1 00:00:00,080 --> 00:00:06,800 Houston We Have a Podcast. Welcome to the official podcast of the NASA Johnson Space Center, episode 419, 2 00:00:07,260 --> 00:00:12,880 telling time on other worlds. I'm Dane Turner and I'll be your host today. On this podcast, 3 00:00:12,880 --> 00:00:19,540 we bring in the experts, scientists, engineers and astronauts, all to let you know what's going on in the world of human spaceflight and more. 4 00:00:19,980 --> 00:00:28,100 Days, hours, minutes, time is so ubiquitous to our everyday lives that we often just think of it as numbers on a clock face. 5 00:00:28,420 --> 00:00:34,280 We forget that these numbers are tied to the motion of our planet, but what do we do when we aren't on Earth? 6 00:00:34,460 --> 00:00:39,560 How do we tell time in a place where maybe morning, afternoon and evening, 7 00:00:39,560 --> 00:00:47,740 don't necessarily align with our typical earthly 24-hour day or even seconds themselves may tick faster on the moon. 8 00:00:47,740 --> 00:00:50,160 On this episode we have Kevin Coggins, 9 00:00:50,340 --> 00:00:56,340 Deputy Associate Administrator for NASA's Space Communication and Navigation or SCaN program. 10 00:00:56,700 --> 00:01:06,200 To help us understand how NASA plans to keep time on other planetary bodies and why accurate timekeeping is so important to spaceflight, let's get started. 11 00:01:06,880 --> 00:01:32,800 Hi Kevin, thank you so much for coming on Houston We Have a Podcast today. Hey, thanks for having me. 12 00:01:33,440 --> 00:01:36,680 Can you tell us a little bit about your background and how you got started NASA? 13 00:01:37,160 --> 00:01:42,180 Yeah, so let's see. It's a strange background. It's a strange loop that got me to NASA. 14 00:01:42,180 --> 00:01:48,980 Join the Marine Corps at 17. I'm electrical engineer, worked in the defense and aerospace industry for many years. 15 00:01:49,300 --> 00:01:54,040 I found myself doing position navigation and timing for the Department of War, and 16 00:01:54,820 --> 00:01:58,860 then low and behold, I found myself doing space communications and navigation at NASA. 17 00:01:59,500 --> 00:02:06,780 So you've been doing the things that SCaN does for most of your careers, that right? In some way shape or form. 18 00:02:07,580 --> 00:02:15,740 And so SCaN is NASA's Space Communication and Navigation program. Can you use a little more information on what that really covers? 19 00:02:16,380 --> 00:02:24,980 Sure thing. So SCaN is the lifeline, the line of which all data flows to and from any space mission we send up. 20 00:02:25,660 --> 00:02:32,940 Whether it's the International Space Station, the Artemis 2 mission to the moon, the Voyager spacecraft or Europa Clipper. 21 00:02:33,420 --> 00:02:41,340 We manage the Deep Space Network, which are these huge antennas around the world in Madrid, Canberra and California. 22 00:02:41,740 --> 00:02:51,500 We manage the near space network, which are a bunch of smaller antennas to talk to, rockets that we launch and things that are orbiting the Earth for science missions and the ISS. 23 00:02:51,980 --> 00:03:00,300 And we also manage some satellite constellations, and then we have a lot of commercial space partners that bring a lot of capability to help us as well. 24 00:03:01,100 --> 00:03:09,740 So is this a lot like, you know, we're all used to GPS on our phones now these days? Is this like a space GPS? 25 00:03:11,500 --> 00:03:19,740 Yeah, so it's communications, but it's also positioning, navigation and timing or PNT, which you could say is space GPS. 26 00:03:19,900 --> 00:03:28,300 We're putting right now GPS around the moon in a program that's got one of these weird NASA acronyms. We have a ton of acronyms here. 27 00:03:28,300 --> 00:03:35,180 This one's LCRNS, L-C-R-N-S, lunar communications and navigation relay system. 28 00:03:35,660 --> 00:03:46,220 And it's going to include not just the ability to do communications on the moon, but to have GPS-like capability on the moon, just like we have on Earth. 29 00:03:46,780 --> 00:03:54,380 Okay, and these are also communication satellites, so like beaming phone calls and TV signals. Is that about right? 30 00:03:54,860 --> 00:03:55,820 That's exactly right. 31 00:03:56,540 --> 00:04:03,820 Amazing. Okay, so how do these capabilities relate to timekeeping? 32 00:04:05,420 --> 00:04:13,740 See, that is that is the magic question. And that's the question where some people are going to head nod and say I like that answer. 33 00:04:13,820 --> 00:04:25,580 And the people that are really into precision time are going to head nod and say yeah, it's a little harder than that, because it is one of the weirdest things I've ever encountered as my career is time. 34 00:04:26,220 --> 00:04:29,980 And you know, it starts with a question like what is it? What even is time, right? 35 00:04:31,020 --> 00:04:40,220 On the Earth, we have all these atomic clocks. And they're all just a little bit different because clocks drift and believe it or not, 36 00:04:40,860 --> 00:04:47,500 what they're looking at in the clock are oscillations of atoms and gravity affects the oscillation of the atom. 37 00:04:48,300 --> 00:04:53,100 So on the Earth, we're in this Earth gravity well. We're kind of all in the same gravity. 38 00:04:53,660 --> 00:05:02,620 And all these clocks are rotating on this planet. They're experiencing different forces and vibrations and kind of the same gravity. 39 00:05:02,940 --> 00:05:18,060 And they all have to work together to vote to figure out what time is it based on, you know, not only the oscillations of their individual atoms, but also the, you know, kind of like averaging out and norming between their differences. 40 00:05:18,940 --> 00:05:26,700 That's time. That's one definition of time. The moon has different gravity than the Earth. So how do we do it there? 41 00:05:28,860 --> 00:05:35,740 You're starting to break my mind here because I'm realizing that time is so tied to gravity that you're going to get different time. 42 00:05:37,100 --> 00:05:40,860 Basically, anywhere you go, that's 100% right. 43 00:05:42,140 --> 00:05:55,900 So these atomic clocks, are they placed in, are they all at sea level? Are they placed different altitudes? How do we get that average time on the Earth that becomes our Earth time? 44 00:05:55,980 --> 00:06:02,460 You know, it's a, it's a little more complicated. I told you no one's going to like the answers here. No one's going to like it. 45 00:06:03,580 --> 00:06:14,220 Well, what's a day here? It's the rotation of the Earth, right? 24 hours. And how do we know where to begin the measurement and end the measurement of that rotation? 46 00:06:14,780 --> 00:06:20,540 We actually have to pay attention to the reference frame of how the Earth sits in space. 47 00:06:21,020 --> 00:06:30,060 And so we have to look at things that are really far from the Earth. We measure signals off of pulsars. We measure positioning of stars. 48 00:06:30,620 --> 00:06:39,020 They take that data down and calculate it with the clocks to figure out what time is here on the Earth. 49 00:06:39,660 --> 00:06:47,980 And what's really interesting about it is the rotation of the Earth changes a little bit. 50 00:06:48,940 --> 00:06:58,940 And we have this thing called leap seconds. Every once in a while, we shave a few seconds off the clock because, you know, a second is not to find the same way as the rotation of the Earth. 51 00:06:59,100 --> 00:07:07,340 But we have to make a mesh. So there's constant adjustment and calculation. And so there are these computers that take in all this data. 52 00:07:08,780 --> 00:07:17,340 Things that measure the stars, get factored into that. All of these clocks that are at different altitudes. 53 00:07:18,300 --> 00:07:24,380 They're, you know, because they're on the ground or in the ground somewhere in the world in the United States. A lot of these clocks. 54 00:07:25,020 --> 00:07:33,260 And all this data has to go back to one of a few places for this calculation. I call it all this calculation to figure out what time is it. 55 00:07:34,780 --> 00:07:41,900 It's incredible. You know, we're taught in school that a day is the time it takes for the Earth to revolve. And in hours, 56 00:07:42,860 --> 00:07:47,660 one 24th of that and then a second is one sixtieths of a minute. But 57 00:07:48,780 --> 00:07:52,620 it were, we're almost moving away from the definition of 58 00:07:53,660 --> 00:08:00,380 of the Earth's movement and really putting this in into context of you, you said 59 00:08:01,260 --> 00:08:11,340 the vibration of an atom. Is that right? That's right. The vibrations of an atom. It could be rubidium. It could be cesium. It could be different atoms that vibrate. 60 00:08:12,300 --> 00:08:20,140 A different number of times in what's called one second. We just count those vibrations until we get to that magic number for whatever atom it is. 61 00:08:21,580 --> 00:08:27,020 And so that's what becomes one second. And then we extrapolate all of the other times from that second. 62 00:08:28,060 --> 00:08:40,060 Well, that helps us figure out what the second is. And then yeah, we start to extrapolate. And we have, you know, we have to do a lot of calculation based on other measurements to figure out, you know, that second. 63 00:08:40,860 --> 00:08:45,260 That day, et cetera. And where we are in the Earth reference frame. 64 00:08:47,820 --> 00:08:53,420 Wow. It's okay. It's totally wild. The people that do this work are extremely passionate about it. 65 00:08:53,900 --> 00:08:57,180 They can have an argument with you for hours and you wouldn't understand a thing they said. 66 00:08:59,980 --> 00:09:09,260 It's really wild. You go into a topic like this and think, I know what time is. I have a clock. I have a watch. And then all of a sudden you start talking about it and you realize that 67 00:09:10,220 --> 00:09:17,500 time, you know, time is a construct, but also time is something so complex that's incredible. 68 00:09:19,020 --> 00:09:36,220 You know, it's very important in, it's very important to have very precise time measurements because when you're talking about your position measurement, the way these GPS satellites work and the way they'll work on the moon in Mars one day, is each of the satellites is sending you a signal. 69 00:09:36,620 --> 00:09:47,180 And your GPS is calculating the time difference between those signals and a nanosecond is enough to travel about one third of a meter. 70 00:09:47,980 --> 00:09:57,020 And so, you know, like on Mars, clocks will tick an average of 477 millionth of a second faster than clocks on Earth because of gravity. 71 00:09:57,900 --> 00:10:00,540 The gravity is different. The eccentric orbit is different. 72 00:10:01,260 --> 00:10:07,900 And so, it can increase or decrease this amount by as much as 226 microseconds a day over the course of the Martian year. 73 00:10:08,460 --> 00:10:17,260 So, why does that matter? 477 microseconds is enough time to travel 143,000 kilometers at the speed of light. 74 00:10:17,260 --> 00:10:22,460 And so, that's how much distance you get from those microseconds. 75 00:10:22,860 --> 00:10:30,700 We need nanosecond accuracy to get down to a very precise positioning of where you are. 76 00:10:32,990 --> 00:10:44,510 Wow. So, you'd be off by thousands of kilometers, hundreds of thousands of kilometers if your clock was off by a very minuscule amount. 77 00:10:44,510 --> 00:10:48,830 That's right. That's why these precise clocks are so very important. 78 00:10:49,310 --> 00:10:51,310 Incredible. 79 00:10:51,310 --> 00:10:53,310 Well, let's pick on the moon. 80 00:10:53,310 --> 00:10:59,390 Right? The moon, a single lunar day, is about 29.5 Earth days. 81 00:11:00,990 --> 00:11:08,990 That means if we were to base a day on the moon's natural cycles, the length of the day is going to be a lot longer than on the Earth. 82 00:11:09,550 --> 00:11:13,550 And gravity is different on the moon than the Earth. 83 00:11:13,550 --> 00:11:15,790 So, time is passing at a different rate. 84 00:11:16,510 --> 00:11:29,230 And so, it's a very difficult problem to figure out time and then extrapolate that to position on the surface of the moon unless you're doing it from within that reference frame. 85 00:11:31,070 --> 00:11:34,750 Except in the case of one mission at a time. 86 00:11:36,110 --> 00:11:39,870 If it's one mission at a time, that's the history of what we've done at NASA. 87 00:11:40,430 --> 00:11:48,030 When we've sent a spacecraft up like Apollo, we have clocks on Apollo. 88 00:11:48,670 --> 00:11:51,710 We have on the lander, we have clocks on the Earth. 89 00:11:52,270 --> 00:11:59,550 And we could just deal with, we could do that from the Earth and kind of pay attention to its surroundings, figure out where it's at and what time it is. 90 00:11:59,550 --> 00:12:02,590 Kind of like mission time, you could call it, but not lunar time. 91 00:12:03,390 --> 00:12:06,030 But now, we're talking about building a moon base. 92 00:12:06,750 --> 00:12:13,150 We're talking about rovers and landers and humans moving around the surface of the moon. 93 00:12:13,710 --> 00:12:18,030 You can't, from the Earth, do mission time individually for each of them. 94 00:12:18,030 --> 00:12:20,430 They have to be on the same time scale. 95 00:12:21,150 --> 00:12:22,830 And that means they need lunar time. 96 00:12:24,510 --> 00:12:27,390 Interesting. So, let's go back to that history real quick. 97 00:12:28,110 --> 00:12:37,630 So, using the idea of the reference frame with these historical missions like Mercury and Gemini and Apollo, 98 00:12:37,950 --> 00:12:40,350 we use the Earth reference frame then. 99 00:12:41,310 --> 00:12:45,390 What was the actual time keeping on that light? 100 00:12:46,830 --> 00:12:50,830 Well, it could have been a watch on someone's wrist, right? 101 00:12:51,470 --> 00:12:58,830 It could be a clock in one of the capsules or a clock in some other part of the system. 102 00:12:59,390 --> 00:13:04,510 And over the radio link, maybe you did some clock synchronization. 103 00:13:04,510 --> 00:13:10,030 And maybe it was really, really rough because you didn't have a GPS satellite, right? 104 00:13:10,030 --> 00:13:18,670 Given them positioning, it was, you were calculating their positioning based on ranging measurements from the communication signal 105 00:13:18,750 --> 00:13:23,950 and any other observations. And so, it was like laser focused on that one thing. 106 00:13:25,390 --> 00:13:28,910 And yeah, if that watch on Buzz Aldrin's wrist, 107 00:13:30,190 --> 00:13:36,830 what that he took to the moon was very accurate to the nanosecond, it would have drifted away 108 00:13:36,830 --> 00:13:41,070 from the time on the Earth, but it wasn't that accurate. So, it was very not as noticeable. 109 00:13:42,110 --> 00:13:46,190 And so, within that mission time, it was good enough. It was good enough, right? 110 00:13:46,670 --> 00:13:53,310 But when you're going to have some of the technologies we have on the Earth, 111 00:13:53,790 --> 00:13:58,670 like 5G connectivity across the surface assets and the network, 112 00:14:00,190 --> 00:14:05,150 people knowing where they are or machines knowing where they are with respect to where something 113 00:14:05,150 --> 00:14:11,150 else is, you've got to define, now you can't just do it as a one-off, you've got to define it for 114 00:14:11,230 --> 00:14:17,710 that reference frame that they're in. Okay, so for those early missions, having a synchronized 115 00:14:17,710 --> 00:14:23,710 clock set to an Earth time was enough to get them where they need to go because we didn't need the 116 00:14:23,710 --> 00:14:29,230 precision with the satellites and everything at the time. And then as we move into Shuttle, 117 00:14:29,230 --> 00:14:34,910 did that change then or was that still kind of the same idea? Well, you know, 118 00:14:35,710 --> 00:14:40,990 during Mercury and Gemini and Apollo and Shuttle, they use something called Mission 119 00:14:40,990 --> 00:14:46,750 Elapsed Time or Met, right? Kind of like a standardized, continuous counter, days, hours, 120 00:14:46,750 --> 00:14:52,670 minutes, seconds starts the exact moment of launch. For the space Shuttle, they continued using it, 121 00:14:52,670 --> 00:14:57,630 starting at liftoff. All Shuttle operations were planned relative to that mission clock. 122 00:14:58,430 --> 00:15:04,510 However, when they started becoming more reliant on digital avionics and satellite 123 00:15:04,510 --> 00:15:11,150 communications, they needed more precise synchronization. We actually put GPS receivers on the 124 00:15:11,150 --> 00:15:18,270 space Shuttle for some of that. And so we kind of started to move away from the mission clock to 125 00:15:18,270 --> 00:15:28,110 getting time, very accurate time, from Earth-based GPS. Today, the ISS uses coordinated universal time 126 00:15:28,750 --> 00:15:33,710 so that all the international partners and ground controllers can coordinate activities continuously. 127 00:15:33,710 --> 00:15:39,870 So we've kind of shifted away from mission time for the ISS. Artemis II is going to use Mission 128 00:15:39,870 --> 00:15:47,070 Elapsed Time as a primary operational timeline reference starting at launch. And so it's a single 129 00:15:47,070 --> 00:15:53,790 mission. It's going to take off. It's going to go around the moon. It's got ground controllers 130 00:15:53,790 --> 00:15:59,230 and our entire communication network aimed at it. And so we just need that mission alapsed time. 131 00:15:59,870 --> 00:16:05,390 But our broader moon to Mars architecture, as we start to do all these activities on the moon, 132 00:16:05,390 --> 00:16:07,630 we can't continue to use Mission Elapsed Time at all. 133 00:16:09,470 --> 00:16:16,590 Right. And that kind of mirrors our operations on the ISS, the ISS, while being kind of a 134 00:16:16,590 --> 00:16:22,110 singular focus is being focused on by so many different people that we need that one 135 00:16:22,110 --> 00:16:27,710 coordinate of universal time to work to and it's kind of like what we'll be doing on the moon when 136 00:16:27,710 --> 00:16:31,470 you have that moon base with all the multiple rovers and everything. Does that sound about right? 137 00:16:32,190 --> 00:16:37,710 That sounds absolutely right. Big difference is ISS is around the Earth, right? So it can use 138 00:16:37,710 --> 00:16:43,070 Earth's coordinated universal time. And when we go to the moon, we're going to need coordinated 139 00:16:43,070 --> 00:16:48,430 lunar time. So we've talked a little bit about some of the considerations here, but we're 140 00:16:49,550 --> 00:16:56,910 talking about a coordinated lunar time. We're talking about some place with a different gravity 141 00:16:56,990 --> 00:17:04,510 well with a different length of day and everything. What are these considerations that we need when 142 00:17:04,510 --> 00:17:12,350 we're exploring timekeeping on another body like the moon? Well, what's the gravity, right? 143 00:17:13,390 --> 00:17:17,390 Remember, we started this conversation with how gravity affects the 144 00:17:18,670 --> 00:17:23,150 oscillation of these atoms and how we measure them. So one of the things we have to pay attention 145 00:17:23,230 --> 00:17:30,110 is what's the gravity? What's the rotation of the planetary body we're going to be on? A 146 00:17:30,110 --> 00:17:40,750 Martian day is about 24 hours and 39 minutes. And so we have to pay attention to the 147 00:17:40,750 --> 00:17:46,670 Mars mission, what they're going to need locally with time, with positioning, but also there's a 148 00:17:46,670 --> 00:17:52,990 team back on Earth supporting them. In 2012, when Curiosity landed on Mars, the engineers worked on 149 00:17:52,990 --> 00:18:00,190 Mars time. And because of that, their work shifts on Earth moved about 39 minutes later each day 150 00:18:00,190 --> 00:18:07,230 to stay synchronized with the rover's local daylight cycle because daylight mattered. And so this 151 00:18:07,230 --> 00:18:13,070 helped them analyze data from the previous sol, quickly send commands for the next one, but it was 152 00:18:13,070 --> 00:18:19,230 something for these humans to adjust their normal schedules to. They had to work around the daylight, 153 00:18:19,710 --> 00:18:24,030 day night cycle on a different planetary body. That was tough on some of them. 154 00:18:25,310 --> 00:18:32,430 So they were waking up at Mars morning, whatever time that happened to be on Earth. And keeping 155 00:18:33,230 --> 00:18:40,590 their lunchtime was at Mars noon and their end of their day was near the Mars end of day. Is 156 00:18:40,590 --> 00:18:45,710 that right? They were living on the Mars time and just whatever happened to be on Earth, if it's 157 00:18:45,710 --> 00:18:51,470 a mill the night is a mill the night here? Exactly. That's exactly right. Imagine the chaos that 158 00:18:52,270 --> 00:18:57,870 meant for them and just and the adjustment for their family. When they ate, when they slept, 159 00:18:58,830 --> 00:19:06,270 it was quite an adjustment. Oh, I bet going to an Earth store when you're on Mars time is probably 160 00:19:06,270 --> 00:19:13,950 disorienting. Exactly. So our gravity and rotation, the only things that were really 161 00:19:15,710 --> 00:19:21,070 need to keep into consideration when we're building a time for another planet. I know you asked 162 00:19:21,070 --> 00:19:26,590 another planet, but I kind of want to pick on the moon. So let's talk about a complexity of the moon. 163 00:19:27,310 --> 00:19:34,510 The moon's not a planet and the moon has very specific dynamics that aren't the same as the Earth. 164 00:19:35,070 --> 00:19:42,190 We have to root our reference frame for the moon positionally and time to our reference frame on the 165 00:19:42,190 --> 00:19:48,590 Earth and the math of the math of figuring out positioning on the Earth with satellites around the 166 00:19:48,590 --> 00:19:54,190 Earth and clocks on the Earth is hard, but we figured it out. Now you've got to take that math 167 00:19:54,750 --> 00:19:58,750 and you've got to put it around the moon but keep it linked to the math around the Earth. 168 00:19:59,550 --> 00:20:05,630 And I say math because I just want to highlight this stuff's hard. There's a lot of constant 169 00:20:05,630 --> 00:20:12,910 calculations on how we're going to have to synchronize these clocks, have a lunar time reference 170 00:20:12,910 --> 00:20:20,670 scale, an Earth time reference scale where we'll be talking with those missions and make it work 171 00:20:20,670 --> 00:20:27,230 this seamlessly together. There's big questions like when you fly a rocket from the Earth reference 172 00:20:27,230 --> 00:20:34,590 system, where's that border with the moon where you switch clocks? Or do you just have two clocks now? 173 00:20:36,590 --> 00:20:41,790 It's going to be quite interesting because if the communication services in and around the moon 174 00:20:41,790 --> 00:20:48,350 depend on lunar time, when you move into that reference frame, you've got to switch to that time 175 00:20:48,350 --> 00:20:52,990 to be able to communicate with everything in that environment. It's things we've never encountered before. 176 00:20:54,990 --> 00:20:59,790 And to top it all off, everything's always in motion. That's something that I've had to learn 177 00:20:59,790 --> 00:21:05,710 when dealing with the orbital mechanics of the ISS and spacecraft and stuff. And the moon is 178 00:21:05,710 --> 00:21:10,270 no different. Everything is always in motion. So that's just another wrench in the system. 179 00:21:11,550 --> 00:21:19,550 Exactly. Exactly. Yeah, it's going to be fun. We're going to spend a lot of energy and brain power 180 00:21:20,030 --> 00:21:25,150 over the next few years figuring out how to do this and implement in capability. 181 00:21:25,470 --> 00:21:32,030 On this, that LCRNS project, I told you about that, lunar communications relay and nav system, 182 00:21:33,230 --> 00:21:39,710 we're going to start seeing satellites go up there in the next year or two. And we'll start 183 00:21:40,590 --> 00:21:45,630 building that reference frame around the moon, having those clocks begin to do their first ticks 184 00:21:46,190 --> 00:21:52,830 and start on these hard math problems so that when a receiver on the moon receives the signal from 185 00:21:52,830 --> 00:21:59,710 these satellites, it's getting that data from those precise clocks, but it can determine exactly 186 00:21:59,710 --> 00:22:07,230 where it is on the surface of the moon. That brings me to another challenge. Most people don't know, 187 00:22:07,230 --> 00:22:14,430 but there's groups in the government that work really hard to define how coordinates work on the 188 00:22:14,430 --> 00:22:22,190 surface of the earth. And they work really hard to make sure those, you know, with magnetic deviation 189 00:22:22,190 --> 00:22:28,430 at the poles, with the wobble of the earth and the shape of the earth, that they've got it well 190 00:22:28,430 --> 00:22:34,990 characterized so that a point is a point and it's always that place because the earth isn't 191 00:22:34,990 --> 00:22:38,670 static. It's just not set and still, it's moving, it's shifting and doing weird things. 192 00:22:39,470 --> 00:22:47,150 Well, we've got to do that same kind of work on the moon so that we can define, you know, a coordinate 193 00:22:47,150 --> 00:22:54,190 system so that when you receive these signals from these satellites and you do the math, the answer 194 00:22:54,190 --> 00:22:59,950 comes out the same coordinate every time, no matter when you took the measurement. That's hard. 195 00:23:00,830 --> 00:23:06,830 And there are some amazing people that work in this every day on the earth and I know I've talked 196 00:23:06,830 --> 00:23:13,630 to them recently. They're really excited to settle this on the moon. So with the earth, do you know what 197 00:23:13,630 --> 00:23:22,750 is that central point of the coordinate system or is there one? Oh yeah, now you pass in my knowledge 198 00:23:22,750 --> 00:23:28,510 here. I think that's one of their hotly debated topics as to what is that central point or is there 199 00:23:28,510 --> 00:23:33,790 a central point at all? That's part of the weird math they do. Oh yeah, I was just thinking about it. 200 00:23:33,790 --> 00:23:38,990 I'm like the North Pole, we think of that as static, but it shifts and then you've got plate 201 00:23:38,990 --> 00:23:44,190 tectonics so no matter where it is that you say, oh, you know, this point right here on this continent, 202 00:23:44,190 --> 00:23:48,830 well, that's not going to be, you know, in the exact same place and even just a year's time, 203 00:23:48,830 --> 00:23:53,550 it will move by a centimeter or two. We have a prime meridian. It gives us, it gives us on the 204 00:23:53,550 --> 00:23:58,830 surface a basic reference frame to measure off of. However, when you start to talk about what is the 205 00:23:58,830 --> 00:24:05,470 center point of the earth, you know, there's all kinds of questions like, you know, based on its motion, 206 00:24:05,470 --> 00:24:11,710 based on its mass, two different things. And based on its wobbling motion, that center point's 207 00:24:11,710 --> 00:24:17,390 probably moving around a little bit. But maps can handle things moving around. When you get the 208 00:24:17,390 --> 00:24:22,590 signals, you have to have an answer that comes out the other side of the calculator that says, 209 00:24:22,590 --> 00:24:29,790 I'm exactly at this location to some degree of accuracy. And you know, that's I think a continuing 210 00:24:29,790 --> 00:24:36,590 challenge that never stops. Now, I know that the moon doesn't have plate tectonics. Do you know like 211 00:24:38,030 --> 00:24:43,390 what kind of challenges there are with the moon with this similar to what there are with the earth? 212 00:24:43,390 --> 00:24:50,270 Does the moon have a magnetic field or anything? No, you know, it doesn't have a lot of the characteristics 213 00:24:50,270 --> 00:24:57,550 of a planet that we're used to. And so, yeah, we don't have to deal with a lot of those factors. 214 00:24:58,030 --> 00:25:02,830 You know, however, I don't think we know everything about the moon yet. 215 00:25:03,790 --> 00:25:09,470 From what I understand, I think you're right. We're going to find out exciting things soon. 216 00:25:09,470 --> 00:25:15,470 And we're going to go find out. You've talked about how we have multiple atomic clocks around the 217 00:25:15,470 --> 00:25:21,550 earth to measure the different times and then calculate that coordinated universal time. 218 00:25:22,510 --> 00:25:27,550 Do we know how many clocks and where we want to place them on the moon yet? 219 00:25:28,830 --> 00:25:37,550 That's a great question. We don't. You know, the heart of every GPS receiver actually is an okay 220 00:25:37,550 --> 00:25:44,750 clock, but the heart of every device that generates position, navigation timing is a really great clock. 221 00:25:45,390 --> 00:25:51,390 And so, you can imagine that as we begin a footprint on the South Pole and Equatorial, 222 00:25:51,390 --> 00:25:58,110 you're only going to need enough clocks to handle positioning really well in those areas. 223 00:25:58,110 --> 00:26:02,990 And so, maybe you don't need all your clocks at once. We're going to have some clocks on the surface 224 00:26:02,990 --> 00:26:09,630 that are equipped to survive the night. And because clocks, by the way, they like stability, 225 00:26:09,630 --> 00:26:14,270 they like stable temperature. So, they like to be turned on and they like to warm up, 226 00:26:14,270 --> 00:26:19,790 and they like to stay warm. And so, you're going to need continuous power. You're never going to 227 00:26:19,790 --> 00:26:23,950 want to power it down because you'll have to go through a warm up and synchronization cycle. 228 00:26:23,950 --> 00:26:29,870 And so, surviving the night's important. We're also going to have clocks on the satellites in orbit 229 00:26:29,870 --> 00:26:36,270 and in different places around the moon. And all of these clocks will talk to each other 230 00:26:36,270 --> 00:26:43,070 and share data and synchronize so that we can determine, you know, what is time at given points. 231 00:26:43,070 --> 00:26:50,830 We're also going to have clocks on the earth that are going to be tied and forming these 232 00:26:50,830 --> 00:26:56,990 clocks up on the moon. They're in a different gravity well. It's characterized. We know how they're 233 00:26:56,990 --> 00:27:00,830 going to be ticking on the earth. We're going to characterize and know how they're going to be 234 00:27:00,830 --> 00:27:06,030 ticking on the moon. That characterization is what's going to allow us to have them all work together 235 00:27:06,030 --> 00:27:18,330 to form really precise time. Interesting. So, it's kind of a backup and just a system to make 236 00:27:18,330 --> 00:27:25,210 sure that what you're receiving from the moon is what you're expecting to see. Exactly right. Exactly 237 00:27:25,210 --> 00:27:31,130 right. And they're going to be things that happen where you have to make adjustments. And we're going 238 00:27:31,130 --> 00:27:40,410 to see very, very small perturbations based on gravity differences, based on, you know, all kinds 239 00:27:40,410 --> 00:27:46,410 of factors that will have to constantly calculate and factor in. Some clocks may be affected by 240 00:27:47,050 --> 00:27:51,530 something happening in space and maybe the ones on the ground are more shielded and not as impacted. 241 00:27:51,530 --> 00:27:54,650 Those are the kind of errors that you have to constantly look for and work out. 242 00:27:54,650 --> 00:28:03,450 I've got a really good use case for you for why these clocks and why precise positionings important. 243 00:28:05,450 --> 00:28:11,530 Imagine you're an astronaut on the surface of the moon and maybe you've walked away from your 244 00:28:11,530 --> 00:28:19,370 rover a couple hundred meters. And you've got a habitat, maybe a mile or two away. And all of a 245 00:28:19,370 --> 00:28:26,090 sudden you get an alert on your communication system that says, hey, there's a solar flare. 246 00:28:26,810 --> 00:28:34,810 You've got this amount of time to seek cover or you're going to endure some radiation that's above 247 00:28:34,810 --> 00:28:40,330 our safety limits. Well, first thing you're going to want to know is, all right, where do I go? 248 00:28:40,330 --> 00:28:44,170 You're going to have to go back to your habitat. You need the most expedient route. 249 00:28:44,970 --> 00:28:50,330 You're going to navigate back, probably visually. You'll probably see where you park the rover. 250 00:28:50,330 --> 00:28:55,850 You're going to get back, get in that rover, turn around. You're going to have to drive that rover 251 00:28:55,850 --> 00:29:04,010 precisely. Without hitting an obstacle, going around different types of terrain and maybe there's 252 00:29:04,010 --> 00:29:09,770 power cables you have to avoid running over. You're going to need to get there as quick as you can 253 00:29:09,770 --> 00:29:15,290 and you want the most accurate route. And this positioning capability is a way to get that 254 00:29:15,290 --> 00:29:20,650 accurate route. I remember a nanosecond about a third of a meter. And so you need really good 255 00:29:20,650 --> 00:29:27,050 timing accuracy. So you're going to drive back that distance through who knows what obstacles, 256 00:29:27,050 --> 00:29:32,570 what kind of terrain that's been plotted for you, precisely back computer using this position 257 00:29:32,570 --> 00:29:39,370 navigation and timing data and get back into that habitat before these solar winds arrive and 258 00:29:39,370 --> 00:29:46,810 causes health, health concern. So we're talking this is a safety feature and not just 259 00:29:47,530 --> 00:29:51,450 to make sure we get our spacecraft to the moon and back. Absolutely. 260 00:29:53,450 --> 00:30:00,090 So one of the things that you said just a minute ago was that these clocks will have to endure 261 00:30:00,090 --> 00:30:03,930 temperature. Is temperature something that affects time? 262 00:30:06,570 --> 00:30:14,570 You know, it is for me. I'm from Florida when it's cold, things feel like they're moving a 263 00:30:14,570 --> 00:30:22,890 little too slow. But you know what, you know, the way these atomic clocks work is you use a laser 264 00:30:22,890 --> 00:30:27,610 typically to excite an atom into a vibration state and you measure the vibration. 265 00:30:28,410 --> 00:30:35,450 And that's a setting. You want a very predictable outcome and so you want temperature stability. 266 00:30:35,450 --> 00:30:42,650 So many different clocks depending on their mode of generating a stable frequency depend on 267 00:30:44,170 --> 00:30:49,370 an oven or something to warm them up to a certain temperature where their performance is 268 00:30:49,370 --> 00:30:54,170 characterized. That means you know what it is at that temperature and it's predictable. 269 00:30:54,810 --> 00:31:03,530 And so let's say you need something to run at, you know, a megahertz. Very precisely, one dot lots of 270 00:31:03,530 --> 00:31:11,370 zeros. And you've characterized some materials to do that at a certain temperature. 271 00:31:12,490 --> 00:31:16,810 That temperature becomes essential to getting that predictable behavior out of the clock. 272 00:31:16,810 --> 00:31:25,050 Clocks are all about predictable measurements. So this is about making sure that our measurements 273 00:31:25,050 --> 00:31:31,530 are the same. We're recording what this frequency of this atom is at this temperature. So it's 274 00:31:31,530 --> 00:31:37,210 standardized and not that time moves differently in different temperatures. That's correct. That's 275 00:31:37,210 --> 00:31:44,330 correct. Okay. Remember, you know, is there really such thing as time? We know there's such thing as 276 00:31:44,330 --> 00:31:52,090 a vibration of an atom. We know there's such thing as a frequency. But time is just a measurement we 277 00:31:52,090 --> 00:31:59,370 create off of those vibrations. So you could argue that time is just something we created that we 278 00:31:59,370 --> 00:32:06,650 need to be predictable and stable. So we've been talking about the moon here a lot. And we're 279 00:32:06,650 --> 00:32:16,570 going to the moon to then go on to Mars. Looking at these considerations of the gravity and 280 00:32:16,570 --> 00:32:25,850 and the rotation, everything, they're different on Mars. So are we looking at the second being 281 00:32:25,850 --> 00:32:34,640 different on Mars? Well, you know, remember clocks on Mars will take an average of 477 millionth 282 00:32:34,640 --> 00:32:45,440 of a second faster than clocks on Earth. And it's orbit and the gravity from its neighbors can increase 283 00:32:45,440 --> 00:32:51,600 or decrease this amount by as much as 226 microseconds a day over the course of the Martian year. 284 00:32:52,560 --> 00:32:58,880 That's a lot of variability on time. What is the second, right? On the Earth, we have a very 285 00:32:58,880 --> 00:33:06,800 precise definition of a second. If we take that definition to Mars and it's based on the number 286 00:33:06,800 --> 00:33:14,880 of vibrations, it's going to be 477 millionth of a second faster. And so it's going to be different. 287 00:33:14,880 --> 00:33:23,840 It's going to be different. Different gravity means the different rate of vibration of the atoms 288 00:33:23,840 --> 00:33:29,040 when they're at the right temperature, excited by a laser. And when we do that measurement, it's going 289 00:33:29,040 --> 00:33:36,480 to be different. So we're looking at having Earth time, Moon time, and Mars time, all just a little bit 290 00:33:36,480 --> 00:33:41,520 different. That's exactly right. Anytime you go to a different gravity well, you're going to have 291 00:33:41,520 --> 00:33:49,120 different time reference frame. So in 2024, SCaN was tasked by the White House with developing this 292 00:33:49,120 --> 00:33:58,720 coordinated lunar time. How is that project coming along? So really well. You know, the key part of 293 00:33:58,720 --> 00:34:05,680 that is working with the different parts of the government that have roles to play in defining time 294 00:34:05,680 --> 00:34:11,280 on the Earth and how we work together to define time on the Moon. We have an active work going with 295 00:34:11,280 --> 00:34:15,920 the company name and two of the machines to put satellites around the Moon, you know, this 296 00:34:15,920 --> 00:34:22,000 LCRNS acronym, lunar communication relay and nav system. They're well underway. I know they're 297 00:34:22,000 --> 00:34:27,440 wrapping up some of their satellites and preparing to launch them. And you know, the next part is going to be 298 00:34:27,440 --> 00:34:33,040 to once they're on orbit and we have some user equipment on the surface, getting that cranked up, 299 00:34:33,040 --> 00:34:40,000 refining it, and improving that accuracy so that when we send astronauts and more systems to the 300 00:34:40,000 --> 00:34:45,680 surface, they don't only have uninterrupted comm, right? They'll have communications all around the 301 00:34:45,680 --> 00:34:49,920 Moon from these relays orbiting. They'll have position navigation timing wherever they're at. 302 00:34:51,360 --> 00:34:57,920 You mentioned earlier, this is a lot of math, a lot of really difficult math. Has all that math 303 00:34:57,920 --> 00:35:02,800 been completed or is it kind of a new things are popping up and we're having to solve problems as 304 00:35:02,800 --> 00:35:10,460 we find them? Yeah, that's a really good question. So, Dane, I don't have the complete answer to that. 305 00:35:10,460 --> 00:35:17,340 I think there's more math to do, man. You know, there's definitely more math to do. I think 306 00:35:17,340 --> 00:35:23,420 the experts really understand what it's going to take to do this. It's a matter of 307 00:35:24,300 --> 00:35:29,980 giving them time to complete the work. We have to get the clocks up around the Moon in these 308 00:35:29,980 --> 00:35:35,100 satellites and get data back of how it's synchronizing and working. I'm sure there's going to be 309 00:35:35,100 --> 00:35:40,060 adjustments just like there were with the GPS system when we started to put it up around the Earth. 310 00:35:40,060 --> 00:35:47,420 As we see, how does it really play in the environment? I mean, the Moon is going to be a very 311 00:35:47,420 --> 00:35:54,620 interesting environment to solve these problems in. You've got Earth's gravity on one side, you've got 312 00:35:54,620 --> 00:35:59,340 lunar gravity, you've got these different kind of orbits we're going to use around the Moon that are 313 00:35:59,340 --> 00:36:03,580 different from the ones we use around the Earth. So, I'm sure there's going to be fine tuning and 314 00:36:03,580 --> 00:36:10,140 adjustments as we deploy this capability. And, you know, one advantage we have on the Earth is we 315 00:36:10,140 --> 00:36:16,780 can move around the Earth freely and take measurements of the signals we're getting from GPS satellites. 316 00:36:16,780 --> 00:36:21,580 Right now, we can't, we're not yet at that point where we have the ability to take measurements 317 00:36:21,580 --> 00:36:27,340 all over the Moon as fast as these scientists and engineers would like to have this data. And so, 318 00:36:27,340 --> 00:36:31,180 you can imagine that as we continue to take measurements, we're going to continue to have some 319 00:36:31,180 --> 00:36:37,260 adjustments. You had that great example of the astronaut trying to avoid the solar flare. So, 320 00:36:37,260 --> 00:36:43,260 we've seen, you know, that this is a great way for astronauts to track the amount of time they have 321 00:36:43,260 --> 00:36:52,380 and help navigate safely back to their base. We also talked about how having this accurate time 322 00:36:52,380 --> 00:37:01,660 helps make sure that we know where things are in space and not, you know, thousands of kilometers 323 00:37:01,660 --> 00:37:08,220 away from where we think they should be. Are there any other applications to having this accurate 324 00:37:08,220 --> 00:37:16,620 time for the Moon? Well, accurate time means accurate position. And, if you just look down on the 325 00:37:16,620 --> 00:37:24,300 Earth, let's just look at what's fun, right? It's fun to get in your car and program in your GPS 326 00:37:24,300 --> 00:37:29,900 somewhere you want to go and go there. And if you're driving some of these newer electric cars for 327 00:37:29,900 --> 00:37:38,620 it to drive you there itself, it's fun to, it's fun for a kid to have a drone and, you know, 328 00:37:38,620 --> 00:37:43,420 fly that drone around and maybe you're using GPS or time to help you do that. 329 00:37:43,980 --> 00:37:51,340 You know, think about the things that make it really fun here on the Earth using GPS. 330 00:37:51,340 --> 00:37:54,380 Those same things are going to apply on the Moon just a little different way sometimes. 331 00:37:55,340 --> 00:38:03,420 If we wanted to do very precise sampling, very precise sampling of the lunar surface and the near 332 00:38:03,420 --> 00:38:09,660 term, this kind of capability can allow you not only to go to very precise spots and take these 333 00:38:09,660 --> 00:38:15,260 samples, but you can revisit those spots extremely accurately autonomously. 334 00:38:16,940 --> 00:38:25,100 And so, as we explore the Moon with autonomous capabilities, this ability to, for a location to be a 335 00:38:25,100 --> 00:38:31,500 location, no matter when you go, it's going to be a game changer, an absolute game changer. 336 00:38:32,220 --> 00:38:37,260 You know, imagine that you need a lot of systems to work cooperatively together. 337 00:38:37,820 --> 00:38:42,540 And they can each know their very precise location in the same reference frame, 338 00:38:43,180 --> 00:38:48,540 just like we do here on the Earth. I think it's going to provide a lot of advantage. 339 00:38:50,220 --> 00:38:56,380 And that coordination sounds like it's going to be that big leap compared to what we've done 340 00:38:56,380 --> 00:39:00,220 the past where it's been one mission at a time, but having all that coordination 341 00:39:01,180 --> 00:39:06,460 is really going to make the Moon its own place. 342 00:39:07,660 --> 00:39:16,220 Yeah, absolutely. You know, imagine this, imagine a steady stream of robotic missions to the Moon, 343 00:39:17,100 --> 00:39:26,620 where we have to have precise landing, precise placement of logistics, maybe there's some robotic 344 00:39:26,620 --> 00:39:33,420 craft on the Moon that have to go to certain points and retrieve these logistics or do different 345 00:39:33,420 --> 00:39:41,260 missions. The amount of autonomy and capability they're going to have to build a lunar base, 346 00:39:41,260 --> 00:39:47,820 to explore the Moon, to conduct, you know, really precise science is going to be directly 347 00:39:47,820 --> 00:39:55,420 enabled by their ability to have accurate positioning. So, looking back, well, looking forward to 348 00:39:55,420 --> 00:40:05,020 Mars again, we talked about how some of the rover missions were on Mars time, but they didn't have 349 00:40:05,900 --> 00:40:12,860 the all the atomic clocks and all the GPS navigation satellites, everything at four Mars yet. 350 00:40:12,860 --> 00:40:22,060 Do they? Oh no, not yet. Remember, they're on the mission time. And so, they'll have a clock, 351 00:40:22,060 --> 00:40:27,260 but it's the mission clock that they'll be synchronized to. And so, and they operate very 352 00:40:27,260 --> 00:40:32,860 independently of one another. You know, remember, it's old school the way Gemini and Apollo 353 00:40:33,660 --> 00:40:39,100 was done, because there's not distributed infrastructure there. And so, you've got to work 354 00:40:39,100 --> 00:40:43,660 focused solely on that mission and that time for that mission only. 355 00:40:44,860 --> 00:40:50,380 Right, okay, so the people working it were on the day night cycle and not living on the Martian clock. 356 00:40:52,460 --> 00:40:59,100 Okay, so, is Mars our next focus after we get the Moon infrastructure up, we're going to start 357 00:40:59,100 --> 00:41:02,620 looking at putting this infrastructure into Mars? Is that what we're looking at? 358 00:41:03,740 --> 00:41:08,140 You know, our Moon to Mars program says, let's go do the Moon and let's move on to Mars based 359 00:41:08,140 --> 00:41:13,980 on what we learn. So, yeah, absolutely. And, you know, Mars is going to be an interesting problem 360 00:41:13,980 --> 00:41:21,180 to solve. One thing we haven't talked about is the distance of Mars. You know, when we, 361 00:41:21,900 --> 00:41:27,900 you know, right now the Moon is so close, the speed of light distance to the Moon is negligible. 362 00:41:27,900 --> 00:41:34,220 It you don't even notice it. When we talk to Voyager, which is outside of the solar system, 363 00:41:34,220 --> 00:41:41,580 it takes 23 and a half hours for a signal to get from the Earth to Voyager. And then Voyager 364 00:41:41,660 --> 00:41:46,300 does something and sends something back and takes 23 and a half hours more. So, two days 365 00:41:46,860 --> 00:41:55,500 for round trip, comms to Voyager, Mars is an orbiting planet around the Sun. And so, it's not a 366 00:41:55,500 --> 00:42:02,220 set distance from the Earth. The Earth is moving around the Sun at one rate and one orbit, 367 00:42:02,220 --> 00:42:07,980 and Mars is moving around another. And so, the time difference to Mars ranges from four to, 368 00:42:07,980 --> 00:42:15,900 you know, 44 minutes. And so, when it's at a distant point, and I send a radio wave to Mars, 369 00:42:15,900 --> 00:42:20,060 it takes 44 minutes for it to get there, and then 44 minutes for it to get back. 370 00:42:22,380 --> 00:42:30,060 And so, we have to factor that in for when we start doing these Mars missions and we start sending 371 00:42:30,060 --> 00:42:33,180 humans. It's going to be a very different experience than the Moon. 372 00:42:34,060 --> 00:42:41,180 And I'm sure that the lessons that we learn on the Moon are going to inform all of those 373 00:42:41,180 --> 00:42:48,060 challenges that we have going to Mars. Yeah, absolutely. Just like the lessons we learned on the Earth 374 00:42:48,060 --> 00:42:53,180 are giving us huge advantages for how we are applying technology to the Moon. 375 00:42:54,220 --> 00:42:57,660 This has been fantastic. I have learned so much today. 376 00:42:58,540 --> 00:43:05,740 Was I right that you might not be satisfied with all the answers? It's a crazy topic. 377 00:43:07,020 --> 00:43:12,780 You know, the dissatisfaction I have with some of the answers has just inspired me to learn more 378 00:43:12,780 --> 00:43:19,740 about what it takes to tell time on this kind of accurate scale. Oh, that's the goal right there. 379 00:43:20,460 --> 00:43:25,260 Well, thank you so much for coming on and taking the time to talk about time with me. 380 00:43:25,820 --> 00:43:27,260 Absolutely, Dane. Thanks for having me. 381 00:43:46,430 --> 00:43:50,750 Thanks for sticking around. I hope you had a good time. You can check out the latest from around 382 00:43:50,750 --> 00:43:56,590 the agency at NASA.gov and to find out more about SCaN, you can go to NASA.gov slash SCaN. 383 00:43:57,230 --> 00:44:01,470 Our full collection of episodes and all of the other wonderful NASA podcasts can be found 384 00:44:01,470 --> 00:44:07,710 at NASA.gov slash podcasts. On social media, we're on the NASA Johnson Space Center pages of Facebook, 385 00:44:07,710 --> 00:44:12,750 X and Instagram. If you have any questions for us or suggestions for future episodes, 386 00:44:12,750 --> 00:44:20,510 email us at nasa-houstonpodcast at mail.nasa.gov. This interview was recorded on March 10th, 2026. 387 00:44:20,510 --> 00:44:25,550 Our producer is Dane Turner, audio engineers are Will Flato, Daniel Tohill and Mani Cooper, 388 00:44:25,550 --> 00:44:30,510 and our social media is managed by Leah Cheshire and Kelsey Herron. Houston We Have a Podcast was 389 00:44:30,510 --> 00:44:36,030 created and is supervised by Gary Jordan. Special thanks to Catherine Schauer and Kali Dusenbery for 390 00:44:36,030 --> 00:44:40,510 helping us plan and set up this interview. And of course, thanks again to Kevin Coggins for 391 00:44:40,510 --> 00:44:44,110 taking the time to come on the show. Give us a rating and feedback on whatever platform you're 392 00:44:44,110 --> 00:44:47,870 listening to us on and tell us what you think of our podcast. We'll be back next week. 393 00:44:52,140 --> 00:45:02,140 This is an official NASA podcast.