Showing papers on "Arcjet rocket published in 1990"

Plasma properties of a hydrocarbon arcjet used in the plasma deposition of diamond thin films

Abstract: Plasma‐deposited thin films of polycrystalline diamond were achieved with an arcjet plasma. The jet operated with hydrogen gas with small admixtures of CH4. The diamond films were highly nonuniform, probably due to the very high gradients of the chemical species and temperatures within the arcjet‐substrate system. The arcjet apparatus, and optical emission spectra and Langmuir probe diagnostics of the plasma are described. Also presented are results for the surface chemical analysis of the diamond film using surface analysis by laser ionization.

Preliminary plume characteristics of an arcjet thruster

Abstract: An experimental investigation of a low power arcjet plume was conducted using emission spectroscopy. A laboratory model arcjet incorporating a segmented anode was run on simulated hydrazine at a flow rate of 5 x 10(exp -5) kg/s. The complete visible spectrum measured in the exit plane of the arcjet showed the presence of N2, N2(+), NH, and H. Radial intensity profiles for the H alpha, H sub beta, and the NH A(sup 3)Pi yields X(sup 3)Sigma(0,0) transitions at four different axial locations were measured. These line of sight intensity measurements, spaced 0.05 mm apart, were deconvoluted to give the radial intensity distribution using an inverse Abel transformation. The ratio between the intensities from the H sub alpha and H sub beta transitions indicated a non-Boltzmann energy distribution between excited states in the plume. Axial intensity profiles taken on center line indicated the decay rate of excited states in the plume. An electron number density of 2 x 10(exp 13)/cu cm at the exit plane was determined based on Stark broadening of the H sub beta line. Rotational temperatures of 750 K, 1750 K, and 2500 K were determined for N2, N2(+), and NH respectively. The results demonstrate that the location of the current attachment on the anode has a measurable effect on the electronically excited species in the plume and that dissociation is the dominant frozen flow loss mechanism in low power arcjets.

Numerical modeling of an arcjet thruster

Abstract: A numerical model of an arcjet thruster was developed and the results of calculations using this model are compared to the experimental data from a 30 kW arcjet using ammonia as a propellant. The model contains equations for the conservation of mass, radial, axial, and azimuthal momentum, energy, and the radial component of the magnetic field and provides a solution for three components of velocity, temperature, and the axial and radial current as a function of position in an axisymmetric flowfield. The model predicts 12 percent more specific impulse than the experiment when the mass flow and power input are constrained to the experimental values. A major conclusion of this study is that improved procedures for calculating transport properties are necessary if the accuracy of the model is to be improved.

Performance characterization of a segmented anode arcjet thruster

Abstract: A modular, 1 to 2 kW class arcjet thruster incorporating a segmented anode/nozzle was operated on a thrust stand to obtain performance characteristics of the device and further study its operating characteristics under a number of experimental conditions. The nozzle was composed of five axial conducting segments isolated from one another by boron nitride spacers. The electrical configuration allowed the current delivered to the arcjet to be collected at any combination of segments. Both the current collected by each segment, and the potential difference between the cathode and each segment were monitored throughout the test period. As in previous tests a similar device, current appeared to attach diffusely in the anode when all of the segments were allowed to conduct. Improvements to the device allowed long term (4 to 8 hour) operation at steady-state and operating characteristics were repeatable over extended periods. Performance characteristics indicated that the segmented anode reasonably simulates the behavior of solid anodes of similar geometry. Current distribution depended on flow rate as the arc attachment moved downstream in the nozzle with increases in the mass flow rate. The current level had little effect on current distribution on the anode segments. Thrust measurements indicated that the current distribution in the nozzle did not significantly affect performance of the device.

Medium power arcjet thruster experiments

Abstract: Experimental results on the electrothermal behavior and operating performance of water-cooled laboratory model arcjet thrusters using a variety of propellants in the range of 5-50 kW are reported. The highest voltage and specific impulse are attained with hydrogen propellant and the lowest with argon propellant; intermediate results are obtained with nitrogen and a mixture of hydrogen and nitrogen. The highest cathode erosion rate is measured with argon while the lowest is associated with hydrogen.

Investigation of the arcjet plume near field using electrostatic probes

Abstract: The near field plum of a 1 kW class arcjet thruster was investigated using electrostatic probes of various geometries. The electron number densities and temperatures were determined in a simulated hydrazine plume at axial distances between 3 cm (1.2 in) and 15 cm (5.9 in) and radial distances extending to 10 cm (3.9 in) off centerline. Values of electron number densities obtained using cylindrical and spherical probes of different geometries agreed very well. The electron density on centerline followed a source flow approximation for axial distances as near as 3 cm (1.2 in) from the nozzle exit plane. The model agreed well with previously obtained data in the far field. The effects of propellant mass flow rate and input power level were also studied. Cylindrical probes were used to obtain ion streamlines by changing the probe orientation with respect to the flow. The effects of electrical configuration on the plasma characteristics of the plume were also investigated by using a segmented anode/nozzle thruster. The results showed that the electrical configuration in the nozzle affected the distribution of electrons in the plume.

Low Power Arcjet Performance

Abstract: An experimental investigation was performed to evaluate arc jet operation at low power. A standard, 1 kW, constricted arc jet was run using nozzles with three different constrictor diameters. Each nozzle was run over a range of current and mass flow rates to explore stability and performance in the low power engine. A standard pulse-width modulated power processor was modified to accommodate the high operating voltages required under certain conditions. Stable, reliable operation at power levels below 0.5 kW was obtained at efficiencies between 30 and 40 percent. The operating range was found to be somewhat dependent on constrictor geometry at low mass flow rates. Quasi-periodic voltage fluctuations were observed at the low power end of the operating envelope, The nozzle insert geometry was found to have little effect on the performance of the device. The observed performance levels show that specific impulse levels above 350 seconds can be obtained at the 0.5 kW power level.

Arcjet nozzle having improved electrical-to-thrust conversion efficiency and high voltage operation

Abstract: An arcjet thruster is disclosed which has an electrically conductive anode body having an anode cavity therein which defines a nozzle symmetrical about a central axis. The anode cavity has a tandemly arranged divergent recombination portion and a divergent expansion portion. The expansion portion has a greater rate of divergence than the recombination portion. The anode body further preferably comprises a cylindrical constrictor portion upstream and in tandem with the recombination portion. An electrically conductive cylindrical cathode body is coaxially arranged and spaced from the anode body by a gap. An electrical current source connected to the cathode and the anode produces an electrical arc across the gap. A vortex flow of propellant gas is fed through the gap and through the nozzle to produce thrust. The vortex flow of propellant gas pushes the arc through the constrictor into one of the divergent portions of the nozzle. The recombination and expansion portions merge at a transition being between a divergence of 5 and 15 degrees and within a diameter ratio range of the transition to the constrictor of about 1.5 to 4.0. The divergent recombination portion causes a portion of the ionized and disassociated propellant gas passing therethrough to recombine, recovering frozen flow losses prior to entering the expansion portion and increasing the overall energy conversion efficiency of the thruster.

Qualification and life testing of a flight design hydrazine arcjet system

Abstract: This paper describes the design and the requirements of a low-power hydrazine arc jet system and presents the results of tests on the system's performance, vibration, and lifetime. The system consists of an arcjet, catalyst bed, power control unit, and interconnecting power cable. Operating at 1.4 kW input power, the system provides a minimum of 450 sec mission average specific impulse, yielding greater than a 100 kg propellant savings over standard monopropellant or bipropellant systems used on communication satellites.

Arcjet load characteristics

Abstract: Experiments were conducted to define the interface characteristics and constraints of 1 kW class arcjets run on simulated decomposition products of hydrazine and power processors. The impacts of power supply output current ripple on arcjet performance were assessed by variation of the ripple frequency from 100 Hz to 100 kHz with 10 percent peak-to-peak ripple amplitude at 1.2 kW. Ripple had no significant effects on thrust, specific impulse or efficiency. The impact of output ripple on thruster lifetime was not assessed. The static and dynamic impedances of the arcjet were quantified with two thrusters of nearly identical configuration. Superposition of an AC component on the DC arc current was used to characterize the dynamic impedance as a function of flow rate and DC current level. A mathematical model was formulated from these data. Both the static and dynamic impedance magnitude were found to be dependent on mass flow rate. The amplitude of the AC component was found to have little effect on the dynamic impedance. Reducing the DC level from 10 to 8 amps led to a large change in the magnitude of the dynamic impedance with no observable phase change. The impedance data compared favorably between the two thrusters.

The 30-kW ammonia arcjet technology

Abstract: The technical results are summarized of a 30 kW class ammonia propellant arcjet technology program. Evaluation of previous arcjet thruster performance, including materials analysis of used thruster components, led to the design of an arcjet with improved performance and thermal characteristics. Tests of the new engine demonstrated that engine performance is relatively insensitive to cathode tip geometry. Other data suggested a maximum sustainable arc length for a given thruster configuration, beyond which the arc may reconfigure in a destructive manner. A flow controller calibration error was identified. This error caused previously reported values of specific impulse and thrust efficiency to be 20 percent higher than the real values. Corrected arcjet performance data are given. Duration tests of 413 and 252 hours, and several tests 100 hours in duration, were performed. The cathode tip erosion rate increased with increasing arc current. Elimination of power source ripple did not affect cathode tip whisker growth. Results of arcjet modeling, diagnostic development and mission analyses are also discussed. The 30 kW ammonia arcjet may now be considered ready for development for a flight demonstration, but widespread application of 30 kW class arcjet will require improved efficiency and lifetime.

End-hall thrusters

Abstract: The end-Hall thruster can provide electric propulsion with fixed masses, specific impulses, and power-to-thrust ratios intermediate of an arcjet and a gridded (electrostatic) ion thruster. With these characteristics, this thruster is a candidate for missions of intermediate difficulty, such as the north-south stationkeeping of geostationary satellites.

Effect of arcjet plume on satellite reflector performance

Abstract: The effect of an arcjet plume on the performance of onboard reflector antennas is studied. The arcjet plume is modeled as an inhomogeneous scatterer with a smoothly varying refractive index. The spatial distribution of the refractive index is related to the measured electron density data based on the cold plasma model. Since the plume size of interest is more than several wavelengths in extent, geometrical optics is used to calculate the microwave propagation through the plume. The trajectory, phase, amplitude, and polarization of the high-frequency ray field transmitted through the plume are numerically computed based on the laws of geometrical optics. Once the ray optics field transmitted through the plume on the near-field aperture is found, the far-field pattern of the antenna can be calculated by a ray-tube integration scheme. Results obtained with the proposed method are presented. >

Operational characteristics and discharge mechanisms of quasisteady magnetoplasmadynamic(MPD) arcjet for space propulsion.

Abstract: Experimental researches on the operational performance and the arc structure of a quasisteady magnetoplasmadynamic (MPD) arcjet was made to develop a high-performanceaccelerator in space. The results showed that the current pattern, which depended strongly on gas species and discharge current levels, influenced the thruster performance. It was found that the plasma produced in the discharge chamber was compressed radially and that 50% on the input power was consumed in the cathode region. From the plasma potential distribution, a positive voltage slope and mass starvation were found to be present near the anode surface beyond the predicted critical current level.

Effect of nozzle and cathode configuration on arcjet performance

Abstract: Experimental investigations were conducted to evaluate the effects of a bell-shaped contoured nozzle and modified cathode tip shape on 30-kWe-class ammonia arcjet engine performance. The experiments were conducted in a fully instrumented facility which included a thrust stand. The performance data for an arcjet with a bell-shaped nozzle were compared to the performance data of an arcjet that had a 38-deg included-angle, conical nozzle. Thrust improvements of up to 10% were demonstrated which corresponded to a 10% improvement in thrust efficiency and up to a 35-s increase in specific impulse. The modified cathode tip had a reduced diameter and more acute conical tip with respect to the baseline cathode design. A uniform 15% decrease in arc voltage was noted over a mass flow range of 0.175-0.350 g/s using the modified cathode. However, there was no change in the engine performance characteristics.

Arcjet plasma plume effect on a microwave reflector antenna. [thruster plasma effects on reflector antenna microwaves

Abstract: A configuration is described to measure the effect of the plasma produced by an arcjet thruster on a reflector antenna. The diagnostic consists of a small movable rf probe coupled to a Hewlett–Packard 8510 network analyzer. Because the perturbation is expected to be small (<10° phase shift), wall reflections are an important consideration. To minimize their effect we use Fourier transform gating techniques.

Arcjet plasma plume effect on a microwave reflector antenna

Abstract: A configuration is described to measure the effect of the plasma produced by an arcjet thruster on a reflector antenna. The diagnostic consists of a small movable rf probe coupled to a Hewlett–Packard 8510 network analyzer. Because the perturbation is expected to be small (<10° phase shift), wall reflections are an important consideration. To minimize their effect we use Fourier transform gating techniques.