I've often wondered why this hasn't been implemented. Seems that engine technology and the capabilities of modern composite materials will make it a reality.

https://www.radianaerospace.com/

Zooms down a 2 mile track to mach 0.7 then it fires its own engines and launches to low Earth orbit

 

Watch this video on how to construct an orbiting space torus using designed robotics. Seems like a sound idea, but without astronomical (pun intended) funding, will just be a pipe dream...

 

I'm wondering if rather than a rocket sled, some form of electromagnetic sled would be better. Some linear motor action.