Reactor Radiator Assembly
Stirling Cold-Side Waste Heat Rejection Radiator
The reactor radiator assembly is an 8 m² deployable panel array that rejects approximately 33 kWt of waste heat to space via thermal radiation, maintaining Stirling converter cold ends at 300°C to sustain the driving thermodynamic cycle. In the lunar vacuum, radiation is the sole available heat transfer mechanism. Operational efficiency is challenged by daytime lunar surface infrared emissions at roughly 270 K, which reduce the effective sink temperature and require elevating panels to minimize the surface view factor. Additionally, settling lunar dust degrades the high-emissivity coating, while micrometeorite strikes risk puncturing the pumped fluid loops.
Radiator panel array that rejects approximately 33 kWt of waste heat from Stirling converter cold ends to space via thermal radiation.
Purpose
Maintain the Stirling converter cold-side temperature at approximately 300°C by radiating waste heat to space, which is essential for maintaining the temperature differential that drives the Stirling thermodynamic cycle.
Context
Receives waste heat from Stirling converter cold ends (L3-PWR-NUC-STIRL) and radiates it to the deep space environment. Sized by Stefan-Boltzmann law for the required heat rejection at 300°C. Interfaces with the broader thermal control system (L1-TCS) for overall Ark thermal management coordination.
Principles
- ▸Radiative heat rejection follows Stefan-Boltzmann law: Q = epsilon * sigma * A * (T_hot^4 - T_sink^4)
- ▸High-emissivity coatings maximize radiative efficiency (epsilon > 0.9)
- ▸Low solar absorptivity minimizes parasitic solar heat input (alpha/epsilon ratio)
- ▸Radiator panel orientation must minimize view factor to lunar surface and sun
- ▸Fluid loop or heat pipe manifold distributes heat evenly across radiator panels
Typical implementations
- ▸Kilopower reference design: flat panel radiators with NaK loop, ~5 m2 area
- ▸ISS External Active Thermal Control System: ammonia loop radiators, deployable panels
- ▸Spacecraft body-mounted radiators with Z-93 or AZ-93 white paint coatings
- ▸Carbon-carbon composite radiator panels for high-temperature applications
Lunar considerations
- ▸Lunar surface IR emission (~270 K during day) reduces effective sink temperature
- ▸Radiator panels should face away from lunar surface and be elevated for clear space view
- ▸Lunar dust accumulation degrades emissivity and increases solar absorptivity
- ▸Micrometeorite damage can cause fluid leaks in pumped-loop radiators
- ▸Thermal cycling between lunar day and night stresses panel joints and coatings
Specifications
Functional
| primary function | Reject 33 kWt of Stirling waste heat to space via thermal radiation |
| inputs | Waste heat from Stirling cold ends at ~300°C via thermal fluid loop or conduction |
| outputs | Infrared radiation to space (net heat rejection of ~33 kWt) |
| heat rejection kwt | 33 |
| radiator temperature c | 300 |
| emissivity | 0.9 |
| solar absorptivity | 0.15 |
| effective sink temperature k | 200 |
| radiator area m2 | 8 |
Physical
| mass kg | 120 |
| dimensions | Approximately 8 m2 total radiating area, deployable panel configuration |
| materials | Aluminum honeycomb core panels, Carbon-carbon face sheets (high-temperature option), AZ-93 or Z-93P white thermal coating, Stainless steel or titanium fluid manifolds, NaK or water heat transport fluid (depending on loop temperature) |
| operating temperature c | 300 |
| exposure | Direct space view, partial lunar surface IR loading |
| dust | Exposed to lunar dust deposition |
Operational
| power consumption w | 20 |
| thermal range c | -170, 350 |
| lifetime years | 15 |
| mtbf hours | 150000 |
Interfaces
Provides
- Cold-side heat sink at ~300°C for Stirling converter waste heat rejection
Requires
- 33 kWt waste heat from Stirling cold ends via thermal transport loop
- Structural mounting and deployment mechanisms for radiator panels
- Coordination with overall Ark thermal management for radiator orientation and thermal environment
Decomposes into
Cite this entry
Lunar Ark Codex. "Reactor Radiator Assembly" (L3-PWR-NUC-RAD). Retrieved 10 September 2026, from https://lunarark.com/entry/L3-PWR-NUC-RAD
Licensed CC-BY-SA 4.0. You may reuse and adapt this entry with attribution, under the same licence.