Dr. Alec Gallimore Talks about Space Electric Propulsion and How the University Michigan is Helping to Shape the Future of Space Travel

Robert J. Vlasic Dean of Engineering, Richard F. and Eleanor A. Towner Professor, and Arthur F. Thurnau Professor at the University of Michigan, Dr. Alec D. Gallimore was born in Washington DC to Jamaican immigrant parents. Inspired by science fiction classics like Star Trek and 2001: A Space Odyssey, he became interested in space travel and set his sights on joining NASA’s astronaut corps. As part of this ambition, he came to the University of Michigan to work on electric propulsion as a stepping stone to going into space, but his plan to stay for three years has now grown to 30 years and counting as he pursues cutting-edge space propulsion research and trains the next generation of aerospace engineers. 

Known for his pioneering work on Hall thrusters, Dr. Gallimore is also the founder of the Plasmadynamics and Electric Propulsion Laboratory (PEPL) – one of the world’s premier laboratories for the development of electric propulsion systems. We recently got together with him to find out more about PEPL and his part in its evolution.

Tell us about the Plasmadynamics and Electric Propulsion Laboratory (PEPL). What was your role in its establishment?

PEPL is the lab that I started when I came to Michigan back in the early 90s. It’s the lab that was formed around the big vacuum chamber that I inherited, which is now called the Large Vacuum Test Facility – a 20 by 30-foot vacuum chamber and a small standalone vacuum antechamber connected to it that we call Junior. A Hall thruster is used in space, so to test it on the ground, one has to simulate the vacuum of space. And that’s why you need these vacuum chambers.

What I did was essentially create PEPL with the vacuum chamber, the big one, as the centerpiece. Fast forward now, we’ve greatly enhanced the capability of the vacuum chamber, both in terms of its ability to maintain a low pressure, given the amount of gas you put in through the various Hall thrusters that we test there, as well as a suite of diagnostics we provide, which is probably unmatched, frankly, in any laboratory in this country.

You put all those things together and the laboratory has been really a showpiece in terms of our ability to develop electric propulsion on the globe – certainly in the U.S.

So it isn’t simply a matter of just simply having a vacuum chamber. It’s been specially modified to help with the testing of these engines then. 

Right, it’s more to it than that. The chamber has been modified by replacing and adding more and better pumps, so the chamber now is about 30 times more capable than it was when I inherited it.

What are some of the major projects that the laboratory has been working on? 

If you go by decade, in the first 10 years, it was to take off-the-shelf Russian thrusters and analyze the exhaust coming out of the engine to understand the energetics, the distribution of particles, their speed and also how it affects radio waves to help American companies integrate them with their satellite space systems. Loral, for example, which integrated a Russian Hall, thruster back around 2003, relied on our measurements to help them feel comfortable about integrating the thruster with their satellite and learning how to integrate it. That meant making sure you understand what’s going on, the cost of keeping the life of the spacecraft long but not so far that it’s detrimental to performance.

In the second decade, we did a lot with NASA and the Air Force, mostly to develop a series of prototype thrusters. From 2001 to 2008, we focused a lot on developing our own thrusters and learning how they operate through R&D, modeling, and simulation. And then we worked with NASA to extend the performance so they could be used for deep space. The thrusters that the Russians developed are not optimized for deep space in the higher performance range.

More recently, the big one, of course, is the X3 Mars engine that is the world record holder in terms of power, current, and thrust. This was a three-channel 100-kilowatt class thruster that was a big, important technology demonstration project. And more recently, we worked on a smaller version called N-30 – a two-channel Hall thruster that demonstrated ultra-long life and is probably more like the first kind of Hall thrusters to be used for piloted missions to Mars.

Finally, while as good as our facility is, it’s not a perfect facsimile of what’s going on in space. We’re trying to understand how to take measurements that we collect on the ground and extend them appropriately to space conditions. And then we’re looking at a whole bunch of different types of thrusters beyond Halls and developing very advanced diagnostics so we understand the dynamics of these thrusters.

What would you say were the biggest turning points in your career at Michigan?

I would say a few things. First of all, turning the then-defunct very large vacuum chamber into an electric propulsion facility. That was when Tom Adamson was the chair of the aerospace engineering department. It was really his vision and foresight to rescue this chamber, which people were thinking about dismantling, selling the parts, and then using the floor space. He thought this was an amazing gem that could be used for advanced spacecraft propulsion. And then through his due diligence, he found me. 

I think another turning point is the fact that Dr. Len Caveny was, I think, the director for technology programs for the Ballistic Missile Defense Organization (BMDO). This was in the early 90s, a few years after the Iron Curtain came down and, believe it or not, the BMDO, which is an organization that is supposed to protect the U.S. against ballistic missile attack, ostensibly from the Soviet Union and then ultimately Russia and Ukraine, was actually dealing with Russian and Ukrainian research enterprises to get access to their technology to advance the ballistic missile defense organization mission. So one of those technologies was this Russian nuclear reactor called TOPAZ. Literally, the ballistic missile defense organization that was going to buy a nuclear reactor from the Russians to learn how to build space nuclear reactors to protect us against the Russians.

And then the other one was the Hall thrusters, which appeared to be better than anything we had at the time, at least for Earth orbit applications. And Caveny funded a number of people to go to Russia to bring the Russian thrusters back to be tested at a number of government labs in the U.S. It was at the end of that period that they concluded that these Russian thrusters were for real. They work as advertised. That was when I came to the conclusion that we were in the Hall thruster business. I made that pivot, which now I look back on it, was pretty bold for a junior faculty member because nobody else had decided to go in that direction. 

So that was a big thing. By deciding to adopt the Hall thruster and because of the large chamber that we had, we had a first-mover advantage.

I would also say that one milestone was when I became an associate dean of graduate studies. That was my first formal administrative role. I would guess it kind of set me on the path to where I am right now. 

You are known for your work with Hall thrusters, which we’ve discussed. It’s a type of electric propulsion, but what is electric propulsion? 

In electric propulsion, what happens is a gas is heated to very high temperatures. It converts into a plasma and then we can use electric fields, which are differences in voltages, and magnetic fields to trap and direct and accelerate the plasma to very high speeds, sometimes 10 times faster than what you can get through a chemical system. 

In a chemical system, we might have an exhaust velocity of around four thousand meters a second, which is like 9 thousand miles per hour. We can do 10 times or more that with an electric system, albeit a much lower thrust. So electric thrusters, because of the low thrust and high performance, they’re used once you go up in space. You still need a chemical rocket to get the spacecraft in space. But once it’s in space and you have a lot fewer gas molecules to exert drag on the spacecraft. So there’s almost a pure vacuum. There’s no drag and gravity is different there. Not that it operates in a different way, but the way you counteract gravity is different in space than on the ground. You can actually accelerate spacecraft, even if your thrust to weight ratio is much less than one, which is hard to do on the ground.

And so that’s really the idea of electric propulsion. It’s taking the power generated by the spacecraft and using electric and magnetic fields to accelerate the propellant to produce a lot more thrust per unit mass flow rate than you can with the chemical system. What that allows you to do is to either do the same mission as you would be able to do with a chemical system with a lot less propellant or have the spacecraft accelerate to a much higher speed.

Electric propulsion has been used on certain deep-space missions such as the one to visit various asteroids. Is that the only thing it’s used for or does it have other applications?

Well, actually, it’s been used in Earth orbit for actual missions probably since the early 80s. Many, if not most, of the satellites that are up in geosynchronous orbit, which is around 40,000 kilometers up use it. That’s where your DirectTV satellite is. There’s a dish on the top of the awning of a building. It points to this satellite in orbit, etc. These large and very expensive spacecraft have used some form of electric propulsion for decades.

In fact, they’ve been using Hall thrusters on Russian spacecraft since the ’80s. And they’ve been using Hall thrusters for many types of missions since the turn of the century. They’ve been used for a variety of commercial and even military Earth-orbiting spacecraft. 

What do you see as being the future of electric propulsion?

I think you’re going to see smaller, lower power thrusters. They’re used for CubeSats propulsion and things like that. And then you’re going to see more powerful ones – certainly ones more powerful than what we commonly use right now. They’re going to be used for piloted missions to the Moon and beyond. Then there will be different kinds of electric propulsion devices. Water seems to be commonplace, if not ubiquitous throughout the solar system, so why not try to develop an electric propulsion device that can use water propellant?

I think electric propulsion also will continue to be the mainstay satellite propulsion. Certainly, it is right now for commercial geosynchronous types of missions. But we’re starting to see these constellations like OneWeb and the SpaceX constellation operating in low or medium orbit but they’re also using electric propulsion. It’s just going to be more and more commonplace. It’s going to the standard type of propulsion you start with versus what you add onto later. 

Michigan is also a teaching institution. Its product is people as well as hardware. So how do the students and your colleagues working in the lab contribute to the future of space propulsion?

Another decision I made was that I wanted to do good fundamental research and advance the state of the knowledge, but do it in a relevant setting – not just create argon plasma in a configuration that has almost no bearing on a thruster. Why not do the same sort of research, but do it on a thruster that either will fly or has the capability of leading to a flight unit? 

The way we do the research, of course, is through students and postdocs. The research is part of the learning process. Students learn by doing this on flight-relevant technology, so they’ve become scientists as well as engineers. A major impact of the lab has been through those 40 plus Ph.D. students and a dozen or so Master’s students who have graduated from the lab. They’re doing great things and many are still in the field of electric propulsion working at NASA, the Air Force, in industry, or as professors with their own labs…including at Michigan!

Others are taking what they’ve learned through this process and applying it in myriad different fields – almost all engineering. So that’s really, in some respects, where the technology transfer and the impact really happen by educating these very talented people who want to do great things.