Mass accelerators aren’t useful because the atmosphere limits their final velocity. You’d need to have an enclosed vacuum tube with an exit north of 20,000 feet

Mass accelerators aren’t useful because the atmosphere limits their final velocity. You’d need to have an enclosed vacuum tube with an exit north of 20,000 feet. There have been proposals to build something just like that with a “plasma” door at the end that can snap open and closed to keep the atmosphere out of the tube. It still can’t get anywhere near orbital velocity, so the plan is to use it to accelerate a second stage that uses rocket engines after it is released to provide the rest of the orbital DeltaV. The Problem is rockets are relatively fragile and the high gees and hitting an even thin atmosphere at Mach 6 would destroy them. Look up “spin launch” for an even crazier idea that’s actually funded.