Showing papers on "Arcjet rocket published in 1995"

Validation of Multitemperature Nozzle Flow Code

Abstract: A computer code nozzle in n-temperatures (NOZNT), which calculates one-dimensional flows of partially dissociated and ionized air in an expanding nozzle, is tested against three existing sets of experimental data taken in arcjet wind tunnels. The code accounts for the differences among various temperatures, i.e., translational-rotational temperature, vibrational temperatures of individual molecular species, and electron-electronic temperature, and the effects of impurities. The experimental data considered are (1) the spectroscopic emission data; (2) electron beam data on vibrational temperature; and (3) mass-spectrometric species concentration data. It is shown that the impurities are inconsequential for the arcjet flows, and the NOZNT code is validated by numerically reproducing the experimental data.

Characterization of arcjet flows using laser-induced fluorescence

Abstract: A sensor based on laser-induced fluorescence has been installed at the 20-MW NASA Ames Aerodynamic Heating Facility. The sensor has provided new, quantitative, real-time information about properties of the arcjet flow in the highly dissociated, partially ionized, nonequilibrium regime. Number densities of atomic oxygen, flow velocities, heavy particle translational temperatures, and collisional quenching rates have been measured. These results have been used to test and refine computational models of the arcjet flow. The calculated number densities, translational temperatures, and flow velocities are in moderately good agreement with experiment

A simplified analytical model of diamond growth in direct current arcjet reactors

Abstract: A simplified model of a direct current arcjet-assisted diamond chemical vapor deposition reactor is presented. The model is based upon detailed theoretical analysis of the transport and chemical processes occurring during diamond deposition, and is formulated to yield closed-form solutions for diamond growth rate, defect density, and heat flux to the substrate. In a direct current arcjet reactor there is a natural division of the physical system into four characteristic domains: plasma torch, free stream, boundary layer, and surface, leading to the development of simplified thermodynamic, transport, and chemical kinetic models for each of the four regions. The models for these four regions are linked to form a single unified model. For a relatively wide range of reactor operating conditions, this simplified model yields results that are in good quantitative agreement with stagnation flow models containing detailed multicomponent transport and chemical kinetics. However, in contrast to the detailed reactor models, the model presented here executes in near real-time on a computer of modest size, and can therefore be readily incorporated into process control models or global dynamic loop simulations.

Nonintrusive electron number density measurements in the plume of a 1 kW arcjet using a modern microwave interferometer

Abstract: Reported is the use of a microwave interferometric technique for making nonintrusive measurements of plasma electron number density in the plume of a space electric propulsion thruster. The technique is capable of providing good sensitivity and accuracy as well as resolution using modern microwave network analyzer technology. Density profiles were obtained throughout the plume of a 1 kW hydrogen arcjet based on accurate microwave differential phase measurements. Spatially resolved integrated phase shifts for a 17.5 GHz signal radiated through the plume at various radial positions were Abel inverted to calculate radial electron density profiles. All measurements were taken in the University of Michigan's Large Chamber Plasma Facility, a 6 m by 9 m vacuum chamber, at pressures of 2/spl middot/10/sup -4/ Torr or less. The interferometer measured electron densities as low as 1/spl middot/10/sup 15/ m/sup -3/ with a predicted capability to measure peak densities as high as 3/spl middot/10/sup 18/ m/sup -3/. The accuracy of this technique is estimated to be on the order of /spl plusmn/10%. Comparison with Langmuir probe electron number density measurements demonstrate relative agreement between the two methods. Further, a previously reported tendency for the Langmuir probe to underpredict electron number density was consistent with our measurements. It is postulated that this underprediction may be due to small Langmuir probe perturbations in the local plasma of the far-field plume and errors in estimation of the probe collection area. >

Integrated arcjet having a heat exchanger and supersonic energy recovery chamber

Abstract: A gas ionizable to produce a plasma is introduced into an arcjet whose design includes integration of performance enhancing components in a complimentary manner to significantly improve arcjet performance and capabilities. Major integrated design features include an energy recovery chamber, heat exchanger and by-pass gas flow system which enable the integrated arcjet to operate with minimal frozen flow energy losses, high specific powers and very high thrust levels.

Plasma diagnostics of a direct‐current arcjet diamond reactor. II. Optical emission spectroscopy

Abstract: Diagnostic analyses were performed on a dc arcjet diamond reactor using optical emission spectroscopy. Rotational and vibrational excitation temperatures were determined from C2 and CH emission spectra and observed to differ widely at all locations in the plasma except near the substrate. Temperatures were observed to converge at the substrate, indicating thermal equilibration of the plasma. Rotational excitation temperatures for C2 and vibrational excitation temperatures for CH appear to closely track the plasma gas temperature, while vibrational excitation temperatures for C2 and rotational excitation temperatures for CH are anomalously high. A detailed analysis was conducted to identify the dominant excitation processes responsible for producing emission. Results show that (1) excitation to the excited state for both C2 and CH is most likely due to thermal excitation near the substrate, (2) in the plasma bulk, emission by CH is produced primarily by chemiluminescent reactions while emission by C2 is pr...

Effects of Applied Magnetic Fields on Performance of a Quasisteady Magnetoplasmadynamic Arcjet

Abstract: A quasisteady magnetoplasmadynamic arcjet with applied magnetic fields was studied to clarify the influence of axial magnetic fields on the thruster performance and the discharge feature. Pulsed axial magnetic fields were applied by a few-turn coil, which was connected with a pulse-forming network independent of the main discharge circuit. An increase in axial-field intensity raised the discharge voltages at constant discharge currents below the limiting current with H2, the mixture of N 2 + 2H 2 simulating fully decomposed hydrazine, and Ar. The thrust characteristics for H2 and the mixture of N 2 + 2H 2 showed that there was the optimum axial-field intensity with which the maximum thrust was achieved for each gas, although at low discharge current levels for H, and Ar the thrusts increased with axial-field intensity. The discharges for all gases were inclined to occur more upstream with an increase in axial-field intensity. It was inferred that these effects of axial magnetic fields on the thruster performance and the arc feature were due to the rotating motion of — Jr x Bz, i.e., swirl acceleration and enhanced thermalization.

Laser induced fluorescence of ground state hydrogen atoms at nozzle exit of an arcjet thruster

Abstract: : We report the first observation of a two-photon laser-induced fluorescence (LIF) technique in an arcjet plume. Ground state hydrogen atoms are detected with high spatial resolution near the thruster nozzle exit. Number density, axial and radial velocity, and translational temperature distributions are obtained in the expansion plume of a 1 kW arcjet operating on hydrogen propellant. Comparison of the ground state properties with previously measured excited state hydrogen data and recent computational data is discussed.

Electric Propulsion Space Experiment (ESEX) flight qualification and operations

Abstract: : The Electric Propulsion Space Experiment (ESEX) is one of eight experiments being launched in early 1997 on the Advanced Research and Global Observation Satellite (ARGOS). ESEX has successfully completed flight qualification and is awaiting integration. ESEX will be the first flight of a high power arcjet propulsion subsystem. The arcjet experiment will nominally fire 10 times for a total of 150 minutes. The flight data will include measurements of both performance and spacecraft integration issues, as well as ground and space observations of the arcjet plume.

Method for re-orbiting a dual-mode propulsion geostationary spacecraft

Abstract: At the end of the operative life of the spacecraft, when all the propellant has been consumed for the normal attitude and orbit control operations, the arcjet thrusters are connected to a feed line for being fed with the helium still remaining in the pressurant tank and the arcjet thrusters are then fired to perform the complete re-orbiting maneuver until the spacecraft is placed in a graveyard orbit.

Increased deposition rate of chemically vapor deposited diamond in a direct‐current arcjet with a secondary discharge

Abstract: A secondary discharge was used to enhance chemical nonequilibrium in the boundary layer of a stagnation point flow reactor during the atmospheric pressure deposition of chemically vapor deposited (CVD) diamond with a direct‐current (dc) arcjet. The secondary discharge was induced by means of a positive potential on the deposition surface to drive a current through the boundary layer and produce energetic electrons. These electrons can promote superequilibrium concentrations of radicals at the growth surface. It was found that with 3.5 A/cm2 at 115 V in the secondary discharge, the growth rate of diamond in this reactor increased by a factor of 6 as compared with the floating or grounded substrate case.

Relationship between diamond growth rate and hydrocarbon injector location in direct-current arcjet reactors

Abstract: A series of detailed calculations have been carried out using a stagnation flow model to examine the dependence of diamond growth rate on hydrocarbon injector location in dc arcjet reactors. It is predicted that, for methane feed, growth rate can be increased by as much as 75% by relocating the injector from a position near the plasma torch exit to one near the diamond surface, but outside the boundary layer. As the injector is moved towards the surface from the plasma torch, the concentrations of C and CH3 present at the surface increase. When the injector is located within the boundary layer, the lower atomic hydrogen concentration and short residence time leave most of the injected CH4 unreacted, causing growth rates to drop.

Performance of a Miniaturized Arcjet

Abstract: Performance measurements were obtained and life-limiting mechanisms were identified on a laboratory-model arcjet thruster designed to operate at a nominal power level of 300 W. The design employed a supersonic-arc-attachment concept and was operated from 200 to 400 W on hydrogen/nitrogen mixtures in ratios simulating fully decomposed hydrazine and ammonia. Power was provided by breadboard power processor. Performance was found to be a strong function of propellant flow rate. Anode losses were essentially constant for the range of mass flow rates tested. It is believed that the performance is dominated by viscous effects. Significantly improved performance was noted with simulated ammonia operation. At 300 W the specific impulse on simulated ammonia was 410 s with an efficiency of 0.34, while simulated hydrazine provided 370 s specific impulse at an efficiency of 0.27.

Low Power Arcjet Performance Evaluation

Abstract: : The use of electric propulsion for stationkeeping and orbit repositioning missions offers significant' advantages to Air Force users. Commercial interest in electric propulsion has largely focused on geostationary north-south stationkeeping of high power communication satellites. and has resulted in the development and flight qualification of several thruster types operating in the 1500-2000 W power range. Since the power available for propulsion on many current and future Air Force satellites is substantially less. the development of high performance, low power thrusters is important to the support of Air Force missions. To support this development effort, the Air Force Phillips Laboratory has begun a low power arcjet research project to quantify and improve thruster performance. The objective of this effort is the improvement o thruster performance over the powe rrange of 300-600 W using storable propellants. In this first phase, thrust, specific impulse. thrust efficiency and arcjet anode temperature were measured over the power range of 900-1200 W. A 1 kW modular arcjet operating on simulated hydrazine N2-2H2, propellant with regular and extended length anodes was used for testing; the extended length. anode provided a larger surface for temperature measurements. Thrust stand measurements were used to obtain arcjet performance data and two-color optical pyrometry and thermocouple systems were used to measure anode temperature. Performance measurements were taken with both nozzles while temperature measurements were made with the extended anode alone. Measurement errors were quantified at 5% for thrust and 6-8% for temperature. Methods of reducing these errors to 2% for both cases are discussed.

Parallel arcjet starter system

Abstract: There is disclosed an arcjet starter for igniting and sustaining an electric arc in an arcjet thruster. The arcjet starter is capable of delivering a short duration, high voltage pulse for igniting the arc and then providing a continuous low voltage, high amperage current for sustaining the arc. The starter has two separate magnetics, one for initiating breakdown in the arcjet and another for sustaining breakdown during steady state operation.

Experimental investigation of velocity slip near an arcjet exit plane

Abstract: A simple approach, for the purpose of evaluating slip in a hydrogen-fueled arcjet, is to seed the flow with a species that is accessible with the same laser used to probe atomic hydrogen.In the present study,helium was chosen as the seed species owing to its inertness,its relative mass and its convenient electronic transitions in the visible wavelength region.Velocity and temperature are measured by LIF of both helium and atomic hydrogen .Absence of slip between helium and atomic hydrogen would suggest that slip is not a dominant mechanism in the nozzle or exit plane vicinity of our hydrogen arcjet.

Laser Induced Fluorescence of Ground State Hydrogen Atoms in an Arcjet Plume

Abstract: : We report two photon laser induced fluorescence measurements near the nozzle exit and in the plume of a 1 kW arcjet thruster. Atomic hydrogen number densities, axial and radial velocities, and translational temperatures are measured in the expansion plume of a 1 kW arcjet operating on hydrogen propellant. Data from recent computational models are compared with the atomic hydrogen density measurements.

Low power electric propulsion for minor body applications

Abstract: The authors present the results of a specific application of low power solar electric arcjets (400-700 Watts) for minor body (asteroid and extinct comet) rendezvous and departure. Low power arcjets offer advantages for such operations; among them are higher I,, relative to conventional chemical propulsion and a concomitant propellant savings at minimal impact to spacecraft power requirements. They can simplify propellant feed systems because they use many existing components and may eliminate oxidizer propellants. Also, because these propulsion systems are inherently low thrust, they offer flexibility in launch and arrival dates as well as stay time relative to high thrust (nearly impulsive) propulsion. Following a description of the numerical procedure used to perform the trajectory and system analysis, results comparing state of the an bi-propellant and low power arcjet propulsion options are presented. The results are used both to identify system level requirements and to establish propulsion technology needs not met by available arcjet propulsion systems. Conceptual designs for these systems are presented for these systems and conclusions based upon this investigation are given.