ST7-DRS Colloid Thruster System Development and Performance Summary

Hruby, Vlad; Spence, Douglas; Demmons, Nathaniel; Roy, Thomas; Ehrbar, Eric; Martin, Roy; Ziemer, John; Randolph, Thomas; Connolly, William; Rhodes, Scott A.; Tolman, Warren

doi:10.2514/6.2008-4824

Cited by 29 publications

(17 citation statements)

References 4 publications

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“…Busek Co. Inc. designed, tested, and operated an ionic liquid capillary system for the NASA LISA (Laser Interferometer Space Antenna) mission before its ultimate cancelation. [2][3][4] State-of-the-art needle-style emitters include the scalable ion Electrospray Propulsion System (s-iEPS), which was recently delivered to NASA for use as a propulsion system for cubesats. [5] Mass spectra of ionic liquid electrospray thruster systems have been reported in the literature for both styles of emitters operating in the low mass-to-charge regime.…”

Section: Introductionmentioning

confidence: 99%

Mass Spectrometry of Selected Ionic Liquids in Capillary Electrospray at Nanoliter Volumetric Flow Rates

Miller

Prince²,

Bemish³

et al. 2016

52nd AIAA/SAE/ASEE Joint Propulsion Conference

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Capillary-based electrospray thrusters allow user-enabled control of the volumetric flow rate of the propellant. This control, coupled with mass spectrometry techniques spanning a large mass-to-charge range, enables elucidation of the composition of the electrospray beam and through further analyses, a better understanding of the physics occurring at the liquid/vacuum interface. In this work, mass spectra of selected ionic liquids electrosprayed from a capillary emitter are measured, using time-of-flight mass spectrometry, over a wide range of volumetric flow rates. The time-of-flight mass spectrometer enables simultaneous acquisition over a mass-to-charge range of 20 amu/q to ~500,000 amu/q in a single pulse cycle. Additionally, the use of orthogonal extraction enables direct determination of the kinetic energies of ions present in the electrosprayed beam. The presented data reveal a complex emission process occurring for ionic liquid capillary-based electrospray at nanoliter volumetric flow rates. The electrospray beam mass-to-charge composition includes a sequence of singly-charged ions and doubly-charged ions at nearly all sampled flow rates for all electrosprayed ionic liquids. In addition to the small ion-clusters, two Maxwell-Boltzmann distributions from approximately 10,000 amu/q to 500,000 amu/q exist in the spectra each with mass-to-charge distribution sensitive to the volumetric flow rate. The volumetric flow rate dependence of the largest charge-to-mass ratio droplets appears to be consistent with previously measured scaling laws, although exhibiting a wide mass-to-charge distribution. The flow rate dependence of the lower mass-to-charge distribution is more complex and is discussed in some detail. Measurement of the time-of-flight mass spectrum for a number of different ion kinetic energy defects over a number of different volumetric flow rates results in a more thorough understanding of kinetic energy losses experienced in the jet structure of the Taylor cone, with direct impacts to the thrust performance of these types of devices. The appearance of these ions and distributions alter the thought on the emission mechanism at work in the electrospray system. No longer is electrospray defined and easily explained by the Iribarne emission mechanism and droplet generation by the Rayleigh instability.

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Section: Introductionmentioning

confidence: 99%

Mass Spectrometry of Selected Ionic Liquids in Capillary Electrospray at Nanoliter Volumetric Flow Rates

Miller

Prince²,

Bemish³

et al. 2016

52nd AIAA/SAE/ASEE Joint Propulsion Conference

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“…k ( k s mgL cm for hanging pendulums k s − mgL cm for inverted pendulums (6) Clearly, for inverted pendulums, the gravity torque must not exceed the spring torque; otherwise, the restoring force is negative and the pendulum is unstable.…”

Section: B Pendulum Thrust Stand Dynamicsmentioning

confidence: 99%

“…In some cases, the frequency-dependent thrust noise level generated by the thruster is an important measurement parameter. For instance, the thrusters for the Space Technology 7/Laser Interferometer Space Antenna (ST7/LISA) Pathfinder mission had to demonstrate a thrust noise level less than 0.1 μN∕ Hz p for frequencies between 1 mHz and 4 Hz, which is a requirement driven by the control algorithm for the disturbance reduction system [6]. In addition to having adequate frequency response, as discussed previously, the thrust stand must have a noise floor (noise in the response with no thrust load) significantly lower than the requirement the thruster must meet.…”

Section: Resolutionmentioning

confidence: 99%

“…With an inverted pendulum configuration, the torque produced by the thruster weight counters the spring torque and reduces the effective spring constant, as shown in Eq. (6). By carefully balancing the length of the pendulum and the thruster mass with the spring stiffness so that the gravity torque approaches the spring torque, very large deflections in proportion to applied thrust can be obtained.…”

Section: B Inverted Pendulum Thrust Standsmentioning

confidence: 99%

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Recommended Practice for Thrust Measurement in Electric Propulsion Testing

Polk

Pancotti

Haag

et al. 2017

Journal of Propulsion and Power

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The accurate, direct measurement of thrust or impulse is one of the most critical elements of electric thruster characterization, and it is one of the most difficult measurements to make. This paper summarizes recommended practices for the design, calibration, and operation of pendulum thrust stands, which are widely recognized as the best approach for measuring micronewton-to millinewton-level thrust and micronewton-per-second-level impulse bits. The fundamentals of pendulum thrust stand operation are reviewed, along with the implementation of hanging pendulum, inverted pendulum, and torsional balance configurations. The methods of calibration and recommendations for calibration processes are presented. Sources of error are identified, and methods for data processing and uncertainty analysis are discussed. This review is intended to be the first step toward a recommended practices document to help the community produce high-quality thrust measurements.

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“…The DRS includes two clusters of four Colloid MicroNewton Thrusters (CMNT) 6,7 . The cesium propellant used by the Cs-FEEP is a reactive metal that could potentially cause the CMNT thrusters to short out if a monolayer of cesium accumulated on the insulator between electrodes.…”

Section: Introductionmentioning

confidence: 99%

Cesium Exposure Test of the Colloid Micro-Newton Thruster for the LISA Pathfinder Mission

Anderson¹,

Ziemer²,

Bulit³

2012

48th AIAA/ASME/SAE/ASEE Joint Propulsion Conference &Amp;amp; Exhibit

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The LISA Pathfinder (LPF) Mission, a joint ESA-NASA mission, is a demonstration mission of technologies needed for future laser interferometry gravity wave observatory missions. Such missions would consist of multiple spacecraft flying in formation with each spacecraft surrounding a proof mass at the end of a laser interferometer leg. The spacecraft is used to shield the proof mass from disturbances such as the solar wind. Among the technologies to be demonstrated on LPF are micro-propulsion thrusters that are part of the Disturbance Reduction System (DRS) designed to maintain the spacecraft position relative to the proof mass within 10 nm. Both cesium Field Emission Electric Propulsion (Cs-FEEP) thrusters and Colloid Micro-Newton Thrusters (CMNT) are candidate micro-propulsion technologies for these missions. It is possible that both Cs-FEEP and CMNT thrusters may be flown on the same spacecraft in a future mission. If both types of thrusters are flown on the same spacecraft it is likely that a neutral cesium flux from the Cs-FEEP will impinge on the CMNT. A monolayer of cesium on the CMNT insulator would cause the impedance between electrodes to decrease below the 10 GΩ level required for the thruster to operate properly. Modeling and testing was performed to determine if cesium exposure would cause the CMNT insulator impedance to decrease enough to cause a failure or degraded CMNT performance. Cesium exposure testing of a CMNT was performed at ESTEC. The test conditions were more severe than the conditions expected in space during a mission. The CMNT passed the test with full operational capability indicating that cesium exposure would not be a problem during a mission.

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ST7-DRS Colloid Thruster System Development and Performance Summary

Cited by 29 publications

References 4 publications

Mass Spectrometry of Selected Ionic Liquids in Capillary Electrospray at Nanoliter Volumetric Flow Rates

Mass Spectrometry of Selected Ionic Liquids in Capillary Electrospray at Nanoliter Volumetric Flow Rates

Recommended Practice for Thrust Measurement in Electric Propulsion Testing

Cesium Exposure Test of the Colloid Micro-Newton Thruster for the LISA Pathfinder Mission

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