As NASA prepares to send astronauts to the Moon through the Artemis program, engineers are working on technologies that will give these explorers power – solar power, that is. In space, the harsh radiation and huge temperature changes make for a challenging environment.Lyndsey McMillon-Brown at NASA’s Glenn Research Center leads a study of solar cells made from a material called perovskite. This material has the potential to help power lunar habitats one day. Learn about this innovation andLyndsey’sjourney to NASA.

Jim Green: We get energy here on Earth in many different ways, such as using the Sun with solar cells. But we use them in space also.

Lyndsey McMillon-Brown:You go from, very hot to very cold, very often in space. So we’re looking at how do we protect these materials? And how do we design them to be robust?

Jim Green:Hi, I’m Jim Green. And this is a new season of Gravity Assist. We’re going to explore the inside workings of NASA in making these fabulous missions happen.

Jim Green:I’m here with Lyndsey McMillon-Brown and she is a research scientist and engineer at NASA Glenn Research Center in Cleveland, Ohio. Lyndsey is the principal investigator for a project that is working on solar cells for space applications, including the Moon and Mars. Welcome, Lyndsey, to Gravity Assist.

Lyndsey McMillon-Brown:Hello, and thank you for having me. I am so excited to be here with you.

Jim Green:Well, how did you get started working with NASA?

Lyndsey McMillon-Brown:It was really fortunate, you know. When I was younger, actually, I went to space camp. So I always want to mention that first.

Jim Green:Cool, mhm.

Lyndsey McMillon-Brown: I was in fourth grade, and went on a Space Camp trip. And like everyone, I feel like, you can’t go there without being amazed and really intrigued by the work. But then fast forward a few years, when I was in college, I was really interested in working at NASA again. And since that love for science stuck with me, you know, over all those years since Space Camp, I was an engineering undergrad. So I applied for an internship. And for me, the access to NASA wasn’t super difficult because NASA Glenn is in Cleveland, and I grew up outside of the Cleveland area. So I was pretty familiar with knowing there was a NASA center close to home.

Jim Green: Well, that’s really great. So that internship program is called a co-op program. So what did you do as a co-op?

Lyndsey McMillon-Brown:Yeah, I had a great time as a co-op. And I feel like it really allowed me to find and center myself as an engineer, and then discover research and realize that I wanted to pursue that as a career. So as a co-op, I had this opportunity to do work in school rotations. And on each rotation, maybe I would be, you know, at NASA for about eight to 10 weeks.

Lyndsey McMillon-BrownSo one thing I was able to do was work on transparent solar cells for adaptive windows. For example, if you think of smart windows for your home that would tint dark to prevent the Sun from coming in and heating your home. And we wanted those to be powered by solar. So we were working on: Is there a thin coating you could develop that could be on your window, but not disruptive to the light that you’re getting in your home? So I worked on that for a while. And that was my introduction to solar cells. And I found the work to be really intriguing and exciting.

Lyndsey McMillon-Brown:Another project I got the opportunity to work on during a different rotation was a Mars hopper. We were looking at carbon sequestration. So, can you have a hopper that sits on the surface of Mars, absorbs the CO2, and then basically splits it and harvests energy from, you know, the resulting water or oxygen. And I was really thrilled to know that in my tinkering in the lab, I was helping this mission that we’ve had in our minds to go to Mars, you know, and sustain life for a long time. So I really enjoyed that work, too.

Jim Green:Well, then you became a regular employee at Glenn Research Center, and steeped into solar systems and solar cell technologies. And I heard you’d written a paper about what happened on Mars with Opportunity’s solar panels. Can you tell us about it?

Lyndsey McMillon-Brown:Yes, I was so excited about that work. So with that one, we took a look at standard, state of the art solar cells that are triple junction solar cells. So they’re, if you think of like a sandwich, they have many different layers, three layers, triple junction, and each layer is responsible for optimizing a certain part of the solar spectrum. And one of the challenges with those cells is sometimes they can be brittle, because they’re crystalline. So they are sometimes susceptible to breaking or cracking.

Lyndsey McMillon-Brown:And we set up an experiment in our lab that would expose these solar cells to Mars dust storm conditions. So we varied the angle that the solar cells were placed at and we had this oncoming high speed wind blowing Martian simulated dust, since we don’t have real Mars dust in hand yet in the labs. And this was really fun. I was working in the sandblaster box so I was able to get dirty. You know, I would come out kind of dusted with this, you know, red dust, and I got a kick out of that.

Lyndsey McMillon-Brown:But we were also really able to accurately model and simulate how these solar cells perform on Mars. And we checked that our in-lab simulation was accurate by using Opportunity rover data that we had courtesy from JPL.

Lyndsey McMillon-Brown:The Opportunity rover had a really long life and great exploration, and it provided us with lots of data. But ultimately, it stopped operating because a lot of dust accumulated on it solar cells, and it didn’t have enough power to operate anymore.

Lyndsey McMillon-BrownAnd we were able to compare our simulations to the actual solar cell performance on Opportunity. And that was such a rewarding experience.

Jim Green:So how did they turn out in that comparison?

Lyndsey McMillon-Brown:Yeah, they turned out really interesting. So a couple of the things that we learned was that when these solar cells are exposed to dust, of course, the dust will accumulate on the cell, and then less light will get through the coating of dust. Think of a dirty windshield, you know, in your car, you’re getting less light as the driver. But another thing that happened, we would then clean off the cells, blow them with air to clean off the dust.

Lyndsey McMillon-Brown:So we figured the solar cells would then return back to normal. But actually, we don’t fully understand what, but something electrical changes inside those solar cells as a result to the exposure to dust. So even the cells that looked fine, there’s no cracks or damage to them. Their open circuit voltage decreased a bit. So the efficiency that the electrons move around in the solar cell changes when it’s exposed to those dust storms.

Jim Green:Wow. Okay.

Lyndsey McMillon-Brown:Yeah.

Jim Green:So there’s other types of solar cell technology, then that we need to use on Mars to maintain that high efficiency once you blow the dust off.

Lyndsey McMillon-Brown:Right!

Jim Green:Since dust seems to be a concern on Mars, are we still going to need solar panels on future experiments?

Lyndsey McMillon-Brown:I think we will. Dust is a concern. But through this investigation, we found ways that you can mitigate it. For example, if you place your solar cells between a 45 to 60 degree angle, that’s really helpful for the dust to roll off. And we’re also learning other things about coatings that will help keep the dust off of the solar cells and prolong the lifetimes.

Jim Green:Well, you’re also working on solar cells for future lunar missions.

Lyndsey McMillon-Brown:Yes.

Jim Green:Are they the same as what you would use on Mars or not?

Lyndsey McMillon-Brown:So that’s what we’re looking at, we think they could be the same, we could continue to use these triple junction, you know, state of the art solar cells. But the Moon affords us another opportunity that we might be able to use lower cost solar cells, which is what I’m studying right now. And those are called perovskites. And perovskites are like plastic solar cells, more or less. So they’re made from a solution. And since they’re thin, that allows them to be deposited on different types of substrates. So they can be flexible, and lightweight. And they have a lot more versatility than these more rigid triple junction crystal solar cells that we’ve been talking about earlier. And the Moon affords us this opportunity, because there’s a lot of real estate on the Moon. So we can really spread out and have a very large solar farm, if you would imagine, of these thin and flexible arrays and that would significantly drop the cost of production, manufacturing, and it drops the cost potentially, of launch. How do you get it up to the Moon?

Lyndsey McMillon-Brown:So the way I envision this is: You’re gonna have different kind of habitats, almost like different houses. And you will have these large solar farms like an array that you might see when you’re driving down the highway now. So we’ll have this large area, many different panels all lined in a row, we’re going to have to find the best angle to set them at or perhaps they track the Sun, so that they’re always illuminated, appropriately without shadow.

Jim Green:Well, what’s really exciting about going to the Moon and the Artemis program is we’re going to the South Pole. And on the South Pole, there are places where there’s eternal darkness, we call those permanently shadowed craters. But at the higher altitudes, at the crater rims, there are places of eternal light, and they see the Sun all the time. Perfect place to be able to put these type of solar panels. Are discussions going on at Glenn about using those places on the Moon of eternal light?

Lyndsey McMillon-Brown:Absolutely those you know, as a solar cell engineer, that’s where you’d like to find me. So we definitely want to follow the light. But we work very closely with the battery people, power storage, management and distribution, because I’m one piece of a larger puzzle that has to work together and make sure you know if I can absorb it, and collect it, can you store it? Can you get it where it needs to go? Because we’re also very interested in exploring some of those dark and permanently shadowed regions.

Jim Green:Yeah, the ability to then acquire that but then beam that energy somewhere that you need it down to a habitat or some other location, that’s going to be real important. Well, do special materials like that suffer in space?

Lyndsey McMillon-Brown:They do. And that happens with any material you know, we have yet to find the “holy grail” perfect material that’s impervious to space. Especially because space is particularly harsh. So for the perovskites that I’m looking at right now, they do a fairly good job at dealing with the radiation in space. And we call that radiation tolerance. So they have a high radiation tolerance. Now to study that, we’ve been sending some samples up to fly on the International Space Station.

Lyndsey McMillon-Brown:I’m largely involved with Materials in the International Space Station Experiment, which we call MISSE. And MISSE is this great opportunity for us to send up samples aboard the ISS. And our samples are placed outside of the International Space Station on the wing, and they’re exposed to low-Earth orbit for six months, then the best part is those samples are really collected and returned to us. And we’re able to analyze them and see exactly what changes they underwent when they were exposed to low-Earth orbit. So specifically, I’ve been able to send up these perovskite thin film samples. And we’re interested in seeing how do they perform and how durable are they when they’re exposed to all of the, you know, all the intricacies of space at once. That’s the thermal cycling, that’s being in vacuum, that’s having radiation, and that’s being illuminated by the Sun. And these are things that on the ground, we can test one by one in our different experimental chambers. But it’s so valuable to be able to test it all at once in the true environment.

Lyndsey McMillon-Brown:And they do a better job than some of the existing technology. But we still do see some damage even when exposed to some higher energy particles. So we’re concerned about that. And another challenge is the temperature cycling because you go from very hot to very cold, very often in space. So we’re looking at how do we protect these materials? And how do we design them to be robust to thermal cycling?

Jim Green:Perovskite sounds really bizarre and exotic, but what is it and how is it made? What are its elements?

Lyndsey McMillon-Brown:Yeah, so perovskites for solar cells actually get that name, because the solar cells take on the same crystalline structure that the natural occurring perovskite mineral has.

Lyndsey McMillon-Brown:We generate our perovskites in the lab by combining various chemicals in a solution and when those chemicals come together, they arrange themselves in this order. And that results in a perovskite thin film.

Jim Green:Well, you know, I heard him about a method of making these called electrospraying.

Lyndsey McMillon-Brown:Yes.

Jim Green:What is that all about?

Lyndsey McMillon-Brown:Yeah, so electrospraying, that work is led by our collaborators at U.C. Merced. And electrospraying is really cool because it uses electricity to disperse a liquid into like a fine aerosol, like a cone of spray. And that cone of your dispersed material allows you to coat your substrate evenly. And once that, that liquid aerosol arrives to your substrate, we’ve noticed that the particles merge together, and they coalesce, and they make a really nice organized crystalline film without us having to do anything, and we call that self-assembly. So we really like the concept of electrospray. Because this can allow us to more quickly manufacture these solar cells. If you imagine like an assembly line, you have this substrate moving through, and it gets coated by the spray, and it just keeps on going for future processing down the line.

Jim Green:So it sounds like electrospraying is just like spraying on paint?

Lyndsey McMillon-BrownExactly. It’s just like spray paint.

Jim Green:So it sounds like there’s still so many different techniques that you need to investigate to really be able to create the right solar panels. And it’s different between solar panels on spacecraft or those on Mars or the Moon. What do you think the future of solar cell research is all about? Can we make them more efficient and smaller? Or, or is it going in a different direction?

Lyndsey McMillon-Brown: Yeah, I think the future is bright, pun intended. But I think that we have so many opportunities. And what I would love to see is us designing unique solar cells for specific applications. I think some are really good. They have a high power density. So you only need a few solar cells to get a lot of power. Maybe we want to use those on smaller satellites or things like that, then if you open up and you’re on the Moon, maybe you want to have this large, cheap, but flexible array. So I would love to see us tailor-making solar cells or have you know, a Rolodex, so to speak of: these are the four solar cells that go best for these different types of missions.

Jim Green:So Lyndsey, what’s a typical day like for you when you go to work?

Lyndsey McMillon-Brown:So a typical day is pretty diverse. And I love that. So I will collect some data and work in the lab and maybe make some thin film samples by spin coating. Then I will take those samples and I will measure them. I’ll expose them to some light and see how well do they perform. Then I also have to analyze the data. So, in the afternoons, I’ll typically sit down and have a lot of data in front of me. I’ll make some graphs. I’ll compare some things and get a plan. And then at least once a week I meet with my team, and we discuss other experiments that we’re interested in and we devise a plan so that we’re always kind of moving forward in the right direction.

Jim Green:So Lyndsey, what is the next step in your research?

Lyndsey McMillon-Brown:So to date in our research, we’ve been looking at the different layers of a perovskite solar cell, and we’ve been working to improve them so that they can be durable in space. And now it’s the time for us to combine them all and really work on the solar cell as a whole. And we’re going to be looking at exactly how we might be manufacturing this solar cell for space.

Jim Green: Well, you know, you have a bachelor’s degree at Miami University in mechanical and manufacturing engineering and a Master’s and PhD at Yale in chemical engineering. But I also noticed that you really Recently, were named as a notable alumni from the Miami University College of Engineering and Computing. How does that make you feel?

Lyndsey McMillon-Brown:I was elated when I found that out. I was so proud and honored and shocked. That list of notable alums is not very long. And I was so thrilled that my alma mater, you know, thinks that I’m deserving to be on that list. So it makes me so happy. I love Miami University, and I’ve remained engaged with them. But that was definitely one of the brightest moments in my career so far.

Jim Green:Lyndsey, what is your advice to the young people out there that would love to have an engineering career at NASA?

Lyndsey McMillon-Brown:I would give the advice to have fun and learn something new. But don’t be too hard on yourself. To be a NASA scientist, you don’t have to have perfect grades. We have our weaknesses, too. But view your weaknesses as an opportunity to improve and learn more.

Jim Green:Yeah, that’s fantastic. Well, Lyndsey, I always like to ask my guests to tell me what was that event, person, place, or thing that got them so excited about being the engineer they are today. And I call that a gravity assist. So Lyndsey, what was your gravity assist?

Lyndsey McMillon-Brown:My gravity assist was my village. You always hear, you know, “it takes a village to raise a child.” And I feel like there’s so many great people, my parents, my husband, a great professor I had in college, Dr. Osama Ettouney. And they all rallied around me and encouraged me and inspired me, and gave me the tools that I needed and helped me build that skill set to be the scientists that I am today.

Jim Green:Well, that’s fantastic. Lyndsey, thanks so much for joining me in discussing your career. It’s bright. It’s all about solar cells.

Lyndsey McMillon-Brown:Thank you so much for having me. This was so fun.

Jim Green:You’re very welcome. Well, join me next time as we continue our journey to look under the hood at NASA and see how we do what we do. I’m Jim Green, and this is your Gravity Assist.

Credits

Lead producer: Elizabeth Landau

Audio engineer: Manny Cooper