Rotor Lamination

Laminated launch loop rotors will have good magnetic properties and will rapidly disperse and oxidize in the atmosphere after a rotor-release catastrophe. Worst case, thin flakes survive and cut.

Metglas 2605SA1 looks good, higher temperature than 2605HB1M. datasheet downloaded 2017/02/11

Metglas 2605SA1

Curie temperature

395C / 668K

saturation induction

1.56 Tesla


23 μm


7.18 g/cm³

Thermal Expansion

7.6 ppm/°C

Iron vaporization temp

3140 K

Tensile Strength

1 GPa

Elastic Modulus

100 GPa


85 to 95%




5 to 10%




1 to 5%




1.3 μΩ-m

60 Hz and 1.4 T

Induction at 80 A/m

≥1.35 T

Core Loss

≤0.17 W/kg

Exciting Apparent Power*

1.1 (VA/kg)


Core loss appears proportional
to (frequency × flux )1.8 .

Figure from datasheet.

Naively, assume that the rotor is excited at 100 KHz and produces 150 KN of thrust against a payload moving at a relative speed of 3 km/s with a wavelength of 0.1 m, an excitation frequency of 30 KHz. Assume a similar synchronous frequency (it will actually be slightly lower). Assume a sled length of 100 meters.

End of acceleration and track conditions

payload speed

11 km/s


1.65 GW

extracted from rotor

track coil pitch

0.11 m

track field frequency

100 KHz

rotor speed

14 km/s

rotor mass density

3 kg/m

rotor relative speed

3 km/s

rotor ΔV

13.1 m/s

Slowdown under sled

rotor time under sled

33.3 ms

100m / 3000 m/s relative

rotor acceleration under sled

393 m/s²

delta V / time

rotor force per meter

1179 N/m

acceleration times mass density

rotor total force

117.9 KN

the rest goes into the (rebounding?) track

rotor coil pitch

This varies along the track, longer at the end

rotor field frequency


in rotor frame of reference

Failure and oxidation

Iron has a specific heat of 25.1 J/(mol·K), vaporizes at 3140K, and has a heat of vaporization of 340 kJ/mol . Naively, to go from 400K to vaporization requires 410 kJ/mol or 16 MJ/kg . The rotor moves at 14 km/s, the kinetic energy is 98 MJ/kg, so there is more than enough energy to vaporize the rotor foil and ignite it. Further study and experimentation needed; perhaps most of the energy will end up heating the surrounding air, and the foil will fragment and fall to the ocean surface and then the sea floor.

RotorLamination (last edited 2017-02-12 05:57:56 by KeithLofstrom)