L2-TCS-FLOP CRITICAL thermal transport Level 2 · hardware

Fluid Loop System

Pumped Fluid Loop Thermal Transport System

Mechanically-pumped coolant loops that transport thermal energy between heat sources and heat sinks throughout the Ark, using single-phase and two-phase working fluids.

Purpose

Provide the primary thermal transport mechanism for the Active Thermal Control System by circulating working fluid through closed-loop piping networks connecting heat acquisition interfaces, heat exchangers, and heat rejection radiators. Must support variable heat loads across the 354-hour lunar diurnal cycle.

Context

The Fluid Loop System forms the circulatory backbone of L1-TCS. Multiple independent and cross-strapped loops serve different thermal zones (vault interior, exterior electronics, cryogenic pre-cooling). Pumps must be robotically replaceable. Working fluid must remain liquid across the operational temperature range without freezing during lunar night or boiling during peak daytime loads. Accumulators manage fluid volume changes with temperature. The system must tolerate single-fault failures without loss of critical thermal control.

Principles

▸Forced convection heat transfer in closed-loop piping: fluid absorbs heat at source, releases heat at sink
▸Single-phase loops: sensible heat transfer with temperature rise proportional to flow rate and heat load
▸Two-phase loops: latent heat transfer at constant temperature, higher heat transport capacity per unit flow rate
▸Accumulator pressure regulation: compensates for fluid thermal expansion/contraction across temperature range
▸Redundant loop architectures: cross-strapped loops prevent single-point thermal failures

Typical implementations

▸ISS Internal Thermal Control System (ITCS): water single-phase loops at 40-50 deg F
▸ISS External Thermal Control System (ETCS): ammonia two-phase loops rejecting up to 70 kW
▸Orion MPCV single-phase propylene glycol/water loops
▸James Webb Space Telescope cryogenic helium loop for instrument cooling
▸European Columbus module single-phase water loops

Lunar considerations

▸Working fluid must not freeze at -173 deg C: ammonia (freezes at -78 deg C) requires trace heating or alternate fluids for extreme cold segments
▸HFE-7100 freezes at -135 deg C: better cold tolerance but lower thermal capacity than ammonia
▸Silicone oils (e.g., Syltherm XLT) viable to -100 deg C with very long life but lower conductivity
▸Pump seals and bearings must last decades with periodic robotic replacement
▸Micrometeorite protection for external fluid lines: armored conduit or buried routing through regolith
▸Lunar dust infiltration at connector interfaces must be prevented with sealed quick-disconnect fittings
▸Loop routing through structure (L1-STR) must accommodate thermal expansion differentials

Specifications

Functional

primary function	Transport thermal energy via pumped working fluid between thermal source interfaces and thermal sink interfaces throughout the Ark
inputs	Thermal energy from heat-generating components via L2-TCS-INTF cold plates and heat exchangers, Electrical power for pump motors from L1-PWR, Control commands from L2-TCS-CTRL for flow rate adjustment, valve actuation, loop mode selection
outputs	Heated working fluid delivered to L2-TCS-RAD radiators for heat rejection, Heated working fluid delivered to L2-TCS-HTR heat exchangers for heat recovery/redistribution, Cooled working fluid returned to thermal source interfaces, Telemetry: flow rates, pressures, temperatures, pump speeds, valve positions
number of independent loops	TBD (minimum 3: vault, external, cryo-support)
heat transport capacity per loop kw	TBD (estimated 20-80 kW per loop)
flow rate range lpm	TBD
pressure range kpa	TBD (100-500 kPa nominal)
single fault tolerance	Any single pump or valve failure shall not cause loss of critical thermal control

Physical

materials	Stainless steel 316L (fluid lines, fittings for corrosion resistance), Aluminum 6061-T6 (pump housings, manifolds), Titanium Grade 5 (high-pressure fittings, flex couplings), PTFE / Viton (pump seals, O-rings), Ammonia or HFE-7100 (working fluids), Kevlar / Nextel (micrometeorite shielding for external lines)
operational temp range c	-80, 80
survival temp range c	-173, 127
vacuum exposure	External line segments exposed to vacuum
internal pressure kpa	100-500 nominal

Operational

thermal range c	-173, 127
lifetime years	100
notes	Pumps are the primary wear item with estimated 5-10 year replacement interval. Modular pump cartridge design enables robotic hot-swap without loop drain-down.

Interfaces

Provides

→Radiator Arraysfluidcritical
Hot working fluid delivered to radiator inlet manifolds for heat rejection; cooled fluid returned from radiator outlets
→Thermal Interface Hardwarefluidcritical
Cooled working fluid supplied to cold plates and heat exchangers at component interfaces; warmed fluid returned
→Heater Systemfluidessential
Working fluid circulated through heater heat exchangers for heat acquisition during cold operations
→Heat Pump Systemfluidessential
Working fluid circulated through heat pump evaporator/condenser for active temperature lift operations

Requires

←Power Generation Systempowercritical
Electrical power for pump motors, valve actuators, and trace heaters on fluid lines
←Thermal Control Electronicsdatacritical
Commands for pump speed control, valve position settings, and loop mode selection
←Primary Structuremechanicalessential
Structural mounting and routing support for fluid lines, pump assemblies, and accumulators
←Robotic Operationsmechanicalessential
Robotic maintenance for pump replacement, valve servicing, leak detection/repair, and fluid top-off