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Proceedings ArticleDOI

Effect of current ripple on cathode erosion in 30 kWe class arcjets

TL;DR: In this paper, the effect of current ripple on cathode erosion in 30 kWe class arcjets was investigated to determine the change in the cathode degradation rate for high (11 percent) and low (4 percent) current ripple values.
Abstract: An investigation was conducted to study the effect of current ripple on cathode erosion in 30 kWe class arcjets to determine the change in the cathode erosion rate for high (11 percent) and low (4 percent) current ripple. The measurements were conducted using a copper-tungsten cathode material to accelerate the cathode erosion process. It is shown that the high ripple erosion rate was initially higher than the low ripple erosion rate, but decreased asymptotically with time to a level less than half that of the low ripple value. Results suggest that high ripple extends the cathode lifetime for long duration operation, and improves arc stability by increasing the cathode attachment area.
Citations
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01 Jan 1992
TL;DR: In this paper, the design and development of 10 kW hydrogen arcjet power electronics and results of arcjet integration testing were presented. Butler et al. used a full bridge switching topology similar to that employed in state of the art 5 kW power electronics, and the output filter included an output current averaging inductor with an integral pulse generation winding for arcjet ignition.
Abstract: A combination of emerging mission considerations such as 'launch on schedule', resource limitations, and the development of higher power spacecraft busses has resulted in renewed interest in high power hydrogen arcjet systems with specific impulses greater than 1000 s for Earth-space orbit transfer and maneuver applications. Solar electric propulsion systems with about 10 kW of power appear to offer payload benefits at acceptable trip times. This work outlines the design and development of 10 kW hydrogen arcjet power electronics and results of arcjet integration testing. The power electronics incorporated a full bridge switching topology similar to that employed in state of the art 5 kW power electronics, and the output filter included an output current averaging inductor with an integral pulse generation winding for arcjet ignition. Phase shifted, pulse width modulation with current mode control was used to regulate the current delivered to arcjet, and a low inductance power stage minimized switching transients. Hybrid power Metal Oxide Semiconductor Field Effect Transistors were used to minimize conduction losses. Switching losses were minimized using a fast response, optically isolated, totem-pole gate drive circuit. The input bus voltage for the unit was 150 V, with a maximum output voltage of 225 V. The switching frequency of 20 kHz was a compromise between mass savings and higher efficiency. Power conversion efficiencies in excess of 0.94 were demonstrated, along with steady state load current regulation of 1 percent. The power electronics were successfully integrated with a 10 kW laboratory hydrogen arcjet, and reliable, nondestructive starts and transitions to steady state operation were demonstrated. The estimated specific mass for a flight packaged unit was 2 kg/kW.

9 citations

References
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Journal ArticleDOI
J. Mentel1
TL;DR: In this paper, it was shown that the appearance of arc roots is caused by the superposition of several phenomena, such as ion currents, and that arc roots at which marked vaporization occur are unstable and therefore in general nonstationary.
Abstract: Arc roots at which marked vaporization occur are unstable and therefore in general non-stationary. High speed photography of arc roots using various electrode materials in Ar, SF6, and N2 shows that the appearance of the arc roots results from the superposition of several phenomena. On graphite cathodes in Ar it was possible to observe these phenomena separately by varying the cooling of the electrodes. It is shown that distinctions must be drawn between the real current transfer region with relatively weak vaporization, vaporization from the electrode surface outside this region and vaporization from within the body of the electrode. The energy-balance determined experimentally confirms the theoretical prediction that the energy for strong vaporization of the cathode is supplied by an ioncurrent.

16 citations

15 Feb 1990
TL;DR: In this paper, a 30 kW class ammonia propellant arcjet technology program is described, and a flow controller calibration error was identified, which caused previously reported values of specific impulse and thrust efficiency to be 20 percent higher than the real values.
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.

10 citations

Proceedings ArticleDOI
29 Jun 1987
TL;DR: In this paper, the authors describe a recent long-duration test of a 30-kW arcjet engine 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.
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.

8 citations

Proceedings ArticleDOI
01 Sep 1985
TL;DR: In this paper, an experimental investigation was performed in an effort to measure and increase lifetime of electrodes in an arcjet thruster, and the electrode erosion of various anode and cathode materials was measured after tests in an atmospheric pressure nitrogen arc discharge at powers less than 1 kW.
Abstract: An experimental investigation was performed in an effort to measure and increase lifetime of electrodes in an arcjet thruster. The electrode erosion of various anode and cathode materials was measured after tests in an atmospheric pressure nitrogen arc discharge at powers less than 1 kW. A free-burning arc configuration and a constricted arc configuration were used to test the materials. Lanthanum hexaboride and thoriated tungsten had low cathode erosion rates while thoriated tungsten and pure tungsten had the lowest anode erosion rates of the materials tested. Anode cooling, reverse gas flow, and external magnetic fields were all found to reduce electrode mass loss.

4 citations

Proceedings ArticleDOI
12 Jul 1989

3 citations