Hydroponics for plant cultivation in space – a white paper

The microgravity conditions experienced in space prevent the proper distribution of water throughout root modules of plant growth hardware, and the lack of convective mixing and buoyancy reduces gas exchange. To overcome this problem, cultivation technologies should be designed that take advantage of the unique traits of the spaceflight environment instead of attempting to recreate Earth-like conditions. Such technologies should be adaptable to both the microgravity of spaceflight and the low gravity environments of the lunar and Martian surface. Current space plant cultivation relies on traditional terrestrial practices and uses porous substrates that are nutrient poor and difficult to regenerate, and does not consider the dominance of surface- or thermal gradient-controlled rather than gravity-controlled water flow in space as a potential beneficial property. We propose systems that control water dispensation and removal by parallel but independent means in a soil-free cultivation system that is adaptable and expandable to crops of varying sizes and shallow or deep rooting plants. Water dispensation and removal in a substrate-free hydroponic system can be achieved through the misting of nutrient solutions combined with special root module geometry and temperature gradients. The use of hydrogels as substrate, and a means of providing required nutrients and water for plant cultivation in space, can aid in the transition to low-gravity systems by eventual incorporation of on-site regolith to establish Earth-like soil.