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Alpha Magnetic Spectrometer: The Science

Season 1Episode 117Nov 8, 2019

Dr. Brandon Reddell discusses astrophysics, cosmology, and the science behind the Alpha Magnetic Spectrometer (AMS), an experiment looking for evidence of antimatter and dark matter in the cosmos. This is part one of a three-part series on AMS. HWHAP Episode 117.

AMS Science

AMS Science

If you’re fascinated by the idea of humans traveling through space and curious about how that all works, you’ve come to the right place.

“Houston We Have a Podcast” is the official podcast of the NASA Johnson Space Center from Houston, Texas, home for NASA’s astronauts and Mission Control Center. Listen to the brightest minds of America’s space agency – astronauts, engineers, scientists and program leaders – discuss exciting topics in engineering, science and technology, sharing their personal stories and expertise on every aspect of human spaceflight. Learn more about how the work being done will help send humans forward to the Moon and on to Mars in the Artemis program.

In Episode 117, Dr. Brandon Reddell discusses astrophysics, cosmology, and the science behind the Alpha Magnetic Spectrometer (AMS), an experiment looking for evidence of antimatter and dark matter in the cosmos. This is part one of a three-part series on AMS. This episode was recorded on October 8, 2019.

Houston, we have a podcast


Gary Jordan Host:Houston, we have a podcast. Welcome to the official podcast of the NASA Johnson Space Center, Episode 117, “Alpha Magnetic Spectrometer: The Science.” I’m Gary Jordan, I’ll be your host today. On this podcast we bring in the experts, scientists, engineers, astronauts all to let you know what’s going on in the world of human spaceflight. Coming up very soon, this November, 2019, astronauts aboard the International Space Station are set to kick off a unique and difficult set of spacewalks to repair an experiment called the Alpha Magnetic Spectrometer. Sounds a lot like something straight out of a sci-fi, right? But it’s very real and a very complicated piece of equipment. The Alpha Magnetic Spectrometer, or AMS, is looking at high energy particles and looking for evidence of antimatter and dark matter in the cosmos, which may reveal more about the formation of the universe. No big deal. Now with such a complicated particle physics experiment, comes some complicated spacewalks, very much on par with the Hubble Space Telescope Servicing Missions. We’ll have to do a podcast on that sometime. So to help bring to light the significance of this experiment and these spacewalks, we are going to dive deep into the story of the AMS and this repair, and break it into three parts — the science, the spacewalks and the tools — all with fascinating discussions with the experts that are working on repairing and upgrading the AMS. So today for part one of this three-part series, we are discussing the science of the AMS focusing on cosmology and astrophysics with Brandon Reddell. Reddell is an assistant program scientist in the International Space Station program, here, at the Johnson Space Center. He has a Ph.D. in physics specializing in high energy space physics. Most of his graduate work was focused on modeling high energy collisions, produced in accelerators on Earth, and at NASA, he spent over ten years testing and modeling spacecraft hardware and the human body for radiation effects. Here he also collaborates with one of the primary authors of the Galactic Cosmic Ray Model that NASA uses to predict astronaut health risks. As well as hardware reliability to improve model predictions for these deep space missions. The AMS is one such instrument providing data on cosmic ray species that are of interest in improving these NASA models. So let’s get right into it. Astrophysics and Cosmology 101 and the science of the Alpha Magnetic Spectrometer with Dr. Brandon Reddell. Enjoy.

[ Music ]

Host:Brandon, thank you so much for coming on the Podcast today.

Brandon Redell: Well, thank you. It’s a pleasure to be here and I’m looking forward to it.

Host: I am both excited and very nervous to talk about this today because we had talked a lot about human space flight, which is part of this story because it is an experiment on the space station, there’s going to be some spacewalks to actually go fix it. But now we’re getting into cosmology, we’re getting to astrophysics, so I’m going to do my very best to try to ask very appropriate and relevant questions for you.

Brandon Redell: No, that’s great. It’s a very complex experiment and it covers a lot of fields, so I’ll do my best to try to answer everything.

Host: Well, let’s go right into it. I wanted to start by, kind of, setting the background of what it is exactly that the AMS is exploring, by giving kind of a 101. So let’s go into cosmology and astrophysics. Tell us about the universe, Brandon.

Brandon Redell: Okay. Well, first of all, we know the universe is very big but we also know that it had a beginning, right? That’s been pretty well confirmed, really in the last century. Edwin Hubble, you may have heard of, first measured redshift is which is sort of a measure of how everything’s leaving, spreading away from us, right? At some velocity. So there’s been a whole slew of other satellite measurements like of the cosmic microwave background and things like that that have confirmed this. There’s no doubt that we know that it’s expanding and if you just take one over the expansion rate you can sort of derive how old the universe is, and so we know we’re about 14 billion years old. Now so the expansion rate is still under investigation, there’s some variations in the numbers, but they’re all indicating 13, 14 billion years old, something like that. And so what we do know too is we have a lot of theories, like from general relatively and things like that, that also point that there was an ultimate beginning that also fit the model and predict what the future of distribution of galaxies look like, you know, how the universe is spatially organized and things like that, and in the right elements that are in the universe. So we have really good models that help support that. And so we feel like we have a pretty good view of the universe.

Host: And that view, the thing you’re talking about right now, is the big-bang theory?

Brandon Redell: Yeah, it’s the big-bang theory, that’s sort of the generic term, but there’s actually several different models and we can talk about that now or later but–

Host: Let’s go right into it, yeah.

Brandon Redell: So one of the big models is called the “Lambda CDM Model,” [Cold Dark Matter]. So Lambda is just a Greek letter, looks like an upside-down triangle, kind of, like an upside-down V basically. And it’s really the value that refers to dark energy, OK? So the C D M part of Lambda, the CDM, is cold dark matter. So really this model is purely a mathematical model that’s a fit to only using only six parameters that basically described the overall evolution of the universe today. And so what we use is there’s something called the “Baryon Density” and we can talk about baryon’s here in a little bit. These are all inputs, baryon density, dark matter density, the age of the universe, and there’s a couple of other parameters, they’re pretty complex. But with only just six parameters we can actually from right after The Big Bang, using the current laws of physics, this model will run and it’ll predict basically the existence and the structure of the cosmic microwave background radiation, which we measure all the time. It also predicts the large scale of the universe. The distribution of galaxies, the abundance’s of hydrogen and helium, which are the abundant elements in the universe and so forth. So we have a — it matches a lot of what we observe, so it’s probably the most successful model, but there are some shortcomings and there’s some competitors, but that’s predominately the major model used today. And it’s sometimes it’s often referred to as the “Standard Model of Cosmology.”

Host: Yeah. So basically what you’re doing is you’re looking at the universe and you’re saying, here’s all the things that exist, this cosmic microwave background, right? Something’s that’s — it’s like, what is it three, four, Kelvin?

Brandon Redell: Yeah. Yeah. Yeah. That’s the current temperature.

Host: Yeah, it’s just so it’s fizzling in the background. So we’re like, what made this, what made the galaxies the way they were and you — this particular big-bang theory is a way of modeling that mathematically.

Brandon Redell: Right. And that’s just one thing that it models, right? It successfully models, like, what’s really important is the abundance of elements that were created initially in the Big Bang because once that’s said, that determines how much mass you have in the universe and how much stars and galaxies you have, and so forth. So that’s really an important feature as well.

Host: See, that’s one thing that’s really it’s fascinating to the point where I don’t think anyone can really fully comprehend just, you know, when you’re talking about stuff in the universe.

Brandon Redell: Yeah.

Host: How much stuff there is. You know, we’re looking at our galaxy and we’re like, wow, that is huge.

Brandon Redell: Right.

Host: That’s full of billions of stars. And now we’re figuring out that a lot of these stars, or maybe most of them, have planets. So it’s just becoming so big just in one galaxy and then you find out, yeah, there’s a few more galaxies.

Brandon Redell: Well, there’s that, right? So the current estimates are there’s billions of galaxies.

Host: Yeah.

Brandon Redell: There’s been some research done in the last year that if you look at smaller galaxies that are called “dwarf galaxies” so like the Milky Way Galaxy has several dwarf galaxies, like, we have the large and small Magellanic Clouds, but outside of that, they’re so small that we can’t even see. So most galaxies have maybe hundreds to thousands dwarf galaxies. So when you factor all that in, some of the estimates in this recent research estimate trillions of galaxies.

Host: Oh, see, now, don’t do that to me. [laughter]

Brandon Redell: They’re big numbers but not all galaxies are as life, as we know it, might not be suitable for life because there’s a lot of instability and irregular and elliptical galaxies, and things like that. But nevertheless, there’s a large amount of material. And one thing that’s kind of interesting is when you actually look at all the galaxies and stars, when you talk about the total content of the universe, matter and energy, that’s only about 5% of what we really see out there. So the rest of it is unknown, so we only know a lot about a small amount, right?

Host: Yeah.

Brandon Redell: When you look at just as mass alone, the amount of stars and galaxies is approximately 15% of the universe, by mass. And this mysterious material of dark matter is another part of it for mass.

Host: It has to do with the way that you’re modeling the predictions of the universe, right? So there’s — if you just do the calculations based on what you observe mass wise, it just — it doesn’t work out, there’s this other thing that’s helping out with the formation of the universe.

Brandon Redell: In a sense you could say that.

Host: OK.

Brandon Redell: Now, we know observationally, and we have indirect evidence of dark matter. I mean, we can look at the galaxies, the rotation curves. In fact, that’s sort of how it was first determined, was that there had to be a lot more mass around galaxies to account for the rotation of stars around the out on the spiral arms and things like that. We also know the universe is expanding and that’s related to this dark energy term. So these are all parameters that we can measure. Going back to this Lambda CDM model, those are all predicted based on these initial six inputs, and so we can compare that with what we measure as long as, you know, we know the model’s predicting everything we see we have good reasons to believe that what that model predicts for these values are indeed close to what they are in reality.

Host: So what does that say about what we know about the formation of the universe? Like, what questions I guess what I’m leading to, is what questions do we have even with this model that we still need to answer?

Brandon Redell: Well, so – yeah, that’s a great question. And so, again, this model sort of picks up at some small amount of time after the Big Bang, right? So we don’t know obviously what was before the Big Bang, right? The current understanding when you look at the space time theorems that there was nothing, right? So that’s really hard to comprehend.

Host: Oh, yeah.

Brandon Redell: That actually gets into the metaphysics and things like that. But once we have something started, there’s a lot of uncertainty of what initially happened in that first ten to the minus 38th seconds or something like that, right? So one of the current theories is called “Inflation” so for approximately a ten to the minus thirty six seconds or so, the universe expanded twenty orders of magnitude. We don’t know how to model that, but we do have some evidence that that actually occurred. So that part of the model has not been sorted out as far as modeling that Initial Inflationary epoch of time, so that needs to be incorporated. And then on top of that, you might have heard of this term called “Quantum Gravity” we don’t know how gravity works at the quantum level. And so our understanding of physics and recombining all these forces back at that earlier time, that’s sort of a — that’s current modern research in particle physics and its astrophysics, cosmology, it sort of all blended together at that point. But there’s a lot of understanding of the physics going on at the smallest times scales right at the beginning of the universe.

Host: So naturally, and this can sort of lead into our discussion about AMS, is based on these models of how we think the universe is created and what we would like to understand, what are things that we can look for that would provide the evidence?

Brandon Redell: Right. And so — yeah, that’s exactly right. AMS is looking for antimatter and I can talk about that here in a second.

Host: Yeah.

Brandon Redell: Dark matter and just cosmic rays in general. One of the big questions is — and this is perplexed astrophysicists, cosmologists for decades now is when we look out at everything, why is there only matter and no antimatter? Because these initial models, like Lambda CDM, they actually predict we should have a 50/50 mix of antimatter and matter. Antimatter is simply it’s the same thing as matter but it has the opposite charge, if you think of a proton as a plus charge to it, an antiproton is the same mass but it has a negative charge and it also has some different quantum numbers that kind of determine the spin and angular momentum and things like that. But effectively, it’s the same particles with negative charge. And so AMS is looking at signs from antimatter to try to understand, is there any original antimatter out there from the creation of the universe or maybe is it there’s some theories that talk about dark matter either decaying or annihilating each other that could produce antimatter. So that’s sort of why it’s designed and located in space, is to make these measurements to try the help sort that out. And at the same time a lot of these things, as they travel from distant parts of our universe, our galaxy, to Earth, they become high energy and they’re just high energy particles moving and we call those cosmic rays. And so those have direct application in bearing on success for human space flight as well.

Host: OK. So I want to go through. So you talked about what it’s looking for, you said antimatter is one of them because there should be antimatter, so where is it? The other part was did you say dark matter? Was it what it’s looking for?

Brandon Redell: Yes, dark matter.

Host: So how do you — what’s going on there? How could we look for that?

Brandon Redell: OK. So for dark matter?

Host: Yeah.

Brandon Redell: OK. So dark matter, so we know observationally, like we mentioned earlier, we definitely know that there’s a lot of mass sitting out there around galaxies, for instance, in between a lot of the voids in space. The Lambda CDM model actually predicts 26% of the mass energy content of our universe is dark matter.

Host: Wow.

Brandon Redell: And so that’s in conjunction with predicting everything else in the universe. So we know there’s probably a significant amount of it, and most importantly, we can actually observe it. Also through gravitational lensing, we know that there’s got to be additional mass out there. And that’s light bending around other galaxies when we’re looking out in the distance.

Host: You’re measuring how much light is bending essentially?

Brandon Redell: Well, you’re looking at objects behind more massive objects, and so the light kind of gets bend around them and so you might see maybe two images because the light kind of gets split and you’re seeing — it looks like two different angles, but it’s really being bent around a large massive objective. And so we know, just looking at the normal matter there, that there’s got to be more mass to bend that light because we know general relatively pretty well. In fact, it’s probably the most accurate or the most well tested of the physics theories. I think we know it out to an accuracy of 15 or 16 decimal places.

Host: And what’s that, general relatively?

Brandon Redell: Yeah, the general — Einstein’s theory of general relatively.

Host: Which says space and time, is that the one or is it something else?

Brandon Redell: Yeah, yeah, yeah it’s related it’s– you know, defined by a very complex math but in effect really what it’s saying is it’s another form of gravity, but it basically tells you that mass warps the space around it and it’s that warping of the space that controls how that mass moves in there.

Host: I see.

Brandon Redell: So it’s very interlocked. It’ll make you think a little crazy if you think about it too much, but it’s very — mass and gravity are effectively, you know, related.

Host: OK.

Brandon Redell:To that. So dark matter, we’re trying to measure that because nobody knows physically what’s it consist of, right? We know indirectly it exists, but we don’t know what particles it’s made of. And so there’s some theories out there that don’t have any direct scientific evidence, but mathematically, if you extend the standard model of physics, which predicts all the right particles out there, there’s various forms of that that lead to prediction of these exotic particles. Things called “WIMPs, axions”.

Host: Cool.

Brandon Redell: Things like that. A WIMP is a Weekly Interacting Massive Particle that’s just an acronym because it’s called dark matter, it’s dark, it doesn’t give off or interact with light. So that it’s really hard to see, it’s hard to probe it and test for it and so that’s why we can’t measure it. But the idea is if these — if this dark matter consisted of these other particles, it can interact with itself and create secondary particles that we know about and maybe can detect. And so that’s what we’re looking for, detecting these secondary interactions that indicate, you know, some other type of particle that’s theorized right now.

Host: OK. Yeah. And this is along the lines of things we can look at to, sort of, help us give that evidence of how the universe forms, we talked about antimatter, we talked about dark matter. The other one you mentioned was cosmic rays?

Brandon Redell: Yeah. Cosmic rays, yes.

Host: So what’s that one?

Brandon Redell: So if you think — so I said the universe was about let’s say 14 billion years old, the first generation of stars, they’re actually called “generation three stars” in galaxies they kind of formed a couple hundred — when the universe was a couple hundred million years old. From that time forward, there’s been generations of stars in galaxies that have gone through these lifecycles and processes. And so for massive stars, one of their end states is they swell up and then they get so big and then gravity pulls them back down when they exhaust their fuel and they explode as a super nova. And so a lot of the cosmic rays, are just — if you think about the periodic table of elements from hydrogen all the way up to iron, they’re just the nuclei, no electrons around them, just the nuclei’s zipping through space at relativistic speeds. As they travel, they interact with magnetic fields and they get accelerated. So they’re moving very fast, you know, the speed of light and they’re all over, they come from every possible direction at random angles and they’re floating around the universe everywhere.

Host: Wow. So they’re high energy, are they heavier particles too?

Brandon Redell: Yeah, yeah, yeah. So like a proton has — it’s just a proton with an electron around it. You go to helium, you have two protons and two neutrons, right? So as you go up the periodic table of elements, all the way up to iron which has 26 protons and 56 nuclei protons and neutrons. So, yeah, the higher you go up in the periodic table, the bigger the nucleolus is and therefore, the more damage they could cause too.

Host: OK. Now, there’s something else here that it might be a separate topic or it might be along the lines of stuff that we can look for are “quarks” are they intermingled in this in anyway?

Brandon Redell: So quarks, yeah, they’re — they play a role in this.

Host: OK.

Brandon Redell: But they don’t exist by themselves. Quarks, they basically the only way we really can see those is through — like, currently, if you look at, like, particle gliders like at CERN, right? It uses very high energy interactions. So it accelerates, let’s say, two protons near the speed of light and collide them and then for a brief amount of time you, sort of, break it up into its parts, and we can talk about that in a minute. But a proton’s made up of three different quarks. So for baryonic matter, which is another name for saying all the matter that we see and that you and I are made up of and all the stars and everything, pretty much made up of quarks and there’s six different flavors of quarks. But this strong nuclear force sort of binds them together and so it’s so strong that you really can’t separate them for that long without them recombining or interacting some other way. So they don’t exist by themselves, but you can infer things about quarks based on studying these other particles.

Host: I see. So that’s where they come in, by studying the other particles?

Brandon Redell: Yeah.

Host: OK. OK. So now, I think we set a nice base for cosmology and astrophysics. We have this idea of how we think the universe formed and we’re looking at these things to help us give evidence of that. So now let’s go to the Alpha Magnetic Spectrometer.

Brandon Redell: OK.

Host: What is this thing and how it is helping to answer those questions?

Brandon Redell: OK. So I like to think of the Alpha Magnetic Spectrometer Version 2, which is on space station, as basically a particle physics experiment that you might see at CERN [Center European Research Nuclear, Geneva, Switzerland]somewhere. But instead of being at CERN, it’s mounted on the trust of the space station, right? So it’s unique in the sense that it is a modern physics particle detector, a very complex one out in space, right? On the space station. And so what it — and we can talk more about the hardware if you want but it basically has six, seven different type of detector systems to help you measure all the parameters that you need to help sort out these big questions about antimatter, dark matter, and cosmic rays, right? Like as far as measuring the charge of these particles, the masses, and if it’s antimatter versus matter.

Host: OK. So it is — the position in space has a certain benefit to it.

Brandon Redell: Yeah.

Host: In terms of finding where these particles come from.

Brandon Redell: Yeah. OK. So yeah, that’s a good point.

Host: Yeah.

Brandon Redell: So being up on space station where we’re above most of the Earth’s atmosphere, if we weren’t, if we’re down on, let’s say, on the surface, you have this column of atmosphere above us. And most of the cosmic rays interact with the oxygen and nitrogen in the atmosphere and they break apart, and so you really don’t get a direct measurement of the primary cosmic rays. So we’re above most of that and so we have a direct path of measuring those primary particles and then we also have the infrastructure on space station with power and data and so forth that helps make it possible.

Host: OK. So you mentioned going into the hardware of AMS, like what —

Brandon Redell: Yeah.

Host: — is inside of it that actually helps to — so how’s that work?

Brandon Redell: Okay. So basically there’s — AMS, so the A M in the AMS is magnetic, Alpha Magnetic Spectrometer. So basically it has this large magnet in the center that’s approximately three thousand times the strength of the Earth’s magnetic field, so that sounds like a lot.

Host: Wow.

Brandon Redell: But it’s over — let’s say, about a meter or so in space, right? Whereas, Earths field’s around the planet, right? So it has more bending power. But nevertheless, that’s a very powerful magnet to be in space, and so what we do as these charged particles zipping along in space, when they come near a magnetic field, they like to spiral around magnetic field lines. And so the direction they spiral, tells you the charge, right? If it’s a positive charge, it’ll spiral in one direction, if it’s negative, it’ll go the other. So the purpose of the magnetic field is just strictly to get particles to bend it a little bit. And so all of the material around that magnet is six or seven different detectors, let’s say. So there’s silicon trackers that basically measure the trajectory and that’s how we can get the curvature so we know which way it’s a parameter when you know to help based on the magnetic field strength, to get the charge and the momentum of the particle, which is related to its energy.

Brandon Redell: OK.

Host: There’s transition detectors that help distinguish protons and electrons versus really just between protons and electrons. As it comes in, it transverses many layers of materials, you get different X-rays that are created from, let’s say, the electrons that don’t get generated by protons, so we can distinguish between those two types of particles. There’s something called “Time of Flight Counters” that use energy lost to basically help understand the charge of the cosmic rays. Also, it helps on timing the events because we need to count the ones that enter in one side and travel out the other side, not coming in through the side of it. So as it trans you know, basically, when it goes through one end of it, it kind of starts it kind of resets all the other detectors. It says okay start counting at this point so it can measure all the right parameters and tie it to the same event. And then there’s something called “Anti coincidence detectors” to help roll out particles coming in from the side because you don’t want to count those if you don’t have the full — having the particle interact with all the detectors where you could set all the full information, you’re only going to get a subset of information and that could be erogenous on some of the data analysis. And then there’s something called a rich — it’s called, “RICH” it stands for the Ring Imaging Cherenkov Detector. So when particles move faster than the speed of light inside a material, they admit a light cone, it’s a well-known, it’s called the Cherenkov Effect. And so the size of that cone tells you a lot about the velocity of that particle, so that helps really measure the velocity. And then finally there’s a thing called the “E Cal” it’s an electromagnetic calorimeter and it’s just a bunch of material. And so when a proton type particle comes in versus an electron, it has a different type of particle shower. So it can basically distinguish electrons and positrons separately from protons and heavier nuclei, like helium and stuff. So between all these six detectors, we’re basically measuring the charge, the mass, the momentum or energy. And so you build up this — you just collect particles over time to build up statistics so that you can get more accurate answers to understanding, you know, the distribution of particles that are coming in.

Host: So it’s more collecting information about what’s happening to the particles as they pass through, based on how they react with the magnetic field?

Brandon Redell: Right, right. Exactly.

Host: Yeah. OK.

Brandon Redell: The magnetic field, it’s all about the magnetic field.

Host: Yeah.

Brandon Redell: So and that’s related to the AMS EVA’s. The magnetic field causes the particle to go through the silicon trackers. And so that’s really key to understanding if it’s matter versus antimatter because if it curves one way or the other. We need to be able to measure that, and if you can’t measure that there’s no way — you can’t tell.

Host: Oh.

Brandon Redell: So that’s sort of why the reason for the EVA’s to repair some equipment on that.

Host: I see.

Brandon Redell: And we can talk about that in a minute. But ultimately, it’s a very complex system, it has a lot of computers in it, a lot of data channels and but it’s all about counting particles, counting particles, their energy and their charge, basically, and mass.

Host: Yeah, just a massive collection of data.

Brandon Redell: Yeah.

Host: Because, like you said, there’s particles flying everywhere.

Brandon Redell: Yeah.

Host: Space happens to be a great place to do it and it’s measuring the way they’re interacting. That’s interesting. I did have a clarification point because this part is just kind of rattling around in my brain, you said when positively charged particles go through the magnetic field they spin one way.

Brandon Redell: Yeah.

Host: And when negatively charged, they spin the other way.

Brandon Redell: Yeah.

Host: Now, what’s the difference between antimatter?

Brandon Redell: So, antimatter’s, it’s the same thing as matter but it has the opposite charge.

Host: Yeah.

Brandon Redell: So for instance, the positron is the antimatter equivalent of an electron. So electron, as we all learn in high school chemistry, has a negative charge, right? E with a minus sign. Well, positron is the exact same mass, 9.1 times 10 and minus 31 kilograms, but it has a plus charge. So there’s this fundamental physics theorem called the “Lorentz force” and it has to do with a charged particle moving in the presence of a magnetic field. And so there’s a force that causes the beginning of the bend. So a positive charge, when you do the math, it’ll tell you, let’s say, go clockwise, if it’s traveling a certain direction around the magnetic field. The opposite charge, the math, the force bends it the opposite direction and it’s strictly because of the minus sign difference.

Host: I see.

Brandon Redell: It’s really I mean, mathematically, it’s just the difference of a sign but that’s — it’s been verified since Isaac Newton’s time, probably, right?

Host: Yeah.

Brandon Redell: Probably not that far back, but they didn’t know about electrons and stuff back then. But it’s really well known.

Host: So a proton has a positive charge too —

Brandon Redell: Yeah, proton’s positive.

Host: — but it’s just basically the way that an electron would interact and the way a proton would interact are different they would just spin opposite because they’re antimatter?

Brandon Redell: Yeah. The direction well, OK, a proton is not antimatter, but a positron is.

Host: That’s what I’m saying is that, like, the way a proton goes through and it has a positive charge, it spins like a positive charge but it interacts with the magnet because it’s a proton, it’s not a positron, right?

Brandon Redell: Right.

Host: Yeah.

Brandon Redell: So all charged particles will spin one way or the other.

Host: Right.

Brandon Redell: So if it’s positive, let’s say for the sake of the argument, based on the configuration of the magnetic field, like, what directions they’re pointing in. All positives will go one direction, all negatives will bend the other way.

Host: Yes.

Brandon Redell: And so whether its so all you know from that is just really is it plus or minus? So you need other instruments to tell you what the mass is. Now, this silicon tracker may whole because you’re recording the trajectories it goes through. So a proton’s about a thousand times heavier than electrons. So it’s harder, it can’t, you know, depending on the energy, right? It’s going to have a slightly different curvature than that. So there’s some information gain from that but that’s where these other detectors come in to help you sort that out.

Host: Got it. OK. So that’s different. I was thinking positive charge but they’re just different so that does make sense.

Brandon Redell: I would like to — can I go back and say one thing?

Host: Yeah. Please do.

Brandon Redell: So since you were talking about antimatter and matter, so that’s one of the outstanding questions in all of the physics. You know, like we said earlier, about it should have been about a 50/50 mix, there’s actually some research out there, based on theory, that says shortly after the beginning of the universe, the amount of positive matter was just barely above the count for negative matter. So, like, I think the number’s about ten billion, so for every ten billion antimatter particles, there’s ten billion in one. So it’s just the slightest imbalance. The current theory is that all this matter, antimatter annihilated each other and that’s why it’s gone. And then you had the small residual positive matter that ultimately led to, you know, having a positive matter dominating the universe. So that’s why it’s really important to try to understand is there any original antimatter left over because we could have antimatter galaxies or gas clouds out in space or stars made out of antimatter. Theoretically, it’s possible, especially if it wasn’t all used up or interacted early in the universe, so that’s sort of what the AMS is looking for. And it’s hard to distinguish between, is it the original antimatter or is it antimatter created because of dark matter interacting with itself? And so that’s what it’s trying the sort out. It’s possible to measure antimatter but where is it coming from? That’s big question.

Host: OK. Yeah. This is super complicated.

Brandon Redell: Oh, yeah. There’s a lot.

Host: So speaking of complicated, going to how the AMS works, I know you said this was the second iteration that we’re going to be working on the space station, there was one I believe to just make sure that this technology works in space.

Brandon Redell: Right.

Host: So that was actually even before space station.

Brandon Redell: Yeah, yeah, that flew on the space shuttle back in–

Host: ’98.

Brandon Redell: Yeah, 98.

Host: Yeah.

Brandon Redell: And so that was called AMS-01 and it was, you know, so most shuttle missions were pretty short, like less than weeks. I think this one flew for ten or eleven days, I believe. And it was very similar, maybe not quite as complex, but it was sort of a pathfinder to prove out this technology. And in fact, I believe there’s been six or seven papers that came out of that work, even though it was active for maybe ten days or so, it collected enough information to make some statistically relevant observations. And it sort of — one of its primary claims that it made was that a lot of people still quote and we’re trying to verify now is sort of an upper limit to this helium, anti-helium ratio. So anti-helium is just another antiparticle, right? So helium, which has two protons, two neutrons but it has a negative charge. So AMS has the ability to distinguish between the two. And so a lot of people think if it can measure so protons are the most abundant elements and then helium’s the second most. So the protons interact a lot with other materials. So you have — let’s say more noise, a lot of other things to consider, whereas, the helium’s probably a cleaner signal. And so it’s really important to try to measure the helium component to get let’s say, a more accurate understanding of what the origin of dark matter. So that was an important find and then the AMS-02 detector is designed to try to probe a little bit — the same number, right? But with more accuracy.

Host: OK. So yeah, let’s go into AMS-02. It looked at this helium, anti-helium and then actually proved that that technology works. Now the AMS-02, it’s a very complicated piece of equipment and it took a long time to get up there, especially because of several delays too.

Brandon Redell: Yeah.

Host: Like that’s even Columbia I think had it.

Brandon Redell: Yeah, so there was — yeah, you know, I think there was probably delays even on the ground because it’s such a complex experiment.

Host: Yeah.

Brandon Redell: It’s a typical experiment you might see at CERN. It involves what? Sixty different institutions as of now, that number can change a little bit, but sixteen different countries. So, like I said we had, I think six different detector systems or so. So there’s a lot of hardware and so there’s a lot of integration involved and a lot of different individual things that have to come together at once, plus combining with typical, putting hardware up in space schedules, things like that. So that made it difficult but it did make it up on Shuttle Discovery in ’98. And like I said, I think it was a ten day mission or so.

Host: I was thinking about AMS-02 though, AMS-02.

Brandon Redell: Oh, the AMS-02?

Host: Yeah, AMS-02.

Brandon Redell: Yeah, so it’s the same thing. It flew up on STS-134 in 2011, I believe. And yeah, I mean, I think the collaboration after AMS grew, the sixty number I was mentioning, I think that’s really AMS-02.

Host: Yeah. Yeah.

Brandon Redell: So it grew after that once it was proved successful and plus it had extra hardware added to it too to help with the measurements. So it’s a big integrated effort because, not only is it massive, you need the space shuttle to take it up. It’s an external payload, and that’s on the outside of the space station, you have the power data connection you had to use ISS communication, the high bandwidth we have, to transmit all that data down and you have a ground station. So there’s a lot of working with that that sort of played in setting up all that and — to help, you know, get that infrastructure in.

Host: Yeah, that’s a huge part of the story. I know it was difficult to get up there, you know, you said there was this big collaboration to make AMS-02 this possibility, but, you know, it needed to go to the space station because of how complex it is and you said it’s observing so many particles. The space station had an abundance of power and a great system to transmit data that can actually make this thing work in space and I was think one — maybe the only place that it–

Brandon Redell: Yeah. Right now it’s the only place like this, right?

Host: Yeah.

Brandon Redell: I mean, it’s a National Laboratory, it’s in orbit up there, couple of hundred kilometers up and it’s the only place right now that we could have the infrastructure to do these sorts of things so.

Host: OK. So that’s a big part of the story. I did want to take this time though to plug — and I’ll plug it at the end too, there’s this great documentary, I don’t know if you’ve seen it. It was actually produced at NASA, here, but it’s called “AMS: The Fight for Flight”. And it’s a whole story —

Brandon Redell: Yeah.

Host: — from AMS-02 to the ground–

Brandon Redell: Yup.

Host:Fighting its way, and then finally getting up to the space station in 134.

Brandon Redell: Yeah, no. I’ve seen that, that is —

Host: Yeah.

Brandon Redell: I would recommend that too.

Host: Oh, yeah. So that’s a great snap shot of the history of AMS. So let’s get into what’s happening and fixing it. So what is — what’s going on with the AMS that we need to fix it right now?

Brandon Redell: I think, you know, so the AMS originally I think had a three year design life and so we’re well passed that, right? It started, I think, what? I think it became operational in 2011, shortly after it was installed. So we’re well passed that design life it has, you know, like a lot of satellites and major pieces of hardware, you to want built redundant systems. And so it has these four cooling pumps to help circulate liquid carbon dioxide through the various detector systems to help radiate absorb the heat and then radiate it off into space, right? To help keep the instrumentation cool. The reason why we need to do that is we’re measuring these individual particle impacts that are very — each one by itself is a small amount of energy, but the electronics is very sensitive to temperature, right? If you have very warm electronics you’re going to have a lot of electrons bouncing around and it’s just noise and it’s hard to distinguish between the noise and the actual signals, so if you cool it down you minimize the electron noise. And so that’s the purpose of the pumps and I think three of them have pretty much failed and we’re on the last one. So the experiment was never designed to, sort of, be fixed in space, so there’s been a lot of planning for that. But the idea is to go up there, remove the old system, put up a new pump system and extend the life, and I think the numbers I’ve seen is that we can extend it probably for the rest of the life of the station since all the other detectors seem to be operating really nice, it’s just a matter of getting the cooling pumps. I mean, it’s still working now but, you know, we don’t have any more redundancy, so if we can those up there and working that’ll guarantee more signs.

Host: That’s awesome. Now, you as a physicist, I’m sure — I mean, you’re here now talking about this because you’re interested in this, why is it important — why is the AMS important for this discovery?

Brandon Redell: Well, it’s important because, you know, we all have the big question of about life, the origin of life, the lower origin of the universe, there’s a lot we don’t know so ultimately this is answering these big questions. So there’s actually multiple fronts. There’s a curiosity point, you know, for me I like to add, but in my day to day job I’ve done a lot of work in the past with cosmic rays and so we’re actually gathering a lot of information on cosmic rays. And so NASA’s main goal right now is to eventually spend more time out in space, right? Let’s say at the Moon and eventually go to Mars, right? So that means more time, radiation’s a big problem. So the better we can characterize the radiation and learn how to work in those environments makes a big difference, and so I’m always interested to get more data in that because I enjoy some of the modeling we’ve done to create that because there’s a lot of physics and science involved in that. So I would say just in conjunction with that and just answering fundamental questions about the universe, if we actually find out what if dark matter is and how that plays into cosmological models, you know, that can reveal some information about unknown energy sources that we can maybe tap into also to help for the benefit of humanity. So there’s a lot of very futuristic, kind of, goals that come out of this, but it ultimately leads to greater understanding and opening up the gateways for us to explore space.

Host: Yeah, there’s multiple different physics disciplines I think that this will help with.

Brandon Redell: Definitely.

Host: And you specifically, you’ve done a lot of — you even mentioned, a lot of research on cosmic rays.

Brandon Redell: Yeah.

Host: And like you said, the effects on the human body.

Brandon Redell: Yeah.

Host: You know, what are some of the things that you studied in terms of how cosmic rays affect the body?

Brandon Redell: Yeah, well, so I didn’t necessarily look at the biological damage.

Host: I see.

Brandon Redell: But there’s a whole suite of scientist here at the Space and Live Scientist Group that does a lot of that work. We do know radiation’s bad, right? There’s two types of effects, there’s some called “acute effects” which are short term high dose, like we’ve all seen the movies when, you know, when bombs go off or whatever and there’s a lot of radiation, people can die from that, right? So that’s a big problem because when we travel to Mars there’s bursts from the sun that are high — could be potentially high sources of radiation. So there’s ways to partially shield some of that, so that’s always an active experiment or understanding of engineering problem, right? Just how can we maybe avoid shield some of that or what. Using magnetic field is possibly one way to do it, at least the shield part of it but these things, these cosmos rays are very high energy, so we may never fully be able to shield them 100% but understanding the –how the body tries to repair itself on certain kinds of radiation is an active area of research. One of the bigger things that we’re trying to protect most our astronauts from right now is the risk of getting cancers from exposures, right? So we’re trying to minimize their risk. They’re categorized as radiation workers, just like nuclear power plant workers are, slightly different limits to be contusive for space work. But so that’s stuff’s carefully monitored and practiced when they select crews and so forth, so that’s always a consideration. My particular area that I was really focused in on is a lot of people don’t know radiation is really bad for electronics. So as opposed to a dose, which is an accumulation of a lot of particles, you can actually have a single particle come in and take out your main processor and your flight computer and you can lose your computer, right? And lose control of the vehicle for it, you know? So there’s a lot of engineering designs and so we’ve designed the Orion vehicles quite hardened to radiation, so that that’s been a consideration. And just about any satellite that goes off beyond Low Earth orbit or let’s say geosynchronous orbit and beyond, have to consider these things.

Host: Yeah. That’s actually — we had an episode on that.

Brandon Redell: OK. Yeah.

Host: We had an episode on how Orion has radiation hardened.

Brandon Redell: Yeah.

Host: And like you said, it could take out computer systems. So the way, you know, understanding how cosmic rays effect that, what they ended up doing is build redundancies.

Brandon Redell: Yeah, and that costs money.

Host: Sure.

Brandon Redell: But in space, in real estate, right? And mass. So you have to figure all these things out. So it’s an integrated problem but ultimately it’s a reliability problem too. And just one other thing that people might not know is just like radiation doesn’t necessarily mean you’re going to die if you get an exposure to your body. The analogy for electronics is it doesn’t always break parts it can just change your data.

Host: Oh.

Brandon Redell: That’s the more dangerous stuff. Is when it flips your data around, how do you handle that? So you have to have smart software and things like that.

Host: Yeah.

Brandon Redell: So those are all similar things, but radiation in general is one of the bigger risks to a long duration space flight that’s still being worked on the human level and to a lesser degree, probably on the electronic side.

Host: Wow. OK.

Brandon Redell: But it’s nevertheless, drivers for designs and things like that.

Host: Yeah. So AMS is helping us to understand, kind of, the formation of the universe, but then understand more about these particles and how they may interact with stuff.

Brandon Redell: Well, yeah. It’s so we’re learning, you know, we’re basically accounting them, right? So we’re understanding the distribution of the types of particles and improving our ground base models that let us predict what the fluxes of these particles are, let’s say at the Mars orbit or something, right? So when we do — when we plan flights we try to predict ahead of time what the radiation levels are going to be depending on the length of the mission and the solar cycle, all these things, right? So the AMS data is helping us improve these models.

Host: That’s awesome. So, you know, AMS is on the space station, we’re coming up on some spacewalks that are helping to fix this piece of equipment well, I guess, like you said, not necessarily fix but just add the redundancies and extent life because some of those cooling pumps have failed, so just adding those. But, you know, we’re dedicating human space flight to this effort, you know, we have people going out and fix and what we learn from it can be used for future human space flight. So, you know, you being a physicist, why is it important to explore with humans?

Brandon Redell: Well, you know, this is a question that has answers, pros and cons both ways, right? I think most people probably would consider robotic maybe as a pathfinder for humans. Obviously, sending humans is a risk, right? So there’s always that risk that we have to weigh for. But some of the advantages for human space flight, I would say, you know, humans can have — make quick decisions when need to be. I remember when Apollo 17 astronauts talking about their mission, looking at the geology on the Moon and so forth, you know? So in the course of eight hours I think they covered twenty two miles of surface. Well, if you look at Mars Opportunity Rover, it took eight years to cover that same area. So functionally, I mean, I think humans because you can make the decisions to cover more territory, might be a little bit more efficient once the, let’s say, they establish, an infrastructure’s established. And also humans maybe can deploy certain things if we’re looking at, let’s say, drilling for In Situ Resource Utilization, that’s a hard thing to do with satellites — I mean, with robotics controlled through satellites, and so forth. So I think there’s some advantages to have humans doing some of that work. Certainly, if we’re going to have a human presence somewhere, maybe for scouting out territories or things like that, that might be better off for robotic type missions. But I think in the end because we want a human presence, we have to prepare to get us used to working in these environments and so forth, so there’s that part of it too. So I think they both have their uses, it’s just really what phase in the exploration we’re in. Also, some of the robotic missions can go to hostile environments that we can’t do with humans, so that’s the advantage probably for robotics as well.

Host: Yeah. And we get a lot of the same answers but I just love asking that question.

Brandon Redell: Yeah.

Host: Because we’re in the business of human space life. So just I think, you know, one of the biggest things that I appreciate definitely is the inspiration value. I mean, you’re not going to get someone too attached to a robot but you can see them really, really feeling like the same feelings with a person.

Brandon Redell: Yeah.

Host:Going to explore.

Brandon Redell: Yeah. And I would say — I would just add, like, if we’re just strictly talking — if I’m only interested if particle physics, I don’t need a human to do that right? We can build a detector and send it somewhere.

Host: Yeah.

Brandon Redell: And that’s just as good from that perspective.

Host: You don’t want a person grabbing particles as they go through?

Brandon Redell: Well, it’s just unnecessary really. But I think overall, in the category of human space exploration, you have to have humans involved, right?

Host: Yeah.

Brandon Redell: And there’s efficient reasons why to do that.

Host: Yeah. Well, Brandon Reddell thank you so much for coming on and taking us through this history of astrophysics, cosmology and AMS, all fascinating stuff. I think I stayed in step with you, I think.

Brandon Redell: Well.

Host: But if not, we’ll have you on again because I can talk about this I think all day.

Brandon Redell: Oh, great.

Host: It’s just so fascinating.

Brandon Redell: All right. Well, appreciate it.

Host: Appreciate your time.

Brandon Redell: All right. Well, thank you and I appreciate the time and I hope it made sense too. Thank you.

[ Music ]

Host: Hey, thanks for sticking around. I hope you enjoyed this conversation about the science of the Alpha Magnetic Spectrometer and some basics of astrophysics and cosmology with Dr. Brandon Reddell. Definitely a fascinating discussion and I really should have him back on to talk more about this stuff because it’s super interesting. If you like podcasts there’s actually a few more NASA podcasts that you can listen to, I know specifically gravity assist goes into a lot of planetary science and talks a lot about these astrophysics and cosmology, it goes deep into that so you could definitely listen to them. Otherwise, check out some of the many other shows on We’re going to have updates on the Alpha Magnetic Spectrometer at and you can watch the spacewalks live. Just go to you can look at the schedule there and see when the spacewalks are going to be. I would highly recommended that you watch the NASA documentary called “AMS: The Fight for Flight” and learn more about the history and struggle of getting the Alpha Magnetic Spectrometer on the space station. It’s available through the link in the episode web page. If you have a question for us go to Facebook, Twitter, Instagram we’re on the NASA Johnson Space Center pages of any one of those social media platforms, whichever one you like best, use the hashtag #AskNASA on your favorite platform to submit an idea for the show, make sure to mention it’s for “Houston, We Have a Podcast.” This episode was recorded on October 8, 2019. Thanks to Alex Perryman, Pat Ryan, Norah Moran, Belinda Pulido, Rachel Barry and the International Space Station Program Science Office team. Thanks again to Dr. Brandon Reddell for taking the time to come on the show. And we’ll be back next week with more about the Alpha Magnetic Spectrometer.