Planetary Radio: Space Exploration, Astronomy and Science - Solar Cruiser: A Giant Sail Prepares for Space

Episode Date: January 6, 2021

It is many times larger than any previous solar sail, and it will pave the way for even bigger spacecraft propelled by light. Solar Cruiser principal investigator Les Johnson tells us about his latest project and looks to humanity crossing the gulfs of interstellar space. Stellaris: People of the Stars is a collection of science fact and fiction co-edited by Les. Mat and Bruce offer a copy in the new What’s Up space trivia contest. There’s more to discover at https://www.planetary.org/planetary-radio/0106-2021-les-johnson-solar-cruiserSee omnystudio.com/listener for privacy information.See omnystudio.com/listener for privacy information.

NASA greenlights a gigantic solar sail, this week on Planetary Radio. Welcome, and Happy New Year again, all. I'm Matt Kaplan of the Planetary Society, with more of the human adventure across our solar system and beyond. I wish I could say it's as big as an American football field, but at nearly 1,700 square meters, Solar Cruiser would cover a third of that field, and it will fly before the middle of this decade, according to principal investigator Les Johnson. Les has returned for a wonderful conversation about this sail and even bigger ones in our future, along with much more. We'll give away Les' book Stellaris in this week's What's Up segment with Bruce.

It's a terrific collection of science fact and fiction about what it will mean to be human when we become an interstellar species. There are a couple of space headlines worth mentioning that didn't quite make it into the New Year's Day edition of The Downlink, our free weekly newsletter, recent Planetary Radio Space Policy Edition guest Scott Pace has returned to academia from his service as Executive Secretary of the U.S. National Space Council.

It's still not known if the incoming Biden administration will retain the council. I suspect we'll talk about this in the January Space Policy Edition, premiering on Friday, January 8th. The Puerto Rican government is not giving up on the Arecibo Observatory. Outgoing Governor Wanda Vázquez Garcet has set aside $8 million for repair or replacement of the big radio telescope. Of course, much more than that amount will be needed before work could begin. Japan's Hayabusa 2 returned a total of 5.4 grams, or two-tenths of an ounce,

of material from asteroid Ryugu. Not bad, considering the goal was just a tenth of a gram. There's much more about this mission and many others at planetary.org. Lastly, I read in the downlink about the delicate balance required for the generation and evolution of life on Earth and other Earth-like planets. A new computer simulation that includes asteroid impacts, solar flares, and volcanic eruptions on thousands of simulated Earth-like worlds indicates that we and all the other living things on this planet beat the odds. So, good on us. That's just part of what you'll find in the downlink at planetary.org. We've also got a new collection of space art for you to explore. Les Johnson last joined us in 2018.

We talked then about the Near-Earth Asteroid, or NEA Scout mission, the nearly 100 square meter solar sail effort headed by Les at NASA's Marshall Space Flight Center in Alabama. As you'll hear, we are nearing the launch of this asteroid explorer, and it was only days ago that the space agency gave Les and his team the go-ahead for construction of Solar Cruiser, a sail with 17 times as much sail as NEA Scout. Les is also a noted writer of science fiction and non-fiction science books. If there's anything that unites his writing and the work he does for NASA, it may be optimism and cheerful passion.

I think you'll hear them in the conversation we recorded as the new year began. Les Johnson, welcome back to Planetary Radio and congratulations on all the good things, the good news that you've gotten in the last few weeks and what's coming up later this year. Mostly, I'm very glad to have you back on the show. Well, it's good to be back. And I have to admit, as rough as 2020 was, we did get some good news toward the end of it that made it a little bit brighter. Yeah, you know, as we have said before on this show, 2020 was a much better year once you got off the surface of the planet.

Well, my stuff hasn't gotten us off the planet, although I think my feet were in the clouds for a few days when we found out that the solar cruiser was selected. Oh, I bet. And that's a major congratulations on that recent announcement by NASA that that big sail has been green-lighted. We're going to talk more about that later. Let's start with this more general question. Where are we in the evolution of light-driven sails? Well, we are in a revolution in in sales that I didn't really envision happening when I first started working on solar sails. The work of the Planetary Society, the Japanese, the Europeans, what we've been doing at NASA,

there's been a lot of advancement on various fronts with flights over the last 10 years, actual demonstrations, technology work, the interest coming with taking sails and putting lasers on them with the breakthrough star shot is exciting. So you put it all together and it really bodes well for this kind of propulsion becoming more common over the next few years and enabling scientists to do things that they just couldn't do before. So I'm optimistic. You are sure a big part of that trend. We talked a lot, not surprisingly, about NEA Scout, Near-Earth Asteroid Scout, in our last conversation a couple of years ago.

We'll put a link up to that on this week's show page as well at planetary.org slash radio. You must be thrilled to know that it just might be carried into space later this year. Is that still what you're hoping for? That is our plan. In fact, we've been told to prepare for a late 21 launch, and we're doing final integration of the NEA Scout spacecraft really as we speak. They don't typically let the PI touch the final hardware because I might break something, but the engineers and technicians who are doing that last bit of integration are busy doing that. And we anticipate shipping to the launch site probably within the next six weeks or so. That's fantastic. By the way, it reminds me of the visiting Cal Poly San Luis Obispo, where I was encouraged to pull

LightSail 2 out of its little Peapod ejector. And I said, I don't want to touch that. Do you know what Bruce Betts will do to me if I break this? Well, that's how the PI of this whole thing feels. I'm the idea person, the analysis person. I'm not the final touches on the hardware person. And I'm glad there are people that do that so I don't have to worry about those things. Talk a little bit more about your ride into space. I didn't realize that you're getting this ride along with a whole bunch of other spacecraft, CubeSat-based spacecraft, as far as I know. Space Launch System, Artemis I. And after the Orion spacecraft goes off to do its job at the moon, those small CubeSats will be deployed at various points in the trajectory of the upper stage that they're calling bus stops, which is kind of cool. At each bus stop, different CubeSats get deployed, call home to the Deep Space Network or whatever ground system that they have to work on, and then

they go about doing their mission. So it'll be after that, we'll be on a trajectory toward the moon. We'll deploy our sail, go into an elliptical orbit around the moon. And then when the phasing's right, we will spiral out and go to our target asteroid, which will take about two years of light sailing to get there, carrying a camera to do some asteroid science. Do you know yet which asteroid you'll be targeting? We have candidates. And the nice thing about a solar sail, which is one of the reasons to fly a sail, is we are not as dependent on launch window. We can reach a whole host of different

asteroids. It's just a matter of trip time. And so we have a list of candidates. Our original 1991 VG may or may not still be our primary. We're going to nail that down over the next couple of months, depending on when we actually launch. In terms of NEAs, we're pretty flexible. There are several on the list. It's what's called the NHATS database. And those are asteroids of interest for human exploration in the future. And as long as we visit one of those, we're going to be good. And having our scientist at JPL, Dr. Julie Castillo-Roger, who is the PI for the camera and the science side of things, to get her the data she needs. It's our job on the sales side to make sure she gets there in a timely way to get that data. I learned something else about the

unique capabilities of salesils for missions like the one that you're going to undertake for NEA Scout. And that is that you have the shot at getting a second pass, I guess, depending on which of the asteroids you head for. That just seems marvelous. Well, that's one of the advantages of a sail, right? I mean, you're not going to run out of fuel. It depends on the incident sunlight and the amount of time you have on your spacecraft. So our goal is to do a slow flyby, just a few tens of meters per second to take pictures of the asteroid. But if for some reason we don't get sufficient coverage, you know, 80% or more of the asteroid surface, because as we fly

by and it's rotating, then we have the option, if the spacecraft is still functional, and all indications are with a reasonable time of flight, it should be, we're really only limited by the total radiation dose that our electronics will get before we anticipate having a failure, that we could take a few months, which is how long it would take to basically fly out, loop around, reverse course, and fly by again. So that's certainly an option. It's not part of the baseline plan, but it is an extended mission that we might want to put out there if there's a sufficient reason to do that. And if the spacecraft's still very functional and looks like it has lots of life remaining, we might see if

there's another target nearby that we could go visit. So it really just depends. It'll be a mission of opportunity. That is just fantastic. I do want to thank you on behalf of the Planetary Society for regularly acknowledging our own LightSail spacecraft, as you already have in this conversation. How has light sail aided your work on NEOSCOUT and another sail that we're about to talk about? Well, first off, the Planetary Society did a great thing, flying these in Earth orbit, showing on light sail two that you can actually do real sailing to adjust your orbital parameters. I think what it did is it made the public and decision makers around the world

realize that sails were no longer theoretical and they're real. I mean, we flew NanoSail-D, the Japanese flew the Icarus back in 2010. Those were great demonstrations, but they didn't really, in my opinion, have the impact on people's thinking in terms of the reality of solar sailing the way that the Planetary Society missions did. I think the technical work that the Planetary Society did, as well as the outreach and awareness and education component, has been really critical toward making this capability more real in the minds of decision makers and scientists and people interested in sailing. I think it's contributed in many fronts. Well, thank you for that. And we're, of course, very proud of this. I am told by my friend and colleague, Bruce Betts, that there's been quite a conversation going on between your team and ours.

Well, that's right. It's been a back and forth since the NanoSail-D, which flew before you guys did. And then your flight, we had people looking at your deployment test, your day in the life, folks on your review team, because we were anxious to get your lessons learned because it came at a critical time for Neoscout. We were in development of our hardware while you were flying LightSail 1 and preparing to fly LightSail 2. And so anytime you have somebody that you can kind of roll up your sleeves and say, you know, we did this or you did that. How did it go? Well, we tried that and it didn't work. So we did this other thing. I mean, that just benefits everybody. The collaborative papers that are being published. I know we have some folks working with yours looking at the orbital dynamics and mission analysis.

I think it just helps give us more confidence in our tools for predicting solar sail trajectories and flight to be able to benchmark them with real data that you obtain. So it's useful all around, I think. Let's talk about the next big step. And I do mean a big step. So I'll just congratulate you again on that recent green lighting from NASA for Solar Cruiser. Talk about this ambitious new sail. I'll be glad to. I'm thrilled. It's really almost a quantum leap. It's definitely an orders of magnitude leap in sail capability over anything that's been demonstrated so far. Just to give your listeners

an idea, NanoSail-D was 10 square meters. The light sails were 32 square meters. The Near Earth Asteroid Scout is going to be about 86 square meters, almost 100 square meters. But Solar Cruiser is a technology demonstration mission to show the capability of an integrated sail craft using a sail that's 1,600 square meters. And for those that don't think metric, that's about 17,000 square feet, which is about a third the size of a football field or the floor area of your favorite big box retailer that will be packaged on a spacecraft that will fly as a secondary payload in 2024 with the IMAP mission, and this little spacecraft is about 100 kilograms in weight, and we'll be deploying four big composite booms, which is also a first. Instead of using metallic booms, we'll be using lighter weight composite booms. We will deploy this big sail and demonstrate the capability of a solar sail to fly sunward of the Earth-Sun Lagrange point, and create an artificial halo orbit. Basically, that's just a fancy way of saying that we're going to do station keeping

to keep the sail on the Earth's sun line as the Earth goes around the sun. Usually, a spacecraft that's in that location is going to drift because it's in a different orbit. It has a different orbital period. But we'll be using the constant sunlight pressure to stay on the Earth's sun line. That's exciting because there are a lot of missions for space weather and heliophysics But we'll be using the constant sunlight pressure to stay on the Earth's sun line. That's exciting because there are a lot of missions for space weather and heliophysics that need this kind of an observation and the ability to do sustained station keeping there to answer some questions about the sun. And there are lots of other missions we enable, too, but I don't want to go on and on. Keeping track of solar weather, this might just save people trillions of dollars someday back here on Earth, right? Because we need to know what's coming at us from the sun.

Well, and got to be careful here. We are actually not a science mission. We are demonstrating a capability for science. In our detailed study, we originally were going to carry an instrument called a coronagraph. Oh, I saw that. Yeah. But we had to de-scope that. And we did that very painfully. I didn't want to do that. But because we started being concerned about the overall cost, we had a cost limit for what the demo could be. And by including the development of this new instrument, it really put us over the cost cap. And so we had to remove our science instrument to really make sure we had enough margin in our cost and mass to be able to demonstrate the sale

without too much risk. So at this point, we aren't actually performing science, although we are in discussions that I can't go into a lot of detail about, about maybe adding a small instrument on board, but it would not be the coronagraph that we had originally wanted to fly. It certainly stands alone in its value as a technology demonstration. You said there were other possible missions, and this is something I heard you talk about, a presentation that you gave at the 2019 Tennessee Valley Interstellar Workshop, where you said that after establishing this sort of halo orbit, it's just possible that Solar Cruiser might leave the plane of the ecliptic, where all of us live and all the other planets live,

and give us a much better look, almost a first-ever look, not quite, at our stars' north and south poles. Is that something you're hoping for? Well, the solar cruiser won't actually make it to the poles, but we're going to demonstrate exactly what you said. We're going to take the sail and we're going to change the sun incidence angle so that instead of accelerating or decelerating in the direction we're already moving around the sun in the ecliptic plane, that we start around the sun in the ecliptic plane,

that we start raising ourselves out of the ecliptic plane. And so we're going to demonstrate the capability of a sail to change inclination at about seven degrees per year. We won't actually be doing that change at that magnitude because our mission's not that long, but we will be demonstrating the capability. And that's the important thing for heliophysics and the people that are funding us. They want to know that we can do, a sail can do what it's claimed to do, and then they can propose follow-on missions that are instrumented to go do that. This high inclination solar imaging is really important because I was really stunned to learn this a few years ago. As much as we know about the sun, there's a lot we don't know.

And one thing we don't know is we don't have high resolution images of the sun's poles over sustained periods of time. And therefore it makes it really hard to understand space weather because how can you do a weather forecast on earth if you don't know what's going on at the poles all the time, right? So the space scientists are real eager to, in the future, have missions that allow continuous observations at high inclinations and over the sun's poles. And the only way to do that, really, that we know of, or the best way to do it efficiently, is a solar sail.

really, that we know of, or the best way to do it efficiently is a solar sail. I'm thinking back to the Ulysses spacecraft, which gave us those earlier looks at the sun's poles, pretty much the only ones we've had. And didn't it have to go all the way out to Jupiter to be able to leave the plane of the ecliptic and then make its way back in toward the inner portions of our solar system? It did. And it took a long time. They had to design the spacecraft to operate in deep space, which is a lot more expensive and a lot harder than just a sunward of Earth.

And they didn't get that long a view of the poles. They only had, it was a matter of weeks or months. A solar sail would let you go in toward the sun and do that inclination change and then observe the whole time. And so you don't have to wait until you've flown back from Jupiter to do that. That's physicist Les Johnson, principal investigator for both the NEA Scout and Solar Cruiser sails. He and I will be right back with more great stuff. This is Planetary Radio. You've already addressed this somewhat, but say a little bit more, if you will, about why sails are the ideal vehicles for missions of discovery like the ones

that we've just been talking about, Neoscout and Solar Cruiser, or at least the potential that they offer for missions well into the future. I have to give a caveat because I don't want to ever claim that there's one propulsion system that meets everybody's needs. There are different kinds of propulsion that are good for different kinds of missions. It turns out that there are a lot of robotic science missions that don't require very heavy payloads like tons, right? That we can build a sail of size to support, to give them propulsion today. Now within that, that scope, there are a lot of destinations that scientists want to go to that are very propulsive intense. They require very efficient propulsion and lots of propellant, which translates into pounds and pounds of fuel.

And you still eventually run out of that fuel. I've mentioned one, which is the sustained station keeping on the sun earth line. Another is changing heliocentric inclination, getting out of the ecliptic plane. That takes a lot of propellant. And the reason for that is unlike when you launch a rocket into space on a mission that's in the e for that is unlike when you launch a rocket into space on a mission that's in the ecliptic plane, which you launch, you automatically get the Earth's velocity added to it because the Earth's moving around the sun, right? So you've already got a lot of velocity before you even get off the ground. And then you add to it with a rocket to get into space and escape the Earth's gravity well, you're moving pretty fast and you're already in orbit around the sun

with some velocity that's much greater than zero. But when you try to get out of the ecliptic plane, you're essentially starting with zero velocity in that direction and have to build it all up. It takes a lot of propellant to move these things to get them going fast. And the sail lets you do that without fuel, right? So you don't have to run out of gas. Their other vantage point, scientists in the heliophysics community want to put spacecraft orbiting the sun, both leading and trailing the earth and have them stay

in a fixed position and not drift. They've done missions like that before, a mission called stereo, but over time the spacecraft drifted because they couldn't carry enough propellant to remain on station. A sail would let them remain on station. It would also let them dynamically reposition if for some reason they decide, well, you know, we're getting good imaging here at this angle, but it'd be great if we moved ahead two degrees. Well, with a sail, you just fly there and do it, right? It's just a matter of taking a little time to do that. And then there are planetary missions. I've been contacted by some folks that are interested in sample return missions for Mercury, and they're really limited on payload mass, and the SAIL gives you a lightweight return

stage that you might be able to bring small samples back from Mercury using a SAIL spacecraft. There are innovative things that you can embed in the sail, thin film dust sensors to characterize interplanetary dust and various inclinations in the solar system, which is not well characterized. So there are lots of interesting science questions to be answered by relatively small spacecraft that just require a lot of fuel and a sail lets you get around that limitation. sail lets you get around that limitation. Well, thanks for keeping me out of trouble with friends like Mark Raymond at JPL, who of course has had great success with another form of propulsion, ion propulsion, electric propulsion, and many others, of course. There is one other mission profile for a sail that I've heard you talk about, and that would be to hover not over the poles of the sun or to orbit the poles of the sun, but to hover over one of the poles on our own planet.

Well, that would be a capability for a sail that would be substantially larger than Solar Cruiser and one that we could potentially scale the technology up to do, because I want to mention that we designed Solar Cruiser in its 1,600 square meters to be this point design. But in principle, there's no reason that you can't make the booms longer and add more sail material and build a sail with our technology out to about 7,000 square meters or almost 10,000 square meters. Beyond that, you really need to start thinking about different technologies for the sail. Beyond that, you really need to start thinking about different technologies for the sail. These Earth pole sitters, which you're describing, would be a way to take a sail craft and instead of orbiting the Earth, you angle it such that you reflect the light to give you a net lift thrust to counteract the Earth's gravitational pull at the poles. And rather than orbit, you hover, balancing the force of gravity with the upward force of sunlight at the angled sail. Wow.

Now, in order to do that, you have to have a much lighter weight, much larger sail than solar cruisers. So we aren't going to be able to demonstrate that, but we are the next step toward enabling that capability. And I really believe that that is a capability that will be within reach by the time we fly solar cruiser in early 2025. That won't be something we'll demonstrate then, but I think by the time we've learned all the nuances of building this hardware, we'll have a pretty good idea of how to extend that sail size up beyond that 7,000 to 10,000 square meters. Are there other innovations that will be incorporated with Solar Cruiser that bode well for the future? Absolutely.

One of them that I'm pretty excited about is we will be flying embedded thin film photovoltaics, solar panels. But instead of being rigid, thick, heavy panels, these are essentially the terrestrial thin film, low cost solar cells that you'll find on calculators and you'll find on various devices that are being deployed all over the world. And these thin films are what you would expect. I mean, they're as thin as, they're thinner than aluminum foil. They're like saran wrap and they have decent efficiency of converting sunlight to electrical power. And we've demonstrated you can embed those into the sail and only increase its mass slightly and generate pretty significant power. So we're going to fly some coupons of this on Solar Cruiser to demonstrate that. There's also a flight in 2022 that I'm a co-investigator on

that is funded by a different part of NASA called the Lightweight Integrated Solar Array, which will demonstrate this capability in Earth orbit using a CubeSat. Sound familiar? Demonstrate first using a CubeSat. Sound familiar? Demonstrate first with a CubeSat. Why this is exciting is because if you were to take a solar sail the size of the NEA Scout, not even solar cruiser class, 86 square meter NEA Scout, and you were to cover it with these thin film photovoltaics, you could get enough power for a spacecraft well beyond Jupiter to Saturn, perhaps out to Uranus and power a spacecraft out there with sunlight. Wow. Not requiring a nuclear power source. So what's exciting for me about this evolution of sail technology is that you wouldn't

necessarily be solar sailing, but you'd be taking the same fundamental technology and solving one of the other persnickety problems for deep space missions, which is power. And it might be a more affordable way to do outer planetary missions than having to go the route of including a radioisotope power source on board. I think of what they had to go to, the lengths they had to go to with more sort of standard solar arrays to get Juno out to Jupiter. That's pretty exciting in itself. How will you be controlling? How will Solar Cruiser orient itself? It's complex. And one of the things, having worked on solar sails for almost 20 years off and on, as funding allowed, I used to think it was all about making it big and deploying the sail. All the effort went into how do we make it bigger, lighter?

How do we do deployment? What's the big risk with deployment? And what Planetary Society has shown, and we've shown in our tests for NEA Scout, and what we did on NanoSailD, is deployment works. We know how to deploy a sail. We can do this. The challenge is managing the momentum. That constant sunlight pressure means that any asymmetries between your center of

pressure of the light and your center of mass of the spacecraft results in a torque, a push on one edge of the sail that is more on one side than the other side. And unless you can control that momentum, that little push over time, you'll lose control of the sail and not be able to fly anywhere. We really believe now that the biggest challenge we're going to face is controlling this momentum during the flight. And so the technologies we're going to do that with are your traditional spacecraft technologies of reaction wheels, et cetera. But we're also including an active mass translator, which is basically a slider in the X and Y that allows you to slide sideways and up and forward and back your spacecraft relative to the center of the sail to try to balance that center of mass and center of pressure. It'll be motorized. But even that's not enough. So there is another thin film we're embedding in the sail, which is a liquid crystal that when you pass a little current

through it, it changes its transmissivity. And you can change the sail from being reflective to mostly absorptive. And what that does is it changes the amount of and you can change the sail from being reflective to mostly absorptive. And what that does is it changes the amount of pressure you get by the light hitting it wherever you're changing that, which allows you to adjust the light pressure as you want on the various edges of the sail to help control that momentum. I hope that all made sense. Absolutely. Now, is that last, the use of these

LCD panels, is that the work that was pioneered by the Japanese with Icaros? They did that. We tried to license their technology and they wouldn't license it to us. No kidding. So we had to go initially to the University of Maryland and a researcher there who's now moved to UC Davis, Dr. Jeremy Munday, to do some pioneering work in establishing a domestic capability to do this. And now he's working with one of our subcontractors, Nexol, who also provides the fabric of the sale through Rokor. Rokor is a small business that's our primary contractor for the sale hardware. I want to give a shout out to them because they're the primary small business that we're working with,

but they have a subcontractor, Nexol, who is taking these formulations and embedding them in the sale material itself. So the Japanese pioneered and said it could be done, but we had to learn how to do it ourselves. Let me change gears slightly here. I mentioned the Tennessee Valley Interstellar Workshop, which you seem to be a regular at, that annual gathering, though I imagine it didn't happen in 2020 or at least didn't happen in person. We will put a link up to your excellent 2019 presentation on this week's show page, also at planetary.org slash radio. Do you agree with our co-founder, Lou Friedman, and the people behind Breakthrough Starshot that you mentioned, and we've talked with them on the show, that sales remain the most or maybe even the only practical way for us to reach the stars, at least with technologies that we currently have within

our reach? Off and on throughout my career, since I had the privilege of having probably the coolest job title that anyone's ever had at NASA, which was manager of interstellar propulsion technology research. That was back in the early 2000s. I did that for two years before the funding dwindled, and that's where I got interested in sales. But we looked at all the different options for how you might reach the stars someday. I looked at fusion propulsion, antimatter, laser sales, solar sales, microwave sales, Project Orion. You go down the list of all these far out ideas that physics says are possible, but

we don't know how to engineer yet. And I came to the conclusion that is aligned with what you just said with Lou Friedman and a lot of the folks at the folks at Breakthrough Starshot, that the technology that looks like it's most in reach, even though we don't have it yet, is going to be some kind of a solar sail or its cousin, a laser beamed energy sail to take our first spacecraft to another star. I want to emphasize this is, you know, my opinion. NASA doesn't endorse any of these projects, of course, but based on my

analysis and what I've looked at, that's one of the reasons I chose to work on solar sails is because I believe that the work I'm doing on it is going to help lay the foundation for my technological descendants someday to send that mission to another star. So yeah, I firmly believe that's the case. You clearly have kept your eyes focused on interstellar distances and reaching the stars. I'm thinking of the book that you edited only, what, about a little over a year ago now, a year and a quarter or so, called Stellaris, a little over a year ago now, a year and a quarter or so, called Stellaris, that you wrote with Robert Hampson, a collection of science fiction stories and fact-based speculative essays.

I just bought it. And I think that we may have a nice announcement about that book in this week's What's Up. What were you setting out to do with Stellaris? Well, first thing I have to do is let your listeners know that my book writing has nothing to do with my day job at NASA. I do that totally on my own time. NASA doesn't endorse it. And I really don't try to mix the two a whole lot, but I can't answer questions about it. And if you get an author talking, they never want to shut up. That's all right with me.

Yeah. But yeah, no, it's an outgrowth of meetings of the Tennessee Valley Interstellar Workshop where we talked about the issues associated with eventually going to the stars. And it really became clear that sending a robotic probe is one thing. But if we ever want to send people, the challenges are just enormous. And there's going to be a question of, do we modify where we're going to suit earth life and earth people, or do we modify people to suit that environment to which they go? And what are the issues associated with these, you know, squishy people having to take voyages that might take centuries, right, to get to another star and to

give that a serious treatment. And so the book idea and the collection of stories with essays came about as a result of that, because we wanted to basically take the public, people who are interested in the topic, on a ride that would inspire them with the science fiction stories, which are all based on real science. We couldn't invent just speculative, you know, faster than light drives for people to zip here, there, and yon. But within the laws of physics, there's interesting stories to tell. And then intersperse that with essays by different experts on human spaceflight and what happens to the body for long duration spaceflight. Got an essay in there for Martin Rees, talking about the future of intelligent life in the

cosmos, which is absolutely inspiring. I heard him give that talk at a Breakthrough Initiatives meeting and ask him to turn it into an essay for the book. So the goal is just to get people to realize that interstellar travel may be possible, how tough it will be, and to entertain as we think about it, which is one of the things that got me interested in science and studying physics was reading science fiction, just like what we tried to do in Stellaris. You and me both. There's another book that you and chemist Joe Meany wrote not too long ago about that fascinating and very promising material called, well, I've always called it graphene, but I note that you pronounce it graphene, emphasis on the second syllable. It said on the cover of the book,

do you still believe it will revolutionize the world? I do. I think we're seeing more and more graphene coming into products. Oh my goodness, we're going to be seeing it in things called supercapacitors to replace chemical batteries. I got interested in graphene because I read a paper by a longtime friend and collaborator and someone I'm sure who's familiar to you, Dr. Gregory Matloff, who wrote a paper shortly after the discovery of graphene about how you could make a huge solar sail from it to go to the stars. What was exciting to me about that is that when we first looked at these really big sails back in the day where I mentioned I managed interstellar propulsion research, and we concluded that you might need a sail the size of Texas that's one

atom thick, made from a material at the time in the early 2000s that we called unobtainium. And it was pure science fiction in terms of the material. The science was good, but the materials and the material science was fiction. But when graphene was isolated in 2004 and its discoverers got the Nobel Prize in 2010, and we looked at the properties of graphene, it is a one atom layer thick material substrate that exactly fits what we need to build these big sails. Now, we don't know how to build a sail that big. I would never claim that we do right now, but someday we will. And someday we might be able to make graphene sheets that large. The exciting thing is that when we first looked at it, it was theoretically possible, but the material didn't exist. And in two short decades, the material now exists. And it's a question of how do you engineer it? And that's exciting. And that's exciting.

That is both exciting and I love your optimism. And I look forward to seeing those even bigger sales. Les, before we go, another part of your life, non-NASA life, is your own science fiction. Your next novel comes out, what, this summer, I think? I'm looking forward to taking a look at Saving Proxima when it appears. But I also want to note that your very first science fiction novel you co-wrote with the great author and space advocate Ben Bova back in 2014. Rescue Mode was about the first human journey to Mars. As you know, Bova passed away barely a month ago. When I first met him many years ago, he was still president of the National Space Society, and he gave me some pivotal words of encouragement. Would you like to say something about Ben? Well, Ben will be sorely missed. I first discovered his work when I was in high school, and he was editing Analog Magazine and then Omni Magazine. And he wrote the kind of science fiction that really inspired me. I mean, it was believable stuff, real people in believable situations that I could see happening in my lifetime for the most

part. When I first started working in the field, I was asked by the local chapter here in Huntsville, Alabama, to bring in a keynote speaker for a conference. And so I had a little bit of a budget to pay travel expenses. So I thought, why not? I'll ask Ben Bova. And to my great surprise, he agreed. So this was in the late 80s. I was green behind the ears working in my first aerospace job. Didn't know much about anything at all. But he came to Huntsville, had him over at my home. We talked.

I guess it was early 90s. Had a great connection made. Our paths crossed over the years. And I was given the opportunity to write a book with him. He actually wrote my publisher after he read some of my stuff and said, hey, do you think Les would want to co-author a book with me? And that's one of those questions. How could you say no? So he was a great mentor, collaborator. I learned a great deal from him. And one of the things I do want to say about Ben is he was one of the most sincere, nicest people I've ever met. He never seemed to have a negative word to say about anyone. He was always giving constructive, thoughtful advice and just seemed to be a genuinely nice person.

person. And I was very impressed by that. He is going to be missed, I know, by the community of science and science fiction and his family. But I think it was a loss for the world. He was a true gentleman. Boy, that description of Ben Bova sure fits my own very limited experience with him. And I only regret that I never asked him to join us on Planetary Radio. You want to leave us with a little bit of a tease for that next book that I guess might just be taking us out to that nearest star where we now know there is a world that just possibly might support, be capable of supporting life. Well, the only teaser I can give you is that we hope that the people who read it will not only be entertained, but give some serious thought about what it means to be human.

Because this is actually the first book in a three book series. And we are going to be exploring a lot of questions about, you know, are we alone in the universe? If somebody else is out there, where are they? Why? And then we have a lot of fun on the techno geek side, playing around with time dilation and what happens when spacecraft are traveling close to the speed of light. And the experience of time passing is different for people on board versus the society, the left behind or where they're going. We've got hopefully an entertaining story of discovery that'll also make folks think a little bit about on those starry nights when you're out looking at the conjunction of Mars and Saturn and you see all the stars up there and you wonder, you know, are we alone?

Who else is out there and are we ever going to go? That's what we're trying to convey in this book is that sense of wonder, which really motivates me in everything I do. It motivates my day job working on solar sails. I am thrilled to be working on hardware that'll probably be flying in space a million years after I'm dead. Something that I've been involved with, which is kind of a neat personal, I don't know, gratification of doing this beyond the science that it's going to do. You mentioned already, I'm an optimist and I like my work to convey that. And I like my fiction to convey that. I think tomorrow can be better than today. And it's really up to us.

And I believe that. Thank you, Les. I look forward to reading Saving Proxima in a few months and not long after that, the launch of NeoScout and a few years down the line, that much bigger sail, Solar Cruiser. So much to look forward to. Well, thanks for having me. It's a lot of fun. Always enjoy our chats.

Physicist and author Les Johnson is at NASA's Marshall Space Flight Center in Huntsville, Alabama. Stay with us for a chance to win Stellaris, his collection of science fiction and fact. Hi, I'm Kate from the Planetary Society. For all its troubles, 2020 has still seen some terrific space accomplishments. We asked our members and supporters to vote for their 2020 favorites. You can see the results at planetary.org slash best of 2020. We're talking about the best solar system image, the most exciting moment in planetary science, and much more. That's planetary.org slash best of 2020. Happy holidays from the Planetary Society.

It's time for the first What's Up of 2021. So we welcome back the chief scientist of the Planetary Society, Bruce Betts, whose name was heard, taken in vain a couple of times in that conversation with Les Johnson. Now you'll have to listen to it. I know you haven't heard it yet. Hi. It's okay. It's all good. It's all good. We say nice stuff. I pay you to delete those things. You would not want me to. You'd pay me to keep these in this time. In fact, that's a racket I should have thought of a long time ago.

Oh, no. No. Let's just talk about the night sky and hope you forget this. I'll settle for that. Mars up high, looking reddish, fairly bright in the south in the early evening. You might catch Jupiter and Saturn low in the west shortly after sunset. Jupiter looking much brighter. They are getting lower and lower. And then we've got in the pre-dawn still Venus getting lower and lower in the east. And in the early evening, keep checking out fabulous Orion coming up in the east in the

early evening. That's what's up in the sky. Well, I mean, it's some of what's up in the sky. There's a lot more. But instead, we're going to go on to this week in space history. But instead, we're going to go on to this week in space history. 1968, the last Surveyor mission, the robotic soft landers of the U.S. program, Surveyor 7, landed on the moon. What a spectacular robotic program. I mean, just so much more successful than it probably had any right to be.

Yeah. had any right to be. Yeah. And often, of course, overshadowed legitimately by Apollo, but it was quite the successful program in the 60s. Do you remember which Apollo mission they landed on purpose close enough to one of the surveyors that they went over and took it apart a little bit? I always thought it was an amazing coincidence that they ended up so close to it. an amazing coincidence that they ended up so close to me. Well, look over there. That was Apollo 12 and Surveyor 3. And it makes for rather interesting, spectacular pictures on the moon of them going over to the robotic lander that preceded them. Figured you'd be on top of that.

Yeah, no, I love that. Some of my favorite pictures from the surface of the moon are showing both the lunar module and the Surveyor 3 spacecraft and the astronaut. Humans and robots together. Yeah, it's a thing. It's a good thing. Speaking of good things, we're going to go on to random space facts. That was gentle. It was gentle. Even though I haven't heard it yet, you talk solar sails. Even though I haven't heard it yet, you talk solar sails. So I thought I'd point out that as of the day this airs, 1st, January 6th, 2021,

LightSail 2, our solar sail spacecraft, has traveled over 350 million kilometers. Oh my gosh. More than 200 million miles during more than 8,000 orbits of the Earth. That's amazing. I'm really blown away. I had no idea it would be that much after this long. I mean, it goes in circles, but it does more than that. If it had gone in a straight line, where could we have gone by now?

Almost to Jupiter? No, but you'd get out significantly past Mars. You'd be pushing the asteroid belt. Of course, that would be a different mission with different physics requirements to escape Earth, et cetera. But yeah, or you could, as long as we're in a fantasy world, you could fly to the sun and back.

Sure, why not? We'll go at night. Love that joke. All right, let us go We'll go at night. Love that joke. All right, let us go on to the trivia contest. And I asked you, what is the approximate ratio of the average density of Jupiter to the average density of Saturn? In other words, how many times denser is Jupiter than Saturn? How'd we do, Matt? We got some wonderful responses.

This one, now you did say approximate, so he's able to squeak in. Most people gave us a very precise amount. It came to like 1.93 times as dense. Did that match up with what you had in mind? Yeah, but I was just looking for approximate. I'd take an integer if you've got one. Mike Fowler has one for you. Mike Fowler of Texas.

First time winner. Congratulations, Mike, he said. Approximately two. You have won yourself the brand new Planetary Society baseball cap from the Chop Shop Planetary Society store. You can find it at planetary.org slash store, of all things. Fascinating. A whole bunch of people talked about that old thing I've heard before about how Saturn is so not dense that it's less dense than water and therefore would be able to float. We heard this from Robert Laporta, Laura Dodd, Bob Lee, and some other folks. But I think you'll like this one. John Leindeker in Colorado, he said, yeah, it would float if you had a bathtub big enough, but it might leave a ring. I would be so scared of that bathtub if you found one that big. And that much water, too. Bob Klain in Arizona says, it took me a long time to figure this out, leading me to the conclusion that my own mean density is very high. Joseph Boutre in New Jersey, must resist reference to holiday fruitcake. Yeah, that's a much bigger difference in density.

And here's that poem from Dave Fairchild. If you measure densities of planets in our 10, Saturn is the least of them, despite its gorgeous zen. A planet light enough to float upon an ocean wide. Uncounted tons of rocket fuel. Of course, it's liquefied. And if we check on Jupiter when all is said is done, it beats its nearest neighbor by a score of 2 to 1. But let me add a random fact for densities, y'all. For every planet that we've got, the Earth will rule them all. One planet to rule them all.

Does he mean what I think? We are the densest? Are you referring to the people on this show right now? Yes. Are you referring to Earth as compared to other planets in our solar system? Yes. All of the above. We are the densest, and we're proud. All right. Take us on to another contest. You heard about Near Earth Asteroid Scout, NEA Scout.

What's the approximate mass of NEA Scout? Go to planetary.org slash radio contest. You have until the 13th. So that would be Wednesday, January 13, 2021 to get us this particular answer. And if you make it past random.org, you might just win yourself a copy of one of those books we talked with Les Johnson about, Stellaris, People of the Stars, that he edited with Robert Hampson, collection of science fiction and science fact.

Wonderful essays about how humanity may change as we become an interstellar species someday. Good stuff. I have it and I'm enjoying the book. I'm done. All right, everybody, go out there, look up I haven't and I'm enjoying the book. I'm done. All right, everybody go out there, look up the night sky and think about the year 2021. 21 is one more than 20. Thank you. Good night. That's why I love doing this with you because you can count on you to bring us these profound revelations. That's the Chief Scientist of the Planetary Society with us for another year, 2021, as we do What's Up on Planetary Radio.

Planetary Radio is produced by the Planetary Society in Pasadena, California, and is made possible by its starry-eyed members who wish you smooth sailing in this new year. starry-eyed members who wish you smooth sailing in this new year. Mark Hilverde is our associate producer. Josh Doyle composed our theme, which is arranged and performed by Peter Schlosser at Astra.