Planetary Radio • Mar 18, 2020

Building Our Future on Mars

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On This Episode

Peter carrato

Peter Carrato

Peter Carrato, Civil Engineer, Bechtel Company Emeritus Fellow

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Bill Nye

Chief Executive Officer for The Planetary Society

Bruce betts portrait hq library

Bruce Betts

Chief Scientist / LightSail Program Manager for The Planetary Society

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Mat Kaplan

Senior Communications Adviser and former Host of Planetary Radio for The Planetary Society

How will we build the structures, roads and landing pads humans will someday need on Mars? Civil engineer Peter Carrato has been building grand structures on Earth for decades. He says the skills we’ve learned over thousands of years are well-suited for the much more challenging Martian environment. Planetary Society CEO Bill Nye the Science Guy returns with a message of care, hope and vision for our troubled times. And a bacon asteroid is just one of the absurdities Bruce Betts and Mat Kaplan discover on the way to a new What’s Up space trivia contest.

Artist’s rendering of the Mars Ice Home concept
Artist’s rendering of the Mars Ice Home concept The “Mars Ice Home” is a large inflatable torus, a shape similar to an inner tube, that is surrounded by a shell of water ice.Image: NASA / Clouds AO / SEArch
Team SEArch+/Apis Cor 3D-printed habitat concept
Team SEArch+/Apis Cor 3D-printed habitat concept Team SEArch+/Apis Cor won first place in the Phase 3: Level 4 software modeling stage of NASA’s 3D-Printed Habitat Challenge. The unique shape of their habitat allows for continuous reinforcement of the structure. Light enters through trough-shaped ports on the sides and top.Image: Team SEArch+/Apis Cor
Trulli in Alberobello, Italy
Trulli in Alberobello, Italy Row of stacked stone trullo houses in Alberobello, Bari Province, Italy.Image: Berthold Werner

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Trivia Contest

This week's prizes:

A Planetary Society r-r-r-rubber asteroid and a copy of Spacefarers by Christopher Wanjek. We were kidding about the bacon grease option.

This week's question:

The Chandrasekhar limit is the maximum mass of a stable white dwarf star. In solar masses, what is the approximate value of the Chandrasekhar limit?

To submit your answer:

Complete the contest entry form at or write to us at [email protected] no later than Wednesday, March 25th at 8am Pacific Time. Be sure to include your name and mailing address.

Last week's question:

What is the second largest planetary moon in our solar system that orbits retrograde? (Neptune’s Triton is by far the largest.)


The winner will be revealed next week.

Question from the March 4 space trivia contest:

Where in the solar system is there a feature named Bilbo?


Bilbo Colles is a feature on Saturn’s moon Triton. And yes, there’s also an asteroid named Bilbo.


Mat Kaplan: [00:00:00] Building our future on Mars, this week on Planetary Radio.

Welcome. I'm Mat Kaplan of The Planetary Society with more of the human adventure across our solar system and beyond. I hope you're all staying safe and healthy.

You want to spend a few months or a lifetime on the red planet? You're going to need a home, garage, a place for rockets to land and take off, maybe a few roads. Sounds to me like you could use a civil engineer, and I've got just the guy for you. Peter Corrato will tell us how we'll build that future. Bill Nye is here too. He'll join me right after we get a few space headlines from the downlink. A Bacon asteroid and other absurdities are also ahead when we're joined by Bruce Betts for what's up.

You probably know by now that the downlink has entered a new era. Planetary Society editorial director, Jason Davis has been joined by other [00:01:00] colleagues to create this weekly collection of news, fascinating facts and updates about the Planetary Society itself.

You'll always find the latest edition at which is also where you'll find a link to get the free newsletter version delivered to your inbox each week. Here are those headlines I promised beginning with one less mission heading to Mars this summer.

Europe and Russia's ExoMars won't be ready for launch in time for the window that opens in July. It will be two years before earth and the red planet are again in the right spots. NASA's 2020 Mars Rover now known as Perseverance, a Chinese mission and one from the United Arab Emirates are all on track. NASA's Orion Spaceship is back at the Kennedy Space Center in Florida. The capsule shaped vehicle has completed all of its testing. Now it will wait for the first space launch system rocket to send it toward lunar [00:02:00] orbit. That is now not expected till 2021.

Speaking of the moon, China's Yutu too may soon set out on a pretty amazing journey. Another one that is. Officials say that little Rover could attempt a nearly two kilometer drive to some far side rocks that scientists are very curious about.

One more, We poor earthlings are facing so many challenges right now. I decided to invite Planetary Society CEO Bill Nye back for a brief conversation about things that matter, things on the personal level and things on the grandest scale that exists.

Bill, welcome back to the show. It's, uh, an interesting time and I will note that we're, we are speaking to each other in a virtual sense where we're much more than six feet apart. Even with this terrible pandemic and how we are all trying to adapt to it, uh, on our minds, our minds are capable of, uh, still [00:03:00] looking up at the sky and wondering about the universe.

Bill Nye: Well, we want to know, uh, where we all came from. What are we doing on this planet. And who knows Mat, when you understand the nature of mass and energy and the cosmos, maybe you will understand how living things work. And I'll give you an example that wasn't my idea but is amazing. Is guys trying to understand dark matter, the distribution of the matter in the universe that, that we cannot see yet somehow produces this gravity that is pulling everything apart, that somehow follows the same pattern as slime molds. Everybody loves a slime mold Mat.

Mat Kaplan: [Laughs].

Bill Nye: It's what in the world is this? I remember this from many years ago. I, you know, I did not become a professional life scientist. It's a, a single celled organism with many, many, many thousands, tens of thousands, [00:04:00] hundreds of thousands of nuclei. So it is a Eukaryote, Eukaryote is a cell with a nucleus. It means, it's from the Greek word for having nuts, having kernels-

Mat Kaplan: Mm-hmm [affirmative].

Bill Nye: Uh, not to get us in trouble there. Having kernels.

Mat Kaplan: [Laughs] I get ya.

Bill Nye: Yeah. And so, uh, the, the slime mold finds its way, slime molds find their way around the forest floor eating bacteria and fungi by moving the way amoebas move. Then amoeboid leeway their way around. Apparently the way dark matter seems to interact with itself follows the same patterns. So these guys, uh, slime mold, you know, lives in a gravity field. All the ones that we know about-

Mat Kaplan: Mm-hmm [affirmative][laughs].

Bill Nye: But they had to somehow make it a three dimensional model, and they did. It's crazy.

Mat Kaplan: And it works. It works.

Bill Nye: Yeah.

Mat Kaplan: It, it actually, you can match it up to the reality that they've seen with tools like the Hubble Space Telescope, [00:05:00] and sure enough these [crosstalk 00:05:01]-

Bill Nye: [crosstalk 00:05:03] x-ray, yeah, [crosstalk 00:05:04]-

Mat Kaplan: Yeah.

Bill Nye: And so, everybody ... I just reflect on this all the time. When my grandparents were my age, they had become aware of the practical use of relativity. When they were little kids that no one had discovered relativity. No one had had, any idea that it was important. Where the speed of time, as I like to describe it, changes with gravity. Or, or your speed relative to a gravitational object or something in the space time that has gravity. Whoa dude. Anyway, they will live to see nuclear weapons developed and nuclear power, and just understanding of of the quantum, of quantum electrodynamics and so on. They, they live for all that.

So I just reflect all the time about dark energy and dark matter Mat. Will there be a time 20 years, 30 years hence, where [00:06:00] there are practical applicant- the dark matter is understood so well that there'll be practical applications? There'll be the equivalent of a laser or a ultrasound machine, or magnetic resonance for scanning your brain or what have you. Will something like that emerge from this kind of research, mixing astronomy and what people like to call astrophysics, the physics of stars, with the chemistry of life?

Mat Kaplan: Mm-hmm [affirmative].

Bill Nye: It's amazing. It's amazing. And as the kids say, "How cool is that?" The kids say that, man/

Mat Kaplan: [laughs]. I listen to them now and then saying that/ It's pretty darn cool. Thank you Bill. I, I think I'll hold out for warp drive coming out of, uh, um, the next discovery from slime molds or something else that we share this planet with.

Bill Nye: But really it's this crazy pattern where it seems to have agency, it seems to have a plan.

Mat Kaplan: Yeah.

Bill Nye: It moves, it moves to where the food is. And then when it's [00:07:00] time to reproduce, it produces spores. And the DNA of slime mold is a fraction, a 10000th of the DNA that you and I have. I mean, it's a, it's something like 187 base pairs instead of three billion. [laughs] like what?

Mat Kaplan: [Laughs].

Bill Nye: Or maybe it's if you're talking about killer basis, 30,000, that's just amazing to me. That's amazing. It shows you how little you need to get by. What do we put in right here Mat? Old boss joke. A joke about my old boss right there.

Mat Kaplan: [Laughs].

Bill Nye: How the guy functioned with so little, it's amazing.

Mat Kaplan: Life finds a way. Bill, I'm, I'm giving you a, a virtual, uh, elbow bump or maybe a live long and prosper.

Bill Nye: Oh, let's do both. Yeah. Live long and prosper. Yeah, there you go. I can do it with either hand. You know, our beloved, uh, Robert Picardo on the board of directors of The Planetary Society who played the doctor on star Trek Voyager is right-handed. I can assure you he's right-handed. He's a [00:08:00] good friend of the Society, but he can only do the Vulcan, uh, live long and prosper greeting with his left hand.

Mat Kaplan: Oh, that's [crosstalk 00:08:08]-

Bill Nye: I think that's, that's proof of the paranormal right there.

Mat Kaplan: Well, that or that, he needs to be reprogrammed. Uh-

Bill Nye: It's the freaking sub routines. It's always trouble. Hey man, e- everybody, let's keep our chins up. Let's, let's be together. We're all self isolating, but be sure to check on your neighbors, cause if we've gotten nothing else out of astrobiology, Mat, the study of life here on earth and, and imagining what life must need to exist elsewhere, we have learned that we have a common ancestor. All the living things on our slime molds, sea jellies, my old boss, everybody has a common ancestor. And so check on your neighbors. Make sure they're doing okay and, and ask them to check on you. We're going to get through this.

Mat Kaplan: Thank you Bill.

Bill Nye: Thank you Mat.

Mat Kaplan: That's the CEO [00:09:00] of The Planetary Society, which is, uh, taking this stuff seriously. But uh, we're still looking, looking upward.

There's a NASA webcast series, I love to join when I can. I have no expertise to contribute to them, but I'm fascinated by the content of the human landing sites study or HLS2 briefings. Each takes up a different aspect of what will be one of humanity's greatest challenges, putting men and women safely on the surface of Mars, supporting their work there for hundreds of days and returning them to earth.

The most recent of these discussions was titled, paving the road to Mars civil engineering at the human landing site. As always, it welcomed an outstanding selection of the people who will enable us someday to achieve these goals. Peter Corrato was one of them. Pete spent several decades at Bechtel Corporation, rising to corporate manager of building information modeling and virtual design and [00:10:00] construction. He is now a Bechtel Ameritas fellow, and a fellow in life member of the American Society of Civil Engineers. Also, a fellow of the Institution of Civil Engineers in the UK.

As you're about to hear in this unique Planetary Radio conversation, Pete has given a lot of thought to how we will build that future on Mars, the moon, and elsewhere around the solar system.

Pete, thanks very much for joining us on Planetary Radio. I got to say I thoroughly enjoyed your contribution to that, uh, NASA, NASA sponsored discussion just a couple of weeks ago. It's a good thing that you were there. I mean, all of the presenters in that webcast were terrific, but I think you were the only one who has actually built a structure on this planet to say nothing of Mars. So let me start there. How can our knowledge of construction on earth prepare us for building on Mars or perhaps the moon?

Pete Corrato: Well, Mat, that's a great question, [00:11:00] and the answer any engineer will give you is it's absolutely essential preparation. There's a, uh, story told about bridge builders, early bridge builders walking through the woods and they see a tree that's fallen down across a Creek. They walk across the fallen down tree, then they find a bigger river so they go and they try and knock a tree down across it and that works. And they walk across and then they find a much bigger river and they try and knock a bigger tree down across it and they get out on it and that tree breaks.

So they then have to go and invent something called a trust. So the moral here is engineers work based on what they've seen, their experience, and then they push the envelope of that experience until it doesn't work anymore. And that's how they invent new engineering structures.

So I personally believe that when we go to build structures on the surfaces of the moon or [00:12:00] Mars or any other planetary body, we will be bringing our engineering experience from the earth with us, whether we do it consciously or not.

Mat Kaplan: Do we know enough now to go to Mars and build some of the structures that were being talked about, uh, in, in that webcast?

Pete Corrato: Absolutely, we can. Uh, actually I believe much more readily than building on the moon because the, uh, geology of Mars is more similar to that of the earth specifically when it comes to sedimentary rocks.

Mat Kaplan: Mm-hmm [affirmative].

Pete Corrato: So if you go and look at historical structures, let's say the pyramids in Egypt, these are built out of limestone, which is, is a sedimentary type of rock. And you can find sedimentary rock structures that are thousands of years old in many places around the earth. That type of rock is prevalent on Mars, and literally picking them up and [00:13:00] stacking rocks together, you can build serviceable structures, and you have to define what serviceable is, uh, that will last for thousands of years.

Serviceable might mean, let's say I want to protect a robot from a solar flare. Well, the robot doesn't need a pressure tight, uh, structure to take shelter in, so you could create a stacked stone structure that would absolutely provide shelter for a robot from certain events that it needs to be protected from.

Mat Kaplan: One of my favorite quotes, and it was, uh, something you said during that webcast was that when you see, uh, these wonderful images coming back from Mars that show us layered sedimentary rock, that it had you drooling [laughs].

Pete Corrato: Well, that's because I, I've been spending a lot of time looking at the moon. The moon is, does not have me drooling as a place to [00:14:00] want to go and build on using the local resources, without a lot of, let's say, modification to what you pick up.

You can see and, and these images have been out for decades, different images of villages on the moon, and some even look like you just took Manhattan and moved it to the moon and maybe-

Mat Kaplan: [Laughs].

Pete Corrato: ... Thousands of years from now we'll do that. But in the near term, if, if you're not bringing your, your habitat with you to inflate or somehow deploy to take lunar materials and turn them into a habitat will require a large amount of energy to melt them or modify them in some fashion so that they turn into a structure. So when you go to Mars and you see these beautiful outcrops of sedimentary rock that you know you don't even have to remove regular to expose, they're just exposed [00:15:00] and you just basically walk your robot up to it with some very simple tools like a pick, start knocking out blocks of material that you can start stacking together and producing real structures.

Mat Kaplan: You mentioned the pyramids. You showed us a picture of another structure which I had never seen or heard of, and it was something that looked like apparently it's about 3, 000 years old in Ireland that was constructed just the way you're talking about.

Pete Corrato: That's correct. That's just again, another example of people stacking stones to produce structures, and you can find examples like that, like it's South America, look at what the Aztecs did, or the Incas. And I'm sure you can find similar structures in Asia as well.

To me, the, the pyramids are just a very unique analog or something you could compare to the only real building that's been [00:16:00] done off of this world, and that's the International Space Station.

Mat Kaplan: Mm-hmm [affirmative].

Pete Corrato: So as background, no one has built anything on the moon. It's the only place we've gone ... Or Mars, having so much as stack one rock on top of another. So-

Mat Kaplan: [crosstalk 00:16:18].

Pete Corrato: [Laughs]. So th- the space station took almost as long to build as the pyramids did as the great pyramid did. The great pyramid took about five years longer. The space station cost $150 billion to build. It has a service life of about 20 years. The great pyramid was built entirely out of institute resources, and current design life is in the order of 5,000 years. So, kind of the messages, you don't want to build the spaceship on the surface of the moon or Mars. You want to and have to use the resources you find there.

Mat Kaplan: And this of [00:17:00] course, is a huge topic, institute resource utilization. You've already talked about this with the, the presence of these sedimentary rock layers on Mars. Other people talk about them in terms of creating the air that we'll need to breathe up there, the water we'll need to drink and the rocket fuel we'll need to, to leave Mars, uh, when we decide to do that. Obviously ISRU is something that you also think is going to be essential.

Pete Corrato: That's correct. As you pointed out, there's different ways to look at the local resources. I look at them from a building point of view. The other way of course, to look at, as I mentioned, to modify those to produce breathable gases or water or fuel. You can even of course, as time progresses, uh, get into the production of metals, extracting rare earth elements, all kinds of things like that. But I like to look at them from what can I make out [00:18:00] of this stuff. I'm at the very low tech end of this.

Um, so we talked about stacking stones to build a habitat. If you want to see something to really get you interested in what these structures could look like, there's a structural form on the Adriatic coast of Italy called a Truli T-R-U-L-I, that's the plural of Trullo. And it is stacked stones, the roots are very old, but the actual application's recent because the residents of this one particular province are not taxed on Trullos because the government does not consider them permanent structures. So they're very popular housing form. And some are quite beautiful inside and you can go vacation in one if you'd like to.

Mat Kaplan: Mm-hmm [affirmative].

Pete Corrato: The other place you can use these resources are in, let's call it horizontal structures. Easiest way to think of that [00:19:00] as a road. So building a road is a very well worn, uh, technique within the, uh, the toolbox of the civil engineer. And the best roads, in my opinion, of course have the roots in the Roman roads, many of which are thousands of years old and still quite serviceable today. The key to a Roman road is the depths at which you prepare what's called the sub base for the road.

So a Roman road might have, you might have to dig down four or five feet and then start filling that up with engineered material. Layers of rock layers of gravel. And then when you get up to the surface, you have what's called a wearing in course, which is the part you want to drive on, and it has certain attributes as far as friction and smoothness and things like that. You've probably written the number road, which was not prepared with that deepest sub base. And it's a, it's ripely and it's got rocks in [00:20:00] it and, uh, it just shows that even on earth, we don't necessarily prepare the roads the way we would have done in ancient times.

So on the moon or Mars, there's going to be a need for roads. Those two heavenly bodies are dramatically different when it comes to roads. The moon has lots of dust on it, various thicknesses of dust layers. And the only driving that's occurred on the moon with the Rover, kicked up huge amounts of dust. And it's recognized that this is obviously not what we're going to do in a permanent settlement. So you would have to prepare a wearing surface you could drive on, which would not produce as much dust.

So how would you go about doing that? Now I'm in the land of pure conjecture here. So to create a road on the moon, the steps to create in a road anywhere, start out with a, a route [00:21:00] survey, where you say, I want to go from here to there, and you look at various ways you could do that. By that I mean, you know, is there a mountain in my way and do I want to put a tunnel through the mountain, or do I want to go around the side of the mountain? So there's various ways you can prepare your route.

So on the moon, you probably want to go around some of the deeper craters and you might want to build a causeway or fill in part of a shallow crater to go over that crater.

So the first thing you'd do is you'd develop your route. Then you have to basically smooth out that route. So this is cutting material, removing material from the surface of the planet, and filling where you would take some of that, that you took away from a mound and say you put it into a crater. A good civil engineer will do what's called balance the cut and fill. So you want a route where whatever you strip away, you go to another place along the [00:22:00] route and you fill in with it. And that saves you energy, it saves you having to get rid of material. It also assumes that whatever material you take away is material that you can use to fill, and that's not always the case.

So once you've, you've smoothed out your, your way, now you start to prepare the road bed. Okay, so I now have my path and I have it smoothed out. So now I want to start covering it with layers of gravel, and this would be the simplest way to do it on the moon. So you need to collect in-situ material, run it through a SIM, like the thing you took out on the beach where you put sand in and shook it out. But you have sieves with different hole sizes of them so that you get a range of sizes of material. And you would want to start your first layer to be a little bigger than a pebble, say about an inch and a half in diameter average.

Mat Kaplan: Mm-hmm [affirmative].

Pete Corrato: So you laid out a layer of [00:23:00] that, that would be four to five inches thick. And then you take a, a heavy smooth roller and roll over the top of that. Then you would put down another layer and now it'd be slightly smaller, say three quarters of an inch in diameter. And again, three or four inches thick and you roll that out and then maybe on the top you go to something, say by the eighth of an inch in diameter. And now you have a pretty robust wearing surface. You could smooth that surface, you could on the earth, we would put asphalt down now or concrete. People talk about centering on the moon where you basically go and melt the rocks together. I'm not real excited about, it's a highly energy intensive operation and I'm not sure the benefit to the vehicles for having that smooth surface.

I think a nice well graded gravel surface would serve the purposes for the early residents of the [00:24:00] moon, and a similar road structure could be used on Mars.

Mat Kaplan: I'll be back with civil engineer Pete Corrato in seconds.

Deborah Fisher: Hi. I'm your astronomer Deborah Fisher. I've spent the last 20 years of my professional life searching for other worlds. Now I've taken on the 100 earth's project. We want to discover 100 earth sized exoplanets circling nearby stars. It won't be easy. With your help, The Planetary Society will fund a key component of an exquisitely precise spectrometer. You can learn more and join the search at Thanks.

Mat Kaplan: Welcome back to Planetary Radio. I'm Mat Kaplan with more from civil engineering expert Pete Corrato.

Short of building a road, I mean there was discussion in this webcast of the possibility that because of, um, uh, the rockets in the descent vehicle taking humans down to the Martian surface might kick up so much [00:25:00] dangerous debris that we might have to pre construct a l- a landing site, a pad. Would this be the same kind of structure you've just described for a road or, sounds like you wouldn't want gravel on top.

Pete Corrato: [laughs] no, you wouldn't. And the pad I believe will be one of the most valuable structures either on the moon or Mars and exactly for the reason you described. That descent, the rocket engines on descent are bringing obviously a lot of energy in a very concentrated space, and they will get airborne lots of material that's impacted by that engine.

So the engine will do two things. It will reject material to the sides. If you have multiple engines, it will actually start churning up the material in the space between the engines-

Mat Kaplan: Mm-hmm [affirmative].

Pete Corrato: Uh, potentially bringing up damaging materials into the engines [00:26:00] themselves. And it will scour out the area it's landing on. So if it's not robust competent material, you're basically digging a hole to land it.

Mat Kaplan: And some of your colleagues actually showed us computer models done of exactly this with multiple engines. It was pretty scary stuff.

Pete Corrato: There's a lot of study on this done at the University of Central Florida. Some of the images that come out of the, the researchers down there are quite exciting and should be potentially scary. They've actually gone through all the video of say the Apollo landers, and when you see their presentations, they will run the slow-mo videos and go, "Oh look, here is a rock leaving at 75 miles an hour [laughs] as it flies out of there."

So to get a, a prepared landing surface, especially if you're going back to the same place over and [00:27:00] over again, this really hasn't happened yet. I mean, all of our, our trips are exploratory. Where are we going, "Okay, we've been there, let's go somewhere else." So there's no opportunity to build a landing pad.

If you're going to say, "Well no, I'm going to mine ice on a glacier on Mars and I'm going to keep coming back over and over again." Now having a landing pad makes a lot of sense. So will it be different than the road? Absolutely. The road is a very low energy put on the road, and I would think off-world you're talking if a vehicle can go 30 miles an hour, that's probably a really fast vehicle on Mars. So you're not ejecting a lot of material when you're driving at 30 miles an hour even on a gravel road.

The other thing is it's not bringing any heat. Heat is a big challenge here, but we know how to do this on, on the earth. There's a couple of ways. I've had the opportunity to work on our [00:28:00] launch pads. Most are very sophisticated because the launch energy is much higher than the landing energy. A large steel chute and the chute is actually made of tubes with very fine holes on the top of the tube where the flame would impact it.

So this chute, before they launch a rocket, they start pressurizing it with water-

Mat Kaplan: Mm-hmm [affirmative].

Pete Corrato: ... And you get this spray of water coming out of a chute. When the rocket flame hits the spray of water, the water turns into steam and the steam actually protects the metal from the flame impacting it. So the flame follows the chute and goes out to the side.

Mat Kaplan: Yeah, we've, we've seen this of course, uh, of rockets through many decades. Uh, Saturn five and the space shuttle-

Pete Corrato: Yep.

Mat Kaplan: And you can see those flames shooting out the, uh, of these, uh, off to the sides of the pad.

Pete Corrato: That's right. [00:29:00] So a water enabled liftoff is probably many, many decades in the future. So for right now, what you need is you need a material that is temperature resistant. There are temperature resistant materials, uh, there's a concrete, uh, it goes by the name of refractory concrete or refractory materials. So these are ceramic or, uh, brick like materials. Uh, they're used all the time in steel mills for example. When you see that big ladle of steel, you might say, "Well that looks like a steel ladle full of molten steel. How does that work?" Well that's cause that ladle is lined with refractory materials.

Mat Kaplan: Huh.

Pete Corrato: The steel is there for the strength, the refractory material, which is in that case brick like, is there just to resist the heat. The landing and launch pads will need to be built of refractory materials Which you can find they're actually [00:30:00] quite, quite available on the moon and I'm sure you can find them on Mars. It would take a little bit more effort than just going finding some sedimentary rock and stacking together. This so be a little bit more of a challenge from the material science point of view.

Mat Kaplan: Hmm. You made another great point. Uh, you've made several during your presentation, you're a portion of that, uh, NASA webcast and it was that, uh, before you do any of this construction, you've touched on this already. You got to know where you're building and, and you gave an example and it was actually an image looking back, uh, from one of the Mars Rovers at, uh, soil that it had crossed. And it made your point that soil can change from meter to meter, obviously on Mars as it does here on earth. And that you better know a lot about the site that you plan to build on.

Pete Corrato: That's the key to success for any large construction project, uh, whether it's on this [00:31:00] world or some other world. Personally been associated with too many projects where not enough soil bearings were taken, and somewhat built something and now it's not performing the way it was supposed to be built. So it's, it's a tried and true lesson. The reason you have those terrestrial experiences like that, it's because soil bearings even on earth are expensive to perform. Soil bearings off of this earth are going to be much more expensive. So there'll be a natural desire by, let's call it project management, to limit or eliminate the need for any soil bearings. As we say in the business. I've seen that movie too many times. I want lots of soil bearings

Mat Kaplan: You gave a great example, a very famous example, uh, it would take us back to Italy. You know the one I'm talking about?

Pete Corrato: Yeah, so a Leaning Tower of Pisa is probably the most universally known example of what happens when you don't [00:32:00] have proper soil investigation when you build a, an iconic heavy structure. Of course we don't want to be doing that off the world here.

Mat Kaplan: Well let's ignore that for the moment that, uh, some of this evaluation and construction may have to be done before humans arrive, maybe we'll come back to that. But what tools do we need to take to these places, the moon or Mars, uh, so that we can both evaluate the soil that we're going to be building on, and, uh, get the construction done? I mean, there must be some stuff that we're not going to be able to get out of materials that are already there on these worlds.

Pete Corrato: The challenge and, and there's different ways to overcome the challenge is, what can I bring with me? There are commercial spaceflight companies out there that are talking about payload capacities measured in the hundreds of tons.

Mat Kaplan: Mm-hmm [affirmative].

Pete Corrato: You can, you can bring a lot of gear with you when you have a hundred tons to play with. [00:33:00] If you're looking at, you know, a Mars Rover, which is, you know, about a ton, then, you're not bringing a lot of tools with you there. So what can you do to do simple soil investigations using limited capacity of cargo?

There is actually quite a lot you can do, and it really depends on how heavy the structure is you want to build. Most of the first structures will be very light. Even if you're stacking stones, you're not going to stack them that tall. If you're talking about inflatable structures or deployable structures, again, they're going to be very light compared to say a large concrete structure on the earth.

So that means you can probably limit your soil investigation to just the upper layers of the soil. So to investigate the upper layers, there are actually rule of thumb techniques which most civil engineers had been taught. I mean, it's kind of funny, we'll you use [00:34:00] the term rule of thumb. The simplest technique for checking bearing capacity on a terrestrial soil, is you take your thumb-

Mat Kaplan: [Laughs].

Pete Corrato: ... And you push it into the dirt.

Mat Kaplan: [Laughs].

Pete Corrato: And you see how far your thumb goes in. Actually, if your thumb just goes to where your fingernail is touching it, you can build almost anything on that. That's about, uh, what we call [laughs], about 2,000 pounds a square foot of bearing capacity.

Mat Kaplan: Wow.

Pete Corrato: If your thumb goes in much further, then you know, okay, I'm going to have to do something light or I'm going to have to improve the ground. There of course are calibrated tools that mimic that, and the simplest one is something called a cone penetrometer, which is nothing more than a metal cone of a known weight, or something you put on the ground point down and push with a known force and see how far it goes in. It's, it's the same as the [00:35:00] push your thumb in test. And based on that you can do a lot of very lightweight structures.

You need deep soil investigations as your soils get heavier, and the weight of the structure you're putting on the soil has an influence on soil layers that are at greater depths. So you can think of the way the load from a structure on the surface spreads out into the earth as you go deeper. If you assume that ... If you draw a 45 degree line from where the foundation is downward into the earth, projecting away from your structure, that's roughly the way the soil force will spread out.

So say at the surface of the earth, you might have a bearing pressure of a 1,000 pounds per square foot. As you go down two feet, the bearing pressure will be smaller because the force will have spread out at some angle-

Mat Kaplan: Mm-hmm [affirmative].

Pete Corrato: 45 degrees or [00:36:00] so. So that the layers as you go down can be softer than the surface layers. So if you have something really heavy, it will have a very deep influence. And if you have a soft layer that's say 10 feet below the surface, you start to get that Leaning Tower of Pisa effect.

Mat Kaplan: What are the other tools that you would tell the first humans headed to Mars that they'd better bring along with them if they want to put up a structure?

Pete Corrato: Well, I think the first humans will have a real good idea because the real key is what are the first robots gonna do?

Mat Kaplan: Ah, yes.

Pete Corrato: So to me a robot is, is a tool carrier. It doesn't have to look like Robby the robot and walk around on two feet.

Mat Kaplan: [Laughs].

Pete Corrato: Although, it'd be nice to have [crosstalk 00:36:50] some of those.

Mat Kaplan: [Laughs.

Pete Corrato: To me you need, you need a whole civilization of robots, you know. Some that crawl, some that roll, some that leap, some that walk. [00:37:00] Designing those are the tools you want to bring. Uh, so a hauler, a digger, they used to be a video game called Lemmings [laughs].

Mat Kaplan: Yeah, yeah.

Pete Corrato: [crosstalk 00:37:11] play that, you can think about, "Oh I need a minor and I need a lifter." You know, in the Lemmings game, you you got many, many different challenges, but you only had like eight or 10 different kinds of Lemmings, and you just put them together to achieve whatever goal you're looking for. It's kind of that, that sort of game I, I see with the, uh, first waves of robots.

Mat Kaplan: Are you fairly confident based on all the work that's being done on earth that robots will be capable, by the time we're ready to send them of 'em of, uh, on their own building the kinds of structures will need before the humans get there?

Pete Corrato: I would say the biggest challenge is that landing path-

Mat Kaplan: Mm-hmm [affirmative].

Pete Corrato: ... Because it's not just a structural problem, it's a large material challenge, [00:38:00] and it might even be that you might need to bring refractory material with you. It would be not ideal because that material is quite heavy. It's like shipping concrete to the moon. It's, it's not something you want to do. It's something you want to avoid.

Mat Kaplan: Yeah.

Pete Corrato: The actual robots, I mean you can see the, uh, I mean the rovers on Mars to me are, are just miracles of mechanical engineering. They show what we can do. The people who built those, if you said, "Look, I need you to build me a mobile crane that can lift 20 times, or a, uh, a shovel that can dig three cubic feet of soil, or a truck that can pul 20 tons of material, I, I'd say they are definitely up to the challenge. The biggest challenge I would see for robots in the near term are trying to extract water ice on the moon from [00:39:00] the permanently shadowed regions, because the temperatures are just so incredibly cold. I'm not sure what even works there.

Mat Kaplan: Wow. When the humans are finally ready to go to Mars, would you be advising NASA that they ought to include a civil engineer among them?

Pete Corrato: Actually, we did a ... Recently within my organization, did a little thought exercise. You had to make up a 20 person crew to go to Mars. And the key is you have to spend normally 450 days on the planet before you have an opportunity to return, who do you bring? And my list was about 60% engineers. Civil engineers, mechanical engineers, electrical engineers, chemical engineers. Because you're going to be making fuel, uh, you're going to be generating power, you're going to have a lot of robots. Things are bregging.

I need an electrical engineer to keep my power grid [00:40:00] off. I need my chemical engineer working on the process plant to produce methane, I need mechanical engineers keeping my robots happy and keeping all the pumps and condensers and valves working. You know, the balance of the mission is doing science of exploration with a smattering of folks whose job it is to keep society going. Like maybe a librarian or an archivist who is like documenting this historic 450 day mission. Or even as simple as a barber who's cutting everybody's hair-

Mat Kaplan: [Laughs]. A, a hair engineer. [Laughing].

Pete Corrato: Well you'll, you'll cross train the chemical. They can probably figure it out.

Mat Kaplan: [Laughs]. With apologies to the chemical engineers who are out there listening right now. Um, you closed your presentation at that webcast by showing us a sign, a sign put up by your, [00:41:00] your former employer Bechtle, back in 1942 which, uh, says a lot to us today about the challenges that are gonna be faced by these humans in this environment, that's going to be much more difficult than anything ever faced before. Uh, could you talk about that?

Pete Corrato: Everybody who has ever worked for Bechtle since 1942 has seen this sign and has a copy of it somewhere either on their desk or in their computers in big bold letters at the top of it, it says, 'this is no picnic.'

Mat Kaplan: [Laughs].

Pete Corrato: And, it describes environmental challenges that the people doing the construction will face, rivers of ice, temperatures from -60 degrees to 100 degrees, gnats and mosquitoes will not only be annoying, but will be life threatening. That says, if you're not prepared to work in these conditions, do not apply. And this was a sign [00:42:00] for construction workers to build the first highway into Alaska at the beginning of the World War II in order to move, uh, military material up there to, uh, blunt any invasion threats from Asia.

That philosophy still has to apply. The people who've gone to space so far are, you know the pilots, the geologists, they were explorers. The next wave of people have to be builders to go there and expect stuff to break. Like I don't even believe this is going to be working. I need bailing wire and duct tape and three different hammers and stuff is just going to break and I know I can fix it. To me it's maybe a different philosophy you have to take with you.

Mat Kaplan: Pete, if uh, if we were ready to go tomorrow and administrator Brydenstein came to you and said, "Pete, you're the guy. You've got the skills. [00:43:00] We need you to build this stuff on Mars." Would you go?

Pete Corrato: If I was a younger man, I would be very tempted. I had a reputation when I was working full-time. I went to anywhere. You know, people would walk in and say, "Okay, we've got a, a problem with some bolts in Kazakhstan, who's getting on an airplane?" I always had my hand up-

Mat Kaplan: [Laughs]. let Pete do it. [laughs].

Pete Corrato: And there's a breed of people like that, and there are plenty of engineers out there who hate the office. They have to be in the field. And this is the field, this is where you go to solve the problems to make it happen.

Mat Kaplan: I could stop there, but I saved one example. You actually contradicted yourself, cause you said that we've never built anything on another world. And yet in your talk, you gave us an example of, of the only construction project that you could come up with and it was on the moon about 50 years ago.

Pete Corrato: [00:44:00] I'm glad you were paying attention Mat-

Mat Kaplan: [laughs].

Pete Corrato: ... So, as I was preparing for that talk, I, I had sat down to ask myself, so what have we built? You know, what can I use as past experience to talk about? And I do a lot of work in the writing and updating of building codes, uh, in the United States. What, what has building code ever been used for or could have been used for on the surface of the moon or Mars? And there is actually one such item and it's the flag pole. So every Apollo has gone and set up a flag, and there's a section within the international building code, which is the building code used to design whatever structure you're in and listening to this in right now. There is a section in there if you Google it and search for flagpoles where it talks about-

Mat Kaplan: [laughs].

Pete Corrato: ... Lateral soil restraint of the bottom of [00:45:00] flagpoles. And lo and behold, when Apollo 11 landed and set up their flag, the mission report says they had trouble pushing it into the ground and we're having trouble with lateral resistance for the flagpole. So we had an example of the very first humans up there building the structure according to the building code and sending back a construction report saying they were having trouble meeting the code.

Mat Kaplan: [laughs]. Pete, I hope that you and I are both still around when the first flag pole is successfully erected on Mars. Thank you for this. This is, I mean, we've done this show for 17 and a half years now, hundreds and hundreds of programs. I don't think we've ever had a discussion quite like this one. It has been absolutely fascinating. Now, thank you for sharing this expertise.

Pete Corrato: It was my pleasure, Mat. Thank you.

Mat Kaplan: Distinguished civil engineer and Bechtel, Ameritas fellow, Pete Corrato.

[00:46:00] Time for what's up on Planetary Radio. We are joined by the chief scientist of The Planetary Society. That is Bruce Betts, who is, uh, at home exactly where he should be and exactly where you should be listening to this right now. I'm right, right?

Bruce Betts: Right. Right, right.

Mat Kaplan: [laughs].

Bruce Betts: Right, right.

Mat Kaplan: All right. I hope you're not going to stir crazy there. You're getting to look at the sky or ... What?

Bruce Betts: I mean, listen to me. I'm just growling with ferocity.

Mat Kaplan: [laughs]. That is one of your dogs, right? That's not you? It's a cooped up dog.

Bruce Betts: All right, yes.

Mat Kaplan: [laughs].

Bruce Betts: Yes. And there's the other dog, so who knows what noises we may hear.

Mat Kaplan: If we were to go outside with proper precautions and social distancing, what might we see in those things that are so far away we probably don't have to worry about them giving us anything?

Bruce Betts: We would see planets and stars. I mean, we wouldn't because we live in Southern California and it's [00:47:00] just, it's oddly cloudy all the time. But, for those who don't have clouds, check out the morning predawn east. We have Jupiter, Mars and Saturn doing a little dance. Jupiter look is the brightest of the three. Mars is near Jupiter. Mars being reddish, Jupiter being really, really bright. And then Mars is sliding down towards yellowish Saturn and they're all very close together.

Uh, Mars will be snuggling with Saturn, it's the technical term on the 31st of March. And if you got a clear view to the horizon, way down to the lower left is Mercury. In the evening, we of course have Venus dominating the western sky. It's moving up and will line up with, uh, Aldebaran on Taurus and then farther to the upper left, beetle juice in Orion and the crescent moon, the, the very fresh crescent moon, uh, joins them between Venus and Aldebaran on March, uh, [00:48:00] well it's March 27th and 28th that's near Venus.

We move on to this week in space history. It's a Soviet Russian week, not officially. 1965 the very first spacewalk taken by Alexei Leonov. Uh, tragedy in 1980, a rocket explosion on the pad killed 50 people, and then 2001 Mir space station re-entered the earth's atmosphere.

Mat Kaplan: That's such a great story about Alexei Leonov who, uh, just a heroic cosmonaut. How he could barely get back into the spaceship, uh, into his, uh, uh, capsule because his suit had expanded so much. Who's ... Some scary stuff?

Bruce Betts: Scary stuff. A lot of, a lot of brave people. We move on to random space fate, you'll like this Mat. There's an asteroid named Bacon. Did you know this?

Mat Kaplan: No. [laughs]. Where is it and how do I get a piece [00:49:00] of this?

Bruce Betts: Well, first before he get too excited, oddly enough, rather than being named after the meat product, it is for named English philosopher and statesman and father of the scientific method, Sir Francis Bacon.

Mat Kaplan: Who was named after bacon, of course?

Bruce Betts: Yes. No, so it all ties back.

Mat Kaplan: I'm thrilled. Is this out in the main belt or, do- do- does this have a chance of, uh, striking our planets someday and there'll be an odd, there'll be a silver lining?

Bruce Betts: [laughs]. Is it less terrifying if the asteroids named Bacon are made of bacon? I- I don't know. I don't know. I see you're so excited there was an asteroid named Bacon, I didn't check its orbital parameters. I apologize.

Mat Kaplan: You and me both, bro.

Bruce Betts: [Laughs]. All right, we move on to the trivia contest, where I asked you where in the solar system, where in the solar system is there a feature named Bilbo. Turned out feature was a significant [00:50:00] word, uh, because in the list of crazy asteroids, there's a Bilbo, but I was looking for a feature-

Mat Kaplan: [Laughs].

Bruce Betts: ... On an object in the solar system. How'd we do, man?

Mat Kaplan: Well, many of you out there found that asteroid, didn't necessarily find the feature that Bruce had in mind and that's, that's good. You know, that's fine. It doesn't exactly fit the definition of a feature, but good on ya.

Uh, before we get into it, we had a request literally from Robert Johannesson in Norway. He wants to know if, uh, if, uh, you or I can sing a short extract of Leonard Nimoy's ballad of Bilbo Baggins before you announce the winner.

Bruce Betts: Well, that's clearly you.

Mat Kaplan: [singing]. You know how I know that This will cement ... I think I may have mentioned this in the past, but if you didn't know I was a nerd, I have not one but two Leonard Nimoy LPs.

Bruce Betts: Oh my gosh. [laughs]. There were [00:51:00] two?


I thought everyone else in the world is saying, your own Shatner as well?

Mat Kaplan: No, I don't have a Shatner.

Bruce Betts: But you've got two Nimoys. That's impressive.

Mat Kaplan: I do. I do. And, and the first one is, he's in full Spock regalia too-

Bruce Betts: [laughs.

Mat Kaplan: Uh, holding the model of the enterprise. It's fun. Here's our actual winner. And she is one of those who picked the feature on Titan. Here's her little poem to answer us.

On Titan, the sixth moon of Saturn, the names of the hills have a pattern. It's hobbits, not trolls, such as Bilbo coals. Hence, to [inaudible 00:51:36] our praises must turn. Last line is a little bit free verse, but that's okay. She's a retired teacher and her name is Maureen Benz in Washington State. She says that she found our, uh, recent astronomers without borders episode especially compelling. It's her first time entering the contest, and, uh, she just wanted to give us that little limerick since, uh, St. [00:52:00] Patrick's day was around the corner when she sent it to us. Here's to new frontiers.

Well, here's to you Maureen. You've won big time. [laughs]. You're going to be getting a Planetary Radio T-shirt from The Planetary Society store at And a Planetary Society rubber asteroid. So congratulations.

Dave Fairchild, our poet Laureate in Kansas, he came up with the asteroid so it'll get equal time. Martin Watt who works at Lowell telescope, this guy's found a main belt asteroid, about eight clicks in size tagging it as Bilbo in the solar space frontier, matching one he'd labeled token earlier that year.

Bruce Betts: [Laughs].

Mat Kaplan: Robert Klane in Arizona, Bilbo's highly eccentric orbit, it comes closer to Mars than most asteroids made me think of you guys. [laughs].

Bruce Betts: Great, great. That was a compliment, right?

Mat Kaplan: Yeah, I think so. Joseph Putray, uh, we hear from pretty frequently. He's in New Jersey. [00:53:00] He said, yeah, he found the asteroid, but he also wanted to make sure we knew that there is Bilbo mound in Savannah, Georgia, Bilbo canal, also in Savannah and restaurants. Bilbo Pizza, Kalamazoo, Michigan, Bilbo Pub in Bossier City, Louisiana, and my favorite Bilbo Barbecue in Bremen, Georgia. Well, I'll have some bacon with that brisket please.

Bruce Betts: [Laughs].

Mat Kaplan: [inaudible 00:53:25]. I'm avoiding beef but I'm not off bacon. Also two beetle and one wasp, s- uh, species, but they're mobile and so it wouldn't count as features.

Bruce Betts: So other, other than the wasp, should we try to visit all of those and maybe have Planetary Radio live [laughs] at each of the

Mat Kaplan: Road trip.

Bruce Betts: The Bilbo tour?

Mat Kaplan: Did you want to say anything else about Titan? 'Cause I guess, uh, we had a bunch of people who told us there were lots of features. There are lots of features on Titan named after, uh, middle earth Denison's.

Bruce Betts: Yeah, the name Bilbo follows the convention that Titanian coales, coales, [00:54:00] coales, I don't know, meaning hills or small knobs in geologic terms, are named after characters in Tokens works.

Mat Kaplan: Well we just have one more to share with you. It's Laura Weller in the UK. She says, Bilbo and Gandalf in space, I had a Lord of the rings themed wedding. I can't believe I could have merged it with a space theme. What a missed opportunity.

Bruce Betts: [laughs].

Mat Kaplan: Thank you, Laura. You've out nerded me.

Bruce Betts: I dunno. Token themed wedding or two Leonard Nimoy LPs. [laughs].

Mat Kaplan: All right. All right. It's, it's a close one. I- I won't call it. Uh-

Bruce Betts: Maybe [crosstalk 00:54:38] I know ... We'll give the nod to her. [laughs] All right, you ready for more?

Mat Kaplan: Please.

Bruce Betts: Going in a different, uh, non Token direction, in the land of stellar astrophysics. The Chandra Sekar limit is the maximum mass of a stable white dwarf star. Here's your question. In solar masses, [00:55:00] so that's the unit to use, solar masses, what is the approximate value of the Chandra Sekar limit? Go to

Mat Kaplan: I used to know this limit and so it's killing me that I can't think of it now. Because anything bigger right will collapse into a black hole?

Bruce Betts: If you get above that mass, it'll collapse more and it'll first would go to a neutron star. But if you have more mass than the neutron star can handle, then it goes to a black hole.

Mat Kaplan: Okay. Well, regardless of what your favorite wide dwarf may become someday, or whether it'll just hang around forever, uh, you have until March 25th, it probably won't collapse before then. Wednesday, March 25th at 8:00 AM Pacific time to get in on this contest. And if you come up with the correct, uh, value for the Chandra Sekar limit, we've got a book for you. Spacefarers by Christopher Wanjek? Wanjek? I hope I have that right. Nice book recommended for, uh, the- to me by, a friend of ours at [00:56:00] Jackson, the Japanese Space Agency. And we will throw in a Planetary Society rubber asteroid. And I'm afraid we're fresh out of the bacon ones.

Bruce Betts: [laughs]. But we can just smear some on it for you.

Mat Kaplan: Yeah, it's a good idea [laughs]. All right, you can let us know if you win, if you want br- bacon grease, uh, smeared on your [crosstalk 00:56:21]-

Bruce Betts: [Laughs].

Mat Kaplan: Oh God, let's get outta here.

Bruce Betts: [laughs]. I, [laughs], I'm sorry, you've broke-

Mat Kaplan: [crosstalk 00:56:30] yourself.

Bruce Betts: ... You've broken me. Uh, all right everybody. Go out there and look up the night sky and think about what else? Bacon. Thank you and good night.

Mat Kaplan: He's Bruce Betts. He's bacon. I'm in a, no, I'm sorry. He's the chief scientist, uh, of the Planetary Bacon si- Society, and he joins us every bacon here on Planetary Bacon.

Bruce Betts: [Laughs].

Mat Kaplan: Planetary Radio is produced by The Planetary Society in Pasadena, California, and is made possible [00:57:00] by its members who are helping to build our future in space. You don't need a hammer to help out. Join us by visiting

Mark Hilverda is our associate producer, Josh Doyle, composed our theme, which is arranged and performed by Peter Schlosser.

Be safe everyone. Ad astra.