Showing papers on "Arcjet rocket published in 1997"

Monte Carlo simulation of nonequilibrium flow in a low-power hydrogen arcjet

Abstract: A particle-based Monte Carlo numerical method is developed for computation of flow in a low-thrust hydrogen arcjet. The method employs the direct simulation Monte Carlo technique to compute the nonequilibrium fluid mechanics and thermochemical relaxation. Simulation of plasma effects is included at a simple level that ensures charge neutrality. A new model is developed to include Ohmic heating in the simulation. Results are presented for a flow condition that has been studied experimentally with a number of different diagnostic techniques. A strong degree of thermal nonequilibrium is found in the flow. It is demonstrated that Ohmic heating is important, and that the Monte Carlo model captures the important physics very well. The predicted results are in very good agreement with most of the experimental data.

Spatial density distributions of c2, c3, and ch radicals by laser-induced fluorescence in a diamond depositing dc-arcjet

Abstract: Quantitative measurements of C2(a3Πu), C3(X,1Π), and CH(X,2Π) have been made by calibrated linear laser-induced fluorescence in the plume of a dc-arcjet (Ar/H2/CH4 1.1:1:0.005) reactor during the chemical vapor deposition of diamond. The peak number density in the arcjet plume for CH is (3.7±0.8)×1012 molecules/cm3, for C2(3a)(3.1±1.3)×1010 cm−3, and for C3∼3×1012 cm−3 with 25 Torr reactor pressure. The radial spatial distributions for C2 and CH have a maximum in the center of the plume; however, C3 is distributed as a hollow cylinder with a pronounced minimum at the center. The variation in number density and in spatial distribution is investigated for changes in chamber pressure, methane flow, and distance from the nozzle.

Performance and Acceleration Process of Quasisteady Magnetoplasmadynamic Arcjets with Applied Magnetic Fields

Abstract: A quasisteady magnetoplasmadynamic (MPD) arcjet with an applied magnetic Ž eld was investigated to improve the thruster performance and understand the complex acceleration mechanisms with both the self-induced and applied magnetic Ž elds. The MPD arcjet was operated with hydrogen, a mixture of nitrogen and hydrogen simulating hydrazine, and argon at discharge currents of 3 – 18 kA in high speciŽ c impulse levels around a critical discharge current predicted from the rules of Alfven’s ionization velocity or minimum input power. The application of axial magnetic Ž elds achieved higher thrust efŽ ciencies than those for only the self-induced magnetic Ž eld at constant speciŽ c impulses, and still achieved stable operations at higher speciŽ c impulses with less electrode erosion. The following guidelines were suggested to achieve higher thruster performance: 1) the axial magnetic Ž eld strength must be smaller than the azimuthal self-Ž eld strength in the main discharge region near the cathode tip, and 2) the applied magnetic Ž eld lines must expand gradually downstream for smooth expansion of plasma. Furthermore, the measured pressures on the electrodes and the current distributions in the discharge chamber showed that the overall thrust measured by a pendulum method increased, in spite of a decrease in the electromagnetic pumping thrust and a small contribution of Hall acceleration. Thus, an additional thrust component because of the axial magnetic Ž eld, such as that caused by swirl acceleration, is expected to exist.

Absolute concentration measurements of CH radicals in a diamond-depositing dc-arcjet reactor.

Abstract: Laser-induced fluorescence in the CH (B–X) and CH (A–X) electronic transitions is used to measure absolute number density versus position for CH radicals in the plume of a 25-Torr hydrogen/argon/methane (0.8:1:0.005) dc arcjet during the chemical vapor deposition of diamond film. The laser-induced-fluorescence signal is calibrated with argon Rayleigh scattering, and the resultant concentration of the CH radical in the center of the arcjet plume is found to be (3.5 ± 0.8) × 1012 molecules/cm3. The characterization of the plasma plume shows three different regions in the reacting gas: nozzle, plume, and boundary layer. We observe substantial differences in spatial distribution of gas temperature, collisional quenching, and CH number density among these regions.

Flexible microwave system to measure the electron number density and quantify the communications impact of electric thruster plasma plumes

Abstract: An advanced microwave interferometric system operating in the Ku (12–18 GHz) band has been implemented for use in very large vacuum chambers to determine the effects of electromagnetic wave propagation through a plasma plume created by a space electric propulsion thruster. This diagnostic tool is used to nonintrusively obtain the local electron number density as well as provide information necessary for understanding impact to communications and other spacecraft electromagnetic systems. The use of a nonintrusive electromagnetic measurement provides highly accurate line integrated density and avoids problems caused by intrusive measurement techniques. If the plasma is symmetrical, local plasma density can also be determined accurately using well known inversion techniques. A network analyzer acts as a transmitter and receiver while a two axis positioning system maps the amplitude and phase variation of a transmitted signal over one plane of the plasma plume. The utilization of a 6 m×9 m vacuum chamber effectively minimizes plasma boundary effects, but the longer cable path lengths have required a frequency conversion circuit to reduce power loss and phase uncertainty at high frequencies. Two studies are presented: the first is a measurement of the local electron density in the plume of a 1 kW arcjet and the second is a measurement of attenuation in the plume of a stationary plasma thruster. Both the arcjet and SPT emit a steady state conical unmagnetized plasma that is radially symmetric. The arcjet peak density is 1015–1016 m−3 along centerline and the SPT peak density is 1016–1017 m−3 along centerline.

CH3 detection in a low-density supersonic arcjet plasma during diamond synthesis

Abstract: We report on the measurement of methyl radical (CH3) densities in a low-density supersonic arcjet plasma used in the synthesis of diamond films. Single-pass, high-sensitivity ultraviolet (UV) absorption spectroscopy has been employed to study the X(2A2″)→B(2A1′) transition of the methyl radical near 216 nm. The minimum detectable CH3 density is found to be ∼4×1013 cm−3, which corresponds to a fractional absorption of 2×10−3 at a gas temperature of 1200 K. The dependence of the measured methyl column density on pressure and CH4/H2 flow ratio has been studied. The results are used to revise our previous estimates of the reactive “sticking” coefficient for CH3, and we now find that it is of order 10−2 under conditions where we have previously documented the growth of high quality diamond films.

Optical diagnostics for temperature measurement in a DC arcjet reactor used for diamond deposition

Abstract: a-state in this plume. LIF measurements of CH are complicated by the presence of C3 and we discuss strategies to deal with this interference. The gas temperature describing the rotational distributions obtained for NO, C2 and CH agree within experimental error. Optical emission measurements indicate that the rotational and vibrational distributions of the excited A-state of CH and a-state of C2 are characterized by vibrational and rotational populations which are at least 1000 K above the ground state distributions. The excited states are collisionally quenched before their population distributions equilibrate with the gas temperature. We also determine relative populations of the ground and excited states along the axis of the plume between the arcjet nozzle and the substrate and relative populations for a cross section of the jet, midway between the nozzle orifice and the substrate. The measured relative ground and excited state populations for both CH and C2 show different trends along the plume axis, indicating that the ground and excited states of these molecules are products of different chemical mechanisms; such mechanisms are discussed.

Optimal earth-moon trajectories using combined chemical-electric propulsion

Abstract: Minimum-fuel, three-dimensional Earth ‐moon trajectoriesareobtainedforspacecraftusing bothchemicaland electricpropulsion stages. The problem involvesmaximizing thee nal spacecraft mass delivered to a circular, polar midlunarorbit. Themissiondee nition involvesa chemical-stageboostfrom low-Earthorbitinto acoasting ballistic trajectory followed by a lunar capture trajectory performed by the electric propulsion stage. For this analysis, the ballistic orbit transfer and the powered orbit transfer to a circular orbit within the lunar sphere of ine uence are modeled by the dynamics of the classical restricted three-body problem, and two body-centered coordinate frames are utilized. The subsequent descending three-dimensional spiral trajectory to circular polar midlunar orbit is computed via Edelbaum’ s analytic equations in order to eliminate the need to numerically simulate the numerous near-circular lunar orbits. Two classes of current-term electric propulsion thrusters are utilized (arcjet and plasma thrusters ) along with current-term launch vehicle cone gurations. Numerical results are presented, and the optimal chemical ‐electric propulsion transfers exhibit a substantial reduction in trip time compared to Earth‐moon transfers using electric propulsion alone.

Optimization of arc constrictor sizes in low power arcjet thrusters

Abstract: It is known that the performance of a low power arcjet is influenced by the geometry of the constrictor. The merging of the arc with the propellant gas in the constrictor is a complex process involving electrical and non-equilibrium chemical phenomena with high energy transport rate to the wall. An experimental investigation was performed to investigate the effect of the constrictor geometry on the characteristics of arc discharges and the heat transport rate to the wall, using quartz glass constrictors with different geometries. Following results were obtained. 1) The discharge voltage of the arc increases with the constrictor length (/con) almost linearly, though no distinct effect of the constrictor diameter (cfcon) is observed on it. 2) The thermal efficiency, defined as the ratio of the power of gas ejected from the constrictor (Peject) to the input electrical power (Pin), increases with increasing gas pressure (Peon) and with decreasing /con generally, while with decreasing rfcon the efficiency takes a maximum value at a middle length of dcon. 3) The diameter of arc column decreases with increasing Peon, with increasing /con, and with decreasing rfcon by the thermal pinch effect. 4) The main feature of the variation of constrictor gas temperature with /con and fifcon coincides with that of ejected power and thermal efficiency. It is suggested that the existence of the maximum in the thermal efficiency for the change of cfcon, at a fixed Peon and a fixed mass flow rate of propellant, is due to the coexistence of two type processes, one suppresses heat transport to the constrictor wall and another promotes it.

Measured specific intensity from 130 to 900 nm at the stagnation point of a model in an arcjet flow of 7.8 km/sec

Abstract: The absolute specific intensity (W/cm2-μ-sr) spectrum (also known as the radiative heating rate spectrum), incident on the stagnation point of a blunt model placed in an arcjet wind tunnel, is presented. The test model was a flat disk, 15 cm in diameter, which produced an effective nose radius of about 60 cm. The test conditions in the arcjet arc column were 80% air, 20% argon, 1.02 atm pressure, 950 A, and 1800 V. The flow conditions in the test section were 0.51 atm and 7.8 km/sec, which correspond to flight in the Earth's atmosphere at about 76 km altitude. The total spectrum was recorded and calibrated from 110 to 900 nm. The intensity calibration is considered to be accurate to within about a factor of 2 from 130 to 900 nm. The tests were made in a separate experimental setup. The measured radiative heating rate in the vacuum-ultraviolet, from 130 to 200 nm, is about 10% of the total heating rate from 130 to 900 nm. This result is in qualitative agreement with an estimate of 25% for a larger vehicle (nose radius of 259 cm) flying in the Earth's atmosphere at 77.1 km altitude and 9.5 km/sec. These data show that the radiation and its spectral content, incident on a blunt model in an arcjet, are similar to those expected for flight in the Earth's atmosphere at similar conditions, except for much stronger NO radiation from 200 to 300 nm. The source of this strong NO radiation appears to be in the freestream ahead of the bowshock wave. The physical and chemical conditions in the freestream of an arcjet are far more complex than those in actual flight, due to the excitation and expansion processes. However, the results presented show that arcjet tests can be used to simulate the radiation environment during atmospheric entry, and can provide the data needed to advance the ability to calculate realistic radiative heating rates under non-equilibrium flight condition.

Extensive Validation of a Monte Carlo Model for Hydrogen Arcjet Flowfields

Abstract: A particle-based Monte Carlo numerical method is applied for the e rst time to model the nozzle and plume e ows of a low-thrust hydrogen arcjet. Starting from a continuum solution of the e ow just downstream of the constrictor, the present analysis employs the direct simulation Monte Carlo technique to compute the nonequilibrium e uid mechanics and thermochemical relaxation. Simulation of plasma e eld effects is included at a simple level using charge neutrality. A model is implemented to include ohmic heating in the simulation. Results are presented for two different arcjet e ow conditions. Comparisons of Monte Carlo results with experimental measurements for a variety of e owe eld properties are made in the nozzle interior, the nozzle exit plane, and the near-e eld plume e ow. Comparison of prediction with measurement is also made for thruster performance. For almost all e ow properties, good agreement is obtained between simulation and measurement. This indicates that the Monte Carlo model is a viable approach for optimization of arcjet performance, and for the prediction of spacecraft interaction effects.

Numerical Analysis of a Two-Dimensional Magnetoplasmadynamic Arcjet

Abstract: The effect of electrode cone guration on thrust characteristics of a two-dimensional magnetoplasmadynamic (MPD) arcjet was numerically investigated. A simple magnetohydrodynamics (MHD) model was developed and the numerical results were compared with the experimental data for several electrode geometries. To understand the features of the e owe eld, we introduced a magnetosonic Mach number, which is dee ned as local velocity divided by a propagation speed of the MHD disturbance. Based on the magnetosonic Mach number distribution of the e owe eld, the model can explain the thrust characteristics of the MPD arcjet, especially the superiority of a short cathode under various anode cone gurations. Because the electromagnetic thrust is unaltered for the same anode cone guration, the electrothermal component of thrust makes a difference between the long and the short cathodes. With a short cathode cone guration, the large heat deposition near the cathode tip, which is inevitable to MPD arcjets, can be cone ned in the submagnetosonic region where the local e ow is accelerated to magnetosonic velocity. Then the thermal deposition into the submagnetosonic region can be efe ciently recovered through transmagnetosonic acceleration, resulting in a large thrust generation.

Velocity and Temperature Measurements in a Low-Power Hydrazine Arcjet

Abstract: Recent advances have been made in low-power (1 – 2 kW) arcjet performance with the aid of numerical, nonequilibrium plasma  ow models. Consequently, validation of these models through experimentation has become increasingly important. We discuss diagnostic probe techniques for measuring the exit plane  ow of a 1 kW class hydrazine thruster. A spatially resolved time-of- ight electrostatic probe method is described for measurements of radial proŽ les of the plasma axial velocity ui. These measurements are combined with previous quadruple probe measurements of Te and the ion speed ratio ui/cm to estimate the ion temperature Ti, resulting in Ti/Te ’ Tg/Te ; 0.4 at the thruster exit. The exit plane data for ui and Ti are compared with computational arcjet model predictions and previous experimental results, showing substantial agreement.

Optimal Control of Quasi-One-Dimensional Self-Field Magnetoplasmadynamic Arcjet Flowfields

Abstract: The e owe eld of a self-e eld magnetoplasmadynamic (MPD) arcjet was analyzed to establish the optimum geometry that produces the highest possible thrust for specie ed operating conditions. A set of simplie ed assumptions, within a quasi-one-dimensional framework, was used to establish how the optimum e owe eld was coupled to the thruster geometry. The resultant distribution of discharge current was smooth without any prominent concentration along the electrodes. The approach employed a purely mathematical method of engineering optimal control to suggest design guidelines for MPD arcjet thrusters within the idealized constraints. The optimum was found to be a slowly convergent and quickly divergent geometry that maximized the exit velocity for a e xed electrical input power.

Atomic hydrogen concentration in a diamond depositing dc arcjet determined by calorimetry

Abstract: The fraction of hydrogen dissociated in the plume of a dc arcjet used for diamond deposition is determined by calorimetry to be 0.33±0.12. A dc arc is struck in a mixture of argon and hydrogen at 90 psi and the effluent is expanded through a converging/diverging nozzle into a reactor maintained at 25 Torr. Methane (<1%) is added to the luminous gas plume in the diverging nozzle. This supersonic jet impinges on a water cooled molybdenum substrate, and diamond thin film grows from the reactive mixture. The electrical power input of the arcjet (1.6 kW) is balanced by the power losses due to cooling of the nozzle, enthalpy change in the gas, ionization of the gas, dissociation of H2, and the directed velocity of the gas phase. The gas temperature is determined by linear laser-induced fluorescence (LIF) measurements of several rotational lines of NO seeded to the gas plume. The velocity of the gas plume is obtained via the Doppler shift between LIF signals measured simultaneously in a stationary reference cell...

Characterization of Plenum Spectra in an Arcjet Wind Tunnel

Abstract: An optical fiber is used to collect radiation from the plenum of an arcjet wind tunnel. Studying the spectra, the electronic excitation temperatures are determined from the Boltzmann plots of atomic oxygen and nitrogen emission lines. In the case of atomic oxygen, the temperature is found to be about 15,000 ± 3400 K, and that of nitrogen is found to be 7600 ± 1500 K. Determination of molecular vibrational-rotational temperature is made by comparing experimental and theoretical spectra of the N 2 + molecular radiation. The temperature is estimated to be 9700 ± 1200 K, using an integrals ratio method.

Observation and spatial distribution of C3 in a DC arcjet plasma during diamond deposition using laser-induced fluorescence

Abstract: radical in the plume of an arcjet plasma during diamond film chemical vapor deposition. C3, identified using laser-induced fluorescence, is distributed in a shell surrounding the diamond-depositing core of the arcjet plasma plume.

Electron densities and temperatures in a diamond-depositing direct-current arcjet plasma

Abstract: Langmuir probe measurements of electron density and temperature are made in the plume of a dc arcjet reactor. A dc arc is struck in an argon or argon/hydrogen mixture at 6 atm pressure and expands through a converging/diverging nozzle into the reactor with a pressure of 25 Torr. Methane and methane/nitric oxide are added in the diverging nozzle, and diamond film grows on a substrate in the gas plume. Electron temperatures of 1–2 eV are significantly hotter than the neutral gas temperature in the plume. Electron densities range from 1010 to 1013 cm−3, well above the Saha equilibrium for the gas temperature and pressure and well below the equilibrium for the electron temperature.

Arcjet anode plasma measurements using electrostatic probes

Abstract: A 1-kW hydrazine arcjet thruster has been modie ed for internal probing of the anode sheath boundary layer with an array of 14 electrostatic microprobes e ush mounted into the anode body. Axial and azimuthal distributions of the plasma properties e oating potential, anode sheath potential, wall current density, electron number density, and electron temperature have been obtained for arc currents between 7.8 and 10.6 A and propellant e ow rates of 40 ‐60 mg/s. The specie c power ranged from 18.8 to 27.4 MJ/ kg. Azimuthal symmetry has been verie ed for all arcjet operating conditions. The electron temperature data show that the near-anode plasma is highly nonequilibrium. Most of the current density and anode heating is located within 2 ‐4 mm of the constrictor exit, with the location affected more by mass e ow rate than by arc current. The axial anode heating distribution is closely coupled to current density and accounts for ;18‐24% of the total input power. Reasonable agreement between a numerical model and experimental results is found for a constant value of the electron inelastic energy-loss factor.

Space Propulsion Applications of Helium Arcjets

Abstract: : With currently available space electric power systems, the optimum specific impulse for electrically propelled satellite transfers from low Earth orbit to geosynchronous Earth orbit appears to be in the 1000 to 1200 second range. Arcjets operating with helium as a propellant may be the most efficient electric thruster capable of operating in this specific impulse range. This work reports on a recent set of experiments which examined the effects of arcjet configuration, and propellant composition and flow rates, on arcjet performance. In these tests, it was found that increasing the cathode-anode gap over that normally used with hydrogen or ammonia propellants increased arc stability and significantly improved specific impulse and electrical efficiency. Hydrogen seeding was found to improve arc stability, particularly at smaller cathode gaps, but it had a very small effect on overall performance of the arcjet. The primary variable which affected arcjet performance was found to be propellant flow rate. The efficiency of the helium arcjet was found to increase with increasing propellant flow rate up to the maximum flows available for the current set of experiments.

Decomposition of dichloroethane in a plasma arcjet reactor: experiment and modeling

Abstract: A plasma arcjet reactor has been constructed to study the fundamental reaction kinetics for decomposition of hazardous liquids. The temperature profile of the plasma jet was measured using an enthalpy probe, and the profile was used to model the arcjet as a nonisothermal tubular flow reactor. A surrogate liquid waste-1,2 dichloroethane-was injected into the plasma reactor, and the decomposition byproducts were monitored using a residual gas analyzer. The experimental results were compared to the predicted byproducts from the tubular reactor model and indicated that a photochemical dissociation process accounted for some of the decomposition of dichloroethane. This research also provided a more comprehensive understanding of the critical parameters associated with thermal plasma chemistry and the destruction of liquid waste.

System and Mission Optimization of Geostationary Tele- communication Satellites using Arcjet Propulsion Systems

Abstract: The objective of this paper is to investigate the economic and technical potential of electric arcjet propulsion systems for their application on telecommunication satellites. The demonstration are done for the most typical spacecraft mission: the mission of a commercial geostationary telecommunication satellite launched with an Ariane IV into geostationary transfer orbit. The task is formulated numerically as a combined trajectory- and system optimization problem comprising three mission phases: the launcher ascent and separation, the low thrust transfer mission segment as well as the operational phase in GEO after transfer mission completion. Spacecraft's subsystems are modelled concerning recurring cost, mass, performance and power consumption. Special emphasis is put on accurate quantitative assessment of radiation impact on solar arrays and electric equipment due to multiple crossing of the VanAlien belts. This is done by modelling proton and electron particle flux as functions of orbital position and time. The design and mission results are compared with those of corresponding conventionally (chemically) propelled satellite systems. Hereby, it can be concluded that the arcjet propulsion system offers a reduction in propellant consumption of about 30 % leading to an increase in payload transponders (Ku-Band) from 20 to more than 31. Taking into account overall mission cost this leads to an increase in return of invest by 18 % with respect to the baseline mission. Therefore, the arcjet propulsion system appears to be a very attractive option to increase the economic benefit of satellite missions.

Benefits of Low-Power Electrothermal Propulsion

Abstract: Mission analyses were completed to show the benefits of low-power electrothermal propulsion systems for three classes'of LEO smallsat missions. Three different electrothermal systems were considered: (1) a 40 W ammonia resistojet system, (2) a 600 W hydrazine arcjet system, and (3) a 300 W ammonia resistojet. The benefits of using two 40 W ammonia resistojet systems were analyzed for three months of drag makeup of a Shuttle-launched 100 kg spacecraft in a 297 km orbit. The two 46 W resistojets decreased the propulsion system wet mass by 50% when compared to state-of-art hydrazine monopropellant thrusters. The 600 W arcjet system was used for a 300 km sun synchronous makeup mission of a 1000 kg satellite and was found to decrease the wet propulsion mass by 30%. Finally, the 300 W arcjet system was used on a 200 kg Earth-orbiting spacecraft for both orbit transfer from 300 to 400 km, two years of drag makeup, and a final orbit rise to 700 km. The arcjet system was determined to halve the propulsion system wet mass required for that scenario as compared to hydrazine monopropellant thrusters.

Decomposition of dichloroethane in a plasma arcjet reactor: experiment and modeling

Abstract: Summary form only given. A plasma arcjet reactor has been constructed to study the fundamental reaction kinetics for decomposition of hazardous liquids. The arcjet was operated at a power level of 1.5 kW and an argon flow rate of 17.5 LPM. The temperature profile of the plasma jet was measured using an enthalpy probe and the maximum temperature measured in the plasma jet was 1850/spl deg/C. A surrogate liquid waste, 1,2 dichloroethane, was injected into the plasma jet and the decomposition byproducts were monitored using a residual gas analyzer. A removal efficiency greater than 99% was obtained. The temperature profile was used to model the arcjet as a non-isothermal tubular now reactor.

Studies of nonequilibrium hydrogen/nitrogen plasmas using a cascade arc

Abstract: A cascade arc facility has been constructed at UTSI to study the effect of nonequilibrium transport properties in hydrogen-nitrogen arcjet propellant plasmas. These studies will be used to guide development of the physical models required for further development of arcjet computational codes. The cascade arc has been operated on hydrogen at 50 Amps and at pressures of 13.8 kPa (2.0 psi) and 41.3 kPa (6.0 psi). Preliminary spatially resolved spectral data at these conditions have been collected for the Balmer Hα line. Theoretical, Stark broadened, Hα lineshapes have been fitted to the experimental lineshapes to determine the radial distributions of electron number density. These number densities were compared to values taken from the nonequilibrium and equilibrium cascade arc simulations. The simulations underpredict the peak experimental number densities; however, the profile of the nonequilibrium solution matches the experiment.