"Of the $1.2 trillion amount, acquisition costs...would total just over $1 trillion. That amount includes costs for the system's major components -- namely, the interceptor layers and a space-based missile warning and tracking system," CBO said in a report.

"The most expensive component is the space-based interceptor layer, which accounts for about 70 percent of acquisition costs and 60 percent of total costs," it said.

Average annual costs for operations and support would meanwhile come in at $8.3 billion, the report said.

Trump ordered the Pentagon to develop plans for a high-tech missile defense shield in late January 2025, initially dubbing it "Iron Dome for America."

In May 2025, Trump announced that $25 billion had been earmarked for the project, estimating its total cost at $175 billion.

However, CBO said the same month that the cost of space-based interceptors to defeat a limited number of intercontinental ballistic missiles could be between $161 billion and $542 billion over 20 years.

And the goals for Golden Dome are significantly more expansive, with the 2026 National Defense Strategy saying the Pentagon will "focus on options to cost-effectively defeat large missile barrages and other advanced aerial attacks."