Robert Lobbia

Robert Lobbia
California Institute of Technology | CIT · Jet Propulsion Laboratory

Doctor of Philosophy

About

40
Publications
2,910
Reads
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430
Citations
Citations since 2016
16 Research Items
323 Citations
2016201720182019202020212022020406080
2016201720182019202020212022020406080
2016201720182019202020212022020406080
2016201720182019202020212022020406080
Additional affiliations
June 2011 - August 2017
Air Force Research Laboratory
Position
  • Engineer
Education
September 2003 - December 2009
University of Michigan
Field of study
  • Aerospace Engineering
October 1998 - August 2003
October 1998 - August 2003
University of California, Los Angeles
Field of study
  • Aerospace Engineering

Publications

Publications (40)
Article
We present time-resolved laser-induced fluorescence measurements of ion velocity distributions in a 12.5 kW Hall Effect Rocket with Magnetic Shielding (HERMeS) operating in both quasi-periodic and aperiodic oscillation regimes. Transfer function averaging in Fourier space is used to obtain useable signal-to-noise ratios and synchronize data traces...
Article
We present time-resolved laser-induced fluorescence measurements of ion velocity distributions in a 12.5 kW Hall Effect Rocket with Magnetic Shielding (HERMeS) operating in both quasi-periodic and aperiodic oscillation regimes. Transfer function averaging in Fourier space is used to obtain useable signal-to-noise ratios and synchronize data traces...
Article
We present time-resolved laser-induced fluorescence measurements of ion velocity distributions in a 12.5 kW Hall Effect Rocket with Magnetic Shielding (HERMeS) operating in both quasi-periodic and aperiodic oscillation regimes. Transfer function averaging in Fourier space is used to obtain useable signal-to-noise ratios and synchronize data traces...
Article
We present time-resolved laser-induced fluorescence measurements of ion velocity distributions in a 12.5 kW Hall Effect Rocket with Magnetic Shielding (HERMeS) operating in both quasi-periodic and aperiodic oscillation regimes. Transfer function averaging in Fourier space is used to obtain useable signal-to-noise ratios and synchronize data traces...
Article
We present time-resolved laser-induced fluorescence measurements of ion velocity distributions in a 12.5 kW Hall Effect Rocket with Magnetic Shielding (HERMeS) operating in both quasi-periodic and aperiodic oscillation regimes. Transfer function averaging in Fourier space is used to obtain useable signal-to-noise ratios and synchronize data traces...
Article
We present time-resolved laser-induced fluorescence measurements of ion velocity distributions in a 12.5 kW Hall Effect Rocket with Magnetic Shielding (HERMeS) operating in both quasi-periodic and aperiodic oscillation regimes. Transfer function averaging in Fourier space is used to obtain useable signal-to-noise ratios and synchronize data traces...
Article
We present time-resolved laser-induced fluorescence measurements of ion velocity distributions in a 12.5 kW Hall Effect Rocket with Magnetic Shielding (HERMeS) operating in both quasi-periodic and aperiodic oscillation regimes. Transfer function averaging in Fourier space is used to obtain useable signal-to-noise ratios and synchronize data traces...
Article
We present laser-induced fluorescence measurements of acceleration zone scaling with discharge voltage (Vd), magnetic field strength (B), and facility background pressure (PBG) in NASA’s 12.5 kW Hall Effect Rocket with Magnetic Shielding. At fixed discharge current, the plasma potential profiles at discharge voltages from 300 to 600 V approximately...
Conference Paper
Self-heating hollow cathodes are central components in modern electric thrusters. The plasma discharge inside these devices heats the internal components, thus maintaining the temperatures required for electron emission. Precise knowledge of the physical phenomena governing hollow cathode operation is key to predict their lifetime, specifically, th...
Article
Presented in this work is a guide to standardize the methods of performing correct and accurate Langmuir probe measurements within the plasma environment produced by an electric propulsion device. The construction, installation, operation, and data interpretation of the full family of Langmuir probes are addressed including single Langmuir probes,...
Conference Paper
During a component compatibility test of the NASA HiVHAc Hall thruster, a number of plasma diagnostics were implemented to study the effect of varying facility background pressure on thruster operation. These diagnostics characterized the thruster performance, the plume, and the plasma oscillations in the thruster. Thruster performance and plume ch...
Conference Paper
Past investigations of the 6kW-class H6 Hall thruster during low-voltage operation revealed two operating modes, corresponding to the presence or absence of azimuthal propagating plasma spokes. New evidence is presented that provides insight into the transition between operating modes, including hysteresis and the impact of cathode location. Global...
Article
Improved Hall-effect Thruster (HET) efficiency would enable more extensive cost-capped, Discovery class NASA missions such as robotic missions to Mars and near-Earth asteroids to perform round trip sample-returns. HET efficiency would be further improved if electrons with energies that contribute to ionization are increased, and those involved in t...
Article
Full-text available
The finite, electrostatically achievable, temporal resolution of plasma properties from a turbulent discharge is limited by an array of effects wherein the theory of Langmuir probes breaks down. Formulations for the particle transit time, sheath formation time, plasma-probe resonance, polarization current, sheath capacitance, stray capacitance, and...
Article
Full-text available
In an effort to temporally resolve the electron density, electron temperature, and plasma potential for turbulent plasma discharges, a unique high-speed dual Langmuir probe (HDLP) has been developed. A traditional single Langmuir probe of cylindrical geometry (exposed to the plasma) is swept simultaneously with a nearby capacitance and noise compen...
Article
Summary form only given. Using direct back-to-back high-speed swept Langmuir probe biasing and current measurement, the plasma properties of electron density, electron temperature, plasma potential, floating potential, and the electron energy distribution function are all acquired at a rate of 1-MHz for seamless records in excess of 1-sec. A unique...
Article
The existence of plasma oscillations in the near and far field discharge of a Hall effect thruster alters the conventionally held view of their operation as steady electrostatic propulsion devices. Indeed, the consequences from fluctuations in ionized propellant density, temperature, and potential may include increased thrust, exacerbated engine er...
Conference Paper
Full-text available
Single-point measurements of time-resolved plasma density fluctuations are collected throughout a planar region of the exhaust plume downstream from a Hall effect thruster. A matrix of empirical discrete time transfer functions is created between the thruster discharge current (input) signal and the measured (output) electron density signals, thus...
Article
Full-text available
A High-speed Dual Langmuir Probe system (HDLP) and a high-speed camera tracked 19.6-kHz waves of ionized propellant emitted by the unsteady ionization process or "breathing mode" of a cluster of Hall thrusters. Two 600-W, low-power Hall thrusters were operated together in close proximity with 200-V, 2-A xenon discharges, producing the plume examine...
Article
Summary form only given. The unsteady behavior of a Hall effect thruster discharge is investigated via two-dimensional, time-resolved optical (109,500 frames-per-second) and plasma measurements (100 kHz). Large amplitude unsteady ionization "breathing-mode" fluctuations at 18.4 kHz are observed in the near- and far-field plume electron density, opt...
Conference Paper
In an effort to study the transient fluctuations of plasma properties downstream of a Hall Effect Thruster (HET) on a microsecond timescale, a high-speed Langmuir probe measurement system is developed and tested. A high-voltage (±225 V), broadband (DC - 2 MHz) 30-W power amplifier is constructed to drive the Langmuir probe voltage sweep signal, and...
Article
Full-text available
In an effort to verify the existence of and study the characteristics of the dynamic magnetic fields generated by supplying inner and outer coil Hall thruster electromagnets with wide bandwidth (DC to 200 kHz) currents, B -dot probe experiments have been performed. Several different locations w ere mapped and all three components of the magnetic fi...
Article
This experimental study focused on methanol droplet combustion characteristics during exposure to external acoustical perturbations in both normal gravity and microgravity. Emphasis was placed on examination of excitation conditions in which the droplet was situated (1) at or near a velocity antinode (pressure node), where the droplet experienced t...
Conference Paper
While preliminary experiments with a cluster of four Busek 200-Watt (BHT-200-X3) Closed Drift Hall thrusters indicate reasonable performance scalability from single thruster experiments, cluster plume interactions are believed to give rise to an increased ion energy spectrum as well as cross-talk and synchronization between the thruster discharges....
Conference Paper
This experimental study focused on methanol droplet combustion characteristics during exposure to external acoustical perturbations in both normal gravity and microgravity conditions. Focus was placed on examination of excitation conditions in which the droplet was situated at either: 1) a velocity antinode (pressure node), where the droplet experi...
Article
This study focuses on preliminary experiments involving closed-loop, real-time control of gaseous jets in crossflow via acoustical excitation. Prior studies on the actively controlled transverse jet have involved an open-loop shaping procedure(M'Closkey, R. T., King, J. M., Cortelezzi, L., and Karagozian, A. R., ``The actively controlled jet in cro...
Article
This experimental study focuses on development of a method for performing sustained droplet combustion experiments via closed-loop control. The methodologies described here are especially pertinent in conducting microgravity droplet experiments, where the effects of perturbation conditions on droplet combustion behavior may be explored successively...
Article
This experimental study focuses on understanding and quantifying the effects of external acoustical perturbations on single fuel droplet combustion processes. In the present configuration, a liquid methanol droplet and its surrounding diffusion flame are situated within an essentially one-dimensional (cylindrical) acoustic waveguide where standing...
Article
This talk focuses on controller development studies relevant to mixing optimization associated with the actively controlled jet in crossflow. Complexity in the active (closed loop) control of this flowfield arises due to multiple time scales present in the flow, challenges in the ability to sense data relevant to mixing and/or penetration, and the...
Conference Paper
In general the problem of feedback control for an unsteady fluid flow is nonlinear. Especially challenging is the control of mixing processes in a hot, potentially reactive environment. Because of the high temperatures present, realistic sensors can only operate mainly in cool regions, e.g., away from flames and hot exhaust regions. Consequently, t...
Article
Full-text available
Planar measurements of near-and far-field plume-plasma fluctuations are cataloged for Hall thruster anode operation between 200 V and 400 V, with discharge currents of 1.5-A, 2-A, and 3-A. Single-point temporally resolved electron density, electron temperature, and plasma potential data are acquired by means of an electrostatic High-speed Dual Lang...
Article
Full-text available
A cluster of four 600 Watt Busek BHT-600 Hall thrusters has been evaluated in terms of performance characteristics including the measurement of thrust, anode efficiency, and anode specific impulse. Operation of Hall thrusters in a clustered configuration may conceivably lead to increased charge exchange ions, amplified discharge current instabiliti...
Article
Full-text available
This paper presents preliminary findings from high speed (2 MHz) synchronous measurements of discharge current and ion current density from the far field to very near field of a Hall thruster plume. Recent work in this vein has applied statistical methods to create transfer functions between the thruster discharge current and spatially resolved plu...

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