[mlindner]

Except they're completely inverting the rocket. The rocket goes slow in the lower atmosphere where the forces are lower. This allows them to lose much less energy in the lower atmosphere from drag.

If they could just launch at 45 degrees to get to orbit the rockets would do that too, but no they don't. They go straight up at first because the drag is such a huge penalty to the performance.

If they actually build this thing, the most efficient way to launch is to launch it almost straight up at 90 degrees so they lose the least energy. However the hardest part is going to be immediately after exiting this thing where they hit the atmosphere going mach 6-7 and instantly turn into a glowing ball of plasma, which is what happens if you try to move that fast at sea level.

Drag forces increase with the square of the velocity and linearly with fluid density. The instant it leaves the cannon it will feel like it's hitting a brick wall.