Paul Birch

Paul Birch proposed in 1982 that where we cannot have practical geosynch space-elevators, we might try "Orbital Ring Systems and Jacob's Ladders".

[ADVISORY! The pagination is wrong between I.3.3 and I.3.4. p. 482 is 483; 483, 482.]

And yeah: Inyalowda cannot have an elevator. Deimos, even if it's in synch, cannot dangle a ladder past Phobos' ap'ares; must make do with a shorter tether. Earth's proposal keeps butting against ... what material can bear 35,786 km of its own mass. And then we got Venus, our own Moon, and Mercury which all spin so slowly they have no synchronous orbit. Ditto Jupiter's inner moons which (like Mercury) have prohibitive delta-V and radiation, anyway. We're stuck with Ceres down here.

And then, in 1982, came Paul Birch, to save us. Rather: to save Mars. But we'll get to that.

Birch figured Earth, at least, will have no worry if we had a series of interconnected stations all in LEO, chained together. The stations move; the circle doesn't. The circle is, further, magnetic. Magnetise a Ring Station and that station just ... sits there. It dangles its tether down to wherever on Earth you want it. That's not 35,786 km; that is more like 600 km, depending on how far out you put the ring, presumably beneath Van Allen thus protecting the magnet. 600 km of rope is as nothing to tether-enthusiasts.

The problem thus shifts away from "unobtanium" and toward - who gets to pay for 180 kilotonnes of various pricey metals in LEO (semimajor 6678 or 6978 km). Also minor issues like space-junk and other satellites. Reading Gregory Leal's 2018 lecture, I cannot see Earth agreeing to this in the near future... before seeing how it works already. Just look at Elon's Starship today (well, in 2023); it inspires us because it has been showing results. So, for the orbital ring, we need first to see it work on some other planet.

The Federation in Starship Troopers paid for Birch II.3.5 - a smaller version, ringing our Moon.

Leal recommended to do this for Venus, also. That is a harder sell in that, although Venus is only 6051.8 km around, its atmo extends much higher and, in fact, blows out a coma on the night side. Birch wouldn't worry about drag and needn't worry about Venus' magnetic field (there isn't one) but he might worry about ions. The wind will push out the ring... but, I fear, to bend the ring into an oval if all goes uncorrected (Birch I.4.1). So if Venus gets an orbital ring I should run it at the same 6678-978 km semimajor. Venus gets its materiel from asteroids.