Oxygen Reactant Storage Tank
Cryogenic / High-Pressure Stainless O2 Storage Vessel with MLI
Cryogenic/high-pressure oxygen storage vessel paired with the H2 tank, holding ~800 kg O2 in a stainless-steel pressure shell with MLI vacuum jacket; can also serve as a shared O2 reserve for L1-WMS life-support, L1-HAB, and ISRU propellant uses.
Purpose
Store the oxygen reactant inventory for the fuel cell across the lunar night while minimising boil-off and complying with strict oxygen-compatible materials and cleanliness requirements (no hydrocarbon contamination, no ignition risk).
Context
Filled by L3-ESS-FC-ELEC at 30 bar; supplies L3-ESS-FC-STACK via L3-ESS-FC-BOP. May share inventory with L1-WMS for crewless life-support emergencies (if Ark ever supports crewed visit). Located in a separate cluster from H2 tank for safety separation.
Principles
- ▸Liquid oxygen density 1141 kg/m³ at 90 K (much denser than LH2 — 16:1 volume advantage)
- ▸Stoichiometric H2:O2 mass ratio is 1:8 → for 100 kg H2 storage, ~800 kg O2 needed
- ▸Oxygen is non-cryogenic-fragile (boils 90 K vs H2 20 K) — broader MLI and cooling tolerance
- ▸Oxygen-compatible materials must meet NASA-STD-6001 / ASTM G63 for ignition resistance; stainless 316L, Monel 400, and PTFE-lined seals are standard
- ▸No hydrocarbons (oils, greases) allowed in O2-wetted surfaces — risk of ignition under impact or adiabatic compression
- ▸Stratification in cryogenic LO2 tanks causes pressure rise; thermodynamic vent (sub-cooler) or stirring required
Typical implementations
- ▸Apollo Service Module LO2 storage — supercritical fluid storage (~1000 psi, 100 K)
- ▸Space Shuttle Power Reactant Storage and Distribution (PRSD) tanks — cryogenic supercritical
- ▸Ariane 5 ESC-A LO2 tank — aluminum alloy
- ▸ULA ACES cryogenic LO2 storage with thermodynamic vent
- ▸NASA OASIS oxygen reservoir for ISS
- ▸Lunar GATEWAY cryogenic O2 storage concepts
Lunar considerations
- ▸Oxygen boiling point 90 K is achievable with passive radiator alone at south pole (PSR floor ~88–110 K) — no active cooling required in best siting
- ▸Equatorial / non-PSR siting requires cryocooler (~10 W at 90 K, much cheaper than H2 at 20 K)
- ▸Material cleanliness for O2 service is more stringent than for H2 — installation and maintenance protocols required
- ▸Stratification under 1/6 g still occurs; thermodynamic vent design must account for reduced gravitational settling
- ▸Co-located WMS and HAB oxygen demands can buffer through the same tank if life-support is added later
- ▸Dust ingress risk to fill/vent valves — labyrinth seals and EDS protection required
Specifications
Functional
| primary function | Store O2 reactant inventory between charge and discharge cycles |
| inputs | Pressurized O2 from L3-ESS-FC-ELEC (30 bar), Cryocooler cold-finger from L1-CRY (if active cooling required), Sensors for pressure / temperature / mass gauge |
| outputs | Regulated O2 to L3-ESS-FC-STACK via L3-ESS-FC-BOP, Optional O2 to L1-WMS / L1-HAB during emergencies, Tank telemetry, vent status, Pressure-relief vent (safety only) |
| capacity kg o2 | 850 |
| internal volume m3 | 0.95 |
| operating pressure bar | 30 |
| burst pressure bar | 67 |
| operating temperature k | 90, 130 |
| max boil off percent per day | 0.1 |
| design lifetime years | 25 |
| cleanliness class | ASTM G63 oxygen-compatible |
Physical
| mass kg | 80 |
| dimensions | 1.2 m diameter × 1.0 m length (cylindrical, hemispherical end caps) |
| materials | 316L stainless steel inner pressure vessel (O2-compatible), Monel 400 fill/vent fittings, 30-layer MLI blanket inside vacuum jacket, Outer vacuum jacket: 6061-T6 aluminum, PTFE-lined metal seals at all O2-wetted joints, Thermodynamic-vent sub-cooler tube, Mass gauge: capacitance probe with PTFE dielectric |
| operating temperature k | 90, 130 |
| exterior temperature c | -180, 130 |
| vacuum jacket pressure torr | 1e-05 |
| ultimate load g | 6 |
Operational
| power consumption w cooling | 10 |
| thermal range k | 90, 130 |
| lifetime years | 25 |
| mtbf hours | 250000 |
| expected o2 loss kg per year | 31.0 |
Interfaces
Provides
- Regulated O2 supply at 5–10 bar
- Backup O2 for life-support emergencies (optional)
- Tank state telemetry
Requires
- O2 charging at 30 bar
- Cold-finger interface for active cooling (~10 W at 90 K)
- Outer-jacket radiator path
- Anchored mounting separated from H2 tank by ≥10 m
Cite this entry
Lunar Ark Codex. "Oxygen Reactant Storage Tank" (L3-ESS-FC-O2TK). Retrieved 10 September 2026, from https://lunarark.com/entry/L3-ESS-FC-O2TK
Licensed CC-BY-SA 4.0. You may reuse and adapt this entry with attribution, under the same licence.