Initial closed operation of the CELSS Test Facility Engineering Development Unit.

As part of the NASA Advanced Life Support Flight Program, a Controlled Ecological Life Support System (CELSS) Test Facility Engineering Development Unit has been constructed and is undergoing initial operational testing at NASA Ames Research Center. The Engineering Development Unit (EDU) is a tightly closed, stringently controlled, ground-based testbed which provides a broad range of environmental conditions under which a variety of CELSS higher plant crops can be grown. Although the EDU was developed primarily to provide near-term engineering data and a realistic determination of the subsystem and system requirements necessary for the fabrication of a comparable flight unit, the EDU has also provided a means to evaluate plant crop productivity and physiology under controlled conditions. This paper describes the initial closed operational testing of the EDU, with emphasis on the hardware performance capabilities. Measured performance data during a 28-day closed operation period are compared with the specified functional requirements, and an example of inferring crop growth parameters from the test data is presented. Plans for future science and technology testing are also discussed.

An introduction to the nitrogen dynamics in controlled systems workshop. Life support and nitrogen: NASA's interest in nitrogen cycling.

NASA: A Workshop on "Nitrogen Dynamics in Controlled Systems" was held September 26-28, 1995 at the Lawrence Berkeley National Laboratory. The meetings were sponsored by the NASA Advanced Life Support program and the Lawrence Berkeley National Laboratory, and hosted by Prof. Lester Packer of the University of California at Berkeley, and of the Lawrence Berkeley National Laboratory. The Workshop participants were asked to: 1. summarize current knowledge on the cycling of nitrogen in closed systems; 2. identify the needs that closed systems may have for specific forms of nitrogen; 3. identify possible ways of generating and maintaining (or avoiding) specific forms and concentrations of nitrogen; 4. compare biological and physical/chemical methods of transforming nitrogen.^ieng

Controlled Ecological Life Support Systems (CELSS) flight experimentation.

The NASA CELSS program has the goal of developing life support systems for humans in space based on the use of higher plants. The program has supported research at universities with a primary focus of increasing the productivity of candidate crop plants. To understand the effects of the space environment on plant productivity, the CELSS Test Facility (CTF) has been been conceived as an instrument that will permit the evaluation of plant productivity on Space Station Freedom. The CTF will maintain specific environmental conditions and collect data on gas exchange rates and biomass accumulation over the growth period of several crop plants grown sequentially from seed to harvest. The science requirements of the CTF will be described, as will current design concepts and specific technology requirements for operation in micro-gravity.

Life support systems for Mars transit.

The long-held human dream of travel to the stars and planets will probably be realized within the next quarter century. Preliminary analyses by U.S. scientists and engineers suggests that a first trip to Mars could begin as early as 2016. A proposal by U.S.S.R. space planners has suggested that an effort involving the cooperation and collaboration of many nations could begin by 2011. Among the major considerations that must be made in preparation for such an excursion are solidification of the scientific, economic and philosophical rationales for such a trip made by humans, and realistic evaluations of current and projected technical capabilities. Issues in the latter category include launch and propulsion systems, long term system stability and reliability, the psychological and physiological consequences of long term exposure to the space environment, the development and use of countermeasures to deleterious human physiological responses to the space environment, and life support systems that are both capable of the immense journey and reliable enough to assure their continued operation for the duration of the voyage. Many of the issues important in the design of a life support system for a Mars trip are based on reasonably well understood data: the human requirements for food, oxygen and water. However, other issues are less well-defined, such as the demands that will be made on the system for personal cleanliness and hygiene, environmental cleanliness, prevention or reduction of environmental toxins, and psychological responses to the environment and to the diet. It is much too early to make final decisions about the characteristics of the long-duration life support system needed for travel to Mars, or for use on its surface. However, it is clear that life support systems will evolve during the next few decades form the relatively straightforward systems that are used on Shuttle and Soyuz, to increasingly more complex and regenerative systems. The Soviet Union has an operating life support system on Mir that can apparently evolve, and the United States is currently planning the one for Space Station Freedom that will use partial regeneration. It is essential to develop concepts now for life support systems on an advanced Space Station, the lunar outpost (to be launched in about 2004) and the lunar base. Such concepts will build on current technology and capabilities. But because of the variety of different technologies that can be developed, and the potential for coordinating the functions of very diverse sub-systems within the same life support system, the possibility of developing an efficient, reliable mixed process system is high. It is likely that a life support system for Mars transit and base will use a composite of physical, chemical, and biological processes. The purpose of this paper is to explore the potentially useful structural elements of a life support system for use on a Mars trip, and to identify the features that, at this time, appear to be most appropriate for inclusion in the system.

The CELSS Test Facility project: an example of a CELSS flight experiment system.

NASA: The CELSS Test Facility (CTF) is a device for measuring crop plant productivity in the micro-gravity environment of Space Station Freedom. It will allow us to address questions of crop productivity in space, versus that on the ground. The crop productivity factors that will be measured are rates of: 1) biomass production, 2) food production, 3) O2 and CO2 exchange, and 4) water transpiration. In addition, other productivity factors of specific crops will be determined, such as : 1) the ratio of edible to inedible biomass (harvest index), 2) leaf area exposed to and collecting light (leaf area index), 3) ratio of root mass to total biomass, and 4) photosynthetic efficiency (ratio of moles of CO2 fixed (or O2 produced), per mole of photons of specific energies used). Plant and crop morphology, at several levels, ranging from the community to the sub-cellular, will also be evaluated.^ieng

Effect of iodine disinfection products on higher plants.

Iodine is used to disinfect potable water on United States spacecraft. Iodinated potable water will likely be used to grow plants in space. Little is known about the effects of iodine disinfection products on plants. Seeds of select higher plants were germinated in water iodinated using the Shuttle Microbial Check Valve, and water to which measured amounts of iodide was added. Percent germination was decreased in seeds of most species germinated in iodinated water. Beans were most affected. Germination rates, determined from germination half-times, were decreased for beans germinated in iodinated water, and water to which iodide was added. Development was retarded and rootlets were conspicuously absent in bean and several other plant species germinated in iodinated water. Iodide alone did not elicit these responses. Clearly iodine disinfection products can affect higher plants. These effects must be carefully considered for plant experimentation and cultivation in space, and in design and testing of closed environmental life support systems.

Productivity and food value of Amaranthus cruentus under non-lethal salt stress.

Stress effects from the accumulation of metal salts may pose a problem for plants in closed biological systems such as spacecraft. This work examined the effects of salinity on growth, photosynthesis and carbon allocation in the crop plant, Amaranthus. Plants were germinated and grown in modified Hoagland's solution with NaCl concentrations of 0 to 1.0%. Plants received salt treatments at various times in development to assess effects on particular life history phases. For Amaranthus cruentus, germination, vegetative growth, flowering, seed development and yield were normal at salinities from 0 to 0.2%. Inhibition of these phases increased from 0.2 to 0.4% salinity and was total above 0.5%. 1.0% salinity was lethal to all developmental phases. Onset of growth phases were not affected by salinity. Plants could not be adapted by gradually increasing salinity over days or weeks. Water uptake increased, while photosynthetic CO2 uptake decreased with increasing salinity on a dry weight basis during vegetative growth. Respiration was not affected by salinity. After flowering, respiration and photosynthesis decreased markedly, such that 1.0% NaCl inhibited photosynthesis completely. Protein levels were unchanged with increasing salinity. Leaf starch levels were lower at salinities of 0.5% and above, while stem starch levels were not affected by these salinities. The evidence supports salt inhibition arising from changes in primary biochemical processes rather than from effects on water relations. While not addressing the toxic effects of specific ions, it suggests that moderate salinity per se need not be a problem in space systems.

Carbon balance and productivity of Lemna gibba, a candidate plant for CELSS.

The photosynthesis and productivity of Lemna gibba were studied with a view to its use in Controlled Ecological Life Support Systems (CELSS). Photosynthesis of L. gibba floating on the nutrient solution could be driven by light coming from either above or below. Light from below was about 75% as effective as from above when the stand was sparse, but much less so with dense stands. High rates of photosynthesis (ca. 800 nanomoles CO2 g dry weight (DW)-1 s-1) were measured at 750 micromoles m-2 s-1 PPF and 1500 micromoles mol-1 CO2. This was attained at densities up to 660 g fresh weight (FW) m-2 with young cultures. After a few days growth under these conditions, and at higher densities, the rate of photosynthesis dropped to less than 25% of the initial value. This drop was only partly alleviated by thinning the stand or by introducing a short dark period at high temperature (26 degrees C). Despite the drop in the rate of photosynthesis, maximum yields were obtained in batch cultures grown under continuous light, constant temperature and high [CO2]. Plant protein content was less than reported for field grown Lemna. When the plants were harvested daily, maintaining a stand density of 600 g FW m-2, yields of 18 g DW m-2 d-1 were obtained. The total dry weight of L. gibba included 40% soluble material (sugars and amino acids), 15% protein, 5% starch, 5% ash and 35% cellulose and other polymers. We conclude that a CELSS system could be designed around stacked, alternate layers of transparent Lemna trays and lamps. This would allow for 7 tiers per meter height. Based on present data from single layers, the yield of such a system is calculated to be 135 g DW m-3 d-1 of a 100% edible, protein-rich food.

Waste recycling issues in bioregenerative life support.

Research and technology development issues centering on the recycling of materials within a bioregenerative life support system are reviewed. The importance of recovering waste materials for subsequent use is emphasized. Such material reclamation will substantially decrease the energy penalty paid for bioregenerative life support systems, and can potentially decrease the size of the system and its power demands by a significant amount. Reclamation of fixed nitrogen and the sugars in cellulosic materials is discussed.

Use of Martian resources in a Controlled Ecological Life Support System (CELSS).

The exploration of Mars has long been considered as a major goal in the exploration of the Solar system. The Space Station Freedom will make such missions feasible because it will provide a site for the assembly and launch of the large vehicles required. Interest in manned visits to Mars often focus on the possibility of collecting information about the origin of that planet, & hence of the solar system, including the Earth. Interest also involves the history of the planet, its past record of geological and fluvial activity, atmospheric and thermal history and surface chemical activity. The latter is of particular interest to exobiologists who would like to seek evidence of pre-biological physical and chemical activity involving organic molecules. Finally, there is interest in the possibility of planetary ecosynthesis, i.e. specific intervention in the evolution of Mars that could result in the development of a second habitable planet in the solar system. The scenarios for visits and the establishment of bases on Mars are being developed now. The intent of this paper is to consider various possibilities for crew life support on Mars and particularly to explore the use of Martian resources as life support materials.

Inter-chain proline:proline contacts contribute to the stability of the triple helical conformation.

The triple helical conformation observed in the collagen group of proteins is related to the presence of large numbers of imino residues and is derived from the stereochemical properties of these residues. The triple helix is stabilized by increasing numbers of these residues. Hydrogen bonds are usually considered to be a major factor in the formation and stability of protein conformation, however, imino residues are not hydrogen bond donors. We have evaluated the role of these residues in stabilizing the triple helix by re-examining two X-ray based structures of the triple helical polypeptide (Pro-Pro-Gly)10 using molecular mechanics calculations. The two minimized structures are comparable in energy and have helical parameters close to the starting values for each starting structure. Our studies suggest that clusters of close van der Waals contacts between proline residues in adjacent chains contribute significantly to the stability of the triple helix. Preliminary NMR studies support this concept. We propose that non-bonded interactions between proline residues may be a significant stabilizing force in the triple helix generated by (Pro-Pro-Gly)10.

Molecular dynamics study of ion capture from water by a model ionophore, tetraprotonated cryptand SC24.

A molecular dynamics study of chloride capture from water by the tetraprotonated cryptand SC24 is presented. The system under study consisted of a cryptand molecule, chloride ion, and 319 water molecules. Calculations were performed for 19 distances between the cryptand and the chloride. For each distance a trajectory of at least 60 ps was obtained. Two anion binding sites of comparable energy were found. The chloride can bind either inside the cryptand cavity or more loosely outside of the ligand. The binding sites are separated by an energy barrier of 20 kcal/mol. Chloride movement toward the cryptand is accompanied by stepwise dehydration of the anion. The energy loss due to this dehydration is offset by the electrostatic attraction between the anion and the ligand and by an increase in favorable water-water interactions. The most striking feature of chloride capture is a rapid cooperative change in the conformation of the cryptand when the Cl- starts to enter the ligand and just as it encounters the energy barrier. The conformational transition is associated with a shift of three N-H bonds from the pure endo orientation, so that they point toward the chloride. The shift provides electrostatic stabilization, which compensates for the loss of the remaining three water molecules from the hydration shell of the anion. The N-H bonds remain directed toward the anion during its further movement into the ligand and guide chloride into a stable position inside the cryptand cavity. The flexibility of the receptor, the stepwise dehydration of an ionic substrate, and the characteristic balance between different energy components in the system all may be features of ion binding common to a wide range of abiotic and biological ionophores.

A molecular dynamics study of chloride binding by the cryptand SC24.

The capture of chloride from water by the tetraprotonated form of the spherical macrotricyclic molecule SC24 was studied using molecular dynamics simulation methods. This model ionophore represents a broad class of molecules which remove ions from water. Two binding sites for the chloride were found, one inside and one outside the ligand. These sites are separated by a potential energy barrier of approximately 20 kcal mol-1. The major contribution to this barrier comes from dehydration of the chloride. The large, unfavorable dehydration effect is compensated for by an increase in electrostatic attraction between the oppositely charged chloride and cryptand, and by energetically favorable rearrangements of water structure. Additional assistance in crossing the barrier and completing the dehydration of the ion is provided by the shift of three positively charged hydrogen atoms of the cryptand towards the chloride. This structural rigidity is partially responsible for its selectivity.

Comparison of the structure of harmonic aqueous glasses and liquid water.

Glassy structures of water were generated by rapidly quenching configurations of 64 and 343 molecules of liquid water. The potential energy was then expanded through quadratic order around local minima generated this way and properties of the resulting harmonic system were calculated. The results were used to test the extent to which the structure of liquid water is similar to that of a harmonic aqueous glass. The radial distribution functions for the glass are remarkably similar to those of the liquid. The vibrational density of states for the glassy water exhibits a gap between 300 and 400 cm-1. The normal modes below 300 cm-1 correspond to molecular translations while the modes above 400 cm-1 are ascribed to molecular librations. Translational modes are almost entirely responsible for the broadening of oxygen-oxygen radial distribution function of the quenched configuration. They are also primarily responsible for the broadening of other radial distribution functions. Vibrational density of states leads to classical and quantum free energies for the harmonic system equal -9.62 +/- 0.12 and -8.89 +/- 0.12 kcal/mol, respectively, at T = 300 K. Both free energies were found to be insensitive to sample size and to the configurational differences between the quenched structures.

A review of recent activities in the NASA CELSS program.

A CELSS (Controlled Ecological Life Support System) is a device that utilizes photosynthetic organisms and light energy to regenerate waste materials into oxygen and food for a crew in space. The results of theoretical and practical studies conducted by investigators within the CELSS program suggest that a bioregenerative life support system can be a useful and effective method of regenerating consumable materials for crew sustenance. Experimental data suggests that the operation of a CELSS in space will be practical if plants can be made to behave predictably in the space environment. Much of the work currently conducted within the CELSS program centers on the biological components of the CELSS system. The work is particularly directed at ways of achieving high efficiency and long term stability of all components of the system. Included are explorations of the conversion of non-edible cellulose to edible materials, nitrogen fixation by biological and chemical methods, and methods of waste processing. It is the intent of the presentation to provide a description of the extent to which a bioregenerative life support system can meet the constraints of the space environment, and to assess the degree to which system efficiency and stability can be increased during the next decade.

A simple experimental model for hydrophobic interactions in proteins.

The compound N-cyclohexyl-2-pyrrolidone contains a substantial apolar region as well as a peptide bond-like moiety. This solvent, therefore, provides a useful model for protein interiors. Under certain conditions of temperature and salt concentration, cyclohexylpyrrolidone forms a two-phase system with water. This permits partition coefficients and subsequent free energies of transfer of amino acid side chains from cyclohexylpyrrolidone to water to be simply determined. Free energies of transfer measured in this manner for 21 amino acids are found to be substantially less than those obtained from the commonly used ethanol/water solubility model. This suggests less of a contribution of hydrophobic interactions to the stabilization of protein structure than is conventionally assumed.

Solution influence on biomolecular equilibria: nucleic acid base associations.

This paper consists of two parts. In the first part, the general problem of biomolecular equilibria in solution is considered, stressing that molecular interactions ultimately determine the answer to this problem. It is discussed how computer simulation techniques can reliably treat the problem and several pitfalls of computer simulation to be avoided are pointed out. Other approaches based on modeling and conceptual simplifications such as perturbative methods, long-range interaction approximations, surface thermodynamic approaches, and hydration shell models are discussed. In the second part, the results of Monte Carlo calculations on the associations of nucleic acid bases in water and carbon tetrachloride are presented. Stacked self-associations are found to be preferred in water and hydrogen-bonded complexes are favored in nonpolar solutions, in agreement with experimental data. The influence of the solvent on base associations is explained in terms of solute-solvent and solvent-solvent contributions to the total energy. No enthalpic stabilization of the complexes by the solvent was found. The results are used to examine the validity of various approximations discussed in the first part of the paper.

Current concepts and future directions of CELSS.

Studies of bioregenerative life support systems for use in space indicate that they are scientifically feasible. Preliminary data suggest that they would provide cost- and weight-saving benefits for low Earth orbit, long duration space platforms. Concepts of such systems include the use of higher plants and/or micro-algae as sources of food, potable water and oxygen, and as sinks for carbon dioxide and metabolic wastes. Recycling of materials within the system will require processing of food organism and crew wastes using microbiological and/or physical chemical techniques. The dynamics of material flow within the system will require monitoring, control, stabilization and maintenance imposed by computers. Future phases of study will continue investigations of higher plant and algal physiology, environmental responses, and control; flight experiments for testing responses of organisms to weightlessness and increased radiation levels; and development of ground-based facilities for the study of recycling within a bioregenerative life support system.

Analyzing and comparing the performance of two real-time playback systems.

A technique used in animated computer graphics involves the use of real-time playback. This method is used when it is not possible to display frames of display code in real-time. Instead, frames are compiled in advance at non realtime rates, saved in secondary storage, and played back at desired realtime speeds. The basic design and operation of two such systems will be considered. The more powerful of the two is built upon an Evans and Sutherland picture System I and utilizes animated vector graphics. The other playback system is built upon a Terak micro computer display and represents an example of rudimentary raster graphics animation. The synchronization, buffering, blocking and man-machine interfaces of both systems are detailed thus spotlighting their operational behavior. A comparison of the two systems show: that similarities in the logical organization of each system exist; that both systems are input bound; and both require their image files to be built on other computer systems. The differences in the performance of the two systems can be attributed to technological differences between the two systems; the retrieval rates of their respective disk subsystems; and differences in the intent and purpose behind the design of each machine. The systems are demonstrated by applying them to chemical modeling. It is determined that playback is a useful technique for examining complicated sequential situations or for providing the concise and convenient representation of large amounts of data.