EPISODE 3: MUSHROOMS ON MARS
CLOSED LOOP SYSTEMS IN SPACE
Closed-Loop Systems and Growing in Space: An Overview
A closed-loop system refers to a self-sustaining cycle in which resources such as water, air, and nutrients are continuously recycled and reused with minimal waste. In the context of space exploration, closed-loop systems are essential because resupply from Earth is limited, especially for long-duration missions to destinations like Mars or lunar bases. These systems aim to create a self-sufficient environment where astronauts can live and work for extended periods by recycling their waste into usable resources like food, water, and oxygen.
The Need for Closed-Loop Systems in Space:
Space habitats, such as the International Space Station (ISS) and future lunar or Martian bases, cannot rely on regular resupply missions for essential resources like water, oxygen, and food. The cost of transporting these materials is incredibly high, and the logistics of resupplying missions further from Earth, such as Mars missions, are extremely challenging.
Closed-loop systems allow for:
1. Minimizing Resource Usage: Limited space and weight for carrying resources on spacecraft means that efficient recycling of water, air, and nutrients is crucial.
2. Waste Reduction: By converting human waste, carbon dioxide, and other byproducts into useful inputs for food production and oxygen generation, closed-loop systems greatly reduce the need for external resources.
3. Self-Sustainability: The goal is to create a self-sustaining environment where everything astronauts need for survival—air, water, food—can be continuously produced and recycled.
Components of a Closed-Loop System
A fully functional closed-loop system in space must cover all aspects of human life support: air, water, food, and waste. Each component must be interconnected so that the outputs of one process can serve as the inputs for another.
1. Air Regeneration (Oxygen and Carbon Dioxide Management)
- Oxygen Production: Plants and algae play a key role in producing oxygen through photosynthesis, using carbon dioxide (CO₂) exhaled by astronauts. This process is vital for maintaining breathable air in a closed-loop environment.
- Carbon Dioxide Removal: Astronauts and other living organisms produce CO₂, which must be removed from the air to prevent dangerous levels from building up. This CO₂ can be captured and fed into a plant growth system, where it is used for photosynthesis.
2. Water Purification and Recycling
- Water Recovery: Water is perhaps the most critical resource in space. In a closed-loop system, water from sweat, urine, and other waste sources is captured and purified for reuse. This process ensures that the water supply remains sustainable over long periods.
- Hydration for Plants: Recycled water is also used to hydrate plants and crops, which can be grown hydroponically (without soil) or in specially designed growth chambers.
3. Food Production
- Growing Plants in Space: Plants are grown in controlled environments to provide astronauts with fresh, nutritious food. Crops like lettuce, radishes, wheat, and even tomatoes have been successfully grown on the ISS. These crops not only provide calories but also essential vitamins and minerals that are important for long-term health in space.
- Mushrooms and Algae: Mushrooms and algae are other potential food sources for closed-loop systems. Both can grow on organic waste, recycling nutrients while providing protein and other nutrients for human consumption.
4. Waste Recycling
- Organic Waste Management: Organic waste, including food scraps, plant material, and human waste, is broken down by bacteria and other microorganisms in bioreactors. This process produces usable nutrients for plants, as well as methane or other gases that can be captured for energy or further recycling.
- Composting and Nutrient Recycling: Organic waste can also be composted to create nutrient-rich substrates for plants, ensuring that nothing goes to waste.
Closed-Loop Systems in Current Space Missions**
1. International Space Station (ISS)
The ISS is equipped with a partial closed-loop life support system, which recycles water and removes CO₂ from the atmosphere, but it still relies on periodic resupply missions from Earth. The ISS features several systems that provide a basis for developing full closed-loop systems in the future:
- Water Recovery System (WRS): The WRS on the ISS recycles 93-98% of water used aboard, including urine, sweat, and condensation from the air. This water is purified and made safe for astronauts to drink again.
- Oxygen Generation System (OGS): The OGS uses electrolysis to split water molecules into oxygen (O₂) and hydrogen (H₂). The oxygen is fed into the cabin atmosphere, and the hydrogen is either vented into space or combined with CO₂ to produce more water through a process called the Sabatier reaction.
- Vegetable Production (Veggie): The Veggie Plant Growth System allows astronauts to grow fresh crops like lettuce, radishes, and mustard greens on the ISS. While this system is primarily for research, it demonstrates the potential for growing food in space.
2. MELiSSA Project
The MELiSSA Project (Micro-Ecological Life Support System Alternative) by the European Space Agency (ESA) is one of the most advanced closed-loop systems being developed for long-term space missions. It uses a multi-compartment system that includes plants, bacteria, algae, and humans to create a fully self-sustaining ecosystem. MELiSSA’s compartments include:
- Anaerobic bioreactors to break down organic waste into simpler compounds,
- Bacteria to convert these compounds into nutrients for plants,
- Algae and plants to produce oxygen and food.
MELiSSA’s system is designed to be scalable for future missions to Mars or lunar bases.
Challenges of Growing in Space and the Role of Closed-Loop Systems
1. Microgravity Effects on Plant Growth
- In microgravity, water and nutrients don’t move through the soil or substrate the same way they do on Earth. This can lead to uneven moisture levels, which affects plant growth. Closed-loop systems use techniques like hydroponics (growing plants in nutrient-rich water) and aeroponics (growing plants in an air or mist environment) to manage this.
- Plants also exhibit gravitropism, meaning they grow in response to gravity. In space, plants may grow in unusual directions, but they can still photosynthesize and produce food. Lighting systems and artificial gravity in rotating habitats could be used to guide plant growth.
2. Water and Nutrient Delivery
- In microgravity, delivering water and nutrients to plant roots is more complex because water forms droplets and doesn’t flow as it does on Earth. Closed-loop systems solve this by using capillary systems or wicks to distribute water evenly. These systems ensure that plants get the necessary moisture and nutrients without the reliance on gravity.
3. Air Circulation and Gas Exchange
- In the absence of gravity, natural convection doesn’t occur. This means air does not circulate on its own, leading to potential problems with CO₂ buildup around the plants. Forced air systems are needed to maintain proper air circulation, ensuring that plants receive enough oxygen for respiration and CO₂ for photosynthesis.
4. Energy Requirements
- Closed-loop systems require energy to maintain the necessary lighting, temperature, and airflow conditions for plant growth. This can be challenging on long-duration missions where energy supplies are limited. Solar energy, nuclear power, or other renewable sources will likely be needed to power these systems on the Moon or Mars.
5. Contamination and Sterilization
- The risk of contamination from other microorganisms in a closed-loop system is high, especially in the confined environment of space habitats. If harmful bacteria, fungi, or other pathogens infiltrate the system, it could jeopardize both the food production and the health of the crew. Sterilization protocols and constant monitoring of the system are necessary to ensure that it operates without contamination.
Future of Closed-Loop Systems for Space Agriculture
1. Mars and Lunar Bases
- Future habitats on Mars or the Moon will rely heavily on closed-loop systems for resource management. Spacefarers on these missions will need to recycle all air, water, and nutrients efficiently, and plants will play a key role in producing food and oxygen.
- Myco-architecture (using fungal mycelium to build structures) could be combined with plant growth systems to create habitats that not only provide shelter but also support life by recycling resources and growing food within the habitat’s walls.
2. Terraforming Support
- On a planet like Mars, closed-loop systems could help in early terraforming efforts by enriching the soil with nutrients from recycled waste and organic matter. Fungi and bacteria could be used to process Martian regolith and create fertile ground for plants, helping to establish a sustainable ecosystem over time.
Closed-loop systems are critical to the future of space exploration and long-duration missions, as they enable the recycling of waste into valuable resources like oxygen, water, and food. Growing plants and other organisms in these systems provides astronauts with fresh food and plays a crucial role in life support by converting CO₂ into oxygen.
The ongoing research aboard the ISS and in projects like MELiSSA continues to refine these systems, bringing us closer to a future where astronauts can live self-sufficiently on the Moon, Mars, or even deeper in space.