Offshore launches would be needed because of the noise of the blast-offs
Mr Musk revealed the idea while discussing the progress of reusable rocket tech
Such spaceports would launch Starship, SpaceX's planned long-duration rocket
With space for 100 people, Starship could also travel between points on Earth
Elon Musk envisages building commercial spaceports that float around 20 miles (32 km) out at sea from which Starship rockets can launch towards the Moon and Mars.
An offshore location would be needed to ensure that routine, noise-polluting, blast-offs from such spaceports would not disturb anyone, he tweeted.
Starship — formally dubbed the Big Falcon, or F******g, Rocket (BFR) — is SpaceX's planned long-duration cargo and passenger spacecraft.