President Trump has told the Pentagon to take another look at missile defense. Technology to shoot down missiles has existed for decades, but the kind of missile shield Trump is looking to build would be much more complex -- and expensive.
A key part of the new missile defense system, which Trump described as "Golden Dome" in a speech earlier this year, will likely be space-based interceptors, according to experts and an executive order signed by the president.
A number of defense companies have expressed interest in trying to build the Golden Dome. Last week, Reuters reported that Elon Musk's firm SpaceX had joined a bid for the project. Musk later refuted that claim in a post on X.
Here's why a critical part of Golden Dome might be built on the final frontier, and what building such a system would involve.
Golden Dome would be very different than Israel's Iron Dome
Trump's speech to Congress and his executive order have both referenced Israel's Iron Dome missile shield.
Iron Dome has proven itself incredibly effective during Israel's latest wars at intercepting missiles and rockets. It depends on a powerful network of radars, computers, and interceptor missiles to defend cities and military sites throughout the country.
But building Iron Dome is a much more modest proposal than building a Golden Dome.
"It's the difference between a kayak and a battleship," says Jeffrey Lewis, a professor at the Middlebury Institute of International Studies at Monterey, who studies missile defenses.
A big part of that difference is the size of the landmass that needs to be protected — Israel is more than 400 times smaller than the United States, and it's mostly flat desert that's easy to defend.
The missile threat is fundamentally different for America
"Iron Dome, fundamentally, is designed to deal with slow moving, short-range projectiles," Lewis says.
For the most part, it shoots at missiles and rockets fired from near the border that can typically fly just tens of miles.
But the missiles Russia and China have pointed at the U.S. are completely different. They include huge, powerful intercontinental ballistic missiles that soar into space and shriek back to Earth at hypersonic speeds. Iron Dome could never intercept them.
In fact, these bigger missiles are hard for any existing missile defense system to intercept, says Laura Grego, a physicist at the non-profit Union of Concerned Scientists. The best thing to do is try to hit these ICBMs right as they're launching from their silo, but "the launch phase of those missiles only lasts three to five minutes, so you only have some hundreds of seconds that you have available to catch them as they're launching."
In order to catch these missiles, Golden Dome must have the high ground
This leads to the third big difference between the real Iron Dome and President Trump's futuristic Golden Dome — to hit these missiles early, a Golden Dome will likely need to include technology in space.
The idea is to have satellites in orbit that could spot missiles as they leave the ground and then shoot them at the beginning of their flight.
It's a system that's been thought of before. The problem, says Grego, is that the Earth is really big, and satellites spin around it really fast.
In order to ensure you have a satellite in position above the right patch of Earth, "you need a lot of things in space in order to have them at the right place at the right time," she says.
Grego was part of an independent panel set up by the American Physical Society, which took a look at missile defense. Earlier this year, they concluded a constellation of about 16,000 interceptors would be needed to attempt to counter a rapid salvo of about 10 solid propellant ICBMs similar to North Korea's Hwasong-18 missiles.
A huge constellation is possible to build but would be expensive
The idea of having 16,000 satellites in orbit seemed impossible, until recently. Elon Musk's company SpaceX has been building a constellation of internet satellites called Starlink.
It has put around 7,000 satellites in orbit, with plans to launch thousands more.
According to the Reuters article, SpaceX was looking at partnering with defense tech firms Palantir and Anduril. The constellation would include hundreds of missile sensing and attack satellites, the report claimed.
In his post on X, however, Musk said "our strong preference would be to stay focused on taking humanity to Mars. If the President asks us to help in this regard, we will do so, but I hope that other companies (not SpaceX) can do this."
Separately, the consulting firm Booz Allen Hamilton recently unveiled a proposal for a system of 2,000 anti-missile satellites it said could provide a good initial defense, in conjunction with other systems. The constellation's satellites would act as both sensors and interceptors — some satellites might detect the launch and then others passing near would whizz off to strike the incoming missile.
The firm believes it could field the constellation for $25 billion, "and that would include the R&D, etc.," says Trey Obering, an executive vice president at Booz Allen Hamilton who formerly served as the head of the Pentagon's Missile Defense Agency during George W. Bush's administration.
Lewis thinks the numbers for Booz Allen's constellation could end up being higher. Moreover, he points out, the constellation would require new satellites to be continually added, because gradually these satellites would fall out of their orbits. "That's $4 to $5 billion a year just to sustain," he points out.
If Golden Dome gets built, America's rivals might adapt
Still other experts say it is the time to take another look at space-based systems, and Trump's Golden Dome proposal provides that opportunity.
"It's a welcome development and it's, in some respects, overdue," says Tom Karako, director of the Missile Defense Project at the Center for Strategic and International Studies. Karako says the wars in the Middle East and in Ukraine show why missile defense is needed. Non-nuclear missiles have become a go-to weapon, he says, and Golden Dome could serve as a powerful deterrent.
"I don't want to just deter a nuclear exchange, I want to deter a conventional war with China and Russia and we do that by raising the threshold," he says.
But Lewis is more skeptical. Conventional wars aside, he says, Russia and China still depend on nuclear weapons to maintain a strategic balance with America. If we try to build a Golden Dome, he warns, they will rapidly expand and upgrade their nuclear arsenals in response.
"We will end up with vastly larger Russian and Chinese nuclear forces. We will end up with the Russians and the Chinese having all kinds of crazy sci-fi weapons," he says. "In short we will end up spending tens if not hundreds of billions of dollars to be in, at best, the same place we are today, and most likely a much worse place."
It could spark a new nuclear arms race, he warns, and Russia may already be preparing. The U.S. believes it's experimenting with ways of putting nuclear weapons in space, in order to destroy large constellations of satellites like the ones needed for Golden Dome.
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