Water management in space – examples of hydration systems for cultivation in microgravity and future prospects

The movement of water in, across and out of the plant is a key factor when growing plants as part of a closed regenerative life support system required for long duration space missions. Under microgravity conditions, it has been proven that transpiration rate of leaves is suppressed by retarding the water vapour transfer due to restricted free air convection. Previous experiments on Mir and the International Space Station (ISS) illustrated the importance of monitoring the water status of plants in space. A frequently reported cause for loss of science in space experiments is wilting of seedlings because the water supply system in the growth facility (hardware) was not working properly. This could possibly have been detected earlier and prevented if better tools for monitoring the plant water status were available. Currently, experiments in existing growth facilities on the ISS, as well as new hardware, are being designed to assess and monitor plant water uptake and transport in microgravity. However, finding suitable watering technologies and methods for monitoring water status in space facilities has proven to be challenging. These challenges include the confined environment, the limited amount of available water, as well as restrictions on upload mass and crew time on the ISS. Examples of hydration systems for plants grown on Mir and the ISS and technologies used for monitoring the water status in the growth media in previous space experiments, as well as future prospects will be presented.