Chapter 4

Closed Ecosystems

Need for Closed Ecosystems

If space habitats depend on Earth resupply, long-term habitation is impossible due to cost and logistics. Launching 1kg to ISS costs ~$10,000. Closed ecosystems recycle resources internally, achieving self-sufficiency. A closed ecological system recycles air, water, and nutrients without external input. Complete closure is extremely difficult - ISS currently recycles 93% of water.

Bioregenerative Life Support Systems

Biological life support systems use plants, microorganisms, and potentially animals to regenerate air, water, and food. Core cycles: - Oxygen Cycle: CO₂ (human breath) → Plant photosynthesis → O₂ - Water Cycle: Wastewater → Purification → Clean water - Nutrient Cycle: Waste → Microbial decomposition → Plant nutrients - Food Cycle: Nutrients + water + CO₂ → Plant growth → Edible crops Plants provide multiple benefits: oxygen production (20-30m² per person), food production, water cycling through transpiration, and psychological benefits.

Space Agriculture Technology Details

1. Hydroponics

Growing plants without soil by dissolving nutrients in water. Most widely used cultivation method in space.

Advantages:

• 90% less water than soil cultivation
• 30-50% faster growth
• Easier pest management
• Less weight and volume

Disadvantages:

• Power outages can quickly kill plants
• Complex nutrient solution management
• Difficult recovery from system failures

2. Aeroponics

Plants suspended in air with nutrient solution sprayed on roots. NASA is actively researching this technology.

Advantages:

• Even less water than hydroponics (98% reduction)
• Optimal oxygen supply for fastest growth
• Easy root observation and management
• Most suitable for microgravity

Disadvantages:

• Risk of spray nozzle clogging
• Complex system prone to failures
• Plant damage within minutes of power loss

Cultivable Crops

Space-suitable crops must meet these criteria:

• Fast growth cycle
• High nutritional value
• Low space requirements
• Hardiness and disease resistance

Water Recycling System Details

Water is one of space's most precious resources. ISS currently achieves ~93% water recycling rate, with goal of 98%+.

Water Cycling Stages

1. Collection:
   • Toilet water, handwashing, shower water
   • Atmospheric humidity (dehumidifier collection)
   • Plant transpiration vapor
   • Human sweat and breath vapor
2. Pre-treatment:
   • Remove large particles (filtering)
   • Remove chemicals (activated carbon)
   • Break down organics (microbes or chemical reaction)
3. Purification:
   • Distillation (heat to vapor then condense)
   • Reverse osmosis (RO membrane removes impurities)
   • UV sterilization (removes microorganisms)
   • Ion exchange (mineral adjustment)
4. Quality Testing:
   • Chemical sensors detect contaminants
   • Microbial testing
   • Taste and odor evaluation
5. Storage and Distribution:
   • Drinking water, cooking water
   • Hygiene water
   • Plant irrigation
   • Oxygen generation (electrolysis)

ISS Water Recovery System

ISS water recovery system consists of two main components:

System	Processes	Recovery	Technology
Urine Processor	Urine	~85%	Distillation + chemical treatment
Water Processor	Greywater, humidity	~99%	Multi-stage filtration + catalyst

These systems save ISS approximately 2,700 kg of water launches annually, equivalent to ~$27 million in cost savings.

Conclusion

The principles and technologies covered in this chapter on Closed Ecosystems are essential for successful space habitat operations. Each element is interconnected and requires an integrated approach. As space technology advances and experience accumulates, these systems will become more sophisticated and efficient.

Space habitation is no longer science fiction but becoming reality. Following the philosophy of 弘益人間 (Benefit All Humanity), we are opening a new era that will benefit all of humanity.