Leaving the EU with no negotiation means no flights to europe or the U.S. Overfly rights still exist because the UK signed up to Chicago Convention. There's a fair few countries where the UK will still have rights to fly to - Singapore for one, I suspect much of Africa too.

The UK is a member of the Outer Space treaty, has been since 1967, so I don't think there's a technical hurdle to launching a rocket from Brexit Britain (Assuming the fuel and rocked is already on the island).

(Of course whether we can afford to when we can't export any goods is another matter)

Your assessment is absurdly dramatic, and I make that claim without evidence until your claims have evidence.