Background info

On May 2, 2017, Tom Mueller, propulsion CTO at SpaceX, conducted a speech/interview with some members of the New York University Astronomy Society. This was streamed live on Twitch; I’ve transcribed it with the help of u/dansemacabred2, u/jclishman, and u/Zucal. Many thanks!

Check out the interview on twitch.tv, and the post in the SpaceX subreddit.

Transcription

We have a little, like, amateur setup… Um, so I’ll just give, like, a quick introduction basically; I’d like to introduce Mr. Tom Mueller, who is the cofounder and Chief Tech Officer at SpaceX; he’s the champion of the Occupy Mars movement, which I am proudly representing on my shirt; and the brains behind SpaceX’s rocket designs, as one of the world’s foremost rocket engine designers, he’s responsible for developing propulsions systems and engines for both the Falcon launch vehicles and the Dragon spacecraft, and much more, obviously.

Before we start I just want to say thank you from all of us for taking time out of your busy schedule to talk with us. We’re all very amazed at the work you do at SpaceX, and congratulations on all the success you’ve been having with the recent launches.

Thank you!

If you want to— do you have anything—

Did everybody see that launch yesterday?

Yes, yes.

The launch?

The launch, yesterday morning. [Of NROL-76.]

Okay, so shall I go ahead?

Yes. If you have, like, a talk prepared, we have some questions.

Okay, so I’m going to talk about low-cost access to space. When I was a kid, you know, in the 60s, I used to watch Star Trek; I was 8 years old when they landed on the moon. Of course, a lot of us thought 50 years from now, we’d be on Mars, maybe travelling to other planets, you know, a more Star Trek-like experience. It didn’t really happen though, did it?

Right.

You know, the invention of modern rocketry, until they put a man on the moon, was about 40 years. From Goddard to Armstrong. It’s been over 50 years since then and it seems like we haven’t really achieved all that much. In fact, we no longer have the ability to put a man on the moon; we don’t have the hardware. Why is that?

I think one of the big reasons is that it’s prohibitively expensive to get to orbit. And why is that? It’s because rockets are very expensive.

The mass of a rocket is about 95% propellant by weight; of the Falcon 9 rocket. So is it the propellant that’s expensive? No, actually not, it’s less than 0.5% of the cost of the rocket. It’s the structure of the rocket and the engines that is very expensive. The problem is, we throw these rockets away. Until very recently, that was just the way you thought about rockets is that they’re expendable.

Because they were originally developed as ICBMs, and of course that’s not reusable, so nobody ever really thought to make them reusable. It’s the only form of transportation I can think of where people don’t think of it as being reusable. They just think of it as expendable. Can you think of anything else you would throw away after one use that, that, you know, as a form of transportation?

The only thing I could ever come up sort of like that is is a Top Fuel dragster. You know, they make one run down the quarter mile and they have to rebuild the engine. When you design that way, you can do incredible things. Those cars do a quarter mile in less than four seconds, and they’re doing over 300 mph at the end of a quarter mile; actually a thousand feet now, the run. It’s pretty incredible when you build, uh, design something as single use; you can push the bounds of engineering and get incredible performance. And that’s true with rockets.

If you make a rocket reusable, you have to give up some performance. Your family car can be used tens of thousands of times and drive hundreds of thousands of miles. It doesn’t have anywhere near the performance of a Top Fuel dragster, but it’s affordable and very reusable. We’ve got to find something in-between; where we have close to the performance of a Top Fuel dragster, but somewhat closer to the reuse and utility of something like a household car.

So what we need to do is design a rocket that can be reusable. That’s what we set out to do. So first, you’ve got to make the rockets relatively low-cost. If your rocket costs a billion dollars, even if you use it 100 times, it’s still going to be very expensive to use. So we set out to build low-cost rockets from the very beginning. The cost that the government cost-plus programs charge for their rockets are ridiculous. We don’t compare our prices to any space vendors; any government-subsidized space vendors. Because it’s just not a good starting point. What we try to do is compare our cost to commercial products.

Even airliners are kind of expensive for our cost trades. From Elon, I’d always get, you know, how much does it cost to make a Model S, a Tesla? Start from there, and work my way up to the rocket.

Like, here’s a conversation I had maybe about five years ago on the Merlin 1D when we first developed it. He asked me; he said, “How much do you think it costs to make a Model S?” And I’m like “I don’t know; 50 thousand dollars?” He said “No, about 30 thousand dollars.” That’s the marginal cost for that car.

And he said, “How much does that car weigh?” And I said, “About 5 thousand pounds.” And how much does a Merlin engine weigh? I go, “About a thousand pounds?” So, he’s like, “So why the heck does it cost, you know, some fraction of a million dollars to make a Merlin engine?”

And I mean, he has a good point. And the material you’re using isn’t aluminum, it’s not stamped, so I’ll give you a factor of five. So it’s equivalent to a five-thousand-pound rocket engine. So why’s it 20 times the cost? So that’s the way we look at it and the way we think at SpaceX trying to get the amortization cost of the rocket down. Once you start reusing it, the real big cost becomes the amortization cost of the rocket, the operational costs, and the fuel costs, which is basically the same model as the airliners.

We looked at the airliners, and they’re about 50% operation cost, and I think about [inaudible; 50% amortization cost?] the cost of the $300 million aircraft over its life. And that’s the sort of modeling we like to do to make access to space very affordable.

Like I said, we don’t use space— we avoid space vendors like the plague. When we started developing the Merlin engine, you know, I needed valves; I needed liquid oxygen and kerosene valves that had to work. So I went to some of the vendors that supplied these valves and I said, “Hey, can you give me a good price on your existing product?” And no, they couldn’t. So I said, “Can you design a much lower-cost one?” So they came back; and you know, if it takes two weeks or a month to give you a quote, you already got the wrong vendor. If it takes them that long to just give you a price, how long does it take them to build the actual part?

So they come back with a quote of hundreds of thousands of dollars for their part, and you know, it’s going to take eighteen months to develop it. And I say, “No, I need it in like three months.” And so they kind of laugh at you. And so we ended up designing our own components; you know, pre-valves, main valves. We’d already developed the injector, the combustion chamber; the main parts of the engine. We were hoping we could just go buy some of this other stuff from existing suppliers, and no, the cost was just— the cost and schedule weren’t close for us. So we— [inaudible] Anybody that provides you know, space hardware to government contractors is just not at the performance level we want to be at. So, that’s how we get the cost of the hardware down; also, we had to have control of our own test site. So we developed a test site in Texas and did our own testing because a huge cost of developing and testing rockets is the test site cost. So we needed to get that under control.

In my previous career, when we were at TRW, we ran an engine; it was a big engine, a 650,000 lb engine, but it was very simple. And we ran it at a government test site; NASA’s test site at Stennis. And they had a crew of 100 people, basically. They had two shifts of about a hundred people. And we ran an equivalent complexity engine, maybe not that size, but a 40,000 lb engine at our site, and we could run it with like between 5 and 10 people. So that’s what I was looking for; even running a large pump-fed engine like the Merlin engine, it doesn’t take an army of people to run an engine like that. And I think the government contractors have convinced themselves it does.

When I first started developing the Merlin engine, the conventional thinking was, “Only governments can develop rockets. Private companies could never have the resources.” So it was really kind of SpaceX that broke the ice on that. No, it doesn’t take a government to do it, it doesn’t take billions of dollars; it takes; it took us hundreds of millions [laughing] but it didn’t take billions to do it. So you’ve got to minimize fuel costs since, you know, you get the hardware costs down; now fuel is the major component of your cost. So you have efficient combustion, and we’ve built our injectors— running at about 96%, 97% combustion efficiency; you can’t get much more out of a rocket injector than that. And you use low-cost propellants. We actually picked the wrong propellant. It wasn’t too bad, but we picked RP-1, rocket-grade kerosene, which at the time was, you know, 8 dollars a gallon. We tried jet fuel, which is more like 2 dollars a gallon, but it just didn’t run very good. But recently, we re-negotiated the cost of the kerosene fuel and we got it close to the cost of jet fuel.

But what we’ve found, in more recent studies, is that methane— natural gas— is the cheapest form of fossil fuel energy. That is mainly what they’re— getting rid of coal, getting rid of oil, and they’re running on natural gas. And it’s the cheapest fuel you can get. It also has a great property that it can be made easily on Mars, so that figures in too. But our next vehicle’s gonna be all methane fuel. Oxygen is a no-brainer. It’s so cheap; our cost for oxygen is about 70 dollars per ton. It’s almost free. If you look at the costs, it’s actually the fuel that has the more significant cost. Even though there’s more oxygen; there’s three times as much oxygen on the rocket as there is, uh, methane, and two and a half times as much oxygen as kerosene. It’s far cheaper because it’s just so easy to make from air, from cooling air.

So you get the fuel [costs] down, and then you’ve gotta make the rocket completely reusable, which we’re still struggling with. When that rocket came back, like yesterday [with NROL-76], it’s smoking, it’s sitting there smoking; we burned a lot of the ablative [material] on it; we have to remove the legs in order to lower it, and reinstall them; it’s not a quick turn. What we want is like an aircraft; you know, it pulls into the airport, the people get off, they fuel it up while the people are getting back on, they do some checks, you know; some inspections, and everything looks good and you go again. And that’s where we want to get to.

The Block 5 Falcon rocket that we’re rolling out later this year is going to have, uh, reusable thermal protection on it; so we don’t burn up the heat shielding on it. And it’s going to have a much better landing legs that just fold up and; just drop the rocket, fold the legs, ship it, fold the legs out when it lands. Making it turn very fast; our goal is; Elon asked us to do a twelve-hour turn. And we came back and said without some major redesigns to the rocket, with just the Block 5, we can get to a 24-hour turn, and he accepted that. A 24-hour turn time. And that doesn’t mean we want to fly the rocket, you know, once a day; although we could, if we really pushed it. What it does is, limits how much labor, how much [touch?] labor we can put into it. If we can turn a rocket in 24 hours with just a few people, you’re nuts. [inaudible] low cost, low opportunity cost in getting the rocket to fly again.

So those were all the things we did; that we’re doing; to get the cost of access to space down. Hopefully by a factor of 100 when we do the Mars vehicle. We can’t do that right now with the Falcon because we still throw away the upper stage. So maybe later, so maybe a third of the cost of the rocket is the upper stage. It has a single Merlin engine on it, but it’s a fairly sophisticated version of the engine. It’s also got the guidance computer, and a lot of [inaudible] avionics on it. So it’s a significant cost with the marginal performance that [inaudible] gets returned [inaudible] reusability, able to throw some of the biggest satellites, we can’t make it close, with that size of rocket, to recover the upper stage. We’re gonna try in the next few years to start recovering the upper stage, but we won’t be able to do it for all missions. That’ll help reduce costs quite a bit.

The Mars rocket is meant to be completely reusable. Both stages, ship and [inaudible] can lift hundreds of tons in a single flight; it can go all the way to Mars and back, and you’ll have to fuel it on Mars; we’ll need to make about 1000 tons of propellant on Mars over a two-year cycle; bring it back; and that’s a tall order. You need about half a megawatt of energy to [inaudible] that much propellant [inaudible]

That rocket is going to be the real game-changer. I would say that the Falcon 9 is evolutionary, you know, a reusable rocket that greatly reduces the cost of access to space. Maybe we can achieve ten reduction in cost over, you know, like what ULA or the Russians or the Chinese are doing, with the Falcon. But we want like a hundred or more reduction in costs; and that’s what the Mars rocket’s gonna do. That’s going to be the revolutionary rocket.

So once we’re flying that, all other rockets will probably be obsolete. [laughs] Luckily, Blue Origin is working on a fully-reusable rocket [inaudible] But we’ve really changed this industry that the other guys are really scrambling. It’s pretty funny to watch this, because when we first started the company 15 years ago, my fifteen-year anniversary was Monday, May 1st. [clapping] Thank you.

We started the company on May 1st, 2002. Well, I started there; I consider—. Elon incorporated the company I think in February, but he didn’t have any employees yet. But I consider when he had his first employees when he had his company. But anyway, over the fifteen years, we’ve gotten, you know, this far; and when I was first hiring people, you know, that’s when I heard [inaudible] money to develop this rocket. And then we built the Falcon 1, which had a single Merlin engine on it, could throw about 1,000 lbs into LEO; and they said, you guys, you guys were able to build a small rocket. But you’ll never be able to build an EELV-class, EELV-mission class rocket. And so we built the Falcon 9 and started flying it. And they said you’d never be able to reuse it; you’ll never be able to get to the space station. And at some point, you stop listening to it. And I think it’s great, you know, if people think what you’re doing is impossible then you must be doing the right thing. You can still find the YouTube video online where people are critiquing our recovery thing as being photoshopped or CGI’d. That’s pretty high praise, when people don’t actually believe you’re doing. [laughter]

And you know, we were ridiculed by the other big companies in the launch vehicle business. At first, they ignored us; and then they fought us; and then they— we found out; they found out that they couldn’t really win in a fair fight because we were successful and we were, you know, factors of two or three or perhaps even five lower costs than what they can do. So then it becomes an unfair fight, where they, you know, try to destroy you politically, and use other means. And then at some point, they figure out that they’ve got to do what you’re doing. So there’s a lot of talk at these other companies about how they’ll make reusable rockets; recover the engines, recover the stages, come up with a much lower-cost rocket so that they can compete. You know, there’s no way that ULA would have considered buying engines from Blue Origin except for the pressure that SpaceX is putting on them. There’s no way that the French would have quickly abandoned the Ariane 5 and moved to the Ariane 6 design because— except for the pressure we’re putting on.

So we’re really changing the world. The Russians are saying they’re coming up with a rocket that can beat SpaceX, which is entertaining, [laughs] which is entertaining, because they’ve been working on their Angara rocket for 22 years, and launched it once. And suddenly they’re going to be coming up with a low-cost one.

Anyway, it’s great that we’re changing the paradigm and causing everybody else to think differently about how this is done. So once [inaudible] and everybody else starts doing it, then what’s going to happen? I think the transport problem has to get solved, and then the killer apps in space are going to appear. And we don’t know what they are yet; it’s like when the internet first came out. And people were like, “what good is that?” People couldn’t imagine what you’d use it for. I think we can imagine a lot of things to use a low-cost rocket for, and the common ones you see are, you know, space tourism, of course; hotels in space; Bigelow has his inflatable hotels; trips around the moon, which we’ve already got people signed up to do that; resort on the moon, perhaps. Certainly Mars; that’s what we’re doing; we’re looking to colonize Mars. Space mining, you know, metallic asteroids are— could be worth trillions of dollars. Resources on the moon; there’s water on the moon, there’s helium-3 on the moon; of course, you’d need to get fusion working first. But if you do, helium-3 would be very useful. And of course, mining metals on the moon. Satellites; bigger constellations, satellites with lower-cost rockets. I think there’ll be a lot more done in space if the cost comes down by a factor of a hundred. Less running wires on Earth and just transmitting from space.

Which is what we’re doing; the satellite constellation we’re developing is basically to put the internet in space. Eventually, we want to put what is the current bandwidth on terrestrial, like on fiber, in space, where we can eventually double the bandwidth of the internet that exists. It would be everywhere; in fact, it would be better out in the middle of nowhere because you would have the satellites to yourself. If you are like in northern Alaska, or Wyoming, or the Sahara desert, you’d have a great connection, because you’d have all the satellites overhead to yourself. If you’re in LA, it won’t really help that much. Because, you know, eleven million people using those satellites. People out in the middle of nowhere are going to love it.

Google really loves it too; that’s why they invested about 900 million dollars, almost a billion dollars, into SpaceX; because we can quickly move what they call backbone; like I think 70 to 80 percent of the information you pull up on your computer is stored locally. If you’re here in LA and you pull up some viral video, it’s probably stored locally; it’s not coming from wherever the; wherever it’s generated. And moving that information from city to city and from place to place is called backbone; and the example I got was, if you wanted to move data from LA to South Africa right now, it goes across the US to New York, it jumps across the Atlantic to Europe, it travels down through the MIddle East, and gets to South Africa. It’s a lot of server hops and a lot of latency. [inaudible] you know, gigabytes of data to South Africa.

With our satellite network, it’d be line-of-sight straight to South Africa with low-latency, with laser links. That’s what we’re working on. And imagine if you had a launch vehicle that could put hundreds of tons of satellites equivalent in a single launch for just a few million dollars. It just completely changes the game. Then you start thinking about putting, you know, big satellites up, hundreds of them up there, and being able to service them; it really changes the whole dynamic. So that’s what we’re working on right now.

So the transportation from Earth is like developing the western US. They had the covered wagons at first which got people over here, but they really didn’t enable development of the west until they put in the railroad. Now you can move tons of hardware and tons of people for low cost. That’s what we need to build; is the railroad to space, basically. That’s what we’re working on, you know. We’re just the transportation; like, colonizing Mars; we’re— we need a lot of help to colonize Mars. We want to provide, basically, the airliner ticket to Mars, but someone else needs to provide the rental car, the housing, the food, just building up. [inaudible] When Elon said we’re gonna provide, you know, easy access to Mars, that means we’re gonna be able to move you there, but it’s going to be up to other companies and other industries to help make that happen. So it’s going to be a huge collaboration to make this really happen.

So I’m really excited about what we’re doing; we’re kind of hitting the limits of chemical rocket technology; the new engines we’re developing for the Mars ship are very high-pressure staged combustion engines. Getting all the energy you can out of fossil fuel propellants; you know, 99% combustion efficiency over four thousand PSi combustion chamber pressure; full-flow. So all of the propellant goes through the main combustor; it’s not an open-cycle; it’s a closed-cycle. So all the energy from the propellant is going to thrust. It’s basically, you can’t get any more energy out of a chemical propellant. You can get a little bit more performance if you went to hydrogen and oxygen, but it actually; the rocket gets much bigger and more expensive, so the sweet spot is not hydrogen and oxygen; a lot of people thought that, and I did too. The original Raptor engine was hydrogen and oxygen, and we did the studies that showed if we used hydrogen and oxygen, the rocket is lighter, because the propellant is lighter, but the propellant costs more, it’s harder to make on another planet (it takes a lot more energy), and the rocket is bigger; the structure is bigger, the engines are bigger. So it costs more to make it even though it’s carrying less weight.

So you can look at that and compare the Delta rocket to the Atlas rocket. The Delta rocket is a hydrogen-oxygen booster. And it’s bigger, it’s 5 meters in diameter, compared to the Atlas which is like 3m in diameter, but it’s actually lighter and, you know, has a smaller 650,000 lb thrust engine whereas the Atlas has a 950,000 lb engine on it. And Atlas can throw more; it can throw more payload. And you look at the Falcon 9; it’s a small rocket, 12 feet in diameter, but it can throw a lot, more than the standard Atlas. Using a high-performance low-density propellant is not the answer. So we’ve gotten everything we’re going to get out of chemical propellants.

So we’re looking, actually, at like electric propulsion for the satellites, and we’re talking to people about nuclear-thermal, you know, the NASA centers are working on nuclear; it’s just prohibitively expensive to test because you can’t; it’s not like the 60s, like when you can just let fission products fly out of your rocket into the desert. You’ve now got to scrub it and clean it and capture it, which is super-expensive. I don’t think SpaceX could really afford to develop that rocket ourselves. If NASA ever gets turned on to develop those test stands, we’d probably want to jump in on that. You can just about double the performance of a rocket to Mars compared to a really-good, like a Raptor system, a chemical system, with fission; nuclear fission. Theoretically, fusion may be ten times better, and antimatter maybe a thousand times better, but I think those are certainly not going to happen in my lifetime. Maybe in your lifetimes.

The warp drive is still a long way away. [laughter] So we’re stuck with chemical propellant for quite a while.

So that was my ramble; that’s what I want to talk about today. So we can open up for question.

Thank you so much! We’ve collected a few questions; can you hear me okay?

Yeah.

Okay, so… um, our first one is: how far is too far for the rockets? The Mars Colonial Transporter was renamed the Interplanetary Transport System, because it was deemed that travel could be made further than Mars; and similarly, do you think deep space travel will ever be possible or are we limited by distance?

Uh, yeah. I mean, some things are too far, like you can’t get— you can’t get to Mars with our system about [inaudible] you know, about 24 out of about 26 months, you can’t get to Mars. It’s on the other side of the sun. You want to go to Mars when it’s swinging by you. You want to go when it’s [inaudible], you know, [inaudible] miles, not when it’s like 210 million miles away. We can obviously go to the outer planets, like we have with the planetary probes, it’s just that the way to do that is with gravitational assists. And it takes years. If we wanted to go direct to Jupiter, we could do it with this system, but we couldn’t throw a lot of mass. It’d probably be— we can put a hundred tons onto Mars; we can probably put, I don’t know; I’m guessing like 20 tons, quickly, to Jupiter. And it would take much longer; Jupiter is much further than Mars. You wouldn’t be able to do it with people because you wouldn’t be able to provide the supplies they’d need; the oxygen and the food and the water and everything. So I think the system we have in work for Mars would not work to go directly to the outer planets; but if you had, you know, a system of depots along the way, you could do it. You’d have to kind of hop along the way. I don’t think you could go much farther than Jupiter; it’s twice as far to Saturn, and it’s getting so cold; there’s a lot of moons on Jupiter, a lot of surface there, so I think it’s definitely the place to go.

But as far as sending big probes to the outer planets, um, absolutely. You know, we could send huge robotic missions to the outer planets. What I’m waiting for is for somebody to start developing these satellites and probes that are, you know, somebody like SpaceX could come along and make it affordable. Like, you know, you guys are all into astronomy, and I’m sure you’re all huge fans of the Hubble, which was a bargain at what, a couple of billion? What, I think 3 billion? And now there’s the Webb, the JWST’s coming up here, launching in a year and a half; and 8 billion dollars. That’s not a deal. I mean, that thing better make it to orbit. [laughs] That could probably be developed for like one-tenth that cost. So what we need is a SpaceX-type contractor to give the— to match our low-cost rockets. We’ve reduced the cost of access to space by three or four; shooting for a factor of ten. Somebody needs to reduce the cost of scientific equipment to match what we’re doing. So I’d love to see that happen.

SpaceX would love to do that, but we’re kind of busy. [laughter]

One of our members [name redacted] asked: what’s it like working for Elon Musk? How is he as a boss, and how is he out of the office?

[laughter]

It’s really— it’s quite a trip, working for Elon. It’s different every day [laughter] because it all depends on what mood he’s in [laughter] — they think he’s joking. You know, he’s been in a great mood lately; we’ve been very successful, and Tesla’s been doing quite well. So it’s been good recently. Um, he still; he’s still extremely demanding. One thing I tell people often is that— I’ve seen this happen quite a few times in the fifteen years I’ve worked for him. We’ll have, you know, a group of people sitting in a room, making a key decision. And everybody in that room will say, you know, basically, “We need to turn left,” and Elon will say “No, we’re gonna turn right.” You know, to put it in a metaphor. And that’s how he thinks. He’s like, “You guys are taking the easy way out; we need to take the hard way.”

And, uh, I’ve seen that hurt us before, I’ve seen that fail, but I’ve also seen— where nobody thought it would work— it was the right decision. It was the harder way to do it, but in the end, it was the right thing. One of the things that we did with the Merlin 1D was; he kept complaining— I talked earlier about how expensive the engine was. [inaudible] [I said,] “[the] only way is to get rid of all these valves. Because that’s what’s really driving the complexity and cost.” And how can you do that? And I said, “Well, on smaller engines, we’d go face-shutoff, but nobody’s done it on a really large engine. It’ll be really difficult.” And he said, “We need to do face-shutoff. Explain how that works?” So I drew it up, did some, you know, sketches, and said “here’s what we’d do,” and he said “That’s what we need to do.” And I advised him against it; I said it’s going to be too hard to do, and it’s not going to save that much. But he made the decision that we were going to do face-shutoff.

So we went and developed that engine; and it was hard. We blew up a lot of hardware. And we tried probably tried a hundred different combinations to make it work; but we made it work. I still have the original sketch I did; I think it was— what was it, Christmas 2011, when I did that sketch? And it’s changed quite a bit from that original sketch, but it was pretty scary for me, knowing how that hardware worked, but by going face-shutoff, we got rid of the main valves, we got rid of the sequencing computer; basically, you spin the pumps and pressure comes up, the pressure opens the main injector, lets the oxygen go first, and then the fuel comes in. So all you gotta time is the ignitor fluid. So if you have the ignitor fluid going, it’ll light, and it’s not going to hard start. That got rid of the problem we had where you have two valves; the oxygen valve and the fuel valve. The oxygen valve is very cold and very stiff; it doesn’t want to move. And it’s the one you want open first. If you relieve the fuel, it’s what’s called a hard start. In fact, we have an old saying that says, “[inaudible][When you start a rocket engine, a thousand things could happen, and only one of those is good]”, and by having sequencing correctly, you can get rid of about 900 of those bad things, we made these engine very reliable, got rid of a lot of mass, and got rid of a lot of costs. And it was the right thing to do.

And now we have the lowest-cost, most reliable engines in the world. And it was basically because of that decision, to go to do that. So that’s one of the examples of Elon just really pushing— he always says we need to push to the limits of physics. Like, an example I’ll give is, on the car factory; you know, a car moves through a typical factory, like a Toyota or a Chevy factory; a car is moving at you know, inches per second. It’s like, much less than walking speed. And his thoughts are that the machinery, the robots that are building the car should move as fast as they can. They should be moving so fast you can’t see them. That’s why you can’t have people in there, because they’d get crushed; people move too slow. That’s the way he thinks. “So, what are the physical limits of how fast you can make a car?” He looks at videos of like, coke cans being made, and things like that, where you can’t even see them; it’s just a blur. And, you know, the puck of aluminum, cut it up, deep-draw, fill it with coke, you put the lid on, you put the lid on it; it’s just like going down the assembly line so fast you can’t even see it. And Elon wants to do that with cars.

That’s just the way he thinks. Nobody else thinks that way. And that’s why he’s going to kill the industry; cars also. Because it’s just going to make these cars— basically, you can make, you know, ten times as many cars in the same size factory if you do it that way. And that’s, you know, the major cost of the car is not the material in the car; it’s the factory that builds the car. So that’s the way he thinks. He looks at it from first principles, like “Why does a car cost so much to make?” Well, you’ve got this gigantic piece of real estate, and all these employees in this gigantic building; and you can only make so many cars in this building. You need to make more cars in the same building with the same number of people. And that’s what they’re working on at Tesla.

So it’s pretty trippy working for Elon— [laughter] really, really stressful, but really rewarding too. I’m proud of what we’ve achieved; I’ve always felt like we’re way behind schedule and way under-performing because we never got it in time, or never as good as, uh, physically possible. But it was way better than anybody else could do it, and way faster than anybody else could do it. So we’re really proud of that.

Fantastic.

I wouldn’t want to have Elon as a father. I think he’d never [laughter from crowd] [laughter from Mueller]

Do you guys have a question? [asking the room]

I have a long one.

Here’s another question from [name redacted]: a common misconception about early rocket science is that people didn’t understand Newton’s third law of motion and thought that the rocket fuel needed something to push against. Therefore, nothing could travel through the vacuum of space. Is this still a common misconception, and are there any other common misconceptions like that that you try and educate the public on?

Yes. [laughter] But it’s funny; we’re in the era of disinformation. You can find all kinds of people that think the earth is flat. And nothing you can tell them will convince them that it’s not. And it’s those people that you just don’t want to waste your time with them. But I’ve seen people say, like I’ve seen Quora answers that, they’re still saying that rocket engines can work in space when it’s clearly impossible because they have nothing to push against. Which is just, uh, it’s just so easily provable [laughs] it’s… you know, it’s ridiculous. But think of it this way: this is the way I always explain it to people. If you’re sitting in a wagon with a bunch of bricks, and you pick up a brick and throw it out the back of the wagon, you know, it’ll move you. Right? You can move yourself by throwing bricks out of the wagon. So you’re not pushing against anything; you’re pushing against the brick. That’s what the rocket engine is doing.

I’ll give you an example. The Merlin engine, the current version of the rocket engine, basically throws 800 pounds per second of bricks out the back at about, uh, ten thousand five hundred feet per second. So if you’re throwing eight hundred pounds of bricks at Mach 10 out of the back of your wagon, you’re going to get a lot of thrust out of it. That’s how a rocket engine works.

And the way that you move that mass is you, is you convert pressure into velocity. And the way you convert pressure into velocity is with a nozzle. The more pressure ratio you can have, which is the bigger nozzle you can have, the more velocity you can get out. So when you’re in the vacuum of space, you can basically have a smuch nozzle as you want, because you have infinite pressure ratio. You’re only limited by the size of the nozzle you can put on the rocket.

So once you’re in space, you can expand that gas to a higher pressure ratio, to get more velocity, so you’re moving your bricks faster, basically. So it’s actually quite simple to explain how a rocket engine work, but people still think you have to push on air or something, but you really don’t. There’s just no air in the way.

Okay, here’s a fun question from [name redacted]. S/he’s wondering where you get your methane from.

So, on Earth, you get it from high-purity wells; there are some in Texas and various states have high-purity natural gas wells. And then you actually; we subcool the methane so it actually will tend to drop out when you do that. The higher carbon compounds drop out, so you want to get rid of the propanes and butanes and just run pure methane. And there’s ways to purify it.

On Mars, it’s actually quite easy to make. All you need is water and CO2. So you gotta find the ice on Mars, and there’s lots of ice— subsurface ice— on Mars. There’s glaciers that, as far as they can tell, are several km thick. And you know, tens of kilometers long and wide. So if you’d land at one of those sites, you would have enough water to last a giant city for hundreds of years. And then Mars’ atmosphere. Even though it’s very thin, it’s about 95% CO2. So you use multi-stage compression pumps to pump the Mars atmosphere up to something you can work with, like say, you know, three to five atmospheres. You know, three to five bar. And you take the water and you electrolyze it. You basically un-burn it. Water is the combustion product of hydrogen-oxygen combustion. So it takes a lot of energy to basically un-burn it. It’s called electrolysis. So about half of the— a little bit more than half the energy you need to make propellant is decomposing the water back into hydrogen and oxygen gas. Then there’s a lot of energy to liquefy it; there’s some to compress the Mars atmosphere; but most of it is to un-burn the hydrogen and oxygen.

So now you have oxygen gas, very pure, and hydrogen gas, very pure. The oxygen you liquefy and store in a tank; the hydrogen, you react with, um, the CO2 gas over a catalyst. And actually, it’s exothermic; you actually get energy out. And you form methane and more water. So the water goes back to electrolysis, and that hydrogen goes back into the methane reaction. And you take the oxygen and liquefy it.

And if you do that, the stoichiometry of water and CO2 comes out at a mixture ratio of oxygen to fuel of about four to one. So for every pound of methane, you get four pounds of oxygen. Which is perfect, because the rocket engine runs at 3.6. Three and a half, or 3.6. So you have excess oxygen which people can breathe, and the rest is used as propellant. So it works out quite nicely, to make the propellant on Mars. It takes a lot of energy. If you try to do it with solar; it’s extremely difficult, but doable. To get one ship back, you need about eight football fields worth of solar cells on Mars. And you have to keep the dust off them. Um; so that’s tricky. It’s much better to use nuclear, fission reactor, it gets, you know, more compact; you actually get more; you get more power out per pound of reactor than you do out of solar cells, so it’s more mass-efficient. So if you’re taking it to Mars, it’s more efficient to ship reactors than it is to ship solar; it’s just that nobody’s really developed a space reactor yet. We’re working with NASA on that, and hopefully they’ll get funding to develop that. They’ve got a program called kilopower going that’s like, ten thousand watts, a 10 kilowatt reactor. We need a megawatt, but you know, you need to start somewhere.

Eventually, the right way to have power on Mars is fission, but initially, it’ll probably be solar. But in order to get the rockets back, we need a lot of power there to make propellant.

Here’s another fun question: does SpaceX have any protocols in place in case of signs of previous life are found on Mars?

[laughter]

Sorry, I didn’t quite get that.

Does SpaceX have any protocols in place in case of signs of previous life are found on Mars?

Oh! [laughs] Um… well, NASA has protocols… [laughter from crowd] which we’re following, initially. [laughs] Yeah, we want to go there and explore and, uh, find the signs of life. You know, it’s very possible that there is life there; you know, probably microbes in the dirt; and there was probably a lot more when Mars was wet. So there’d probably be signs of previous life. Um… I think Robert Zubrin explained it quite well, how overblown this “not mixing up the biologies” is, when you know, one of these anthrax poisoning cases happens, they can find out which lab the anthrax came from by looking at the genes. So if you’re trying to tell Earth life from Martian life, you look at the genes and it’s going to be very easy to determine that. So it’s— I think it’s way overblown; but we want to do exploration first, before we do colonization, and at that time, humans there are going to have a much, much better chance of digging up and finding where the life is. You know, if it exists there— did exist— I think the best way to do it is to put humans there.

In the meantime, they should be sending more robotic missions there. I think that, you know, they should be doing ten times as many robotic missions as they’re doing. And doing, you know, way more focused on trying to find life. Because I think that’s a huge, really important [question] to answer. And I’m all for going to Enceladus and finding life on those oceans; it looks like, you know, these ocean planets or ocean moons can support life. We need to go find out, you know. It’s probably very; it’d be much easier to do that remotely— robotically, to go to, you know, these moons; Jupiter or the moons of Saturn, to look for life. SO we need to send missions to do that.

So this is going to be our final question—

Okay.

Where is it… oh, I lost it. Wait, hold on—

Many of us look up to you as a role model. Who do you find inspirational?

“Who do I find inspirational?” Hmm. Elon, of course. [laughter from crowd] He’s a huge influence on me. When I left TRW, I thought, “If we fail”— which at the time I thought was a high probability because nobody had done this— “I’ll just go back to TRW.” So I didn’t burn any bridges. But once I saw how he thought and how he operated and— I became an entrepreneur. He influenced me so much, you know, there was no way I could go back to working for a big, bureaucratic company like Northrop Grumman. So it was quite profound. And the way that I deal with life, I think much differently now, just because of the Elon influence. And I, uh, you know, I live a lot bigger. I make bolder decisions, I take higher risks, and, you know, I’m not this conservative TRW engineer that I was that I was when I first met Elon. I’m an entrepreneur. So Elon’s probably my biggest influence, for sure.

Very nice. Well, all of us are so excited that you called and we just want to say— give a huge thank you— [audience clapping]

Thank you! I’m always glad to talk with fans; you know, as you know, I’m a member of the LA astronomy society. I’m hugely into astronomy. I always was, as a kid… I think I have one of these minds— well, nobody can really fathom how big space is, but I’m one of the people— who can fathom how unfathomable space is. And one of the things that always— that I always thought about— is every planet and every moon that we went to in this solar system was like a wow factor. There’s just so much there; like Pluto, recently; there’s so much more there than anybody ever thought. Just imagine what’s out in the universe, in other star systems; you know, other galaxies. You can’t imagine; it’s just incredible. And it pains me that we’re [inaudible; confined?] to Earth, and I’m trying to fix that as fast as I can.

In the meantime, we have nice pictures to look at, of space.

All right, thank you so much.

Thank you!

Let’s all give one giant round of applause.

Again? [laughter]

[crowd applauds]

Thank you very much, and good luck to all of you.

And good luck on your future launches, and getting everyone to Mars.

Thank you so much! I really appreciate it.

Thank you, and take care! Signing off.

See you!

Bye.

Bye!