The futuristic dome would likely cost about $US1.2 trillion ($A1.7 trillion), according to a new analysis from the Congressional Budget Office, a far heftier sum than the initial $US175 billion ($A242 billion) price tag Trump gave last year.
The nonpartisan CBO report, published Tuesday, is described as an analysis that reflects "one illustrative approach rather than an estimate of a specific Administration proposal."
The dome was ordered by Trump in an executive order during his first week in office. He said then that he expected the system to be "fully operational before the end of my term," which wraps up in January 2029.
"Over the past 40 years, rather than lessening, the threat from next-generation strategic weapons has become more intense and complex with the development by peer and near-peer adversaries of next-generation delivery systems," Trump said in his executive order, justifying the need for the missile defence system.
The concept for the missile system is at least partly inspired by Israel's multi-tiered defences, often collectively referred to as the "Iron Dome," which played a key role in defending it from rocket and missile fire from Iran and allied militant groups as it prosecutes the war on Iran alongside the US.
The US Golden Dome is envisioned to include ground and space-based capabilities able to detect, intercept and stop missiles at all major stages of a potential attack.
Congress has already approved roughly $US24 billion ($A33 billion) for the missile defence initiative through Republicans' massive tax and spending measure signed into law last summer.
Last May, the president said the Golden Dome would cost $US175 billion ($A242 billion). The CBO last year estimated that just the space-based components of the Golden Dome could cost as much as $US542 billion ($A750 billion) over the next 20 years.
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