Showing papers on "Arcjet rocket published in 1987"

Arcjet starting reliability: A multistart test on hydrogen/nitrogen mixtures

Abstract: An arcjet starting reliability test was performed to investigate one feasibility issue in the use of arcjets onboard a satellite for north-south stationkeeping. A 1 kW arcjet was run on hydrogen/nitrogen gas mixtures simulating decomposed hydrazine. A pulse width modulated power supply with an integral high voltage starting pulser was used for arc ignition and steady-state operation. The test was performed in four phases in order to determine if starting characteristics changed as a result of long term thruster operation. More than 300 successful starts were accumulated over an operating time of 18 hrs. Overall results indicate that there is a link between starting characteristics and long term thruster operation; however, the large number of starts had no effect on steady-state performance.

Arcjet thruster with improved arc attachment for enhancement of efficiency

Abstract: An arcjet thruster has a constrictor and nozzle defining an arc chamber. The constrictor has an insulator and an anode. The constrictor defines a subsonic-to-supersonic transition zone axially coextensive with the inculator and anode. The anode is disposed side-by-side with the insulator and located upstream therefrom. A rod defines a cathode spaced from the anode by a gap. An electrical potential is applied to the anode and cathode to generate an electrical arc in the chamber which produces thermal heating of propellant gases flowing through the chamber and expansion thereof through the nozzle. Location of the insulator downstream from the anode causes diffusion and attachment of the arc to occur at the region of the anode in the constrictor and prevents movement of the arc diffusion and attachment region downstream past the insulator to the nozzle in response to propellant gas mass flow variations through the constrictor. The thruster can also include an expansion and compression cavity in the arc chamber to provide a low pressure region at the anode for arc attachment and diffusion. Further, a zone of thermal and mechanical isolation can be provided between the anode and insulator to reduce the temperature at the insulator and displace its location farther away from the region of arc attachment and diffusion at the anode. Still further, a passage is defined through the insulator to provide a path for secondary flow of propellant gas into the chamber downstream of the arc attachment and diffusion region in order to reclaim frozen flow losses.

Low Power Arcjet Thruster Pulse Ignition

Abstract: An investigation of the pulse ignition characteristics of a 1 kW class arcjet using an inductive energy storage pulse generator with a pulse width modulated power converter identified several thruster and pulse generator parameters that influence breakdown voltage including pulse generator rate of voltage rise. This work was conducted with an arcjet tested on hydrogen-nitrogen gas mixtures to simulate fully decomposed hydrazine. Over all ranges of thruster and pulser parameters investigated, the mean breakdown voltages varied from 1.4 to 2.7 kV. Ignition tests at elevated thruster temperatures under certain conditions revealed occasional breakdowns to thruster voltages higher than the power converter output voltage. These post breakdown discharges sometimes failed to transition to the lower voltage arc discharge mode and the thruster would not ignite. Under the same conditions, a transition to the arc mode would occur for a subsequent pulse and the thruster would ignite. An automated 11 600 cycle starting and transition to steady state test demonstrated ignition on the first pulse and required application of a second pulse only two times to initiate breakdown.

Performance characterization of a low power hydrazine arcjet

Abstract: Hydrazine arcjets, which offer substantial performance advantages over alternatives in geosynchronous satellite stationkeeping applications, have undergone startup, materials compatibility, lifetime, and power conditioning unit design issues. Devices in the 1000-3000 W output range have been characterized for several different electrode configurations. Constrictor length and diameter, electrode gap setting, and vortex strength have been parametrically studied in order to ascertain the influence of each on specific impulse and efficiency; specific impulse levels greater than 700 sec have been achieved.

Low power DC arcjet operation with hydrogen/nitrogen/ammonia mixtures

Abstract: The effect of gas composition and ambient pressure on arcjet operation was determined. Arcjet operation in different facilities was also compared to determine the validity of tests in small facilities. Volt-ampere characteristics were determined for an arcjet using hydrogen/nitrogen mixtures (simulating both ammonia and hydrazine), hydrogen/nitrogen/ammonia mixtures, and pure ammonia as propellants at various flow rates. The arcjet had a typical performance of 450 sec specific impulse at 1 kW with hydrogen/nitrogen mixures. It was determined that the amount of ammonia present in the gas stream had a significant effect on the arcjet volt-ampere characteristics. Also, hydrogen/nitrogen mixtures simulating ammonia gave arc characteristics approximately the same as those of pure ammonia. Finally, no differences in arc volt-ampere characteristics were seen between low and high ambient pressure operation in the same facility. A 3 to 5 V difference was seen when different facilities were compared, but this difference was probably due to differences in the voltage drops across the current connections, and not due to arcjet operational differences in the two facilities.

Langmuir probe surveys of an arcjet exhaust

Abstract: Electrostatic (Langmuir) probes of both spherical and cylindrical geometry have been used to obtain electron number density and temperature in the exhaust of a laboratory arcjet. The arcjet thruster operated on nitrogen and hydrogen mixtures to simulate fully decomposed hydrazine in a vacuum environment with background pressures less than 0.05 Pa. The exhaust appears to be only slightly ionized (less than 1 percent) with local plasma potentials near facility ground. The current-voltage characteristics of the probes indicate a Maxwellian temperature distribution. Plume data are presented as a function of arcjet operating conditions and also position in the exhaust.

Arcjet component conditions through a multistart test

Abstract: A low power, dc arcjet thruster was tested for starting reliability using hydrogen-nitrogen mixtures simulating the decomposition products of hydrazine. More than 300 starts were accumulated in phases with extended burn-in periods interlaced. A high degree of flow stabilization was built into the arcjet and the power supply incorporated both rapid current regulation and a high voltage, pulsed starting circuit. A nominal current level of 10 A was maintained throughout the test. Photomicrographs of the cathode tip showed a rapid recession to a steady-state operating geometry. A target of 300 starts was selected, as this represents significantly more than anticipated (150 to 240), in missions of 10 yr or less duration. Weighings showed no apparent mass loss. Some anode erosion was observed, particularly at the entrance to the constrictor. This was attributed to the brief period during startup the arc mode attachment point spends in the high pressure region upstream of the nozzle. Based on the results obtained, startup does not appear to be performance or life limiting for the number of starts typical of operational satellite applications.

Non-erosive arcjet starting control system and method

Abstract: A non-erosive arcjet starting control system and method are provided in combination with an arcjet thruster which includes an anode, a cathode and a gap defined therebetween. The starting control system and method include the operative steps of, first, actuating a valve in a propellant gas feed path to an opened position thereby permitting flow of propellant gas at a predetermined pressure into the thruster past the gap therein, second, applying to the anode and cathode an electrical potential of a predetermined magnitude being less than that required to generate an electrical arc across the gap through propellant gas at the predetermined flow pressure and, concurrently, actuating the valve to its closed position thereby preventing flow of propellant gas into the thruster past the gap and thereby lowering the flow pressure of the propellant gas in the thruster below the predetermined pressure such that an electrical arc is now generated in the thruster across the gap and, finally, actuating the valve to its opened position thereby permitting propellant gas to flow again at the predetermined pressure into the thruster past the gap and force the electrical arc to move downstream within the thruster so as to minimize erosion in the constrictor. The flow of propellant into the thruster is prevented for only a short period of time.

Arcjet power supply and start circuit

Abstract: A dc power supply for spacecraft arcjet thrusters has an integral automatic starting circuit and an output averaging inductor. The output averaging inductor, in series with the load, provides instantaneous current control, and ignition pulse and an isolated signal proportional to the arc voltage. A pulse width modulated converter, close loop configured, is also incorporated to give fast response output current control.

Low power arcjet life issues

Abstract: The present evaluation of the results of arcjet engine lifetime testing attempts to deepen understanding of the electrode erosion process, with a view to its minimization. Attention is given to the compatibility of materials with N2H4, the dependence of electrode erosion on geometry and flow field, and the erosive effects associated with the arcjet power supply. Results are presented for thrusters employing either decomposed N2H4 or cold mixed gases, over a power range of 900 to 2000 W.

Space station propulsion

Abstract: Two propulsion systems have been selected for the space station: gaseous H/O rockets for high thrust applications and the multipropellant resistojets for low thrust needs. These two thruster systems integrate very well with the fluid systems on the space station, utilizing waste fluids as their source of propellant. The H/O rocket will be fueled by electrolyzed water and the resistojets will use waste gases collected from the environmental control system and the various laboratories. The results are presented of experimental efforts with H/O and resistojet thrusters to determine their performance and life capability, as well as results of studies to determine the availability of water and waste gases.

Long duration test of a 30-kW class thermal arcjet engine

Abstract: The paper describes a recent long-duration test of a 30-kW arcjet engine. This engine performed very well for 573 hours at power levels between 24 and 29 kW and with ammonia as the propellant at a mass flow rate between 0.25 and 0.27 g/s. The specific impulse varied between about 850 and 950 s and the thrust efficiency between 36 and 40 percent. The cause of final engine failure and the conditions of the electrodes and insulator are discussed in detail. An important part of this very long-term test effort was the performance and efficiency of the facility. The construction of this facility and the performance of the various critical components are discussed.

Development of a quasi-steady MPD arcjet thruster for near-earth missions

Abstract: A quasi-steady multimegawatt magnetoplasmadynamic (MPD) arcjet thruster with applied magnetic fields has been investigated to achieve the high thrust performance at the specific impulse between 1000 and 2000 sec, which is demanded for space missions near the earth. The applied field coils are connected in series with a power source (pulse forming network). Field application causes lower discharge voltages and greater thrusts than those for no applied field under the following special conditions: (1) the applied field intensity is equal to the self-field one only in the main current conduction region in front of the cathode tip, and (2) the magnetic field line is parallel to the anode inside surface. The cathode diameter has no influence on the thrust performance with the applied field for ammonia propellant. According to these guidelines, a method for generation of the preferred field is proposed. A new MPD thruster with the preferred field is designed and is further improved in the thrust performance. 9 references.

The design and operating characteristics of an advanced 30-kW ammonia arcjet engine

Abstract: Experimental investigations were conducted to evaluate the effects of a contoured nozzle and modified cathode shape on ammonia arcjet engine performance. The contoured nozzle performance data were compared to the performance data of an arcjet which had a 38-deg included-angle, conical nozzle. Thrust improvements of up to 10 percent were demonstrated which corresponded to 3 percent improvements in specific impulse and 10 percent improvements in thrust efficiency. Performance characterizations for the modified cathode tip were conducted with the contoured nozzle arcjet. A uniform 15 percent decrease in arc voltage was demonstrated over a mass flow range of 0.175 to 0.350 g/s. A 4 percent improvement in thrust efficiency was noted at 22.0 kW.

High- and low-thrust propulsion systems for the space station

Abstract: The purpose of the Advanced Development program was to investigate propulsion options for the space station. Two options were investigated in detail: a high-thrust system consisting of 25 to 50 lbf gaseous oxygen/hydrogen rockets, and a low-thrust system of 0.1 lbf multipropellant resistojets. An effort is also being conducted to determine the life capability of hydrazine-fueled thrusters. During the course of this program, studies clearly identified the benefits of utilizing waste water and other fluids as propellant sources. The results of the H/O thruster test programs are presented and the plan to determine the life of hydrazine thrusters is discussed. The background required to establish a long-life resistojet is presented and the first design model is shown in detail.

Performance and Long Duration Test of a 30 kw Thermal Arcjet Engine.

Abstract: : The objective of this effort was to evaluate the lifetime and performance of a 30-kWe constricted arc ammonia arcjet This engine was based on a design developed by Avco Corporation in 1963 that delivered 978 seconds of specific impulse with ammonia during a 50-hour test After 573 hours of operation, a short circuit between the cathode and anode of JPL's thruster forced the life test to end Throughout the 573-hour test, the thruster operated at 249 kWe, delivering 229 N (015 lbs) of thrust, 865 seconds of specific impulse, and 37% efficiency Although the lifetime of JPL's thruster fell short of AFAL's original 1500-hour goal for the effort, the arcjet demonstrated a duration of over eleven times the lifetime of the 1963 Avco arcjet Further, the demonstrated lifetime of 576 hours is adequate for many orbit raising missions Keywords: Electric propulsion; Electrothermal arcjet, Space propulsion

Long duration test of a 30-kW class thermal arcjet engine

Abstract: The paper describes a recent long-duration test of a 30-kW arcjet engine. This engine performed very well for 573 hours at power levels between 24 and 29 kW and with ammonia as the propellant at a mass flow rate between 0.25 and 0.27 g/s. The specific impulse varied between about 850 and 950 s and the thrust efficiency between 36 and 40 percent. The cause of final engine failure and the conditions of the electrodes and insulator are discussed in detail. An important part of this very long-term test effort was the performance and efficiency of the facility. The construction of this facility and the performance of the various critical components are discussed.

Velocity measurements in the plume of an arcjet engine

Abstract: A nonintrusive technique has been used to conduct a radial survey in the flow field of an arcjet engine plume. The technique measures the Doppler shift of an optically thin line resulting from recombination and relaxation processes in the high Mach number stream, in order to determine flow velocities. Atom temperature can also be calculated from the same Doppler-broadened line widths, when these shifts are measured with a scanning Fabry-Perot spectrometer whose design is presented in detail. 19 references.

Multi-channel two-dimensional MPD arcjet

Abstract: A multichanneled MPD arcjet, which approximated an ideal two-dimensional discharge, was successfully operated in a quasi-steady mode. This device allows easy access to the discharge region by means of optical techniques for obtaining particle species, temperature distribution, and current patterns. Such data are analyzed in order to clarify the correlation between the thrust performance and plasma condition. It was found that the onset phenomenon should be more clearly defined by Isp, which strongly depends on the electrodes design, than the parameter J-squared/m, very low electron temperature of 0.3 eV was found to prevail in H2 propellant, which explained the current concentration on the cathode tip due to dissociative energy absorption of molecular propellant. 7 references.

A low-power arcjet cyclic lifetest

Abstract: A cyclic lifetest of a low power dc arcjet thruster using a hydrogen/nitrogen propellant mixture simulating hydrazine is currently in progress. Over 300 hr of operation have been accumulated to date in 2 hr duty cycles at a power level of about 1.15 kW, approximating that available on commercial communications satellites. A burn-in period was carried out before consistent operation was attained. After this period, the arcjet operated in a very stable fashion from cycle to cycle. At the beginning of each cycle, there was a brief starting transient followed by a rapid rise to a steady-state voltage. The steady-state voltage increased by about 5 V over the first 95 cycles. After this, it increased by only 1 V through the remainder of the test. Thrust measurements taken before the life test and again after the completion of the 144th cycle showed that both thrust, specific impulse, and arc voltage had increased over this period of operation. No life limiting mechanisms were observed during the course of the testing.

Electric propulsion options for the SP-100 reference mission

Abstract: Analyses were performed to characterize and compare electric propulsion systems for use on a space flight demonstration of the SP-100 nuclear power system. The component masses of resistojet, arcjet, and ion thruster systems were calculated using consistent assumptions and the maximum total impulse, velocity increment, and thrusting time were determined, subject to the constraint of the lift capability of a single Space Shuttle launch. From the study it was found that for most systems the propulsion system dry mass was less than 20 percent of the available mass for the propulsion system. The maximum velocity increment was found to be up to 2890 m/sec for resistojet, 3760 m/sec for arcjet, and 23 000 m/sec for ion thruster systems. The maximum thruster time was found to be 19, 47, and 853 days for resistojet, arcjet, and ion thruster systems, respectively.

The NASA/USAF arcjet research and technology program

Abstract: Direct current arcjets have the potential to provide specific impulses greater than 500 sec with storable propellants, and greater than 1000 sec with hydrogen. This level of performance can provide significant benefits for such applications as orbit transfer, station keeping, orbit change, and maneuvering. The simplicity of the arcjet system and its elements of commonality with state-of-the-art resistojet systems offer a relatively low risk transition to these enhanced levels of performance for low power (0.5 to 1.5 kW) station keeping applications. Arcjets at power levels of 10 to 30 kW are potentially applicable to orbit transfer missions. Furthermore, with the anticipated development of space nuclear power systems, arcjets at greater than 100 kW may become attractive. This paper describes the ongoing NASA/USAF program and describes major recent accomplishments.

Arcjet thruster research and technology, phase 1

Abstract: The objectives of Phase 1 were to evaluate analytically and experimentally the operation, performance, and lifetime of arcjet thrusters operating between 0.5 and 3.0 kW with catalytically decomposed hydrazine (N2H4) and to begin development of the requisite power control unit (PCU) technology. Fundamental analyses were performed of the arcjet nozzle, the gas kinetic reaction effects, the thermal environment, and the arc stabilizing vortex. The VNAP2 flow code was used to analyze arcjet nozzle performance with non-uniform entrance profiles. Viscous losses become dominant beyond expansion ratios of 50:1 because of the low Reynolds numbers. A survey of vortex phenomena and analysis techniques identified viscous dissipation and vortex breakdown as two flow instabilities that could affect arcjet operation. The gas kinetics code CREK1D was used to study the gas kinetics of high temperature N2H4 decomposition products. The arc/gas energy transfer is a non-equilibrium process because of the reaction rate constants and the short gas residence times. A thermal analysis code was used to guide design work and to provide a means to back out power losses at the anode fall based on test thermocouple data. The low flow rate and large thermal masses made optimization of a regenerative heating scheme unnecessary.

Experimental and theoretical study of a low-pressure axisymmetric arcjet

Abstract: An experimental study of a helium plasma axisymmetric arcjet has been conducted. The laminar and compressible He jet flows in a low-pressure (p = 130 Pa), ambient-temperature, helium gas at rest. Pressure measurements using static and differential pressure probes were carried out. The temperature is measured at one point from the analysis of the Boltzmann equilibrium between rotation levels. A numerical integration of the jet governing equations leads to the prediction of the pressure, temperature, and velocity fields. A modified version of the TEACH-L computer program is used. The comparison between predictions and experiments is very satisfactory. 38 references.

Anode configuration for electrothermal/electromagnetic arcjet

Abstract: To improve the performance of an MPD thruster in the range of a specific impulse near and above 1000 s, which corresponds to the electrothermal/electromagnetic hybrid mode of operation, the anode configuration was modified by changing: (1) the axial length of the metal anode and insulator nozzle, and (2) anode segments in the azimuthal direction as experimental parameters. The anode which was 5 percent the axial length of the nozzle resulted in a drastic improvement of thrust efficiency.