Been a hot minute since I last dropped in on the ToughSF X account. Ten days ago it linked to a cycler plan - to which I may or may not get. Right now I'd like to discuss its own source, Elliott Orion Ruzicka's submission to the IAF's 75th congress 2024. In his capacity as head of "Orbital Design" in New York.
That's a "Mr.", not a "Dr.". Shows how much credentials matter for awesome material-science papers.
Ruzicka notes that the Halo doesn't work, much less the Ringworld. Since they both spin, each puts pressure on her outer wall. Maximum pressure happens to correlate with radius (or diameter, or circumference): F / gr. Humans like g=9.8 m/s2. I'm willing to negotiate for Venereal 8.7 - but now we have to consider the tensile strength of the outer hull, and how thick that might be. The outer shell can't be allowed to dip much less than 9.8.
Given alla'that, cometh our list of tensile materials before this contraption flies apart. As usual Kevlar is in here, maxing out 0.513 mega-meters... 513 km across. As a post-1980 paper we can also use Zylon 759 km. Nanotubes and graphene also make their appearances but I consider them unobtania. Six years ago our boy ToughSF related the T1100G. This was density 1790 and max force 7000 MPa. That last looks rounded: I get 400 km radius = 800 km diameter.
Janhunen's dumbbell and Jensen's smaller stuff were keeping it to decakilostructures, fit for high Earth orbit where space is at a premium and we don't want to bombard our green home. The max-out hectakilostructures were more than enough and, who cared about muh nanotubes. Ruzicka, mad lad, wants a MEGA structure. He floats up to 102,040 km held by 100 m of graphene; compare Earth equatorial 12,756 km... or Saturn 120,536 km. Maybe keep this monster at Venus Equilateral.
But even if we're not demanding this absurd artificial subSaturn, Ruzicka can still save on construction-material to keep it together. A 10,204 km subEarth might need that 100 m now; this would go down to 9.09 m.
Ruzicka's magic is in installing a torus within a torus. The outer ring keeps the micrometeors out and does not spin. Only the inner ring rotates for the artificial gravity. The inner and outer rings are thereby decoupled. They just need to keep from mutually crashing into each other, which can be gently nudged by magnets.
Ruzicka proposes to spin it up in the first place, by - you guessed it - magnets (but stronger). This will require the outer ring to spin in the opposite direction, at first; but this can be mitigated either by using rocket-engines or, better, building two at a time to spin in opposite directions, which would cancel each other's twists.
THERMO 9:50 AM: A hot minute indeed.
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