Showing papers on "Arcjet rocket published in 1996"

Plasma generators for re-entry simulation

Abstract: The qualification of thermal protection systems (TPS) and numerical design tools for re-entry vehicles and space probes requires the ability to understand and duplicate the prevailing complex physico-chemical phenomena, including thermal and chemical nonequilibrium near the surface of a body that enters the atmosphere of the Earth or another celestial body. At the Institut fur Raumfahrtsysteme of the University of Stuttgart, four plasma wind tunnels (PWK1-4) are in operation to simulate the thermal, aerodynamic, and chemical loads on the surface of a space vehicle. Three different plasma sources have been developed for this purpose: 1) a magnetoplasmadynamic generator for the simulation of the highenthalpy and low-pressure environment during the first phase of re-entry, 2) a thermal arcjet device for the follow-on flight path at moderate specific enthalpies and higher stagnation pressures, and 3) an inductively heated generator for basic materials experiments over a wide range of specific enthalpies and pressures. Special efforts were made to avoid electrode erosion to preclude impairing the erosion and catalytic behavior of TPS materials. A detailed description of these plasma generators and an overview of the simulation regions and operation areas of the plasma wind tunnels are presented.

Plasmadynamics model for nonequilibrium processes in N2/H2 arcjets

Abstract: A two-temperature chemical nonequilibrium model is developed for nitrogen/hydrogen (N 2/H2) arcjet thrusters. All viscous flow properties are considered assuming steady, laminar, continuum, and axisymmetric flow. A seven-species N2/H2 plasma composition of molecules, atoms, ions, and electrons is assumed, and a finite rate chemistry model is employed to model collisional processes among the species. Separate energy equations are formulated for the electrons and heavy species. The anode temperature distribution is included, and propellant electrical conductivity is coupled to the plasma properties, allowing for a selfconsistent current distribution. The numerical solution employs the compressible form of the pressureimplicit with splitting of operators algorithm to solve the continuity and momentum equations. Numerical results are presented for a low-power simulated hydrazine thruster. The centerline constrictor region of the arcjet flowfield is predicted to be near thermal equilibrium, whereas a high degree of thermal nonequilibrium is predicted in the near-anode region of the arcjet nozzle. Strong electric fields near the anode produce elevated electron temperatures that enhance ionization levels and electrical conduction through the arcjet boundary layer. Radial diffusion of electrons from the arc core also enhances the near-anode ionization levels. Thus, the nonequilibrium approach is required to accurately model the plasma current distribution.

Two-fluid nonequilibrium simulation of hydrogen arcjet thrusters

Abstract: A detailed numerical model has been developed to study the gasdynamic flow in an electrothermal arcjet thruster. This two-temperature Navier-Stokes model consistently incorporates viscosity, heat conduction, ohmic dissipation, collisional energy transfer between electrons and heavy species, ambipolar diffusion, nonequilibrium dissociation and ionization, and continuum radiation. The fluid equations are solved by MacCormack's method while an iterative procedure is used to relax an electric potential equation, from which the current distribution in the thruster is obtained. Using hydrogen propellant, solutions are achieved for a range of input parameters and the underlying physics and internal structures of these arcjet flows are revealed. In particular, a mechanism for self-sustaining anodic arc attachment is identified. Numerical solutions are compared with experimental results from the Stuttgart TT1 radiation-cooled arcjet thruster. Calculated discharge voltage is within 1-10% of experimental measurements, and predicted specific impulse is within 5-10% agreement. In addition, flow solutions are used to explain observed trends in performance as quantities such as the specific energy and mass flow rate are varied.

Exit-plane electrostatic probe measurements of a low-power arcjet

Abstract: Improved understanding of the flow processes in a 1-kW hydrazine constricted arcjet is achieved with multiple electrostatic probe surveys in the exit-plane region of the plume. Quadruple, triple, and single electrostatic probe techniques are utilized for measurements of the electron temperature Te9 density ne, and ratio of ion axial velocity to most probable thermal speed n,/cm,H+. Centerline axial profiles of Te and nc are presented for 2.2-6.2 mm downstream of the exit-plane, yielding Te = 6600 K ± 15% and nc 3.6 x 10 12 cm"3 ±60% close to the thruster exit. Quadruple probe theory is modified to account for radial gradients in Te and ne over the probe radial dimension, and is used to extract exit-plane radial Te and ne profiles. Floating probe measurements yield estimates of the radial electric-field profile at the thruster exit, implying a small amount of current and ohmic heating downstream of the exit-plane. Ak cm E e / I lb 7, j k L m n

Arcjet Thruster Development

Abstract: For several years an intensive program has been in progress at the University of Stuttgart to investigate and develop thermal arcjets for propellants including ammonia, nitrogen-hydrogen mixtures simulating hydrazine, and hydrogen. Since hydrogen yields the highest specific impulse /sp and best efficiencies TJ, special emphasis was placed on this propellant. Arcjet power levels between 0.7-150 kW have been studied, including water- and radiation-cooled laboratory models and flight hardware. Results yielded a maximal attainable 7sp as a function of the design and power level and showed that increasing power increased /sp. Radiation-cooled arcjets show better 17 and 7sp than water-cooled devices, but raise technical problems because of the high temperatures of the thrusters, which require the use of special refractory materials. Proper arcjet optimization was done with a thorough thermal analysis, including the propellant flow. A further improvement of these thrusters was reached by regenerative cooling and by optimizing the constrictor contour. The constrictor flow is modeled by a three-channel model, the results of which are compared with experimental data. A new two-dimensional computational fluid dynamics (CFD) approach for hydrogen arcjet thrusters is presented. In 1996 a 0.7-kW ammonia arcjet is scheduled for a flight on the P3-D AMSAT satellite.

Arcjet modeling - Status and prospects

Abstract: The evolution of arcjet thruster modeling to its current state of development is traced, and the most pressing theoretical uncertainties in the way of further progress are discussed. The thrust-producing mechanism is well understood, and so is the general energy balance, leading to voltage prediction, provided anodic attachment is separately known. This particular problem is discussed in some detail. It is argued that three-dimensional arc root constriction is a very likely cause of at least some of the observed anode behavior, and should be theoretically investigated. Other issues examined are electron-molecule interactions, species segregation, and thermomechanical effects.

Development and demonstration of a 600-second mission-average I(sp) arcjet

Abstract: Recent advanced development has resulted in a 550-h demonstration of a hydrazine arcjet at a missionaverage special impulse 7sp of greater than 600 s. The laboratory-type arcjet thruster was operated at 1800 W through a flow rate schedule consistent with a flight application. The thruster demonstrated stable, high-efficiency operation for the duration of the test. The development effort leading to the demonstration addressed the operational and life issues associated with achieving high performance. As a result of the development activity, a wide range of performance was also achieved. Performance levels of greater than 575 s at 1000 W and greater than 675 s at 2000 W were demonstrated. The problems encountered with extending low-power arcjet performance are discussed. Increased thruster component temperatures caused new life issues to be identified, along with low propellant flow rate stability limits. The elevated temperatures caused significant changes in the electrode geometry for a thruster based on the state-of-the-art tungsten anode designs. Three paths to solving the problem were attempted, including lowering the operating temperature through improved heat rejection, mechanical design changes to reduce thermal stresses, and higher strength materials selection. The success of this program provides substantial evidence that an arcjet capable of greater than 600-s mission-average specific impulse will be available in the near term for flight qualification and application.

Directions for arcjet technology development

Abstract: Guidelines for improvements in arcjet performance based on a simplified analysis of advanced mission requirements are presented. The results of this analysis clearly show that to remain competitive with next-generation electric propulsion devices, significant increases in the specific impulse of present arcjet technology must be achieved. Of the various design options available, concepts that improve the thrust efficiency offer the greatest performance leverage, and may, in fact, represent the only approaches capable of meeting the advanced mission goals. If they are to be successful, such concepts will improve the management of energy and mass transport within the arcjet. One method to understand and control the internal plasmadynamics of the arcjet to improve its performance is outlined.

Near- and far-field plume studies of a one-kilowatt arcjet

Abstract: To support studies of transport in arcjet plumes, axial and radial profiles of electron temperature, electron number density, stagnation pressure, and flow field were obtained over an extensive volume of the plume of a 1-kW arcjet operating on hydrogen. All experiments were performed in a 6 by 9 m vacuum chamber at a tank pressure of less than 4 x 10 ~4 torr during arcjet operation. Electron temperatures obtained spectroscopically 1.2 cm downstream of the exit plane ranged from 0.10 to 0.13 eV, while electron number densities determined ~2 cm downstream of the exit plane via langmuir probe varied between 0.3-1 x 10 12 cm~3. Far-field langmuir probe measurements showed that a rapid radial variation in electron number density exists, ranging from 0.5 to 5 x 10 9cm~3, and from 0.5 to 2 x 10 9 cm~3, 30 and 88 cm downstream of the exit plane, respectively. Electron temperatures at these axial locations show much less of an axial dependence, ranging between 0.070.20 eV at both axial positions. Finally, an impact pressure probe was used to measure the radial profiles of stagnation pressure 53 and 64 cm from the exit plane as well as flow angle. The impact pressure probe data compare favorably with stagnation pressures predicted by a source-flow code and suggests that the heavy particles diffuse less radially than do the electrons.

Stark broadening corrections to laser-induced fluorescence temperature measurements in a hydrogen arcjet plume

Abstract: Laser-induced fluorescence of the H(α) transition of atomic hydrogen has previously been performed in the plume of a hydrogen arcjet thruster. Measurements of plasma velocity and temperature, based on the Doppler shift and broadening of the H(α) line shape, were previously published [Appl. Opt. 32, 6117 (1993)]. In that paper the Stark broadening of the H(α) transition was estimated from static-ion calculations performed in the early 1970's and found to be negligible in comparison with the Doppler broadening. However, more recent dynamic-ion calculations have shown the Stark broadening to be considerably larger than was previously assumed, resulting in inaccurate temperature measurements. We present a reanalysis of the fluorescence data, taking into account the improved Stark broadening calculations. The correct atomic hydrogen translation temperature and electron number density are obtained from the Doppler and Stark broadening components of the measured line shape. The results indicate a substantial drop in temperature from those previously reported.

Fluorescence velocity measurements in the interior of a hydrogen arcjet nozzle

Abstract: The first use of laser-induced fluorescence for spatially resolved plasma velocity measurements within an arcjet nozzle are described.The arcjet was operated on a propellant of pure hydrogen.The Balmer-α transition of atomic hydrogen was scanned by the excitation laser source while simultaneously detecting the spectrally integrated resonance fluorescence.Velocity was determined from the Doppler shift in the peak of the laser excitation spectrum relative to a stationary reference.The arcjet operating conditions were chosen to facilitate a comparison between these measurements and arcjet modeling results of Butler et al.

Interior Plasma Diagnostics of Arcjet Thrusters

Abstract: We review past experimental measurements of internal flow properties of arcjet thrusters. These measurements are generally classified as either intrusive, requiring design changes to prototype thrusters, or nonintrusive, and include measurements of cathode temperature, as well as static pressure, flow temperatures (vibrational, rotational, electronic, translational), electron density, and velocity throughout the interior region extending to the exit plane. Comparisons are made to available model predictions. These measurements, performed on a wide range of thrusters, and operating on variety of propellants, indicate that the nozzle plasma flow may be removed from local thermodynamic equilibrium.

Thermodynamical nonequilibrium nitrogen plasmas in a direct-current arcjet engine nozzle

Abstract: Spectroscopic measurements were carried out to understand the arc structure and the flowfield in a 10-kW-class water-cooled direct-current nitrogen arcjet engine with a supersonic expansion nozzle for material processing. In the expansion nozzle, the pressure and electron density drastically decreased downstream, and therefore the plasma was in thermodynamical nonequilibrium, although the plasma in the constrictor was expected to be nearly in a temperature-equilibrium condition. The radial profiles of the physical properties for N/sub 2/ and N/sub 2//sup /showed that there existed a core flow with high vibrational and rotational temperatures and large electron number densities on the center axis, even at the nozzle exit. Both of these temperatures on the arcjet axis at the nozzle exit and the electron temperature in the constrictor increased linearly with the input power, regardless of mass flow rate. The vibrational temperature ranged from 6000 to 10000 K in input power levels of 5-11 kW and the rotational temperature from 500 to 2000 K.

Arcjet Development for Amateur Radio Satellite

Abstract: The radio amateur satellite P3-D, weighing 400 kg, will be launched into a highly elliptical 16-h orbit in 1996. Its final orbit control will be performed by a 750-W ammonia arcjet system. This work describes the arcjet system and its components as well as the qualification and operation philosophy. The implications of the satellite, the planned orbit, and the orbit control strategy for the arcjet propulsion system are also explained. The thruster system has passed two lifetime qualification tests lasting 670 and 1010 cycles with one hour of arcjet operation per cycle, which are briefly discussed.

Spectroscopic Measurement of the Flows in an Arc-Jet Facility

Abstract: To provide the proper test conditions for various applications, the characteristics of arcjet test facilities should be known. To determine the operational characteristics of an arcjet facility, emission spectroscopy measurements have been performed and analyzed in a previous study. As an extension of the study, radiation from the free stream and the shock layer of 15 cm diameter blunt-body test articles is measured under different test conditions in the NASA Ames 20 MW Arcjet Facility. The test gas is a mixture of argon and air or N2 and argon. To capture the spatially resolved emission spectra along the stagnation streamline of the blunt-body, a CCD camera (1024 x 256 array) with .275 m Czerny-Turner spectrograph is used. The optical system is calibrated in situ using tungsten and deuterium radiation sources. The emission measurements supplement the existing data base and will help provide better understanding of the equilibration processes in the shock layer region.

High energy rocket propellant

Abstract: A rocket propellant of improved Isp and thrust is provided by modifying a rocket fuel of RP-1 (a kerosene fraction). Such fuel is combined with an oxidizer (e.g. liquid oxygen, LOX) which defines a rocket propellant of the prior art. Such propellant is modified per the invention by addition to or replacement of, the RP-1 with quadricyclane. In another embodiment, quadricyclane is added to n-Hexane as a fuel composition which is then combined with an oxidizer to define a rocket propellant per the invention. The invention thus provides a number of rocket fuels which upon combination with an oxidizer, provides a high energy density propellant, which can permit increases of over 10 wt % in additional payload for rocket launch vehicles.

Low power arcjet propellant feed system

Abstract: A lower power arcjet propellant feed system for delivering propellant to a low power arcjet. The low power arcjet propellant feed system includes a liquid propellant storage chamber for storing a liquid propellant. A gas generator in communication with the liquid propellant storage chamber generates a gaseous propellant upon receipt of the liquid propellant from the liquid propellant storage chamber. A gas plenum in communication with the gas generator accumulates the gaseous propellant from the gas generator up to a desired pressure. Actively controllable valves actively control the flow of the liquid propellant into the gas generator and actively control the flow of the resultant gaseous propellant out of the gas generator and into the gas plenum up to the desired pressure. A substantially continuous and stable low flow rate of gaseous propellant is then delivered to the low power arcjet.

Converging constrictor for an electrothermal arcjet thruster

Abstract: There is provided an anode for an electrothermal arcjet thruster. A conduit running through the anode body has a converging upstream portion and a diverging downstream portion connected by a constrictor portion having a greater diameter at the interface with the upstream portion than at the interface with the downstream portion. As the result, the cross-sectional area available to a propellant gas passing through the constrictor constantly decreases and the propellent gas velocity continually increases. This constrictor geometry allows the arcjet thruster to be operated at a lower mass flow rate increasing the obtainable specific energy.

Numerical simulation of a hydrogen arcjet

Abstract: The two-dimensional, axisymmetric, nonequilibrium ionizing and reacting flow in a hydrogen arcjet thruster is simulated numerically using the linearized block implicit method. A single ionic species (H), single temperature (i.e., equal electron and heavy particle temperatures), and variable properties are used in this formulation to solve the governing equations of mass, species, momentum, and energy. The current distribution is obtained by solving the magnetic diffusion equation at each time step of the time-marching scheme. As an illustration, a hydrogen arcjet having an exit-to-throat area ratio of 25 (nominal 30-kW geometry) is studied. It is found that the species in order of their abundance at the centerline of the exit plane of the thruster consist of atomic hydrogen (H), ions (H), and electrons (e~), and molecular hydrogen (H2), respectively. As expected, near the colder walls of the anode at the exit plane, this abundance shifts in favor of molecular hydrogen, atomic hydrogen, H, and electrons, respectively.

Mass spectroscopic investigations of a hydrocarbon arcjet plasma operating under diamond deposition conditions

Abstract: We report on mass spectroscopic measurements of species originating near the stagnation point of an arcjet plasma impinging on a tantalum surface. The plasma is produced in a 1‐kW arc through which flows a gas mixture of ∼1% methane in hydrogen. This plasma is near thermal equilibrium, except that a few species such as C2 are slow to equilibrate internally due to the large exothermicity of the reactions that form them. A polycrystalline diamond film grows on the substrate as the measurements are taken. A small gas sampling hole in the deposition substrate samples molecules as they diffuse to the surface. Two stages of differential pumping are used to form a molecular beam which is detected by a quadrupole mass spectrometer. Significant conversion of methane to acetylene (C2H2) and ethylene (C2H4) is observed, as are radicals such as CH3 and C 2H5.

Radiative emission analysis of an expanding hydrogen arc plasma—II. Plume region diagnostics through radial emission

Abstract: A numerical and experimental investigation of the axial emission of 1 and 5 kW radiatively-cooled hydrogen arcjet thrusters is presented. The numerical study consists of an integration of the 1-D radiative transfer equation along the arcjet centerline to predict the axial emission spectral intensity. The complete visible spectrum is modeled, taking into account graybody thermal emission from the cathode and plasma radiation from hydrogen atoms and free electrons. A collisional-radiative model is used to determine the atomic hydrogen line emission. The modeling results suggest the feasibility of determining the cathode temperature and the arc region electron number density from the measured axial emission spectrum. Experimental measurements of the axial emission spectra were performed at several operating conditions. The cathode temperature is found to be in the neighborhood of the tungsten cathode melting point and increases with arcjet power at a constant mass flow rate, suggesting an increase in the current density at the arc attachment point. The measured arc region electron number density is also found to increase with power, confirming an increasing arc current density with arcjet power. Relatively flat radial profiles of electron number density measured in the arc indicate the importance of diffusional transport processes.

Repositioning of geostationary spacecraft - Chemical and electric propulsion options

Abstract: This paper explores the application of electric propulsion to the three major on-board propulsion tasks needed for geosynchronous satellites: north-south stationkeeping, high altitude orbit raising, and station relocation. It is a general survey of practical repositioning in geostationary orbit, making use of on-board electric propulsion and power only. The paper covers two chemical and three electric propulsion options, four levels of longitudinal displ acement, and three spacecraft models across a range of satellite power/mass ratio. In addition, the merit of 'jump-starting' the maneuver with stored power is briefly examined. Chemical propulsion options are hydrazine monopropellant and storable bi-propellant systems. The full range of electric propulsion is explored using the hydrazine arcjet, the SPT-100 gridless ion thruster, and the conventional gridded xenon ion thruster. Velocity increments corresponding to longitude changes of 30, 60, 1200, and 180 deg are considered. Three S/C models are chosen across a range of satellite power/mass ratios. (Author)