On May 20, 2025, President Donald Trump stood before cameras and declared the dawn of a new era in national defense. He called it “Golden Dome.”

“Golden Dome will be capable of intercepting missiles even if they are launched from other sides of the world and even if they are launched from space,” he said.

The price tag? $175 billion. The deadline? Before the end of his term. The promise? Near-total protection from nuclear, cruise, and hypersonic missiles.

But experts say that while the ambition is clear, the science may not be on the administration’s side.

A Bullet for a Bullet

The idea of a missile defense shield covering the continental U.S. isn’t new. Since the Cold War, the U.S. has poured over $400 billion into intercepting threats that might one day arc over the planet. And the logic is understandable. An intercontinental ballistic missile (ICBM) launched at the U.S. could carry a nuclear warhead capable of killing millions of people.

Currently, the nation relies on a system known as Ground-based Midcourse Defense, or GMD. With 44 interceptors stationed in California and Alaska, it was designed to counter a small-scale nuclear attack from rogue nations like North Korea. To increase the overall effectiveness of the system, in 2020 the Missile Defense Agency proposed the layered system depicted here. Intercept attempts by the GMD system would be followed by intercept attempts by the Aegis regional midcourse defense system, and perhaps finally by a terminal defense system based on an enhancement of the existing THAAD system. But even that system, analysts say, offers only uncertain protection.

It has never been tested — and everyone hopes it won’t need to be. But that also means that it might fail in the unlikely scenario that GMD needs to intercept an incoming missile.

In its February 2025 report, the American Physical Society (APS) concluded that defending the U.S. from even a handful of ICBMs launched by North Korea is technically daunting. Extending that defense to handle the more sophisticated arsenals of China or Russia would require capabilities far beyond what the current system can deliver.

“Intercepting even a single, nuclear-armed intercontinental-range ballistic missile or its warheads . . . is extremely challenging,” said physicist Frederick Lamb, chair of the APS study group. “The ability of any missile defense system to do this reliably has not been demonstrated.”

The biggest problem? Space is a great equalizer.

Space Makes Things Complicated

Missiles don’t travel alone. In the midcourse phase — when warheads coast through space — they can release decoys and debris. Because there’s no air in space, real and fake warheads follow the same arc. Remember, a cannonball and a feather dropped from the same height on the moon will hit the ground at the same time.

“One key reason why the midcourse phase is difficult is because you’re in space, and different objects of different mass travel exactly the same,” physicist James Wells, coauthor of the APS report, told ScienceNews. “That’s been the bugaboo of midcourse intercept from the very beginning.”

Even the most successful tests of the GMD system, experts note, occur under artificial conditions. No adversary has launched a nuclear missile at the U.S. under real-world fog, confusion, and decoy-laced salvos.

Boost-phase interception — hitting the rocket just as it launches — is often touted as a cleaner solution. But that window of opportunity is short: typically under five minutes. Unless interceptors are based very close to launch sites, they can’t get there in time. That’s where Golden Dome turns to space.

Trump’s plan calls for thousands of space-based interceptors in low Earth orbit. They would hover over the planet like a high-tech net, poised to strike.

Interceptors, Hypersonics, and Orbital Overload

According to the APS report, intercepting just a single Hwasong-15 missile — a liquid-propellant ICBM that North Korea has already deployed — would require at least 400 space-based interceptors under ideal conditions. To counter a salvo of 10 such missiles launched in quick succession, that number rises to around 4,000. If the target is North Korea’s more advanced Hwasong-18 solid-propellant missile, the requirements balloon further. One would need at least 1,600 interceptors for a single launch, and 16,000 for a ten-missile attack.

The numbers become even more daunting when factoring in the need for decision time. If commanders are to have just 30 seconds to evaluate a launch and respond, the system would need roughly 36,000 interceptors in orbit to defend against a ten-missile salvo from the Hwasong-18.

For context, there are currently about 12,000 active satellites orbiting Earth — most from the commercial Starlink network.

To protect against a more formidable opponent like China or Russia the scale of Golden Dome would have to increase dramatically. These countries boast hypersonic missiles.

“You would be hard-pressed to find a system that could do that for $175 [billion],” said Georgia Tech astrodynamicist Thomas González Roberts. “Even the most optimistic assumptions behind boost-phase missile defense would suggest that that is impossible.”

The timeline is another sticking point. Trump promises a fully operational system by 2028. “That seems to me like a very aggressive timeline,” aerospace engineer Iain Boyd, a professor at the University of Colorado Boulder, wrote in The Conversation. “Putting all of this highly complex system together is likely to take more than three years.”

Still, Boyd acknowledges that with enough funding and political will, some progress is possible. “A significant amount of progress can be made in this time.”

The Iron Dome Analogy — and Its Limits

Proponents often liken Golden Dome to Israel’s Iron Dome, the short-range missile defense system that has protected Israeli cities from rockets fired by Hamas. But that comparison doesn’t hold up.

“The challenges encountered by systems attempting to defend against nuclear-armed intercontinental-range missiles are profoundly different,” notes the APS report. ICBMs travel faster and farther, often at 25,000 kilometers per hour. And while the Iron Dome might face rockets with 10-kilogram payloads, ICBMs carry warheads with the explosive power of a million tons of TNT.

Moreover, as the APS authors emphasize, a system that succeeds 80 or even 90 percent of the time is still a failure if one nuclear warhead gets through.

Political Calculus and Physical Laws

The Golden Dome, in many ways, is not just a technical proposal. It’s a political statement.

Some experts say the system could serve as a deterrent — not by offering 100% protection, but by casting doubt in adversaries’ minds. “All of the new weapons that Golden Dome will defend against are very expensive,” Boyd noted. “The U.S. is trying to change the calculus in an opponent’s thinking.”

If you can convince your adversary that most of the missiles they consider firing on you will be destroyed, this may deter a potentially disastrous nuclear confrontation. If that were to happen, the Golden Dome would truly pay for itself many times over.

But that calculus works both ways. Russia and China, already suspicious of U.S. intentions, have responded to past missile defense initiatives with new offensive weapons, including hypersonic glide vehicles, nuclear torpedoes, and fractional-orbit missiles.

A Dome or a Mirage?

The APS report stops short of calling Golden Dome impossible. But it does raise flags at every turn — physics, engineering, economics, diplomacy.

In the end, even a perfect dome can’t block out sunlight. Nor can it erase the fundamental truth that in nuclear war, defense may never be enough.

As physicist Frederick Lamb put it, “People say, ‘We got to the moon, why can’t we do this?’ Well, the moon didn’t suddenly move out of the way.”