Interstellar Space Travel with Limitless Space Institute’s Sonny White

What are you talking about when you say “advanced propulsion” that takes us beyond Mars? 

Let me start by identifying the problem. What does it take to go beyond Mars? If all we ever wanted to do is to get humans to Mars, then chemical propulsion can do that, and we really don’t need anything else. We’ll just need to accept the fact that it takes 180 to 220 days to get there. But what if we want to get people to Saturn in the same time frame? Well, you can do some simple calculations to kind of get an order of magnitude of what that looks like in terms of the amount of energy you’ll need. And what you’ll find is that you can’t do it with chemical propulsion. The physics and energy isn’t sufficient. That doesn’t mean there’s no hope, though. In fact, we have three core options that we can explore to solve that problem starting from what we know in physics and engineering and leading to the frontiers of what we know in general. 

So strictly within the confines of known physics and engineering, nuclear electric propulsion is a power and propulsion architecture that has the capability to send human beings to every destination in our solar system. We know how to do nuclear reactors that fission uranium and we know how to do forms of electric propulsion like ion engines. So nuclear electric propulsion opens up a lot of doors for us, but there is kind of a limit to it in terms of what it means to go “beyond.” It doesn’t really allow us to think about interstellar human spaceflight because you’re still talking a couple thousand years to the nearest star system. 

So, could we reduce that couple thousand years to maybe a century? Now we need to move a little bit into the unknown when it comes to engineering. We’re going to change from fissioning material to fusing material—so instead of splitting apart atoms, now we’re joining atoms together. We understand the physics of fusion propulsion even if we don’t necessarily have all the engineering ironed out yet. But fusion propulsion allows us to get to higher cruise velocities and we could potentially do an interstellar mission in a century with this kind of architecture. So it’s encouraging to know that there are things just within our reach we might be able to turn to help really address this penultimate “beyond.” 

But if we want to do interstellar in a fraction of a human lifetime—say 20 years or maybe even less—we really need to look to the frontiers of physics. Not only is this unknown engineering, this is also unknown physics. So if you think of physics as a Venn diagram with two circles on that touch at a tangent point, then there would be quantum mechanics in one circle and general relativity in the other. The point, however, is that these two circles don’t overlap. So we know there’s more physics for us to understand and in the process of exploring what might fill in the gaps between these circles, we can start to think about things like the idea of a space drive. Can we interact with the fabric of spacetime to generate a propulsive force? General relativity establishes a kind of cosmic speed limit. It’s what I call the 11th commandment of physics: thou shalt not exceed the speed of light. But it provides some other loopholes that allow us to do some things that maybe would allow us to get to another star system in, say, two weeks as measured by the clocks on board the spacecraft. You could expand and contract space at any speed. We can see that when we look back at the early universe and the question is, could we ever build something that could utilize that principle in some engineering fashion to be able to do rapid interstellar transit? 

These are the things we’re thinking about when we talk about advanced power and propulsion. 

Education is a big part of Limitless Space Institute’s mission, but are you also researching these kinds of advanced propulsion systems?  

Our mission is to inspire and educate the next generation to travel beyond our solar system and to support the research development of enabling technologies. Research is this innovation circle of life, if you will. So on the research side, we’ve had a program for the last four years called LSI grants and fellowships where we fund universities all across the globe that do research on all the categories of advanced power and propulsion. So we funded Texas A&M to do some work on a portable nuclear reactor. We’ve funded some work on fusion propulsion in a number of different instantiations. We’ve funded some work on solar sails. We funded some work on space drives and traversable wormholes. It’s a portfolio and we’ve given out 18 research awards over the past 4 years with some great successes already. One of our grant winners—Helicity Space—has created a commercial company that they started to further their fusion propulsion concept. They just closed a $5 million seed round with Lockheed Martin as their lead investor. Another grant winner, Professor Richard Norte at Delft University of Technology, won a follow-on grant worth several million Euros to improve his relativistic solar sail manufacturing facility, which allows him to make some of the largest structures with the smallest features. He’s essentially doing stuff at nanoscale, but on big sheets and I believe he’s the only person on the planet that does that currently. We’re a nonprofit and give out small grants, but it’s great to see that it’s having a real impact and translating to things that are really moving the needle for advanced propulsion. 

It’s great to see the investment activity, but given that at least one of the advanced propulsion categories—nuclear fission propulsion—uses known physics, why aren’t we seeing more investment into advanced propulsion systems?

It’s a hard question to answer, but I’ll take a crack at it. In terms of the mission architectures that we’re thinking about today—particularly sending human beings back to the surface of the moon—any type of near term procurement will be focused on funding the development of the “Lego bricks” that help facilitate the different aspects of that architecture. So in terms of nuclear power fission systems, the lunar program does have a solicitation out that’s asking industry to provide design ideas for fission surface power. So in some ways, it is moving forward in ways that fit with the architectures we have, but I would love to see some kind of an architecture where a need was identified to put in a lot of delta-V into a system. Maybe with the military expanding what it’s doing in the space environment that may help provide operational requirements to the point where that’s something they really want to invest in.

Nuclear electric propulsion is the thing that’s hard for me to watch as a spectator because it’s a killer app and fully extensible. So when I look at how we could focus the limited government money we have available on a portfolio of advanced power and propulsion systems, a lot of things that we could invest in might be somewhat useful, but they’re not moving the needle very much. Nuclear electric propulsion has a capability that is known physics, known engineering, and extremely enabling. Not only does it help us with the moon and Mars, it also gets humans to Saturn in 200 days. If I’m wearing my NASA cap and thinking like a mission planner for a human exploration architecture, when I’m digging around in my bag of Lego bricks I would love to be able to pull out a nuclear electric propulsion as something I could plug into my architecture because it sure is a killer application. 

There are such a wide variety of advanced power and propulsion systems LSI could support. Do you mostly focus on low TRL projects for grants or is it more about enabling systems that could be tested on missions in the near future?

It’s a balance. We are a philanthropic organization and so we’re trying to do things for the greater good. We do try to be as clever and as savvy as we can be with the pennies that we put out there to make sure we have the most bang for the buck across a multitude of perspectives. So let’s look at Helicity Space as an example. When you talk about fusion propulsion, folks that are familiar with it might think the fusion propulsion system is providing its own power for this propulsive process. But in the process of looking at proposals that came in from some of our calls, we came across this team that included Helicity Space and some universities and national labs that said they can create a fusion propulsion system that has a physics coefficient of performance of 5. So that means for every electric watt you put in, you get five watts of thermal out. With something like that you cannot close a thermodynamic cycle where it can self-power itself. It still has to be plugged in. Where’s the value in that, you might ask? Well, you’re getting this 5 to 1 benefit of every electric watt that you put in. So the newtons per kilowatt for the given specific impulse or “efficiency” of the rocket means you get a lot more energy out of every kilogram of propellant. As peculiar as it sounds, you might have a situation where you’ve got a fusion rocket plugged into solar panels moving stuff around cis-lunar space so it is effectively solar-electric propulsion, but it’s got a fusion rocket on it. The benefit is now you’ve got way more newtons per kilowatt so you have the ability to move more quickly with less propellant usage. So that was an interesting situation where somebody found a clever way to take something people might always associate with the future—fission propulsion—and find a way to create a benefit today.