To develop spacecraft that can “maneuver without regret,” the U.S. Space Force is providing $35 million to a national research team led by the University of Michigan. It will be the first to bring fast chemical rockets together with efficient electric propulsion powered by a nuclear microreactor.
The newly formed Space Power and Propulsion for Agility, Responsiveness and Resilience Institute involves eight universities, and 14 industry partners and advisers in one of the nation’s largest efforts to advance space power and propulsion, a critical need for national defense and space exploration.
Right now, most spacecraft propulsion comes in one of two flavors: chemical rockets, which provide a lot of thrust but burn through fuel quickly, or electric propulsion powered by solar panels, which is slow and cumbersome but fuel efficient. Chemical propulsion comes with the highest risk of regret, as fuel is limited. But in some situations, such as when a collision is imminent, speed may be necessary.
Meanwhile, electric propulsion could be much faster, such as with a 100-kilowatt Hall thruster built at U-M. The problem is finding the power to run these thrusters.
“The space station generates about 100 kilowatts of power, but the solar arrays are the size of a couple of football fields, and this is too large for some of the power-hungry applications that are of interest to the Space Force,” said Benjamin Jorns, associate professor of aerospace engineering and institute director.
To power faster, efficient electric propulsion, one subteam is developing a concept for a nuclear microreactor, exploring the early feasibility of a new path for safe, reliable and sustainable nuclear power for space.
Others will build technologies to turn the heat from a microreactor into usable electricity, and electric engines to turn the electricity into thrust. The propulsion system design includes a chemical rocket for quick maneuvers.
While chemical rockets need fuel to burn, electric propulsion needs propellant to accelerate. Both generate thrust by shooting out material opposite the direction of travel. Electric thrusters strip electrons off the propellant atoms — turning them into ions — and use electric fields to accelerate them to extremely high speeds.
To simplify refueling, the team is trying to demonstrate fuels that can be used to drive the chemical rocket, and which are also effective propellant for electric propulsion.
“The Space Force is tasked with securing America’s interests in, from and to space,” said Joshua Carlson, the Space Force program manager for this effort. “We’re very pleased to work with University of Michigan, and their partners, just like we are for all our other efforts under the USSF University Consortium, as we seek to maintain the Space Force’s edge in great power competition.”
Each piece of this prospective system, and the way the pieces connect, contain interesting problems for the team of researchers to dig into. The subteams building devices combine academic and small-business partners to pave the way for commercial manufacturing. Collaborators at Ultra Safe Nuclear Corp. will design a new lightweight microreactor while engineers at U-M will build a heat source that can mimic its output to test the other components of the power and propulsion system.
Two teams will explore how to extract the thermal energy as electricity. U-M and Spark Thermionics will investigate thermionic emission cells, which take advantage of the difference between the heat of the reactor and the cold of space to help drive an electrical current. Another U-M team will pair with Antora Energy to implement thermal photovoltaics, like solar cells that turn heat into electricity.
Cornell University, Advanced Cooling Technologies and Ultramet will design lightweight panels that can extract waste heat and radiate it out into space, as the reactor will produce more energy than either conversion approach can realistically use. The University of Wisconsin, U-M and Cislunar Industries will design a power processing module that will convert the electricity extracted from the microreactor so that it can meet the high power demands of the electric engine.
Subteams will explore three different styles of electric propulsion: the Hall thruster (Jorns’ team at U-M), the applied-field magnetoplasmadynamic thruster (Princeton University and Champaign Urbana Aerospace) and the electron cyclotron resonance thruster (University of Washington and NuWaves Inc.).
Any of these thrusters will rely on a module that turns the propellant into a gas, developed by Western Michigan University and Champaign Urbana Aerospace, and a cathode to prevent the spacecraft from accumulating an electric charge by neutralizing the propellant, developed by Colorado State University.
A new concept for a chemical rocket will be developed by U-M and Pennsylvania State University. Benchmark Space Systems will provide an already developed commercial system for a proof-of-concept test.
The project will be supported with computer modeling and experimental diagnostics developed by U-M, Cornell, Colorado State and the University of Colorado. Analytical Mechanics Associates will assess the full system.
“We are very grateful to the U.S. Space Force and Air Force Research Laboratory for this opportunity. We’re excited to get started on this work with this exceptional national team,” Jorns said.
Eric Viges, a senior engineer at U-M’s Space Physics Research Laboratory, will be a chief engineer. U-M subteam leads include:
- Andrej Lenert, associate professor of chemical engineering.
- Stephen Forrest, Peter A. Franken Distinguished University Professor of Engineering, Paul G. Goebel Professor of Engineering, professor of electrical engineering and computer science, and of material science and engineering.
- Mark Kushner, William P. Allis Distinguished University Professor of Electrical Engineering and Computer Science, George I. Haddad Collegiate Professor of Electrical Engineering and Computer Science, professor of electrical engineering and computer science, of nuclear engineering and radiological sciences, and of chemical engineering.
- John Foster, professor of nuclear engineering and radiological sciences, and of aerospace engineering.
- Solomon Adera, assistant professor of mechanical engineering.
- Mirko Gamba, associate professor of aerospace engineering.
- Venkat Raman, professor of aerospace engineering, and of mechanical engineering.
- Christopher Limbach, assistant professor of aerospace engineering.
- Alex Gorodetsky, associate professor of aerospace engineering.
- Oliver Jia-Richards, assistant professor of aerospace engineering, and of climate and space sciences and engineering.
Al-Thaddeus Avestruz (electrical and computer engineering) will participate as a consultant.
Leads from other universities are: Sadaf Sobhani, Fabien Royer and Elaine Petro (Cornell); Jinia Roy (Wisconsin); Kristina Lemmer (Western Michigan); John Williams and Azer Yalin (Colorado State); Richard Yetter (Penn State); Edgar Choueiri (Princeton); Justin Little (Washington); and Iain Boyd (Colorado).
Northrop Grumman, Lockheed Martin, Westinghouse and Aerospace Corp. form the advisory board.
