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NASA NTRS1992

Dependence of hydrogen arcjet operation on electrode geometry

The dependence of 2kW hydrogen arcjet performance on cathode to anode electrode spacing was evaluated at specific impulses of 900 and 1000 s. Less than 2 absolute percent change in efficiency was measured for the spacings tested which did not repeat the 14 absolute percent variation reported in earlier work with similar electrode designs. A different nozzle configuration was used to quantify the variation in hydrogen arcjet performance over an extended range of electrode spacing. Electrode gap variation resulted in less than 3 absolute percent change in efficiency. These null results suggested that electrode spacing is decoupled from hydrogen arcjet ignition. The dependence of breakdown voltage on mass flow rate and electrode agreed with Paschen curves for hydrogen. Preliminary characterization of the dependence of hydrogen arcjet ignition on rates of pulse repetition and pulse voltage rise were also included for comparison with previous results obtained using simulated hydrazine.

Pencil, Eric J.↗

NASA NTRS1991

High-power hydrogen arcjet performance

A hydrogen arcjet was operated at power levels ranging from 5 to 30 kW with three different nozzle geometries. Test results using all three nozzle geometries are reported and include variations of specific impulse with flow rate, and thrust with power. Geometric variables investigated included constrictor diameter, length, and diverging exit angle. The nozzle with a constrictor diameter of 1.78 mm and divergence angle of 20 deg was found to give the highest performance. A specific impulse of 1460 s was attained with this nozzle at a thrust efficiency of 29.8 percent. The best efficiency measured was 34.4 percent at a specific impulse of 1045 s. Post test examination of the cathode showed erosion after 28 hours of operation to be small, and limited to the conical tip where steady state arc attachment occurred. Each nozzle was tested to destruction.

Haag, Thomas W.↗

NASA NTRS1991

High-power hydrogen arcjet performance

A hydrogen arcjet was operated at power levels ranging from 5 to 30 kW with three different nozzle geometries. Test results using all three nozzle geometries are reported and include variations of specific impulse with flow rate, and thrust with power. Geometric variables investigated included constrictor diameter, length, and diverging exit angle. The nozzle with a constrictor diameter of 1.78 mm and divergence angle of 20 degrees was found to give the highest performance. A specific impulse of 1460 s was attained with this nozzle at a thrust efficiency of 29.8 percent. The best efficiency measured was 34.4 percent at a specific impulse of 1045 s. Post test examination of the cathode showed erosion after 28 hours of operation to be small, and limited to the conical tip where steady state arc attachment occurred. Each nozzle was tested to destruction.

Haag, Thomas W.↗

NASA NTRS1992

High power arcjet

In this period a new mass flow controller was brought into the gas supply system, so that the upper limit for the mass flow rate could be increased up to 500 mg/s with hydrogen. A maximum specific impulse of 1500 s could be achieved with the high powered arcjet (HIPARC) at an efficiency of slightly better than 20 percent. Different nozzle throat diameters had been tested. The 100 kilo-watt input power limit was reached with the 4 mm nozzle throat diameter at a mass flow rate of 400 mg/s. Tests were carried out with different cathode gaps and with three different cathodes. In addition measurements of pressure and gas temperature were taken in the feed line in order to determine the pressure drop in the propellant injectors.

Goelz, T. M.↗

NASA NTRSDate not supplied

Comparing Particle Flow Regimes in the L2K Arcjet with Martian Entry Conditions

In this study, the US3D-DUST code will be used to simulate particles in the L2K dusty-flow test environments and compare them to conditions in the shock layer of the Schiaparelli capsule during its entry into the Martian atmosphere in 2016. The particle Reynolds, Mach, and Knudsen numbers, key non-dimensional numbers that characterize the dusty-flow environments, will be compared between the L2K and Martian shock layers. This study will provide a preliminary assessment of how well-suited L2K dusty-flow conditions are for particle drag model validation and the development of particle impact surface damage correlations. The results of this study may help to guide the design of future dusty flow environments in the L2K facility

Dusty flow↗

NASA NTRS2013

Radial Profiles of Plasma Electron Characteristics in a Low-Power Arcjet

Since 1960, the Arc Jet Complex at NASA Ames Research Center has been a source of long-duration, high-enthalpy flow for materials testing with application to the thermal protection of aerospace vehicle components. From their inception the facilities have played an integral role supporting many of NASA's space flight programs and numerous DoD projects. In recent years advancements in computational fluid dynamics (CFO) have made the resultant models a valuable tool for assessing and predicting performance, however, the inherent limitation of models to compensate for a dissociated, transitionally high temperature nonequilibrated flowfield have made further measurements necessary. The use of electrostatic probe diagnostics within similarly harsh plasma environments in previous studies have been met with much success. In this study, the use of a single Langmuir probe was implemented to characterize the plasma parameters of interest as they vary radially within a large volume of the plume. Classical Langmuir probe theory was applied to achieve first order estimates of the heavy particle temperature, the ratio T(sub i)/T(sub e), and the ionization fraction. As expected, both the electron temperature and electron density measurements show a dependence on radial distance from the plume centerline, with electron density profiles showing the largest dependence. This paper aims to validate and strengthen modeling work conducted at the NASA Ames Research Center by measuring the critical plasma parameters (electron temperature, electron density, and plasma potential) within the arc plume of a subscale arc jet. These parameters are intended to give physical insight into the flow characteristics while providing the necessary boundary conditions to validate full scale simulations.

Codron, Douglas↗

NASA NTRS1981

Space experiments with particle accelerators

The purpose of space experiments with particle accelerators (SEPAC) is to carry out active and interactive experiments on and in the Earth's ionosphere and magnetosphere. It is also intended to make an initial performance test for an overall program of Spacelab/SEPAC experiments. The instruments to be used are an electron beam accelerator, magnetoplasma dynamic arcjet, and associated diagnostic equipment. The accelerators are installed on the pallet, with monitoring and diagnostic observations being made by the gas plume release, beam-monitor TV, and particle-wave measuring instruments also mounted on the pallet. Command and display systems are installed in the module. Three major classes of investigations to be performed are vehicle charge neutralization, beam plasma physics, and beam atmosphere interactions. The first two are mainly onboard plasma physics experiments to measure the effect of phenomena in the vicinity of Spacelab. The last one is concerned with atmospheric modification and is supported by other Spacelab 1 investigations as well as by ground-based, remote sensing observations.

Obayashi, T.↗

NASA NTRS1993

Development of a high specific 1.5 to 5 kW thermal arcjet

A research and development project on the experimental study of a 1.5-5 kW thermal arcjet thruster was started in 1992 at the IRS. Two radiation cooled thrusters were designed, constructed, and adapted to the test facilities, one at each end of the intended power range. These thrusters are currently subjected to an intensive test program with main emphasis on the exploration of thruster performance and thruster behavior at high specific enthalpy and thus high specific impulse. Propelled by simulated hydrazine and ammonia, the thruster's electrode configuration such as constrictor diameter and cathode gap was varied in order to investigate their influence and to optimize these parameters. In addition, test runs with pure hydrogen were performed for both thrusters.

Riehle, M.↗

NASA NTRS2000

Development of a Methodology for Conducting Hall Thruster EMI Tests in Metal Vacuum Chambers of Arbitrary Shape and Size

While the closed-drift Hall thruster (CDT) offers significant improvement in performance over conventional chemical rockets and other advanced propulsion systems such as the arcjet, its potential impact on spacecraft communication signals must be carefully assessed before widespread use of this device can take place. To this end, many of the potentially unique issues that are associated with these thrusters center on its plume plasma characteristics and the its interaction with electromagnetic waves. Although a great deal of experiments have been made in characterizing the electromagnetic interference (EMI) potential of these thrusters, the interpretation of the resulting data is difficult because most of these measurements have been made in vacuum chambers with metal walls which reflect radio waves emanating from the thruster. This project developed a means of assessing the impact of metal vacuum chambers of arbitrary size or shape on EMI experiments, thereby allowing for test results to be interpreted properly. Chamber calibration techniques were developed and initially tested at RIAME using their vacuum chamber. Calibration experiments were to have been made at Tank 5 of NASA GRC and the 6 m by 9 m vacuum chamber at the University of Michigan to test the new procedure, however the subcontract to RIAME was cancelled by NASA memorandum on Feb. 26. 1999.

Gallimore, Alec D.↗

NASA NTRS1989

Arcjet nozzle design impacts

The effect of nozzle configuration on the operating characteristics of a low power dc arcjet thruster was determined. A conical nozzle with a 30 deg converging angle, a 20 deg diverging angle, and an area ratio of 225 served as the baseline case. Variations on the geometry included bell-shaped contours both up and downstream, and a downstream trumpet-shaped contour. The nozzles were operated over a range of specific power near that anticipated for on-orbit operation. Mass flow rate, thrust, current, and voltage were monitored to provide accurate comparisons between nozzles. The upstream contour was found to have minimal effect on arcjet operation. It was determined that the contour of the divergent section of the nozzle, that serves as the anode, was very important in determining the location of arc attachment, and thus had a significant impact on arcjet performance. The conical nozzle was judged to have the optimal current/voltage characteristics and produced the best performance of the nozzles tested.

Curran, Francis M.↗

NASA NTRS1989

Arcjet Nozzle Design Impacts

Curran, Francis M.↗

NASA NTRSDate not supplied

Validating Arc-jet Condition Targets Using Inverse 1D Material Response Models

Experiments were conducted using both the Interaction Heating Facility (IHF) and Aerodynamic Heating Facility (AHF), two hypersonic arc-jet facilities at NASA Ames. These tests were run to understand the material response of ablative thermal protection system materials by exposing them to high-enthalpy flows. Using thermocouple data from the materials, test conditions were inversely determined and compared with expected results from a one-dimensional model using facility target conditions; this allowed an approximate environmental scale factor to be determined and applied to more accurately predict material response in additional tests.

material response↗

NASA NTRS1991

Arcjet thruster research and technology, phase 2

The principle objective of Phase 2 was to produce an engineering model N2H4 arcjet system which met typical performance, lifetime, environmental, and interface specifications required to support a 10-year N-S stationkeeping mission for a communications spacecraft. The system includes an N2H4 arcjet thruster, power conditioning unit (PCU), and the interconnecting power cable assembly. This objective was met with the successful conclusion of an extensive system test series.

Yano, Steve E.↗

NASA NTRS1989

Development of a hybrid (MPD plus thermal) arcjet engine with an applied magnetic field

Work carried out by the JPL on several applied field MPD (magnetoplasmasynamic) or hybrid engines, both radiation cooled and liquid cooled, is described. A radiation cooled device was successfully life tested for 554 hrs with ammonia as the propellant. While the electrode erosion was moderate, the boron nitride insulator was badly eroded. Hydrogen and lithium were the other propellants used in these devices. In the case of lithium, a radiation cooled engine had an efficiency of 70 percent at about 5500 sec.

Pivirotto, Thomas J.↗

NASA NTRS1993

Development and operation of new arc heater technology for a large-scale scramjet propulsion test facility

An arc-heater technology development effort conducted at NASA-Ames has led to the creation of a 100 MW Huels arc heater which has been integrated into the hydrogen-fueled Direct Connect Arcjet Facility for long-duration, high Mach-number scramjet performance evaluation. This development effort has significantly advanced the design of vortex-stabilized arc heaters; air enthalpy levels of 2.8-7.5 MJ/kg, at stagnation pressures of up to 45 atm, are produced. The facility furnishes technology-development support that is critical to the definition of NASP-related propulsion systems.

Balboni, John↗

NASA NTRS1998

Arc Jet Flow Properties Determined from Laser-Induced Fluorescence of Atomic Nitrogen

An laser-spectroscopic investigation of the thermocheMical state of arcjet flows is currently being conducted in the Aerodynamic Heating Facility (AHF) Circlet at NASA Ames Research Center. Downstream of the nozzle exit, but upstream of the test article, Laser-Induced Fluorescence (LIF) of atomic nitrogen is used to assess the nonequilibriuM distribution of flow enthalpy in the free stream. The two-photon LIF technique provides simultaneous measurements of free stream velocity, translational temperature, and nitrogen number density on the flow centerline. Along with information from facility instrumentation, these measurements allow a determination of the free stream total enthalpy, and its apportionment in to thermal, kinetic, and chemical mode contributions. Experimental results are presented and discussed for two different niti-ogen/argon test gas flow runs during which the current is varied while the pressure remains constant .

Fletcher, Douglas↗

NASA NTRS1991

Arcjet thermal characteristics

The performance of water-cooled and radiation-cooled arcjet thrusters operating on both 1:2 nitrogen/hydrogen mixtures at 1-2 kW and on pure hydrogen at 1-4 kW are compared. To investigate the effects of test facility background pressure on performance, data were taken for both thrusters operating on hydrogen/nitrogen mixtures at facility background pressures nominally at 0.20 Pa and 20 Pa. It is shown that increasing the background pressure decreased the thruster performance, and simple pressure area corrections alone could not account for the observed degradation in performance.

Sankovic, John M.↗

NASA NTRS1993

Low power arcjet system spacecraft impacts

Application of electrothermal arcjets on communications satellites requires assessment of integration concerns identified by the user community. Perceived risks include plume contamination of spacecraft materials, induced arcing or electrostatic discharges between differentially charged spacecraft surfaces, and conducted and radiated electromagnetic interference (EMI) for both steady state and transient conditions. A Space Act agreement between Martin Marietta Astro Space, the Rocket Research Company, and NASA's Lewis Research Center was established to experimentally examine these issues. Spacecraft materials were exposed to an arcjet plume for 40 hours, representing 40 weeks of actual spacecraft life, and contamination was characterized by changes in surface properties. With the exception of the change in emittance of one sample, all measurable changes in surface properties resulted in acceptable end of life characteristics. Charged spacecraft samples were benignly and consistently reduced to ground potential during exposure to the powered arcjet plume, suggesting that the arcjet could act as a charge control device on spacecraft. Steady state EMI signatures obtained using two different power processing units were similar to emissions measured in a previous test. Emissions measured in UHF, S, C, Ku and Ka bands obtained a null result which verified previous work in the UHF, S, and C bands. Characteristics of conducted and radiated transient emissions appear within standard spacecraft susceptibility criteria.

Pencil, Eric J.↗