Interesting. The linear density given is 7 kg/m, which if you wanted to lift to the tropopause (density 0.35 kg/m^3, temperature ~266 K) you would need a contin

Interesting. The linear density given is 7 kg/m, which if you wanted to lift to the tropopause (density 0.35 kg/m^3, temperature ~266 K) you would need a continuous 30 °C solar Molgolfier balloon 18 m^2 in section, or a 10 meter strip of of 15 µm HDPE. Not as bad as I thought. Still, it would be hard to roll it out before sunset. Hydrogen is another possible lifting gas, with all its associated foibles. Obviously lifting bags would have to be isolated to prevent catastrophic failure, but you could get a lot more lift out of them. This must take place in a La Niña year, when the jetstream is north. Reel out the track, drag it into place with two airships, join the parts and start 'er up. You could even name the airships Jupiter and Number 119. ;) This simplified strategy that would avoid the need for aerial stations at both ends, intead using a gentle curve achieved by anchor cables and varying linear density. Acceleration would begin immediately upon departure, leaching energy from the rotor (generating eddy currents), then contributing it back by braking off the rail on the descending side. Of course, maybe I'm just dreaming here…