Showing papers on "Arcjet rocket published in 2010"

Validation of a Three-Dimensional Ablation and Thermal Response Simulation Code

Abstract: The 3dFIAT code simulates pyrolysis, ablation, and shape change of thermal protection materials and systems in three dimensions. The governing equations, which include energy conservation, a three-component decomposition model, and a surface energy balance, are solved with a moving grid system to simulate the shape change due to surface recession. This work is the first part of a code validation study for new capabilities that were added to 3dFIAT. These expanded capabilities include a multi-block moving grid system and an orthotropic thermal conductivity model. This paper focuses on conditions with minimal shape change in which the fluid/solid coupling is not necessary. Two groups of test cases of 3dFIAT analyses of Phenolic Impregnated Carbon Ablator in an arc-jet are presented. In the first group, axisymmetric iso-q shaped models are studied to check the accuracy of three-dimensional multi-block grid system. In the second group, similar models with various through-the-thickness conductivity directions are examined. In this group, the material thermal response is three-dimensional, because of the carbon fiber orientation. Predictions from 3dFIAT are presented and compared with arcjet test data. The 3dFIAT predictions agree very well with thermocouple data for both groups of test cases.

Modelling Study to Compare the Flow and Heat Transfer Characteristics of Low-Power Hydrogen, Nitrogen and Argon Arc-Heated Thrusters

Abstract: A modelling study is performed to compare the plasma flow and heat transfer characteristics of low-power arc-heated thrusters (arcjets) for three different propellants: hydrogen, nitrogen and argon. The all-speed SIMPLE algorithm is employed to solve the governing equations, which take into account the effects of compressibility, Lorentz force and Joule heating, as well as the temperature- and pressure-dependence of the gas properties. The temperature, velocity and Mach number distributions calculated within the thruster nozzle obtained with different propellant gases are compared for the same thruster structure, dimensions, inlet-gas stagnant pressure and arc currents. The temperature distributions in the solid region of the anode-nozzle wall are also given. It is found that the flow and energy conversion processes in the thruster nozzle show many similar features for all three propellants. For example, the propellant is heated mainly in the near-cathode and constrictor region, with the highest plasma temperature appearing near the cathode tip; the flow transition from the subsonic to supersonic regime occurs within the constrictor region; the highest axial velocity appears inside the nozzle; and most of the input propellant flows towards the thruster exit through the cooler gas region near the anode-nozzle wall. However, since the properties of hydrogen, nitrogen and argon, especially their molecular weights, specific enthalpies and thermal conductivities, are different, there are appreciable differences in arcjet performance. For example, compared to the other two propellants, the hydrogen arcjet thruster shows a higher plasma temperature in the arc region, and higher axial velocity but lower temperature at the thruster exit. Correspondingly, the hydrogen arcjet thruster has the highest specific impulse and arc voltage for the same inlet stagnant pressure and arc current. The predictions of the modelling are compared favourably with available experimental results.

Photogrammetric recession measurements of ablative materials in arcjets

Abstract: This paper describes an optical method for measuring the recession time histories of ablative thermal protection system (TPS) materials as they are tested in an arcjet facility. The method is non-intrusive and requires no external light source or modifications to the test article. It does require, first, a test article that exhibits texture as it ablates, and, second, high-resolution video images of the ablating surface from at least two directions. Software automatically reads the sequences of images and, by successive image cross correlation, tracks the deformation of a surface grid that conforms to the shape of the test article. Standard photogrammetric transformations are used to convert image-plane displacements of the surface grid to object-space displacements. The method yields a time history of the displacement of each node of the grid for the full time that the test article is exposed to the arcjet flow. Measurements have been made during many tests in the 60 MW arcjet at NASA Ames Research Center, including tests of TPS materials for the Orion Crew Exploration Vehicle and Mars Science Laboratory. The photogrammetric recession measurements have been in good agreement with post-test measurements of the change in thickness of the test articles.

Modeling Study on the Flow, Heat Transfer and Energy Conversion Characteristics of Low-Power Arc-Heated Hydrogen/Nitrogen Thrusters

Abstract: A modeling study is conducted to investigate the effect of hydrogen content in propellants on the plasma flow, heat transfer and energy conversion characteristics of low-power (kW class) arc-heated hydrogen/nitrogen thrusters (arcjets). 1:0 (pure hydrogen), 3:1 (to simulate decomposed ammonia), 2:1 (to simulate decomposed hydrazine) and 0:1 (pure nitrogen) hydrogen/nitrogen mixtures are chosen as the propellants. Both the gas flow region inside the thruster nozzle and the anode-nozzle wall are included in the computational domain in order to better treat the conjugate heat transfer between the gas flow region and the solid wall region. The axial variations of the enthalpy flux, kinetic energy flux, directed kinetic-energy flux, and momentum flux, all normalized to the mass flow rate of the propellant, are used to investigate the energy conversion process inside the thruster nozzle. The modeling results show that the values of the arc voltage, the gas axial-velocity at the thruster exit, and the specific impulse of the arcjet thruster all increase with increasing hydrogen content in the propellant, but the gas temperature at the nitrogen thruster exit is significantly higher than that for other three propellants. The flow, heat transfer, and energy conversion processes taking place in the thruster nozzle have some common features for all the four propellants. The propellant is heated mainly in the near-cathode and constrictor region, accompanied with a rapid increase of the enthalpy flux, and after achieving its maximum value, the enthalpy flux decreases appreciably due to the conversion of gas internal energy into its kinetic energy in the divergent segment of the thruster nozzle. The kinetic energy flux, directed kinetic energy flux and momentum flux also increase at first due to the arc heating and the thermodynamic expansion, assume their maximum inside the nozzle and then decrease gradually as the propellant flows toward the thruster exit. It is found that a large energy loss (31-52%) occurs in the thruster nozzle due to the heat transfer to the nozzle wall and too long nozzle is not necessary. Modeling results for the NASA 1-kW class arcjet thruster with hydrogen or decomposed hydrazine as the propellant are found to compare favorably with available experimental data.

Steady-State Ablation Model Coupling with Hypersonic Flow

Abstract: A steady-state, one-dimensional ablative surface model has been developed for coupling with hypersonic CFD applications in two- and three-dimensions. Details and assumptions of the steady-state model are presented along with the CFD boundary condition implementation and associated loose-coupling methodology. A preliminary sensitivity analysis for coecients present within the ablation model kinetics and flow transport properties is also presented for one of the primary quantities of interest in ablation modeling, the recession rate. Finally, the coupled approach is applied to a sphere-cone graphite model, corresponding to an arcjet stream experimental configuration performed at NASA’s Ames Research Center.

Plasma Torch Test of an Ultra-High-Temperature Ceramics Nose Cone Demonstrator

Abstract: An ultra-high-temperatureZrB2–SiC ceramic nose cone was tested in an arcjet plasma torch facility for 10min at temperatures above 2000 C. The nose cone model was obtained from a hot-pressed billet via electrical discharge machining.The relevant portions of themodels directly exposed to the hot streamwere analyzedby scanning electron microscopy and energy-dispersive spectroscopy. The posttest cross sectioning of the model showed a nonnegligible surface recession on the tip of the nose. Nonetheless, the material exhibited a promising potential to withstand severe reentry conditions with temperatures exceeding 2000 C in a single-use application. Spectral directional emissivity evaluationswere performed on the fly during the test bymeans of thermography coupledwith dual-color pyrometer. The numerical calculations, which simulated the chemical nonequilibrium flow around the model assuming a low catalytic surface behavior, are in good accordance with the experimental results.

Multidimensional Testing of Thermal Protection Materials in the Arcjet Test Facility

Abstract: Many thermal protection system materials used for spacecraft heatshields have anisotropic thermal properties, causing them to display significantly different thermal characteristics in different directions, when subjected to a heating environment during flight or arcjet tests. The anisotropic effects are enhanced in the presence of sidewall heating. This paper investigates the effects of anisotropic thermal properties of thermal protection materials coupled with sidewall heating in the arcjet environment. Phenolic Impregnated Carbon Ablator (PICA) and LI-2200 materials (the insulation material of Shuttle tiles) were used for this study. First, conduction-based thermal response simulations were carried out, using the Marc.Mentat finite element solver, to study the effects of sidewall heating on PICA arcjet coupons. The simulation showed that sidewall heating plays a significant role in thermal response of these models. Arcjet tests at the Aerodynamic Heating Facility (AHF) at NASA Ames Research Center were performed later on instrumented coupons to obtain temperature history at sidewall and various radial locations. The details of instrumentation and experimental technique are the prime focus of this paper. The results obtained from testing confirmed that sidewall heating plays a significant role in thermal response of these models. The test results were later used to validate the two-dimensional ablation, thermal response, and sizing program, TITAN. The test data and model predictions were found to be in excellent agreement.

Volt-Ampere and Thermal Features of a Direct-Current Dual-Jet Plasma Generator With a Cold Gas Injection

Abstract: Experimental studies on the volt-ampere characteristics and thermal efficiencies of a dual-jet direct-current arc thermal plasma generator with a cold gas injection are conducted. Discharge image processing results using the contour extraction method with the variable binary thresholding technique show that, compared with the conventional dual-jet plasma generator, the length of the high-gas-temperature region increases, the arcjet expands downward with the injection of cold gas, and the arc voltage and the thermal efficiency both increase by increasing the flow rate of the injected cold gas as a whole, accompanied by the more severe electrode ablation. The derived generalized dimensional complex equations concerning the electrical and thermal characteristics of the plasma generator based on the measured data and using the multiple linear regression method can, to some extent, be employed to predict the electrical and thermal features of the plasma generator. These equations are helpful for the design and operation of the dual-jet thermal plasma generator with a cold gas injection in actual applications.

Effect of Nozzle Temperature on the Performance of a 1 kW H2-N2 Arcjet Thruster

Abstract: A 1 kW-class arcjet thruster was fired in a vacuum chamber at a pressure of 18 Pa. A gas mixture of H2 : N2 = 2.8:1.5 in volume at a total flow rate of 4.3 slm was used as the propellant with an input power fixed at 860 W. The time-dependent thrust, nozzle temperature and inlet pressure of the propellant were measured simultaneously. Results showed that with the increase in nozzle temperature the thrust decreased and various losses increased. The physical mechanisms involved in these effects are discussed.

Prediction Accuracy of Thermal Response of Ablator Under Arcjet Flow Conditions

Abstract: Cloth-layered carbon fiber reinforced plastic ablator with a specific gravity of about 1.5 is developed to examine the prediction accuracy of analysis methods associated with the thermal response of ablator. Heating tests are carried out in the arcjet wind tunnel to quantify the thermal performance of ablator so developed. In the tests, the surface temperatures and in-depth temperatures of ablative test pieces are measured during the testing. Thermal response models of ablator are also developed in this study. Thermal conductivity measurements are conducted by using the steady-state method. Thermal diffusivity values of ablator are measured by using the laser-flash method. Thermal gravimetric analysis is also made to model the pyrolysis phenomena of ablating test piece. The experimental results obtained in the heating tests are analyzed by the one-dimensional ablation code with the thermal response models developed in this study. By comparing the calculated results and experimental results, the prediction accuracy of thermal response models of ablator is discussed.

Resistojets and Arcjets

Abstract: The simplest forms of electrically augmented propulsion for spacecraft are resistance-heated and arc-heated thrusters, generally called resistojets and arcjets, respectively. As with all forms of electric propulsion, electric energy added from the spacecraft increases the specific impulse over that achievable with a chemical reaction and expansion through a nozzle. With electrothermal devices, the added energy is imparted to the propellant as thermal energy. In the specific case of the resistojet, energy is added to the propellant with a resistance heater. In the case of an arcjet, an arc is drawn directly through the propellant between a cathode and an anode. The augmented specific impulse is limited by the maximum temperature tolerable by key components over the necessary life of the thruster. The maximum thrust as a function of input electrical power is limited by the efficiency with which the electrical energy is coupled into and contained within the flow and by the efficiency with which the flow enthalpy is converted to axial kinetic energy in the expansion. Resistojets and arcjets have been in development since the late 1950s and have been used on well over 200 spacecraft. This chapter describes the basic construction of these devices, illustrates relationships governing their performance, and surveys the performance demonstrated by a range of laboratory and flight qualified models. Keywords: resistojet; arcjet; electrothermal; electrode; electric propulsion; EHT; arc; anode; cathode; spacecraft propulsion; in-space propulsion

Current Numerical and Experimental Investigations of the Hybrid DC-RF Thruster TIHTUS

Abstract: Electric space propulsion delivers high exhaust velocities usually in combination with relatively low thrust levels. Raising the thrust level at a constant high exhaust velocity, fuel consumption for a specific mission is reduced and payload mass is increased. Also, an increase in mission flexibility and a reduction of duration can be achieved. Promising thrusters are hybrid concepts like TIHTUS. This thruster combines an arcjet and an ICP in series. The proof of concept already shows promising results. After a description of the thruster system actual experimental and theoretical optimizations of the standalone ICP are summarized. For a decrease of wall thickness from 2.3 mm to 1.25 mm the thermal plasma power is increased by 40 % and the thinner quartz tube can resist higher heat loads, too. These results show the potential for large improvements of the overall thruster parameters and motivate a research program for further optimization of the already promising TIHTUS engine. In this program, theoretical and experimental investigation will be accompanied by numerical simulations for a detailed understanding of the relevant processes and the identification of the prospects of success for further optimization. The current status of development of the numerical tool is also described.

Thermal Protection System Crack Growth Simulation Using Advanced Grid Morphing Techniques

Abstract: An extension of previous [Titov, E., Zhong, J., Levin, D., and Picetti, D., "Simulation of RCC Crack Growth Due to Carbon Oxidation in High-Temperature Gas Environments," Journal of Thermophysics and Heat Transfer, Vol. 23, No. 3, July-Sept. 2009, pp. 489-501.] modeling of crack damage growth in reinforced carbon-carbon specimens is presented in this work. The specimens were studied in an arcjet and represented a portion of the space shuttle wing [Lewis, R., "Quick Look Report," Atmospheric Reentry Materials and Structures, 2004.] and a high-velocity meteoroid impact [Curry, D. M., Pham, V. T., Norman, I., and Chao, D. C., "Oxidation of Reinforced Carbon-Carbon Subjected to Hypervelocity Impact," NASA TP 2000-209760, March 2000.]. The test geometry and flow conditions rendered the flow regime as transitional to continuum; therefore, a Navier-Stokes-based gas-dynamic approach with the temperature jump and velocity slip correction to the boundary conditions was used. The modeled mechanism for wall material loss was atomic oxygen reaction with the bare, exposed carbon surface. The purpose of this work is to improve the predictive modeling of crack growth damage assessment by developing procedures that use coupled, advanced topology-based surface and grid-meshing tools. A recessing three-dimensional surface morphing procedure was developed and tested by comparison with arcjet experimental results. A multiblock structured adaptive meshing was used to model the computational domain changes due to the wall recession. This approach made it possible to model full three-dimensional crack growth scenarios as well as to include the presence of realistic reinforced carbon-carbon material features such as delamination, both of which affect damage growth because they enable higher atomic oxygen penetration. Comparison with the arcjet data show that the inclusion of these two factors further improves the comparison between modeling and data. The predicted channel growth and shape change were found to agree with arcjet observations, and local gas flowfield results were found to affect the oxidation rate in a manner that cannot be predicted by previous mass loss correlations. The method holds promise for future modeling of materials gas-dynamic interactions for hypersonic flight.

Evaluation of Prediction Accuracy of Thermal Response of Ablator Under Arcjet Flow Condisions

Abstract: Using a cloth-layered carbon fiber reinforced plastic ablator with a specific gravity of about 1.5, the thermal response model of ablator is studied experimentally and numerically. Heating tests are carried out in the arcjet wind tunnel to quantify the thermal performance of ablator. In the tests, the surface temperatures and in-depth temperatures of ablative test pieces are measured during the testing. The experimental results obtained in the heating tests are analyzed by using a two-dimensional analysis method developed earlier. In the method, the thermal response of ablator is calculated by loosely coupling the shock layer computational fluid dynamics code and the 2-D version of ablation code using an arcjet freestream condition. The arcjet freestream condition in the test section is evaluated by calculating the flows in the arcjet wind tunnel. The present analyses are made especially focusing on an anisotropic nature of thermal conduction of ablator. Thermal conduction inside the ablator is modeled in the present analysis method based on thermal conductivity values measured for different ply angles of carbon cloths of ablator. By comparing the calculated results with the arcjet data, the prediction accuracy of thermal response models of ablator is discussed.

Modeling of Crew Exploration vehicle Re-entry Ablation Flows

Abstract: Statistical BGK simulations coupled with the material response solution were performed to estimate the micro-crack growth in an arcjet AVCOAT coated specimen representing the Crew Exploration Vehicle thermal protection system. The after shock inlet boundary conditions for the BGK studies were obtained from a CFD (DPLR) solution of the arcjet flow. The solution of the arcjet case is followed by a 81 km CEV flow-material response study which represents a point along a CEV re-entry trajectory. Rarefied flow conditions at 81 km prompted using the baseline DSMC technique to solve the shock wave layer flow providing data for the inlet boundary conditions for the local crack-material response studies. The results draw a preliminary conclusion regarding the effectiveness of the AVCOAT protective mechanisms against the growth of the micro cracks during the Earth atmosphere re-entry of the vehicle.

Numerical Simulation of the Thermomagnetic Effect on the Electrodynamic Flow Control System

Abstract: The impact of the thermo-magnetic effect on the electrodynamic flow control system was investigated by numerical analyses to assess the arcjet experiments for the heat flux mitigation performed by G ¨ ulhan et al. To take account of the thermo-magnetic effect, we adopted the Nernst effect, which creates the electric field in the direction normal to both the temperature gradient and the magnetic field vector. The parametric study shows that the Nernst effect affects locally the current distribution in the circumferential direction near the shock and the shoulder region around the capsule. As a result, the efficiency of the heat flux mitigation by the Lorentz force was weaken by the affected current distribution.

Plasma and Electrode Emissions from a 1 kW Hydrogen- Nitrogen Arcjet Thruster

Abstract: Arc root behavior affects the energy transfer and nozzle erosion in an arcjet thruster. To investigate the development of arc root attachment in 1 kW class N2 and H2–N2 arcjet thrusters from the time of ignition to the stably working condition, a kinetic series of end‐on view images of the nozzle obtained by a high‐speed video camera was analyzed. The addition of hydrogen leads to higher arc voltage levels and the determining factor for the mode of arc root attachment was found to be the nozzle temperature. At lower nozzle temperatures, constricted type attachment with unstable motions of the arc root was observed, while a fully diffused and stable arc root was observed at elevated nozzle temperatures.

Plume Parameters and Thruster Properties of a Low Power Arcjet

Abstract: . A low power arcjet-thruster of 1 kW-class with gas mixture of H2-N2 or pure argon as the propellant is fired at a chamber pressure about 10 Pa. The nozzle temperature is detected with an infrared pyrometer; a plate set perpendicular to the plume axis and connected to a force sensor is used to measure the thrust; a probe with a tapered head is used for measuring the impact pressure in the plume flow; and a double-electrostatic probe system is applied to evaluate the electron temperature. Results indicate that the high nozzle temperature could adversely affect the conversion from enthalpy to kinetic energy. The plume flow deviates evidently from the LTE condition, and the rarefied-gas dynamic effect should be considered under the high temperature and low-pressure condition in analyzing the experimental phenomena.

Post-Test Sample Analysis of Fiber Reinforced Plastic Using Arcjet

Abstract: Coking phenomenon for silica fiber reinforced plastic(SFRP) exposed to aerodynamic heating is examined experimentally and numerically. The SFRP material with the nominal virgin density of 1.70 g/cm 3 is heated in an arcjet wind tunnel. The spatial distribution of in-depth gas permeability and material density is measured for post-test arcjet sample. Thermal response analysis is made by evaluating thermophysical parameters for the SFRP material. Comparison of the density and permeability distribution gives a fair agreement between measurement and calculation, suggesting that coking effect could be negligibly small for the case of the high density ablator examined in the present study. Nomenclature A : cross sectional area of unsealed portion of test specimen for permeability measurement