Space Tube

The huge column would be neutrally buoyant so that it could rise to over 100km altitude. The central tube a couple of metres wide would be evacuated. The pipe is gently curved eastwards so that the exit angle is similar to that used by current rockets.

To allow the tube to extend above the altitude at which helium balloons cease to be effective, the tube would contain a number of smaller tubes that contain 'obstructions'. Air is blown through these pipes from the bottom and the resulting friction creates more lift. The air is then directed downwards at the lip of the main tube for an extra little push.

I lack the knowledge necessary to calculate the power available from the moving air or how feasible it is over such a long distance, but to improve the effective range, the air would start off hot and moving fast, then would be cooled as it gets higher in the tube. This system would rely on a large volume of air moving rather than high pressure. To avoid deceleration of the air due to gravity, the mass of the air cannot exceed that of the outside air.

This is similar to the Space Fountain concept, but much easier to engineer IMHO.

Inevitably, some air will get into the top of the tube. This is pumped out from the bottom continuously, but at the time of launch, a series of pre-launch disks are launched up the tube at relatively low velocity to force the air out the top of the tube. They then parachute back to earth to be used again. The last cleaning disk leaves the end of the tube seconds before the main launch vehicle.

This brings us to the launch mechanism. This is a simple magnetic rail, with the power coming from the rail rather than the launch vehicle. In fact the sled on the launch vehicle is a stage which detaches soon after leaving the top of the tube. It should not be a problem to transmit the power 100km or so, but this could be aided by wind turbines tethered near the tube at stages, solar power or the 'obstructions' mentioned earlier could be turbines.

The main problem is that the tube will need to be tethered to prevent it thrashing about in the wind. I think tethering it to the earth would be impractical due to the cable weight, but it could be tethered to itself to add stiffness. A few ground tether cables could be used by containing them within their own buoyancy tube and perhaps double up as the power cables. Anyway, these are mere details, way below my pay grade.

Back of envelope calculation: Assuming the structure weighs 100kg per metre, it would need to be about 35m in diameter at sea level. I have no idea how this would need to change at altitude.

<aside>Space elevators are not really like a conventional elevator in that it is not contained within a shaft. They should be called Space Cable Cars.</aside>

As a bonus, we can add arms to it and sell used cars to passing aliens.

*Can someone tell me the name of a tube with hollow walls, similar to a dewars flask but without a base? Tubule?