Here's the version sketched in my forthcoming Avon novel THE WHITE ABACUS:
`Shortly before they found the hex, a consortium of the ancient nations
started to build a tower reaching into space.'
`Oh. A Beanstalk.' Ratio recognises this concept: a diamond cable
stretching from geostationary orbit to the ground, tethered atop a suitable
equatorial mountain, balanced by a second cable plunging a further 110,000
kilometers into cislunar space. It was Faustian technology appropriate to
the culture that captured the mass defect and coupled its orbit to Psyche's.
Only poor timing had prevented the Beanstalk's completion.
`"Spacehook" is how it was normally described,' Cima corrects sem. `No, the
Hyde Fountain was rather more audacious.' He sketches in the air, and the
Rozhdestvensky's watchful ai translates his gestures into a schematic holly
display above the table.
`Fire a stream of nine-kilo aluminum rings up an evacuated tower at 25
klicks a second,' he explains, `and brake them as they rise.'
The ai is nothing if not quick. `Ah. The transferred force will sustain
the tower structure that holds the brake motors,' Ratio sees, nodding.
`It's a reverse mass-driver, fixed to the ground.'
`Nice, isn't it? Twitch the little buggers around at the top with more
magnets, and ram them back down.'
`Reusing the power extracted on the way up, presumably.'
`Yep. Send them around a big loop when they get to the ground,' and he
sketches a vast sub-surface ring of superconducting magnets, `pumping the
speed up again, and shoot 'em out for another trip through the circuit.'
`They'd melt.'
`Oddly enough, no. There's energy loss, but it only raises the temperature
of the projectile rings by 40 degrees. That's dissipated on their return
trip from space.'
`One would wish to employ a measure of redundancy,' Ratio observes
thoughtfully, `if this process is meant to carry an elevator.'
`Ah, ai caution!' Cima laughs gustily. `Well, yes, even the mad dog hu
engineers thought of that. Three, four, ten times redundant. But you can
raise a shaft to geostationary without needing spectacular material
strengths. No need for diamond fibers.'
`Even so, it would clearly be a costly venture.'
`Getting it up, sure.' Cima sprawls. His animation display runs in the air
between them, a monstrous Tower of Babel clawing into heaven, a million
aluminum rings hurled up and down and all around. `Ten terawatts of
circulating power. Of course, that would've been pumped in incrementally as
the tower was raised. Even so, it needed 15 gigawatts to keep it running.'
He leans forward, eyes gleaming. `But it would have given us a permanent
elevator to space, zipping up the tower by magnetic levitation. Linear
motors. [snip]
Damien Broderick