Primary Truss Structure
Primary Load-Bearing Truss Assembly
The primary load-bearing truss assembly is a space-frame structure composed of Al-Li 2195-T8 tubular members and Ti-6Al-4V node fittings that transfers structural, seismic, and pressure-thrust loads between modules and the lunar foundation. In the lunar vacuum, the absence of convective cooling sustains severe thermal gradients across the structure, ranging from -173 °C on shaded surfaces to +127 °C in sunlight. The truss must accommodate this differential expansion, prevent vacuum cold-welding at metallic interfaces, and survive more than 1,200 thermal cycles over a 100-year operational life while maintaining strict dimensional stability for module alignment.
Main longitudinal and transverse truss members forming the backbone of the Ark, transferring all primary loads between modules, foundations, and external equipment
Purpose
Provide the primary load path connecting pressure vessel modules to each other and to the foundation system, carrying all static, dynamic, pressure thrust, and thermally-induced loads
Context
The primary truss is the structural spine of the Lunar Ark. It connects module end-domes, distributes concentrated loads from docking ports and airlocks, and carries seismic and thermal loads to the foundation. Designed as a space-frame truss using Al-Li tubular members with titanium node fittings, it must survive 1200+ thermal cycles over 100 years while maintaining dimensional stability for module alignment.
Principles
- ▸Space-frame trusses provide high stiffness-to-mass ratio through triangulated geometry
- ▸Primary structure must maintain positive margins under worst-case combined loading (pressure + thermal + seismic + MMOD damage)
- ▸Fatigue life under thermal cycling requires S-N curve analysis with mean stress correction for Al-Li alloys
- ▸Fail-safe design requires multiple redundant load paths so loss of any single member does not cause collapse
- ▸Coefficient of thermal expansion mismatch between dissimilar materials at joints requires compliant interfaces
Typical implementations
- ▸ISS Integrated Truss Structure (ITS): Al 6061-T6 longerons with titanium node fittings, 108.5m span
- ▸Lunar Gateway PPE truss: Al-Li 2195 tubular frame for module-to-module load transfer
- ▸Bigelow Expandable Activity Module (BEAM) internal framework: Al longerons with composite struts
Lunar considerations
- ▸Thermal gradient across truss (-173C shadow side to +127C sun side) creates differential expansion requiring flexible joints or thermal breaks
- ▸Low gravity reduces dead-load stresses but pressure thrust loads from module endcaps dominate axial loading
- ▸Vacuum eliminates convective cooling, so thermal gradients persist longer than on Earth
- ▸Cold welding risk between uncoated metallic surfaces in vacuum requires surface treatments (anodization, dry-film lubricant)
Specifications
Functional
| primary function | Transfer all primary structural loads between modules, docking ports, airlocks, and foundations |
| inputs | Module pressure thrust loads (endcap reaction forces), Equipment mass loads transmitted through secondary structure, Thermal expansion/contraction loads from lunar day/night cycling, Dynamic loads from moonquakes and robotic operations |
| outputs | Reaction forces to foundation system, Alignment maintenance for module-to-module interfaces, Mounting interfaces for secondary structural members |
| safety factor ultimate | 2.0 |
| safety factor yield | 1.5 |
| fatigue life cycles | 1500 |
| max deflection mm per m | 1.0 |
| first natural frequency hz min | 5.0 |
Physical
| dimensions | Tubular members 100-200mm OD, 3-8mm wall thickness; overall span TBD by module count |
| materials | Al-Li 2195-T8 (primary longerons and diagonals), Ti-6Al-4V (node fittings and high-stress gussets), Stainless steel 316L (fastener hardware at joints) |
| temperature range c | -173 to +127 (external) |
| pressure | External vacuum |
| radiation | Full GCR and SPE exposure before regolith burial |
| dust | Lunar regolith abrasion on external surfaces |
Operational
| power consumption w | 0 |
| thermal range c | -173, 127 |
| lifetime years | 100 |
Interfaces
Provides
- Hard-point attachment interfaces for secondary structural members and bracing
- Module support cradle points that carry pressure vessel weight and thrust loads
- Load paths from docking port reaction loads into truss structure
- Base attachment interfaces transferring all loads to foundation system
Requires
- Foundation anchorage points providing fixed-base reaction to all truss loads
- High-strength bolted and pinned connections at truss joints
- Thermal coatings and MLI on truss members to reduce thermal gradient severity
- Robotic assembly of truss segments during construction phase
Cite this entry
Lunar Ark Codex. "Primary Truss Structure" (L3-STR-FRAME-TRUSS). Retrieved 10 September 2026, from https://lunarark.com/entry/L3-STR-FRAME-TRUSS
Licensed CC-BY-SA 4.0. You may reuse and adapt this entry with attribution, under the same licence.