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The inedible portion of plant biomass in closed regenerative life support systems must be reprocessed producing recyclable by-products such as carbon dioxide, sugars, and other useful organic species. High solids biomass slurries containing up to 27 wt% were successfully prepared in a stirred batch reactor and then pumped using a single piston valveless pump. Wheat straw, potato, and tomato crop residues were acid hydrolyzed using 1.2 wt% sulfuric acid at 180°C and 1.2 MPa for 0.75-1.5 hours. Viscosity for a 25 wt% acid hydrolyzed wheat straw emulsion (Bingham-plastic) was 6.5 centipoise at 3 cm/sec and 25°C.

Handling and processing human feces in space habitats is a major concern and needs to be addressed for the Crew Exploration Vehicle (CEV) as well as for future exploration activities. In order to ensure crew health and safety, feces should either be isolated in a dried form to prevent microbial activity, or be processed to yield a non-biohazardous product using a reliable technology. During laboratory testing of new feces processing technologies, use of “real” feces can impede progress due to practical issues such as safety and handling thereby limiting experimental investigations. The availability of a non-hazardous simulant or analogue of feces can overcome this limitation. Use of a simulant can speed up research and ensure a safe laboratory environment. At Ames Research Center, we have undertaken the task of developing human fecal simulants. In field investigations, human feces show wide variations in their chemical/physical composition.

Spacelab-J was an international Spacelab mission with numerous innovative Japanese and American materials and life science experiments. Two of the Spacelab-J experiments were designed over a period of more than a decade by a team from NASA-Ames Research Center. The Frog Embryology Experiment investigated and is helping to resolve a century-long quandary on the effects of gravity on amphibian development. The Autogenic Feedback Training Experiment, flown on Spacelab-J as part of a multi-mission investigation, studied the effects of Autogenic Feedback Therapy on limiting the effects of Space Motion Sickness on astronauts. Both experiments employed the use of a wide variety of specially designed hardware to achieve the experiment objectives.

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.

The white rat, Rattus norvegicus has been used extensively in microgravity flights. Initial NASA flight experiments with rats supported the Shuttle Student Involvement Program (SSIP). Hardware to house the rats was called the Animal Enclosure Module (AEM). The AEM for the SSIP, fit into a middeck locker. Potatoes provided water; food bars, glued on the walls, provided nourishment. Waste was absorbed and odor and microbial growth controlled by sandwiched phosphoric acid treated charcoal and filter materials utilizing much of the technology employed in the Rodent Research Animal Holding Facility, a Spacelab piece of equipment. The SSIP AEM potato “watering” system succumbed to mold and had to be replaced by real water contained within plasma bags. A metal enclosure housed the plasma bags between two heavy springs which forced water through animal activated lixits.

The effects of acoustic levels in manned space vehicles was not thoroughly appreciated until the STS 40 mission, Spacelab Life Sciences 1 (June, 1991). Previous to that mission, waivers were submitted and equipment operated without overwhelming effect on ongoing flight activities. The factors of multiple pieces of noise producing equipment operating simultaneously, operating in the vicinity of crew sleep stations, and operating for this long of a mission (10 days) became relevant in crew tolerance, fatigue, communication, and permanent shifts in hearing thresholds. Because this was a life sciences mission, accurate instrument measurements were obtained of acoustic levels in the middeck, flight deck and spacelab during flight and physiological measurements were obtained from the crew members during all phases of the mission. Due to the STS 40 results, a Spacelab/Payloads Acoustics Working Group (SPAWG) was formed post flight to address acceptable acoustic limits.

Nitrogen use efficiency in hydroponic plant growth chambers is reduced by microbial denitrification. A computer-controlled bioreactor system was developed to investigate methods for controlling denitrification in hydroponic plant growth chambers envisioned for use on long duration space missions. Through regulation of O2 and NO3- levels in the bioreactor, the rate of denitrification of pure cultures was controlled. This control strategy may be used to favor plant nitrate uptake in the presence of denitrifying bacteria in hydroponic systems. Reducing denitrification provides advantages to advanced life support (ALS) systems by improving crop nitrogen use efficiency, reducing fixed-nitrogen demand, and reducing gaseous wastes (N2O and N2).