2.3 kW ion thruster wear test

Patterson, Michael J.; Rawlin, Vincent K.; Sovey, James S.; Kussmaul, Michael; Parkes, James E.

doi:10.2514/6.1995-2516

Cited by 30 publications

(20 citation statements)

References 7 publications

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“…During a 2000-h wear test of an NSTAR engineering model thruster (EMT1), significant erosion of the hollow cathode was observed. 3 An engineering solution to this problem was to include an enclosed keeper electrode into the design. This was found almost to eliminate cathode orifice plate erosion during a subsequent 1000-h wear test.…”

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confidence: 99%

Characterization of Cathode Keeper Wear by Surface Layer Activation

Polk

2004

Journal of Propulsion and Power

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The erosion rates of the discharge cathode keeper in a 30 cm NASA Solar Electric Propulsion Technology Applications Readiness (NSTAR) configuration ion thruster were measured using a technique known as surface layer activation (SLA). This diagnostic involved producing a radioactive tracer in the keeper surface by high-energy proton bombardment. The decrease in activity of the tracer material was monitored with a gamma spectroscopy system after the surface was subjected to wear processes. Correlation with a depth calibration curve yielded the eroded depth. The primary objectives were to validate the technique by reproducing erosion data from previous wear studies and to determine the effect of different engine operating parameters on erosion rate. The erosion profile at the TH 15 (2.3-kW) setting observed during the 8200-h life demonstration test was reproduced with a measured maximum erosion rate of 0.085 µm/h. Testing at the TH 8 (1.4-kW) setting demonstrated that variations in keeper voltage had a significant effect on the erosion, with a positive bias with respect to cathode potential decreasing the wear rate significantly. Measurements were achieved after operating times of 40-90 h, with a typical uncertainty of ± ±0.003 µm/h. Nomenclature a = reference count rate, cps h = number of isotopes present in sample spectrum m = spectrum scaling parameteṙ m = mass flow rate, standard cm 3 n = total number of channels in sample spectrum P tot = total thruster power, kW T = thrust, mN W = weight factor array y = sample count rate, cps z = total counts η tot = total thruster efficiency τ = spectrum live time, s Subscripts A = accelerator grid B = beam CK = cathode keeper D = discharge i = channel j = isotope NK = neutralizer keeper

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confidence: 99%

Characterization of Cathode Keeper Wear by Surface Layer Activation

Polk

2004

Journal of Propulsion and Power

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“…Early ion thrusters exhibited higher rates of erosion on the screen grids, 7 but subsequent operational changes to the NSTAR thruster related to the screen grid potential and discharge voltage have significantly reduced the wear of the screen grid. The NSTAR screen grid apertures only exhibited slight chamfering on the upstream side during the 8200 hour test 6 and less than 60 µm of chamfering during the NSTAR ELT.…”

Section: E Screen Grid Erosionmentioning

confidence: 99%

“…Early in the NSTAR program, the thruster was wear-tested without a keeper and severe erosion of the cathode orifice plate and heater ocurred. 7 Subsequent to that test, a sacrificial keeper was added to protect the cathode. 8 Once the keeper is sufficiently eroded to constitute its end of life, the cathode and heater are exposed and their erosion rates dramatically increase, but the keeper end of life would not result in the end of life of the thruster.…”

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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“…Previous ion engine wear tests revealed unanticipated wear mechanisms [16,17,18]. Experimental evaluations form the backbone of the NEXT validation process and are essential to life demonstration.…”

Section: Thruster Life Testing and Assessmentmentioning

confidence: 99%

Ion Engine and Hall Thruster Development at the NASA Glenn Research Center

2002

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NASA’s Glenn Research Center has been selected to lead development of NASA’s Evolutionary Xenon Thruster (NEXT) system. The central feature of the NEXT system is an electric propulsion thruster (EPT) that inherits the knowledge gained through the NSTAR thruster that successfully propelled Deep Space 1 to asteroid Braille and comet Borrelly, while significantly increasing the thruster power level and making improvements in performance parameters associated with NSTAR. The EPT concept under development has a 40 cm beam diameter, twice the effective area of the Deep-Space 1 thruster, while maintaining a relatively-small volume. It incorporates mechanical features and operating conditions to maximize the design heritage established by the flight NSTAR 30 cm engine, while incorporating new technology where warranted to extend the power and throughput capability. The NASA Hall thruster program currently supports a number of tasks related to high power thruster development for a number of customers including the Energetics Program (formerly called the Space-based Program), the Space Solar Power Program, and the In-space Propulsion Program. In program year 2002, two tasks were central to the NASA Hall thruster program: 1.) the development of a laboratory Hall thruster capable of providing high thrust at high power; 2.) investigations into operation of Hall thrusters at high specific impulse. In addition to these two primary thruster development activities, there are a number of other on-going activities supported by the NASA Hall thruster program. These additional activities are related to issues such as thruster lifetime and spacecraft integration.

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2.3 kW ion thruster wear test

Cited by 30 publications

References 7 publications

Characterization of Cathode Keeper Wear by Surface Layer Activation

Characterization of Cathode Keeper Wear by Surface Layer Activation

Lifetime Assessment of the NEXT Ion Thruster

Ion Engine and Hall Thruster Development at the NASA Glenn Research Center

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