Showing papers on "Arcjet rocket published in 1986"

The design and operating characteristics of a 30-kW thermal arcjet engine for space propulsion

Abstract: Attention is given to the design features of a radiation-cooled, 30-kW thermal arcjet thruster, whose laboratory tests have yielded specific impulses of up to 935 sec at 36-44 percent thrust efficiency, together with a cumulative lifetime of over 400 hours. All materials used, including seals, can sustain operation at temperatures sufficiently elevated to require the radiation of all waste heat. This electric propulsion system is ideally suited to missions such as the Space-Based Radar. A detailed consideration is conducted for the thruster's seals, which are the most critical element of the design.

Power electronics for a 1-kilowatt arcjet thruster

Abstract: After more than two decades, new space mission requirements have revived interest in arcjet systems. The preliminary development and demonstration of new, high efficiency, power electronic concepts for start up and steady state control of dc arcjets is reported. The design comprises a pulse width modulated power converter which is closed loop configured to give fast current control. An inductor, in series with the arcjet, serves the dual role of providing instantaneous current control, as well as a high voltage arc ignition pulse. Benchmark efficiency, transient response, regulation, and ripple data are presented. Tests with arcjets demonstrate that the power electronics breadboard can start thrusters consistently with no apparent damage and transfer reliably to the nondestructive high voltage arc mode in less than a second.

Experimental study on a low-power direct current arcjet

Abstract: An experimental investigation on a low-power dc arcjet with helium propellant was conducted. Objectives were to evaluate the thermal efficiency, to assess the performance of various cathode materials, and to investigate the effects of transpirational cooling from the electrodes. The anode was made of porous tungsten so that the propellant could be supplied through the anode. The cathode materials used in this experiment were porous tungsten, thoriated tungsten, lanthanum hexaboride, and porous tungsten impregnated with barium oxide (BaO/W). Two discharge modes of low and high voltages were found, which corresponded to low and high thermal efficiency, respectively. The BaO/W cathode was the best of all the tested materials, demonstrating a thermal efficiency as high as 64.9%. The transpirational cooling resulted in a great decrease of the thermal efficiency.

Critical speed and voltage-current characteristics in self-field plasma thrusters

Abstract: To examine possible exhaust velocity limitations in high power magnetoplasmadynamic (MPD) arcjets, a power balance model is constructed. A special feature of this model is that the discharge thickness is inversely proportional to the velocity of the high-speed electrically conducting flow created by the discharge and its self magnetic field. Resistive dissipation then scales with electromagnetic thrust and flow speed. Ablation of arcjet materials adds to the total mass flow when the input propellant flow is insufficient to carry away the dissipated power. At high power levels, the exhaust velocity may plateau because of such mass addition at values comparable to Alfven critical speed. At lower powers, incomplete ionization and coupling of the injected neutral flow in the discharge can also result in such a velocity plateau (as interpreted by voltage and plume measurements). The voltage-current characteristics of MPD arcjets are discussed and research directions are indicated.

Low power dc arcjet operation with hydrogen/nitrogen propellant mixtures

Abstract: The arcjet assembly from a flight model system was modified with a new thoriated tungsten nozzle insert and has been tested with hydrogen-nitrogen mixtures simulating the decomposition products of ammonia and hygrazine. Arcjet power consumption ranged from 0.7 to 1.15 kW depending on low rate, input current, and mixture composition. At a nominal 1 kW power level the ammonia mixtures thrust efficiency was about 0.31 at specific impulse values ranging between 460 and 500 sec. Hydrazine mixtures gave similar thrust efficiencies at the same power level with specific impulse values between 395 and 430 sec. Large, spontaneous voltage mode changes were not observed once the thruster had passed a period of instability immediately following start up. This period of instability, and the startup at low pressure, were seen as major causes of constrictor damage during the tests.

Development of an arcjet nuclear electric propulsion system for a 1993 flight demonstration

Abstract: The design and performance of an arcjet NEP spacecraft, suitable for use in the Space Nuclear Power System (SNPS) Reference Mission, are outlined. Several arcjet technology levels were considered in this study, and the vehicle design was based on an 30 kW ammonia arcjet system operating at an Isp of 1000 s and an efficiency of 45 percent. The arcjet/gimbal system, PPU and propellant feed-system are described. A 100 kWe SNPS was assumed and the spacecraft mass was baselined at 5500 kg excluding the propellant feed system. A radiation/arcjet efflux diagnostics package was included in the performance analysis. This spacecraft, launched from Kennedy, can perform a 50 degree inclination change and reach a final orbit of GEO with a 180 day trip time providing a six month active load for the SNPS. Advanced ammonia and hydrogen systems were examined for precursor SDI platform applications.

Quasisteady MPD arcjet with hollow cathode

Abstract: Hollow cathodes with various diameters and interelectrode lengths were tested to evaluate their effects on the performance of a magnetoplasmadynamic (MPD) thruster. The thruster was operated in a quasisteady mode in the specific impulse (Isp) range of 1000-2000 s. The arc chamber was designed so that its wall formed a divergent nozzle and the hollow cathode constituted a part of the flow tube. The entire propellant was injected through the hollow cathode and forced to be heated in the arc column so as to enhance the aerodynamic acceleration. An appropriate combination of cathode interior diameter and interelectrode length resulted in the maximum thrust power ratio of 25 mN/kW for hydrogen and a lower cathode erosion rate than occurs with a solid cathode. However, a similar configuration was not effective for ammonia propellant because the mass flow was interrupted by excessively high pressure due to induced electromagnetic pinch force in the hollow cathode interior. Consequently, the hollow cathode exhibited inferior thrust performance but superior erosion characteristics compared to the solid cathode.

Transient heat-transfer analysis of a conical cathode of an MPD arcjet

Abstract: Most magnetoplasmadynamic thrusters operate with high temperatures at the cathode root in order to allow the emission of electrons with a moderate electric field while suffering minimum material loss. Attention is presently given to a two-time level implicit scheme for the numerical solution of the nonlinear transient energy equation of a conical cathode. The scheme is simple, unconditionally stable, and convergent. 7 references.

Oxidizer heat exchanger component testing

Abstract: The RL10-IIB engine, is capable of multimode thrust operation. The engine operates at two low-thrust levels: tank head idle (THI), approximately 1 to 2 percent of full thrust; and pumped idle, 10 percent of full thrust. Operation at THI provides vehicle propellant settling thrust and efficient thermal conditioning; PI operation provides vehicle tank prepressurization and maneuver thrust for low-g deployment. Stable combustion of the RL10-IIB engine during the low-thrust operating modes can be accomplished by using a heat exchanger to supply gaseous oxygen to the propellant injector. The oxidized heat exchanger (OHE) vaporizes the liquid oxygen using hydrogen as the energy source. This report summarizes the test activity and post-test data analysis for two possible heat exchangers, each of which employs a completely different design philosophy. One design makes use of a low-heat transfer (PHT) approach in combination with a volume to attenuate pressure and flow oscillations. The test data showed that the LHT unit satisfied the oxygen exit quality of 0.95 or greater in both the THI and PI modes while maintaining stability. The HHT unit fulfilled all PI requirements; data for THI satisfactory operation is implied from experimental data that straddle the exact THI operating point.

Advanced propulsion for polar-orbiting and coorbiting free flyers

Abstract: Advanced propulsion systems for polar-orbiting and coorbiting free flyers were investigated. Resistojet, arcjet, ion, magnetoplasmadynamic and chemical-bipropellant nitrogen tetroxide/monomethyl hydrazine (NTO/MMH) propulsion systems were compared to the baseline free-flyer hydrazine (N2H4)-propulsion-system performance. Advanced resistojet, arcjet, ion, and NTO/MMH propulsion systems enable significant propellant-mass savings over the baseline N2H4-propulsion system. Using free-flyer mission requirements from the Langley Research Center Mission-Data Base, detailed propulsion requirements for over thirty free-flyer missions were analyzed. The Polar-Platform trip-time constraints may preclude using a low-thrust electric-propulsion system. Electric propulsion will, however, allow a significant coorbiter propellant-mass reduction. Frequent servicing and nodal-regression effects on the coorbiting free-flyer's orbit increase the required mission velocity change and propellant mass. For many coorbiter missions high-specific-impulse resistojet-, arcjet- and ion-propulsion systems allow substantial life-cycle propellant-mass savings.

Coupling between fluid dynamics and energy addition in arcjet and microwave thrusters

Abstract: A new approach to numerically solving the problem of the constricted electric arcjet is presented. An Euler Implicit finite difference scheme is used to solve the full compressible Navier Stokes equations in two dimensions. The boundary and initial conditions represent the constrictor section of the arcjet, and hydrogen is used as a propellant. The arc is modeled as a Gaussian distribution across the centerline of the constrictor. Temperature, pressure and velocity profiles for steady state converged solutions show both axial and radial changes in distributions resulting from their interaction with the arc energy source for specific input conditions. The temperature rise is largest at the centerline where there is a the greatest concentration arc energy. The solution does not converge for all initial inputs and the limitations in the range of obtainable solutions are discussed.