From Earth orbit to the Moon and Mars, explore the world of human spaceflight with NASA each week on the official podcast of the Johnson Space Center in Houston, Texas. Listen to in-depth conversations with the astronauts, scientists and engineers who make it possible.

On Episode 282, Battery Technical Discipline lead at NASA’s Johnson Space Center discusses how a safety device he co-invented while at NASA for spaceflight impacts the entire battery industry. This episode was recorded in August 2022 and March 2023.

Transcript

Gary Jordan (Host): Houston, we have a podcast! Welcome to the official podcast of the NASA Johnson Space Center, Episode 282, “Better Batteries.” I’m Gary Jordan, and I’ll be your host today. On this podcast we bring in the experts, scientists, engineers, and astronauts, all to let you know what’s going on in the world of human spaceflight. We don’t really think about it all the time, but batteries are a part of our everyday lives. Even now, you likely have a phone with a lithium-ion battery in your pocket, or you’re in the car that thankfully started this morning because you had a working battery. But beyond just functionality, we put these batteries in our cars and in our pockets because we have an expectation for them to be safe and reliable. On the International Space Station, astronauts depend on safe and reliable lithium-ion batteries for everyday functions. These batteries are used to power devices on the ISS, such as communication systems, laptop computers, breathing devices, and more. And thanks to some of the work that has made batteries in space safe and reliable, we can have more trust in the battery that’s in our pocket. Joining us for today’s episode to educate us on all things space batteries, we have Dr. Eric Darcy. Eric has spent more than 30 years at NASA in the areas of battery design verification and safety assessment for the rigors of human spaceflight applications. As battery technical discipline lead at NASA’s Johnson Space Center, his main objective has been the development of safe, while high-performing, battery systems with a deep focus on understanding, preventing, and mitigating latent defects that could lead to catastrophic cell internal short circuits. With the National Renewable Energy Laboratory, or NREL, colleagues, he is a co-inventor of the patented on-demand, internal, short-circuit device that has provided significant design insights into the cell response during thermal runaway, enabled valid battery thermal runaway propagation assessment, and received a prestigious R&D 100 award in 2016, and was a runner up of the NASA invention of the year in 2017. A man with over 30 publications and two patents, Darcy has participated in audits of several lithium-ion cell production lines across Asia and North America. If you didn’t know anything about the importance of batteries before and why they need to be tested, now’s your chance to learn more from the best in the field. With that, sit back, relax, and let your mind recharge. Enjoy.

[Music]

Host: Dr. Eric Darcy. Thank you so much for coming on Houston We Have a Podcast.

Eric Darcy: Well, thank you for having me.

Host: This is a very cool topic. We’ve had spinoffs on our podcast quite a bit, but this is a, this is a very interesting one. In fact, we had this on one of our more recent episodes as, as a small highlight in a much, you know, grander, we, we were talking about a lot of topics, but this is our chance to really dive into batteries. Something that you’ve explored for much of your career is, is batteries, and I wanted to sort of start there and understand just, you know, that’s something that you’re, you’re very good at, very passionate about, and I wonder where that all started. You, you were, you know, you, you went to school for chemical engineering, and I wonder, if there was something in your studies that really made you want to pursue batteries or maybe it came later. So tell me about, how you ended up where you are?

Eric Darcy: Sure, Gary. I was interested in chemistry in high school and went into to college. I went to Pomona College, a liberal arts school, and got a Bachelor of Arts in chemistry because that was the small school and realized I also wanted to, love math, and so I wanted to combine it with engineering. Took some engineering classes at Harvey Mudd College, a sister school of there, and that led me to chemical engineering at Texas A&M, which is where I got a master’s in chemical engineering with an advisor, Dr. Ralph White, in batteries. And it was a, a field of chemical engineering that really interests me because of, it introduces, has all the facets or some main facets of chemical engineering: it’s got chemical kinetics, it’s got the thermal aspects to it, it’s got some ion transport; some batteries have fluid flow. And so, all in one simple little package, that’s in everybody’s pocket, it’s, it’s ubiquitous. And so, it felt like a very interesting field to, to get into.

Host: Very cool. Yeah. I guess the idea that a professor, that a person, actually convinced you, I think, I mean, that’s one thing, right? You might have find it, found it interesting in yourself, but you must have had, I mean, this sounds like there was an advisor, there was a person in your life that really helped you to, and guided you into that, that profession.

Eric Darcy: Yes. And it just got me to dive into that field and we did, I did a master’s thesis on modeling the lead acid, or actually the positive electrode of a lead acid battery, which is what’s in your car, in two dimensions, which hadn’t been done. But it was a big Fortran code, and it took forever, but finally got out. And the research, some of the research was funded by NASA. And so that’s, in reporting to the NASA customer, that’s how I made the contact with the battery group at NASA, which the battery group at that time was on the civil servant side was one person.

Host: Oh.

Eric Darcy: And so, I luckily got the opportunity to double the size of the battery group after I graduated with my masters.

Host: What are they going to do with all those people? So the battery group at NASA: what, what were the objectives of the group? Were, were you focused on the batteries helping all parts of NASA, or what, what was the focus of the group?

Eric Darcy: Yeah. Basically, all manned spacecraft batteries on that.

Host: OK.

Eric Darcy: So at the time, it was the shuttle days…

Host: Yeah.

Eric Darcy:…I hired in in ’86 and we were — actually ’87, and we were just recovering from the Challenger accident at the time. And so we were re-looking at all the hazards associated with all the systems, but particularly batteries and seeing what is it that we can do to, for more robust testing and verification that the batteries would be safe. At that time we were mainly supporting the spacesuit and the EVA (extravehicular activity) or the spacewalking tools’ batteries at that time. The shuttle was powered by fuel cells, and so that’s kind of a, a fluid flow battery on that. This is, batteries are batch reactors and they’re self-contained, and, and so we, we had just little applications and it wasn’t until later with the advent of lithium-ion that we grew to a whole lot more applications.

Host: OK. So what were, you, you mentioned safety and testing, so when, when you were working with these fuel cells what were some of the things that you were doing to take, you know, was it off the shelf, commercial off-the-shelf technologies that you were just kind of working with and making it “space ready,” or were, was there a novelty to it? What was, what was some of your work in the battery, in battery?

Eric Darcy: Yes. So when I started out the new chemistry at the time was nickel metal hydride. And it, it had, it was better than nickel cadmium, it had more energy density, or specific energy, and meaning that watt-hours per kilogram was higher. So it had a big advantage of that over the, the NiCads (nickel-cadmium). And so we started developing helmet lights batteries with that technology on that. And then that grew to the Pistol Grip Tool…

Host: Oh, yeah.

Eric Darcy:…we developed a battery for, for that tool using nickel metal hydride. And then we waited patiently for the time to go and do a rechargeable battery for the spacesuit, the primary life support system of the spacesuit on that. At the time, it was using a, what we call a primary one-shot type of battery, or limited cycle life battery.

Host: OK.

Eric Darcy: Could, could only do tens of, of cycles, and then it would, and then the wet life of the battery, when you pour the electrolyte in the clock starts the, the wet life would be on the order of less than a year. And so, it wasn’t something suitable for a space station application where we’d want the batteries to be parked there for many years. And so we had to develop new technology for that.

Host: Interesting. What are the challenges when you’re developing these technologies, when you’re testing, when it comes to operating in the space environment, what are some of the things you have to consider?

Eric Darcy: Yeah. The thermal aspects are big on that. We have to properly insulate the battery or, or protect it from the, the environment, particularly during spacewalks, because from the, the night to the, the Sun-shining portions it can be very extremes, hot and cold. The advantage that we have with batteries is the thermal mass of a battery is pretty large, so it’s got a large heat capacity, so it takes a while for it to change temperature. And a spacewalk is typically less than seven hours, and so we try to use that to our advantage on that. But yeah, those, mainly the quality, because we are using commercial techno, cell technology, putting it into a battery, and so the emphasis there is high-volume production, consistency of the performance…

Host: Right.

Eric Darcy:…we want to make sure we use the best cells. So a battery is made up of cells. So a cell is an electrochemical couple, and then you put cells together to form a battery assembly that provides the power and energy for the application on that. And so, the quality, when we’re trying to spin in technology as opposed to spin off, we’re trying to use what the consumer electronic industry is using because there’s enormous competition in that space, especially back then, to get the best performing battery. And so we took advantage of that to bring it into our space applications. So NASA typically only designs cells custom for space application when you absolutely have to; in other words, there’s some cycle-life requirements that nobody else has. The space station, for example, is, is that: it’s a battery that needs to operate for ten years and do nearly 60,000 cycles…

Host: Yeah, big requirements

Eric Darcy:…on that. And so, the consumer electronic industry doesn’t have a cell technology that meets those requirements, and so that’s a case where it makes sense. But for the majority of the other cases it’s much more effective to bring in commercial elec, technology, lithium-ion technology, for example…

Host: Right.

Eric Darcy:…or other chemistry technologies.

Host: But it’s just a matter of, I’m, in my mind I’m equating it to like cooking. You know, you’re just using the best ingredients, right?

Eric Darcy: Yeah.

Host: You’re sourcing the best ingredients to, for the, for the right recipe that’s very specialized for this particular thing, which is human spaceflight.

Eric Darcy: Right.

Host: Yeah.

Eric Darcy: And then in the early 90s lithium-ion came on, and it was first commercialized in ’91 by Sony. And it was a pretty small capacity cell. They, they standardized the cell size to what’s called an 18650, which is about the size of a male index finger in, in size, as you can see. And they can make it in prodigious rates. And the consistency was really taking advantage. Plus, you get the advantage of the beta testing that’s done by the community, so that if there is a problem with the design you can hear about it from recalls. And so, you get the advantage of all these customers testing this product that you don’t get with a custom cell design that’s just designed for a space application. So when you started out, the cell technology was one amp[ere]-hour, right, which is a small amount of energy; today, that same volume, cell-size cell is at 3.5-amp hours. And you can see over the 30 years how it has progressively gotten better and better on that. And so, it’s, it’s the big ad, one of the big advantages of spinning in that technology on that.

Host: At what point did, you know, because I, there was like, like you mentioned there was a history with using batteries that were not lithium-ion technology, but as you mentioned, you know, with all these consumers using it you were starting getting more and more data to have confidence that lithium-ion can be used for space applications. In your, about what time did your group start seeing more requests and, and, and it became clearer that lithium-ion was going to be more popular when it comes to spaceflight technologies?

Eric Darcy: Yes. It was in, in the 90s it was a, a novelty.

Host: Yeah.

Eric Darcy: And we were pretty guarded about it. We weren’t ready to fly it.

Host: Sure.

Eric Darcy: First the advantage over metal hydride techno, nickel metal hydride technology wasn’t compelling enough at the time, and so we just watched it, we did a lot of safety tests. The flammable electrolyte in lithium-ion technology presents a special hazard. You don’t have that in the aqueous nickel metal hydride chemistry. So there was a big safety advantage with the, the nickel metal hydride technology. But as the performance got better and better with lithium-ion it, it pretty much was, got compelling, particularly in terms of specific energy, efficiency of charge and discharge, the Coulombic efficiency, as they call it — amp-hours in versus amp-hours out — was nearly 100%, unlike the, the aqueous chemistries that always, that have some parasitic or some losses, particularly at the, at the end of charge where you’re just not as efficient, you’ve got side reactions that are producing oxygen and hydrogen, and so it leads to less efficient batteries. And so that amounts to weight, or takes up energy from the power system that’s charging it on that. So we had to get comfortable with the extra hazards. Also, lithium-ion has a voltage window that has to be precisely guarded such that you can’t overcharge or undercharge or you will ruin the battery, unlike the nickel chemistries where there’s electrochemical reactions that you can go into and safely overcharge or over-discharge and the battery will, will recover. So the lithium-ion industry didn’t really blossom until the microelectronics industry got so proficient and so small to be able to control those voltage windows and guard lithium-ion batteries and to be able to make them safe on that. So yeah, there’s some very good electronics and chemical technology in a lithium-ion cell in order to make it safe for consumers. One of the devices that makes it, that made it prevalent, and it was this current interrupt device that is inside every lithium-ion commercial cell, and it’s an additive that’s in the cathode, that’s a lithium carbonate, and that electrochemically produces CO₂, pressure inside the cell, once the voltage gets into the overcharge mode; that generates pressure and disconnects a switch — this current interrupt device — in the cell header to cut off the overcharge. And so it’s a way of passively protecting cells from getting overcharge because overcharge, if it kept, if it kept, keeps going, will lead to thermal runaway.

Host: Ah, and that’s a problem…

Eric Darcy: And that’s a catastrophic event…

Host: Yes.

Eric Darcy:…of fire, flames and shrapnel.

Host: Yes.

Eric Darcy: Yes.

Host: And we’re going to get into that, absolutely. Now, now this, this feature that you’re talking about, how did that compare to, to legacy batteries? Was it, was this a, was this a…

Eric Darcy: No, this was unique to lithium-ion.

Host: This was unique to lithium-ion; interesting. OK.

Eric Darcy: Yep.

Host: Now, when your group started, when it became more and more clear that lithium-ion was going to start making its way into spaceflight, in human spaceflight, how did you first start tackling testing this, this technology? And, and you mentioned following it along and making, seeing the progression; what, what were some of the first things that you were seeing in terms of lithium-ion batteries in, in spaceflight? What were some of the first things?

Eric Darcy: Basically, payloads or crew, crew requests for iPads or that, that type of technology; we had to learn what were the safety hazards with new laptops.

Host: Yeah.

Eric Darcy: Cameras: I think the Canon camera, video camera, was one of the very first lithium-ion tools or gadgets that the crew wanted to fly with, and we had to get comfortable with the battery in there, in that device to make sure that we had it controlled as best we could from a thermal runaway hazard event.

Host: OK. Now, how did you test the lithium-ion battery? Is this, because what I’m trying to lead to is some of these first, some of these first things that were happen, that were going up in space to where we can start talking about your internal short circuit device, right?

Eric Darcy: Sure.

Host: Did that come early, or was this, was, is…

Eric Darcy: So this was proceeded…

Host: So this was proceeding, OK.

Eric Darcy:…in the late 90s, or when we started looking at these payloads…

Host: OK.

Eric Darcy:…early 2000, we started having to approve that, the crew demanded more and more to stay up. I mean, nickel metal hydride was getting phased out. lithium-ion was taking over at the time. We just had to, the inertia was there, we had to get a handle on it.

Host: Got it.

Eric Darcy: And it wasn’t until we got to larger batteries with many cells, or for the, the spacesuit and its tools inside a high, 100% oxygen environment and, and all the hazards of the, the primary life support system of, of the spacesuit, that we had to pay some really special attention on that. And at that time, this is in the year 2000 to 2010, we pretty much assumed that we could only rely on prevention in order to screen out bad product getting, from getting into our battery assemblies. So we spent a lot of time figuring out what were the best ways to figure out what’s the best design, who makes it the, with the most, manufacturing quality, and what tests do we need to do to verify all that to make sure that discrepant cells don’t get into battery assemblies. And then of course, that we operate it within its, its design limits both from a voltage, current, temperature and cycle life on that. So we pretty much just relied on prevention, and we just assumed that if one cell were to have a catastrophic event it’d be a really bad day. But, you know, at the time we thought that we could possibly do something else besides the prevention, but it was just a, a development project, I mean just a, R&D folks on that. And I have to give credit to Tesla, they were one of the very first ones in developing their Roadster vehicle, the very first vehicle, putting the emphasis on achieving a battery that’s passively propagation resistant on that with a large size battery. And so, they were able to achieve that for their requirement with some active, active cooling on that. And so we wanted to see if we could do it passively. And then it really started out getting some emphasis from our customers, our programs, when the Boeing 787 incidents occurred. If you recall, in 2013 they had two battery fires in the 787 airplane that caused the grounding of that entire fleet for like five months on that. They made a lot of news, and it was costing Boeing a huge amount to have that. And it was because the root cause, after much investigation, was that it was an internal defect, a defect-induced event that doesn’t get detected at the point of manufacturing, gets put out in the field, and as the battery exercises during field use — charging and discharging — the expansion and contraction of the electrodes during that process causes the defect to move and no longer become latent, and cause, manifests itself into a thermal runaway event, catastrophic event on that. This is a, a phenomena that’s plagued the lithium-ion battery industry since the beginning, and it’s, with good manufacturing it’s on the rate of about one [in] five million to one in one million. If a battery manufacturer has his processes under control, they can expect one in, in a million to one in five million of these events occurring for all the cells they produce. Well, when you’re dealing with laptops and you’re dealing with small batteries, it’s something that you can deal with: you can throw away the battery or move away on that. But once you start being in a confined space of a spacecraft with a lot, a battery that has many, many cells, thousands of cells, you can’t use that approach anymore.

Host: Right. How, how prevalent are these, these battery fires? Is this something that we even have to worry about nowadays?

Eric Darcy: Yeah, it’s a good question, Gary. As I mentioned, when a battery manufacturer, a cell manufacturer, has his quality control in line, the risk is about one in a million to one in five million. But when the processes don’t work well and even — any manufacturer, even the reputable ones can have a bad day, bad week — and then the risk will get down to one in a hundred thousand or even worse than that. And that’s when recalls occurs. And over the last two years, I can list four different types, or even five more different types, currents, of recalls with electric vehicle manufacturers and with ground battery test, test system energy, battery energy systems. Those are the big trailers that support the grid during the night in order to level out the, the, the power demands on that. And so, yeah, some of these failures have been very catastrophic, taking many firefighters many days to put out. They’re megawatt-hour-type of battery systems that take, that are very challenging to put out…

Host: Yeah.

Eric Darcy:…on that. So they, these are very prevalent. And in every couple months you will hear of some battery fire, or every year you’ll have several recalls of these electric vehicle batteries or ground station batteries on that. So it is a very prevalent failure that we have to deal with.

Host: So this was a, you mentioned that this, this was an issue, it was identified in the manufacturing process. When did it become apparent to introduce some sort of test after the manufacturing to have some level of confidence? Was this something that your group was started, was this something that was in industry? When, when did it become apparent to start this?

Eric Darcy: Yes. So, after the 787 incident, which draw the, the eye of, of NASA and the, and particularly the management of NASA, we — and I have to give credit to Chris Iannello of the NASA Engineering Safety Center — and drafting a plan to figure out how to, the, go with basic con, reducing the severity of the consequence of this failure, as opposed to just relying on prevention. So let’s assume that our prevention isn’t going to be 100% successful and we’re going to have this event: how do we protect the adjacent cells so that we become passively propagation-resistant, like I mentioned Tesla was doing…

Host: Right.

Eric Darcy:…on that with their active cooling. So here we wanted to do it passively because we want the battery to not only be safe, but to be high-performing, because mass and volume is a premium for our applications. So we looked at all our batteries and went into a development program in a big hurry in order to make sure that the battery developed for the Pistol Grip Tool, for the REBA, the Rechargeable EVA Battery Assembly, which powers the helmet lights, the glove heaters of the suit, and then eventually the spacesuit battery which is called the LLB, the Long Life Battery, we wanted to make it passively propagation resistant design. And so I have to give credit to the spacesuit program, because we were flying lithium-ion for about five years very successfully, and did some 25 or more spacewalks with no issues, but the program saw the need to change the design so that it could be passively propagation resistant. And so we pretty much did a clean sheet redesign of the battery, and it involved a very extensive test campaign.

Host: OK. So how did you start that, the, the test campaign? Like Yeah. How’d that go?

Eric Darcy: Yeah. Yeah. So for the spacesuit application, we wanted to be volumetrically efficient, and the best way to do that is with interstitial aluminum heat sink in between the cells. That allows you to bring the cells really close, you can bring them the, to about a half a millimeter apart from each other on that. And in order to do that, the tricky part was, well, how do you trigger thermal runaway in one cell when you’ve got them all embedded in this heat sink? Typically, a way to do that is just to heat them up, put a little heater on that. Well, if you put a heater next to an aluminum heat sink, the heat’s going to go right into the heat sink and not go into the cell and you’re not going to be able to drive thermal runaway. And hence we had to have a different technique, and that’s when the internal short circuit device really saved the day for, for that. So I was fortunate…well, I was very fortunate in 2010 to get a fellowship, it was the NASA Innovative Ambassador program, where I could take a year of leave with pay at somewhere else. And I sold it that if I could spend a year with the battery group at the National Renewable Energy Labs in Golden, Colorado, I could learn about how they do things for supporting the automotive industry and they could learn from me about how we do things for space. And during that one year — it actually was a nine-month phase — I focused in on helping develop this internal short circuit device. So Matt Keyser at the National Renewable Energy Labs and Dirk Long, we, the three of us together worked on developing an idea and I introduced the, the wax portion of it. And we, the wax was the key because we use the wax that melts right now at 57 degrees Celsius, which is a lot lower in temperature, to drive an internal short. So this device is implanted inside: it’s very thin device, basically it’s a layer of aluminum and copper, these little foils, one mil each; the aluminum has a spin-coated layer of wax. It’s a special paraffin wax that is mixed in with hairspray wax in order to make it flexible because the, the, the cells are, their electrodes are wound into a jelly roll, and so the device had to be flexible and couldn’t, and so if you just use paraffin wax it would be stiff and crack and you wouldn’t be able to use that. So the device is only about 100 microns thick, four-thousands of an inch; can be slipped into the cell. The manufacturers, they’re making hundreds of thousands of these cells a day. They would take the, what we call the jelly roll, the dry jelly roll of, that’s inside the cells, take it off the production line, unwind it, implant the device, rewind it by hand, and then they could re-enter the jelly roll into the production line and finish the, the assembly process. So the defect is now built into the cell and it’s an on-demand, all we have to do is heat the cell past the melting point of the wax, that the winding tension of the jelly roll would push the wax out of the way when you got past the 57 degrees melting point, and a hard short would develop and then thermal runaway would ensue on that. So this is a way of creating an internal short without compromising the enclosure of the cell and do it on demand with a low temperature input. And that’s the key because if you have, if you don’t have this and you’re trying to drive a normal cell, you have to drive that cell above 130, 150 degrees Celsius. And you can imagine it’s very hard to do that without also biasing cells that are adjacent to the trigger cell, if you will, on that. So you end up over-testing if you don’t have the cells with the internal short circuitize, those trigger cells on that. The downside is it takes the willingness of the cell manufacturer to implant this device that’s going to make their cells fail. And as you can tell, there’s obviously some resistance in making cells are going to fail by these manufacturers. But I was able to convince a few to, to try it. And it took about four years of trials before we got confident enough to where we could actually use it in a battery application and, and for a, for a test. So we have special versions of the, what we call the PPR, the Passively Propagation Resistant batteries, that we use for our test. And we substitute the cells with trigger cells in various locations to verify the, the battery will, the design will protect the adjacent cells from that hazard.

Host: What technology; wow. Now that, did you, once you, once you, you said it took a while to actually convince folks that this was a, this is an important thing to do. Did you see it take off after, after…

Eric Darcy: No, it took a while.

Host: It took a while? OK.

Eric Darcy: It took a while. So we invented the idea in 2010 and we tried little trials and we were hand brushing the wax, and that really affected the reliability and the performance. It wasn’t until we spin-coated the wax that we got a reliable layer of about ten microns on the aluminum layer. And it was consistent then and low profile and flexible, that then it was ready for primetime use. And so, it wasn’t until I got invited to a battery conference in Korea that I was able to convince LG to implant the device in a small batch of their cells on that, in their very high energy cells. Now, I did work with another manufacturer, E-One Moli Energy, prior to that in a lower capacity cell. And we did several trials, and they were, they were, it was very helpful, that really, we got to test all four different types of shorts that are possible between the electrodes and the current collectors.

Host: Oh.

Eric Darcy: And we made some really good progress there. But in order to be applicable for our batteries, we wanted it on the highest energy cells. And that’s when we got it into the LG cell, and now we have it into the high energy cell versions of E-One Moli. And we, we now have progressed enough to where we’re confident that 95% of the cells that we heat up that have the device will go into thermal runway, that we can build very expensive batteries, test batteries, with it for the validation process.

Host: OK; yeah. This is really, this is really getting into the, the testing component. That’s really what it is, is you’re, what you’re introducing is a measure of confidence into what, what exactly is happening, if thermal runaway were to occur, were to occur with the battery, right, because it would be hard to do without this device to introduce it. But when you understand what happens with the battery with thermal runaway and what is it exactly that, what information are you taking once you have that understanding that gives you confidence in the design for space batteries?

Eric Darcy: Well, it’s the field of, the aspect of prevention and the aspect of reducing the severity of the consequence when it happens. So we do as, as much as we can in both. Now this is, we use a design for minimum risk approach for this internal short-circuit risk because there’s nothing positive, or I should say there’s no fault tolerance that you can use — that’s a standard approach that we use for safety. There’s no amount of fuses or controllers that you can do, it’s inside the cell; and you can’t double or triple the layers of separator between anode and cathode because then you kill the performance of the cell. It’s similar to, the analogy is you can’t have an airplane with three wings, just so in case one falls off, right? So here we have to use this design for minimum risk approach.

Host: Right.

Eric Darcy: And that’s where we basically use best practices, robust design measures and test measures, and real focus on understanding what our margins are for safety in, in this. And so, what we’re, and so it’s an, a very extensive prevention of screening the cells, screening the design, auditing the production line, and making sure we operate it within its limits. And that’s what we do for prevention. And then to reduce the, the severity of the consequence, we do the PPR test. And in order to do the, the passively propagation resistance test, and to be successful, we have to understand how the cell fails.

Host: Right.

Eric Darcy: What, and thermal runaway is a very chaotic behavior, and it doesn’t always happen the same way. And so you have to test a dozen times a same cell design in order to get the range of possible behaviors and understand what the worst case is. And the phenomena of sidewall rupture is when the thermal runaway doesn’t go out the intended design path of the cell’s vent, it goes and burns through the can wall or ruptures through the can wall of the cell. Well, that’s very hazardous when that happens because then it’s a blowtorch towards the adjacent cells in a battery pack and can lead to instant propagation. And so we’ve had in the, in the industry several failures of propagation resistance tests due to not controlling sidewall rupturing.

Host: And so it’s from these tests where you understand what happens in the thermal runaway, well, I’m understanding, I think I’m understanding this now, is now, your, your job is to find the best batteries, have the best understanding of what happens in the case of a battery failure, and have confidence in the batteries that you’re putting into space applications. So it’s by introducing this test and putting it into the commercial market, understanding the data that’s coming from these commercial batteries, so that you can understand what’s happening; pick the batteries that make the most sense for, for space applications, and feel confident. Like for example, you, the, you, you mentioned the spacesuit batteries, right? You wanted to better understand what you were putting inside; based on the data that you collected after introducing the internal short-circuit device into the market, were there any significant changes made into what went into the spacesuit battery based on what you learned from understanding more about thermal runaway in the commercial market?

Eric Darcy: Oh, yes. Yes.

Host: There was.

Eric Darcy: Yeah.

Host: Sweet.

Eric Darcy: Yes. So we, we started characterizing thermal runaway. So we had to figure out a way to quantify the heat of thermal runaway.

Host: Oh, OK.

Eric Darcy: So we developed a, what we call a fractional thermal runaway calorimeter so that we can quantify the total heat, but also the distribution of heat coming out of a cell while it’s going in the thermal runaway. So we designed a calorimeter that has a cell chamber where the cell goes into that’s thermally isolated from the deceleration bores that capture all the ejecta coming out of a cell and decelerate it and cause it to rise in temperature. That rise in temperature of all the components of which we know the mass, and we know the temperature rise because we have lots of thermal couples and thermal sensors, we’re then able to calculate the energy yield from that. And so that then is fed into our designs, and we simulate the design in order to figure out if we get this type of a heat load, how do we protect the adjacent cells? What heat paths do we have to design in the battery pack in order to protect those adjacent cells? It’s all comes down to protecting those adjacent cells…

Host: Got it.

Eric Darcy:…on that. So we developed some guidelines through this process. After many failures, many cells and many batteries going into propagating thermal runway, we developed four design rules — plus another one for space — that helps us make sure that we have successful design campaigns. And so, the first rule is controlling sidewall rupturing. Then the second rule is spacing the cells out properly and providing a heat path for the trigger cell or the, the cell that’s going to have the, the nasty event, such that it doesn’t go directly to the very neighbor cell only. We’ve got to get that spread out. The third rule is how do you electrically isolate the cell that’s got the internal short, because that internal short is going to become an external short to the cells that are connected electrically in parallel with that cell. And those cells are going to start feeding current and getting hot, and, when they’re feeding that short, so that cell that’s got the internal short needs to be electrically isolated. So we have to have a fuse on that cell. And then the fourth rule’s also very important, is how do you manage the ejecta of gases, liquids and solids that are coming out of the cell at a rapid rate, that are molten aluminum, molten copper, thousand degrees Celsius, and how do you prevent that from accumulating near the adjacent cells and then causing them to go into thermal runaway? So you have to build a high temperature path channel that’s sufficiently wide enough, and that can tolerate the heat, the momentum of that ejecta and have it smear out. And then the final rule for our spacecraft batteries is to design the enclosure with a flame-arresting vent port, so that no flames exit the battery pack. So it all stays internal on that. And that’s very challenging to do with the smaller packs where there’s a lot less void volume; easier to do with the larger battery packs.

Host: Do you find that there’s any significant impact to battery performance by introducing all of these?

Eric Darcy: Yes.

Host: There is.

Eric Darcy: Oh, yes. There is. Yeah, there’s quite a burden. It’s about a 20% mass burden.

Host: Wow.

Eric Darcy: And going from a, a design that is not passively propagation resistant to one that is, and it can be an even bigger margin if you don’t follow all those four rules and optimize the materials to, to do it.

Host: But if you really, what, what the community is weighing is that risk, right? It’s just like, is it worth the addition of mass? And I guess it’s a, in the community it sounds like it’s a resounding yes.

Eric Darcy: Yeah. For the spacesuit battery application, we had a perfectly functioning battery. We ended up reducing the amount of cells or energy in that battery, we went from 80 cells to 70 cells, in order to achieve a PPR design.

Host: Got it.

Eric Darcy: But it was worthwhile to the program, and I felt it was the right choice to make in order to have a safer design, particularly for that very critical application.

Host: Yeah. I would think the community would be. And, and so in terms of, you know, with losing all of those cells, do you know about how many hours of performance was shaved off?

Eric Darcy: Yeah, so the original battery had about a nine-hour runtime. And so, now we’re more like seven and a half to eight hours of runtime.

Host: OK.

Eric Darcy: Yeah.

Host: OK. So about an hour…

Eric Darcy: So we’re really kind of close to, seven-hour spacewalks is kind of the limit, so we don’t have as much margin as we used to.

Host: Got it. OK. Yeah.

Eric Darcy: For, for runtime…

Host: But…

Eric Darcy:…we traded it for safety margin.

Host: Yeah. And so, so let’s just, let’s talk about that safety margin, right? So now we have an impact on the performance, it’s about an hour, hour, and a half that you’re losing. But when it comes to the safety, how do you measure the, the increase in safety?

Eric Darcy: Well, that’s a tough question, because it’s, it’s relatively subjective.

Host: OK, interesting.

Eric Darcy: Because, yeah, it’s the, the risk of having a catastrophic thermal runaway…

Host: Right.

Eric Darcy:…eliminated. It’s…

Host: Wow.

Eric Darcy:…it’s, it’s, it’s really important, but I can’t really put a metric on it, if that’s what you’re asking.

Host: Yeah, yeah. No, well, maybe not numbers but, but I think that right there captures it, that risk eliminated, right? That’s really it.

Eric Darcy: Correct.

Host: Yeah.

Eric Darcy: I mean, for sure, specifically with large batteries where there’s thousands of cells, each cell has a one in one million or one in five million chance of going thermal runaway. When you got a thousand cells or more, you’ve really increased your risk. And so it’s really critical for those batteries to have that design feature so that we could tolerate one cell going off. In essence, it’s more of a check engine light problem phenomenon when it occurs as opposed to being a catastrophic failure…

Host: OK.

Eric Darcy:…such as like the 787 where one cell went off and then it propagated through the entire battery on that.

Host: OK. Now, you had, you introduced this technology having a lot of confidence in the design of your batteries. You already, we already talked about the, we’re, we’re talking about the improvements made for safety for the batteries inside a spacesuit. I’m, I’m assuming it really took off at least in the space community after that, right?

Eric Darcy: Yes.

Host: I mean, we’re seeing, I know the, the upgrades on the space station batteries were a huge deal going from nickel hydrogen to, to lithium-ion, right? I’m sure you saw a lot of that trend, more and more lithium-ion batteries in, in space.

Eric Darcy: Yeah. I mean the, a really big impact was on the Orion spacecraft.

Host: Orion, OK.

Eric Darcy: Yeah. So we tested the Orion battery; at the time that battery design used a large cell approach. The cell was about 40-amp-hour cell prismatic, like a brick type of cell. And they were put in packaged very closely together. And in fact, that’s what’s going to be flying on Monday, is that battery design.

Host: Yeah. We’re recording this just a couple of days ahead of Artemis I launch and very exciting and, cool, your battery is…

Eric Darcy: So it’s, it’s a perfectly performing battery, but it does, it does not achieve the PPR safety requirement.

Host: Oh, OK.

Eric Darcy: But we accepted that because it’s an unmanned mission.

Host: Ah, OK. That’s just for Artemis I.

Eric Darcy: Just for Artemis I; when we go to Artemis II…

Host: Got it.

Eric Darcy:…completely new battery design that does achieve the PPR requirement with a smaller, small cell approach, small commercial cells…

Host: OK.

Eric Darcy:…on that, that were extensively tested and demonstrated to achieve the PPR requirement with trigger cells using the internal short-circuit device as the, the trigger.

Host: And the elimination of that risk. Now what, now those Orion batteries for Artemis II and beyond with, with crewed missions, what are you looking at in terms of performance, in terms of, like how long they, the requirement…

Eric Darcy: Well, they actually performed better.

Host: No way?

Eric Darcy: Yes. And that’s mainly because, like I mentioned earlier, the consumer electronic industry is so competitive, and especially now with the electric vehicle industry that’s really taken over the demand…

Host: Yeah.

Eric Darcy:…for high performance, for higher runtime. And those cells are better in terms of specific energy than the cells that are in the Artemis I design. So the, the cells that are in Artemis I design there, it’s an older design but it achieves about 140 watt-hours per kilogram. The, the little cells that the size of your index finger, the 18650s, are about 270 watt-hours per kilogram, as you can see. So, a factor of almost two better.

Host: Wow.

Eric Darcy: And, and so with that we could afford the burden of achieving PPR and still have a net positive in performance with that.

Host: That’s really exciting. It’s probably, it’s probably really exciting in your world, right, that you, you’re, you’re, you’re trying to focus on the safety, you got all these demands and requirements on performance, but the industry itself is accelerate, is excelling so quickly, as you mentioned, with, with increases in demand and, and, especially with EVs (electric vehicles) coming, becoming more and more popular that, that performance now you, now you can, you can achieve that PPR, you can also have the performance you need. I mean, you’re getting the best of both worlds.

Eric Darcy: Yes. Yes.

Host: That’s pretty great.

Eric Darcy: Yeah. And so after Orion, we then went into the other programs, and helped them achieve this, this PPR design feature…

Host: Nice.

Eric Darcy:…on that. And so, we just kept improving and getting better and trying to reduce that burden, both of mass and volume for, for achieving the PPR design…

Host: Wow.

Eric Darcy:…on that. So it’s, yeah, and I have to mention the, the internal short-circuit device has been critical in helping achieve that verification…

Host: Yes.

Eric Darcy:…with a design, well, a feature phenomena or the, the response helps us get a, the happy medium between an under-test and an over-test risk. So you don’t want to over test by overheating the adjacent cells or re, doing a, a thermal response that wouldn’t happen in the field…

Host: Right.

Eric Darcy:…or one that is under-reports, or I should say under-responds, and gives you a more benign response. So we want to replicate the credible failure that happens in the field very rarely. So it’s difficult to, to do that and, but with the internal short-circuit device we’re able to achieve that; was able to get one company, KULR Technology, to become the exclusive licensee for, and so now you can buy the cells with the internal short-circuit device or buy the device from this company.

Host: Yeah.

Eric Darcy: And that’s enabled some spinoffs. So that’s helped battery verification in automotive industry, power tool industry, even medical, aircraft, eVTOLs (electric vertical take-off and landing) on that. So other folks, commercial folks, now are able to do the same type of verification that NASA does to ensure that the, their batteries will tolerate a misbehaving cell in their battery.

Host: It’s got to feel pretty good to work, so, you know, you spent a year, right, with some colleagues making that device, now it’s, it’s something that is that this idea of transferring the technology over from government to commercial and seeing it in applications in so many different industries, that’s got to feel pretty good as, as an accomplishment for, you know, making batteries safer. And especially as, as battery, batteries are becoming, as you mentioned, they’re, they’re, the demand for lithium-ion batteries is, is up there, you know, to know that you’re contributing to understanding, you know, more about these battery failures or thermal runaways, to contribute to safety upgrades for, for batteries, that’s got to feel pretty good.

Eric Darcy: It does feel great. Yeah. And just to go back, if you can imagine, when we came up with this device, I mentioned the difficulties in talking these manufacturers to putting this device in their cells.

Host: Yeah. You said it took a while to convince them.

Eric Darcy: Yeah, to get them to misbehave. A lot of them, their reaction was, “what, you want me to do what to my cell?” Yeah. And, particularly with the international barriers and so, it, it was challenging. So one of the keys to make it attractive and compelling is we had to develop a database or, of their technology or other, or other competing technologies, and how they on data, provide them data that they didn’t have. So with this device we could then test it and understand their failure modes, and then go back to the manufacturer and then show them unique data. And part of this unique data is the X-ray videography that we could get from testing at synchrotrons, where you could see at 2000 frames per second with X-ray videography…

Host: Cool.

Eric Darcy:…the cell misbehaving into thermal runaway. So we learned a lot about that phenomena, that dynamic effluent going, coming out of the cell. How does the internal short developed from a point throughout the cell, how does it vent out the cell? We looked at the feature of a bottom vent; we saw that it had big advantages, or significant advantages, in reducing the violence of thermal runaway. So we could go to the manufacturer and show them, hey, look at this, this design feature. Of course it’s up to them to adopt it or not, but having that data allowed us to be attractive to this mass manufacturer, to listen to NASA who’s only going to be buying ten, ten thousand cells or so, which is less than a couple of minutes of production, or less than an hour’s production, and so it was a real battle for us because we’re such a small portion of their market share…

Host: Right.

Eric Darcy:…in production. And that, so if we had some compelling data or data that they didn’t know about their cell design, we were able to share, share that with them.

Host: Yeah. It was less as like a, like a customer feedback sort of thing, but more of a, what you were identifying was with, with this, with that this incredible data, the X-ray, you know, the X-ray footage and, and the, such fine frames, right? You can identify the path and you can make improvements to your, to your battery for the whole production line. That’s really it…

Eric Darcy: Yeah.

Host:…is really, it’s not just for NASA, this is for your whole, this is for your whole gig.

Eric Darcy: Yeah. Yeah. And so, there’s an interesting story of this, once we invent this, this device and got the word out, the University College of London, who had, who has got really good imaging techniques for batteries, CT (computed tomography) scanning and so forth, contacted us wanting some cells with the internal short-circuit device because they had access to the synchrotrons on that. So a Ph.D. student named Donald Finnegan at the time contacted Matt Keyser and myself, Matt Keyser at National Renewable Energy Labs, and we partnered up and got them some cells. They took some amazing videography at 2000 frames per second, we could see the device going into an internal short, the fluidization of the layers, of the electrodes, and then propagating throughout the cell, and then the, the jelly roll ejecting out of the cell. It was, it was fascinating to see…

Host: Wow.

Eric Darcy:…and it was the first time anybody had seen that before, and it really captured the eye. And then we saw that this was a way of testing design features inside a cell. What, if we go to lower flammability electrolyte, what does that do? If we put a bottom vent in the cell, if we put a thicker can wall in the cell? And now what we’re looking at is, what if you put plastic current collectors?

Host: Oh.

Eric Darcy: Fusible plastic current collectors. So that look, has a lot of promise from what we’re seeing in the data to be able to tolerate internal shorts. So that’s been our focus lately on that.

Host: So you’re not done then.

Eric Darcy: No.

Host: You, yeah. You’re, you want to keep making improvements and, and, and that’s really, is that really your focus is to continue with the improvements to really just understanding things for safety, for battery safety?

Eric Darcy: Yeah. I mean the holy grail in batteries is if we could eliminate that catastrophic failure, the, the thermal runaway aspect, with a cell that still performs like the current cell technology, without a, a penalty in mass and volume.

Host: Yeah.

Eric Darcy: Or at least a penalty that’s less than 20%, which is the burden to have a PPR battery design. And then you’d have a net positive if you could do that.

Host: Yeah.

Eric Darcy: So that’s what we’re looking for. And so, there’s all sorts of development going on in solid state batteries, where you don’t have the liquid electrolyte. There’s all sorts of development in lithium metal anodes that get rid of the graphite. Right now lithium-ion has an anode that has, is made up of graphite, and the graphite has these intercalation areas where the lithium-ions go in and out. Well, that cause volume to do that. And so if you could eliminate that graphite and just go with pure lithium metal, there’s a big volume and mass advantage to doing that. But lithium doesn’t like to recharge very well. It forms dendrites, which poke through the separator and cause hazards and, and shorts. So it doesn’t have good cycle life. So, new types of technologies in terms of the electrolyte and the layering next to the passivation layers, next to the lithium metal, have to be developed to, to make that work on that. There’s a lot of research in there. As you can imagine with the push for electric vehicles, push for eVTOLs (electric vertical take-off and landing), there’s a lot of incentive to getting to higher performing batteries. And so, it’s, in my 30-year career I’ve never seen as much investment in R&D and batteries as there are today…

Host: Wow.

Eric Darcy:…in them. Yeah.

Host: That’s amazing.

Eric Darcy: So it’s, yeah. And the, the world of batteries is so many people want to be portable and so many different applications, it’s a very fast-growing field. And like I mentioned, when I started out, the battery group was two people.

Host: Yeah.

Eric Darcy: We’ve now grown to over ten people, and then with support-people and our testing areas, we’re many more than that. And we stay very, very busy.

Host: I bet. Yeah. Especially if you said, it’s, it’s, you know, we’re at a phase of testing and demand that hasn’t been seen before, that, that, that need to have smart folks that are working on this is, is very apparent. Now, it seems like it’s really important, and we’ll sort of end with this idea is, the, the insertion and the collaboration, what’s interesting about your, your work, Eric, is your immersion into the commercial industry to understand for space application. I mean, you’re, you’re, you had this, the, the program where you were able to go away for a year and work with commercial industry; you’re working, like you, you’re, you’re talking about under like gathering all these data from, from multiple different companies to understand like thermal runaway; I mean, it’s, you’re embedded into this whole industry. It’s, it’s absolutely fascinating. But this idea of the government and commercial combination, right, that the idea of technology transfer, the idea of, of working together to understand this, this seems like something that I think I, I think your perspective is especially interesting on because of your immersion throughout most, most, if not all of your career. Can you, can you, end with thoughts about that, this idea of NASA and its importance in embedding itself in commercial industry to better batteries?

Eric Darcy: Yes. We have strict requirements. We have confined space and spacecraft. We get a chance to push the edge of our knowledge of the risk, and we get a chance to do things and pursue improvements in detecting defects that other folks don’t get a chance to do that. And so we are helping in developing a lot of not only prevention techniques but also this technique of reducing the severity of the consequence. And so, we’re very privileged for that. And so I think it, it’s an onus on us to spread the word to as many people and many as industry as possible to get the benefits of that. And so I feel very fortunate. I’m super-fortunate to have some great folks working in the group. That’s the thing that I love about working in NASA is you get a lot of folks that all their lives wanted to work for NASA…

Host: Yeah.

Eric Darcy:…and so you get some very highly motivated folks with unique talents and, and a real drive. And so that, that’s what’s really kept me for 35 years here at NASA. It’s just and, and the projects you get, because of that are just fascinating. And in the world of batteries, you get involved in nearly every program. So I get to see almost every program, and it’s, you feel like, and it’s quick turnaround in terms of your impact. Because it typically takes two to three years to develop a battery. I mean, we did the Pistol Grip Tool in nine months, that was superhuman effort, but we, yeah. Anyway, so our feedback loop is short, and we get some good feedback and, and, and satisfaction from, from making an impact…

Host: Yeah.

Eric Darcy:…on that. Very, very fortunate. And like I said, it’s very blessed to have some very talented people working for me.

Host: Well, very cool. Yeah. And of, of course, you’re going to share all this knowledge with, with these folks, and, and they’re, they’re going to take their passion, take it to the next level. Like you said, you’re not done, right? You said you’re not done. So there’s just a lot of cool stuff to do, and your impact is, is very apparent. Eric Darcy, thank you so much for coming on Houston We Have a Podcast. This was so cool, just to understand the impacts on spaceflight and just the batteries that we have in our pockets, you know, we’re making, making things better one, one day at a time, one year at a time. So, appreciate you coming on.

Eric Darcy: Thank you, Gary. Thanks for having me.

[Music]

Host: Hey, thanks for sticking around. I hope you enjoyed our conversation with Eric Darcy today. We are coming on the back end of our Mars series. If you’ve been listening to our podcast, it was an 11-part series, we, we sort of rebooted it after doing it back in 2020 and 2021, wanted to do it all in a snapshot. And part of the reason was because I, myself, actually took some leave to be with my family. I just had a, a new son and took a couple of weeks. So I wanted to make sure that we continued giving you some content. We thought it would be smart to reboot that series, and I really hope you enjoyed it. Now we’re back with our regular scheduled programming, and I have a special outro for you because the thing is, we recorded some of the content that you’re going to be hearing throughout 2023, some of it was recorded in 2022, and this episode in particular was recorded back in August. A lot has happened in the battery world since then. And so, for this special outro for you today, we actually are calling Eric Darcy from the phone. He’s out in Colorado, skiing, but take, wanted to take some time to be with us today and give us an update because there’s been some progress in this field. Eric, thank you so much for coming back for this special outro.

Eric Darcy: Yes, thank you, Gary, for having me back. And it’s, it’s great to hear from you.

Host: Yeah. That’s right.

Eric Darcy: Congratulations on your son.

Host: Oh, thank you very much. Really, I wanted to focus on, on the batteries because, you know, we, we had this conversation and it was very detailed, but the thing is there’s been some progress. I know originally you were planning on retiring, but you stuck around to, to see some of this innovation through. So I’m going to pose this question to you just to sort of catch us up on everything that’s been happening over the past couple of months. What near-term battery innovation do you think would most benefit battery safety, and what is NASA doing to advance it today?

Eric Darcy: Yes. So Gary, we’ve made a lot of progress in verifying the safety merits of plastic current collectors in, last year, over, over the last year, and just wanted to give you some more details about what NASA’s been doing there. We have a, like I mentioned, a unique capability to, to get access to the synchrotrons where we can get super-high speed X-ray videography of cells while they’re failing, while they’re being driven into thermal runaway, such as with a, a nail. And so, by high speed, I’m talking 3000 frames per second, which really allows us to go real slow motion with these, and we’re able to see the fusible action of these current collectors. So, let me back up. A current collector is part of an electrode; it’s where all the current collects and gets driven and outputted to a cell, a lithium-ion cell, for example, and to go work in a battery and provide work. So the current collector, once you convert it from metal — which is what the current technology is using, copper and aluminum — if you convert that to polyester and metalize both sides of it with a very thin layer of copper and very thin layer of aluminum, you now have plastic current collectors that are thermally unstable when an, a defect, internal short event, occurs. That means it acts like a fuse. And the benefit of that is that it will vaporize and isolate the, the defect that’s causing the hot spot short inside itself from the rest of the cell, which allows it to tolerate a nail penetration, a metal nail penetration, which is unheard of because all current lithium-ion technology immediately goes into thermal runaway, or nearly all, a very violent reaction with fire and flames and lots of ejected gases and, and molten metals and, and, and all sorts of liquids and, and so forth. And it’s, it, it can lead to some very catastrophic events. So thanks to our team that’s able to go to these synchrotron – we are going to, we just went to one in Grenoble, France — and we were able to fire off some 129 cells. Nearly half of them were, had the plastic current collectors. And we were able to test the, and, and in fact, our results were 37 out of 38 cells that we penetrated with the nail over 2022 tolerated the nail. It’s unheard of, for us in lithium-ion with the flammable electrolyte to have that tolerance. So I just wanted to share that with you. I think that this is the most impactful battery innovation that has a low barrier to adoption by cell manufacturers, because we’re not asking them to change the electrochemistry. We’re asking them to change an inner component, the current collector, with a plastic current collector. And so it has some weight advantages, but really the big one is the safety advantages. And so the, the big thing that we’re doing is trying to understand how it works so that we can develop competence to get these big cell manufacturers that do high volume production to produce batch, small batches of these cells and give it a try and, and get us to a point where maybe they will adopt them and be able to mass-produce these cells for the benefit of the entire industry worldwide.

Host: That is, and, and that’s really why I wanted to have you on, Eric, is because what you’re talking about is a, an extremely significant update from, from our last chat, you’re talking about, I mean, we, we already talked about the advances of the battery industry but this one can truly be, can make batteries just safer across the board. And I’m thinking about the phone in my pocket, right? I’m thinking about the safety of, of even, you know, if, if something were to happen and something were to penetrate the battery, that I could feel that much safer. So Eric, thank you so much for taking time from, from skiing to, to talk with us. It’s a, it’s a, it’s a significant update and I really appreciate you coming on.

Eric Darcy: Thank you.

Host: All right. That was Eric Darcy, again; thanks for, for coming back. Now, if you’re sticking with us, and for 2023 for the upcoming episodes, I want to pitch this next one to you because it’s a big one. We are going to be announcing the new crew for Artemis II, the four astronauts that will be traveling to the Moon as part of the Artemis mission and returning to the lunar vicinity, and eventually leading to boot prints on the Moon. But these four astronauts, we have an opportunity to chat with. And so if you stick around for next week’s episode, you’ll get to hear from all four of those astronauts. You can go to NASA.gov for the latest on that announcement, and really everything NASA. NASA.gov/podcasts, if you want to listen to our full collection or check out some of the other podcasts that we have across the agency. If you want to talk to us on social media, we’re on Facebook, Twitter, and Instagram on the NASA Johnson Space Center accounts. You can use the hashtag #AskNASA on whatever platform you want to ask a question or submit an idea for us; just make sure to mention it’s for Houston We Have a Podcast. Thanks to Will Flato, Pat Ryan, Heidi Lavelle, Belinda Pulido, and Jaden Jennings for their help, help in the production of Houston We Have a Podcast. And of course, thanks again to Eric Darcy for taking the time on the show, for taking the time to come on the show. Give us a rating and feedback on whatever platform you’re listening to us on and tell us what you think of our podcast. We’ll be back next week.