Random and Sine-Spectrum Vibration Testing of Pyrolytic Graphite Ion Optics

Polaha, Jonathan; Meckel, Nicole; Welander, Benjamin; Juhlin, Nils; Haag, Thomas

doi:10.2514/6.2005-4395

Cited by 3 publications

(1 citation statement)

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“…Structural dynamic tests were performed at Aerojet Corporation using identical pyrolytic graphite grids (ref. 19). Aluminum grid extenders were installed around the perimeter of each grid to simulate how a larger flight representative thruster might behave.…”

Section: G Hipepmentioning

confidence: 99%

Mechanical Design of Carbon Ion Optics

Haag¹

2005

41st AIAA/ASME/SAE/ASEE Joint Propulsion Conference &Amp;amp; Exhibit

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Carbon Ion Optics are expected to provide much longer thruster life due to their resistance to sputter erosion. There are a number of different forms of carbon that have been used for fabricating ion thruster optics. The mechanical behavior of carbon is much different than that of most metals, and poses unique design challenges. In order to minimize mission risk, the behavior of carbon must be well understood, and components designed within material limitations. Thermal expansion of the thruster structure must be compatible with thermal expansion of the carbon ion optics. Specially designed interfaces may be needed so that grid gap and aperture alignment are not adversely affected by dissimilar material properties within the thruster. The assembled thruster must be robust and tolerant of launch vibration. The following paper lists some of the characteristics of various carbon materials. Several past ion optics designs are discussed, identifying strengths and weaknesses. Electrostatics and material science are not emphasized so much as the mechanical behavior and integration of grid electrodes into an ion thruster. Nomenclature Eelastic modulus σ f stress at failure ρ material density C TE coefficient of thermal expansion Poisson's ratio r grid radius d grid gap t grid thickness p electrostatic pressure δ axial deflection I. IntroductionElectrostatic ion propulsion is being considered for a number of demanding space missions by NASA and other organizations. The high specific impulse provided by these thrusters is viewed as an enabling technology, without which some missions might be impossible. Some of the first efforts to fabricate carbon fiber ion optics were made by the Jet Propulsion Laboratory. These were relatively small ion optics assemblies, typically 10 to 15 cm in diameter (refs. 1 and 2). Circular and slit-type apertures were investigated, and implied major consequences on carbon fiber integrity (refs. 3 and 4). Success of the NASA Solar Electric Propulsion Technology and Readiness (NSTAR) program focused interest on 30 cm ion optics, and JPL fabricated carbon fiber ion optics intended as an alternative to the molybdenum grids that had been baselined (ref. 5). The more recent Carbon Based Ion Optics (CBIO) program directed significant resources toward large-diameter carbon optics, including both carbon fiber composites and pyrolytic graphite (refs. 6 and 7). NASA Glenn Research Center (GRC) successfully pursued pyrolytic graphite (PG) ion optics development under the Energetics Program, demonstrating good laboratory performance and structural integrity (refs. 8 and 9). Lessons learned in the CBIO program were used as a starting point for the higher power Nuclear Electric Xenon Ion System (NEXIS) thruster (ref. 10). In a similar way, NASA GRC designed and tested large PG ion optics designs under the High Power Electric Propulsion (HiPEP) program (ref. 11). There has also been significant international success with ion propulsion. The Artemis spacecraft, sponsored by the European Space Agency (ES...

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Section: G Hipepmentioning

confidence: 99%