Thomas Underwood Wins AFOSR YIP to Develop Electric Propulsion for Low Orbit Altitudes

December 9, 2020

photo of thomas underwood

Thomas Underwood, who is joining the Department of Aerospace Engineering and Engineering Mechanics as an assistant professor on Jan. 1, 2021, has received an Air Force Office of Scientific Research (AFOSR) Young Investigator Program (YIP) award to develop a novel type of electromagnetic propulsion. This new thruster could enable engineers to design a new class of cost-effective satellites that are capable of flying at lower orbital altitudes, surviving longer mission times and producing higher imaging resolution.

In 2020, the AFOSR awarded approximately $16.1 million in grants to 36 scientists and engineers who submitted winning research proposals from a pool of over 215 submissions. According to an AFOSR news release, the program’s objective “is to foster creative basic research in science and engineering, enhance early career development of outstanding young investigators, and increase opportunities for the young investigators to recognize the Air Force mission and the related challenges in science and engineering.”

Underwood was selected for the proposal titled “Air-Breathing Magneto-Deflagration Propulsion for Sustained Very Low Earth Orbit” for which he and his students will build a new type of “air-breathing” electromagnetic thruster and test it on conditions that replicate very low Earth orbit (VLEO) – altitudes of orbit below 450 km.

Underwood’s goal for this work is to develop an electric propulsion system that allows satellites to fly at VLEO without the need to store propellant onboard. Satellites that have the capability to operate at lower orbits could potentially reduce cost, timelines and requirements that are usually involved with conventional launches.

Currently, electric propulsion (EP) is being used – and works very well – for satellites traveling at high altitude orbits because there are fewer air molecules around to create drag. However, EP typically requires operating on optimized propellants for efficient operation, which means the propellant for the entire mission duration must be stored onboard a satellite.

Sustaining satellite flight at lower altitudes has more engineering challenges. The increased air resistance at lower altitudes creates more drag on the satellite, which requires more thrust, so a tremendous amount of fuel would need to be stored onboard the satellite in order to maintain its operation. These challenges could make long mission designs impractical or even impossible for the satellite to maintain VLEO.

Underwood’s unique solution to tackle these challenges is two-fold. Instead of storing propellant onboard, he proposes taking advantage of the higher density of air molecules that are moving around in VLEO by harvesting them, thus creating an “air breathing” system.

“The challenge for operating in low orbit is that there is a higher density of air molecules,” Underwood said. “This does two things; it increases drag, but also allows for an opportunity to harvest these air molecules and then accelerate them for propulsion, instead of carrying fuel onboard the satellite.”

Underwood said that after the air molecules have been collected, or “scooped in” at a low velocity, they would need to be ejected at a high velocity to create the necessary thrust. This can be done using a “magneto-deflagration thruster” – a type of electromagnetic plasma gun that ionizes propellant streams and then uses the Lorentz force to accelerate them.

“Once we’ve collected the air molecules, how do we accelerate them from a low to high velocity? We pump a lot of electrical energy into them, creating a plasma,” Underwood said. “Once we create a plasma, we can then accelerate it to very high velocities using electric and magnetic fields.” 

photo of magneto-deflagration accelerator
Long exposure image capturing the firing of a magneto-deflagration accelerator. The clear jet that forms at the exit plane of the device results in efficient acceleration.

The ultimate goal of the research is to build a modular air-breathing magneto-deflagration thruster and test it in VLEO environments. Underwood’s team will then assess the performance, longevity and reliability of the novel thruster technology while operating on air.

The AFOSR YIP award is a three-year grant totaling $450,000. Two graduate students will be funded to assist with the research.

Underwood earned his Ph.D. in mechanical engineering from Stanford University where he engineered new methods to visualize and stabilize hydromagnetic plasma jets. As a postdoctoral researcher at Harvard University in Professor George Whitesides’ lab, he explored unconventional techniques to store and compute using chemistry along with applications of reactive chemistry.

Underwood’s research focuses on understanding how reactive transport in fluids can be coupled with interfacial chemistry in the context of hypersonics, space propulsion, catalysis, photonics and chemical separation/recovery, with a primary focus on experimentally investigating how partially ionized and non-equilibrium flows can be applied to enable new technologies. Learn more about his research on the Underwood Lab website.