Green plants produce carbohydrate as an energy for all organisms by photosynthesis. It is therefore considered that plant cultivation is necessary for life support not only on Earth but also in space. To inhabit the space for a long duration, human needs to be closed in the life support system in which plants provide them with foods and a stress-relief circumstance. During evolution, on the other hand, plants developed various strategies to survive terrestrial environment on Earth because of their sessile nature. Plant responses to gravity and lights are examples of such strategy to avoid or mitigate stressful environment they come across. Now, space environment is available for biological studies to understand how plants respond to gravity and how plants are influenced by microgravity and/or space radiation. We extend such studies to understand the effects of space environment on plant growth and development in the seed-to-seed or the generation-to-generation experiments. To explore the deeper space or inhabit planets such as the moon or Mars, we next need to establish a sustainable recycling-oriented life support system with plant cultivation and environmental control facilities. Here, we show our research scenario of the space-utilizing plant science to achieve such objective, which is important to efficiently cultivate plants and develop the life support system in space. We believe our approach, in cooperation with various communities of the related fields, enables us to further reveal the biological systems required for not only colonizing to space but also conserving or improving the living Earth.

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Space radiation is one of the major hazards for human health in space. Space radiation consists of various kinds of radiation including high energy heavy (HZE) ions; these complex radiation fields cannot be produced on the ground. In the International Space Station (ISS), exposure doses are approximately 200 times higher than on the Earth’s surface. On the Moon and Mars, the radiation level is high, due to HZE ions. While the ISS is in free fall, the Moon has 1/6, Mars 1/3 of Earth's gravity. Many aspects of the biological effect of the combination of the lower gravity environment and space radiation remain unclear. But the future mission is now being planned to go to the Moon and Mars. It is necessary to clarify the problem of biological effect and physical dosimetry and then to resolve them as soon as possible. With this thought, here we try to present a scenario of space radiation research for next decades.

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On the occasion of launching the Science Union of Human Planetary Habitation on Space, this document is intended to introduce related activities and possible contributions of the Society of Eco-Engineering. Having started its activity as a small research group on the Closed Ecological Life Support System(CELSS), the life support in space has been one of the main research topics in the society. Recently the society published “Handbook on CELSS and Eco-Engineering” to comemorate its 30th aniversary, which covers the space life support related issues as well as other important Eco-Engineering ones. In addition, it is going to organize several in-house groups on specific topics such as Life Support Technology in Space, Aquaponics, Biomass Utilization, etc. and some of which are expected to work as a counter part for close communication and collaboration with the union.

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According to the detailed discussion of Microgravity Science and Space Life Science, JASMA appoint to promote “The Science Union for Human Planetary Habitation in Space (SUHPHS)” in corporation with the Japanese academic societies: the Japanese Society for Biological Sciences in Space (JSBSS), the Japanese Association of Space Radiation Research (JASRR), the Japan Society of Aerospace and Environmental Medicine (JSASEM), and the Society of Eco-Engineering (SEE). Our common destination of the Union is as follows: 1) We further pursuit the validity of research outputs obtained so far, in the investigation of physical and life sciences in space. 2) According to the science and technology established during ISS operation, we integrate various applied sciences and engineering in the viewpoint of human space exploration, and aim to expand human habitation from the low-earth orbit to the planets, such as Moon and Mars, under the collaboration with the humanities and social science. 3) We contribute to overcome the critical problems of population explosion, resource depletion, global warming on the Earth by investigating the mechanisms of action that threatens the survival of life in space environment and to construct the technological systems of planetary habitation in space. The roadmaps of microgravity science toward future 20 years are depicted to communicate with the existing research communities.

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InxGa1-xSb bulk crystals have been grown on the International Space Station using a GaSb (feed) / InSb / GaSb (seed) sandwich-structured sample. In order to gain a deeper insight into the transport phenomenon and the relevant fundamental mechanisms during the dissolution process of InGaSb in this system, four numerical simulations with different temperature conditions and under the assumption of zero gravity were performed by the volume-averaging continuum model. Simulation results showed the heat loss through the bottom wall did not affect the final feed/seed dissolution lengths and the grown crystal interface shape. The final dissolution lengths of the feed and seed crystals were determined by the temperature calculated along the seed interface. The results also indicate that the actual temperature of the growth ampoule should be around 3K lower than that measured on the outside the protective cartridge.

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The mitigation of space debris is an important issue in current and future space exploration. It is much important to make clear the formation process of space debris as well as their origin for the mitigation, although it is not easy to make clear those of small sized space debris. In the present work, a formation mechanism of microparticle space debris has been proposed through experimental approaches with silicone contaminants outgassed from silicone adhesive deposited on polyimide film and irradiated by ultraviolet (UV) and atomic oxygen (AO). Observation by scanning electron microscopy showed that the silicone contaminants formed droplets with size around 20 µm on the surface of polyimide film. The droplets then solidified under the combined action of UV and AO irradiation, while polyimide film was eroded in the areas not covered by the droplets. Energy-dispersive X-ray spectroscopy showed that microparticles that formed under UV and AO irradiation mainly consisted of silicon and oxygen. The present findings could help to clarify the origin of microparticle space debris found in space.

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