Main Engine Cut Off - T+105: Jonathan McDowell

Episode Date: December 29, 2018

Jonathan McDowell joins me to talk about his recent paper proposing 80 kilometers, rather than 100, as a more appropriate boundary of the edge of space. This episode of Main Engine Cut Off is brought to you by 34 executive producers—Kris, Pat, Matt, Jorge, Brad, Ryan, Jamison, Nadim, Peter, Donald, Lee, Jasper, Chris, Warren, Bob, Russell, John, Moritz, Joel, Jan, David, Grant, Mike, David, Mints, Joonas, Robb, Tim Dodd the Everyday Astronaut, and six anonymous—and 205 other supporters on Patreon. Jonathan’s Space Home Page Jonathan McDowell (@planet4589) | Twitter The edge of space: Revisiting the Karman Line - ScienceDirect Jonathan’s Space Report Email your thoughts and comments to [e-mail] Follow @WeHaveMECO Listen to MECO Headlines Join the Off-Nominal Discord Subscribe on Apple Podcasts, Overcast, Pocket Casts, Spotify, Google Play, Stitcher, TuneIn or elsewhere Subscribe to the Main Engine Cut Off Newsletter Buy shirts and Rocket Socks from the Main Engine Cut Off Shop Support Main Engine Cut Off on Patreon

Where does space actually start? That is the question we're going to be answering today on Main Engine Cutoff. I am Anthony Colangelo, and we've got a special guest with us today, Mr. Jonathan McDowell. He is an astronomer at the Harvard-Smithsonian Center for Astrophysics, works on Chandra, among other things, and recently wrote a paper called The Edge of Space Revisiting the Karman Line, in which he argues that the 100-kilometer Karman Line is not necessarily an accurate description of the edge of space, and something that is closer, if not exactly 80 kilometers, is appropriate. We're going to talk to him all about that, how he got here, why this is the right answer, and what other kind of effects

that might have in the industry. But before I call him up, I just want to say that this is a very readable paper. It might sound intimidating. It might sound very math heavy. It is very readable. It is only about 10 pages, maybe. That includes the references page, which is quite long. So go check it out. There's a link in the show notes to it. Definitely take a read if you're interested in this sort of thing. I think it's very much worth reading because it talks a lot about the historical precedents, why this matters, all sorts of different aspects that you might not have considered if you're only really thinking about this in terms of space launches or satellites or something like

that. There's a lot more that's going into it. And I found it a very interesting paper. So go check it out in the show notes. And let's give Jonathan a call. Hello? Jonathan, thank you so much for joining me. Welcome to Main Engine Cutoff. I'm very excited to have the man that's been at the center of space nerd arguments for the past few months

on the show with me here. Well, it's great to be here, Anthony. I'm interested in, I'm sure at this point people have read many headlines about how you are single-handedly redefining space and other things that are maybe a little over the top. I'm interested, before we dive into the details, to hear a little background about how you decided to do this research, how did you get to this point about publishing this particular paper? Right. And so I've been promising people I'll write this paper for the past 25 years or so. Okay, so no pressure going into it. Well, so, you know, I first started to worry about this when back in the 90s, I was making some of my early lists of rocket launches.

And I'd been making orbital launches, but I branched out into suborbital flight. And so then I had to face the question, what should I include? What's a suborbital flight as opposed to just some boring little toy rocket in the atmosphere? And so that led me down this path of where does space begin? At the same time, I was researching the history of the X-15 rocket plane, which is, you know, for those of us who are like real space nerds, mention the X-15, but brings a little glow to your heart, right? It's one of these things that the public don't know about so much, but it's a great piece of history. The very first reusable space plane dropped from a B-52, popping up 100 kilometers into

space and down again, very much like Spaceship Two does today. And so that led me to the fact that the Air Force pilots who went above 80 kilometers in the X-15 had been awarded astronaut wings. And so I looked into that a little more and the structure of the atmosphere, the fact that the mesosphere ends about there. And I convinced myself to first order that 80 kilometers was a pretty good boundary for space and made maybe a little more sense than the 100 kilometer one that a lot of other

people were talking about. So that's what since the 90s I've been using as my boundary of space. And I wrote about it in my paper on the X-15 that was in a space history magazine called Quest back in 1994. It said, oh, this is where I think it should be. But I didn't really justify it in detail. And I always meant to go back. And I always meant to go back. And as the public interest in suborbital space tourism grew, and first we had Spaceship One, and then Virgin Galactic gearing up to do Spaceship Two, I thought, well, you know, I really better write this paper because if I leave it too long, I'll miss the window of people being interested in it. Well, you just about nailed it exactly on timeline as you needed to, uh,

given the way the years ended. I, I, as I got into the, you know, writing the paper, I realized I needed to learn more atmospheric physics. I needed to, uh, um, learn more about, uh, uh, orbital drag and things like that. And so it actually took me about five years longer than I expected to write the paper, even once I'd started getting into it. But fortunately, it took Virgin Galactic a lot longer, too. I managed to get it out the door while it was still relevant. Yeah, that's the underlying storyline of this, is delays in space are not just the spaceflight participants' side of things.

Right, exactly. So my own delays are just as bad. But finally I wrote it up and got it out, and I'm really gratified by the amount of interest it's gotten. Comparatively warm reception. Of course, I haven't convinced everybody yet. Yeah, exactly. But, you know, give it 10 years and I think people will come around to my point of view. Were you surprised by the reaction that the paper had gotten? Did you expect there to be a lot of argument about it or were you surprised by that? You know, I really didn't know. I submitted the paper to the journal, and I was like,

well, you know, they're just going to reject it and go, this is boring, you know, not what we want to publish. Or it'll be a big thing, right? And either no one will read it, or everyone will read it. So I just had no sense of whether or not it would be hitting the right mark. But it seems to have done. And I was careful to put in some less technical stuff in the beginning of the paper. So it sucks you in a little bit, right? Because you get through the first couple pages and you go, oh, that's not so bad. And then the math hits.

I did like the way that you described your interest in this. And you said specifically that you are doing this because you care about that historical aspect of being able to keep the Jonathan Space report up to date. But that there's all these other considerations that go into this specific definition. There's regulatory approvals, there's geopolitical concerns about when are you in my airspace and when are you not. So, you know, do you think this is going to actually stay in that historical mindset? Or do you think people that are interested in the other areas of definitions are actually going to latch on to this paper and use it

to kind of clarify some of their own definitions? I think they are. And so I was invited to give a talk to the Galloway Symposium last month in Washington, which is an annual meeting of the space law and policy community in the United States. community in the United States. And so the sense from talking to those folks is that this is a question whose time has finally come. People have been arguing about it for 60 years, and since before Sputnik, right? And the fact that there's more activity there, so for a long time, right, the only activity in this sort of liminal region between, say, 50 kilometers at the top of the stratosphere where balloons top out, and 120 or so kilometers where the circular orbit satellites get down to.

There wasn't really a lot going on except for elliptical orbit satellites approaching reentry and sounding rockets that stayed there briefly. And none of those things really forced people to make a choice. But we have now Virgin Galactic flights. force people to sort of make a choice. But we have now Virgin Galactic flights. We have these long-range hypersonic weapons that may or may not be in this altitude range. And so we have space planes that may have long gliding reentries over different countries at altitudes that are on the edge of space.

And so I think over the next 20 years, that area of space is going to be a lot more traveled in a sense, or get a lot more attention than it has done. And so that's going to force regulatory agencies to really make a choice. That's my guess. So can you give us your best elevator pitch style description of what your conclusion is in all this? If I were to go tell somebody, you should read this paper because here is what it says, and this is why it's interesting. What would that be to you? So I claim that there is a reasonably well-defined spot at which space begins, and it is 80 plus or minus 10 kilometers above the Earth. And the reason I come to that conclusion is through both an empirical looking at the data approach and a theoretical approach.

And the fact that they give the same answer is what convinces me that I'm on the right lines. And so the empirical approach is you look at elliptical orbit satellites and you see how low can they go without immediately re-entering. And it turns out that satellites can have perigees in the 80 to 90 kilometer range for days or even weeks at a time before they burn up. But you don't see ones with perigees in the 70s kilometers that last more than an orbit or so.

And so it's a pretty well-defined point at which below there, you melt, you check in and you don't check out. Then if you take Karman's original answer, so the Karman line was the idea of Théodore von Carman, founder of things like JPL and Aerojet. And he said, roughly speaking, in its most abstract form, right, it's where do orbital dynamics forces become more important than aerodynamic forces? become more important than aerodynamic forces. And, you know, even at the space station's altitude, you have to worry about aerodynamics. You have to worry about atmospheric drag. But it's not the dominant force.

Gravity is the dominant force. Whereas down, you know, at sea level, aerodynamics really dominates things. It's a bigger force than gravity. And especially if you're traveling, I should step back. The common question was, if you're traveling at orbital speed, is aerodynamics more important than gravity? So you can't travel at orbital speed near the ground because you immediately melt up, right? You burst into flames. The aerodynamics... The thermal properties become dominant in that case.

Well, that's also true. Yeah, that's a detail that I haven't gotten into. And so, you know, there's a point at which at an orbital velocity, the aerodynamics forces become bigger than the orbital dynamics forces. When you calculate that, the first time people wrote down Kármán line and

calculated it, they got answers like 85 kilometers or thereabouts. The idea that it was 100 didn't really emerge until maybe the 70s, when people, I think, felt that it was the atmosphere very too much to define it precisely, and so you might as well take a really round number. To define it precisely and so you might as well take a really round number But in fact what I showed was that actually at that old to the atmosphere doesn't vary that much And that if you run a whole bunch of different model atmospheres for all kinds of conditions of

Solar activity and latitude and everything you want to change and different kinds of satellites, you basically always get 80 plus or minus 10 kilometers for where this common criterion is met, which is exactly the same region that we got from actually looking at the data. And so that's why I feel like, you know, going into this, I thought, oh, you know, I'm going to get some, solar activity is really going to change things. It's going to be 11-year cycle, and some years the Kármán line is going to be here, and some years it's going to be somewhere totally different. No, it turns out solar activity changes things a lot when you're up at the space station's altitude. But when you get lower in the atmosphere, it doesn't really make that much difference. And so when I saw that, I was like, okay, it's time to publish because this is telling

me that the common criterion actually does point you to a layer that is in agreement with my data and is significantly lower than 100. The variability that you're talking about, where it's 80 plus or minus 10, do you feel that that's as precise as we're ever going to be able to get in this particular instance? Or do you think that there's something else that could make us come up with a more definitive line? Because I think that's the one part that people struggle with, is that we're arguing over 80 versus 100 kilometers, but our variability is still enough that it's, at a certain point,

you're like, okay, does it matter anymore if you're in space or not? I don't even know why I'm reading this kind of stuff. Right, right. Well, I mean, it depends on your personality. That's a personality thing, I think. Yeah, exactly. Whether you care about that or not. They're not the kinds that are writing these papers. Right.

I, you know, ultimately, I have to make a choice for my list. And so I'm writing down my justification for the choice that I've made. And I think it's a good choice and other people should adopt it too. But if you don't, well, that's fine. Pick some other value. The dominant thing in that plus or minus 10 is the type of satellite. If you have a balloon versus a cannonball, the cannonball feels the atmosphere less and so its effective

common line is lower. And so that's really what limits the common argument for where things are. Now maybe you can come up with a different argument of where space should start

or just use the empirical one of how low things fly in practice before they re-enter. And with better data and better orbital fit, you might be able to refine that a little more. Maybe it's not clear to me what the true variability of that is. But my guess is that the atmospheric variability is at least about five kilometers. So that's as narrow as you're ever going to get it. Yeah. And I do appreciate the, you know, I think a lot of times when this paper is written about in different media outlets or anything like that, it gets maybe misconstrued in that you're saying this is the line that works for everything ever and everybody should, you know, follow this as the law. Whereas what you're really saying is, you know, there are lines

for different reasons. Everything's got its own purpose for its own definition. And there's going to be regulatory things that matter in some cases, and others don't care about that line. And we already have 10 different arbitrary boundaries between low-Earth orbit and medium-Earth orbit, or Earth and interplanetary space, or solar system and its interstellar, as we've heard with the Voyager debate in the last month or so.

Did Voyager leave the solar system, or is it just now in a different regime? That's right. And I have a fun little paragraph in the paper where I actually get into those other boundaries a bit. Yeah, yeah, yeah. I like that section a lot. I snuck in my definition of where deep space begins, which I'm very excited about, because one of the things I hope to publish in the next few years is a catalog of objects in deep space and what their orbits are, which

is something that NORAD and Space Command don't track that, right? It's very hard to get that orbital data. So I've been painstakingly compiling it over decades. I'm close to being ready to publish, but again, I'm about the stage where I was when I told people I was close to being ready to publish the Edge of Space paper about 10 years ago. Yeah, exactly. It's going to be a little while. I have about slightly over 1,000 objects in the Deep Space catalog. Wow. All right. Well, that would be very cool to see.

Yeah, so that's my little teaser for stuff to come. And so, yeah, so these boundaries, again, that boundary is even more arbitrary. The boundary I'm making for deep space is I'm looking at basically arguing, where can you ignore the existence of the moon and the sun and say that something's really in a Kepler ellipse around the Earth? You can do that out to about 150,000 kilometers. So Chandra, the spacecraft I work on, is sort of about at that boundary. But TESS, the new exoplanet satellite, is out beyond that,

and its orbit isn't really as simple as just a Kepler ellipse. It's heavily affected by the moon. So it feels like that feels to me like the right point to start talking about deep space is when you really just can't use, you know, can't pretend that Kepler's laws are all you need. So, but that's arbitrary. You could move, you could choose another value.

And I'm, you know, I'm still playing with that. And again, why do you need it? Well, if I'm going to make a list of objects in these spaces, I need to justify what's in the list and what's in the list. Yeah, exactly. And that's really all it goes down to. And I feel like that's the part where people get hung up. When we're talking about regulatory changes in the U.S. right now, we're talking about a lot of different licensing changes and different agencies are going to be taking care of different parts of space regimes in that regard. You know, it doesn't necessarily matter to each individual one which line we use to compile historical lists, but it does matter for SpaceX to know which agency they need to go to to license their reusable rockets. So I feel like in each case, it's specific to the use case of that agency or

of that flight. And they will need definitions at some point, but we don't need one to rule them all. We don't, but I would argue that it's convenient if there is one reasonable, sensible definition. If you have no reason to choose another one, then you might as well pick mine. Yes, I agree. Right. The more people use the same one, the better, maybe. And so I think, you know, in the end, people are either going to pick 80 or 100, depending on whether they feel like round metric numbers are important or at least a pathetic attempt at a physical argument is more important. So given that you're right, let's say your paper checks out on the historical timescale and you nailed it.

What do we actually do from here to change definitions? And how does that kind of mimic the way that it's been for the last 60 years, where the US has said one thing and the international community has said the other? Has that mattered much, the difference internationally for 60 years? And how do we go about changing that across the board? Right. I think, you know, that's going to be a process at COPUS, the Committee on Peaceful Users of Outer Space, ultimately, as well as the FAI, the International Aviation Federation, which currently uses the 100-kilometer Karman line to line to define records, like what's the space flight. And they are actually talking about having a conference next year to rediscuss where the boundary should be.

So that's the short-term next step. In the longer term, I think it will probably take an incident, is what I'm guessing. of some country that objects to sort of motivate people to really get this as international space law. So it just depends when that starts happening. Well, that's a foreshadowing element of this. Yeah, that's pretty intense. The example I give, right, is that one where it's clearly space is all the tearing hair out that happened when the North Korean missile flew over Japan. And so North Korea launched these missile tests, and they flew over Japan and landed in the

Pacific. And there was great panic in the Japanese media about, oh, this missile's flying over Japan. But it was 500 kilometers up the whole time it was over Japanese waters and Japanese territory. So it was above the space station. And no one panics when the space station flies over you. Or any number of spy satellites that are up there. Right, exactly. But because it was suborbital, somehow that felt more invasive

to people. And I think it's because we don't have a boundary of space. And to, you know, to kind of, if the boundaries of space were more official, it might be clearer to people that, okay, that's in space, it's not, you know, bothering Japan any more than a satellite would be. Whereas if it were at 60 kilometers, maybe that would be more of a reason to complain to the North Koreans about what they were doing. Well, that's a good real-world example of this. That's, you know, you can say, how much does this matter? But then you get into that exactly right hot-button issue this year.

That's just like the perfect example of this. So that's a good one. I noticed that wasn't in the paper, but that might've been a whole different paper. Right. Well, I just want to get into the political stuff, right? Because actually that's not my motivation, but, but, but if you ask me, you know, why should other people care? That's an example. Um, before I let you out of here onto your day up there, uh, what other things in space have you been watching lately? What are you particularly excited about this year? I know you've got the space report that you're always working on, so I assume you're getting close to the 2018 edition here.

Right, exactly. So the past few years, as well as the sort of monthly-ish space report, I've put out a year in space paper where I summarize statistics of launches and stuff like that. And so I'll be working on that soon. Might be a little late this year because I'm rewriting all my code that does those statistics. But I think the story of this year is the pivot between a space age in which the Soviet Union and then Russia dominated the launch rate and an era in which China dominates the launch rate. denominates the launch rate. And China, you know, when I started off in this game was sort of, they were very serious about space. They launched like one satellite a year or something like that. And then the early nineties, they decided to invest big and they've been gearing up and gearing up. And this past couple of years, they've finally gotten, uh, to this sort of more serious level where they've been, they've,

I think, now got more spy satellites in orbit than America, for example. They launched more orbital launches this year than anyone else. They still aren't launching as much tonnage. The U.S. launchers typically are launching heavier satellites. But in terms of just straight number of launches, China's now pulled into the lead after having been in sort of, you know, fourth place not so long ago, whereas the Russian space program has continued a slow decline. And so I think that's a huge historic shift that's worth paying attention to.

The other thing I've been looking at is, again, the deep space stuff. And one thing in the big picture I'm looking at is low Earth orbit is sort of basic infrastructure now. And that's reflected in the way that NASA is looking to commercial companies to launch astronauts and so forth. The inner solar system is starting to be at the stage where Earth orbit was in the 80s. And then it's moving from the frontier to the government infrastructure kind of era. And so we're starting to get communication satellites a little bit around Mars. We're starting to get communication satellites and orbit around Mars. We're I think going to have some kind of navigation satellite at some point in interplanetary space where we're going to start seeing these sort of applications where it's not just you but the inner solar system is an arena

which is sort of home territory now. And it's becoming home territory not just for the superpowers, or not just for the original space superpowers of the United States, Russia, now Europe, Japan, but India is now forging out into the inner solar system. China has started more serious planetary exploration. So I think that is a historic shift. The real frontier is now the outer solar system. And of course, as we speak, outer solar system. And of course, as we speak, New Horizons is barreling down on 2014 MU69,

the object in the Kuiper Belt. And so this sort of mental shift from, you know, Earth orbit is like the stuff that we do, and deep space is the special thing, and Mars and stuff is only very special. Now Mars and Venus are going to be ordinary, and it's Jupiter and the asteroids and so on that are more sporty. Well, from your mouth to the Venusian scientists' ears, because they're hoping that Venus gets pretty tired pretty quick. Yeah, yeah. We're overdue for a Venus mission, absolutely.

I've been encouraged this year. You know, Hayabusa was like, what, $150 million of a total budget for a mission like that? That's just doing amazingly out there right now. And you start seeing these missions that are doing this, you know, operationally almost. They had some problems with the old Hayabusa. Hayabusa 2 is doing great. Right. And on these slim budgets

that are just indicative that they're able to do this, you know, multiple times in different destinations. And that is, it's hard not to look at what we're in right now as anything but a golden age in space.

I think that's right. The Japanese space program in particular, I have great respect for. They used to do really good niche stuff very cheaply in a small team. They had a period when they got more ambitious without really changing the way they do things, and that didn't work out so well.

They had a lot of failures for a while. And then they pulled it together again, and they've been doing these ambitious missions, and some of them don't work out. But, you know, there's this old saying that in something like space exploration, if you don't fail, you know fail at least 10% of the time, then you're not being adventurous enough.

If you always succeed, then you're operating too much within your comfort zone. So I think the fact that they do these ambitious missions, they occasionally fail, but then they learn from those mistakes, and they go back and do it right. It's just been very inspiring to see. Well, Jonathan, I've got a link in the show notes to your paper, The Edge of Space, Revisiting the Karman Line. Is there anything else that you would like listeners out there to go check out of your work?

Well, obviously the website. If you Google Jonathan Space Report or just Jonathan Space, you'll find it, planet4589.org. And there's lots of stuff hidden away there. One of these days, I will update the HTML to not look like it was written in 1994, which it was. Hey, you've been working on the paper since then, man. You got other stuff going on. Exactly. So my idea has always been, you know, I have text files.

They're not, you know, Microsoft formats or anything like that. You've got to do some work to use them. But that's right. I'm putting the work in to get the content out there. And then other people are welcome to repackage that in some easier-to-get-at form. So, you know, I've got a lot of info out there. It's all free. Just cite me.

But I hope you enjoy it. And I'm just doing most of this for my own amusement, right? I want to know how many tons we'll launch into low Earth orbit this year and questions like that. And having gone to all that effort to find out the answer, it's fun to share it. Well, I appreciate that. I'm sure everyone else out there does as well. It's been a pleasure having you on, Jonathan. I hope we'll hear from you again when you've got that next paper out, or hopefully before then even. Yeah, hopefully. All right. Cheers. All right. Thank you so much. Talk to you later. So with that, that is it for us today. Thank you so much again to Jonathan for coming on the show. It's amazing to have people like him on the show to share the airwaves with me for a little bit.

Once again, go check out his paper. It is really, really worth a read. So check that out in the show notes if you want some more of that. And on Twitter at Planet4589, he is a must follow if you're interested in any space nerdery like I am. He is a frequent source for me on headlines. If you listen to the headline show where I talk about all the goings on of the week and anytime I'm talking about launches, I'm probably pulling my numbers from Jonathan's Twitter feed. So head over there and check that out. And speaking of headlines, I want to say a very special thank you to all of you supporting Main Engine Cutoff over on Patreon. Patreon.com slash Miko is where you can go to support the show. There are 239 of you supporting the show every single month.

That includes 34 executive producers who made this episode of Main Engine Cutoff possible. Chris, Pat, Matt, George, Brad, Ryan, Jameson, Nadeem, Peter, Donald, Lee, Jasper, Chris, Warren, Bob, Russell, John, Moritz, Joel, Jan, David, Grant, Mike, David, Mintz, Eunice, Rob, Tim Dodd, The Everyday Astronaut, and six anonymous executive producers. Thank you all so much for making this show possible. We could not do it without your support. And the 205 others over at Patreon.com slash Miko. If you are a $3 a month

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I'm finalizing my setup here. I just got a new computer here, got a new studio setup going. So I will keep you abreast of that news when it happens. So thank you so much again for your support. And if you've got any thoughts on the show that you'd like to send my way, head over to Twitter at WeHaveMiko or the email is Anthony at ManagingCutoff.com. Thank you so much for listening today. And I will be talking to you soon.

We've got a Q&A episode coming up next week to end the year. And so you'll hear from me pretty soon here on the main podcast feed. Thanks again. And I'll talk to you soon.