Key details about the Pentagon’s Golden Dome missile defense system remain largely classified, leaving lawmakers without clear answers about what the planned system will protect, what capabilities it will include, and how much it will ultimately cost, according to Sen. Angus King, I-Maine.
During a Sept. 29 Senate Armed Services Subcommittee on Strategic Forces hearing, King pressed witnesses on the system’s intended coverage and the assumptions underlying its cost.
“The American public deserves clarity about what Golden Dome will accomplish and how much it will cost. Particularly because it could be one of the government’s largest and most expensive projects,” King said.
The Golden Dome program, launched under an executive order in January 2025, is intended to defend the United States from advanced missile threats, including hypersonic weapons. Initially projected to cost $175 billion, the program’s price tag has since risen to $185 billion, Golden Dome Director Gen. Michael Guetlein said in March. Completion is now expected by 2035, seven years later than originally planned, Guetlein said at the time.
However, Guetlein’s “estimate is not based on DOD’s developing Golden Dome architecture,” Congressional Budget Office (CBO) Director of National Security Analysis David E. Mosher explained to lawmakers on Tuesday.
In May, CBO estimated that a missile defense system based on requirements in President Donald Trump’s January 2025 executive order could cost roughly $1.2 trillion over 20 years.
“We did not estimate the cost of [the DOD] system at all,” Mosher said. “CBO’s estimate is subject to considerable uncertainty, and it’s based on this notional system.”
He added that the actual cost “could be higher, or cost could be lower” depending on the system DOD ultimately builds.
“If DOD builds a system that’s smaller … that could certainly cost less than our estimate,” Mosher said.
Guetlein has pushed back on trillion-dollar projections, arguing that they are based on assumptions that differ from the system DOD is building.
For King, those competing estimates underscored a more fundamental question: What exactly will Golden Dome defend?
Without a clear picture of the system’s scope, King questioned how lawmakers could evaluate its cost.
Witnesses described approaches that could prioritize certain locations and assets rather than provide the same level of protection across the country.
David J. Trachtenberg, a senior scholar at the National Institute for Public Policy and former deputy under secretary of defense for policy, said the department could approach Golden Dome through a “phased and staged deployment” rather than attempting to provide the same level of protection everywhere at once.
“I think it would be deployed probably in phases or in stages at certain times when the architecture is ready, but I think it should be expansive,” Trachtenberg said.
Thomas Karako, director of the Missile Defense Project at the Center for Strategic and International Studies, pointed to U.S. Northern Command’s defended-asset list as one mechanism for determining which locations and infrastructure receive priority.
Mosher said another option would be to focus some ground-based defenses on specific parts of the country rather than attempting to provide uniform coverage nationwide.
“If you built it in a phased way or built less, it would cost less,” he said.