00:01:37 · Nato Saichek, Jonathan Brebner
[00:01:37] S1: We we usually say fire. Oh. Yeah. [00:01:39] S0: It's a space gun. Yeah. Someone hits that button, what happens?
00:01:45 · Nato Saichek
[00:01:45] S1: So we do have a red button right now, even for the small tests. Like it was important. It's an important characteristic. The first thing that happens is... So so the projectile, you've gotta basically, the projectile fills the the circumference of the of the barrel. And along the length of the barrel are a series of pressure vessels that are fully charged with high pressure hydrogen. Somewhere in the neighborhood of, again, for a space launch system it might be a thousand psi, something like that. And when you push the button, a burst disc gets ruptured on the first two pressure vessels, and those release high pressure hydrogen into the barrel behind the projectile. It starts moving. And then as it moves down the barrel, periodically, down the length of the system, more pressure vessels are are sort of distributed down the length of the barrel. And as the projectile passes each set of pressure vessels, more burst discs pop, more gas floods in, and and accelerates the projectile down the barrel. And that gets you up to a certain speed. That's a pretty traditional... That's a potato cannon. Like, that's a multi injection potato cannon. But you're just pushing a projectile down a barrel with with gas. From a physics perspective, you can only... Know, if you think of a gas as like a collection of particles, those particles are moving at some speed and that speed is governed basically by the the composition and the temperature of that gas. So if it's hydrogen, sort of a proxy for for that, the motion of those particles, the speed of sound in the fluid. So hydrogen has a speed of sound of 1,270 meters per second. That's room temperature hydrogen. What that means is that a a shock wave in hydrogen travels through hydrogen at that speed. And so if if you had a volume full of hydrogen and you moved one of the walls, the hydrogen's gonna wanna fill that void and some of the molecules can travel a little bit faster than that speed of sound of the fluid but but less and less of them the faster you're going. So when you start moving away from this volume of hydrogen, the pressure that the projectile feels drops off, pretty rapidly once you're faster than that speed of sound of the fluid. So you can get up you can get up to the neighborhood of twice the speed of sound just by pushing the the projectile from behind.
00:03:59 · Nato Saichek, Jonathan Brebner
After that you're down in the neighborhood of like, you know, you had a thousand psi behind the projectile, and the projectile's traveling at two and a half kilometers per second, you're feeling something like less than a 100 psi. You're feeling less than 10% of the the actual pressure in the gas. So what that means is you're, you know, all that energy that you put into the gas to pressurize it is is basically being wasted at that point. And two and a half kilometers per second is nowhere near the speed you need to go to space. Eight eight eight and a half kilometers per second is sort of what we target for a Space Launch System, because we're gonna need to punch through the atmosphere and get to orbital altitudes at orbital speeds. So orbital, the speed, you know, typical speeds you're talking about is something like seven and a half kilometers per second. So we expect that we'll lose like a kilometer per second punching through the atmosphere. So we need to, you know, leave the barrel at eight and a half kilometers per second so that we can get to orbit at seven and a half. I've But only described how we get to two and a half. So that's the easy part. That's the part that we did sort of [00:05:08] S0: Yeah, there's a lineage to this. We'll get to that part. So the big potato cannon had been figured out. You came up with a way to then get at that additional kilometers per second. And also presumably to reduce the g forces in such a way that you're not gonna just splatter whatever you put in the projectile. What does it sound like when it leaves the barrel?
00:05:08 · Jonathan Brebner, Nato Saichek
[00:05:08] S0: Yeah, there's a lineage to this. We'll get to that part. So the big potato cannon had been figured out. You came up with a way to then get at that additional kilometers per second. And also presumably to reduce the g forces in such a way that you're not gonna just splatter whatever you put in the projectile. What does it sound like when it leaves the barrel? [00:05:30] S1: Yeah, so we have a couple of systems that we have operational right now. One of them is a six inch diameter system that's 60 feet long. The other is a 30 inch diameter system that's 120 feet long. It's the largest cannon in the world right now. And we have we've only done one commissioning test shot. It's still... We're still in the process of of bringing it up. We insulate the system a lot. Initially, didn't insulate it a lot and it sounded like a shotgun plus a car crash. And... But we we we've added a lot of insulation to the system and now it sounds it sounds like somebody dropping a load of bricks or a shipping container, and there's a very visceral thud as you feel it in your chest and the cuffs of your pants move a little bit. The volume of air that we're moving and the rapidity with which that is happening, like there's a there's a shock wave and the whole thing is anchored to the ground and so the ground moves. [00:06:27] S0: So it's really fun to hit the the red button is what you're saying. Is. Like that has to be the best part of everyone's day is that you get to hit the red button.
00:06:27 · Jonathan Brebner, Nato Saichek
[00:06:27] S0: So it's really fun to hit the the red button is what you're saying. Is. Like that has to be the best part of everyone's day is that you get to hit the red button. [00:06:34] S1: It's a it's a it's an adrenaline it's an an adrenaline shot. And we fired the the six inch system, we fired more than a 100 times. So we've... We had a rule at one point where we we made it so that the... It was the least senior person at the company had to push the button. So that we had to... We were trying to make it so that our CEO would never push the button. That was the goal. [00:06:55] S0: Wait, hold on, why? There are two ways you can interpret that. One is you're the red shirt, so you press it. The other is this is so he's not always just only like pressing the button, we need to get everyone involved. [00:07:11] S1: It was a way to keep everyone involved. It was also sort of an ambitious goal of like, we are gonna make so much progress so fast, we're gonna grow so fast that there will always be new people, and he'll never get a chance to fire it. Unfortunately, he ended up, you know, in in... I think it was in early twenty twenty five. He had to he had to push the button. No one else... We didn't have any... Anybody who we could invite over as a visitor or something, you know, to to push the button unfortunately.
00:07:11 · Nato Saichek, Jonathan Brebner
[00:07:11] S1: It was a way to keep everyone involved. It was also sort of an ambitious goal of like, we are gonna make so much progress so fast, we're gonna grow so fast that there will always be new people, and he'll never get a chance to fire it. Unfortunately, he ended up, you know, in in... I think it was in early twenty twenty five. He had to he had to push the button. No one else... We didn't have any... Anybody who we could invite over as a visitor or something, you know, to to push the button unfortunately. [00:07:35] S0: Okay, well I volunteer. Okay. Is a problem again. All right, so there's like a history to this idea, right? So you just go back at least to Jules Verne, right? 1865 novel around this exact concept except putting people in it. That probably won't work. [00:07:50] S1: Very similar, yeah yeah. [00:07:51] S0: Germans tried to turn it into a weapon in World War II. There was a project in the 60s called Harp. Harp. And there was a project in the 80s and the 90s called Sharp. [00:08:02] S1: Right, Super Harp. [00:08:03] S0: Yeah. Super Harp. Yeah. So I guess the question is, at each of those steps people were conceptualizing it or testing various stages of it. What changed that made you think, oh now actually we can go back to this particular idea that was abandoned at various points.