Lex Fridman Podcast
#356 – Tim Dodd: SpaceX, Starship, Rocket Engines, and Future of Space Travel
02 Feb 2023
Tim Dodd is host of the Everyday Astronaut YouTube channel, where he teaches about rocket engines and all things space travel. Please support this podcast by checking out our sponsors: - BetterHelp: https://betterhelp.com/lex to get 10% off - MasterClass: https://masterclass.com/lex to get 15% off - Shopify: https://shopify.com/lex to get free trial - ExpressVPN: https://expressvpn.com/lexpod to get 3 months free EPISODE LINKS: Tim's YouTube: https://youtube.com/@EverydayAstronaut Tim's Twitter: https://twitter.com/Erdayastronaut Tim's Instagram: https://instagram.com/everydayastronaut Tim's Website: https://everydayastronaut.com PODCAST INFO: Podcast website: https://lexfridman.com/podcast Apple Podcasts: https://apple.co/2lwqZIr Spotify: https://spoti.fi/2nEwCF8 RSS: https://lexfridman.com/feed/podcast/ YouTube Full Episodes: https://youtube.com/lexfridman YouTube Clips: https://youtube.com/lexclips SUPPORT & CONNECT: - Check out the sponsors above, it's the best way to support this podcast - Support on Patreon: https://www.patreon.com/lexfridman - Twitter: https://twitter.com/lexfridman - Instagram: https://www.instagram.com/lexfridman - LinkedIn: https://www.linkedin.com/in/lexfridman - Facebook: https://www.facebook.com/lexfridman - Medium: https://medium.com/@lexfridman OUTLINE: Here's the timestamps for the episode. On some podcast players you should be able to click the timestamp to jump to that time. (00:00) - Introduction (06:18) - SpaceX rockets (26:56) - Falcon 9 (31:08) - Starship (35:27) - SpaceX rocket engines (43:05) - Elon Musk (58:41) - Twitter (1:04:46) - How rocket engines work (1:09:37) - Rocket fuel (1:13:03) - Rocket engine cycles (1:25:27) - Rocket cooling (1:40:24) - Multistage rockets (1:43:57) - Single-stage-to-orbit (1:49:33) - Aerospike engine (1:57:18) - Greatest car engine of all time (2:02:27) - Starship (2:05:19) - Wet dress rehearsal (2:11:29) - Landing (2:25:47) - Seeing starship in person (2:34:54) - Starship orbital test (2:41:32) - Gwynne Shotwell (2:46:43) - dearMoon project (3:05:46) - Fear of death (3:14:12) - Everyday Astronaut origin story (3:40:04) - Soviet Rocket Engine History (3:58:51) - Russia, China, USA (4:13:20) - Starlink (4:21:06) - First human on Mars (4:24:04) - Moon landing (4:30:11) - Nuclear propulsion (4:37:51) - Bob Lazar (4:44:54) - Aliens (4:48:42) - Sci-fi books (4:52:00) - Long-term space travel (4:58:47) - SpaceX competitors (5:10:07) - Kerbal Space Program (5:16:33) - Advice for young people
Chapter 1: What is discussed at the start of this section?
The following is a conversation with Tim Dodd, host of the Everyday Astronaut YouTube channel, where he educates and inspires all of us with detailed but accessible explanations of rocket engines and all things space travel. And now a quick few second mention of each sponsor. Check them out in the description. It's the best way to support this podcast.
We've got BetterHelp for mental health, Masterclass for online learning, Shopify for e-commerce, and ExpressVPN for privacy and security. Choose wisely, my friends. Also, if you want to work with our team, we're always hiring. Go to lexfriedman.com slash hiring. And now onto the full ad reads. As always, no ads in the middle.
I try to make this interesting, but if you skip them, please still check out our sponsors. I enjoy their stuff. Maybe you will too. This episode is brought to you by BetterHelp, spelled H-E-L-P, help. There's quite a few conversations coming up, including with Paul Conti. that really delve into the human mind. The complexities of the human mind formed through
whatever happens to us when we're young in our childhood, the difficult stuff, the good stuff, everything, the whole shebang. And some of that is trauma. And I think the shadow that trauma leaves in the human psyche is significant and deserves to be lit up and ought to be explored, I think.
And talk therapy, sort of talking through it, bringing it to the surface, I think is one of the best, or definitely one of the really effective ways to begin the healing process and to take it to completion. That's something we talk about with Paul, it's something we talk about with Karl Deisseroth, and just in a lot of incredible conversations with Paul.
psychotherapists or psychiatrists and so on. And I think one of the big things is the first step for that kind of process. And so it should be as easy as possible. And that's what BetterHelp does. It's easy, it's private, it's affordable and available anywhere. Check them out at betterhelp.com slash Lex and save on your first month. This show is also brought to you by Masterclass.
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Chapter 2: How did SpaceX's Falcon 1 and Falcon 9 evolve?
booster leader. They're also recovering the fairings, so the nose cone of the rockets are frequently, if not every time, being recovered. Same with the booster for the most part. And the only thing being expended is the upper stage, and that's kind of where the Falcon 9 is ending. It really doesn't make sense to develop that infrastructure any longer.
So they went with the next step, which is go even bigger.
physically so they have more margin for upper stage reusability and that's what we see with starship and super heavy so the super heavy booster uh the whole system is confusing the whole system is kind of considered starship but it technically the starship is just the upper stage which is also like the spaceship which is also the upper stage and then the booster itself is considered the super heavy booster
And that's what they've been working on. Publicly, it came out in 2016 as the, at the time it was the ITS, the Interplanetary Transportation System. Later, and I think about 20, by the end of that year, 2017, it kind of became known as the BFR, the big Falcon rocket. Yeah. And then I think it was about end of 2018, they started calling it Starship. But that is the, that is where we're at today.
And that's what they're working full steam ahead on.
Yeah.
And what about Dragon? We mentioned Dragon, Crew Dragon, Cargo Dragon.
Yeah. So they went from the cargo version of Dragon that flew about 20 times successfully to the International Space Station, except for that one CRS-7 where the rocket blew up in the capsule. Obviously, they didn't make it to the ISS.
um then they went into the dragon true dragon 2 which has two variants it has a crew variant so we just call it crew dragon and then there's the cargo version of of dragon 2. um and that's just an updated sleeker sexier version of dragon and it's ironically it's heavier altogether so it uh you'll never see those those cool return to launch site landing the boosters coming back to land for crs missions anymore like we used to but they landed on the drone ship anyway and um
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Chapter 3: What are the challenges of achieving single-stage to orbit rockets?
So a lot of the things that SpaceX is doing isn't a novel concept per se. Like for instance, the Raptor engine utilizes the full flow stage combustion cycle engine. And that was already developed by the Soviets in the 60s for an engine called the RD-270. And it makes sense. Like on paper, 100%, it makes sense because you're basically extracting the absolute maximum
potential of the chemical energy in both propellants. And at the end of the day, you have to be dumb enough to say we're going to try using this thing because it's actually really complicated to do what they're doing. But at the same time, so are rockets. Rocket engines are already stupid complicated. So adding 10, 20% more
you know, pain in the butt during the R and D if it's, you know, in the long, long, long 20, 30 year existence or whatever, you know, like future of that engine, is that going to be worth it? Obviously SpaceX said, yeah, I think we can actually develop this, this Raptor engine.
So it's, it's just interesting to see the things that have been looked at or even reusability, you know, like the space shuttle was reusable. It was fully, the upper stage, you know, the shuttle itself, the orbiter was, you know, I mean, that thing was, for all intents and purposes, a reusable rocket. Now, did it live up to its expectations? Not necessarily.
So it left a lot of bad taste in people's mouth on the ideas of reusability. So for SpaceX to kind of come back into the room and on the table and say, we're going to use a reusable rocket. Specifically, we're going to do a fully reusable rocket. You know, a lot of people are, even still today, a lot of people are going, yeah, you're not going to be able to do that.
Even today. Even today? So long term, you're not going to be able to reuse at scale.
Yeah. But definitely, I think the number of people that are saying that today is a small portion of those that were saying that type of thing five years ago. When Elon did that announcement in 2016 for the ITS, it was very, very aspirational. And people were just like, yeah, right. And there was a large number of people that had the... factual reasons to think that and do that.
You know, at the time they'd only landed like two rockets or something, you know, when they did that, or maybe three, it was a very small number. When they announced that actually they had just lost a couple of months prior, they just lost a most six.
So they like, there was still this young blossoming company and to come in and be like, we figured out reusability and now we're going to go full scale and make the world's biggest, most heaviest, most powerful rocket ever. And we're going to fully reuse it. And it's going to go to Mars. It was just,
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Chapter 4: What are aerospike engines and how do they work?
Like it, it's the business case is going to send you in one direction pretty quickly.
So you mentioned aerospike engines. I think the internet informed me of your love affair with aerospike engines. Find somebody that looks at you the way Tim Nott looks at aerospike engines. Can you explain what these are? How do they work? What's beautiful to them? How practical are they? Why don't we use them? Oh, my God.
Chapter 5: Why are aerospike engines not widely used in rockets?
Does it just boil down to the design of the nozzle? So maybe can you explain how is it possible to achieve this thing for an engine to be as efficient in a vacuum and sea level and all different conditions?
You know what I love about this is that every question you've asked me is like a one-hour video on my YouTube channel. I was like, now boil it down to 45 seconds. So the aerospike engine basically is an inside-out engine, more or less. So with a traditional engine, we've talked about the combustion chamber and the throat, and then it expands out into the nozzle.
Those walls are containing the pressure, right? Aerospike is the opposite. It's basically the pressure of the engine is on the outside of it, and it's pushing inward against a spike. So it's almost like the difference of if you were... Let me think about this.
If you were standing in like a tent or a teepee, right, and you put your arms at the top and you pushed your arms out like into an iron cross or something, you know, you can physically lift the tent just by pushing outwards on the tent walls, right? Well, that would be like a traditional nozzle. Now, an aerospace would be almost like squeezing an ice cube.
You know, if you squeeze an ice cube, you can push in on it and kind of that wedge force will shoot that ice cube. So that's kind of what is happening. We have the high-pressure gases on the outside of the spike squeezing in on that spike, and then it's pushing up against the – because it's equal on both sides against kind of the ramp. It's pushing up against the rocket.
So that's where that force comes in. It's against the nozzle and against the chambers. The hard part with a narrow spike – so the cool – okay, I guess the cool thing about a narrow spike is – That it can operate in space. You can have what's known as a really big expansion ratio. So that's your ratio between the throat, the area of the throat, versus the area of the nozzle exit.
And remember how the bigger the nozzle is, it's continually just converting more and more. It's converting that high energy, hot, high pressure gas into a cooler nozzle. and cooler, lower pressure and faster gas. So each little millimeter along that nozzle is just getting it lower pressure and cooler, but faster.
Now, if you take a big nozzle on earth and you at sea level and you fire it, you can actually get, even though we're going from say 300 bar, the Raptor engine, Our atmosphere at sea level is about one bar.
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Chapter 6: What are the upcoming milestones for Starship testing?
It's pretty much exactly one bar, depending on conditions. But you can actually get a nozzle to get way below one bar of pressure. So every little, you can go from 300 bar in just two meters down to one bar or below one bar. There's actually a limit. You can actually only expand it below, we'll say something like 70%. So you can get down to like 0.7 bar
at nozzle exit before the pressure of the atmosphere is actually squeezing in on that exhaust and tearing it away from the walls of the engine, the walls of the nozzle exit. And what happens is it's kind of unpredictable. You get these pockets, these oscillations, and they'll be so extreme that they'll end up just destroying the nozzle.
So you can't lower, you can't have a bigger expansion ratio than, again, relatively speaking, something like 0.7. Like you can't go below, you can't get that pressure exit too much below ambient air pressure before flow separation can destroy the engine.
So how come this engine can do so well in different pressure conditions?
So because it's inside out, the ambient pressure is pushing the exhaust gas into the wall. Mm-hmm. As opposed to a conventional engine, the ambient air is actually squeezing the exhaust gas away from the walls of the engine. And that squeezing away from is what can be destructive. So since it's kind of inside out, the ambient air is pushing the exhaust gas into the engine walls.
So you can't have flow separation. You won't have flow separation. Now, what happens is so you can have this huge, amazingly efficient vacuum engine that has, we'll say, a 200 to 1 expansion ratio, which is really big. A lot of sea level engines are like 35, 40, 50 to 1 expansion ratios. And then in space, it's common to use like 150, 180, 200 to 1 expansion ratios.
So an aero spike can have something like 200 to 1. It's just that at sea level, it's kind of just getting pushed and it's kind of getting cut off early almost, but it doesn't matter. It's not like destructive. It's just not running at its maximum efficiency.
As it climbs in altitude, as the ambient air gets thinner and thinner and thinner, it just inherently is pushing less and less and less against the walls of that aerospike engine. So it actually continually gets more efficient. at, you know, as it climbs an altitude.
As does the normal engine, but the difference is that you can use that huge expansion ratio at sea level, and you can't use a huge expansion ratio at sea level with a traditional nozzle. Has anyone actually flown an aerospike engine? No aerospike engine to date has ever been flown on an orbital rocket.
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Chapter 7: What challenges did Tim Dodd face in his early YouTube career?
So what was some of the challenges and the struggles in the early days?
Definitely, at first, you're not going to find your own voice. And I know even Jimmy talked to you about that, how your first video is going to suck. You're not going to be yourself. You're going to be nervous. You're not going to know the tone, the pace, the things that are interesting. And actually, originally, I had constraints.
I was really worried about making a short video because I thought there's no way anyone's going to watch a three-minute video and then a seven-minute video. And pretty quickly I realized like YouTube as a whole was kind of changing, but also there's always that historic backbone of like 22 minutes of programming for a 30 minute spot on TV.
Like no one goes over 22 or 44 minutes, you know, if you have the full hour special or whatever, like that is the absolute limit of what a human being can watch, you know, basically it was what I thought. Yeah. And slowly I just kept playing and getting longer and actually more and more in depth into the topics. And instead of getting like pushback, you know, and being like, this is so boring.
I realized as long as it's like, as I was walking people through the whole step, you know, giving them all the context they need, they're happy to get as deep into the weeds as I can get them. And so that just kind of fed the snowball just kept rolling.
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Chapter 8: How does Tim Dodd handle the psychological aspects of content creation?
And I'm like, all right. And, you know, before you know it, I'm making hour long videos. Like an hour long is more or less a normal length on my channel. for a produced video. And they're really, really in depth, but I love like that process of trying to preemptively kind of guess what the questions might be.
And, you know, part of that is like, we do like script read throughs with like our supporters and do like cuts of videos and people, a decent amount of people see it before it goes public. And we get those questions out of the way, you know, we get those people asking the questions. And then I love nothing more than trying to, you know, get all those questions answered by the end of the video.
a question about being a creator on YouTube that could be a challenging psychological aspect to it, which is like you might invest a huge amount of your effort into a thing and it doesn't receive much attention at all. There's something about YouTube and in general social media that makes you feel really crappy about that if you let it, if you really look at the numbers.
It's very, very difficult not to pay attention to that. I mean, that's the reason why I turn off numbers on my interface for stuff that I've created. Because I just see it having a negative effect on your mind. But even then, it still has an effect. I mean, your epic video on... the history of Soviet rockets comes to mind.
And we'll talk about that in a second, but it's called, people should check it out, The Entire Soviet Rocket Engine Family Tree. So that's something you've researched for two years. You put your heart and soul into it. There's a lot of passion. There's a long journey. I think about an hour and a half video. Is there challenges?
How difficult is that to put so much of yourself into a video and it maybe not do so well?
Yeah, that's the struggle for sure, honestly. Especially as we grow, I try to make better and better videos, which means hiring more and more people to do higher-end animations and spend more time editing and shooting and scripting and just... But at the end of the day, it still can't be just losing money. And I have videos that definitely lose a lot of money because I hire 3D artists and stuff.
And I was so certain. The Soviet rocket engine video I thought was just purely going to be a passion project. I honestly was like, if it ever crosses a million, it's a home run.
And does it cross like a couple of million now?
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