L1-PTC ESSENTIAL THERMAL Level 1 · hardware

Passive Thermal Control

Passive Thermal Control Subsystem

The Passive Thermal Control Subsystem is an unpowered assembly of multi-layer insulation blankets, selective thermal coatings, heat pipes, and phase-change materials designed to maintain settlement hardware within survival and operational temperature limits for a 100-year lifespan. Requiring zero electrical power, consumables, or moving parts, it provides the baseline thermal envelope that sustains critical systems during active thermal control failures. Design is dictated by the lunar vacuum, where the absence of atmospheric convection restricts heat transfer strictly to radiation and conduction. Subsystem elements must withstand 300 K thermal cycling between -173 °C during the lunar night and +127 °C during the lunar day across 29.5-day periods, while resisting optical degradation from dust deposition, ultraviolet radiation, and particle radiation.

Passive thermal control system using MLI blankets, thermal coatings, heat pipes, phase-change materials, and structural thermal design to maintain temperature limits with zero active maintenance for 100 years.

Purpose

Maintains all Ark components within their operational temperature ranges using only passive mechanisms that require no power, no moving parts, and no consumables, providing the thermal baseline upon which active thermal control (L1-TCS) operates.

Context

Works in concert with active thermal control (L1-TCS) but provides the foundational zero-maintenance thermal envelope. During periods of active system failure or power loss, passive thermal control alone must keep critical systems within survival temperature limits.

Principles

▸Passive systems require no power or moving parts, maximizing 100-year reliability
▸Thermal balance between solar input, internal dissipation, and radiative rejection
▸Multi-layer insulation minimizes radiative heat transfer in vacuum
▸Phase-change materials buffer transient thermal loads without active intervention
▸Heat pipes transport thermal energy passively via capillary-driven working fluid

Typical implementations

▸Multi-layer insulation (MLI) blankets with aluminized Kapton/Dacron spacers
▸Selective thermal coatings (high alpha-s/epsilon-IR or low alpha-s/epsilon-IR)
▸Constant-conductance and variable-conductance heat pipes
▸Paraffin-based or salt-hydrate phase-change material modules
▸Thermal doublers and structural heat sinks

Lunar considerations

▸Extreme thermal cycling: -173C lunar night to +127C lunar day every 29.5 days
▸No atmospheric convection; all heat transfer is radiative or conductive
▸Lunar dust deposition degrades thermal coating optical properties
▸100-year UV and particle radiation exposure degrades MLI and coatings
▸Permanently shadowed regions offer stable cold environments for cryogenic systems

Specifications

Functional

primary function	Maintain Ark component temperatures within operational limits using passive thermal mechanisms requiring no power or maintenance
inputs	Solar radiative flux (variable with lunar day/night), Internal heat dissipation from active subsystems, Lunar surface thermal environment
outputs	Temperature-controlled thermal environment for all Ark subsystems, Thermal telemetry data to L1-CDH via embedded sensors
survival temp range c	-173, 127
operational electronics range c	-40, 85
cryogenic zone temp k	<77
zero power survival	True

Physical

materials	Aluminized Kapton and Mylar (MLI), Dacron netting spacers, Ammonia or propylene working fluid (heat pipes), Paraffin wax phase-change materials, Anodized aluminum and white paint thermal coatings
vacuum	True
radiation tolerant	True
dust exposed	True

Operational

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

Interfaces

Provides

→ALL_L1_SYSTEMSPassive thermal environmentessential
Provides baseline thermal control envelope for all Ark subsystems without power or active intervention
→Active Thermal Control SystemThermal baselineessential
Provides the passive thermal foundation upon which active thermal control system operates and supplements

Requires

←Primary StructureStructural mounting and thermal pathsessential
Requires structural attachment points for MLI, coatings, heat pipes, and PCM modules, plus conductive thermal paths through structure
←Dust MitigationDust protection for thermal surfacesessential
Requires dust mitigation to maintain optical properties of thermal coatings and MLI surfaces