💨 Sustaining Life in Space
Space is utterly inhospitable - no oxygen, extreme temperatures, dangerous radiation. The Environmental Control and Life Support System (ECLSS) creates and maintains a habitable environment inside the station.
ECLSS Core Functions
- Atmosphere Management: Oxygen supply and CO₂ removal
- Temperature Control: Maintain comfortable 18-27°C
- Humidity Control: Regulate 30-70% humidity
- Contaminant Removal: Filter harmful substances
- Water Recovery: Recycle water from all sources
💧 Oxygen Generation
Electrolysis Oxygen Generators
ISS primary oxygen source splits water into oxygen and hydrogen using electricity:
2H₂O + electricity → 2H₂ + O₂
US Oxygen Generation System (OGS)
- Production: 5-9 kg/day (enough for 6 crew)
- Power: 1,000-1,500W
- Location: Destiny module
- Byproduct hydrogen sent to Sabatier Reactor
Russian Elektron System
- Production: ~6 kg/day
- Heritage from Mir station
- Over 30 years operational experience
- Location: Zvezda service module
Solid Fuel Oxygen Generators (SFOG)
- Backup/emergency oxygen source
- Burns sodium chlorate candles
- Generates 600L oxygen per candle
- Cannot be stopped once started
- Reaction temperature: 450-500°C
🌬️ Carbon Dioxide Removal
Carbon Dioxide Removal Assembly (CDRA)
US system using zeolite molecular sieves to absorb CO₂.
- Two beds alternate: one absorbing, one regenerating
- Adsorption: 30 min | Desorption: 30 min | Cooling: 90 min
- Removes CO₂ from crew of 6
- Regenerates by vacuum and heating
Russian Vozdukh System
- Uses wet amine scrubber
- Chemically absorbs CO₂ into amine solution
- Regenerates by heating to release CO₂
- Over 30 years heritage
Sabatier Reactor
Recycles CO₂ by reacting with hydrogen to produce water and methane:
CO₂ + 4H₂ → CH₄ + 2H₂O + heat
- Water recycled back to electrolysis
- Methane vented to space
- Recovers ~50% of water
- Operating temperature: 400°C
- Reduces resupply needs significantly
💦 Water Recovery System
Water costs ~$20,000/kg to launch, making recycling essential.
Water Sources (per crew member per day)
| Source | Amount |
|---|---|
| Urine | ~1.5 L |
| Humidity condensate | ~2.0 L |
| Hygiene water | ~0.5 L |
| Sabatier byproduct | ~0.5 L |
Urine Processor Assembly (UPA)
- Vacuum distillation process
- Recovery rate: 85-90%
- Capacity: ~9 L/day
- Pretreatment prevents crystallization
- Concentrated brine disposed periodically
Water Processor Assembly (WPA)
Purifies recovered water to potable standards through:
- Multi-stage filtration (particles, biologicals)
- Catalytic reactor (oxidizes organics at high temp)
- Ion exchange (removes inorganic ions)
- Iodine addition (disinfection)
- Quality testing (conductivity, pH)
Overall water recovery: ~93%
Annual savings: ~2,700 kg water (~$54 million)
🌡️ Temperature and Humidity Control
- Target temperature: 18.3-26.7°C (65-80°F)
- Target humidity: 30-70% (ideally 40-60%)
- Air circulation: 8-10 times per hour
- HEPA filtration removes particulates
Humidity Removal
Condensation on cold surfaces captures moisture:
- ~2L per crew member per day from respiration and perspiration
- Condensate sent to WPA for recycling
- Prevents equipment corrosion and mold growth
🧪 Trace Contaminant Control
Trace Contaminant Control System (TCCS)
- Activated charcoal bed absorbs volatile organics
- Catalytic oxidizer breaks down organics to CO₂ and H₂O
- Operating temperature: ~400°C
- Removes 200+ contaminants (methanol, benzene, toluene, freon, etc.)
🔄 Integrated Closed-Loop System
All systems work together in harmony:
- Electrolyze water → oxygen + hydrogen
- Crew breathes oxygen → exhales CO₂
- Remove CO₂ → react with hydrogen (Sabatier)
- Sabatier produces water → back to electrolysis
- Cycle repeats continuously
This closed-loop approach is essential for future Moon and Mars missions where resupply is impossible.
Next chapter examines power generation and thermal control systems.