Astronauts on a three-year trip to Mars will throw nothing away, including human waste. Precisely how to turn such waste into food, oxygen and water is the subject of MELLISA, an ESA project, that is building a small pilot plant in Spain.
The plant is shortly to be scaled-up and tested on three rats, whose oxygen demand and carbon dioxide production is roughly equivalent to that of one human.
‘We are creating an artificial ecosystem which uses micro-organisms to process the waste so that we can grow plants,’ said Christophe Lasseur from the MELISSA project team at ESA’s technical centre ESTEC in the Netherlands.
MELISSA (Micro-Ecological Life Support Alternative) is reported to go further than other recycling systems used on Mir or the International Space Station, which purify water and recycle exhaled carbon dioxide, but do not attempt to recycle organic waste for food production.
The MELISSA recycling system will consist of five separate, but interconnected, compartments. In three of them, different fermentation processes will progressively break down waste.
In the fourth compartment, algae or plants will grow to produce food, oxygen and water. The fifth compartment is where the consumers will live.
The ESA said that MELISSA can be likened to a lake: at the bottom is sludge (raw waste) which undergoes anaerobic (without oxygen) fermentation in darkness.
Higher up there’s light but no oxygen. Higher still there’s oxygen and it’s possible to transform ammonia to nitrate. At the surface, there’s carbon dioxide, oxygen and light. This is where higher plants can thrive,’ explained Lasseur.
The different components of MELISSA are being studied and built all over Europe and taken to Spain for assembly into the pilot.
So far, small models of the three fermentation chambers are operating there together.
Shortly after the summer, larger chambers will replace them, each with 50-100 litre capacity.
The fourth chamber, where higher plants are grown, is under development at the University of Guelph, Canada, which recently opened a new facility for growing plants at the sort of low pressure found in space.
By 2005, the pilot plant should be fully operational with all five compartments working together.