A zero carbon air travel solution. Well, most of the bits would be made of carbon materials, but it wouldn’t emit any CO2.
The pic says it all. A linear solar farm suspended in the high atmosphere to provide an IT platform for sensors, comms and other functions often accomplished by low orbit satellite. It would float up there thanks to being fixed to a graphene foam base layer that can be made lighter than helium (my previous invention, see https://timeguide.wordpress.com/2013/01/05/could-graphene-foam-be-a-future-helium-substitute/ which has since been prototyped and proven to be extremely resilient to high pressures too). Ideally, it would go all the way around the world, in various inclinations at different altitudes to provide routes to many places. Carbon materials are also incredibly strong so the line can be made as strong as can reasonably be required.
The flotation layer also supports a hypersonic linear induction motor that could provide direct propulsion to a hypersonic glider or to electric fans on a powered plane. Obviously this could also provide a means of making extremely low earth orbit satellites that continuously circumnavigate the ring.
I know you’re asking already how the planes get up there. There are a few solutions. Tethers could come all the way to ground level to airports, and electric engines would be used to get to height where the plane would pick up a sled-link.
Alternatively, stronger links to the ground would allow planes to be pulled up by sleds, though this would likely be less feasible.
Power levels? Well, the engines on a Boeing 777 generate about 8.25MW. A high altitude solar cell, above clouds could generate 300W per square metre. So a 777 equivalent plane needs 55km of panels if the line is just one metre wide. That means planes need to be at least that distance apart, but since that equates to around a minute, that is no barrier at all.
If you still doubt this, the Hyperloop was just a crazy idea a century ago too.