A national missile defense system like President Trump’s proposed “Golden Dome” could cost taxpayers $1.2 trillion over 20 years, according to a government report issued on Tuesday.
To protect the continental United States, Alaska and Hawaii would require four separate layers of defensive assets, the analysis said, including several thousand satellites as well as a half-dozen radar and missile sites to engage intercontinental ballistic missiles and 35 new regional sites to defend against hypersonic missiles and cruise missiles.
Even if the system is built, the report concluded, an adversary like Russia or China that has a large arsenal of nuclear weapons could overwhelm it and some missiles would hit their targets.
The estimate was provided by the nonpartisan Congressional Budget Office using an executive order issued by Mr. Trump in January 2025 as a blueprint.
Mr. Trump has vowed to build a defense system similar to Israel’s Iron Dome, with air defense capabilities that intercept rockets and missiles. He estimated that the project would cost $175 billion.
The budget office report found that the “space-based interceptors” the president envisions — satellites armed with missiles orbiting the planet — would consume about 60 percent of the cost.
The C.B.O. assumed that countering as many as 10 enemy intercontinental ballistic missiles in space simultaneously could require a constellation of roughly 7,800 armed satellites.
To be effective, such space-based interceptors, the C.B.O. said, would need to be placed in low orbit where they would be subject to drag from the planet’s atmosphere — which over a five-year span could cause them to lose enough altitude that they would burn up and need to be replaced.
Tom Karako, a missile defense expert at the Center for Strategic and International Studies, said the C.B.O. report makes several assumptions about the project, including the number and types of space-based interceptors that would be required.
“They don’t know what Golden Dome will cost, and to their credit, they say so,” he said.
No air defense system can protect the entire country all the time, Mr. Karako said, adding that the government would rank critical assets that would require the highest level of protection.
The advent of precision-guided conventional — or nonnuclear — weapons capable of hitting strategic targets inside the United States is a major part of what Golden Dome is meant to address, according to Mr. Karako.
In the past, the only weapons capable of intercontinental ranges contained nuclear warheads, he said, and their use would invite a counterattack. But an attack on the United States with conventional guided weapons could achieve a similar strategic effect without necessarily triggering nuclear retaliation, a scenario Golden Dome is designed — in part — to defeat, Mr. Karako said.
The C.B.O. report did not estimate the cost of protecting U.S. territories specifically but said the territory of Guam, a small island in the western Pacific that hosts Air Force, Marine Corps and Navy bases, was slated to receive “an extensive system of integrated defenses” outside of the Golden Dome project.
American Samoa and the Northern Mariana Islands in the Pacific and Puerto Rico and the U.S. Virgin Islands in the Caribbean could potentially be protected by separate regional missile defense sites, the report says.
In December, the Congressional Research Service said in a report that some lawmakers had expressed concern that, if built, Golden Dome could invite Russia and China to increase their nuclear arsenals in response.
The report noted that the Antiballistic Missile Treaty, which the United States and the Soviet Union signed in 1972, and that Russia later honored, precluded the development of antimissile systems like Golden Dome. But President George W. Bush’s decision to exit the treaty in 2001 paved the way for such a network of defensive missiles.
