An overview of the results from an 8200 hour wear test of the NSTAR ion thruster

Polk, James E.; Anderson, John R.; Brophy, John R.; Rawlin, Vincent K.; Patterson, Michael J.; Sovey, James S.; Hamley, John A.

doi:10.2514/6.1999-2446

Cited by 135 publications

(128 citation statements)

References 3 publications

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“…This agreement is considered sufficient, especially because impingement-limited total voltages are known to decrease with thruster operation. 3 Titanium optics set B was initially tested at an input power range of 0.5 to 4.6 kW, and then 1.0 to 2.3 kW. Impingement-limited total voltages decreased by 45-50 V by the second test.…”

Section: Impingement-limited Total Voltagementioning

confidence: 99%

“…This asymmetry is an artifact of the thruster ctischarge chamber plasma and has been noticed in other NST AR thrusters. 3 Beam ctivergence half-angles were determined in the following manner. Beam current density profiles were taken at five axial locations, examples of which are shown in Fig.…”

Section: Beam Current Density Proflies Beam Divergence and Thrust Lmentioning

confidence: 99%

“…However, most of these missions require increasing the NST AR thruster's propellant throughput and peak input power capabilities beyond the demonstrated 88 kg of xenon at 2.3 kW. 3 Increasing propellant throughput and thruster power is limited, in part, by charge-exchange sputter erosion of the accelerator grid.3.4 Significant chargeexchange accelerator grid sputter erosion can lead to three likely failure mechani sms: 5 1. electron backstreaming due to accelerator aperture enlargement; 2. structural failure of the grid due to pit and groove erosion of the downstream accelerator surface; and 3. an unclearable grid short by a flake from sputtereroded accelerator grid material. Changing the ion optics material to one with a lower volumetric sputter erosion rate addresses all of the…”

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Performance of titanium optics on a NASA 30 cm ion thruster

Soulas

Foster

Patterson

2000

36th AIAA/ASME/SAE/ASEE Joint Propulsion Conference and Exhibit

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Section: Impingement-limited Total Voltagementioning

confidence: 99%

Section: Beam Current Density Proflies Beam Divergence and Thrust Lmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Performance of titanium optics on a NASA 30 cm ion thruster

Soulas

Foster

Patterson

2000

36th AIAA/ASME/SAE/ASEE Joint Propulsion Conference and Exhibit

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“…This profile is similar to those of previous thruster tests. 6 The maximum keeper erosion from the NEXT 2000 hour test was measured to be about 15% of the keeper orifice plate thickness. With the conservative assumption that the eroded depth exhibited in that valley would be linear with time, the keeper orifice plate propellant throughput capability was estimated to be 280 kg.…”

Section: Keeper Wearmentioning

confidence: 99%

Lifetime Assessment of the NEXT Ion Thruster

VanNoord

2007

43rd AIAA/ASME/SAE/ASEE Joint Propulsion Conference &Amp;amp; Exhibit

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Ion thrusters are low thrust, high specific impulse devices with required operational lifetimes on the order of 10,000-100,000 hours. The NEXT ion thruster is the latest generation of ion thrusters under development. The NEXT ion thruster currently has a qualification level propellant throughput requirement of 450 kg of xenon, which corresponds to roughly 22,000 hours of operation at the highest throttling point. Currently, a NEXT engineering model ion thruster with prototype model ion optics is undergoing a long duration test to determine wear characteristics and establish propellant throughput capability. The NEXT thruster includes many improvements over previous generations of ion thrusters, but two of its component improvements have a larger effect on thruster lifetime. These include the ion optics with tighter tolerances, a masked region and better gap control, and the discharge cathode keeper material change to graphite. Data from the NEXT 2000 hour wear test, the NEXT long duration test, and further analysis is used to determine the expected lifetime of the NEXT ion thruster. This paper will review the predictions for all of the anticipated failure mechanisms. The mechanisms will include wear of the ion optics and cathode's orifice plate and keeper from the plasma, depletion of low work function material in each cathode's insert, and spalling of material in the discharge chamber leading to arcing. Based on the analysis of the NEXT ion thruster, the first failure mode for operation above a specific impulse of 2000 s is expected to be the structural failure of the ion optics at 750 kg of propellant throughput, 1.7 times the qualification requirement. An assessment based on mission analyses for operation below a specific impulse of 2000 s indicates that the NEXT thruster is capable of double the propellant throughput required by these missions.

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“…Hollow cathodes used as thermionic electron sources in ion thrusters have demonstrated lifetimes of over 16 000 h in space and over 30 000 h in ground tests, [1][2][3][4] but certain proposed future NASA missions have even more demanding life requirements. The temperature is the primary driver for the chemical processes and physical transport phenomena associated with cathode failure modes and a key indicator of cathode health, but has not been well characterized.…”

Section: Introductionmentioning

confidence: 99%

Scanning optical pyrometer for measuring temperatures in hollow cathodes

Polk

Thornber

Dang

et al. 2007

Review of Scientific Instruments

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Life-limiting processes in hollow cathodes are determined largely by the temperature of the electron emitter. To support cathode life assessment, a noncontact temperature measurement technique which employs a stepper motor-driven fiber optic probe was developed. The probe is driven inside the hollow cathode and collects light radiated by the hot interior surface of the emitter. Ratio pyrometry is used to determine the axial temperature profile. Thermocouples on the orifice plate provide measurements of the external temperature during cathode operation and are used to calibrate the pyrometer system in situ with a small oven enclosing the externally heated cathode. The diagnostic method and initial measurements of the temperature distribution in a hollow cathode are discussed.

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An overview of the results from an 8200 hour wear test of the NSTAR ion thruster

Cited by 135 publications

References 3 publications

Performance of titanium optics on a NASA 30 cm ion thruster

Performance of titanium optics on a NASA 30 cm ion thruster

Lifetime Assessment of the NEXT Ion Thruster

Scanning optical pyrometer for measuring temperatures in hollow cathodes

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