Nuclear Power Subsystem
Kilopower-class Fission Surface Power System
The Kilopower-class fission surface power system is a 1,500 kg, compact uranium-fueled reactor that provides 10 kWe of continuous baseload electrical power via sodium heat pipes and Stirling converters. Generating power independently of solar illumination, it sustains critical systems through the 336-hour lunar night when solar arrays produce zero output. Lunar engineering constraints severely complicate thermal management: the absence of an atmosphere precludes convective cooling, forcing the system to rely exclusively on radiative heat rejection across ambient surface temperature swings from -173°C to +127°C. Furthermore, abrasive regolith dust deposition on radiator surfaces degrades thermal emissivity, threatening the heat rejection required to sustain the 43 kWt core.
Primary power generation using compact fission reactor with Stirling conversion providing 10 kWe baseload
Purpose
Provide reliable continuous electrical power independent of solar illumination, critical for surviving the 336-hour lunar night and ensuring uninterrupted power to preservation systems
Context
Primary power source for the Ark. Nuclear is the only source that provides full power during lunar night. Solar (L2-PWR-SOL) supplements during day, RTG (L2-PWR-RTG) provides emergency backup. Based on NASA Kilopower/KRUSTY demonstrated technology.
Principles
- ▸Uranium fission produces thermal energy from controlled chain reaction
- ▸Sodium/potassium heat pipes passively transfer thermal energy from core to converters via capillary action and phase change
- ▸Stirling engines convert thermal energy to mechanical work via cyclic compression/expansion of gas
- ▸Linear alternators convert Stirling mechanical output to AC electrical power
- ▸Radiators reject waste heat to space via thermal radiation (Stefan-Boltzmann law)
- ▸Beryllium oxide reflector controls reactivity by adjusting neutron economy
- ▸Single-point-of-failure avoidance through multiple Stirling converter units
Typical implementations
- ▸NASA Kilopower (KRUSTY demonstrated 2018, 1-10 kWe, TRL 5-6)
- ▸Soviet TOPAZ-I thermionic reactor (flown 1987, 5-6 kWe)
- ▸Soviet TOPAZ-II / Enisy (ground tested, ~5 kWe)
- ▸US SP-100 (developed 1980s-90s, 100 kWe class, not flown)
- ▸NASA Fission Surface Power (FSP) project, 40 kWe class for lunar/Mars
Lunar considerations
- ▸No atmosphere for convective cooling: radiator-only heat rejection
- ▸Regolith burial possible for radiation shielding (reduces keep-out zone)
- ▸Thermal environment (-173°C to +127°C) affects radiator sizing and cold-side temperature
- ▸Dust contamination of radiator surfaces reduces emissivity
- ▸Autonomous startup, shutdown, and load-following required
- ▸Seismic loads from moonquakes must be considered for reactor structure
- ▸100-year fuel life requires careful burnup management or fuel swapping capability
Specifications
Functional
| primary function | Convert nuclear fission heat to electrical power via Stirling conversion |
| inputs | Enriched uranium fuel (U-235/U-Mo alloy, pre-loaded, ~93% HEU or LEU depending on design), Control commands from L2-PWR-MGMT |
| outputs | Electrical power: 10 kWe DC (after conversion and conditioning), Waste heat: ~20-30 kWt to L1-TCS radiators, Telemetry: reactor temperature, power output, fuel status, control rod position |
| electrical output kwe | 10 |
| thermal output kwt | 43 |
| conversion efficiency pct | 23 |
| availability | 0.99 |
| startup time hours | 4 |
| load following | True |
| design life years | 15 |
| fuel burnup management | Required for 100-year mission (may need multiple reactor lifetimes) |
Physical
| mass kg | 1500 |
| dimensions | Approximately 1.5m diameter x 3m height |
| materials | U-Mo alloy fuel, Stainless steel (structure, containment), Sodium heat pipe working fluid, Beryllium oxide neutron reflector, Boron carbide control elements, MarM-247 superalloy (hot-end components), Inconel 718 (structural components) |
| operating temperature c | 800°C (core) to 300°C (Stirling cold end) |
| radiation field | Significant neutron and gamma - requires shielding and standoff |
| vibration | Stirling engine produces vibration (balanced by opposed-piston design) |
Operational
| power consumption w | 0 |
| thermal range c | 300, 800 |
| lifetime years | 15 |
| mtbf hours | 100000 |
Interfaces
Provides
- Raw AC electrical output from Stirling alternators, ~10 kWe
- Waste heat for rejection, ~20-30 kWt at ~300°C cold-side temperature
- Reactor status telemetry: temperatures, power output, control position, fuel burnup
Requires
- Radiator system for waste heat rejection to maintain Stirling cold-side temperature
- Control commands: startup/shutdown, power level setpoints, emergency scram
- Foundation and mounting structure, supports ~1500 kg reactor assembly
- Additional radiation shielding or regolith burial for crew/electronics protection
- Robotic access for external inspection and non-core component replacement
Decomposes into
Cite this entry
Lunar Ark Codex. "Nuclear Power Subsystem" (L2-PWR-NUC). Retrieved 10 September 2026, from https://lunarark.com/entry/L2-PWR-NUC
Licensed CC-BY-SA 4.0. You may reuse and adapt this entry with attribution, under the same licence.