Search Results

Waste management is a vital function of spacecraft life support systems as it is necessary to meet crew health and safety and quality of life requirements. Depending on the specific mission requirements, waste management operations can include waste collection, segregation, containment, processing, storage and disposal. For the Crew Exploration Vehicle (CEV), addressing volume and mass constraints is paramount. Reducing the volume of trash prior to storage is a viable means to recover habitable volume, and is therefore a particularly desirable waste management function to implement in the CEV, and potentially in other spacecraft as well. Research is currently being performed at NASA Ames Research Center to develop waste compaction systems that can provide both volume and mass savings for the CEV and other missions.

Terraforming of Mars is the long-term goal of colonization of Mars. However, this process is likely to be a very slow process and conservative estimates involving a synergetic, technocentric approach suggest that it may take around 10,000 years before the planet can be parallel to that of Earth and where humans can live in open systems (Fogg, 1995). Hence, for the foreseeable future, any missions will require habitation within small confined habitats with high biomass to atmospheric mass ratios, thereby requiring that all wastes be recycled. Processing of the wastes will ensure predictability and reliability of the ecosystem and reduce resupply logistics. Solid wastes, though smaller in volume and mass than the liquid wastes, contain more than 90% of the essential elements required by humans and plants.

Pyrolysis is a very versatile waste processing technology which can be tailored to produce a variety of solid, liquid and/or gaseous products. The pyrolysis processing of pure and mixed solid waste streams has been under investigation for several decades for terrestrial use and a few commercial units have been built for niche applications. Pyrolysis has more recently been considered for the processing of mixed solid wastes in space. While pyrolysis units can easily handle mixed solid waste streams, the dependence of the pyrolysis product distribution on the component composition is not well known. It is often assumed that the waste components (e.g., food, paper, plastic) behave independently, but this is a generalization that can usually only be applied to the overall weight loss and not always to the yields of individual gas species.

The elemental composition of food consumed by astronauts is well defined. The major elements carbon, hydrogen, oxygen, nitrogen and sulfur are taken up in large amounts and these are often associated with the organic fraction (carbohydrates, proteins, fats etc) of human tissue. On the other hand, a number of the elements are located in the extracellular fluids and can be accounted for in the liquid and solid waste fraction of humans. These elements fall into three major categories - cationic macroelements (e.g. Ca, K, Na, Mg and Si), anionic macroelements (e.g. P, S and Cl and17 essential microelements, (e.g. Fe, Mn, Cr, Co, Cu, Zn, Se and Sr). When provided in the recommended concentrations to an adult healthy human, these elements should not normally accumulate in humans and will eventually be excreted in the different human wastes.

The success of physico-chemical waste processing and resource recovery technologies for life support application depends partly on the ability of gas clean-up systems to efficiently remove trace contaminants generated during the process with minimal use of expendables. Highly purified metal-impregnated carbon nanotubes promise superior performance over conventional approaches to gas clean-up due to their ability to direct the selective uptake gaseous species based both on the nanotube’s controlled pore size, high surface area, and ordered chemical structure that allows functionalization and on the nanotube’s effectiveness as a catalyst support material for toxic contaminants removal. We present results on the purification of single walled carbon nanotubes (SWCNT) and efforts at metal impregnation of the SWCNT’s.

Crop production in space habitats is currently under consideration as part of an advanced life support system. The scenarios for crop production vary depending on the mission objectives. For a mission scenario such as the International Space Station (ISS), current efforts propose only salad crop production. However in order to grow salad crops, there is a need for plant nutrients (elements) such as N, P, K, Ca, etc., which constitutes about 10% of dry weight of the plant. Nitrogen and potassium are the major elements needed by salad crops and currently require resupply on Station. However, it is feasible that these macronutrients could be recovered through the waste materials generated by the crew. The proposed concepts are non-oxidative and simple in design. This paper considers the potential for reclaiming macronutrients from urine and gray water concentrates from water recovery systems.

Pyrolysis processing of solid waste in space will inevitably lead to carbon formation as a primary pyrolysis product. The amount of carbon depends on the composition of the starting materials and the pyrolysis conditions (temperature, heating rate, residence time, pressure). Many paper and plastic materials produce almost no carbon residue upon pyrolysis, while most plant biomass materials or human wastes will yield up to 20-40 weight percent on a dry, as-received basis. In cases where carbon production is significant, it can be stored for later use to produce CO2 for plant growth. Alternatively it can be partly gasified by an oxidizing gas (e.g., CO2, H2O, O2) in order to produce activated carbon. Activated carbons have a unique capability of strongly absorbing a great variety of species, ranging from SO2 and NOx, trace organics, mercury, and other heavy metals.

Pyrolysis is a very versatile waste processing technology which can be tailored to produce a variety of solid liquid and/or gaseous products. The main disadvantages of pyrolysis processing are: (1) the product stream is more complex than for many of the alternative treatments; (2) the product gases cannot be vented directly into the cabin without further treatment because of the high CO concentrations. One possible solution is to combine a pyrolysis step with catalytic oxidation (combustion) of the effluent gases. This integration takes advantage of the best features of each process, which is insensitivity to product mix, no O2 consumption, and batch processing, in the case of pyrolysis, and simplicity of the product effluent stream in the case of oxidation. In addition, this hybrid process has the potential to result in a significant reduction in Equivalent System Mass (ESM) and system complexity.

One of the major problems associated with solid waste processing technologies is effluent contaminants that are released in gaseous forms from the processes. This is a concern in both biological as well as physicochemical solid waste processing. Carbon dioxide (CO2), the major gas released, does not present a serious problem and there are currently in place a number of flight-qualified technologies for CO2 removal. However, a number of other gases, in particular NOx, SO2, NH3, and various hydrocarbons (e.g. CH4) do present health hazards to the crew members in space habitats. In the present configuration of solid waste processing in the International Space Station (ISS), some of these gases are removed by the Trace Contaminant Control System (TCCS), demands a major resupply. Reduction of the resupply can be effective by using catalyst impregnated carbon nanotubes. For example, NO decomposition to N2 and O2 is thermodynamically favored.

The development and characterization of an innovative approach for the control and elimination of gaseous toxins using single walled carbon nanotubes (SWNTs) promise superior performance over conventional approaches. This is due to the ability of the nanotubes to direct the selective uptake of gaseous species based on their controllable pore size, high adsorptive capacity and their effectiveness as catalyst supports for gaseous conversion. A metal impregnated SWNT material has been proposed and synthesized for removing and converting the toxins in the life support system.

Pyrolysis is a technology that can be used on future space missions to convert wastes to an inert char, water, and gases. The gases can be easily vented overboard on near term missions. For far term missions the gases could be directed to a combustor or recycled. The conversion to char and gases as well as the absence of a need for resupply materials are advantages of pyrolysis. A major disadvantage of pyrolysis is that it can produce tars that are difficult to handle and can cause plugging of the processing hardware. By controlling the heating rate of primary pyrolysis, the secondary (cracking) bed temperature, and residence time, it is possible that tar formation can be minimized for most biomass materials. This paper describes an experimental evaluation of two versions of pyrolysis reactors that were delivered to the NASA Ames Research Center (ARC) as the end products of a Phase II and a Phase III Small Business Innovation Research (SBIR) project.

Pyrolysis is a very versatile waste processing technology which can be tailored to produce a variety of solid, liquid, and/or gaseous products. The main disadvantages of pyrolysis processing are: (1) the product stream is more complex than for many of the alternative treatments; (2) the product gases cannot be vented directly into the cabin without further treatment because of the high CO concentrations. One possible solution is to combine a pyrolysis step with catalytic oxidation (combustion) of the effluent gases. This integration takes advantage of the best features of each process. The advantages of pyrolysis are: insensitivity to feedstock composition, no oxygen consumption, and batch operation. The main advantage of oxidation is the simplicity and consistency of the product stream. In addition, this hybrid process has the potential to result in a significant reduction in Equivalent System Mass (estimated at 10-40%) and system complexity.

This paper presents the results from a joint research initiative between NASA Ames Research Center and Lawrence Berkeley National lab. The objective of the research is to produce activated carbon from life support wastes and to use the activated carbon to adsorb and chemically reduce the NOx and SO2 contained in incinerator flue gas. Inedible biomass waste from food production is the primary waste considered for conversion to activated carbon. Results to date show adsorption of both NOx and SO2 in activated carbon made from biomass. Conversion of adsorbed NOx to nitrogen has also been observed.

Since the mid 1980s, NASA has developed advanced waste management technologies that collect and process waste. These technologies include incineration, hydrothermal oxidation, pyrolysis, electrochemical oxidation, activated carbon production, brine dewatering, slurry bioreactor oxidation, composting, NOx control, compaction, and waste collection. Some of these technologies recover resources such as water, oxygen, nitrogen, carbon dioxide, carbon, fuels, and nutrients. Other technologies such as the Waste Collection System (WCS - the commode) collect waste for storage or processing. The need for waste processing varies greatly depending upon the mission scenario. This paper reviews the waste management technology development activities conducted by NASA since the mid 1980s and explores the drivers that determine the application of these technologies to future missions.