Impact of Carbon Dioxide Concentration on Plant and Animal Life Sciences Research on Space Station Freedom 932261

Space Station Freedom will provide an opportunity to conduct long duration life sciences research on plants and animals in a microgravity environment. Studies will be able to determine the rate of change of various processes in animals, e.g., calcium loss from bones, muscle atrophy, etc., determine the effect of microgravity on plant respiration and transpiration, and assess the impact of the microgravity environment over multiple generations for both plants and animals. However, all of these processes may also be affected by the 5.3 mm Hg partial pressure of CO₂ (7000 ppm) currently specified for Space Station Freedom. The specifications for the plant and animal habitats to be developed as part of the Centrifuge Facility require that the CO₂ level for plants be controlled over the range of 0.23 -2.3 mm Hg (300 to 3000 ppm ± 10-50 ppm) and that the atmospheric composition (CO₂ level) for rodents be ± 1 % of the cabin composition. This latter specification was established based on the assumption that the CO₂ level in SSF would be similar to that on Earth (0.23 mm Hg). With the current CO₂ specifications for SSF, if there is a direct exchange of air between the cabin and the habitats, the cabin air will require scrubbing to remove the excess CO₂. In addition, increased airflow may be required to prevent excessive buildup of CO₂ within the animal habitat. This paper will present a discussion of the effects of elevated levels of CO₂ on mammalian physiology, as well as an analysis showing the effect, as a function of different cabin CO₂ levels, on the flow rate within the animal habitats to maintain the habitat CO₂ concentration within 1% and 10% of the cabin concentration.