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Decomposition of hydrazine allows the attitude and altitude control of satellite. Macroporous–mesoporous alumina supported iridium catalyst (KCMC-7) has been developed using the fast dehydration of aluminium trihydroxide and subsequent multiple impregnations. The result of data analysis suggested that the obtained alumina was ρ-Al2O3 with both macro and mesopores. Significant amount of pentagonal Al sites after rehydration of ρ-Al2O3 was responsible for ultra high dispersion for ultra high loading of metal around 30 wt%. The performance of the KCMC-7 measured using 4.5 N dual thruster module was satisfactory until the end of life, providing enough thrust for the attitude and altitude control of satellite in the pressure range of 50–350 psi.

Hydrazine monopropellant has been used in thrusters for maneuvering satellites and landing spacecraft. Testing and handling procedures for hydrazine monopropellant thrusters are complicated, because of the toxicity of the hydrazine and its decomposition product gases. Therefore, simulated numerical analysis can help elucidate the effects of various thruster design parameters and can reduce both development time and expenses. In this study, a simulated numerical analysis was performed in which the catalyst bed was modeled as a one-dimensional porous medium. The resulting physical phenomena were examined by considering variations in catalyst bed characteristics incurred by catalyst pellet failure. From observations of various hot-firing experiments, it was determined that the upper region of the decomposition chamber was preferentially damaged in failure situations, which led to the conclusion that catalyst failure occurs in the upper region only. We simulated various cases based on the crushing and mass lo...

In this paper the Chemical Propulsion Subsystem of COMS is briefly explained and some telemetries acquired by a series operations of CPS during the Launch and Early Operation Phase of COMS are presented. The pressure and temperature of pressurant tank telemetries are compared with the results of the developed computer program. The changes in pressure are due to the two major phases. The first one is the initialization phases of CPS composed of the venting phase to vent the helium gas in the pipe network from the downstream of the propellant tanks to the thrusters for safety, the priming phase to fill the vented pipe network with oxidizer and fuel respectively and then the pressurization phase to pressurize the ullage of propellant tank to regulated pressure. And the other is the apogee engine firings in which COMS CPS is in the orbit raising phase to use helium as a pressurant to keep the pressure of propellant tank as the liquid apogee engine get fired until COMS reached to the target orbit. This program can be applicable to prepare basis design data of the next Geostationary Satellite CPS.

This work studies the performance of an injector for a monopropellant thruster, comparing a conventional and new injector types. The conventional injector consists of 8 nozzles on a convex surface allowing the jet to be diverged. The new injector, we suggested, is an impinging type with nozzle holes on a concave surface. The fuel streams through the nozzle holes are collide at a point on an axial direction, which allow to atomize the liquid streams and to spray more uniformly along circular direction. The performance of the injectors is investigated by using computational fluid dynamics, particle image velocimetry and high speed camera visualization.

Radiative heat transfer in a complex axisymmetric enclosure with participating medium is investigated by using the finite-volume method (FVM). In particular, an implementation of the unstructured polygonal meshes is adopted by connecting each center point of the unstructured triangular meshes rather than joining the centroids of the triangular elements to the midpoints of the corresponding sides to form a polygonal element. Also, typical considerations regarding application of the present polygonal mesh system to axisymmetric radiation are discussed. After a mathematical formulation and corresponding discretization equation for the radiative transfer equation (RTE) are derived, the final discretization equation is introduced with the conventional finite-volume approach by using the directional weights. For validation and comparison, three test examples with complex axisymmetric geometries have been accomplished. The present study shows that not only is the method flexible in treating radiative problems wi...

In this paper, “end effect”, which represents the deflection of meniscus of boundary nozzles in an array due to asymmetric electric field and repulsive forces between adjacent nozzles, is experimentally investigated and a polymer-based electrospray device is fabricated and tested to minimize the end effect. For the electrically conductive nozzles of electrospray, the end effect could be reduced by dummy nozzles, through which no liquid is supplied, mounted at the boundary of the array. However, the polymer-based electrospray device can eliminate the end effect without using the dummy dry nozzles due to dielectric characteristic. A novel multiple nozzles of Polymethyl Methacrylate (PMMA)-based electrospray device was successfully fabricated and evaluated for reducing the end effect, showing no deflection of menisci through the boundary nozzles. And ten nozzles device was fabricated and observed to eject liquid jet simultaneously. The electrical current of the spray issued from the nozzles of the polymer-based electrospray device is measured with respect to flow rate and shows a good agreement with the scaling law.

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(Received August 11th, 2008) Satellite attitude is usually controlled by plume exhaust from thrusters into the vacuum of space. To study the plume effects in the highly rarefied region, the Direct Simulation Monte Carlo (DSMC) method is usually used, because the plume flow field contains the entire range of flow regime from the near-continuum near the nozzle exit through the transitional state to free molecular state at the far field region from the nozzle. The purpose of this study is to investigate the behavior of a small monopropellant thruster plume in the vacuum region numerically by using the DSMC method. To obtain more accurate results, the preconditioned Navier-Stokes algorithm is introduced to calculate continuum flow fields inside the thruster to predict nozzle exit properties, which are used for inlet conditions of DSMC method. As a result, the plume characteristics in the highly rarefied flow, such as strong nonequilibrium near nozzle exit, large back flow region, etc., are investigated.

The interaction between thrust plume and satellite base region was investigated by using direct simulate Monte-Carlo calculations. For the accurate simulation of N2 and H2 collisions and rotation-translation transition, a variable soft-sphere model and a recent rotational relaxation model of N2 and H2 were used. For the investigation of the interaction between thrust plume and base region, the number density distribution for each species, translational and rotational temperature distributions, heat flux, and pressure were examined by direct simulation of Monte-Carlo calculations. It was found that most of the surface properties are affected by H2 collisions and a strong non-equilibrium state is observed at the base region. It was demonstrated that an accurate model is needed to simulate H2 collisions and the rotation-translation transition. The results by the present calculation are more accurate than previous direct simulation Monte-Carlo calculations because more accurate rotational relaxation models were used in simulating the inelastic collisions.

CO2 adsorption measurement at 273 K was employed to see if the porous material has either micropore or mesopore dominantly. The adsorption isotherm of CO2 on microporous solid such as zeolite A and Y was the typical Langmuir type while on SBA-15, silica gel and polymer, the adsorption isotherm was proportional to the applied pressure, following the Henry's law. Such distinctive difference between the adsorption isotherms provided the reasonable basis to discriminate the pore characteristics otherwise it was difficult to obtain it. Also, it was possible to get the surface property of polymer due to the pretreatment using CO2 adsorption measurement at 273 K while the N2 adsorption isotherm measurement at 77 K did not give the meaningful data.

This work was supported by the Korea Research Foundation Grant funded by the Korean Government [Ministry of Education and Human Resources Development (MOEHRD), Basic Research Promotion Fund] (KRF-2006-003-D00092).

The currently developed propulsion system(PS) is composed of propellant tank, valves, thrusters, interconnecting line assembly and thermal hardwares to prevent propellant freezing in the space environment. Comprehensive engineering analyses in the structure, thermal, flow and plume fields are performed to evaluate main design parameters and to verify their suitabilities concurrently at the design phase. The integrated PS has undergone a series of acceptance tests to verify workmanship, performance, and functionality prior to spacecraft level integration. After all the processes of assembly, integration and test are completed, the PS is integrated with the satellite bus system successfully. At present, the severe environmental tests have been carried out to evaluate functionality performances of satellite bus system. This paper summarizes an overall development process of monopropellant propulsion system for the attitude and orbit control of LEO(Low Earth Orbit) observation satellite from the design engineering up to the integration and test.

Experimental and numerical studies have been done to examine the effects of excess air ratio and tertiary air swirl number on the formation characteristics of NO in a pilot scale combustor adopting a multi-air staged burner. In numerical calculation the mathematical models for turbulence, radiation and nitric oxide chemistry were taken into account. The radiative transfer equation was solved using the discrete ordinates method with the weighted sum of gray gases model. In the NO chemistry model, the chemical reaction rates for thermal and prompt NO were statistically averaged using a probability density function. The results were validated by comparison with measurements. For the experiment, a 0.2 MW pilot multi-staged air burner has been designed and fabricated. Using the numerical simulation developed here, a variation of thermal and prompt NO formation was predicted by changing the excess air ratio and tertiary air swirl number. As the excess air ratio increased up to 1.9, the formation of the total as well as thermal NO at exit increased while the prompt NO decreased. The formation of thermal NO was more affected by concentration of O2 and N2 than gas temperature. When the tertiary air swirl number increased, the formation of the total as well as the prompt NO slightly decreased because of enhanced mixing of fuel and oxygen in the upstream reaction zone and reduced gas temperature at exit.

In this study, the nonequilibrium effects at the stagnation wall in one-dimensional unsteady microflow responding to the external sinusoidal oscillation are investigated. The fluctuating behavior of the rarefied medium is simulated by employing the unsteady DSMC method under various conditions with different acoustic Reynolds and Knudsen numbers. As a result, it is found that the nonequilibrium effect exists at the stagnation wall, especially when the gas density number is small. Due to such a nonequilibrium effect found in a fluctuating medium, the Knudsen number representing system size becomes a more important system parameter than the acoustic Reynolds number even for the constant excitation frequency. Also, the validity of the well-known Maxwell-Smoluchowski relation and its higher-order modifications are tested by comparing the heat fluxes from these relations with the direct DSMC result.

Numerical and experimental studies have been conducted to examine the extended weighted sum of gray gases model (WSGGM), which takes account of nongray gases, suspended soot particles, and spray droplets in a multistage air/light fuel oil burner. The Eulerian balance equations for mass, momentum, energy, and species mass fractions were adopted with the standard k-e turbulence model, whereas the Lagrangian approach was used for the particulate phase. The radiative transfer equation was solved using the discrete ordinates method with the two-phase WSGGM. In the NO chemistry model, the chemical reaction rates for thermal and prompt NO were statistically averaged using a probability density function. The results were validated by comparison with measurements. For the experiment, a 0.2 MW prototype multiannular burner was designed and fabricated. Comparisons between predicted and measured results were carried out to investigate the feasibility of application of the extended WSGGM to light fuel oil. Th...

In this study, a numerical simulation was developed which was capable of predicting the characteristics; of NO formation in pilot scale combustor adopting the air-staged burner flame. The numerical calculation was constructed by means of establishing the mathematical models for turbulence, turbulent combustion, radiation and turbulent nitric oxide chemistry. Turbulence was solved with standard k-e model and the turbulent combustion model was incorporated using a two step reaction scheme together with an eddy dissipation model. The radiative transfer equation was calculated by means of the discrete ordinates method with the weighted sum of gray gases model for CO2 and H2O. In the NO chemistry model, the chemical reaction rates for thermal and prompt NO were statistically averaged using the p probability density function. The results were validated by comparison with measurements. For the experiment, a 0.2 MW pilot multi-air staged burner has been designed and fabricated. Only when the radiation was taken i...

A numerical study for simulating a swirling pulverized coal combustion in axisymmetric geometry is carried out here by applying the weighted sum of gray gases model (WSGGM) approach with the discrete ordinate method (DOM) to model the radiative heat transfer equation. In the radiative transfer equation, the same polynomial equation and coefficients for weighting factors as those for gas are adopted for the coal/char particles as a function of partial pressure and particle temperature. The Eul-erian balance equations for mass, momentum, energy, and species mass fractions are adopted with the standard k-ϵs turbulence model, whereas the Lagrangian approach is used for the particulate phase. The eddy-dissipation model is employed for the reaction rate for gaseous mixture, and the single-step first-order reaction model for the devolatili.ation process for coal. By comparing the numerical results with experimental ones, the radiation model used here is confirmed and found to provide sound alternative for simula...

A great deal of eAorts has been exercised to date to accurately model the non-gray behavior of the gases. Among others, the weighted sum of gray gases model (WSGGM), which replaces the non-gray gas behavior by an equivalent finite number of gray gases, is a simplified model yielding reasonable results. However, a discussion on the weighting factors required for an estimation of radiation in a mixture of non-gray gas/gray particulate is not yet established for WSGGM, since they are dependent on the particle number density, particle size distribution, local temperature and partial pressure. Consequently, the relation between the weighting factors used in the WSGGM for a mixture of non-gray gas and gray particles with scattering in the thermal non-equilibrium has been discussed here, which has not been done before to the author’s best knowledge. Weighting factors for the particles, of which temperature is diAerent from that of the gas, were evaluated analytically for the WSGGM. The results were, then, validated for the problem of isothermal gas containing soot particulates between two parallel slab walls. For further application, the approach derived here was implemented to examine the non-gray radiative eAects of the two phase mixture in an axisymmetric cylinder by changing such various parameters as the particle temperature, non-gray gas composition and particle concentration. The eAects of thermal non-equilibrium in a mixture of gas and particles were also discussed in parallel with scattering eAects by particles. Parametric study showed that a variation in the gas concentration yielded a noticeable change in the radiative heat transfer when the suspended particle temperature was diAerent from the gas temperature. New contribution of this study consisted in an extension of applicability of the WSGGM non-gray model to two phase radiation. # 2000 Elsevier Science Ltd. All rights reserved.

In general, thruster hot-firing test should be performed in vacuum condition to simulate space environment. However in case of this study, for reducing cost and development schedule, most performance tests were carried out in atmospheric conditions with continuous nitrogen purging, only baseline hot-firing tests were performed in vacuum conditions for health check. Then we compared the hot-firing test results between atmospheric conditions and vacuum conditions for thruster performance verification. As it turned out, the results of performance degradation in atmospheric conditions with continuous nitrogen purging are quite similar to those in vacuum conditions. Thus, the long duration test in atmospheric conditions with continuous nitrogen purging is also reliable for thruster performance verification in the early development phase. On the basis of the long life test results, it is reasonable to suppose that serious degradation of thruster performance will most likely not occur even into the extension life period.

Corrigendum to “Polymer-based electrospray device with multiple nozzles to minimize end effect phenomenon” [J. Electrostatics 68 (2010) 138e144] Si Bui Quang Tran , Doyoung Byun *, Vu Dat Nguyen , Hadi Teguh Yudistira , Myoung Jong Yu , Kyun Ho Lee , Jaeuk U. Kim c Department of Aerospace and Information Engineering, Konkuk University, Seoul 143-701, Republic of Korea Korea Aerospace Research Institute, Daejon 305-333, Republic of Korea Division of Constitutional Medicine Research, Korea Institute of Oriental Medicine, Daejon 305-811, Republic of Korea