U.S. President Donald Trump's Golden Dome missile defense concept revives a controversial, decades-old initiative whose ambitious construction could upend norms in outer space and reshape relations between the world's top space powers.

The system is intended to protect the United States from ballistic, cruise and hypersonic missiles, and missiles launched from space.

There are doubts from experts on how the US would deliver a comprehensive system and it is unclear how Canada would participate or how much it would pay.