Performance of 8 cm Pyrolytic-graphite Ion Thruster Optics

Haag, Thomas; Soulas, George C.

doi:10.2514/6.2002-4335

Cited by 15 publications

(7 citation statements)

References 5 publications

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“…Impingement-limited total voltage behavior for the flat grids was observed to be similar to an 8-cm ion optics system fabricated from flat pyrolytic graphite that was reported by Haag and Soulas. 12 The dished grids displayed slightly less total perveance margin because of slightly larger gridto-grid spacing than nominal NSTAR values near the central regions of the assembly. The test results obtained to date using C-C composites support the feasibility of directly replacing grid assemblies fabricated from molybdenum.…”

Section: Discussionmentioning

confidence: 98%

“…These perveance limit tests were performed by setting the beam voltage to a value ∼300 V above where direct impingement of ions on the accelerator grid would occur and slowly decreasing the beam voltage until the rate of rise of impingement current rose above 0.003 mA/V. This value was chosen to be near the value used by Haag and Soulas 12 and by the resolution of the impingement current and beam voltage measurements. A typical impingement current vs beam voltage plot is shown in Fig.…”

Section: Ion Optics System Evaluationmentioning

confidence: 99%

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Performance Evaluation of 8-cm-diam Ion Optics Assemblies Fabricated from Carbon-Carbon Composites

Rawal¹,

Perry²,

Williams³

et al. 2006

Journal of Propulsion and Power

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Performance data are presented on two sets of 8-cm-diam carbon-carbon (C-C) composite ion optics assemblies. Each C-C grid was designed and fabricated to grid feature geometries that were identical to the NSTAR ion engine, and their performance was characterized by mounting them to an 8-cm-diam plasma source. The only difference between the assemblies was that one set was dished while the other set was flat. Electron backstreaming and impingement-limited total voltage data were measured over wide beam current ranges for both the flat and dished ion optics assemblies. Electron backstreaming performance was observed to be in good agreement with NSTAR data. Impingement-limited total voltage behavior for the flat grids was observed to be similar to an 8-cm ion optics system fabricated from pyrolytic graphite. The dished grids displayed less total voltage margin because of slightly larger grid-to-grid spacing near the central regions of the assembly. Random vibration tests were successfully performed up to 29 g rms , which demonstrated the structural integrity of both grid assemblies. Test data are also presented for subscale ion optics assemblies (gridlets) that were fabricated from carbon-carbon composites using the same processes used to fabricate full-size grid assemblies. The gridlets were used to characterize impingement and backstreaming limits on beamlet current over intragrid electric field conditions ranging from 2.3 to 3.4 kV/mm. The test results reported herein using carbon-carbon composites support the feasibility of directly replacing grid assemblies fabricated from molybdenum. A discussion is also presented of the anticipated lifetime enhancement afforded by carbon-based ion optics systems that show the promise of low sputter erosion rates. Nomenclatured = diameter, mm f = frequency, Hz Isp = specific impulse, s J = current, A j = current density of bombarding ions, A/m 2 = distance, mm m = mass of an atom of a surface being sputtered by energetic ion bombardment, kg Q = resonance quality factor, m/m t = thickness, mm V = voltage, V Y = sputter yield, atoms/ion β = propellant throughput enhancement factor ρ = density, gm/cm 3 Subscripts a = accelerator B = beam b= beamlet (or per aperture set quantity) C = carbon COL = crossover limit cc = center to center g = grid Mo = molybdenum min = minimum n = natural PL = perveance limit rms = root mean square s = screen t = thickness or total

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Section: Discussionmentioning

confidence: 98%

Section: Ion Optics System Evaluationmentioning

confidence: 99%

Performance Evaluation of 8-cm-diam Ion Optics Assemblies Fabricated from Carbon-Carbon Composites

Rawal¹,

Perry²,

Williams³

et al. 2006

Journal of Propulsion and Power

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“…Initial results showed operational performance similar to that of molybdemun grids. 14 Lifetime estimates using such materials predicts improvements over molybdenum of a factor of 5 or more.…”

Section: Figure 2 Power Processing Unitmentioning

confidence: 99%

“…For the ion thruster system, lifetime was assumed possible using advanced grid technologies including thick molybdenum titanium, or carbon based technologies (pyrolitic graphite). 14 Shown in Table 1 are the system assumptions for the outer p lanetary target orbiters. The housekeeping power was limited to 60 W during thrusting.…”

Section: Systems Analvsesmentioning

confidence: 99%

Radioisotope Electric Propulsion for Fast Outer Planetary Orbiters

Oleson

Benson²,

Gefert³

et al. 2002

38th AIAA/ASME/SAE/ASEE Joint Propulsion Conference &Amp;amp; Exhibit

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“…For the ion thruster system, lifetime was assumed possible using advanced grid technologies including thick molybdenum, titanium, or carbon based technologies (pyrolitic graphite) (Haag, 2002). Specific impulse was optimized in the analysis to guide future development.…”

Section: Systems Analysesmentioning

confidence: 99%