Recent advances in the development of the SVET space greenhouse equipment

Providing optimal living conditions for crew members during future long-term missions to other planets has been one of the most important scientific and engineering tasks of our times. Plant crops grown onboard can supplement the food that is carried along from Earth with vitamin addition, regenerate the spacecraft´s atmosphere and have a significant effect on the crew emotional frame creating psychological comfort for the astronauts during their long isolation. The paper describes the Bulgarian developed automated SVET Space Greenhouse (SG) equipment that is between the first ones in the world and with longest time of functioning in orbit. It also contains a brief report of the main experimental results obtained during the unique plant space experiments conducted onboard the MIR Space Station on Russian and American research programs during the period 1990-2000. They proved that there is not an obstacle of principle for normal plant development and reproduction under microgravity. Next step towards the development of future space greenhouses with a large growing area was to improve the equipment and biotechnology for plant growing under weightlessness and to work out experimentally some important questions concerning plant development in extreme environmental condition. The Bulgarian scientists developed a new concept for adaptive control of the plant environmental parameters for the next generation SUET SG with additional monitoring of some physiological processes which allow evaluating plant status and optimising growth conditions during the experiment. Methods and sensors for measurements of the plant leaf environment parameters (light intensity, air humidity and temperature, air flux velocity, air pressure, gas composition etc.) in SVET-3 SG are being developed. Special attention is paid to the problem of controlling substrate moisture and O₂ content in the plant root environment which is of great importance for normal plant growth. Results obtained in earth experiments imitating some processes that occur in microgravity are discussed.