US President Donald Trump has said he had selected a design for the $175 billion Golden Dome missile defence shield and named a Space Force general to head the ambitious programme aimed at blocking threats from China and Russia.
The programme, first ordered by Mr Trump in January, aims to create a network of satellites, perhaps numbering in the hundreds, to detect, track and potentially intercept incoming missiles.
Mr Trump told a White House press conference that US Space Force General Michael Guetlein would be the lead programme manager for an effort widely viewed as the keystone to the president's military planning.
Golden Dome will "protect our homeland," Mr Trump said, adding that Canada had said it wanted to be part of it.
Watch: Donald Trump announces a Golden Dome defence system for the US
In a statement, the office of Canadian Prime Minister Mark Carney said he and his ministers were discussing a new security and economic relationship with their US counterparts.
"These discussions naturally include strengthening NORAD and related initiatives such as the Golden Dome," it added.
Mr Trump said the defence shield, which would cost some $175bn, should be operational by the end of his term in January 2029, but industry experts were less certain of that timeframe and the cost.
"Ronald Reagan wanted it many years ago, but they didn't have the technology," Mr Trump said, referring to the space-based missile defence system, popularly called "Star Wars", that Mr Reagan proposed.
The Golden Dome programme faces both political scrutiny and funding uncertainty.
"The new data point is the $175 billion, but the question remains, over what period of time. It's probably ten years," said Tom Karako of the Center for Strategic and International Studies.
Silicon Valley and US software expertise can be leveraged to bring advances, while also using existing missile defence systems, he added.
This month, the Congressional Budget Office estimated that Golden Dome could cost as much as $831bn over two decades.
Democrats have voiced concern about the procurement process and involvement of Trump ally Elon Musk's SpaceX, which has emerged as a frontrunner alongside Palantir and Anduril to build key components of the system.
"The new autonomous space-age defence ecosystem is more about Silicon Valley than it is about 'big metal,'" Senator Kevin Cramer of North Dakota said at the White House event.
"So what's exciting about this is it makes it available to everybody to participate, to compete."
"Big metal" refers to legacy defence contractors.
The Golden Dome idea was inspired by Israel's land-based Iron Dome defense shield that protects it from missiles and rockets.
Mr Trump's Golden Dome is much more extensive, including a massive array of surveillance satellites and a separate fleet of attacking satellites that would shoot down offensive missiles soon after lift-off.
Yesterday evening's announcement kicks off the Pentagon's effort to test and ultimately buy the missiles, systems, sensors and satellites that will constitute Golden Dome.
Mr Trump said Alaska would be a big part of the programme, while Florida, Georgia and Indiana would also benefit.
Many of the early systems are expected to come from existing production lines. Attendees at the press conference named L3Harris Technologies, Lockheed Martin and RTX Corp as potential contractors for the massive project.
L3 has invested $150m in building out its new facility in Fort Wayne, Indiana, where it makes the Hypersonic and Ballistic Tracking Space Sensor satellites that are part of a Pentagon effort to better detect and track hypersonic weapons with space-based sensors and could be adapted for Golden Dome.
Golden Dome's funding remains uncertain.
Republicans have proposed a $25bn initial investment for Golden Dome as part of a broader $150bn defence package, but this funding is tied to a contentious reconciliation bill that faces significant hurdles in Congress.
"Unless reconciliation passes, the funds for Golden Dome may not materialise," said an industry executive following the programme, who spoke on condition of anonymity.
"This puts the entire project timeline in jeopardy."
The Kremlin said Mr Trump's missile shield plan required consultations with Russia but was otherwise a "sovereign matter" for the United States, softening its tone after previously criticising the idea as destabilising.
"This is a sovereign matter for the United States. If the United States believes that there is a missile threat, then of course it will develop a missile defence system," Kremlin spokesman Dmitry Peskov told reporters.
"That is what all countries do," he added.
"Of course, in the foreseeable future, the course of events will require the resumption of contacts to restore strategic stability," he added, referring to broader nuclear talks.
Mr Peskov's comments came two days after a call between Mr Trump and Russian President Vladimir Putin that the US leader said "went very well".
Russia previously denounced the Golden Dome plan, warning it risked turning space into a "battlefield".
In a joint statement with China earlier this month, both countries denounced the idea as "deeply destabilising".
China, which has deepened cooperation with Russia in recent years, this morning described Mr Trump's plans as a threat to international security.
Russia and the United States have the world's two largest arsenals of nuclear warheads.
