Space Elevator

Perfect. I think it just needs explanation of Karman line. Why is it 100km. What is the meaning?

It's my understanding that the Karman Line the conventionally accepted "edge" where you leave the atmosphere and enter outer space, but many call this out as a fairly arbitrary point, arguing that there is no measurable boundary. Useful as a point of reference for positioning, though. Neal possibly just used it as a marker but chose to not define it for this reason.

It's an arbitrary number, which is a good enough measure to distinguish an aircraft from a spacecraft.

Kármán said that it's about this height where the aerodynamic lift and inertia being dominant are reversed.

https://en.wikipedia.org/wiki/K%C3%A1rm%C3%A1n_line