Dreaming Up the Future of Interstellar Travel

10:50 minutes

Two years ago, the Voyager 1 space probe finally broke through to interstellar space, 36 years after its launch. Could solar sails, antimatter propulsion, and air-breathing rockets enable more opportunities to travel to distant galaxies? Les Johnson dreams up answers to that question as a NASA technologist at the Marshall Space Flight Center and, in his spare time, as a sci-fi writer.

Segment Guests

Les Johnson

Les Johnson is co-author of Rescue Mode (Baen, 2014) and Back to the Moon (Baen, 2011) and deputy manager of the Advanced Concepts Office at the NASA Marshall Space Flight Center in Huntsville, Alabama.

Segment Transcript

IRA FLATOW: This is Science Friday. I’m Ira Flatow here at the US Space and Rocket Center in Huntsville, Alabama. We won’t be taking your calls today but if you’d like to join our conversation this week you can tweet us at @scifri or leave us a comment at sciencefriday.com.

In the movie Interstellar astronaut Cooper, played by Matthew McConaughey blasts into interstellar space through a temporary wormhole.

MATTHEW MCCONAUGHEY: Everybody ready to say goodbye to our solar system? To our galaxy? Here we go. Controls won’t work here. We’re passing through the bulk. Space beyond our three dimensions

IRA FLATOW: Exciting stuff, but until we can travel through wormholes we’ll have to rely on the spacecraft we have. And in fact, we have gone interstellar. The Voyager spacecraft, launched in the 1970s, did cross over into the space between the stars and that milestone only took, well, 36 years. How could we shave a few years off of that trip, and how might we visit Mars and beyond our galaxy in the future?

My next guest dreams up answers to those questions. He’s a NASA technologist at the Marshall Space Flight Center here in Huntsville and in his spare time, he is a sci-fi writer and has co-authored the novels Rescue Mode and Back to the Moon. Les Johnson, welcome to the program.

LES JOHNSON: Thank you.

IRA FLATOW: I have to ask you, what did you think of the film?

LES JOHNSON: I thought was an awesome film. We saw it the night before it actually opened and had a panel discussion after the movie to talk about what was real and how we might actually go to the stars.

IRA FLATOW: What could we do, what might be too science fiction?

LES JOHNSON: Well, I don’t want to argue with Kip Thorne. I mean he’s way, way up there in terms of the theory, but what we looked at– and what I’ve looked at– are things that are more known physics, things that seem to be possible. Nature hasn’t said you can’t do it, nature’s just said it’s going to be really, really hard to do.

IRA FLATOW: Like what?

LES JOHNSON: I mean, there are all kinds of ways you can do that. One of the best ways would be something using anti-matter.

Here in the world today, we have matter and then there are these particles of matter which are like what we have. Protons that, instead of a positive charge, have a negative charge. Electrons with positive charges. And when they come in contact with regular matter they, basically, annihilate– become energy. And if you could tap that energy, you could drive a starship.

Now that’s kind of far out for me. I’m going to bring it to not quite as far out. But my favorite is something called a solar sail, or a laser sail, which I think if we send a probe to another star first it’ll be done using a solar sail.

IRA FLATOW: You mean just like a ship sail?

LES JOHNSON: Well, I mean, looks like a ship’s sail, but instead of the wind it uses sunlight. Here in the audience or wherever you are, there’s light reflecting from you and you can’t feel it, but as the light reflects from you, it’s pushing on you. Light doesn’t have rest mass, but it has momentum. Just think of all these little ping pong balls bouncing off of you.

And if you’re out in space away from the Earth’s gravity and out of the air as that light reflects from the sail, it’s going to give it a small push.

IRA FLATOW: It’s like that radiometer?

LES JOHNSON: Well, that’s not actually how a radiometer works. That’s a different process. A lot of people bring that up as an example. When you burrow into the physics, it’s a slightly different physics there.

IRA FLATOW: But there’s enough pressure from the sun?

LES JOHNSON: Oh, it’s very small. It’s on the order of maybe an ounce and a half per football field of area. So it’s a very, very small push. But the key is that the sun is always on, right? So it’s a constant low thrust.

And over time you can build up a pretty high velocity. And if you augment that by flying really close to the sun where you have a lot more light shining on your sail.

IRA FLATOW: And so where we go? Where would be a practical mission to use your sail?

LES JOHNSON: You’ve got to define practical when you’re talking to me.

IRA FLATOW: I know, you’re a science fiction writer, so I’ve got to keep that in mind.

LES JOHNSON: OK. In the near term, I think we can use solar sails to send robotic probes pretty much all over the solar system.


LES JOHNSON: Yeah, the Japanese are flying one now. It’s called Icarus. It’s flying in the inner solar system around Venus. You have to wonder if they know their Greek mythology to call it Icarus. But it was 100% successful mission.

The Planetary Society is going to be flying a sail this May, It’s going to be in Earth orbit. And NASA’s actually been investing in solar sails and we have plans to fly a few in the next few years.

IRA FLATOW: And how big a ship? Would it take football field size sails to power these things?

LES JOHNSON: Well, it depends on where you want to go.

IRA FLATOW: Can you give me an example of where you want to go?

LES JOHNSON: In the near term, I think we’re talking sails that might be a few tens of meters to hundreds of meters on a side. If you want to go to the stars, really go to the stars, you got to think big. Think a sail thinner than a human hair, for those that aren’t as follically challenged as I am, and the size of the state of Texas.

IRA FLATOW: State of Texas?

LES JOHNSON: Yeah, think about a sail that large. Now, we have no idea how to build that. I will not claim I know how to build a sail that large. But I will tell you that mother nature has not said it’s impossible.

You can look at the properties of light and what we’re learning about materials and advanced carbon fiber materials, and you can see that perhaps someday we might be able to spin these things like a spider web in space. Get them to fly very, very close to the sun, and maybe also push them with extra kick by big lasers. And get them going fast enough that you could have a realistic trip time to the stars.

IRA FLATOW: But once you get out of the solar system, you’re going to lose the sun, basically.

LES JOHNSON: That’s right, you sure do.

IRA FLATOW: What happens to your sail?

LES JOHNSON: You get most of your kick in close to the sun. You have the advantage of this thing called the inverse square law, which means if you cut the distance to the sun in half you don’t get twice as much thrust, you get four times as much thrust.

So if you deploy this big sail really close to the sun, get a really big kick, and on its way out of the solar system you take a big laser– or several of them– that are getting energy from the sun and focus that light on the sail, you can keep accelerating as it’s leaving. So it goes really fast.

IRA FLATOW: Wow. I’m Ira Flatow and this is Science Friday from PRI, Public Radio International.

So as a science fiction writer, and as other science fiction writers have written, do you think that your science side is informed by science fiction, to think big and think of ideas like this, as people use science fiction?

LES JOHNSON: I can speak personally. I decided to study physics and go to work to NASA because of Robert Heinlein, Isaac Asimov, and Arthur C. Clarke, some of the great science fiction writers. I was in a workshop among my NASA colleagues not too long ago, and we were all asked to name the number one influence to our careers, and two words popped out. And they were Star and Trek. So, absolutely.

So I was inspired by it, and that’s what motivated me. And now I’m actually trying to make that happen in my science fiction writing. I try to go back and I kind of view it as full circle. I’m now trying to get that next generation inspired.

IRA FLATOW: Are we going to get warp speed someday?

LES JOHNSON: I’m very skeptical of this whole warp drive thing.

IRA FLATOW: Tell us why.

LES JOHNSON: To me, I don’t mind talking about things that are outlandishly difficult to engineer, but are within the realm of what we know about how nature seems to work today. And warp drive’s kind of outside of that. And maybe someday– we don’t know everything there is to know about how nature works. I hope you prove me wrong, you next generation of physicists and come up with that, but right now I’m not counting on that.

IRA FLATOW: You’ll stick with the flux capacitor.

LES JOHNSON: I’ll take that.

IRA FLATOW: You’ll take that one.

LES JOHNSON: And Mr. Fusion, to go with it. That would be really good.

IRA FLATOW: It’s always 30 years away, ever notice that?


IRA FLATOW: Fusion is always 30 years away, no matter what happens.

One of your books Back to the Moon involves a secret mission to the moon and it uses something called air breathing rockets. I thought that was the opposite definition of a rocket. I thought a rocket doesn’t have to breathe air. How does that work?

LES JOHNSON: There are different ways you can think about getting to space, and right now we primarily use rockets. But the dream of a certain aspect of the community is that you can actually offload some of the propellant, which is heavy, and maybe use oxygen from the air. And, essentially, take an engine that lets you use your environment here in the atmosphere to accelerate and get to space.

And we don’t have anything that can go multiple times the speed of sound and get you to orbit at those velocities today, but in the book we postulated that somebody finds a way to actually make it work. That’s the fiction part of the science fiction, right? And the story goes from there.

So it makes it reusable and the idea is that this company found a way to do this and they truly have a commercial airline-like process for taking people into space.

IRA FLATOW: Do you think that it’s going to be private? People like Elon Musk, other people like that, who are going to get us to these planets?

LES JOHNSON: Oh, I’m very optimistic that somebody’s going to be able to do that. I think in the near term it’ll be close to Earth. It’ll be the Alan Shepard kind of flights, up and back. I think we’ll eventually see people taking tourist flights to the moon, and it’s my hope while commercial space is doing those things that NASA and the other space agencies are going to the next step and sending people further out into the solar system.

IRA FLATOW: Well, Mars is the next logical step. Do you think we will see it, you and I, in our lifetime?

LES JOHNSON: I have hoped my whole life to see it. But before I came up here today I was talking to someone about a book that was given to me by my first supervisor at NASA before he retired, and it’s a collection of papers from a symposium– here in Huntsville, 1964– looking about how we go to Mars and the challenges for that. And the introduction that von Braun wrote for that volume could be read today.

And the good thing is we have taken a lot of those challenges that they didn’t know how to do and we can put a check mark by that today. So we know how to do that.

IRA FLATOW: We could put a check mark by it, but can we put a checkbook by it?

LES JOHNSON: That’s beyond me to answer. I’m hoping that things like by writing the book Rescue Mode and other things, we can keep people excited in the what if. And I believe we can.

I think part of it is showing relevance. I think it’ll become inevitable that we take that next step to go to the planets and from there, to the stars.

IRA FLATOW: I hope that you are right.

Thank you very much, Les, for taking the time to be with us today. Les Johnson, a NASA technologist at the Marshall Space Flight Center. He is also co-author of Rescue Mode and Back to the Moon. Thanks again.

LES JOHNSON: Thank you

IRA FLATOW: We have to take a quick break. Playing us to the break, Huntsville’s own Microwave Dave and Jim Cavender.

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