Here’s another thing to chew over.
Suppose one of these gets built. Now we have a guided, ultra high speed interplanetary missile, weighing a ton or so, which... could quite well be steered in a U-turn and back onto any site on earth after having achieved some ungodly velocity. Tunguska wherever you want it! Now some of these craft get into the hands of the bad guys. Book of Revelation disasters anybody???
Sounds like another reason for the Anglophone nations to get the high ground first.
So you read that Niven book, too?