Coil Winding

TL;DR

  • Purpose: Electromagnetic windings for projectile acceleration
  • Material: Cryogenic aluminum (360% conductivity at -180°C)
  • Mass: ~100 t per Mass Driver (1,000 coils)
  • Technology: Automated winding + cryogenic cooling

Overview

Mass Driver coils are electromagnets that create the magnetic field for projectile acceleration. Coils are sequentially energized, attracting the projectile and accelerating it to 5 km/s.

Coil Design

Parameter Value
Coils per track 1,000 (1 per meter)
Turns per coil 50-100
Wire Aluminum, 10 mm diameter
Mass per coil ~100 kg
TOTAL winding mass ~100 t Al

Coil Schematic

  Coil cross-section (side view):

  ╭─────────────────╮
  │  ▓▓▓▓▓▓▓▓▓▓▓▓▓  │ ← 50-100 turns Al wire
  │  ▓▓▓▓▓▓▓▓▓▓▓▓▓  │
  │  ▓▓ [NaK] ▓▓   │ ← NaK cooling channel
  │  ▓▓▓▓▓▓▓▓▓▓▓▓▓  │
  │  ▓▓▓▓▓▓▓▓▓▓▓▓▓  │
  ╰─────────────────╯

Cryogenic Aluminum

Problem: Mercury has no copper (the standard winding material on Earth).

Solution: Aluminum at -180°C has conductivity nearly equal to copper at room temperature.

Conductivity Comparison

Material +20°C -180°C Increase
Copper 100% 400% 4x
Aluminum 60% 360% 6x

Conclusion: Cryo-aluminum is an ideal copper replacement for Mass Drivers.

Mass Driver Location

Mass Drivers are positioned at the terminator (day/night boundary): - Working section in shadow (temperature -180°C) - Cooling radiators face the shadow - Electronics and control on the sunlit side (power source)

Coil Production

Winding Process

Stage Equipment Output
Wire production Drawing mill Al, 10 mm diameter
Coil winding Winding machine 50-100 turns
Cooling installation NaK tube welding Cooling channels
Insulation Ceramic coating Arc protection
Testing Ohmmeter Resistance <0.1 Ohm

Productivity: 1 winding machine = 10-20 coils/day

For 1,000 coils: 50-100 days on 1 machine

With 5 machines: ~3 weeks

Details: Rolling Mill

Coil Cooling System

NaK Circuit

Parameter Value
Coolant NaK (eutectic Na-K alloy)
Circuit temperature -150°C
NaK flow rate 100 L/min per track
Tube diameter 20 mm
NaK mass in system ~5 t

Radiators

Parameter Value
Radiator area 5,000 m²
Material Aluminum (thermal conductivity)
Location Facing shadow (-180°C)
Heat rejection ~40 MW

Principle: NaK circulates through coils (absorbs heat) → radiators in shadow (releases heat) → back to coils.

Heat Generation During Launch

Energy Balance per Shot

Parameter Value
Energy per launch 4.7 GJ (including capacitor losses)
Efficiency 40%
Heat loss 2.8 GJ
Shot duration 0.4 sec
Peak heat generation ~280 MW (absorbed by thermal mass)

Average Power

At 600 launches/day:

2.8 GJ × 600 / 86,400 sec = ~20 MW average heat generation

Required rejection: ~20 MW continuous. Peak heat (280 MW for 0.4 sec) is absorbed by thermal mass of coils and NaK coolant, then dissipated over 2-3 minutes between shots.

Coil Wear

Wear Causes

Cause Contribution Consequences
Overheating 40% Insulation degradation
Electric arcing 30% Turn melting
Mechanical vibration 20% Wire breakage
Oxidation 10% Corrosion

Service Life

Mode Launches Service Life
Intensive (600/day) ~500,000 3-5 years
Medium (300/day) ~500,000 5-7 years

Replacement: ~30 t Al/year per Mass Driver.

Material Balance

Per 1 Mass Driver (new):

Component Mass Production
Windings (1,000 coils) 100 t Al 42 t/day → 2.5 days
NaK cooling system 5 t NaK Local
Radiators 50 t Al 42 t/day → 1.5 days

Replacement (wear, 1 Mass Driver over 5 years):

Component Mass/year Production
Windings 30 t Al 0.7 days production
NaK 1 t Top-up

Coil Installation on Track

Stage Time Robots
Coil frame installation 3 days 20 Centaur-M
Coil mounting (1,000 units) 2 weeks 10 Centaur-M
Cooling connection 3 days 10 Centaur-M
Power cable routing 3 days 10 Centaur-M
Circuit testing 2 days Automated

TOTAL: ~3-4 weeks from installation to ready. (Runs in parallel with rail and frame installation.)

Quality Control

Parameter Control Standard Action on Deviation
Resistance Ohmmeter <0.1 Ohm Rewind
Insulation Megohmmeter >10 MOhm Additional coating
Inductance LCR meter Within ±5% Turn adjustment
Cooling Thermocouples T <-140°C Check NaK circuit

See Also