Well. As you're probably aware, one of the big obstacles in space flight is the amount of fuel and oxidizer you need to get into orbit. Back in the 70s, they looked into putting jet engines on the space shuttle to cut back on it's oxidizer needs, but the added weight cut into payload too much.

But why bring along separate jet engines? Jets, rockets, the difference between them is actually pretty thin. Well, actually it's pretty significant, but I'm working on a rocket that will use the atmosphere for it's own oxygen supply up to about Mach 5.5. It might have a thrust to weight ratio as high as 14 if all the tricks I'm planning to use work out. Single stage to orbit capable. It's not a space elevator, but getting out to orbit is halfway to anywhere you want to go.