WASHINGTON (AP) — President Donald Trump's plan to put weapons in space — pitched as a "Golden Dome for America" missile defense program — is estimated to cost $1.2 trillion over a 20 year period, according to a new analysis from the Congressional Budget Office, a far heftier sum than the initial $175 billion price tag he 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 futuristic system 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 defense system.

WATCH: Trump announces concept for 'Golden Dome' missile defense program in the U.S.

The CBO's estimates are in part based on a lack of details from the Defense Department about what and how many systems will be deployed, "making it impossible to estimate the long term cost" of the Golden Dome system, the report says.

The concept for the missile system is at least partly inspired by Israel's multitiered defenses, 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 U.S.

The U.S. 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 $24 billion for the missile defense initiative through Republicans' massive tax and spending measure signed into law last summer.

Sen. Jeff Merkley, D-OR, who requested the estimate from the CBO, said in response to the report that the missile defense project is "nothing more than a massive giveaway to defense contractors paid for entirely by working Americans."

Last May, the president said the Golden Dome would cost $175 billion. The CBO last year estimated that just the space-based components of the Golden Dome could cost as much as $542 billion over the next 20 years.