Reactor Structural Assembly
Kilopower Reactor Support Structure and Thermal Isolation Mount
The reactor structural assembly is a 45-kilogram framework, measuring approximately 1.5 meters by 0.8 meters, that physically integrates and aligns a nuclear core, heat pipes, Stirling engines, and radiation shielding to within a 0.5-millimeter tolerance. On the lunar surface, the titanium and Inconel structure must maintain geometric alignment across severe thermal strain between the 800 °C core region and 100 K radiator tips. Operating in 1/6 g gravity over a 15-year design life, it uses zirconia ceramic standoffs to keep thermal conductance below 0.5 W/K while isolating Stirling engine vibrations and withstanding shallow magnitude 5 moonquakes.
Primary structural framework supporting and aligning all reactor components including core, heat pipes, Stirling engines, radiator, shield, and control assemblies. Provides launch load paths, vibration isolation, and thermal management of structural interfaces.
Purpose
Maintain precise geometric alignment of reactor components under launch, landing, and operational loads while providing thermal isolation between hot and cold sections of the power system.
Context
Backbone structure of the nuclear power subsystem, integrating L3-PWR-NUC-CORE through L3-PWR-NUC-SHIELD into a single deployable assembly. Interfaces with the Ark main structure for installation on the lunar surface.
Principles
- ▸Structural framework must provide load paths for launch quasi-static loads (14g axial, 6g lateral) and pyrotechnic shock events
- ▸Thermal isolation between hot-end (~800C reactor) and cold-end (~200K radiator) requires low-conductivity standoffs and radiation baffles
- ▸Material selection must account for creep and embrittlement under combined thermal and radiation exposure over 15 years
- ▸Vibration isolation needed to prevent mechanical coupling between Stirling engine oscillations and sensitive reactor instrumentation
Typical implementations
- ▸Kilopower flight system structural concept — truss-based support frame with titanium standoffs
- ▸SNAP-10A — conical support frame with NaK pipe routing provisions
- ▸NASA Fission Surface Power reference design — vertical mast configuration with shield/boom separation
- ▸JIMO (Jupiter Icy Moons Orbiter) — reactor-boom-spacecraft structural architecture
Lunar considerations
- ▸1/6g gravity significantly reduces operational structural loads versus launch design cases
- ▸Thermal expansion differentials between 800C core region and 100K radiator tips create significant strain
- ▸Regolith burial of lower structure possible for radiation shielding augmentation
- ▸Moonquake loads (up to magnitude 5, shallow) must be accommodated in structural design
Specifications
Functional
| primary function | Provide structural support, alignment, and thermal management for all reactor subsystem components |
| inputs | Mechanical loads from launch vehicle (quasi-static and dynamic), Thermal loads from reactor core and radiator temperature differentials, Vibration inputs from Stirling engine operation |
| outputs | Load transfer to Ark main structure, Geometric alignment of core, heat pipes, Stirling, radiator, and shield |
| launch load axial g | 14 |
| launch load lateral g | 6 |
| first natural frequency hz | >35 |
| alignment tolerance mm | 0.5 |
| thermal isolation conductance w per k | <0.5 |
Physical
| mass kg | 45 |
| dimensions | Approximately 1.5m height x 0.8m diameter envelope |
| materials | Ti-6Al-4V titanium alloy (primary truss members), Inconel 718 (high-temperature fasteners and brackets near core), Zirconia ceramic standoffs (thermal isolation), Stainless steel 316L (secondary structural members) |
| temperature range c | -170 to 800 (varies by location) |
| radiation exposure | Moderate neutron/gamma behind shield shadow |
| vacuum | True |
Operational
| power consumption w | 0 |
| hot end near core | 600 |
| cold end near radiator | -170 |
| lifetime years | 15 |
| mtbf hours | 500000 |
Interfaces
Provides
- Structural support and alignment for reactor core assembly
- Mounting platform and vibration isolation for Stirling converter assemblies
- Structural attachment for radiator panel deployment and support
- Shield mounting and alignment maintaining radiation shadow cone geometry
- Structural support and alignment for reflector actuator mechanism
Requires
- Interface mounting points to Ark main structure for reactor assembly installation
Cite this entry
Lunar Ark Codex. "Reactor Structural Assembly" (L3-PWR-NUC-STRUCT). Retrieved 10 September 2026, from https://lunarark.com/entry/L3-PWR-NUC-STRUCT
Licensed CC-BY-SA 4.0. You may reuse and adapt this entry with attribution, under the same licence.