"Replicators began not merely to exist, but to construct for themselves containers, vehicles for their continued existence. The replicators that survived were the ones that built survival machines for themselves to live in. The first survival machines probably consisted of nothing more than a protective coat. But making a living got steadily harder as new rivals arose with better and more effective survival machines. Survival machines got bigger and more elaborate, and the process was cumulative and progressive."
-Richard Dawkins, The Selfish Gene
-Richard Dawkins, The Selfish Gene
CELSS DefinedClosed Ecology Life Support Systems (CELSS) are a scientific and cultural endeavor to create self-reliant environments that can support and maintain human life. The situation is somewhat analogous to the evolution of cellular life, whose cell walls and membranes permitted life to survive and thrive beyond the confines of its primordial soup. CELSS are "living machines"Â which, ideally, provides inhabitants with 100% of their life support (organic food, fresh oxygen-rich air, clean water) by recycling the waste products generated by the inhabitants and by the CELSS itself.
Meaning of ClosedWhile CELSS are simplified, scaled down versions of the Earth's ecosystem, they are intended to be isolated and independent from the Earth's ecosystem. In thermodynamic terms, 'Closed' means that no physical matter is needed to be dumped from or added to the system in order to maintain equilibrium. Energy exchange in the form of sunlight, heat, etc is permitted.
Meaning of System
A system is a configuration of components acting as a whole, connected and joined together by a web of relationships.
The major components of CELSS are characterized by human needs, roughly following from Maslow's Hierarchy of Needs, with emphasis on the basic physiological needs (Air, Water, Food, and Energy. Higher psychological needs and long term well being are lumped together under the Spirit category.
Individual subsystems inherently cross boundaries of these categories, because many of the cycles intersect (e.g., the oxygen cycle intersects the carbon cycle; both are part of air flow, water flow, energy conversion/photosynthesis, and food production).
Another way to break it down is to evaluate the system as a cyclic process driven by an energy source (the sun). Autotrophic producers (plants) make solid (food), liquid (water), and gas (oxygen), which all feed consumers (animals). The animals produce waste in solid (feces), liquid (urine), and gas (carbon dioxide) forms. With the help of bacteria, these are utilized by the plants to continue the production cycle. Of course this explanation is grossly simplified, neglecting the food chain within the animal kingdom, other gases like methane, plant wastes, and fungi, etc. However, it becomes evident that the process interfaces governing this system will need to control the flow of produce and waste by its material state: gas (air), liquid (water), or solid (food), as well as mediating the flow of energy throughout the system.
DesignThe system is comprised of subsystems that interface with each other and with external inputs (adapted from NASA Advanced Life Support Baseline Values and Assumptions Document).
|Air||The Air Subsystem stores and maintains the vehicle cabin atmospheric gases, including pressure control, overall composition, and trace constituents. The Air Subsystem is also responsible for fire detection and suppression and vacuum services.||Biomass, Food, Thermal, Waste, Water, Crew, EVA Support, Human Accommodations, ISRU, Integrated Control, Power|
|Food||The Food Subsystem receives harvested agricultural products from the Plant Subsystem, stabilizes them as necessary, storing raw and stabilized agricultural products, food ingredients, and prepackaged food and beverage items. The Food Subsystem transforms the raw agricultural products into a ready-to-eat form via food processing and meal preparation operations.||Air, Plant, Thermal, Waste,Water, Crew, EVA Support,Human Accommodations, Integrated Control, Power, Radiation Protection|
|Energy||The Energy Subsystem is responsible for maintaining thermal balance within appropriate bounds and for rejecting the collected waste heat to the Cooling Interface. Note: Equipment to remove thermal loads from the cabin atmosphere normally provides sufficient air circulation.||Air, Plant, Food, Waste, Water, Crew, Cooling, EVA Support, Human Accommodations, Integrated Control, Power|
|Water||The Water Subsystem collects wastewater from all possible sources, recovers and transports potable water, and stores and provides the water at the appropriate purity for crew consumption and hygiene as well as external users.||Air, Biomass, Food, Thermal, Waste, Crew, Cooling, EVA Support, Human Accommodations, ISRU, Integrated Control, Power, Radiation Protection|
|External Interfaces||Description||Life Support Interface|
|Crew||The Crew Interface interacts with most life support subsystems and external interfaces. Crewmembers have been, and should continue to be, the foremost consumers of life support commodities as well as the primary producers of waste products. Finally, life support technologies are specifically designed to provide for the health, safety, and maximum efficiency of crewmembers.||Air, Plant, Food, Thermal, Waste, Water, EVA Support, Human Accommodations, ISRU, Integrated Control, Power, Radiation Protection.|
|Cooling||The Cooling Interface rejects vehicle thermal loads, delivered by the Thermal Subsystem, to the external environment.||Thermal, Water,Integrated Control, Power|
|Extravehicular Activity Support||The Extravehicular Activity Support Interface provides life support consumables for extravehicular activities, including oxygen, water, and food. It also provides for the removal of carbon dioxide and waste.||Air, Food, Thermal, Waste, Water, Crew, Human Accommodations, Integrated Control, Power|
|Human Accommodations||The Human Accommodations Interface is responsible for the crew cabin layout, crew clothing (including laundering), and the crewÃ¢â¬â¢s interaction with the life support system.||Air, Plant, Food, Thermal, Waste, Water, Crew, EVA Support, Integrated Control, Power|
|ISRU||The In-Situ Resource Utilization Interface provides life support commodities, such as gases, water, and regolith from local planetary materials for use throughout the life support system.||Air, Plant, Water, Crew, Integrated Control, Power, Radiation Protection|
|Integrated Control||The Integrated Control Interface provides appropriate control for the life support system.||ALL|
|Radiation Protection||The Radiation Protection Interface provides protection from environmental radiation.||Food, Waste, Water, Crew, ISRU, Power|
Every organism and piece of equipment can be considered as a module with inputs and outputs for each subsystem. Technologically complex systems tend to break down faster than simple systems. If one piece of hardware can do 3 things simultaneously, it is preferred to more specialized solution. Spare parts and expendables should be manufacturable using labor and material resources within the CELSS. The number of human hours spent per day keeping the system fully operational should also be considered.
There is a dynamic relationship between humans, animals, plants, fungi, and symbiotic micro-organisms. CELSS must optimize these relationships by building containment vessels which provide optimal conditions for each of the above while preventing pathogens from thriving.
SizeHow large should a fully operational CELSS be? Perfect sunlight conditions on Earth (high noon on a cloudless day at the equator) yield about 860 kcal of heat per square meter each hour. Of course, humans have to receive that energy in the form of food (2000 Cal = 2000 kcal, each day for an adult), which, at least initially, must be photosynthesized (~5% efficiency). Thus for a 12 hour day, each person would need roughly 4 sq meters of grow area for food production, as a theoretical minimum.
Here are some optimistic minimum figures from the CELSS life support research community:
ESTIMATED GROW SPACE REQUIRED PER PERSON
14 m2 - Gitalson
56 m2 - Bios3
20-30 m2 - Cullingford & Schwatekopf
13-50 m2 - Bugsbee & Salisbury
56.9 m2 - Oleson & Olson
8-20 m2 - MacElroy? & Averner
15-20 m2 - Eckhart
24 m2 - Hoff
15 m2 - Vasilyew
The above figures are mostly based on human food needs without regard to oxygen production or air filtration. They are tiny compared to the amount of space the average human being requires for life support in both hunter/gatherer and agriculture-based civilizations. Lab work at NASA Ames has already proven that all the air, water, and food for one person can be grown in a 16m x 16m space under optimal conditions with controlled atmosphere, temperature, lighting, and nutrients. Of course this was a highly engineered "hydroponics" style system which required considerable electricity for the lighting, pumps, and climate control plus an outside source of plant nutrients.
Indications are that stability is proportional to size of the system.