L2-TCS-RAD CRITICAL thermal rejection Level 2 · hardware

Radiator Arrays

Thermal Radiator Heat Rejection Arrays

Deployable and fixed radiator panels that reject waste heat from the Ark to deep space and cold regolith via infrared radiation.

Purpose

Provide the primary heat sink for the Active Thermal Control System by radiating absorbed waste heat to the space environment. Radiator arrays must handle peak thermal loads during lunar daytime while surviving the extreme cold of lunar night without structural damage. Surfaces must maintain high infrared emissivity over a 100-year mission despite lunar dust accumulation and micrometeorite degradation.

Context

Radiator arrays are the final heat rejection stage of the L1-TCS thermal transport chain. Hot working fluid from L2-TCS-FLOP flows through radiator panel tubing, transferring heat to the radiator surface which emits it as infrared radiation to the ~3K deep-space sink. Radiator sizing is driven by peak daytime heat loads, solar backloading, and albedo from surrounding terrain. Location and orientation are constrained by Ark layout, with preference for surfaces with persistent deep-space view and minimal solar/lunar-surface IR illumination.

Principles

▸Stefan-Boltzmann law: radiated power proportional to emissivity * area * T^4, driving radiator sizing
▸Radiator effectiveness depends on view factor to cold space vs warm surfaces (sun, lunar surface, Ark structure)
▸High infrared emissivity (epsilon > 0.9) and low solar absorptivity (alpha < 0.2) optimize heat rejection
▸Two-sided radiators radiate from both faces if view factor geometry permits
▸Fluid flow through embedded tube networks or face-sheet channels transfers heat to radiator surface

Typical implementations

▸ISS Heat Rejection System: 14 deployable ammonia-flow radiator panels, each 6.7 x 3.4 m, total 78 m2 per pair
▸Orion MPCV flow-through body-mounted radiators with titanium water heat pipes
▸Space Shuttle payload bay door radiators with silver-Teflon coatings
▸Lunar Gateway HALO module body-mounted and deployable radiators

Lunar considerations

▸Lunar dust accumulation increases solar absorptivity, degrading radiator performance over time
▸Electrostatic dust mitigation (transparent conductive coatings, electric field dust repulsion) may be required
▸Radiators oriented toward lunar poles see cold sky most of the time: favorable geometry
▸Regolith-facing radiators can reject heat to cold ground in PSR regions
▸Deployable radiators allow pre-launch packaging but add mechanical complexity and failure modes
▸Fixed body-mounted radiators are simpler but constrain Ark geometry
▸Micrometeorite impact on flow tubes can cause coolant leaks: redundant tube routing and isolation valves required
▸100-year coating degradation: self-healing or robotically-recoatable surfaces desirable

Specifications

Functional

primary function	Reject thermal energy from pumped fluid loops to the space/lunar environment via infrared radiation
inputs	Hot working fluid from L2-TCS-FLOP at elevated temperature, Deployment/retraction commands from L2-TCS-CTRL (for deployable arrays), Environmental thermal loads (solar flux, lunar IR, albedo)
outputs	Cooled working fluid returned to L2-TCS-FLOP at reduced temperature, Infrared radiation emitted to space/regolith (waste heat rejection), Telemetry: panel temperatures, fluid outlet temps, deployment state
total radiator area m2	TBD (estimated 100-500 m2 depending on total heat load)
heat rejection capacity kw	TBD (estimated 50-200 kW at design conditions)
surface emissivity bol	>0.90 infrared emissivity at beginning of life
surface absorptivity bol	<0.15 solar absorptivity at beginning of life
end of life degradation factor	Design for 30% emissivity degradation over 100 years

Physical

materials	Aluminum honeycomb (radiator panel core structure), Aluminum face sheets (fluid flow channels, radiating surfaces), Silver-Teflon FEP (optical solar reflector thermal coating), AZ-93 white paint (high-emissivity thermal coating alternative), Stainless steel (fluid inlet/outlet manifolds), Carbon-fiber composite (deployment booms for deployable arrays)
operational temp range c	-100, 80
survival temp range c	-173, 127
vacuum	True
solar flux w m2	1361
lunar ir backload w m2	Up to 1300 at subsolar point, near 0 in PSR
dust exposure	High: external surfaces exposed to lunar dust

Operational

thermal range c	-173, 127
lifetime years	100
notes	Radiator panels are passive once deployed (no power needed for heat rejection). Power required only for deployment mechanisms, fluid pumping (accounted under L2-TCS-FLOP), and dust mitigation systems.

Interfaces

Provides

→Fluid Loop Systemthermalcritical
Heat rejection service: accepts hot fluid, returns cooled fluid after radiative heat rejection
→Active Thermal Control Systemthermalcritical
Primary heat sink for the entire Active Thermal Control System

Requires

←Fluid Loop Systemfluidcritical
Hot working fluid supplied to radiator inlet manifolds at design temperature and flow rate
←Thermal Control Electronicsdataessential
Commands for deployable radiator positioning, isolation valve control, and mode selection
←Primary Structuremechanicalcritical
Structural mounting for fixed radiator panels; deployment hinge/boom mounting for deployable arrays
←Power Generation Systempoweressential
Power for deployment actuators, isolation valves, and electrostatic dust mitigation systems
←Robotic Operationsmechanicalessential
Robotic maintenance for radiator panel replacement, coating refresh, and dust cleaning
←Dust Mitigationthermalessential
Dust mitigation to maintain radiator surface optical properties; dust contamination data for degradation tracking