Oscar Monje

Farming in space: environmental and biophysical concerns

The colonization of space will depend on our ability to routinely provide for the metabolic needs (oxygen, water, and food) of a crew with minimal re-supply from Earth. On Earth, these functions are facilitated by the cultivation of plant crops, thus it is important to develop plant-based food production systems to sustain the presence of mankind in space. Farming practices on earth have evolved for thousands of years to meet both the demands of an ever-increasing population and the availability of scarce resources, and now these practices must adapt to accommodate the effects of global warming. Similar challenges are expected when earth-based agricultural practices are adapted for space-based agriculture. A key variable in space is gravity; planets (e.g. Mars, 1/3 g) and moons (e.g. Earths moon, 1/6 g) differ from spacecraft orbiting the Earth (e.g. Space stations) or orbital transfer vehicles that are subject to microgravity. The movement of heat, water vapor, CO2 and O2 between plant surfaces and their environment is also affected by gravity. In microgravity, these processes may also be affected by reduced mass transport and thicker boundary layers around plant organs caused by the absence of buoyancy dependent convective transport. Future space farmers will have to adapt their practices to accommodate microgravity, high and low extremes in ambient temperatures, reduced atmospheric pressures, atmospheres containing high volatile organic carbon contents, and elevated to super-elevated CO2 concentrations. Farming in space must also be carried out within power-, volume-, and mass-limited life support systems and must share resources with manned crews. Improved lighting and sensor technologies will have to be developed and tested for use in space. These developments should also help make crop production in terrestrial controlled environments (plant growth chambers and greenhouses) more efficient and, therefore, make these alternative agricultural systems more economically feasible food production systems.

Characterizing the Adsorptive Capacity of SA9T Using Simulated Spacecraft Gas Streams

New trace contaminant control technologies need to be identified, evaluated and optimized for operating in manned spacecraft (eg. ISS, Orion, Lunar Lander, Outposts). SA9T, a regenerable solid-amine adsorbent, has been proposed as a key technology for controlling cabin CO2 and H2O vapor concentrations in future Exploration Life Support (ELS) open-loop air revitalization (AR) systems. The adsorptive capacity of SA9T, was evaluated using simulated gas streams and environmental ranges (e.g., relative humidities, temperatures, volatile organic compound (VOC) loads, atmospheric pressures, and flow rates) found in manned spacecraft. VOC, CO2 and H2O vapor breakthrough curves were measured for 20 minute and 1 hour adsorption periods in the Regenerable VOC Control System (RVCS), a sub-scale testbed. The amounts of VOC, H2O, and CO2 adsorbed by SA9T were calculated from these breakthrough curves. These tests verified that SA9T adsorbs large amounts of acetaldehyde and that it does not adsorb dichloromethane. Similarly, removal of acetone, ethanol, toluene and xylene by SA9T were demonstrated. Surprisingly, the presence of VOCs in the gas streams affected H2O vapor and CO2 adsorption by SA9T. Increased CO2 adsorption was observed in the presence of acetone, acetaldehyde, ethanol, and dichloromethane, but toluene decreased CO2 adsorption. These effects may reflect an interaction between the properties of the VOC and the SA9T adsorbent itself. Co-adsorption of H2O in humid air decreased the CO2 adsorptive capacity of SA9T, in part due to an exothermic rise in bed temperature caused during adsorption of CO2 and water vapor. Coadsorption of CO2 decreased the H2O vapor adsorptive capacities of SA9T. This work suggests that while SA9T provides some VOC removal that may contribute to smaller trace contaminant control equipment, it does not eliminate the need for a dedicated trace contaminant control function/unit operation and equipment.

Struvite formation and decomposition characteristics for ammonia and phosphorus recovery: A review of magnesium-ammonia-phosphate interactions

Struvite (MgNH4PO4·6H2O) forms in aqueous systems with high ammonia and phosphate concentrations. However, conditions that result into struvite formation are highly dependent on the ionic compositions, temperature, pH, and ion speciation characteristics. The primary ions involved in struvite formation have complex interactions and can form different crystals depending on the ionic levels, pH and temperature. Struvite as well as struvite analogues (with substitution of monovalent cations for NH4+ or divalent cations for Mg2+) as well as other crystals can form simultaneously and result in changes in crystal morphology during crystal growth. This review provides the results from experimental and theoretical studies on struvite formation and decomposition studies. Characteristics of NH4+ or divalent cations for Mg2+ were evaluated in comparison to monovalent and divalent ions for formation of struvite and its analogues. Struvite crystals forming in wastewater systems are likely to contain crystals other than struvite due to ionic interactions, pH changes, temperature effects and clustering of ions during nucleation and crystal growth. Decomposition of struvite occurs following a series of reactions depending on the rate of heating, temperature and availability of water during heating.

Ammonia Offgassing from SA9T

NH3 is a degradation product of SA9T, a solid-amine sorbent developed by Hamilton Sundstrand, that is continually emitted into the gas stream being conditioned by this sorbent. NH3 offgassing rates were measured using FTIR spectroscopy using a packed bed at similar contact times as offgassing tests conducted at Hamilton Sundstrand and at the Ames Research Center. The bed was challenged with moist air at several flow rates and humidities and NH3 concentration of the effluent was measured for several hours. The NH3 offgassing rates in open-loop testing were calculated from the steady state outlet NH3 concentration and flow rate. NH3 offgassing rates from SA9T were found to be influenced by the contact time with the adsorbent (flow rate) and by the humidity of the inlet gas stream, which are consistent with previous studies. Closed-loop vacuum-swing adsorption cycling rates verified that NH3 offgassing continues when a constant source of water vapor is present.

Comparison of spectral combinations of light emitting diodes for crop production

Recent advances in Light Emitting Diode (LED) technology have made it possible for lighting arrays to provide user tunable wavelengths and adjustable intensities. LEDs also provide low radiant heat loads, have longer life spans, and improved energy efficiencies when compared with other light sources such as HID, incandescent and fluorescent lamps. Although currently expensive, these characteristics make LED lighting arrays suitable for their use in growth chambers. This study reports results from two experiments using LED arrays. The first compared a mixture of red (R; 640 nm) and blue (B; 450 nm) LEDs (RB) with a mixture of red, green (G; 540 nm), and blue LEDs (RGB). The second experiment looked at the effect of far red light (Fr; 725nm) on mass partitioning in the plants by comparing a mixture of RGB+Fr light with RGB lighting. In all cases the photosynthetically active radiation (PAR) was equivalent and the effects of spectral quality were compared against compact fluorescent lamps. Fluorescent lamps are the primary light source in modern growth chambers, making their spectral quality a good control for these experiments. PAR was approximately 200 µmol m-2 s-1, and plants were grown under 20 hours of light, 4 hours of dark. Other environmental parameters were identical between chambers and experiments. The crop used in the evaluation of the various light qualities was radish (Raphanus sativum cv Cherry Belle). All LED light combinations demonstrated an ability to grow healthy plants similar to plants grown using fluorescent lighting. In the RGB versus RB experiment, there was little difference in the percentage of mass dedicated to edible radish biomass. However, the plants in the RGB chamber had more leaf area than the plants in the RB chamber. Plants growing under RGB+Fr partitioned significantly more biomass to the edible radish than plants grown under RGB.