“Houston We Have a Podcast” is the official podcast of the NASA Johnson Space Center, the home of human spaceflight, stationed in Houston, Texas. We bring space right to you! On this podcast, you’ll learn from some of the brightest minds of America’s space agency as they discuss topics in engineering, science, technology and more. You’ll hear firsthand from astronauts what it’s like to launch atop a rocket, live in space and re-enter the Earth’s atmosphere. And you’ll listen in to the more human side of space as our guests tell stories of behind-the-scenes moments never heard before.
For Episode 69, Dr. Greg Holt, Navigation Lead for the Orion spacecraft, discusses how the vehicle finds its way through deep space and communicates with Earth along the way. This episode was recorded on August 20, 2018.
Transcript
Gary Jordan (Host): Houston, We Have a Podcast. Welcome to the official podcast of the NASA Johnson Space Center, Episode 69: Navigating Deep Space. I’m Gary Jordan, and I’ll be your host today. On this podcast, we bring in the experts. NASA scientists, engineers, and astronauts. All to let you know the cool stuff about what’s going on right here at NASA. So if you’re familiar with us, you may have heard our episode on space communication networks. It was Episode 26: Can You Hear Me Now? With Bill Foster, a ground controller. It was a really good conversation. And it was a nice overview on how space communication networks work in general. Especially with day-to-day operations on the International Space Station. But today we’re focusing how space communications will work on missions out in deep space. We’re talking with Greg Holt, Orion Navigation Lead here at NASA’s Johnson Space Center. We talked about how Orion, NASA’s deep space vehicle, will communicate with Mission Control. All the way from the moon and beyond. And also what happens if a primary communication system fails. So with no further delay, let’s jump right ahead to our talk with Dr. Greg Holt. Enjoy.
[ Music ]
Host: Thank you for coming on the podcast today, Greg. Nice to have you here.
Dr. Greg Holt: Great to be here, Gary. Thanks.
Host: I love this topic of communication and navigation too. Because a lot of the space movies today. You see them, and there’s always something that goes wrong in the space movie. It’s, it makes for a great narrative. It makes for a great story. But it’s always that lack of communication. And oh no! I’m an astronaut, I’m by myself now. It’s that sort of thing. And so this is an interesting topic on to see how this is going to work. Because we’re talking about Orion. And we’re talking about deep space today. So let’s just kind of start with that. Let’s talk with, we’re talking about navigation. We’re talking about communication with a deep space craft. How does basic communication and navigation with the spacecraft work?
Dr. Greg Holt: So that’s a great question. And you know we’ve all seen those same movies. And us and the crew. And so we also spend a lot of time sitting around thinking about what do we do to make sure we don’t lose communication? And then boy on those very bad days when we do, what is the crew supposed to do about it?
Host: Right.
Dr. Greg Holt: But you know on a normal day out in deep space, we’re normally talking through. As you mentioned, there’s a Deep Space Network out there. That’s managed by our colleagues over at Jet Propulsion Laboratory in California. And they’ve been, had that running for decades now. And use it for a variety of interplanetary spacecraft. And so once we really get outside of our comfort zone around kind of lower-earth orbit. That Deep Space Network becomes our lynchpin for communication out there.
Host: So there’s several space networks then. There’s the Deep Space Network which is communicating with all these different robotic probes that we have all across the solar system. And that’s the primary, I guess network that we’re using for those, right? But there’s one that exists around here. What’s, what’s going on around earth?
Dr. Greg Holt: There is. There’s a Near Earth Network. And that consists of a number of ground-based dishes that communicate with satellites in low-earth orbit. And then of course there’s the TDRS or the Tracking and Data Relay Satellite constellation. That is up in a geosynchronous orbit that’s also communicating with satellites that are in the proximity of earth. In that near, low-earth orbit area. But again, once you get outside there, you’re really back on the Deep Space Network. And you have to use those bigger, more capable dishes to talk out there so.
Host: Right, because those TDRS satellites are geosynchronous, right? So they’re 20–, 22–, 23,000 miles I think away from earth. So once you, I mean, that’s, it sounds pretty far. You’ve got a pretty decent snapshot of earth. But once you cross it, I mean, they’re not, they’re not talking to that spacecraft.
Dr. Greg Holt: That’s right. And it sounds like a long way. But when we’re zooming, for example, out to the moon. Really only in contact really for the first 15, 20 minutes or so. Maybe 30 minutes if we’re lucky on the way out. But then we’ve really got to start handing over to that Deep Space Network because it’s a long way to the moon. And our, we travel fast, getting through that very first low-earth orbit phase.
Host: Oh wow. So you’re talking about after that, I guess it’s called, it’s referred to in all the old space movies TLI, right? Trans-lunar injection? That’s that final burn that gets you, once you’re circling earth.
Dr. Greg Holt: You got it.
Host: Boom! You burn, and you’re on your way. So that’s, you say that’s about 15, 20 minutes until their trans-lunar injection. Until bam! You’re, you’re passing the TDRS satellites?
Dr. Greg Holt: It’s, it’s really fast out there. It’s a lot faster than most of us anticipate.
Host: Yeah!
Dr. Greg Holt: And the very first time that we simulate that for all of our ground control folks. It always catches us by surprise how quickly we zip through the GPS constellation, the TDRS constellation. We’re just going through all of those. And we’re really out there on our own. Having to look back at the Deep Space Network in very short order so.
Host: So what’s the GPS constellation? Is that, is that another network?
Dr. Greg Holt: Yeah, that’s Global Positioning System. They’re the same satellites that you communicate with like your, your car or your smartphone.
Host: Oh, we all need that.
Dr. Greg Holt: Exactly. That at that we receive, we receive that signal from those Global Positioning satellites. Lets us navigate our cars all over the place. Tell us exactly where we are when we’re carrying our phones around. We could use that. Of course, our spacecraft as well when we’re relatively close to the earth. But once we, again, get too far away. Then that Global Positioning System also is out of range. And we’ve really got to go back to some of the more old-school methods of navigation using radio signals. And as you’ll talk about, even some star, star sightings, things of that nature.
Host: Oh, radio signals. I want to definitely get into that. That’d be pretty cool. So these networks. We have, we have GPS, we have TDRS, Deep Space Network. Do we have complete control over these networks? Or is this a shared resource?
Dr. Greg Holt: You know, all of those are really shared resources. And the, both the, especially the Near Earth Network is shared amongst a lot of users. Both from a NASA standpoint. And Department of Defense all kind of shares that resources. And both contribute to its upkeep. And so we do have to share that resource quite a bit. The Deep Space Network is mainly NASA projects on there. But again, there’s enough of them they al– that also has to be shared and scheduled quite a bit in advance. And so lots of times we’ll have to schedule that months in advance. In fact, that time to be on the Deep Space Network just because there’s so many probes. There’s New Horizon’s out at Pluto. And there’s other probes at Mars. And there’s other vehicles near the sun. They’re all wanting to communicate with that Deep Space Network. And so we have to schedule that resource well in advance. And we try to be collegial about it. And make sure that we respect when everybody has critical science going on. Versus obviously for a human spaceflight vehicle, we want to make sure that we have good coverage with our vehicle. Keep it safe, so.
Host: That’s right because obviously, if you’re flying Orion, you want communication with Orion. But that doesn’t mean you’re going to completely dominate all the communication and nobody else can talk to their spacecraft. Because everyone’s, everyone’s got stuff going on.
Dr. Greg Holt: You’re exactly right. And in general, when we have people onboard, we tend to get a little bit higher priority. But we try not to abuse that. Because we again, we realize the Deep Space Network is a shared asset. And we want, you know, we want to make sure that we’re not adversely affecting. The science payloads and the rovers and the unmanned probes out there. As, as much as possible.
Host: Okay. So when it comes to deep space craft, I guess. We’ll talk about Orion. But when it comes to communication and navigation. What are you looking for? What kind of data are we looking at? Why do we want to communicate?
Dr. Greg Holt: So communication and navigation interestingly are pretty interdependent functions. They’re, you know separate but they’re, but they’re very related and interdependent. One of the reasons is that they both use the same radio signal to accomplish their task. So that same radio signal that we’re using to talk to the spacecraft, get data from the spacecraft. We’re also, we’re also encoding navigation information on that radio signal and using it to actually locate the spacecraft as well. So it’s kind of a, it’s kind of a two-fer. We get to piggyback one function on another. But for that reason, they become very, very related and interdependent. And obviously the importance of being able to communicate with the spacecraft is we want to be able to talk to the crew. And make sure they can talk back to the ground for the normal interactions that we need to have with them. We also need to make sure of course we’re getting data back from the vehicle.
And all the telemetry on all the systems. So that the ground controllers and Mission Control can look at the spacecraft systems. Make sure they’re all functioning properly. And then one of the last and most, what I think is one of the more important things, is we want to make sure we get some cool pictures down from the spacecraft. Because you know we’ve got a very unique spacecraft out there in a region of space where we haven’t been in a very long time. So getting some cool, some cool videos down from around the moon. I think is a pretty good task, too.
Host: Definitely looking forward to those pictures. For sure. Especially if they’re high resolution, too. Are we looking at that?
Dr. Greg Holt: We are. So right now the system that we’ve got, for example, on Orion. Gives us about two, two megabits per second at its highest rate. So that’s, that’s plenty good for some compressed HD video. That takes about one and a half megabits. So, so in our, when we’ve got the times allocated for it and the time slots, we’ll turn those HD cameras on and get some really cool shots, I think. Coming, coming to us from the vicinity of the moon. And we’ve got some unique cameras at different locations around the Orion spacecraft, out on the tips of the solar rays that can swivel around and take some neat shots of the spacecraft out there, while it’s navigating to and from the moon.
Host: Now I’m thinking about it, just from watching it on TV. How pretty it’s going to look. But I’m sure that there’s an engineering part to that, too. As a, as a, you’re saying you’ve got folks on the ground that are receiving this telemetry and data about the spacecraft. Numbers can tell you so much. But a good picture can probably tell you a decent amount as an engineer, too.
Dr. Greg Holt: It does. And not only does it tell us about the health of the spacecraft. But it also, especially for the first couple of flights, gives us some really good engineering data about what’s going on with the spacecraft. And if there’s anything that we need to look at either tweaking the design or even fixing the design for future missions. So for example, we see that one side of the spacecraft isn’t, isn’t behaving well. Or the, we’re getting back pictures that show that we didn’t separate cleanly from some piece of the spacecraft where we were supposed to have a separation event. Then we’ll go back and look at that picture in excruciating detail. And watch that video in super slow motion thousands of time and make sure that we really understand what was going on. And what we need to, what we need to tweak in the design.
Host: Yeah, so that’s when that higher resolution and that the more data you’re getting, the better your assessment can be. Because the more you can see and play with that footage. So that’s always good. You were talking about radio signals and, and it being kind of sharing this, this feature of communication and navigation. Interdependent but two separate things. Navigation, I don’t think we’ve actually dove into navigation too much on the podcast before. So, so how does a, how does a spacecraft navigate? How does it know where to go?
Dr. Greg Holt: Very good question, and the answer really depends on where you are relative to the earth. So right when we’re sitting on the pad, obviously, we have a really good idea of where we are. Because.
Host: Well, you can see it. [Laughter]
Dr. Greg Holt: We can see it, and it’s sitting right there on the pad. And so at that point, we have absolute certainty of where the vehicle is.
Host: Cool.
Dr. Greg Holt: But then once we, once we get launched and get further up and then get into our low earth orbit, that’s where we really lean heavily on Global Positioning Systems. So that GPS signal just like you get in your car, your smartphone. And it’s, like I said, it works really well when you’re close to the earth. And we have four antennas and two GPS receivers on Orion. And we get really good signal there. And we have a really good idea of where Orion is. But then after we do that, the big, the big burn. The, the TLI, trans-lunar injection you were talking about. We zip out rapidly past that GPS constellation there. It’s only about 12 and a half thousand miles out there. So really again, we’re zipping past it in the first few minutes of the outbound trajectory on the way to the moon. And then we have to switch to, like I said, some of the more old-school methods of navigation. And so this is where we go back to using those encoded radio sig– encoded information on the radio signals to, to navigate. Just we did back in the Apollo days.
And then they still use that today for deep space probes. So that method of navigating using that encoded information on the radio signal has actually been refined very well by our JPL colleagues out there since Apollo. And so we’re going to take full advantage of course of all the advancements that they’ve made. Both in the ground-side equipment and the onboard radio transponder equipment. Over the past couple of decades. And really gives us a nice modern communication system with upgraded avionics compared to Apollo that makes our job just that much easier. Navigating the spacecraft and telling where it is from the ground. By looking at the signature of those radio signals.
Host: Yeah, so it sounds like, I mean, the, for that little while that the spacecraft is actually close to earth, GPS. It sounds like when it comes to navigation, you’re talking about GPS. You’re talking about radio. But really the theme here is that you really want to know the location of, of the spacecraft. Is that, is that like the main component of understanding how navigation works? Is understanding where the spacecraft is?
Dr. Greg Holt: That’s one part of it. But the other important parts from our prospective not only is where is the spacecraft. But what direction is it going and how fast? So the spacecraft’s velocity is very important to us. And then the spacecraft’s orientations. All three of those play into the navigator’s job of keeping track of where it is, where it’s going, what direction it’s pointing. And how all of those things affect. So we go to great lengths to estimate all those things continuously during the mission so that we can always be prepared. To supply that information to the folks who are calculating the burns, for example. All the maneuvering burns at so that they know which direction that we need to do course corrections. All those things rely fundamentally on that navigation. Knowing where the vehicle is, its velocity and its orientation so that we can do all the fancy math behind the scenes that gets us where we need to go.
Host: So I think when it comes to navigating a craft in space. It’s not like what you see in sci-fi movies where there’s someone with a joystick and they’re just kind of weaving in and out of space, right? I think this, when it comes to deep space navigation. A lot of it is preplanned. So it’s, it’s knowing the velocity at this point in the trajectory, in the mission. It’s supposed to be going this fast at this place and oriented this way. Is that kind of how that works?
Dr. Greg Holt: Very much.
Host: Okay.
Dr. Greg Holt: We plan a lot of that ahead of time. And we have a very detailed reference trajectory before we ever start the mission.
Host: Okay.
Dr. Greg Holt: But inevitably, especially with a crew vehicle. You’re going to slightly get off of that preplanned reference trajectory due to things. You know, all of the events that happen onboard, especially a spacecraft with a crew. The crew is constantly breathing for example. And that’s a good thing. We like the crew to breath. But that also means that carbon dioxide and things are constantly being vented overboard. We have things such as water and urine dumps that we have to deal with. So a lot of things that for example, that robotic spacecraft don’t have to deal with. For a vehicle with people inside, we do have to deal with these, these events, these overboard events that do perturb the trajectory slightly. And so we have to keep track of those things. And that’s a lot of what our job is as navigators on, for human spaceflight missions. Is that we’re constantly keeping track of these small perturbations that accumulate over the course of the trajectory. And then using that to help feed that into what we need to do. As far as make course correction burns to get us back on track and keep us on, keep us on the mission.
Host: Knowing, yeah. Knowing the navigation where you’re supposed to be at what time. But I guess another thing, another consideration is, is fuel and thrust, you know? You can’t just be firing the jets all the time. You have a certain amount of fuel for these deep space missions that, that you have.
Dr. Greg Holt: It is, and we have those preplanned points usually during the trajectory where we have those mid-course corrections sort of scripted into the mission, if you will. Such that every so often we will evaluate how we’re doing. Based on all of those navigation measurements that we’ve taken to that point. And say okay, it looks like we’re off by this much. So we need to correct our trajectory back by this much. We’ll prescribe a burn. We’ll upload that to the vehicle. And the crew will monitor it as it goes, as it happens.
Host: So that’s kind of interesting that just venting CO2 or if you need to go to bathroom and you need to let go some of the urine, right? That’s Orion. Orion’s not going to use this water recycling system. You’re just going to dump it overboard. But just that little bit is enough to push a spacecraft. That’s just amazing how that, how space works like that.
Dr. Greg Holt: It is. And again, we, we love having humans on board spacecraft. But from a navigator’s prospective, sometimes we pull our hair out because those are the things that we have to deal with. Is these, all these little overboard dumps really cause these perturbations to accumulate. And we have to cause our job of keeping track of a vehicle to be that much more challenging.
Host: So another thing you were talking about was, was orientation of the spacecraft. Again, I’m, I, I keep thinking about sci-fi movies here. But you’re not talking about a spacecraft just kind of zipping through. You don’t really have to deal with aerodynamics as much like a plains is shaped away. Because you’re flying through the air. This one, you can sort of face in any direction. But I’m sure there’s some strategy on which direction you want to be facing. So what’s the orientation of the spacecraft when it’s flying?
Dr. Greg Holt: So we have a lot of different orientations that we use. And we’ll use different, different prescribed orientations of the vehicle for different purposes. And one of the ones that we like for Orion specifically is what’s called that tail to sun orientation or attitude.
Host: Tail to sun.
Dr. Greg Holt: And that’s where we basically turn the vehicle around, point the back end right there at the sun. So that lines up our solar rays right there at the sun. Gives us nice, good power consumption. Keeps the, all the components at just about the right thermal, thermal temperature, balance. So we have some electronics are a little bit more sensitive to temperature than others so that tail to sun orientation or attitude, as we call it. Keeps those, keeps the hot things hot. Keeps the cool things cool. And keeps the solar rays pointed right there where we get good power generation and distribution throughout the vehicle.
Host: So that’s a key component of orientation is not, you’re not pointing where you want to be flying. You’re pointing to where you’re getting a good amount of power consumption. But also you’re protecting the systems from the intense, I guess thermal constraints of space. It’s super hot when the sun is shining on it. And in the shade it can be super cold.
Dr. Greg Holt: That’s right. And we use, we have two star trackers on the vehicle that help us determine which direction the vehicle is pointing. So they’re actually constantly looking out at stars. Recognizing the different stars and the different constellations and orientations. And constantly computing automatically on board what the, what direction the vehicle is pointing. And we’re constantly feeding that to our guidance navigation and control system on board. Which is actively keeping the vehicle oriented just in the direction that we prescribe. So it’s a fairly complicated feedback loop of things that have to happen just to keep the vehicle pointed in one direction. But– .
Host: Wow. Yeah, I guess that’s true, right? Because if, if I’m in my car, I want to turn left. I know that I’m going to orient. I’m going to turn the wheel, the car’s going to go left. But this all different directions in space. So the place that you want to orient is based on where the stars are.
Dr. Greg Holt: Exactly.
Host: So you have to know where the stars are going to be at this time in this place. And which way– wow. That’s so interesting. They’re looking at the stars.
Dr. Greg Holt: We really are. That’s the, we’re getting back to some of the more old-school methods of navigation once you get beyond, too far beyond earth orbit there, you really have to use the stars to figure out your orientation. And then the stars of course become important if you happen to lose communication. And that radio link with the earth. That’s, the stars become the only way to know where you are.
Host: Yeah, so that’s, that’s the orientation. That’s the method we use for orientation is, is knowing the stars. You talked about old-school method of, of radio. And that being a way to, to navigate the spacecraft past whenever we’re past the GPS constellation. So how does that work? How does a radio communication work?
Dr. Greg Holt: So that’s that, where I was talking about, we put that signal onto the communication link. So the communication link for Orion operates on an S-Band radio frequency. And so what we’ll do is we’ll encode some navigation information onto the S-Band radio signal. And it’s transparent to the vehicle. It just goes back and forth. But on the ground, we can actually take that signal and do some special post-processing to it. And actually extract a measurement from that. So it actually measures you know the range to the vehicle or the relative velocity of the vehicle to that receiving dish. And so we can actually then take those measurements and plug those into our navigation filters and estimate where the vehicle is and what its velocity is. Just based on that information that’s encoded on the radio signal.
Host: Wow, but it’s obviously pretty reliable because we’ve had spacecraft like you said. All over the solar system, flying in all different directions and going exactly where they need to go. So it’s, so it’s a pretty reliable navigation tool.
Dr. Greg Holt: It is, and that’s been around really since the early days of human spaceflight. So even all the way back to the very first satellite in fact, Sputnik. They were able to track its radio signal and do some very crude post-processing on it. And figure out its velocity and orbit within a few hours. Some of the, some of the first folks that tracked that. Of course the Mercury and Gemini flights refined that. And then the Apollo engineers designed the, the universal S-Band system specifically for Apollo. They had all of those pieces. The communication navigation all integrated together into one nice, tight little package. And really did a great job for them. And really was kind of the precursor to all of the modern communication navigation equipment that we use today on spacecraft.
Host: Wow, you’re not kidding when you say old school. You’re talking about using radio as navigation from the first steps of space flight in general.
Dr. Greg Holt: Absolutely.
Host: Wow, that’s some significant stuff. From what you’re, from what you’re talking about. When it comes to navigating a spacecraft. It seems like a lot of it is done with computers and a lot of it is done and monitored on the ground. How much are the crew doing? They’re not really, it doesn’t sound like they’re doing a lot of flying.
Dr. Greg Holt: So that’s a good point. During the, the normal course of the mission. They’re obviously just sort of keeping track where the vehicle is. They’re up, they’re usually very curious to know how far away am I from earth? How far do I have to go to the moon? So those type of questions always come up and so we keep that navigation information handy for them. But primarily the, the navigation function is accomplished on the ground. Because we have those measurements taken from the radio signal. And of course we have the computers that actually crunch the numbers and figure out where they are. Where the crew does come into play though is if we do happen to lose communication with the ground. And that’s where we spend a lot of our time and effort thinking about those bad-day scenarios. But you know that’s the, the type of things that we have to think through and what is the crew supposed to do if they lose communication with the ground? That radio signal is obviously not there. So that’s where we have to fall to our, to our backup systems of navigation. That are completely self-contained on board the vehicle. And that’s where they use things such as our optical navigation camera. And some of these back-up systems where in the, the very unlikely event that we should lose communication with the ground. We don’t want the crew to be stranded and have no hope of getting back. So we include those, we have those back-up systems. We train them how to use them. And that’s where the crew becomes super involved and very interested in making sure the spacecraft is navigated correctly.
Host: Okay. So, so they’re not, they don’t have their hands at a joystick. And they’re not flying left and right. They’re really just kind of monitoring things. And you guys are, too. As long as everything is going according to plan.
Dr. Greg Holt: Right.
Host: Their expertise is when stuff goes wrong.
Dr. Greg Holt: Exactly.
Host: And you talked about optical navigation. Is it, I mean, you, if, I’m thinking orientation. I’m thinking about the stars. How, how do they optically navigate? How does that work?
Dr. Greg Holt: So this is probably taking it even one more step back into the old school where we’ve lost that radio link, as I mentioned. And, and now we have to really navigate by the stars. And this is going, you know, Christopher Columbus type old school where you have to literally take sightings of the stars. Sightings of the moon. Measure angles between them. And try to deduce from those measurements and triangulate your position in the earth-moon space. And so it gets from a navigator’s perspective, it’s very cool and exciting because you know that’s a, that’s a neat way to navigate.
Host: Yeah, it’s pretty cool.
Dr. Greg Holt: But it, it definitely requires some more, some trickier math and some trickier vehicle design to pull that off. So we have a camera that does that automatically. And so if they do lose communication with the ground. That camera system kicks in. Starts taking pictures of the moon and stars. And automatically deducing where it is based on the size of the, relative size of the moon. Where it is in relation to the background stars. Because the stars can be considered like a fixed target. And then the moon is kind of moving around as you navigate to and from the moon. The moon will appear to move around against the fixed background of stars. So you can infer where you are based on using some really, like I said, some old school triangulation methods. To, to get you where your, your position and velocity and continue to navigate the spacecraft. And pull off those midcourse maneuvers and things that you need. To actually get you back safely.
Host: Oh, okay. So, so they’re not really busting out the old Christopher Columbus, I forget what the device is called, a sextant device? What’s the, the little navigation thing?
Dr. Greg Holt: Right, right, So those, those old mechanical instruments that you see? Well, truth be told as an emergency backup. We at least have it on the, we’re evaluating it right now. That in a really, really bad day situation.
Host: If the back-up fails.
Dr. Greg Holt: Where they might, they will potentially carry one of those along as well. We actually have an experiment on International Space Station right now. Where the crew is actually has a sextant up there. A real marine sextant. Just like you would see out at sea today. And they are practicing taking measurements from the International Space Station. And they’re really doing a great job. Matter of fact, I was just on the, on the loops with them this morning. I was talking with, with the crew members up there. Coaching them through a session of taking sextant measurements out the, out the window. And they’re really doing a great job. They, they actually really like it. It’s, it’s really, I think they feel a kind of a connection to some of the old-school techniques there. In some of the, the ghosts of the sailors past whispering over their shoulder to, helping them make, helping them make good measurements.
Host: Yeah, you feel like a classic explorer.
Dr. Greg Holt: Indeed. Indeed. But you know it’s, it’s interesting. It’s an interesting concept because you know it’s one of those situations that you, you don’t want to, you hope never happens. But you know in a, in a very bad-day scenario where your computers are down. And, and a lot of your back-up systems have failed. It’s nice in a, for a last-ditch emergency to just to have a nice, solid mechanical piece of equipment that doesn’t require a fancy computer or anything like that, that you can just pull out and at least keep track of where you are. And give yourself a fighting chance to get back home.
Host: Yeah. That’s crazy. A back-up to a back-up. Because you had this system that does a lot of, even, even in the case where you would lose that navigation ability. You do have a back-up. Then you have a back-up to that. That’s pretty crazy. Now in this, in this scenario where they lose, in the first one. Where they lose communication and they’re using this back-up system that automatically detects where they are. Are they sending the commands? Or in this scenario, do they still have communication with the ground? And communicating where and when to fire things?
Dr. Greg Holt: So this is a situation where we have lost communication with the ground. So the, the onboard systems now are taking those pictures. Continuing to navigate completely within the vehicle. So not relying on any external assets there. So we’re just relying on those photos that we’re taking to determine where the vehicle is and where it’s going.
Host: Okay.
Dr. Greg Holt: And then the vehicle also has the onboard targeting systems to take that navigation solution. And turn that into a burn to get them back on course. To get them back to earth. So again, a lot of that is all scripted and happens automatically.
Host: Cool.
Dr. Greg Holt: But when communication with the ground is lost. There’s nobody on the ground monitoring to make sure all of that is working correctly. So that’s where the crew member comes in. They now take over the function of watching all of those automating systems. Making sure that they’re all behaving correctly. Doing their job correctly. And that if anything, if it throws any warning flags or has any problems. They’re the ones who have to go in and diagnose and fix things. And so that’s where we spend a lot of our time training the crew. Making them aware of what to look for. When these automated functions are occurring. They have to have the expertise to monitor them. And go in and take action if there’s, if there’s a problem.
Host: Wow, that’s, that seems to be a theme when it comes to crew training is you know what happens when something goes wrong? You’ve got to know. And that’s, like you said, if you’re spending a lot of time on it. And that’s, that’s the truth because when it comes down to it. When it comes down to crunch time. You know, something goes wrong, we have to make sure we’re going the right direction. That is extremely important because you’re on your own. You’ve got to have that baseline knowledge. You don’t have, you can’t just you know, search it up. Or call someone on the ground. Like you have to know.
Dr. Greg Holt: It is. And like I say, we—it seems like we spend an inordinate amount out of time thinking through these scenarios and preparing the crew for when we lose communication. But it, it’s, it’s a big enough deal and it’s a big enough concern to the crew. Because that’s a, just thinking from a psychological point of view. That’s a, that’s a pretty, pretty harrowing experience to have to go through. To lose your safety net. Your communication signal with the ground. The ability to talk to someone and understand that you’re still on track. And everything’s okay. And so that, that not being there is a really, a big psychological hit to the crew. So the more that we can prepare them to understand if you lose communication with the ground, you can still look here and monitor everything. See that you’re still on, on good trajectory. You’re still going to make your entry corridor and everything’s going to be okay. You know, that’s a big, that’s a big deal. Not just you know from a mission success standpoint. But also from a psychological standpoint for the crew.
Host: Yeah, for sure. I’m thinking about some of the first missions of, of Orion, EM-1, EM-2. I’m thinking about those mission profiles. And I know Orion is going to be sent. Those missions are, are to the moon, right?
Dr. Greg Holt: Right.
Host: So, so you’re going to be going that way. Trans-lunar injection. That’s why it’s called that, so you can go around the moon. Now from what I understand from Apollo missions. Once you get behind the moon, that’s where communication gets a little bit tricky. I think you lose communications. Is that part of the mission plan?
Dr. Greg Holt: We do lose communication briefly and that’s expected.
Host: I see.
Dr. Greg Holt: And so we plan ahead of time that we’re going to have a few minutes of brief communication outage behind the moon. The unfortunate thing, at least from our flight-controller ground perspective is that a lot of critical events are happening during that very brief time.
Host: Really?
Dr. Greg Holt: And that’s just, just the way that the orbital mechanics work out.
Host: Okay.
Dr. Greg Holt: So for example, some of our– if we’re trying to, if for example insert into a, a big halo orbiter distant retrograde orbit around the moon, we have to execute that burn just in that spot where we have that lost communication. Right behind the moon. And so we don’t get to monitor that burn and monitor the telemetry and the data from that burn in real time. We have to wait until the burn happens. And then we see it come out from behind the moon. We get our data and telemetry back and then we can tell after the fact. Whether the burn worked or not. But we don’t actually get to see it right during, during the burn. So that gets a little bit of, a little bit of a harrowing time. And that’s where it’s nice to have a crew onboard. They can be obviously right there monitoring the burn. If there’s any problems that happen during the burn, they can take immediate action. As opposed to the ground. Which won’t be able to see the burn or take action until many minutes later.
Host: So in this, in this scenario, you’re going behind the moon. You’re doing that burn. Is that, is that burn to circle around the moon and come back? Or what, what’s, what’s happening in the, in the mission profile? Where’s it going?
Dr. Greg Holt: So that’s, depends on the, where you’re, if you’re going inbound or outbound. So on the way out, we’re generally trying to capture into some sort of a lunar orbit so we can stay there for, for a little while and conduct the mission. And so that first burn is usually to capture you into lunar orbit.
Host: And that happens behind the moon?
Dr. Greg Holt: Right. That happens behind the moon. And then at the end of the mission, when it’s time to come home. We do kind of a reverse where we come back. But again, we have to do another burn to get us back on a trajectory back to the earth.
Host: Behind the moon.
Dr. Greg Holt: Again, behind the moon and–
Host: I’m seeing a theme here.
Dr. Greg Holt: The poor crew has to again, has to pull that one off or at least monitor it on their own. We precalculate it on the ground and get everything set up for them. But you know they’re, they have to monitor it on the ground. I mean on the spacecraft. And then the ground will pick them up on, on the flipside when they come out on the side of the moon. And do a quick radio track from the Deep Space Network. And confirm that everything went off okay. And give them, give them the go to continue on home.
Host: Wow, no kidding, important stuff going on behind the moon there. Wow. Yeah, so definitely something that you want to know. But it sounds like when you, when you come around the moon, you understand, based on whenever you get that signal back. It went successfully or it did not go successfully. Are you getting some– is it recording data behind the moon, moon too? So that whenever you regain communication, you can understand exactly what happened?
Dr. Greg Holt: Yes, absolutely. So we, we have our data recorders going the whole time. Once we get back communications, we’ll set up a, just a file transfer link. And record all that data down to the ground. Double check and make sure that the burn executed successfully. But you know, one of the very first and early indications that we get. And even the Apollo guys used this trick. Is actually just monitoring what time we get communication back. So you know our, our flight dynamics officers there in Mission Control are, are so good at their job. They can usually predict down to the second or two when we’re going to get communication back. So if the burn didn’t go exactly as planned. It was either didn’t, it was either too cold or too hot, didn’t add enough energy or added too much. The communication will even hap, the return of communication will either happen too early or too late. And so if we’re, if we’re a little early getting communication back or a little late getting communication back. Then that’ll give us a very first heads-up. Hey, something didn’t go right with that burn. But if we get it back right on time, that at least gives us our, our very first indication. Yep, we’re right, right on the money. We got comm back right when we expected. And then like I said, we’ll do a quick radio track just to confirm. But.
Host: Yeah. So it sounds like for, for a lot of this you, in, in your position, are you working pretty closely with the operations folks? And because it sounds like a lot of this is, is dealing with, you know, operate, operating the spacecraft. And understanding the navigation of, of yeah, the mission itself.
Dr. Greg Holt: It is, and we have a really great team here that is participating in both the design and the operations of Orion.
Host: I see. Okay.
Dr. Greg Holt: And we work very closely together on a daily basis, really. Because we’re very sensitive to the fact as vehicle designers that the folks who operate this vehicle are going to have to know exactly what to do with it. And so we try to do design operability into the vehicle wherever we can. And of course they’re, as operators, they’re sensitive to the fact that they want all the bells and whistles on, on a vehicle. And we, we always have to be sensitive to how much, how much mass everything adds to the vehicle. How much power it consumes. And so we have to play that balancing game between, you know, both the crew. And, and the flight controllers. You know, want the, the greatest gee-whiz system they can, they can put on there. Which is great. But weighs a million pounds and. [Laughter] And consumes, you know, thousand watts of power. And so we can’t, sorry we can’t, can’t put all that on there. So we, we do have to play those, those system trade games to make sure that we have a vehicle that’s, that’s operable and the crew can understand. But still can get off the launchpad so.
Host: Right, yeah. Orion would be pretty huge if everyone got what they wanted. Right? So alright. So let’s talk about Orion itself. You know, when it comes to the navigation and communication systems that’s on there. What’s happening? Where is it in its construction? In its design? Especially for the EM-1 crew module and, and everything that’s going on there?
Dr. Greg Holt: So we’ve got really communication and navigation equipment sort of scattered all around the vehicle.
Host: Oh really?
Dr. Greg Holt: So the we have antennas sort of distributed all around. We have a handful of antennas around the, the capsule. The cone shape in the front. And then we have more antennas around the, the service module in the back. And these are what we call phased array antennas as our primary communication system. And so they actually have active electronics that will steer and shape that, the beam from the, from the antenna. So it actually shapes that antenna pattern just the right direction that we want it to maximize that bandwidth. As we’re, as we’re flying along and orienting the spacecraft in different directions. The beam will actually use those electronics to steer the beam over to just the right spot on earth. And, and really get us those high bandwidths that I was talking about that gives us the cool HD video and all that. And so those, those antennas are kind of a, the tip of the spear when it comes to the to the communications system. And then of course that all feeds down into the guts of the communication equipment where we have baseband processors. And then our S-Band transponders. That actually do the processing of the signal. And puts all that data and telemetry on there. And of course the crew voice and the video. All the great information that we want to get down. It has to all get mixed together into that radio signal and sent out those antennas down to the ground. To be picked up by the Deep Space Network dishes. And then routed ultimately to Mission Control. Or to wherever we need to, that information to go.
Host: Wow. So there, I mean, when it comes to designing and where they’re going to be. Like you said, they’re all over. I know the ESA, European Space Agency is working on the service module. If I’m, if I’m not mistaken and the crew module’s somewhere else. So they have to talk to each other. They have to make sure everything works. I guess we’ll start with the mission itself. In the mission, how long are the crew module and the service module together throughout the whole mission?
Dr. Greg Holt: So they’re together for most of the mission in fact.
Host: Really? Okay.
Dr. Greg Holt: So all the way through. Obviously they’re mated together early on in the process. Before it ever gets attached to the, to the booster and get rolled out to the pad. For the entire mission all the way to the moon and back, that service module’s attached. Providing power, and consumables to the vehicle. And it will really only detach the, the crew module from the service module for the last 20 minutes or so of the flight. So right before we re-enter the atmosphere. We will detach, and then the crew module itself will reorient. And that’s the only part that comes back and is the recovered part that has the crew inside, of course. And survives the re-entry and splashes down for recovery. The service module just burns up in the atmosphere as it comes back. But for the majority of the mission, we have that service module attached. And we take advantage of that, of course. Like I said because we have antennas on there that we can use to talk to the ground. We have our nice solar rays there that provide us the power. We have fuel tanks and the like there that provide us fuel. And of course we have our big orbital maneuvering system engine on the service module as well. So it’s, it really is sort of a workhorse for us while we’re up there. And we only separate from it at the very last minute.
Host: Right. It’s, I mean, all the, seems like a lot of the, a lot of the efforts of the mission itself are, are coming from the service module. You’ve got the fuel, the things that’s actually orienting you. Point, pointing you where you want to go. That’s all important stuff.
Dr. Greg Holt: It is. It is. But the, the bulk of the avionics. And like I was saying before, the communication, navigation equipment. That all has to be there up there in the crew module. Because we, we still need that after we separate and want to come back. So our GPS receivers. Our inertial measurement units. Which include our accelerometer and gyroscopes. And you know a lot of the other, like I said, communication, navigation gear. Are all housed up in that command module, the crew module so that we can hang onto that after we separate. And use that to help us navigate during the entry phase as well. We still have to be able to fly the vehicle down and get it now, get it to where we go for splashdown.
Host: Wow. Seems like the communication and navigation system just in general consists of a lot of components. You’re, you’re listing all these different things that have to talk to each other in order to make this thing successful. How many of them? It sounds like a lot of them are, are proven. Used before technologies? How many of them are, are in this scenario? And then how many of them are, are more novel, newer technology?
Dr. Greg Holt: It’s, a, it’s a mix.
Host: Okay.
Dr. Greg Holt: We obviously try to lean on the, the time-tested and proven methods for kind of our primary systems.
Host: Yeah. Of course.
Dr. Greg Holt: And obviously crew safety’s a big consideration so we, we want to try to, try to stick with things that we know or at least have high confidence that will work. So these S-Band radio signals through the Deep Space Network are, are tried and true. And so we, we use those for the primary communication and navigation. When we’re navigating to, to the moon and back. Global Positioning System, obviously’s been out there for a long time now, since the eighties. And everybody, like I said, uses it in their car and smartphones. And does a great job telling us where we are. So those systems have been around for a while. And we, and we trust those pretty well. Some of those, the new, the new back-up systems is where we get into some of the more experimental things. So the optical navigation system, for example, is, is brand-new. It’s a brand-new technology that we developed just for Orion to have that back-up capability and navigate to the moon and back. If we happen to lose communication. So the other new technology that we’re working on now is even an optical communication system that uses, uses lasers instead of radio to communicate. So it’s, the example I like to give is like the, the, it’s the difference between talking on a, on a normal ethernet line and talking on a fiber line. You just, the bandwidth just [whoosh] skyrockets. Once you can get that, get that laser column. So we do have some experiments there on some of the earlier Orion missions. With a, with some laser communications. We call it optical communications. And it, it, it’s trickier and it’s more experimental. But once we get the kinks worked out on that, that’ll really increase the bandwidth. And again, allow us to do even more great video and the ability to interact with a vehicle and get a lot more data down as well.
Host: Yeah, and when you talk about bandwidth, you talk about total information that you can deliver at once, right? So if you can increase that, that’s more information that you can put onto the vehicle. Of course that means mass. So you know, there’s, there’s that consideration too. But still, I mean my hope as, as the public affairs guy is like you’re, you’re just beaming four-K images down. Now that is my dream. But I don’t know. That would be pretty cool. So, so when it comes to these experimental things. And, and even some of the older proven technologies. What’s being done to test it? To make sure everything’s going to work come mission time?
Dr. Greg Holt: So especially with a crew on board, we have to make sure everything is, is really ship shape. So we, we do test those out pretty, pretty thoroughly. We have communication tests that we regularly do between the Orion’s equipment and the Deep Space Network. So the folks at JPL actually have a, a little mobile net, network simulator. They can send around and go test out your equipment. They, they provide that to all the, the robotic probes that are going out to the solar system. They will actually put a little mini-Deep Space Network on a truck and send it out to your assembly facility. And you can plug in and make sure that your equipment works with the Deep Space Network before you ever leave the ground. So, so we do that same thing on Orion. It’s really got, kind of neat to see them pull, pull up in their, pull up in their truck with the, with the mini DSN. And– .
Host: Mini DSN is a pretty cool thing to have inside of a truck.
Dr. Greg Holt: But yeah, it provides an exact replica of the type of signals that you’re going to see. And so you can test out your actual flight hardware right there on the spot. Make sure that it’s going to work. And so we, we do those tests. And I, in addition to obviously testing out all of our navigation equipment. You know, our global positioning system. We can test that out. Obviously, just using the live sky signal, coming from the GPS satellite’s broadcast here down to the earth. We can turn that on and make sure that’s all working. And we test that out on all of our other equipment. Not only on the, on the hardware side, but the software side. We run that software through, through millions and millions of different simulations with every different kind of perturbation of failure that we can think of to really wring it out. And make sure that it’s responding correctly in all those situations.
Host: Wow. So, I mean, when we’re talking about Orion and the, and the communication and navigation of this deep space vehicle, it is exactly that. It’s a deep space vehicle. And obviously we have some missions already planned except for it to go around the moon. But you know once we do that. You’re talking about something that can go out to, to Mars. And, and, and even further, further than that. It’s, it’s a deep space vehicle. So once we build this technology and we go through some of these first missions. How much of it is translatable to just deep space travel? How much can we take with us to future missions?
Dr. Greg Holt: Quite a bit actually. And so the good news is we’re, we’re designing this as a deep space vehicle from, from its conception. So it has all of the systems that you need to, to go out beyond earth orbit. Just kind of designed in from, from the start. So we have all of the, the communication equipment. So that S-Band communications equipment, the, the locations of the antennas. All of the redundant features that you need to have ultra, ultra-reliable communication. Not only to the moon, but beyond. So all of that compatibility is already built in. So really from a communications standpoint going to Mars just means you just start using a little bit bigger and bigger dishes on the Deep Space Network. On the ground side. The further, the farther that you go out. And your bandwidth, you’ll dial back the bandwidth just a little bit to account for the losses that you get as you’re going further and further out. But the, the fundamental equipment is, is all still there. And you know really the fundamental navigation doesn’t change a whole lot, either.
You’re still using that encoded radio signal. And so you know that’s really kind of what, what I like to think sets Orion apart. Is kind of having that built into the vehicle as you know kind of the first, from a first consideration. Having all of that capability to communicate and navigate all the way out to the very deep, distant objects. So you know that same communication nav system that we have going to the moon. Can take us to Mars. Can take us to any number of deep space destinations that we’ve got out there. And you know, it’s, it’s not quite. It, it, it’s a little bit of overkill. If they’re just going around, just going up to, to low-earth orbit, for example. You know, all that equipment and all the redundancy that’s built in. But you know, it’s really the only thing that can get you out to those deep space destinations.
Host: Yeah, redundancy is, is a key theme here. But it’s, but it’s very exciting how translatable a lot of that is. Maybe you know small tweaks here and there. And you can keep increasing reliability but, but the systems, the functions, they’re, they’re all there. That’s very exciting stuff. So, so we’ll kind of end with that. Just how exciting this time is. Looking forward to some of these first mission. What, what do you really looking forward to, EM-1, EM-2? The first missions of Orion?
Dr. Greg Holt: Boy, I think seeing those first, those first signals there from Mission Control. Getting those first navigation measurements back. And seeing that we’re on course. We’re, we’re, we’re, we’re really getting the moon the very first time that we, you know, that we take a pass. And do a measurement predict and show us heading out to the moon. Instead of just, instead of just going around the earth. That’s going to be pretty exciting. That hey! We’re, we’re on our way, guys. It’s [laughter], it’s show time.
Host: Yeah! That’s going to be a good moment! When you see everything coming back, and you’re like wow! We are on our way.
Dr. Greg Holt: Absolutely! And then just like everybody else. You know, the very first time that we get that, get that HD video down from, from the vicinity of the moon. And get to see those close-ups there. And some really cool shots of the moon as we’re flying by. You know, that’ll be exciting.
Host: I will definitely be looking forward to that as well. Greg, thank you so much for coming on! And sharing this insight into communication and navigation of the deep space spacecraft.
[ Music ]
Host: Hey, thanks for sticking around. So today we talked with Dr. Greg Holt. About the navigation and communication of the Orion spacecraft that’ll take us out into deep space. We’ve talked about communications before. Again, check out Episode 26: Can You Hear Me Now? With Bill Foster. We’ve also talked about Orion before. We gave a nice overview of the spacecraft just in general on Episode 17. And then we talked about how the crew will operate inside for missions that can go up to three weeks on. We talked about, I think that’s Episode 28, yeah. What was that? 3 Weeks In a Capsule was the name of that. And we also take, this one’s actually a good one. A Ride Inside The Capsule for Episode 35. We talked with Jeff Fox for that one. And actually brought the audio from the first test mission, EFT-1. And we brought it onto the podcast. So you can actually just kind of sit back and imagine what it’s like to take off and to land and splashdown from, in the Orion spacecraft. You can go to NASA.gov/orion to learn more. They have a great article that released recently, Top Five Technologies Needed for a Spacecraft to Survive Deep Space. Navigation is one of those. So you go and read a little bit more there. Otherwise, you can follow us on social media. We’re at the International Space Station, Orion, or the NASA Johnson Space Center accounts on Facebook, Twitter, and Instagram. Use the hashtag #AskNASA on any one of those platforms. Submit an idea for the show. We’ll bring it right here. This episode was recorded on August 20, 2018. Thanks to Alex Perryman, Bill Stafford, Pat Ryan, Laura Rashan, and Rachel Craft. Thanks again to Dr. Greg Holt for coming on the show. We’ll be back next week.