Heinlein had a discussion about the "place a large mass just over a particular point on the Earth's surface" approach in "- We Also Walk Dogs" at https://archiv

Heinlein had a discussion about the "place a large mass just over a particular point on the Earth's surface" approach in "- We Also Walk Dogs" at https://archive.org/details/isbn_9780739410516/page/306/mode/2up?q=%22large+mass+just+over%22 https://archive.org/details/isbn_9780739410516/page/306/mode... . How big as mass? After some calculations on a slide rule: > “I’m almost afraid to answer. You would need a good sized asteroid, of lead, to get anywhere at all.” > “Asteroids have been moved before this.“ > “Yes, but what is to hold it up? No, Chief, there is no conceivable source of power, or means of applying it, that would enable you to hang a big planetoid over a particular spot on the Earth’s surface and keep it there.” But wait, what about something dense, like core material from a dwarf star? > “All we would need for that would be a ship capable of going light-years in a few days, some way to mine the interior of a star, and a new space-time theory.” > “Oh, well, skip it." Oh, yeah. In this space-age future where people can travel across the Solar System, they also use punched cards.