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PubMed1996

Mission simulation as an approach to develop requirements for automation in Advanced Life Support Systems.

This paper examines mission simulation as an approach to develop requirements for automation and robotics for Advanced Life Support Systems (ALSS). The focus is on requirements and applications for command and control, control and monitoring, situation assessment and response, diagnosis and recovery, adaptive planning and scheduling, and other automation applications in addition to mechanized equipment and robotics applications to reduce the excessive human labor requirements to operate and maintain an ALSS. Based on principles of systems engineering, an approach is proposed to assess requirements for automation and robotics using mission simulation tools. First, the story of a simulated mission is defined in terms of processes with attendant types of resources needed, including options for use of automation and robotic systems. Next, systems dynamics models are used in simulation to reveal the implications for selected resource allocation schemes in terms of resources required to complete operational tasks. The simulations not only help establish ALSS design criteria, but also may offer guidance to ALSS research efforts by identifying gaps in knowledge about procedures and/or biophysical processes. Simulations of a planned one-year mission with 4 crewmembers in a Human Rated Test Facility are presented as an approach to evaluation of mission feasibility and definition of automation and robotics requirements.

Automation↗
PubMed1995

System issues for Controlled Ecological Life Support Systems.

There are several characteristics of a Controlled Ecological Life Support System that are distinct from commonly engineered systems. These are: 1) the uncertainty, due to limited data availability, and variability due to the heterogeneity of biological subsystems; 2) the closed, ecological nature of the system; and 3) the primary criterion of maximizing the probability of survival. Consequences of these features include: complex dynamics characterized by time scales ranging from milliseconds to months, posing difficult problems with respect to mathematical modeling and predictability; and the necessity for a unique controller design that can translate the high level requirement of survivability to low-level actuator tasks. Future research in the systems and control area should include an ecological perspective focusing on the unique dynamical characteristics of a Controlled Ecological Life Support System.

Ecological Systems, Closed↗
PubMed1996

A system and methodology for measuring volatile organic compounds produced by hydroponic lettuce in a controlled environment.

A system and methodology were developed for the nondestructive qualitative and quantitative analysis of volatile emissions from hydroponically grown 'Waldmann's Green' leaf lettuce (Lactuca sativa L.). Photosynthetic photon flux (PPF), photoperiod, and temperature were automatically controlled and monitored in a growth chamber modified for the collection of plant volatiles. The lipoxygenase pathway products (Z)-3-hexenal, (Z)-3-hexenol, and (Z)-3-hexenyl acetate were emitted by lettuce plants after the transition from the light period to the dark period. The volatile collection system developed in this study enabled measurements of volatiles emitted by intact plants, from planting to harvest, under controlled environmental conditions.

Air↗
PubMed1996

Charge balance--a theoretical basis for modulating pH fluctuations in plant nutrient delivery systems.

Existing control systems for pH and nutrient supply in hydroponic space plant growth units and bioregenerative life support (BLS) systems require acid and base additions to correct plant-induced charge imbalances in the nutrient solution. Plant growth is dependent on nutrient availability, and the active uptake of ions by roots changes the pH of the nutrient solution. This change in pH is an integrated response to nutrient and organic ion influx/efflux by the plant. Plant nutrient requirements, as a function of crop development and driven by specific environmental conditions, influence the magnitude of the charge balance requirement. Nitrogen is the dominant nutrient taken up by plant species. If the daily crop nutrient (N) requirement at each developmental stage is known, and the daily addition of nutrients (relative addition rate = RAR) to the plant growth system is calculated, controlling the daily addition of ammonium (NH4+) and nitrate (NO3-) offers a mechanism whereby pH fluctuations in the nutrient solution could be largely minimized and controlled, reducing acid or base additions to the system.

Anions↗
PubMed1994

Bios-3 project in Krasnoyarsk, Russia

The article in this issue by Gitelson and Okladnikov provides a valuable summary of some of the work conducted at the Bios-3 project in Krasnoyarsk, Russia. As the title suggests, the focus is on humans and their role in a CELSS biosphere. I am aware of several translated reports and some recent articles by Dr. Gitelson and colleagues in which the Bios project is described, but this paper provides some information that I have not seen previously in an english article. Although the discussion is focused on bioregeneration, the authors state that complementary physicochemical technologies and some stowage may be needed in a CELSS. For example, animal protein foods were taken into the Bios-3 chamber, since, as the authors state, "products of animal origin would make the system considerably more complicated and energy inefficient."

Carbon Dioxide↗
PubMed1996

Consideration in selecting crops for the human-rated life support system: a Linear Programming model.

A Linear Programming model has been constructed which aids in selecting appropriate crops for CELSS (Controlled Environment Life Support System) food production. A team of Controlled Environment Agriculture (CEA) faculty, staff, graduate students and invited experts representing more than a dozen disciplines, provided a wide range of expertise in developing the model and the crop production program. The model incorporates nutritional content and controlled-environment based production yields of carefully chosen crops into a framework where a crop mix can be constructed to suit the astronauts' needs. The crew's nutritional requirements can be adequately satisfied with only a few crops (assuming vitamin mineral supplements are provided) but this will not be satisfactory from a culinary standpoint. This model is flexible enough that taste and variety driven food choices can be built into the model.

Crops, Agricultural↗
PubMed1992

CELSS system control: issues, methods, and directions.

In the general control perspective, the CELSS concept implies a very complex system and presents challenges at every level. These challenges are generated by: (1) the prospect that the system will be inherently unstable, (2) the prospective difficulty of establishing an adequate mathematical model of the system for the purpose of control law synthesis (dimensionality is high, and the dynamics and interactive processes of some of the subsystems are not understood well), (3) assuring control law robustness (assuring that the resulting control law(s) will be effective over the domain of the specified uncertainties), (4) hardware realization of the control law, (5) hardware system robustness ("fault tolerance") and (6) achieving the logistics of the automation (or "management") aspects of the problem. A suggested organization of the problem, a sketch of the issues related to perceived difficulties, a commentary/evaluation of the issues, a review of methods available to address the issues, and a suggested strategy to address the broad CELSS systems control problem are presented.

Computer Simulation↗
PubMed1987

Operation of an experimental algal gas exchanger for use in a CELSS.

Concepts of a CELSS anticipate the use of photosynthetic organisms (higher plants and algae) for air revitalization. The rates of production and uptake of carbon dioxide and oxygen between the crew and the photosynthetic organisms are mismatched. An algal [correction of aglal] system used for gas exchange only will have the difficulty of an accumulation or depletion of these gases beyond physiologically tolerable limits (in a materially closed system the mismatch between assimilatory quotient (AQ) and respiratory quotient (RQ) will be balanced by the operation of the waste processor). We report the results of a study designed to test the feasibility of using environmental manipulations to maintain physiologically appropriate atmospheres for algae (Chlorella pyrenoidosa) and mice (Mus musculus strain DW/J) in a gas-closed system. Specifically, we consider the atmosphere behavior of this system with Chlorella grown on nitrate or urea and at different light intensities and optical densities. Manipulation of both the photosynthetic rate and AQ of the alga has been found to reduce the mismatch of gas requirements and allow operation of the system in a gas-stable manner. Operation of such a system in a CELSS may be useful for reduction of buffer sizes, as a backup system for higher plant air revitalization and to supply extra oxygen to the waste processor or during crew changes. In addition, mass balance for components of the system (mouse, algae and a waste processor) are presented.

Air Conditioning↗
PubMed1996

Nitrogen dynamics in the CELSS Breadboard facility at Kennedy Space Center.

For the past 9 years, the Breadboard Project at Kennedy Space Center has studied the feasibility of using crop plants in bioregenerative life support systems for long-duration space missions. Nitrogen (N) has been emphasized in nutrient balance studies because it is a major plant nutrient, undergoes biogenic and abiogenic transformations, and is often limiting to plant growth under field conditions. Nitrogen budgets have been calculated from experimental results to quantify utilization and losses associated with specific crop production systems. The Breadboard Project has recently completed a 418-day potato crop study using recycled nutrient solution to evaluate the impact of continuous production on life support functions. A continuous production system is desirable in maintaining N balance within a solution because crop uptake rates vary dramatically depending upon the stage of crop development. Strategies for recycling N using biological techniques (e.g., biomass degradation with microbial bioreactors) have required that the production system be modified to distribute inputs more evenly over time. Recovery of N is dependent on the form of N entering the bioreactor and the desired output. Aerobic and anaerobic bioreactors for the recovery of N from waste streams and its transformation into a form usable by higher plants are being designed and tested.

Aerobiosis↗
PubMed1996

Johnson Space Center's Regenerative Life Support Systems Test Bed.

The Regenerative Life Support Systems (RLSS) Test Bed at NASA's Johnson Space Center is an atmospherically closed, controlled environment facility for human testing of regenerative life support systems using higher plants in conjunction with physicochemical life support systems. The facility supports NASA's Advanced Life Support (ALS) Program. The facility is comprised of two large scale plant growth chambers, each with approximately 11 m2 growing area. The root zone in each chamber is configurable for hydroponic or solid media plant culture systems. One of the two chambers, the Variable Pressure Growth Chamber (VPGC), is capable of operating at lower atmospheric pressures to evaluate a range of environments that may be used in a planetary surface habitat; the other chamber, the Ambient Pressure Growth Chamber (APGC) operates at ambient atmospheric pressure. The air lock of the VPGC is currently being outfitted for short duration (1 to 15 day) human habitation at ambient pressures. Testing with and without human subjects will focus on 1) integration of biological and physicochemical air and water revitalization systems; 2) effect of atmospheric pressure on system performance; 3) planetary resource utilization for ALS systems, in which solid substrates (simulated planetary soils or manufactured soils) are used in selected crop growth studies; 4) environmental microbiology and toxicology; 5) monitoring and control strategies; and 6) plant growth systems design. Included are descriptions of the overall design of the test facility, including discussions of the atmospheric conditioning, thermal control, lighting, and nutrient delivery systems.

Atmospheric Pressure↗
PubMed1996

NASA's Advanced Life Support Systems Human-Rated Test Facility.

Future NASA missions to explore the solar system will be long-duration missions, requiring human life support systems which must operate with very high reliability over long periods of time. Such systems must be highly regenerative, requiring minimum resupply, to enable the crews to be largely self-sufficient. These regenerative life support systems will use a combination of higher plants, microorganisms, and physicochemical processes to recycle air and water, produce food, and process wastes. A key step in the development of these systems is establishment of a human-rated test facility specifically tailored to evaluation of closed, regenerative life supports systems--one in which long-duration, large-scale testing involving human test crews can be performed. Construction of such a facility, the Advanced Life Support Program's (ALS) Human-Rated Test Facility (HRTF), has begun at NASA's Johnson Space Center, and definition of systems and development of initial outfitting concepts for the facility are underway. This paper will provide an overview of the HRTF project plan, an explanation of baseline configurations, and descriptive illustrations of facility outfitting concepts.

Air Conditioning↗
PubMed1992

The Breadboard Project: a functioning CELSS plant growth system.

The primary objective of the Breadboard project for the next 3-4 years is to develop, integrate and operate a Controlled Ecological Life Support System (CELSS) at a one person scale. The focus of this project over the past two years has been the development of the plant growth facility, the first module of the CELSS. The other major modules, food preparation, biomass processing, and resource recovery, have been researched at the laboratory scale during the past two years and facilities are currently under construction to scale-up these modules to an operational state. This paper will outline the design requirements for the Biomass Production Chamber (BPC), the plant growth facility for the project, and the control and monitoring subsystems which operate the chamber and will present results from both engineering and biological tests of the facility. Three production evaluations of wheat, conducted in the BPC during the past year, will be described and the data generated from these tests discussed. Future plans for the BPC will be presented along with future goals for the project as the other modules become active.

Biomass↗
PubMed1984

Dynamic considerations for control of closed life support systems.

Reliability of closed life support systems will depend on their ability to continue supplying the crew's needs in the face of perturbations and equipment failures. These dynamic considerations interact with the basic static (equilibrium) design through the sizing of storages, the specification of excess capabilities in processors, and the choice of system initial state (total mass in the system). This paper uses a very simple system flow model to examine the possibilities for system failures even when there is sufficient storage to buffer the immediate effects of the perturbation. Two control schemes are shown which have different dynamic consequences in response to component failures.

Ecological Systems, Closed↗
PubMed1996

Bioregenerative life support systems for long-term space habitation: a conceptual approach.

Life support systems represent one of the most critical aspects of human space exploration. Future long-term missions such as the establishment of human-tended Lunar and Martian bases require closed life support systems. A conceptual approach to an Engineered Closed/Controlled EcoSystem incorporating bioregenerative capabilities by integrating humans, plants, and waste management processes is presented. The integration of physical/chemical and biological waste treatment processes is suitable for supporting plant growth through hydroponics and materially closing the human and plant metabolic loops. This conceptual design separates wastes into individual loops for treatment according to the specific metabolic needs of humans and plants. The means through which an integrated Engineered Closed/Controlled EcoSystem meets the life support objectives of long-term space habitation are summarized.

Biomass↗
PubMed1996

Volatile organic compounds detected in the atmosphere of NASA's Biomass Production Chamber.

Atmospheres of enclosed environments in which 20 m2 stands of wheat, potato, and lettuce were grown were characterized and quantified by gas chromatography-mass spectrometry. A large number (in excess of 90) of volatile organic compounds (VOCs) were identified in the chambers. Twenty eight VOC's were assumed to be of biogenic origin for these were not found in the chamber atmosphere when air samples were analyzed in the absence of plants. Some of the compounds found were unique to a single crop. For example, only 35% of the biogenic compounds detected in the wheat atmosphere were unique to wheat, while 36% were unique to potato and 26% were unique to lettuce. The number of compounds detected in the wheat (20 compounds) atmosphere was greater than that of potato (11) and lettuce (15) and concentration levels of biogenic and non-biogenic VOC's were similar.

Air↗
PubMed1996

Anaerobic degradation of inedible crop residues produced in a Controlled Ecological Life Support System.

An anaerobic reactor seeded with organisms from an anaerobic lagoon was used to study the degradation of inedible crop residues from potato and wheat crops grown in a closed environment. Conversion of this biomass into other products was also evaluated. Degradation of wheat volatile solids was about 25% where that of potato was about 50%. The main product of the anaerobic fermentation of both crops was acetic acid with smaller quantities of propionate and butyrate produced. Nitrate, known to be high in concentration in inedible potato and wheat biomass grown hydroponically, was converted to ammonia in the anaerobic reactor. Both volatile fatty acid and ammonia production may have implications in a crop production system.

Ammonia↗