increasingly concerned about the proliferation of the constellations of commercial satellites in orbit, such as those from companies such as Maxar and Planet, that have allowed real-time imagery of the war as it has unfolded. Other constellations, such as SpaceX’s Starlink internet system, which now has about 5,400 satellites in orbit, have allowed Ukraine to remain online during the Russian onslaught and have served as a communications lifeline for the war-torn country.

The capabilities are the result of a revolution in manufacturing that has allowed satellites to become smaller and relatively inexpensive, yet still enormously robust. Instead of putting up just a few large and expensive satellites that serve as easy targets, the Pentagon has increasingly looked to “proliferated architectures” where hundreds, even thousands, of satellites swarm around the globe. If one goes out, another can replace it.

Still, Moscow has experimented with its Tobol electronic warfare systems in a bid to disrupt Starlink’s transmissions in Ukraine, according to a cache of sensitive materials leaked online last year through the messaging platform Discord. It did not indicate whether any of Russia’s tests with the Tobol system were successful. But Pentagon officials have said that Russia has tried unsuccessfully to jam Starlink’s constellation.

The Pentagon’s reliance on commercial technology has even been codified in the National Defense Strategy released by the Defense Department in 2022: “We will increase collaboration with the private sector in priority areas, especially with the commercial space industry, leveraging its technological advancements and entrepreneurial spirit to enable new capabilities.”

Eight months after Russia’s invasion of Ukraine in 2022, Lt. Gen. John Shaw, then the deputy commander of U.S. Space Command, said that he was “certain that my counterpart in Russia, whoever that is, is not very happy with Starlink, as it’s assisting Ukraine. And with commercial imagery, such as Maxar’s products, that are plastering all over the world news the things that are going on, I don’t think they’re very happy about that either. And we know that they’re probably going to take steps to try to stop those commercial services because they run counter to Russia’s national interest.”

A few days later, during a meeting at the United Nations, Konstantin Vorontsov, deputy director of the Russian Foreign Ministry’s department for nonproliferation and arms, said in a speech that the proliferation of privately operated satellites is “an extremely dangerous trend that goes beyond the harmless use of outer-space technologies and has become apparent during the latest developments in Ukraine.”

He warned that “quasi-civilian infrastructure may become a legitimate target for retaliation.”

A nuclear-powered weapon, such as an electronic warfare or directed energy system, would make more sense than a nuclear warhead, several space national security experts have said, because it could be targeted more precisely, frying onboard computers or rendering satellites blind.

Russia has been developing such weapons for some time, according to the Secure World Foundation. In a report last year, it wrote that a “nuclear reactor would be powerful enough to support jammers operating on a wide range of frequencies and interfering with electronic systems over a wide area,” including some of the orbits where the Pentagon parks its most sensitive satellites.

Such a system “is much more plausible than the ‘nuclear bomb asat’ [antisatellite weapon],” Jonathan McDowell, of the Harvard-Smithsonian Center for Astrophysics, wrote on X. “The Soviet Navy had a long record of launching reactor-powered radar satellites (from 1970 to 1988), so this would not be a new power capability for Russia, but it would be its first use in a space-based weapons system.”

“I suspect they might want to use it against one of our big, juicy targets,” he said. “For some of our military systems, you only have to take out a couple of satellites to have a huge effect.”