The Secret to Survival in Space
Closed Ecosystems and the Science of Self-Contained Worlds
Imagine being sealed inside a giant, glass-enclosed world for two years, cut off from the Earth's natural resources. Your every breath, every sip of water, and every bite of food must be generated and recycled within this miniature planet. This isn't a scene from a science fiction novel—it was the reality for eight crew members of Biosphere 2, a groundbreaking experiment that tested our ability to recreate Earth's life support systems.
As we set our sights on establishing bases on the Moon and Mars, scientists are racing to solve one of our greatest challenges: how to build tiny, self-sustaining ecosystems that can keep astronauts alive indefinitely in the harsh environment of space. These closed ecological systems represent one of the most fascinating frontiers in science today, blending biology, technology, and systems thinking to potentially enable humanity's future among the stars.
Biosphere 2
3.14-acre enclosed facility testing closed ecological systems
8 Crew Members
Lived sealed inside Biosphere 2 for two years
What Exactly is a Closed Ecological System?
In nature, most ecosystems are open—they exchange both energy and matter with their surroundings. A forest, for instance, receives water from rainfall, nutrients from the air and surrounding land, and animals that move in and out. A closed ecological system (CES), by contrast, is an ecosystem that does not rely on matter exchange with any part outside the system 1 . Think of a sealed glass jar containing water, algae, and tiny shrimp—an ecosystem where nothing enters or leaves, but where life inside can thrive for years.
Open Ecosystem
- Exchanges both energy and matter
- Example: Forest receiving rainfall
- Animals move in and out freely
- Nutrients flow across boundaries
Closed Ecosystem
- Energy flows in, matter stays contained
- Example: Sealed jar with algae and shrimp
- All organisms remain inside
- Nutrients are constantly recycled 9
The key distinction lies in what crosses the boundary:
- Energy can (and must) flow into a closed ecosystem, typically in the form of light.
- Matter—the physical stuff like water, air, and nutrients—is contained and constantly recycled within the system 9 .
In practice, a functioning CES must carefully balance its components. Any waste produced by one species must be used by at least one other species. If the system contains animals or humans that breathe oxygen and produce carbon dioxide, there must be photosynthetic organisms like plants or algae to convert that carbon dioxide back into oxygen. Similarly, waste products like feces and urine must eventually be converted into nutrients, food, and water through natural processes or technological means 1 . This delicate dance of elements is what allows a small world in a bottle—or a future space habitat—to sustain life indefinitely.
The Science of Interconnectedness: Systems Biology
Understanding how closed ecosystems function requires more than just studying their individual components—it demands a holistic approach that examines how all parts work together. This is where systems biology comes in. Rather than focusing on single genes or proteins in isolation, systems biology uses computational and mathematical modeling to understand complex interactions within biological systems 2 . It's the difference between examining a single watch gear and understanding how all the gears work together to tell time.
Systems Biology Applications in CES
Model Complex Interactions
Between plants, microorganisms, animals, and environment
Understand System Resilience
How ecosystems respond to disturbances
The Institute for Systems Biology describes this approach as recognizing that our bodies—and indeed all ecosystems—are fundamentally "a network of networks" 7 . From molecular interactions within cells to the complex relationships between species in an ecosystem, systems biology provides the tools to understand these connections and predict how the system will behave under different conditions.
This holistic perspective is particularly crucial for space applications, where a failure in one part of the ecosystem could have catastrophic consequences for astronauts depending on it.
Biosphere 2: A Landmark Experiment in Closed Ecology
No discussion of closed ecological systems would be complete without examining Biosphere 2, the most ambitious attempt ever made to create a self-sustaining miniature world. Located in Oracle, Arizona, this massive 3.14-acre enclosed glass facility was designed as a prototype for future space habitats and an unprecedented laboratory for studying global ecology 5 .
The Grand Experiment
Between 1991 and 1993, eight people sealed themselves inside Biosphere 2 for two years, during which they produced their own food and recycled their air, water, and waste using the enclosed ecosystems. The facility contained five distinct wilderness biomes mimicking different Earth environments:
- A tropical rainforest with over 90 species of plants
- A mangrove wetland with saltwater species
- A miniature ocean with a coral reef
- A savannah grassland with acacia trees and grasses
- A fog desert with specialized desert plants 5
The Biosphere 2 facility in Arizona, a massive enclosed ecological system
Water Recycling: A Technical Marvel
One of the most impressive achievements of Biosphere 2 was its sophisticated water recycling system, which had to manage approximately 6 million liters of water distributed across different reservoirs 5 . The system employed multiple technologies to maintain water quality and availability:
| Reservoir | Approximate Capacity | Primary Function |
|---|---|---|
| Ocean/Marsh | 4,000,000 L | Marine ecosystems, humidity regulation |
| Soil | 1,000,000-2,000,000 L | Plant growth, water filtration |
| Primary Storage Tank | 0-800,000 L | Irrigation supply, water management |
| Condensate & Mixing Tanks | 160,000 L | Collecting atmospheric moisture |
| Atmosphere | 2,000 L | Humidity, transpiration pathway |
The system collected moisture through condensation from humidity in the air handlers and from the glass space frame, producing high-quality freshwater. Wastewater from all human and animal uses was treated and recycled through a series of constructed wetlands, which served as natural water purification systems. These wetlands not only cleaned the water but also produced 1,210 kg of emergent and floating aquatic plants that were used as fodder for the domestic animals 5 .
Lessons from the Sealed World
Despite its impressive engineering, Biosphere 2 encountered significant challenges that provided valuable lessons for future closed ecological systems:
| Challenge | Impact on the System | Solution Implemented |
|---|---|---|
| Oxygen depletion | Oxygen levels dropped from 20.9% to 14.5% | Added oxygen from external sources in year 2 |
| Carbon dioxide fluctuations | CO² levels became extremely high during the night | Installed a CO² scrubber similar to those used in spacecraft |
| Food production | The agricultural system produced less food than expected | Crew members lost weight but adapted their diets |
| Ecological imbalances | Some species populations exploded while others died out | Manual intervention to maintain balance between species |
The psychological challenges were equally significant. Crew members reported symptoms similar to those experienced in other isolated, confined environments (ICE): depression, irritability, insomnia, and cognitive impairment 5 . These findings highlight that designing closed ecological systems for space must address both technical and human factors.
Oxygen Levels in Biosphere 2
Oxygen levels dropped dangerously during the mission, requiring external intervention.
The Scientist's Toolkit: Building Miniature Worlds
Creating and studying closed ecosystems requires specialized materials and approaches, from simple classroom experiments to sophisticated space-life-support systems.
| Item | Primary Function | Application Example |
|---|---|---|
| Autotrophic organisms (e.g., green algae, cyanobacteria) | Produce oxygen and biomass from CO² and light; form the base of the ecosystem's food web | Primary producers in BIOS-3 and MELiSSA projects 1 |
| Heterotrophic organisms (e.g., shrimp, snails, microorganisms) | Consume organic matter, recycle nutrients, help maintain ecological balance | Small aquatic animals in classroom ecospheres 8 |
| Constructed wetland components | Natural wastewater treatment through plant-based filtration | Used in Biosphere 2 to recycle human and animal wastewater 5 |
| Soil and growth media | Support plant growth, host microbial communities, nutrient storage | Agricultural areas in Biosphere 2; soil-based systems in Laboratory Biosphere 5 |
| Water quality testing kits | Monitor pH, salinity, nutrient levels, and contaminants | Essential for maintaining balanced aquatic ecosystems in closed systems |
| Gas exchange monitoring equipment | Track O² and CO² levels to ensure atmospheric balance | Critical in Biosphere 2 when oxygen levels dropped unexpectedly 5 |
| Genetic sequencing tools | Analyze microbial diversity and ecosystem health | Systems biology approaches to understand community dynamics 7 |
Building a Simple Classroom Ecosphere
For educational purposes, building a simple closed ecosystem can be surprisingly straightforward 8 :
Step 1: Container Preparation
Obtain a large clear bottle with a tight-fitting cap
Step 2: Collect Components
Collect several small plants, aquatic organisms (like shrimp or snails), some soil, and water (preferably from a pond, which contains diverse microorganisms)
Step 3: Assembly
Place all materials into the bottle
Step 4: Sealing
Seal the cap tightly, using melted wax or another sealant to make it airtight
Step 5: Placement
Place the container where it will receive at least indirect sunlight
Students can then observe and record changes in their miniature worlds, noting temperature variations, color changes in the water, and population dynamics among the organisms—all valuable lessons in ecological principles.
The Future of Closed Ecosystems: From Laboratories to Space Colonies
Current research in closed ecological systems builds on the lessons of Biosphere 2 and similar projects. The European Space Agency's MELiSSA (Micro-Ecological Life Support System Alternative) project aims to develop a closed life support system for long-duration space missions using interconnected compartments where waste is broken down by microorganisms and converted into food, water, and oxygen 1 . Similarly, China's Lunar Palace 365 experiment has demonstrated closed life support systems with human crews for extended periods.
MELiSSA Project
European Space Agency's initiative to develop a closed-loop life support system using interconnected biological compartments to recycle waste into food, water, and oxygen.
Lunar Palace 365
China's experiment demonstrating closed life support systems with human crews for extended periods, paving the way for future lunar bases.
The emerging field of multiomics—the integration of genomic, proteomic, metabolomic, and other biological data—is revolutionizing our ability to understand and optimize these systems 7 . By analyzing the molecular interactions within closed ecosystems, scientists can develop predictive models that anticipate problems before they occur and design more resilient ecological communities.
Roadmap to Space Colonies
As we look toward establishing permanent settlements on the Moon and Mars, closed ecological systems will likely evolve through several stages:
Initial Deployment
Small, simplified systems to supplement physical/chemical life support
Expansion
Include more diverse biological components as understanding improves
Development
Fully bioregenerative systems that can support human life indefinitely
"It's not wise to violate rules until you know how to observe them," wrote T.S. Eliot 6 . As we continue to explore the boundaries of closed ecological systems, we're not just learning the rules of sustainable life support—we're learning how to rewrite them for worlds yet to be inhabited.
The journey from the simple sealed jar on a classroom shelf to a life-sustaining habitat on Mars represents one of humanity's most ambitious scientific and engineering challenges. Each miniature world we create and study brings us closer to becoming a multi-planetary species, capable of carrying the gift of Earth's ecological wisdom to the farthest reaches of our solar system and beyond.