The magnetic launch track
Picture a bullet train that never stops accelerating, running inside a sealed tunnel up a mountain. At the top, it lets go of a rocket already moving at several kilometers per second.
Launch console
Like a bullet train
Superconducting magnets on the sled induce currents in the track as it moves. Those currents push back and lift the sled, so nothing touches the track at speed.
Like a particle accelerator
Coils along the track switch on in sequence. The sled rides the moving magnetic wave, just as a particle rides the radio-frequency wave in a linac.
Unlike either
It keeps accelerating the whole way. Track length is set by the exit speed and the g-load you allow.
How the wave pulls the sled
Each coil switches on as the sled approaches and off as it passes, so the pull is always forward.
Why the track must be straight
Any bend at speed pushes the sled sideways with an acceleration of v²/r. At 8 km/s, even a gentle curve is punishing, so the track is nearly straight and climbs a mountain along one shallow slope.
| Allowed g-load | Track length to reach 8 km/s | Minimum turn radius |
|---|---|---|
| 3 g (passengers) | about 1,000 km | about 2,200 km |
| 30 g (cargo only) | about 110 km | about 220 km |
The hard parts
The air
At 8 km/s at sea level, air pressure on the front of the sled would be around 380 atmospheres. The track runs in a vacuum tunnel, exits high on a mountain, and uses a plasma window, a magnetically confined plasma that holds back air with no solid barrier.
The power
Energy is cheap, about 9 kWh per kilogram at 8 km/s. Delivering it in a few minutes is the problem, and it needs huge capacitor banks or flywheels.
The scale
The physics is straightforward. The infrastructure is not: 100 to 1,000 km of precisely aligned, superconducting track.
The last step
The sled gets the rocket most of the way to orbital speed (7.8 km/s). A small rocket stage then circularizes the orbit.
Real work behind it
| Project | What it showed |
|---|---|
| NASA Maglifter | Maglev sled launching rockets at 270 to 600 m/s up a mountain slope |
| StarTram | Evacuated-tunnel launcher with a plasma window exit |
| Navy EMALS | A working linear motor launching aircraft from carriers |
| Holloman test track | A 15 km straight rocket-sled track, showing what a long launch track looks like |