Uday Hegde

Development and Validation of a Model for Hydrogen Reduction of JSC-1A

Hydrogen reduction of lunar regolith has been proposed as a viable technology for oxygen production on the moon. Hydrogen reduces FeO present in the lunar regolith to form metallic iron and water. The water may be electrolyzed to recycle the hydrogen and produce oxygen. Depending upon the regolith composition, FeO may be bound to TiO2 as ilmenite or it may be dispersed in glassy substrates. Some testing of hydrogen reduction has been conducted with Apollo-returned lunar regolith samples. However, due to the restricted amount of lunar material available for testing, detailed understanding and modeling of the reduction process in regolith have not yet been developed. As a step in this direction, hydrogen reduction studies have been carried out in more detail with lunar regolith simulants such as JSC-1A by NASA and other organizations. While JSC-1A has some similarities with lunar regolith, it does not duplicate the wide variety of regolith types on the moon, for example, it contains almost no ilmenite. Nonetheless, it is a good starting point for developing an understanding of the hydrogen reduction process with regolith-like material. In this paper, a model utilizing a shrinking core formulation coupled with the reactor flow is described and validated against experimental data on hydrogen reduction of JSC-1A.

Component and System Sensitivity Considerations for Design of a Lunar ISRU Oxygen Production Plant

Component and system sensitivities of some design parameters of ISRU system components are analyzed. The differences between terrestrial and lunar excavation are discussed, and a qualitative comparison of large and small excavators is started. The effect of excavator size on the size of the ISRU plant’s regolith hoppers is presented. Optimum operating conditions of both hydrogen and carbothermal reduction reactors are explored using recently developed analytical models. Design parameters such as batch size, conversion fraction, and maximum particle size are considered for a hydrogen reduction reactor while batch size, conversion fraction, number of melt zones, and methane flow rate are considered for a carbothermal reduction reactor. For both reactor types the effect of reactor operation on system energy and regolith delivery requirements is presented.

Waste Management Options for Long-Duration Space Missions: When to Reject, Reuse, or Recycle

The amount of waste generated on long-duration space missions away from Earth orbit creates the daunting challenge of how to manage the waste through reuse, rejection, or recycle. The option to merely dispose of the solid waste through an airlock to space was studied for both Earth-moon libration point missions and crewed Mars missions. Although the unique dynamic characteristics of an orbit around L2 might allow some discarded waste to intersect the lunar surface before re-impacting the spacecraft, the large amount of waste needed to be managed and potential hazards associated with volatiles recondensing on the spacecraft surfaces make this option problematic. A second option evaluated is to process the waste into useful gases to be either vented to space or used in various propulsion systems. These propellants could then be used to provide the yearly station-keeping needs at an L2 orbit, or if processed into oxygen and methane propellants, could be used to augment science exploration by enabling lunar mini landers to the far side of the moon.

NUMERICAL INVESTIGATION OF BUOYANCY EFFECTS ON TRIPLE FLAME STABILITY

Numerical simulations of laminar two-dimensional triple flames are conducted to investigate the mechanisms of buoyancy-induced instabilities. These simulations are implemented for a selected range of gravity conditions and inlet scalar mixing widths for downward-propagating triple flames (propagating in the same direction as the gravity vector). Increases in the gravity force result in a transition from a stable to an unstable behavior. A linear inviscid stability analysis is performed to explore the mechanisms of instability and to estimate the most amplified frequencies. Unstable triple flame simulations provide detailed flow and scalar information for interrogating the mechanisms of buoyancy-induced instabilities in triple flames. These instabilities are accompanied by baroclinic generation of countervortices consistent with the Kelvin–Helmholtz instabilities. The computed onset of instabilities is accompanied by the advection of the triple flames downstream from their stabilization point. This advection plays a dominant role in the unstable behavior, further illustrating the hydrodynamic, buoyancy-induced nature of these instabilities. The most amplified frequencies from the linear stability analysis are in reasonable agreement with those determined from simulations of unstable triple flames. A parametric study using the linear stability analysis suggests that both the frequencies and amplitudes of disturbances increase with the magnitude of the gravity acceleration constant. Furthermore, the magnitude of amplification is largest just downstream of the two premixed branches. This trend implies the important role of baroclinic vorticity in the onset of instabilities. From the results of unsteady flame simulations, the onset of instability was found to correlate best with the Froude number based on premixed flame thickness and the triple flame propagation speed.

Radiative Loss from Non-Premixed Flames in Reduced-Gravity Environments

This paper presents the results of an experimental and theoretical study of radiation from luminous jet diffusion flames in partial-gravity environments. Tests were conducted for laminar, non-premixed methane flames burning in quiescent air on-board the NASA KC-135 research aircraft for a range of gravity levels. Flame radiation and gravitational acceleration were measured, and flame imaging was performed. The radiation data are compared with those obtained from normal-gravity and microgravity tests, conducted in a drop facility. Effects of g-jitter on radiation measurements are discussed. With the aid of predictions from a numerical model of jet diffusion flames, the influence of gravity on radiation through its effects on the temperature, species, and velocity fields is analyzed. Good agreement between predictions and measurements is obtained.

Analysis of Water Extraction From Lunar Regolith

Distribution of water concentration on the moon is currently an area of active research. Recent studies suggest the presence of ice particles, and perhaps even ice blocks and icecemented regolith on the moon. Thermal extraction of the in-situ water is an attractive means of satisfying water requirements for a lunar mission. In this paper, a model is presented to analyze the processes occurring during the heat-up of icy regolith and extraction of the evolved water vapor. The wet regolith is assumed to be present in an initially evacuated and sealed cell which is subsequently heated. The first step of the analysis involves calculating the gradual increase of vapor pressure in the closed cell as the temperature is raised. Then, in the second step, the cell is evacuated to low pressure (e.g., vacuum), allowing the water vapor to leave the cell and be captured. The parameters affecting water vapor pressure build-up and evacuation for the purpose of extracting water from lunar regolith are discussed in the paper. Some comparisons with available experimental measurements are also made.

Hydrogen Reduction of Lunar Regolith Simulants for Oxygen Production

Abstract Hydrogen reduction of the lunar regolith simulants JSC-1A and LHT-2M is investigated in this paper. Experiments conducted at NASA Johnson Space Center are described and are analyzed utilizing a previously validated model developed by the authors at NASA Glenn Research Center. The effects of regolith sintering and clumping, likely in actual production operations, on the oxygen production rate are studied. Interpretations of the obtained results on the basis of the validated model are provided and linked to increase in the effective particle size and reduction in the intra-particle species diffusion rates. Initial results on the pressure dependence of the oxygen production rate are also presented and discussed. Nomenclature c o molar concentration of hydrogen in regolith bed (moles/m 3 ) D effective gas diffusion coefficient (m 2 /s) F factor defined by Equation (1) (s –1 ) k equilibrium constant L length of regolith bed (m) p gas pressure (Pa) r p regolith particle radius (m) t

Turbulent Structure Dynamics of Buoyant and Non-Buoyant Pulsed Jet Diffusion Flames

The flame structure dynamics of strongly pulsed, turbulent diffusion flames were examined experimentally in a co-flow combustor. High-speed visual imaging and thermocouple measurements were performed to determine celerity, defined as as being the bulk velocity of a given flame puff structure in the large-scale, turbulent flame structures. Tests were conducted in normal gravity and microgravity with a fixed fuel injection velocity with a Reynolds number of 5,000 and also with a constant fueling rate where the Reynolds number ranged from 5,000 to 12,500. The celerity of strongly interacting flame puffs is as much as two times greater than for the case of isolated flame puffs. The amount of decrease in celerity at the visible flame tip due to the removal of buoyancy ranges from 7% to 11% in most cases, to as much as 36% for both fixed jet injection velocity and constant fueling rate. At the same time, the flame length is modestly affected by the removal of positive buoyancy, amounting to a decrease of as much as 20%. These observations hold for both fixed injection velocity and constant fueling rate cases. The observed increases in the flame puff celerity and the mean flame length with decreasing jet-off time, for a given injection time and gravity level, are consistent with a decreased rate of oxidizer entrainment into each flame puff structure due to increased flame puff interactions. A scaling argument accounts for the decrease of the flame puff celerity with downstream distance when both quantities are normalized by the appropriate injection conditions. The celerity, as characterized by the temperature measurement method, appears to be essentially unaffected by buoyancy at any given downstream location when appropriately scaled. The visual tracking method suggests a modest buoyancy effect at a given downstream distance, suggesting a subtle impact of buoyancy on the flame puff structures that does not impact the bulk motion.

Heating-Rate-Coupled Model for Hydrogen Reduction of JSC-1A

A previously developed and validated model for hydrogen reduction of JSC-1A for a constant reaction-bed temperature is extended to account for reaction during the bed heat-up period. A quasisteady approximation is used wherein an expression is derived for a single average temperature of reaction during the heat-up process by employing an Arrhenius expression for regolith conversion. Subsequently, the regolith conversion during the heat-up period is obtained by using this representative temperature. Accounting for the reaction during heat-up provides a better estimate of the reaction time needed at the desired regolith-bed operating temperature. Implications for the efficiency of the process, as measured by the energy required per unit mass of oxygen produced, are also indicated.

Analysis of Water Recovery Rate From the Heat Melt Compactor

Human space missions generate trash with a substantial amount of plastic (20% or greater by mass). The trash also contains water trapped in food residue and paper products and other trash items. The Heat Melt Compactor (HMC) under development by NASA Ames Research Center (ARC) compresses the waste, dries it to recover water and melts the plastic to encapsulate the compressed trash. The resulting waste disk or puck represents an approximately ten-fold reduction in the volume of the initial trash loaded into the HMC. In the current design concept being pursued, the trash is compressed by a piston after it is loaded into the trash chamber. The piston face, the side walls of the waste processing chamber and the end surface in contact with the waste can be heated to evaporate the water and to melt the plastic. Water is recovered by the HMC in two phases. The first is a pre-process compaction without heat or with the heaters initially turned on but before the waste heats up. Tests have shown that during this step some liquid water may be expelled from the chamber. This water is believed to be free water (i.e., not bound with or absorbed in other waste constituents) that is present in the trash. This phase is herein termed Phase A of the water recovery process. During HMC operations, it is desired that liquid water recovery in Phase A be eliminated or minimized so that water-vapor processing equipment (e.g., condensers) downstream of the HMC are not fouled by liquid water and its constituents (i.e., suspended or dissolved matter) exiting the HMC. The primary water recovery process takes place next where the trash is further compacted while the heated surfaces reach their set temperatures for this step. This step will be referred to herein as Phase B of the water recovery process. During this step the waste chamber may be exposed to different selected pressures such as ambient, low pressure (e.g., 0.2 atm), or vacuum. The objective for this step is to remove both bound and any remaining free water in the trash by evaporation. The temperature settings of the heated surfaces are usually kept above the saturation temperature of water but below the melting temperature of the plastic in the waste during this step to avoid any encapsulation of wet trash which would reduce the amount of recovered water by blocking the vapor escape. In this paper, we analyze the water recovery rate during Phase B where the trash is heated and water leaves the waste chamber as vapor, for operation of the HMC in reduced gravity. We pursue a quasi-one-dimensional model with and without sidewall heating to determine the water recovery rate and the trash drying time. The influences of the trash thermal properties, the amount of water loading, and the distribution of the water in the trash on the water recovery rates are determined.