No, not a balloon-assisted rocket launch, but an Air-Breathing Inflatable Solar Thermal Rocket" or "Balroc".

Excerpt:

- "The Balroc is a very long tube-shaped balloon that flies along the long axis of the balloon. The initial model I toyed with numerically was 10 meters long by 3 meters wide. The top half of the balloon is clear, the bottom half is a parabolic Mylar reflector that runs the length of the balloon, focusing the light from the sun (assuming you are pointing the right direction) onto a metal tube that runs the length of the balloon, down the center of it. A ram scoop exists at one end of the tube, about the same area as the nose of the balloon. A small nozzle is situated at the other end of the tube. Simply, you move through the air, scoop in air which goes into the tube, gets heated up by the solar heating tube, and exhausts out your nozzle, producing thrust. The faster you go, the more air you scoop in. At some point your drag will equal your thrust, and you will stop accelerating. That, very roughly, is how it will work.

- "The "break point" of the acceleration sequence, the point where drag=thrust, is modifiable by quite a few factors. To begin with, the higher you go, the thinner the air, but since you are accelerating, you can maintain a fairly constant "chamber pressure" for your rocket. Since the air is thinner, your drag is lower, somewhat, though this is not linear; the drag increases as a function of the square of the velocity, only partially countered by the decrease in density. The bottom line, though, is the higher you go, the thinner the air, and the higher your maximum speed. You can also increase your max V by making the tube hotter, that is, make the balloon longer."

Is this the breakthrough in CATS we've all been waiting for or just a lot of hot air?