Daniel J. Barta

Evaluation of light emitting diode characteristics for a space-based plant irradiation source.

Light emitting diodes (LEDs) are a promising irradiation source for plant growth in space. Improved semiconductor technology has yielded LED devices fabricated with gallium aluminum arsenide (GaAlAs) chips which have a high efficiency for converting electrical energy to photosynthetically active radiation. Specific GaAlAs LEDs are available that emit radiation with a peak wavelength near the spectral peak of maximum quantum action for photosynthesis. The electrical conversion efficiency of installed systems (micromole s-1 of photosynthetic photons per watt) of high output LEDs can be within 10% of that for high pressure sodium lamps. Output of individual LEDs were found to vary by as much as 55% from the average of the lot. LED ratings, in mcd (luminous intensity per solid angle), were found to be proportional to total photon output only for devices with the same dispersion angle and spectral peak. Increasing current through the LED increased output but also increased temperature with a consequent decrease in electrical conversion efficiency. A photosynthetic photon flux as high as 900 micromoles m-2 s-1 has been produced on surfaces using arrays with LEDs mounted 7.6 mm apart, operating as a current of 50 mA device-1 and at an installed density of approximately 17,200 lamps m-2 of irradiated area. Advantages of LEDs over other electric light sources for use in space systems include long life, minimal mass and volume and being a solid state device.

Photosynthesis and respiration of a wheat stand at reduced atmospheric pressure and reduced oxygen.

A 34-day functional test was conducted in Johnson Space Centers Variable Pressure Growth Chamber (VPGC) to determine responses of a wheat stand to reduced pressure (70 kPa) and modified partial pressures of carbon dioxide and oxygen. Reduced pressure episodes were generally six to seven hours in duration, were conducted at reduced ppO2 (14.7 kPa), and were interrupted with longer durations of ambient pressure (101 kPa). Daily measurements of stand net photosynthesis (Pn) and dark respiration (DR) were made at both pressures using a ppCO2 of 121 Pa. Corrections derived from leakage tests were applied to reduced pressure measurements. Rates of Pn at reduced pressure averaged over the complete test were 14.6% higher than at ambient pressure, but rates of DR were unaffected. Further reductions in ppO2 were achieved with a molecular sieve and were used to determine if Pn was enhanced by lowered O2 or by lowered pressure. Decreased ppO2 resulted in enhanced rates of Pn, regardless of pressure, but the actual response was dependent on the ratio of ppO2/ppCO2. Over the range of ppO2/ppCO2 of 80 to 200, the rate of Pn declined linearly. Rate of DR was unaffected over the same range and by dissolved O2 levels down to 3.1 ppm, suggesting that normal rhizosphere and canopy respiration occur at atmospheric ppO2 levels as low as 11 kPa. Partial separation of effects attributable to oxygen and those related to reduced pressure (e.g. enhanced diffusion of CO2) was achieved from analysis of a CO2 drawdown experiment. Results will be used for design and implementation of studies involving complete crop growth tests at reduced pressure.

Astroculture™ root metabolism and cytochemical analysis

Physiology of the root system is dependent upon oxygen availability and tissue respiration. During hypoxia nutrient and water acquisition may be inhibited, thus affecting the overall biochemical and physiological status of the plant. For the Astroculture (TM) plant growth hardware, the availability of oxygen in the root zone was measured by examining the changes in alcohol dehydrogenase (ADH) activity within the root tissue. ADH activity is a sensitive biochemical indicator of hypoxic conditions in plants and was measured in both spaceflight and control roots. In addition to the biochemical enzyme assays, localization of ADH in the root tissue was examined cytochemically. The results of these analyses showed that ADH activity increased significantly as a result of spaceflight exposure. Enzyme activity increased 248% to 304% in dwarf wheat when compared with the ground controls and Brassica showed increases between 334% and 579% when compared with day zero controls. Cytochemical staining revealed no differences in ADH tissue localization in any of the dwarf wheat treatments. These results show the importance of considering root system oxygenation in designing and building nutrient delivery hardware for spaceflight plant cultivation and confirm previous reports of an ADH response associated with spaceflight exposure.

Development of Life Support System Technologies for Human Lunar Missions

ABSTRACT With the Preliminary Design Review (PDR) for the Orion Crew Exploration Vehicle planned to be completed in 2009, Exploration Life Support (ELS), a technology development project under the National Aeronautics and Space Administration’s (NASA) Exploration Technology Development Program, is focusing its efforts on needs for human lunar missions. The ELS Project’s goal is to develop and mature a suite of Environmental Control and Life Support System (ECLSS) technologies for potential use on human spacecraft under development in support of U.S. Space Exploration Policy. ELS technology development is directed at three major vehicle projects within NASA’s Constellation Program (CxP): the Orion Crew Exploration Vehicle (CEV), the Altair Lunar Lander and Lunar Surface Systems, including habitats and pressurized rovers. The ELS Project includes four technical elements: Atmosphere Revitalization Systems, Water Recovery Systems, Waste Management Systems and Habitation Engineering, and two cross cutting elements, Systems Integration, Modeling and Analysis, and Validation and Testing. This paper will provide an overview of the ELS Project, connectivity with its customers and an update to content within its technology development portfolio with focus on human lunar missions.

Atmospheric leakage and method for measurement of gas exchange rates of a crop stand at reduced pressure

The variable pressure growth chamber (VPGC) was used in a 34-day functional test to grow a wheat crop using reduced pressure (70 kPa) episodes totalling 131 hours. Primary goals of the test were to verify facility and subsystem performance at 70 kPa and to determine responses of a wheat stand to reduced pressure and modified partial pressures of carbon dioxide and oxygen. Operation and maintenance of the chamber at 70 kpa involved continuous evacuation of the chamber atmosphere, leading to CO2 influx and efflux. A model for calculating CO2-exchange rates (net photosynthesis and dark respiration) was developed and tested and involved measurements of chamber leakage to determine appropriate corrections. Measurement of chamber leakage was based on the rate of pressure change over a small pressure increment (70.3 to 72.3 kPa) with the pump disabled. Leakage values were used to correct decreases and increases in chamber CO2 concentration resulting from net photosynthesis (Ps) and dark respiration (DR), respectively. Composite leakage corrections (influx and efflux) at day 7 of the test were 9% and 19% of the changes measured for Ps and DR, respectively. On day 33, composite corrections were only 3% for Ps and 4% for DR. During the test, the chamber became progressively tighter; the leak rate at 70.3 kPa decreasing from 2.36 chamber volumes/day pretest, to 1.71 volumes/day at the beginning of the test, and 1.16 volumes/day at the end of the test. Verification of the short-term leakage tests (rate of pressure rise) were made by testing CO2 leakage with the vacuum pump enabled and disabled. Results demonstrate the suitability of the VPGC or conducting gas exhange measurements of a crop stand at reduced pressure.

New Direction of NASA Exploration Life Support

NASAs activities in life support Research and Technology Development (RT how it differs from ALS, and how it supports critical needs for the CEV, LSAM and LO. In addition, this paper provides rationale for changes in the scope and focus of technical content within ongoing life support R&TD activities.

Optimization of a Membrane-Aerated Biological Reactor in Preparation for a Full Scale Integrated Water Recovery Test

Water recycling is a fundamental component of life support systems due to the substantial contribution of water to the total equivalent system mass. Optimizing the integrated water recycling systems is essential in any efforts to enable long term space habitation. Membrane aerated biological reactors (MABRs) have proven to be an efficient and sustainable pretreatment process for extra terrestrial wastewater recycling applications in closed loop life support systems. The CoMANDR (Counter-diffusion Membrane Aerated Nitrifying Denitrifying Reactor) system can be used to treat unstabilized wastewater composed of urine, hygiene water, humidity condensate, and laundry water. The operation and assessment of the CoMANDR is in support of the integrated systems test to be implemented by Johnson Space Center pairing a biological reactor with a forward/reverse osmosis unit to treat the aforementioned waste stream. After a two month start up period we have systematically evaluated the CoMANDR performance for a variety of loading rates and verified the operation of the system under pressurized conditions. Results support the ability of the system to effectively reduce organic carbon by over 90% and convert up to 70% of the total influent N to non-organic forms (e.g. NOx or N2). Operation has been demonstrated using both air and pure O2, although in each case further control refinements are required to help maximize the denitrification potential of the reactor. We have also demonstrated that for at least up to 3 weeks, CoMANDR can be put into recycle and brought back on line with no start up required supporting the ability to intermittently operate the system.

Alternative Water Processor Test Development

The Next Generation Life Support Project is developing an Alternative Water Processor (AWP) as a candidate water recovery system for long duration exploration missions. The AWP consists of biological water processor (BWP) integrated with a forward osmosis secondary treatment system (FOST). The basis of the BWP is a membrane aerated biological reactor (MABR), developed in concert with Texas Tech University. Bacteria located within the MABR metabolize organic material in wastewater, converting approximately 90% of the total organic carbon to carbon dioxide. In addition, bacteria convert a portion of the ammonia-nitrogen present in the wastewater to nitrogen gas, through a combination of nitrification and denitrification. The effluent from the BWP system is low in organic contaminants, but high in total dissolved solids. The FOST system, integrated downstream of the BWP, removes dissolved solids through a combination of concentration-driven forward osmosis and pressure driven reverse osmosis. The integrated system is expected to produce water with a total organic carbon less than 50 mg/l and dissolved solids that meet potable water requirements for spaceflight. This paper describes the test definition, the design of the BWP and FOST subsystems, and plans for integrated testing.

Life Support and Habitation Systems: Crew Support and Protection for Human Exploration Missions Beyond Low- Earth Orbit

The National Aeronautics and Space Administration (NASA) recently expanded its mission set for possible future human exploration missions. With multiple destination options it is of interest to identify technology needs across these missions to focus technology investments. In addition to the Moon and other destinations in cislunar space, destinations including near-Earth objects and Mars have been added for consideration. Technology programs and projects have been recently re-organizing to better meet the Agency’s strategic goals and to address needs across these potential future missions. Life Support and Habitation Systems (LSHS) is one of 10 Foundational Domains that are part of the NASA Exploration Technology Development Program. The chief goal of LSHS is to develop and mature advanced technologies to sustain human life on missions beyond low-Earth orbit to increase reliability, reduce dependency on resupply, and increase vehicle self-sufficiency. Further closure of life support systems is of interest for long duration exploration missions. The focus of LSHS includes key technologies for atmosphere revitalization, water recovery, waste management, food production, thermal control, crew accommodations, environmental monitoring, fire protection, and radiation protection. The aim is to recover additional consumable mass; reduce requirements for power, volume, heat rejection, and crew involvement; and meet exploration vehicle requirements. This paper provides a brief description of the LSHS Foundational Domain as defined for fiscal year 2011.

Exploration Life Support Technology Development for Lunar Missions

Exploration Life Support (ELS) is one of the National Aeronautics and Space Administration’s (NASA) technology development projects managed by NASA’s Exploration Technology Development Program (ETDP), under the guidance of the Advanced Capabilities Division of the NASA’s Exploration Systems Mission Directorate (ESMD). ELS plans, coordinates and implements the development of new life support technologies for human space exploration. ELS content includes four functional elements: Atmosphere Revitalization Systems (ARS), Water Recovery Systems (WRS), Waste Management Systems (WMS) and Habitation Engineering, and two cross cutting elements, Systems Integration, Modeling and Analysis (SIMA), and Validation and Testing. The ELS project utilizes in-house efforts at five NASA Field Centers. EL S is managed from the Johnson Space Center and includes Marshall Spaceflight Center, Kennedy Space Center, Ames Research Center and Glenn Research Center. The ELS project also incorporates aerospace industry contracts, university grants, Small Business In novative Research (SBIR) contracts and other means to develop advanced life support technologies. Testing, analysis and reduced gravity flight experiments are also conducted at the NASA field centers. The International Space Station could be used as a te st bed for certain technology development efforts. This paper gives a current status of technologies under development by ELS that will allow space exploration beyond low Earth orbit.