Understanding electric propulsion: Aerospace researcher shares expert knowledge with NASA

KALAMAZOO, Mich.—Former NASA chief scientist and current undersecretary for science and research at the Smithsonian, Dr. Ellen Stofan, says that one of the best-kept secrets is that those working in STEM have all the fun. “We get to ask, how does the world work? And we go figure it out.” 

For Dr. Kristina Lemmer, associate professor and aerospace researcher at Western Michigan University, working in STEM means figuring out electric propulsion for rockets, Hall thrusters and cube satellites—and sharing expert knowledge with students and the aerospace engineering community, including NASA. 

Lemmer leads important research in plasma engineering with a focus on space electric propulsion—a highly specialized scientific arena—and leads the research and education efforts of the WMU Aerospace Laboratory for Plasma Experiments (ALPE). With funding in excess of $4.5 million, the lab conducts research, testing and modeling for electric propulsion under Lemmer’s expert supervision.

Electric Propulsion: Electric propulsion is a type of in-space propulsion that makes use of electrical power to accelerate a propellant via electric and/or magnetic means. ALPE is developing small thrusters and supporting technologies for a variety of uses, including testing, microwave thruster technologies, cathode oscillation in magnetic fields, and electrospray thruster integration in CubeSats. 

Hall thrusters: The team designed a prototype of a small Hall effect thruster (HET) that is accessible to any university with standard high vacuum, electrical and machining resources. This resulted in significant educational value to students working on the project, while also opening this field of study to additional researchers and encouraging more universities to get involved in electric propulsion research.

Electrospray: Electrospray studies in Lemmer’s lab have been funded by the Air Force Office of Scientific Research’s Space Power and Propulsion Directorate and the Air Force Research Laboratory’s Electric Propulsion Group. This combined experimental and numerical modeling effort was designed to understand how ionic liquids such as hydroxylammonium nitrate (HAN) and Han-based propellants decompose and ionize. Preliminary research resulting from the effort has been published in numerous journals, including Journal of Molecular Liquids and at the 10th and 12th Spacecraft Propulsion Joint Army, Navy, NASA, Air Force Conferences. 

So what is on the horizon for this prolific researcher?

“Really high-power is the next thing,” says Lemmer. “It is almost exclusively a NASA interest at this point, but looking out, I can see a need. Right now, I look for pieces where my research can help, since the facilities for testing nuclear and other high-power propulsion are limited.”

Another area on the horizon is space debris.

“Space debris is a really interesting problem,” says Lemmer. “There are an enormous number of small satellites and constellations that need to de-orbit in 25 years, and the most up-to-date regulation for newly launched satellites is de-orbit in 5 years. How will we clear out the junk?” In her lab, efforts continue toward integration of propulsion systems for CubeSats for maneuvering and de-orbit.

About Dr. Kristina Lemmer

Lemmer earned a Ph.D., M.S. and B.S. in aerospace engineering from the University of Michigan. She is an expert in both physical and non-intrusive plasma diagnostics, electric propulsion and experimental plasma engineering. She teaches courses in thermodynamics; space propulsion systems; advanced and electric propulsion systems; and molecular gas dynamics. 

In recognition of her work to build a space research program at Western and her ongoing research progress, she was elected to the American Institute of Aeronautics and Astronautics (AIAA) Class of 2022 Associate Fellows. “I am very honored to be among the elite in my field of aeronautics and astronautics,” says Lemmer. “To know that the work I do has made an impact is very important to me.”

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