Eu:CROPIS (Euglena and Combined Regenerative Organic-Food Production in Space) was a life science satellite developed by the German Aerospace Center (DLR) and intended to investigate the possibility of growing plants (specifically tomatoes) in different levels of gravity, such as that of the Moon and Mars, as a sustainable food source using human urine for moisture and as the source of fixed nitrogen. Overview This orbital mission was intended to simulate and teste two greenhouses that could be scaled up and assembled inside a lunar or Martian habitat to provide the crew with a local source of fresh food, while recycling human urine into fertiliser. Some microorganisms would be added to convert synthetic urine into easily digestible fertilisers for the tomatoes. The aim was to develop a stable, closed-loop, bio-regenerative life support system functioning in low gravity. In more detail, porous lava stones were fitted in trickle filters and dried soil containing normal soil microbial colonies. Microbes would then use nitrite () to convert the harmful ammonia () into nitrate (), which is then added to six tomato seeds as liquid fertiliser. In addition, the system incorporated a colony of the single-cell microorganism Euglena gracilis, a photosynthetic algae able to produce oxygen and biomass while protecting the entire system against high ammonia concentrations. This oxygen is necessary for the conversion of urine to nitrate until the photosynthetic oxygen production by the tomatoes is sufficient. The spacecraft was designed replicate lunar gravity on one greenhouse for a period of six months before simulating Martian gravity on the second greenhouse for the next six months. The level of gravity on the Moon (0.16 g) and Mars (0.38 g) was simulated by rotating the spacecraft's cylindrical body around its longitudinal axis. The various payload experiments were placed in different areas within the cylinder. Tomato seed germination and plant growth were monitored with 16 cameras, while the RAMIS (RAdiation Measurement In Space) radiometers monitored the radiation inside and outside the spacecraft. The greenhouse was made of clear polycarbonate, with an approximate volume of . The closed system featured moisture, pH, oxygen, pressure and temperature sensors, and was capable of controlling these parameters. Four small fans created airflow through a cooling device to maintain a stable "atmospheric" temperature. On top of the greenhouse, three lamps provided light in the correct spectrum for photosynthesis. Scanners and fluorometers measured cell density and photosynthetic yield. The fluids were to