Tim DoddHi, it's me, Tim Dodd, the Everyday Astronaut. Welcome to Starbase, Texas. This is where SpaceX is building, testing, and even launching their Mars-bound rocket Starship. Today, I'm gonna take you inside the gates and show you things that have never been shared outside of SpaceX. First of all, we have the ultimate tour guide, Elon Musk, who answers all of my questions and gives us unbelievable insights into the rocket's development. We talked and walked around for over two hours, so I'll be cutting this up into three parts. The first two are at the Starbase factory and the last one is at the launch pad. Each section has a goldmine of valuable information, so make sure you're subscribed, you've got your notifications on, and you've got your notepads ready to jot some notes.
Tim DoddNow heads up, we talk about some pretty advanced concepts and subject matter that can be pretty intimidating on first listen, but don't worry, I've got you covered with lots of informational videos here on my channel. So perhaps if you are new to Starship, or really all of this stuff, consider watching my complete guide to Starship. That'll be a really good overview for you for some of the things that we talk about here in this conversation. And I'll also be linking to some of my other videos that will help out with some of the stuff that we talk about as well.
Tim DoddNow you might notice we mention Soviet rocket engines quite a bit in this conversation. Maybe it's because I was wearing my new Soyuz shirt that you can get at everydayastronaut.com/shop, or perhaps it's because I've been working on a complete history and family tree of Soviet rocket engines for almost two years now. And that video is currently in the works, and it will be out when it's done.
Tim DoddAnd one last thing, this video is broken up into sections and we have links in the description for those sections. We also will occasionally be putting up a little map, courtesy of Ring Watchers on Twitter, that will help you keep your bearings as we're walking around. I think that'll help quite a bit. And we also have an article version of kind of our conversation and some of the key points that we bring up over at everydayastronaut.com. There is a link in the description to that as well. Okay, enough talking, let's go hang out with Elon.
CrewIs it the camera? Probably with the camera, and then somebody else for the camera.
Tim DoddIt's just camera envy at this point. He saw me with this and he's like, listen-
Elon MuskI'll get my camera out.
Tim DoddYeah, you take a video of me.
Elon MuskSo I can take a video of this, of you guys taking the video.
CrewMake sure this is going through there. Just shoot the screen the whole time. I don't want anything else.
Elon MuskAll right, so this is... Okay, so this is, I'm being videoed here. And then the video of the video. This is the video on the video of the video.
CrewGo back there. (laughs)
Tim DoddSo I feel like I got here maybe at about the most exciting peak of insanity.
Elon MuskIt's definitely a very exciting time, 'cause we are in kind of a final push to complete the launch pad system, stage zero, essentially. So we're saying that the launch system, the tower and the chopstick arms to catch the rocket are as complex as either of the stages.
Tim DoddReally?
Elon MuskYeah, absolutely, if not more. We could produce boosters and ships way easier than we could make the launch site. So therefore I'll say it is harder, suddenly, than any single booster or ship.
Tim DoddI think that's one of the things people don't even realize, is the manufacturing out here. That's kind of one of the things that you harp on so much, is how that's so important and that's, in the long scheme, the hardest part of all of this is just manufacturing.
Elon MuskI think currently a factory is underrated and design is overrated. So people generally think that, like, this Eureka moment of, like, you come up with this idea and that's it, now it's good. But the design, like this, literally a thousand percent, maybe 10,000% more work that goes into the production system than the thing itself. So, say like how much effort we put into, say, designing Raptor versus designing the manufacturing system, it's 10 to 100 times more effort to design the manufacturing system than the engine.
Tim DoddEven of a Raptor?
Elon MuskOh yeah, absolutely. Especially with Raptor. Basically the amount of effort that goes into the design rounds down to zero.
Tim DoddRight, right.
Elon MuskRelative to the amount of effort that goes into the manufacturing system. And if this was not true, I'd like 1,000 Raptors please. Oh, you can't make them? Oh, okay.
Tim DoddRight, right.
Elon MuskSo this is just very fundamentally underappreciated. If people have not been in manufacturing, especially manufacturing of something that's relatively new, then they don't understand. And they think the design is the hard part, and they think production is like a copier or something like that. This is completely false.
Tim DoddIt's definitely not as sexy as the end thing. Like, the end product is very sexy and that's what draws people's attention, but the whole back end of it is what makes it possible.
Elon MuskI can't emphasize enough, I'm trying to correct the misperception that design is the hard part. It is not the hard part. There have been lots of great rocket engines designed. You've spent a lot of time looking at the Russian rocket engine designs. There's some amazing Russian rocket engine designs. They've been doing staged combustion for a long time. And they've done, I don't know, hundreds of different designs, literally.
Elon MuskSo the hard part is not, can you design a staged combustion engine? This has been done. Now admittedly, ours is a higher pressure than before, and it is a full-flow staged combustion, but that's a relatively minor increment relative to what the Russians have already done. What is super hard about Raptor is, how do we make a Raptor where the cost per ton of thrust is under a thousand dollars?
Elon MuskYeah, I mean, we definitely don't wanna cut... the fundamental thing that needs to be fixed is the cost per ton to orbit. So things that address the cost per ton to orbit are good. If humanity will be a multi-planet species, if we get cost per ton to orbit to a point where we can afford to become a spacefaring civilization and a multi-planetary species... So this is, at its heart, fundamentally an optimization of cost per ton to orbit, and then ultimately cost per ton to the surface of Mars.
Tim DoddRight.
Tim DoddWell, if you're working on getting the cost of, even when you're starting to think of it as dollars, dollar per ton of thrust, I don't know if anyone's ever considered that as a key metric. That's a new thing that I've never thought about, never considered, well, not even...
Tim DoddRaptor is kind of unique. And now you start also thinking about, instead of thrust-to-weight ratio, when you have a fixed diameter and fixed circle area, you're also worried about the nozzle exit to thrust ratio as being a pretty strong consideration too.
Elon MuskYeah, you basically end up pulling up all the area under the rocket. So for this version, we have 29 engines. There is a lot of beeping. I'm not sure having this many things beep is actually helpful.
Tim DoddIt's a sensory overload.
Elon MuskIt's like everything around you is crying wolf.
Tim DoddIf everything's in danger, nothing is in danger-
Elon MuskAnd you just gotta tune it out. Yeah, exactly. So it's pretty silly, but-
Tim DoddSo this is obviously the nose of Booster 4.
Elon MuskThis is basically, that's the interstage and the fuel tank of Booster 4.
Tim DoddWhat are the little... So obviously that's where the grid fins go, right? And then what's the thing in between them?
Elon MuskThat's basically, that's actually the mount point. There are two. It's debatable whether this is the right design or not. In fact, it's like the whole design is wrong, just a matter of how wrong. But that's one of the load points for picking up the booster.
Elon MuskIt's just like tiny little, it looks small, but it's actually not that small. Like, close up, this thing is just high in the air. Like, all your sense of perspective is wrong. And when this lands, it has like basically the density of a beer can. An empty beer can. With like some mass, you know, with the engine, is obviously-
Tim DoddWhat is the dry mass, are you under 200 tonnes?
Elon MuskWe should be under 200 tonnes. The mass is a moving target. You often say, like, what are propellant residuals when you land? That's a big deal. Like, both how much margin on what you have and what are the unusable propellant. Like you can't just go to zero margin, you know? Because the thing's going to, like, crater. And it should be under 200 tonnes though.
Elon MuskBut as a rough rule of thumb, like the engines, including mount mass, are roughly two tonnes. So that's 29 engines at 58 tonnes. Then the sort of the fuel tank itself, and the oxygen tank, it's probably on the order of... Well, it's a little heavy right now. So maybe it's like 80 tonnes or so. Then you've got the interstage, we've got the grid fins, batteries, and a bunch of other things. So that's around 20 tonnes. And then you got propellant residuals, which might be on the order of 20 tonnes too. All of that should come to, I don't know, call it 160 to 200 tonnes depending on the sort of final mass numbers. But like right now everything is too heavy, like avionics too heavy.
Tim DoddThe avionics even?
Elon MuskYeah.
Tim DoddI thought it was just a little-
Elon MuskI mean, it should be, but the grid fins are electrically powered so we have batteries that are energy optimized instead of power optimized. So like this grid fins only need things to work for like two or three minutes. So it's very different from like an electric car, which you wanna have several hours of driving. So really, we need power-optimized batteries, not energy-optimized batteries. This is just a short-term thing. So the battery mass can probably drop by maybe a factor of 10. So that's just one example.
Tim DoddShould we back up a little bit so there's little-
Elon MuskYeah, less banging. And then we're trying to get that crane in here and do work.
Tim DoddYou got a lot of people on set right now.
Elon MuskYeah, I mean, that residuals number is a super big deal on the mass though, because the booster is designed to have 3,600 tonnes of propellant, which is almost 80% liquid oxygen by mass, like 78%-
Tim Dodd'Cause you burn at what? Is it 3.71-
Elon Musk3.5, 3.7.
Tim DoddOkay, yeah.
Elon MuskAnd you wanna bias in favor of oxygen because oxygen is denser and cheaper. So in terms of improving your payload and reducing cost per ton, oxygen is basically, plants make it for free and plankton. So it's basically like electricity cost of separation and distillation.
Tim DoddRight. Now, remind me though. Is it like, as far as the ratio goes, fuel OF ratio, having a lighter molecule, do we kind of want that to be spewing out faster or something, 'cause it's less reaction? It can be accelerated quicker or faster.
Elon MuskYeah, there's a trade-off between... Well, I mean, what you tend to get limited by is you don't wanna go too close to stoichiometric 'cause the heat basically melts your engine. So that tends to limit you on trying to go to higher OF, that's the actual thing limiting you. You tend to hit the stoichiometric melting point before you roll over on ISP.
Tim DoddOkay, okay.
Elon MuskGenerally.
Tim DoddThat makes sense. And remind me of the grid fins. Do they still fold in?
Elon MuskNo.
Tim DoddNo, is that gonna be permanently that way?
Elon MuskYeah. I have a rule that I implement rigorously, it's the sort of five-step process. First, make your requirements less dumb. Your requirements are definitely dumb. It does not matter who gave them to you. It's particularly dangerous if a smart person gave you the requirements, because you might not question them enough.
Tim DoddYeah, you might take it as like gospel. Like you have to do this.
Elon MuskEveryone's wrong, no matter who you are, everyone's wrong some of the time. So make your requirements less dumb, then try very hard to delete the part or process. This is actually very important. If you're not occasionally adding things back in, you are not deleting enough. The bias tends to be very strongly towards, let's add this part or process step in case we need it. But you can basically make in-case arguments for so many things.
Elon MuskAnd for a rocket that is trying to achieve, trying to be the first fully reusable rocket—there's never been a fully reusable rocket, people don't understand, like this is like the holy grail of rocketry, okay—and so you have to run tight margins, because if you don't run tight margins, you're gonna get nothing to orbit. So you've got to delete the part or process step, it's super important. And you can like hedge your bets.
Elon MuskSo that's why the grid fins, for example, do not fold down, because that's a whole extra mechanism that we don't need.
Tim DoddAnd that's just compensated for by having strong enough engine authority to steer it in the little atmosphere.
Elon MuskActually our simulations show we don't really need any extra engine authority. As long as the grid fins basically follow the flow, they're not really disturbing the flow, it's really neither here nor there. As long as they don't have a high angle of attack, it doesn't matter.
Tim DoddA few degrees or something, within a degree or two.
Elon MuskBut in any case, it's the thing we could add later. So now these grid fins are humongous. We will go see them. But they're like, I mean, like a dinosaur bear trap. It's like you build a bear trap for a dinosaur, that's what these things look like. And if you have a whole mechanism for folding them, that's like clearly a part that we don't need. So this is a good design decision that, actually, I didn't come up with it, and it was like, great. But it followed the principle of like delete the part of the process. I was like, great, good idea, let's not fold them. Why are we folding them, anyway? It's so random.
Elon MuskWhatever requirement or constraint you have, it must come with a name, not a department. 'Cause you can't ask the departments, you have to ask a person, and that person who's putting forward the requirement or constraint must agree that they must take responsibility for that requirement. Otherwise you could have a requirement that basically an intern two years ago randomly came up with, off the cuff, and they're not even at the company anymore. But it came from the, let's say, air loads department. They're like, actually there's no one at our current department that currently agrees with that. This, by the way, has happened several times.
Tim DoddSo again, it could be literally thought of...
Elon MuskThis could be, it's every department.
Tim DoddIt can be thought of as gospel again, but it might be something that's just totally in passing. Or someone played too much Kerbal and had fins at the top of the rocket. And then it just, you know, it did this.
Elon MuskThese things are often just way more silly than you think. Anyway, so step one, make your requirements less dumb. Step two, delete the part or process step. If you're not deleting a part or process step, at least 10% of the time—basically if you're not adding things back in 10% of the time, you're clearly not deleting enough.
Elon MuskAnd then only the third step is simplify or optimize. The reason it's the third step is 'cause it's very common, possibly the most common error of a smart engineer, is to optimize the thing that should not exist. And say, well, why would you do that? Well, everyone has been trained in high school and college that you gotta answer the question, convergent logic. So you can't tell a professor, your question is dumb. You will get a bad grade. You have to answer the question. So everyone is basically, without knowing it, they've got like a mental straitjacket on, that is, they'll work on optimizing the thing that should simply not exist.
Elon MuskI'll give you an example from way back in the day of Falcon 1. So in the original, sort of like, when Tom Mueller and I were like batting around, like, okay, what should this rocket look like? I think I was literally in like Tom's kitchen or something. And we had like the spreadsheet and like, okay, we need to make a minimally viable rocket, like with half a tonne or whatever, something like that. And then initially the spreadsheet had, we had an NTO/MMH upper stage, so sort of hypergol upper stage, kind of like a variant of the TRW LMDE.
Tim DoddWhich I think Tom worked on, right?
Elon MuskWell, we trained... Tom worked on it, he's not that old. It was like a baby, you know. (laughs) A very advanced baby. But his mentors did work on the LMDE. So, you know, lunar module descent engine. Basically a pintle injector-
Tim DoddThat's right, 'cause that's where the pintle injector comes from.
Elon MuskYou can also deep-throttle it and everything. Now the problem with that is, how much this NTO/MMH costs. It's super expensive, okay. It's like a rare chemical. So even if you're like, you know, if Edison and Tesla had a baby and that baby was smarter than both of them combined and said, your job is to optimize an NTO/MMH upper stage, you're screwed, okay? So like nitrogen tetroxide or monomethyl hydrazine are super expensive and they're also toxic.
Tim DoddThey're super nasty, yeah. The handling costs alone are pretty appreciable.
Elon MuskI mean, I do think that safety is over-corrected on the NTO/MMH. It went from like, nobody had any protection and breathed the fumes all day, to it's cyanide. And neither of those are true, it's not cyanide. You won't die. Bill Gerstenmaier told me this story of, like, when he started at NASA, they actually, I think, passed around like a cup of like hydrazine so that everyone knew what hydrazine smelled like.
Tim DoddNooo....
Elon MuskSo, 'cause it has like a lot more rotten egg smell or something like that. So he literally opened a cup of hydrazine and, like, obviously he's still alive. So that's an example of, like, don't optimize the thing that shouldn't exist. We should not have an NTO/MMH upper stage. Now Dragon does have that, but that's because Dragon's got to do a lot of like nuanced firings of the Draco engines, you know, with very short pulse durations.
Elon MuskAnd trying to have something that's not hypergolic is very difficult. It can be done, like, not hypergolic and not cryogenic. Now your options tend to suck. So, you know, they start going down the peroxide, barking up the peroxide tree or something like that. Or super esoteric mono props. And that's, like, again, back to big money.
Tim DoddThat's step three.
Elon MuskYeah, so exactly. Thanks to these quite laborious... sorry for the laborious explanation here... and then finally you get to step four, which is accelerate cycle time. You're moving too slowly, go faster, but don't go faster until you've worked on the other three things first. If you're digging your grave, don't dig it faster, stop digging your grave. But you can always make me go faster. And then the final step is automate.
Elon MuskAnd now, I have personally made the mistake of going backwards on all five steps multiple times. So I have to repeat this.
Tim DoddWell, on Model 3.
Elon MuskYes, multiple times, but on Model 3, where literally I automated, accelerated, simplified, and then deleted. But like, one example I've talked about before is, like, there were these like fiberglass mats on top of the Model 3 battery pack, they were in between the floor pan and the battery. And at one point, stuck in the battery pack production line, I was like, basically living on the battery factory production line, like, probably to fix the line, 'cause it was, like, choking the entire Model 3 production program.
Elon MuskSo the first mistake was we should not have... I, like, tried to fix the automation, like, make the robot better, make it like move faster, shorter path, increase the torque, delete the reverse 720 degrees on the bolt, 'cause that's unnecessary. Just go forward fast at a 100% rate. And instead of spackling glue on the entire battery pack, just put little dabs of glue, because the fiberglass mat was sandwiched between the battery pack and the floor pan anyway. So all you need is, like, somebody to hold it in place until you put the battery pack into the car.
Elon MuskSo automating was a mistake. Then accelerating was a mistake. Then optimizing was a mistake. And finally I said, what the hell are these mats for? And I asked the battery safety team, 'cause I was like, what are these mats for? I said, are they for fire protection or something? They said, "No, they are for noise and vibration, so you don't get that." And I said, "But you're the battery department." And I asked the NVH, noise vibration harshness team, what's it for, they said fire safety. So literally it was like being in a Goldberg cartoon.
Elon MuskIt was like, actually, I feel like I'm in a Goldberg cartoon quite frequently. So I'm like, you know, are we in like some simulation where I'm like trapped in some, like, Kafkaesque / Goldberg cartoon situation? But that's what it feels like a lot. So then finally, okay, great. Let's try a car with the fiberglass mats and without, and they put a microphone in both, and see if you could tell the difference. You cannot. In fact, I was like, which one is which? So we just deleted them and just bypassed this $2 million robot cell as a complete pile of nonsense.
Elon MuskAnother mistake that has to happen in production is too much in-process testing. So when you're first setting up a production line, you don't know where things are breaking. You don't know where things are breaking, so you'll test, like, work-in-process at various steps, 'cause you wanna isolate, where's the mistake occurring? So a very common issue with production lines is to not remove the in-process testing after you diagnose where the problems are.
Elon MuskSo basically, if you have like a very high acceptance, like if things are getting to end-of-line testing and are passing, then you don't need to do in-process testing. But what used to happen is, there'll be, like, an initial development engineering team that will be, like, basically debugging the production line, but then they will forget to take out the in-process testing steps. So then what happens is the in-process tester will often choke the cycle time. Choke the line production time. It'll be like the limiter and also have some number of false positives and false negatives. But they'll be, like, false positive, like then you're, like, rejecting good parts.
Elon MuskSo really, in volume production, if things are working well, you're really just taking a risk: will this subsystem be rejected in the in-process production or at the end? And so you just really wanna move things pretty much almost always to just test at the end of line, and that's it. Maybe there's like one or two in-process steps that are hard to test at end of line, but basically remove almost everything.
Elon MuskAnd there is another thing with the battery pack where this is so crazy. Like, one of the things the battery pack has to do is to resist water ingress, so it has to be leak-proof. So if you drive through deep water, water doesn't come into the battery pack, you short the battery pack. You might have seen some of the videos of, like, people driving Teslas in like extremely flooded waters, where it's like half underwater. Yeah, like there was literally a guy, I believe in Kazakhstan, literally drove a Model S through a submerged water tunnel. All the other cars were out, and he basically steered the car with the wheels and used the wheel rotation like a boat and drove out of the tunnel.
Elon MuskSo it's important to have the battery pack resist water ingress. But then instead of us doing a pressure test on the battery pack, we were actually pressurizing the inside of the battery pack, which was the wrong direction. And the battery pack lid was glued. But, you know, we basically had resin that was not cured. And so we were just blurting out the resin, which doesn't make sense. 'Cause you should actually be drawing your vacuum on the front of the pack and not pressurizing it. And especially not pressurizing it when there's uncured resin that's what's holding down the battery pack. So the pack was failing quite often on the pressurization tests, which should have been a vacuum test.
Tim DoddOh, speaking of grid fins.
Elon MuskYeah, great.
Tim DoddLook at that. Man, that thing is huge.
Elon MuskYeah, that's right, so it's like a-
Tim DoddDinosaur bear trap?
Elon MuskDinosaur bear trap.
Tim DoddOh wait, that's just a dinosaur trap, wouldn't it?
Elon MuskThis is a dinosaur trap.
Tim DoddThat's insane, honestly.
Elon MuskThis thing could catch a T-Rex. (laughs)
Tim DoddOh my gosh, that's crazy. And of course it's got the serrated teeth, which help in the transonic regimes, right? Is there any other reason for the teeth other than that?
Elon MuskNo, it's just... well, it actually helps in transonic and subsonic, but the effectiveness is better if you've got a pointy... if it's more pointy basically. There is a lot of pointiness. Sorry, hey Marvin. So he just gets crushed under a...
Tim DoddWow, so how heavy are these guys?
Elon MuskThese are, I like... actually I don't know the number offhand, but probably at least three tonnes, I'm guessing. When I say it's like a moving target, this is not the... like, I wouldn't take this to the bank. Like, it's not, you know... There's quite a lot of mass we can get out of this.
Tim DoddIt's just good enough for now. Like, that's-
Elon MuskYeah, it's good enough now. But like, you know, we're basically... it just needs to be like enough control authority to get this through the atmosphere and positioned well enough so that when the engines light, the engine can correct whatever error is left after that, that we couldn't take out with the grid fins.
Tim DoddMan, that is crazy. Those are huge. It looks like the motor will mount to the lever arm there, is that just...
Elon MuskSo this is, yeah... This will react onto the dome, basically a fuel dome. So there's like kind of like a C-channel around the fuel dome at the top. And there's a motor that's gonna rotate this with a gearbox, and that's basically... the load will be reacted between the circular feature that you see there. And the sort of... I shouldn't say C-channel, sort of an L-channel on the dome. So it's just a simple sort of ring on the dome.
Tim DoddAnd then, so what I'm seeing there, where there's the rope, is actually a through-hole on the end here, is that the lever arm for the thing? Or is that just...
Elon MuskYeah.
Tim DoddAhh, I see, it slides over, it's like...
Elon MuskYeah.
Tim DoddOkay.
Elon MuskThat's where the motor will interact, so yeah. But it's just basically, it's using like Model 3 motors basically.
Tim DoddYeah, which is so cool.
Elon MuskYeah, might as well use it.
Tim DoddSo you mentioned, you know, really trying to simplify it. There's been talks that they're not... Did you say it on Twitter that you're gonna eliminate the cold gas thrusters or hot gas thrusters on the B4, for the first orbital test?
Elon MuskYeah, well, we can move to like maybe a quieter location. I'm pretty sure we can cut the weight of that in half. Like that's, you know, we're not even really trying to optimize the gauge. That's just basically plate. That's just like cut plates welded together. First just got to, like, make that thing work and then we'll optimize it.
Tim DoddYeah, of course. Which again is some of what the Soviet Union was so good at. It was like minimum viable product basically, get it good enough to fly and test it. And obviously you guys did that with Starship, big time, with 8, 9, 10, 11, 15, it was like, let's just get it out there, see what works, see what doesn't, and iterate, you know?
Elon MuskYeah, and if you look at, like, the various reasons, like, why we blew up Starship, and you looked at the risk list, none of the reasons that blew up are on the risk list.
Tim DoddReally?
Elon MuskYeah, it was like, no... maybe you can argue, like, one of them maybe was on somebody's risk list, but it wasn't brought up beforehand, if you can put it that way. I mean, there's a crazy amount of new technology happening here and it's all evolving simultaneously, we need to iron out, like, the unknowns sort of thing. Yeah, the unknowns are the big ones.
Tim DoddIs that the new flaps for 20 down there?
Elon MuskYeah.
Tim DoddSo remind me the numbering scheme. 'Cause you were talking about version two Raptor the other day. What we've seen so far, are those original version two yet, like the green nozzles, those aren't version two yet, right? Have you started making version two?
Elon MuskWe've made parts of version two. So we've made the thrust chamber assembly. And we have, I think, pretty much finished the design of the pumps, we're gonna make the pumps. So hopefully we'll have, either Raptor 2... in about a month we might be testing the first one.
Tim DoddOkay, and will that be... you said you're going to be kind of producing stuff, or the prototypes are kind of gonna be always in Hawthorne, that eventually you're gonna be moving mass production to McGregor.
Elon MuskYeah, we're doing volume production of Raptor at McGregor. We will keep the California factory operating basically for development engines and the Raptor vacuum version.
Tim DoddSo if you're reaching 230 tonne on version two, what's that gonna be at, like 330 bar?
Elon MuskWell technically, I think 298, but I think we should, come on, we've got like get two more bar out of that thing.
Tim DoddWait, wait, so even only 300, big air quotes on 300, you're getting to 230 already?
Elon MuskYeah, but then we're opening the throats and reducing the area ratio. The extra thrust is like... there's a slight... I think we lose two or three seconds of ISP, but we gain a lot more in thrust. And the increase in thrust outweighs the slight drop in ISP.
Tim DoddYeah, especially on the first stage, yeah.
Elon MuskI mean, basically any thrust-to-weight below one is worthless.
Tim DoddIt's worthless, yeah. So if we go from .4 to .5, it's a massive leap compared to even...
Elon MuskYeah, yeah.
Tim DoddOkay, so that makes total sense. So the RVac currently, what's that for thrust? Is it still around that same number, about 200 tons?
Elon MuskThe Raptor vacuum, or RVac as we put it... we will actually be... the 230 ton gross number is the thrust at sea level of the sea-level version of version two of the... It's essentially... it's helpful to, certainly like, quibble about, like, why are you talking about thrust in tonnes? That's not technically a scientific thing. It's because you can do the math in your head really easily if you have a rocket in tonnes and thrust in tonnes.
Tim DoddRight, of course.
Elon MuskThat's why. And Newtons have got, like, divide by 10 all the time, which is, like, annoying. And then you only get kilograms, now you've got to, like, divide by 10,000 to get tons, which is ridiculous. Okay, so you're like, this is absurd. Only a fool would use Newtons, in my opinion, if you're designing a rocket. And especially big rockets, 'cause you just, like, have a zillion Newtons. But if you measure things in tons and you measure thrust in tons, now you know thrust-to-weight very easily.
Tim DoddIs that like the only Imperial thing you measure then?
Elon MuskNo, these are still metric tonnes.
Tim DoddOkay, that makes sense. I was getting nervous for a second.
Elon MuskThe pressure is in bar, 'cause everybody kinda knows, like, what's one atmosphere. So... but Pascal's another trash unit. I hate Pascals. That's why, it's so tiny, it's absurd.
Tim DoddWe did have a whole segment of units that Elon hates and it's just... (laughs)
Elon MuskIt's like units that make understanding things more hard instead of easier. But everyone understands, like, a bar or an atmosphere essentially. And everyone, like, crew, can get their mind around a tonne. Like you have an intuitive sense for a ton. Like your car is like two tons.
Tim DoddYou have some grasp, you have some context.
Elon MuskYeah, if you got hit by a tonne, you'd know what that meant. If you got hit by a Pascal, that's like, I dunno, a mouse fart. (laughs) That's like one Pascal.
Elon MuskThere's another important principle, which is that you really want everyone to be chief engineer. So if everyone is chief engineer, that means that people need to understand the system at a high level to know when they are making a bad optimization. It's like... because we've done this many times where we've, like, put immense effort into reducing the engine mass, but hardly any effort into reducing propellant residuals, or like an order of magnitude less effort into reducing propellant residuals. And then you land with a literal ton of unused fuel.
Elon MuskAnd actually we still kind of do that with Falcon 9. It has about a tonne of unused fuel upon landing, which is pretty annoying.
Tim DoddOh, that's still not much in the grand scheme of everything. It's still not much, but that is in context. So it still is quite a bit though.
Elon MuskYeah, but like we spend so much effort getting a ton out of engines, like, you know, that sort of whatever, like 130 kilograms per engine, like that's, yeah... So that's like 120-ish.
Tim DoddWow, look, the sunsets out here are pretty hard to beat. That's insane. God, that's amazing. So congrats on the HLS, solidified a little more today.
Elon MuskThat was cool. The GAO was a staunch defender of good contracting.
Tim DoddCan we head over and check out the mock-up there? Because there's still a lot that we don't know about HLS publicly, at least. I assume that, you know, you know a decent amount more.
Elon MuskI don't know if I do, but...
Tim DoddWell, first off, I guess the most obvious one that I'm excited about is those thrusters.
Elon MuskSo the thrusters are a good example of running that algorithm I just mentioned, laboriously mentioned, which is, question the requirements, making requirements... delete the part. When we're looking at, what does the booster actually need to do with stage separation? If you put rotation into the stack, like, before you turn off the main engines, so they're both rotating, they're gonna rotate and just-
Tim DoddWait, sorry. Like pitching and yawing or rolling?
Elon MuskSo like you got the integrated stack. We do this with...
Tim DoddWith Starlink!
Elon MuskWith Starlink. So we rotate the stage and-
Tim DoddAnd kind of fling it out.
Elon MuskYes, but they basically have different amounts of inertia, essentially rotational versus linear inertia. They basically move at different rates. So if you rotate the thing, depending on where you are, you will move at a different speed. And so it automatically separates if you rotate and then separate. So there's no actual separation mechanism for the Starlink satellites and they technically can bump into each other and occasionally do, but if they bump into each other for, like, one mile an hour, doesn't matter. So they bounce off.
Tim DoddIt's already made it through the pretty harsh environments of launch.
Elon MuskYeah, it's fine. But like, I'm pretty sure this is like... this might be the only ride... we were like literally tossing 60 satellites off with like a, hey, bundle of hay, like dry, you know? Dumping the rods that hold them down. Like a hay bale and just flinging them. And it's fine, then they just separate, split up and go to their position.
Elon MuskSo we've got the stage step, instead of asking the attitude control thrusters, the reaction control thrusters, to do the booster rotation, which has a lot of force, you have the main engines initiate rotation. Now this is quite a complex space ballet, 'cause everything's got to happen in just the right way. But you basically initiate the rotation of the stack, kind of stop the main engines, then the two will actually separate by themselves.
Elon MuskAnd you need like a little bit... we have like cold gas ACS, or reaction control system. It's like, depending on who you ask, it's a reaction control system, or an attitude control system. So it's basically like small maneuvering thrusters. So you fire those on the ship, that gives you a little bit of maneuvering. And then on the booster, we actually have quite a lot of ullage gas, like basically you've got a lot of hot gaseous oxygen and hot methane, which actually have, you know, if you've got a big enough area, it's got decent thrust in vacuum.
Tim DoddThe actual-
Elon MuskThe vents. But literally you use the vents to vent the stage.
Tim DoddYeah, so not in a separate bottle, but literally like the ullage of the main tanks.
Elon MuskYes.
Tim DoddOkay.
Elon MuskSo just use the ullage as your thrusters and just control the orientation of the venting. So it is not just venting out sideways, but it is venting in a direction that will just work. Which can be sideways sometimes. Anyway, we've got like basically a lot of gas in this thing, which would have to actually just vent to vacuum anyway, 'cause it's got too much gas. And that's just extra mass that you don't need.
Elon MuskSo if you've got basically enough control authority because of the kicking the whole stack over before main engine cutoff, plus using the ullage gas to vent, you don't need a separate hot gas thruster system. You don't even need a cold gas thruster system. You already have hot gas. Question the requirements, delete the part.
Tim DoddBut this is only for the booster, right?
Elon MuskYes. Although arguably, now you mentioned it, it might be wise to do this for the ship too. At least mostly, well-
Tim DoddBecause the tanks are what, six or eight bar or something? The main tanks?
Elon MuskYeah, there'll be like six-ish bar.
Tim DoddAnd so one of those would be pretty low pressure, low ISP gas thrusters. If you're only doing the gas from there, or is there some trick you can do to...
Elon MuskIn vacuum, like, it's this different in atmosphere. Like six bar in vacuum is actually decent. It's like common to have thrusters in space, thrusters that are, let's say, eight bar, like the Draco thrusters that maneuver Dragon are operating around a chamber pressure of around eight or nine bar.
Tim DoddWhat?
Elon MuskYeah. Like Dragon is still in PSI. So it's like 120, 130 PSI. Technically it's a pressure pulse, but you know, so 120 PSI is like roughly eight bar-ish, maybe eight and a half bar. So it's not that far from the tank pressure.
Tim DoddRight. So you don't even need to store the gas in an even higher, like in a bottle that's like 200 bar or something. You don't even need to do that to operate RCS.
Elon MuskNo, if you've got hot gas... first of all, it's like, we really want the ullage gas to be as hot as possible, up to the point where it is impacting the strength of the hull. Like we don't wanna soften the metal so much that it pops basically. So the hotter the gas is, the higher the ISP. So having hot gas is good, and it's already there, and you already have the pressure vessel, and you're gonna choke it away anyway. So obviously you just use it for attitude control.
Elon MuskSo like, obviously... initially you can't do this with the ship because everything's cryo, but once the ship is mostly empty and you drive to orbit, it also is in the same situation with a lot of hot gas. So actually, we should really... the vast majority of our maneuvering should be with the hot gas that's in the ship. Thanks, now we are gonna fix that.
Tim DoddSo the thrusters on HLS that are gonna be around the ring, the renders showed like 24 or something of like-
Elon MuskThose are different. That's for landing on the moon.
Tim DoddOkay, yeah, yeah. Are those pressure fed? Like, what are those? Do you have a name for them yet or anything?
Elon MuskLet's just say, like, this is the tentative design right now. But with the agreement with NASA, I think we may see that design evolve, and it may be better actually.
Elon MuskLike, a big question here is, like, can you land on the moon with the main engines, or do you need a separate thruster system that's way up there? Like basically, if you land with the main engine, you're gonna dig a big ditch in the moon and then fall over, 'cause you landed in a ditch that you dug. It's like, literally, dig your own grave. That would be obviously bad. So we don't wanna dig our own grave and then fall in it.
Elon MuskBut, more analysis... like, I think we could probably land with the main engine and not dig a grave and die in it, but we would have to prove that, you know, get something that's like, I don't know, the consistency of like lunar regolith and, like, something that's like a good-
Tim DoddA good analog.
Elon MuskAnalog of that, and then like, land the ship in that and see how big is the hole that we're digging. If you've got low pressure engines that have high up naturally, you're not gonna dig a hole basically. So that's kind of like the sure thing. But I think if we can prove that the main engines do not dig a giant hole, then we can land with the main engines and then not have-
Tim DoddAny of those, the ring. What about the... are you gonna have any sea-level Raptors on the lunar variant or are you only gonna have vacuum optimized? Because I assume, like, on a normal Starship, even at stage separation, you'll probably light all six at first, just to minimize gravity loss or something, right? So you'll still fire all six, then probably shut down the sea levels and let the vac ones optimize, you know, like they probably do, what, like half the second stage burn time or something with sea level? Or do you?
Elon MuskWell, so the vacuum engines don't gimbal. So you'd have to have some things to provide the control authority. I mean, technically you could say, like, well, if you're in a low disturbance situation, like the moon has no atmosphere... Man, this is beeping city.
Tim DoddYou wanna move on?
Elon MuskYeah. If you're not facing, like, a lot of atmospheric disturbances, then you need much less control authority, and you could probably land with three just by differential throttling of three engines. But if you lost any of the engines, you'd be toast. So it probably makes sense to, I don't know, probably keep the same config, you know?
Tim DoddOr like you can even just have one in the middle that would offer, you know, a decent amount of gimbal authority and all that.
Elon MuskIt's based on how much optimization we're aiming for here.
Tim Dodd'Cause you're only going to make one of these things, right? Or are you planning on, like, is NASA wanting multiple, or... oh, my word.
Elon MuskSo by the way, I think there's a good chance that ITAR and comms might not want all of this. Wait until you see part two, it's unbelievable.
Tim DoddAnd I promise I'm going to get it to you as soon as I can. Thank you, Elon, for spending so much time with me and allowing me to ask all of the questions I had. It was amazing. And thanks to the teams at SpaceX for allowing me to share this all with you. And thanks to Cosmic Perspective for helping shoot this and just kind of helping out all the time. Find them on YouTube and on Patreon as well.
Tim DoddAnd I owe a huge thank you to my Patreon supporters for helping make this and everything else we do here at Everyday Astronaut possible. If you want access to our Discord channel, where we're probably going to be talking about this conversation a lot, or live streams, or lots of other fun stuff, head on over to patreon.com/everydayastronaut.
Tim DoddAnd while you're online, be sure and check out our awesome web store. You can find shirts like this, the R7 / Semyorka, the predecessor to Soyuz, new shirt that we have that is awesome. As well as our new Mars hats. You can also find some classics like the full flow staged combustion cycle shirt and hoodie, and the future Martian shirts, and schematics collection, and lots of other fun stuff. So head on over to everydayastronaut.com/shop.
Tim DoddThanks everybody, that's gonna do it for me. I'm Tim Dodd, the Everyday Astronaut, bringing space down to Earth, for everyday people. (upbeat music)