Another possibility is using aerostatic forces to support a giant platform in the sky, anchored to the tops of buildings. Would need to support an additional 200kg of weight climbing up the anchor line, to heights as high as 20km. From there, could rocket launch, fly, etc. https://en.m.wikipedia.org/wiki/Atmospheric_satellite#High-a....

In addition to nanotube cables, we'd also need to develop ways to mitigate the acoustic and electrical vibrations in the cable. Might be a way to generate electricity and dampen at the same time.