Thermal Storage System Controller
PCM Charge/Discharge Supervisory Controller
Rad-hard embedded controller coordinating the thermal storage loop — pump speed, Stirling stroke, HEX flow direction, and safety interlocks — with model-based melt-fraction estimation and dispatch coordination with L2-ESS-MGMT.
Purpose
Operate the thermal storage subsystem autonomously across charge/discharge cycles, ensuring PCM cycling within design temperature bounds and managing transitions between charging (reactor surplus) and discharging (Stirling generation) modes.
Context
Embedded controller on L3-ESS-MGMT-PROC compute platform or on dedicated FPGA. Talks to L3-ESS-THRM-PUMP, L3-ESS-THRM-CONV, L3-ESS-THRM-HEX. Reports SOC (melt fraction × latent heat) and SOH (cycle count, ESR-equivalent) to L2-ESS-MGMT.
Principles
- ▸Melt fraction estimation: temperature inside PCM tank held near melting point during phase change; fraction inferred from enthalpy balance
- ▸Charge mode: pump heat from external source through HEX into PCM tank; melt fraction increases
- ▸Discharge mode: pump heat from PCM tank through HEX to Stirling cold side; melt fraction decreases
- ▸Standby mode: low-rate trace heating maintains loop above salt freezing point
- ▸Temperature sensors at multiple tank locations measure stratification and melt-front propagation
- ▸PID + feedforward control of pump speed and Stirling stroke to track demand setpoint
Typical implementations
- ▸Industrial molten-salt CSP plant control systems (Solar Two, Andasol-1 SCADA)
- ▸NASA Glenn lunar TES demonstrator control software
- ▸Stirling engine controllers (Sunpower, Infinia)
- ▸ESA lunar surface thermal management studies
Lunar considerations
- ▸Day/night autonomous transition without ground intervention
- ▸Salt-freeze prevention is mission-critical; trace heaters always-on regardless of dispatch
- ▸Long mission requires drift compensation in melt-fraction estimator using periodic full-cycle calibration
- ▸SEU-tolerant FPGA logic for fast pump/Stirling control
- ▸Dispatch coordination with L2-ESS-MGMT ensures TES is used when economic vs. RFC/batteries
Specifications
Functional
| primary function | Control thermal storage charge/discharge and report state |
| inputs | Temperature sensors throughout PCM tank, Pump telemetry from L3-ESS-THRM-PUMP, Stirling telemetry from L3-ESS-THRM-CONV, Setpoints from L2-ESS-MGMT-DISP and L3-ESS-MGMT-CHG |
| outputs | Pump speed/flow setpoints to L3-ESS-THRM-PUMP, Stirling stroke amplitude commands to L3-ESS-THRM-CONV, Trace heater enable signals, SOC (melt fraction × latent heat) and SOH telemetry to L2-ESS-MGMT |
| control loop rate hz | 10 |
| melt fraction estimation error percent | 5 |
| trace heater response time s max | 60 |
| salt freezing prevention | trace-heater always-on |
| supported modes | off, standby, charge, discharge, fault |
Physical
| mass kg | 1.0 |
| dimensions | 180 × 120 × 30 mm 3U cPCI card |
| materials | Microchip RTG4 FPGA or Vorago ARM Cortex-M0, Rad-hard SRAM with EDAC, Polyimide PCB, Aluminum chassis |
| operating temperature c | -40, 70 |
| radiation tid krad | 100 |
Operational
| power consumption w | 5 |
| thermal range c | -40, 70 |
| lifetime years | 25 |
| mtbf hours | 300000 |
Interfaces
Provides
- Speed/flow commands
- Stirling stroke setpoint
- TES SOC/SOH/dispatch availability
Requires
- Dispatch schedule
- Logic power (~5 W)
- Time reference for control loops
Cite this entry
Lunar Ark Codex. "Thermal Storage System Controller" (L3-ESS-THRM-CTRL). Retrieved 10 September 2026, from https://lunarark.com/entry/L3-ESS-THRM-CTRL
Licensed CC-BY-SA 4.0. You may reuse and adapt this entry with attribution, under the same licence.