NaS Battery Production

TL;DR

  • Purpose: Power supply for Gen-2 robots
  • Technology: Sodium-Sulfur battery (NaS)
  • Localization: 85% local (Na + S), 15% import (β-Al₂O₃ ceramics)
  • Production rate: 500 kWh/day (various pack sizes)

Overview

Gen-2 robots run on sodium-sulfur batteries (NaS Battery). Unlike Li-Ion batteries for Gen-1 robots (from Earth), NaS batteries are manufactured from local materials — sodium and sulfur extracted from regolith.

Key advantage: High operating temperature (+300°C) is compatible with Mercury: in the terminator zone (+50…+150°C), vacuum thermal insulation and a built-in heater (~50 W) easily maintain 300°C — energy costs are lower than terrestrial equivalents (NGK Insulators).

NaS Battery Operating Principle

Construction

Component Material Source
Anode Liquid sodium (Na) Distillation
Cathode Liquid sulfur (S) Titanium Line
Electrolyte β-Al₂O₃ (beta-alumina) Import from Earth (initially)
Case Steel Fe-6%Mn Iron

Chemical Reaction

Discharge:

2Na + 5S → Na₂S₅

Charge:

Na₂S₅ → 2Na + 5S

The β-Al₂O₃ electrolyte conducts Na⁺ ions but is impermeable to liquid metals.

NaS Battery Specifications

Parameter Value
Specific energy 150-240 Wh/kg
Operating temperature 300-350°C
Service life 15 years / 4500 cycles
Efficiency 85-90%
Voltage 2.0 V per cell

Comparison with Li-Ion:

Parameter NaS Li-Ion
Specific energy 150-240 Wh/kg 150-250 Wh/kg
Service life 4500 cycles 500-1000 cycles
Mercury localization 85% 0% (all import)

Conclusion: NaS loses to Li-Ion in specific energy, but wins in service life and localization.

NaS Battery Thermal Management

NaS batteries operate at 300-350°C. At Mercury’s pole (Prokofiev crater, 85°N), the ambient temperature in the working zone is +50…+150°C — significantly warmer than on Earth (-20…+40°C), where NaS batteries are successfully deployed (NGK Insulators, Japan, 700+ MWh installed capacity).

Thermal Insulation Design

Component Description
Outer casing Steel Fe-6%Mn
Vacuum gap Double-walled construction (thermos principle)
Inner casing Steel + β-Al₂O₃ electrolyte
Heater Resistive, 50-100 W, inside casing

Thermal Balance

Mode Ambient ΔT Heat loss Heating Battery autonomy
Operation (discharge) +100°C 200°C ~30 W Not needed (self-heating) ∞
Standby +50°C 250°C ~50 W 50 W (built-in) Crab: 400 h, Centaur: 100 h
Earth (reference) -20°C 320°C ~100 W 100 W —

Self-heating during discharge: Internal resistance of NaS cells generates heat. At 5-10 kW load, losses amount to 0.5-1.5 kW of heat — the battery maintains operating temperature without the heater.

Standby mode: The 50 W heater consumes ~1.2 kWh/day. For Crab-M (20 kWh), this provides >16 days of autonomous standby; for Centaur-M (5 kWh) — >4 days.

Emergency cooldown: If the battery cools completely (power loss), Na and S solidify without cell damage. Restart: external heating via cable (~1 kW, ~2 hours). Robots do NOT operate in shadow (-180°C) — the standard working zone is +50…+150°C.

Battery Composition (1 kWh)

NaS Battery Production

Process

Step Description Equipment
1. Case fabrication Steel tube Ø50 mm, length 1 m Lathe
2. Electrolyte installation β-Al₂O₃ ceramic tube inside case Manual assembly (Centaur-M)
3. Na and S filling Sodium in center, sulfur outside Vacuum filling
4. Sealing Laser welding of caps Laser welder
5. Initial charge Electrolyte activation (12 hours at 350°C) Charging station
6. Testing 10 charge/discharge cycles Automated

Production time: 24 hours per battery (including initial charge)

Parallelism: 24 hours per battery, but 10 parallel lines enable 10 batteries/day output. Each line starts a new battery daily.

Production Line Capacity

Production rate: ~500 kWh/day (various pack sizes) = 500 kWh/day

For 5 robots/day:

Robot type Battery capacity Batteries per robot
Mole-M Cable (no battery) 0
Crab-M 20 kWh 1
Centaur-M 5 kWh 1

Average mix: ~2 packs 20 kWh (Crab) + ~2 packs 5 kWh (Centaur) ≈ 50 kWh/day for robots. Remaining (450 kWh/day): reserve, replacement, stationary energy storage.

Material Balance

For 500 kWh/day production capacity (daily material consumption):

Material Mass for 10 batteries Source
Sodium (Na) 250 kg Distillation
Sulfur (S) 250 kg Titanium Line
Ceramics β-Al₂O₃ 100 kg Import from Earth
Steel (case) 60 kg Iron
TOTAL ~660 kg ~85% local

Consumption from daily production: - Na: 250 kg from 1000 kg/day = 25% - S: 250 kg from 500 kg/day = 50% - Fe: 60 kg from 18 t/day = 0.3%

Battery Maintenance

Operation Frequency Performed by
Temperature monitoring Continuous Automated
Calibration (charge/discharge) 1 month Automated
Battery replacement 5-7 years Centaur-M at assembly station

Disposal: - Sodium and sulfur extracted → reuse - β-Al₂O₃ ceramics → regeneration (if possible) - Steel case → remelting

Production Energy Consumption

Component Power
Vacuum filling 20 kW
Charging station (12 hours) 30 kW
Testing 10 kW
TOTAL ~60 kW

Quality Control

Parameter Method Standard Action on deviation
Seal integrity Vacuum test <10⁻⁶ mbar·L/s Reject
Capacity Charge test >90% nominal Repeat activation
Temperature Thermocouples 300-350°C Adjust heating
Cycles 10 test cycles Capacity >95% Reject

Future Localization of β-Al₂O₃

Problem: β-Al₂O₃ ceramics are imported from Earth (15% of battery mass).

Solution: β-alumina production on Mercury:

Step Process
1. Obtaining Al₂O₃ From regolith (bauxite Al₂O₃·2H₂O → calcination)
2. β-phase stabilization Adding Na₂O (0.5-1%) + sintering at 1600°C (solar concentrator, 1500-2000°C)
3. Ceramization Tube forming + sintering

Implementation timeline: After construction of high-temperature furnaces (Year 2-3)

See also