Post-Test Analysis of the Deep Space 1 Spare Flight Thruster Ion Optics

Anderson, John R.; Sengupta, Anita; Brophy, John R.

doi:10.2514/6.2004-3610

Cited by 14 publications

(24 citation statements)

References 11 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…By examining the beam profiles and radial dependence of grid erosion observed during the ELT [7], it is apparent that the changes in screen grid ion transparency observed during the ELT must be primarily caused by erosive thinning of the screen grid that predominately occurred near the center region of the overall grid area. Therefore, increases in screen grid ion transparency over the life of the thruster at the center gridlet (as observed in the ELT results discussed later) should be much higher than that of the entire beam.…”

Section: B Electron Backstreaming Integration Over Single Gridlets Amentioning

confidence: 98%

“…Posttest analysis of the NSTAR thrusters at the conclusion of the LDT and ELT tests showed that the center region of the grids experienced the most erosion and accelerator grid aperture enlargement, features which lead to increased electron backstreaming [1,7]. This worst-case erosion was simulated in [6] for the full duration of the ELT.…”

Section: A Inputs and Gridlet Potential Solutionsmentioning

confidence: 99%

See 1 more Smart Citation

Electron Backstreaming Determination for Ion Thrusters

Wirz

Katz

Goebel

et al. 2011

Journal of Propulsion and Power

View full text Add to dashboard Cite

Electron backstreaming in ion thrusters is caused by the random flux of beam electrons past a potential barrier established by the accelerator grid. A technique that integrates this flux over the radial extent of the barrier reveals important aspects of electron backstreaming phenomena for individual beamlets, across the thruster beam, and throughout thruster life. For individual beamlets it was found that over 99% of the electron backstreaming occurs in a small area at the center of the beamlet that is less than 20% the area of the beamlet at the potential barrier established by the accelerator grid. For the thruster beam it was found that over 99% of the backstreaming current occurs inside of r 6 cm for the over 28 cm diameter NSTAR grid. Initial validation against extended life test data for the NSTAR thruster shows that the technique provides the correct behavior and magnitude of electron backstreaming limit, jV ebs j. From the sensitivity analyses it is apparent that accelerator grid chamfering due to sputter erosion contributes significantly to the sharp rise in electron backstreaming limit observed in the extended life test, but does not explain the rise in grid ion transparency. Reduction of the grid gap over the life of the thruster also contributes to increases in electron backstreaming limit and increases in ion transparency. Screen grid erosion contributes generally to rises in jV ebs j and grid ion transparency, but for the assumptions used herein, it appears to not have as much of an effect as chamfering or grid gap change. Overall, it is apparent that accelerator grid chamfering, grid gap change, and screen grid erosion are important to the increase in electron backstreaming observed during the NSTAR extended life test. Nomenclature c = average thermal speed e = electron charge f ebs = electron backstreaming fraction I ebs = electron backstreaming current I i = ion current n bp = average downstream beamlet plasma density n e = electron density r = radius r max = maximum radius of the accelerator grid aperture T e = electron temperature V ebs = electron backstreaming limit e = electron flux = local potential bp = beam potential m = minimum potential along for a radial distance from beamlet axis

show abstract

Section: B Electron Backstreaming Integration Over Single Gridlets Amentioning

confidence: 98%

Section: A Inputs and Gridlet Potential Solutionsmentioning

confidence: 99%

Electron Backstreaming Determination for Ion Thrusters

Wirz

Katz

Goebel

et al. 2011

Journal of Propulsion and Power

View full text Add to dashboard Cite

show abstract

“…Posttest mass measurements of the screen and accelerator-grid assembly made with a high-precision balance concur with the profilometry calculations to within 2 and 10%, respectively, thereby validating the profilometry mapping technique and subsequent data analysis performed [18].…”

Section: Posttest Inspectionmentioning

confidence: 99%

“…Analytical and computational analysis [17] is also associated with the posttest analysis, including a finite element model analysis of the stresses experienced by the grids during operation. A more detailed quantitative analysis of the ion-optics wear and posttest condition, as well as measurement techniques used, can be found in [18].…”

Section: Posttest Inspectionmentioning

confidence: 99%

Deep Space 1 Flight Spare Ion Thruster 30,000-Hour Life Test

Sengupta¹,

Anderson²,

Garner³

et al. 2009

Journal of Propulsion and Power

Self Cite

View full text Add to dashboard Cite

The extended-life test of the Deep Space 1 flight spare ion thruster was voluntarily terminated on 26 June 2003. During its five-year run, the thruster operated for a total of 30,352 h, processed 235.1 kg of xenon propellant, and demonstrated extended operation at multiple throttled conditions. The objectives of the test were to characterize failure modes and quantify thruster performance as a function of engine wear and throttle level. Degradation processes included erosion of the discharge cathode keeper, accelerator-grid sputter erosion, and deposition of material in the neutralizer cathode at low power. Performance degradation was limited to a reduction in measured thrust at the full-power point for the final 1000 h of operation. Posttest inspection of the engine was initiated following the test termination to ascertain causes of the wear and to look for any previously unknown wear processes. Significant findings included facility-induced flakes in the discharge chamber, the presence of through-pits in the accelerator-grid webbing, significant erosion of the discharge cathode orifice plate, and healthy cathode inserts. A summary of the beginning-of-test and end-of-test performances and results of the posttest destructive evaluation are presented.

show abstract

“…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. 51 It is possible to correlate the net erosion of the screen grids between the NSTAR thruster and the NEXT thruster. The net erosion on the screen grid per mass of propellant throughput, shown in Eq.…”

Section: E Screen Grid Erosionmentioning

confidence: 99%

Lifetime Assessment of the NEXT Ion Thruster

VanNoord

2007

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

View full text Add to dashboard Cite

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.

show abstract

Post-Test Analysis of the Deep Space 1 Spare Flight Thruster Ion Optics

Cited by 14 publications

References 11 publications

Electron Backstreaming Determination for Ion Thrusters

Electron Backstreaming Determination for Ion Thrusters

Deep Space 1 Flight Spare Ion Thruster 30,000-Hour Life Test

Lifetime Assessment of the NEXT Ion Thruster

Contact Info

Product

Resources

About