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Professor Ben Jorns receives AIAA Best Paper Award for electric propulsion research

Congratulations to Dr. Ben Jorns for receiving the AIAA Best Paper Award from the Electric Propulsion Technical Committee!| Medium Read
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IMAGE:  Assistant Professor Ben Jorns receives AIAA Best Paper Award

Congratulations to Dr. Ben Jorns for receiving the AIAA Best Paper Award from the Electric Propulsion Technical Committee for his publication, “Mechanisms for Pole Piece Erosion in a 6-kW Magnetically-Shielded Hall Thruster.”

Dr. Jorns is shedding light on fundamental phenomena, such as “pole erosion,” that limit the performance of highly efficient electric propulsion technologies, specifically Hall (effect) thrusters. In contrast to conventional rocket engines that combust propellants, Hall thrusters accelerate streams of ions to great velocities to propel spacecraft. Their low-thrust nature means they must be operated for long durations, as Dr. Jorns explains:

“While [Hall thrusters] have excellent performance and efficiency, both of which can translate to significant spacecraft mass and mission cost savings, one of the traditional limitations of these devices is lifetime.  They are inherently low-thrust devices; so, to generate meaningful maneuvers in orbit, they must be operated continuously for thousands of hours. Due to the interaction of their high-energy exhaust with the thruster support structure, wear and erosion of the device can be problematic on these long timescales.”

A current technique for mitigating this observed erosion involves incorporating ‘magnetic shielding’ into the spacecraft to prevent high-energy ions from bombarding the discharge chamber.  Though early experiments indicate that such shielding can successfully decrease erosion of these chambers, a baffling new incidence of wear has been observed. Dr. Jorns notes:

“It was found in the some of the life studies where magnetic shielding was demonstrated, other parts of the thruster, namely the downstream surfaces of the magnetic poles, exhibited unexpected erosion. While follow-on studies showed that this erosion rate was low and could be in principle mitigated through the use of a sacrificial graphite shield, there was not a first-principles understanding of what caused this erosion.  This lack of understanding represents a potential risk for flying this hardware.”

We showed for the first time - unambiguously - that the erosion of the poles in the magnetically shielded thrusters can in part be attributed to ions that have trajectories directed back toward the poles.Ben Jorns

Dr. Jorns’ winning paper was dedicated toward examining, both analytically and experimentally, the unknown mechanisms driving this downstream pole erosion. He explains:

“We performed measurements of the ion velocity flow field and flux in this region of interest. This was particularly challenging… as the signal to noise in this area is very low. With significant iteration, we were able to make this measurement and generate maps of the flow fields in these regions.  We showed for the first time – unambiguously – that the erosion of the poles in the magnetically shielded thrusters can in part be attributed to ions that have trajectories directed back toward the poles.”

These insights are actively guiding Dr. Jorns’ investigations through UM Aero’s PEPL research groups:

“One of the conclusions that emerged from this work is that the pole erosion may be attributed to oscillations in the thruster exhaust or shifts in the plume divergence. I am exploring both of these hypotheses with members in my group by leveraging sophisticated time-resolved Laser Induced Fluorescence techniques.”

Dr. Jorns conducted this research as a Technologist in the Electric Propulsion group at the NASA Jet Propulsion Laboratory. This study was performed in support of the joint NASA Glenn Research Center and JPL development of Hall Effect Rockets with Magnetic Shielding (HERMES) by NASA’s Space Technology Mission Directorate through the Solar Electric Propulsion Technology Demonstration Mission (SEP TDM).

He would like to acknowledge his fellow co-authors:

  • Christopher Dodson, JPL Affiliate, Electric Propulsion Group; Doctoral Candidate, UCLA
  • John Anderson, Senior Engineer, Electric Propulsion Group, Jet Propulsion Laboratory
  • Dan M. Goebel, Senior Research Scientist, Thermal and Propulsion Engineering Section, Jet Propulsion Laboratory
  • Richard R. Hofer, Group Supervisor, Electric Propulsion Group, Jet Propulsion Laboratory
  • Michael Sekerak, Spacecraft and Mission Systems Engineer, NASA Goddard Space Flight Center
  • Alejandro Lopez Ortega, Engineer, Electric Propulsion Group, Jet Propulsion Laboratory
  • Ioannis Mikellides, Principal Engineer, Electric Propulsion Group, Jet Propulsion Laboratory
Portrait of Kim Johnson

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