What the ground assist really costs.
A linear motor gives a rocket a running start. The physics is unforgiving in one direction: track length grows with the square of exit speed, and it's capped by how many g the payload survives. Dial the exit speed and the g-limit and watch the track stretch to tens of kilometers, and the switching electronics into the kilohertz.
Track length is quadratic
To reach speed V at acceleration a you need L = V²/2a. Double the exit speed and the track quadruples. That's why kinetic assist stays modest: a few hundred m/s is cheap, multi-km/s means tens of kilometers of guideway.
g-load is the ceiling
People tolerate ~3 g, hardened cargo ~10–20 g. Lower g means gentler acceleration means a longer track for the same exit speed. Passengers and high exit speed are nearly incompatible: this is a cargo game.
Where physical AI is the gate
The traveling magnetic wave must commute coils in step with the vehicle as it accelerates, switching frequency climbs into the kilohertz at exit, while holding a millimeter levitation gap. Fast power electronics and control, not a person.