L2-PTC-PCM ESSENTIAL THERMAL Level 2 · hardware

Phase Change Materials

Phase Change Material Thermal Buffer Modules

Phase change material thermal buffer modules are passive energy storage units that absorb and release latent heat during solid-liquid phase transitions to buffer temperature swings during lunar day-night cycles. The 29.5-day lunar cycle includes 14-day nights, producing sustained thermal transitions that place heavy demands on settlement heating and cooling systems. By utilizing latent heats of fusion exceeding 200 kJ/kg—yielding 5 to 14 times the energy storage capacity of sensible heat per unit mass—these zero-power modules maintain component temperatures within ±3 °C during phase change. Encapsulated in metallic shells to accommodate phase volume changes, they supplement insulation and heat pipes over operational lifetimes exceeding 1,500 freeze-thaw cycles.

Phase change material modules that absorb and release thermal energy during melting and solidification cycles, buffering temperature swings during lunar day/night transitions.

Purpose

Provides passive thermal energy storage to dampen temperature excursions during the 14-day lunar day and 14-day lunar night transitions, protecting thermally sensitive components from rapid temperature changes.

Context

Supplements MLI insulation and heat pipes by adding thermal inertia to the passive thermal design, reducing the active heating/cooling load on L1-TCS during transition periods.

Principles

▸Phase change (solid-liquid) absorbs/releases large amounts of energy at nearly constant temperature
▸Latent heat of fusion provides 5-14x the thermal storage capacity of sensible heat in same mass
▸PCM melt point selected to match the desired component temperature setpoint
▸Encapsulation prevents liquid leakage and maintains thermal contact during cycling

Typical implementations

▸Paraffin waxes (n-octadecane, n-eicosane) for 20-40C electronics protection
▸Salt hydrates for higher energy density at specific temperature ranges
▸Metallic encapsulation with internal fin structures for enhanced conductivity
▸Microencapsulated PCM embedded in structural panels
▸NASA heritage PCM units from ISS and planetary mission electronics thermal control

Lunar considerations

▸29.5-day lunar cycle means PCM must store energy for ~14 days of night
▸Massive PCM quantities needed for full night buffering; practical for local hotspot protection
▸Paraffin volume change during phase transition must be accommodated in encapsulation
▸100-year cycle life: ~1,240 freeze-thaw cycles minimum
▸PCM thermal conductivity is low; internal fins or graphite matrices needed for heat transfer

Specifications

Functional

primary function	Buffer temperature excursions during lunar day/night transitions using latent heat storage in phase change materials
inputs	Thermal energy from adjacent components and environment
outputs	Temperature-stabilized thermal interface to protected components
latent heat kj per kg	>200
cycle life	>1500 melt/freeze cycles
temperature stability c	+/- 3 during phase change
power consumption w	0

Physical

materials	N-octadecane paraffin wax, Aluminum encapsulation shells, Expanded graphite thermal conductivity enhancers, Stainless steel containment for salt hydrates
vacuum	True
sealed containment	True

Operational

power consumption w	0
thermal range c	-173, 127
lifetime years	100

Interfaces

Provides

→Passive Thermal ControlThermal bufferingessential
Provides temperature-stabilized thermal mass at protected component interfaces

Requires

←Primary StructureStructural mountingessential
Mounting locations adjacent to thermally sensitive components requiring temperature buffering
←Passive Heat PipesHeat transport to PCMsupporting
Heat pipes may deliver thermal energy to PCM modules from distributed sources