Why SpaceX’s BFS will fall like a skydiver and not fly like an airplane
Hi it's me Tim Dodd the everyday astronaut I just recently got back home from SpaceX's, headquarters where, I witnessed history as Elon Musk introduced us to yuusaku, Miyazawa from Japan as SpaceX's, first privately, funded passenger, the, destination, is a quick flight around the moon on SpaceX's, enormous, next-generation spaceship, the, BFS, or big, Falcon, spaceship, that's. The upper stage portion, of the bfr the big Falcon, rocket we only get updates, on SpaceX, is behemoth, of a rocket about once a year or so so. I have to say I was a little disappointed, in the lack of technical, updates, in the presentation, that being, said there is one thing, that was so mind-blowing. Ly crazy, Elon. Had to show us it twice, because it's so counterintuitive, and, so unique I think. It deserves its own deep dive today, we'll cover three topics first, we'll, compare the re-entry of the space shuttle to the re-entry of the BFS, and show, how they differ then. We'll explain the control, surfaces, that allow the BFS to perform this reentry, and then. We'll compare the thermal protection systems, of the space shuttle and the BFS, we'll look back at all the little clues and past presentations. Tweets and Retta AMAs I think. There's actually a lot of information, out there that will help us understand just how exactly the BFS, will re-enter and land, let's, get started. Ever. Since SpaceX tweeted this photo on September, 13th 2018. A lot, of people fear the bfr is slowly turning into the Space Shuttle quoting. Ever growing wings and a giant heat shield covering the belly of the ship so. How, is this any different than, the space shuttle so first up to compare the two let's. Look at them side-by-side the, space shuttles body and Delta wings provided, lift then kept the vehicle in the upper atmosphere longer. Leading, off speeds slowly so as not to overheat, the silicon tile heat shield then. The wings and control surfaces were, used to glide albeit.
Very, Steeply, to the runway to make a horizontal landing, like, an airplane now, on the BFS instead of having the fins and body of the vehicle generate, lift it's, trying to create as much drag as possible, using the entire, broad, side of the vehicle to aerobrake. Its, purpose is basically, to scrub off as much speed as possible very quickly, when the Space Shuttle reentered, had a 40, degree angle of, attack, that's. Quite, a bit different from the BFS which is going to have about a 90. Degree angle of attack the reason the BFS will be able to do this is because of those wings now. Really, these, aren't wings and we shouldn't call them that we, need to think of these more as air brakes as they, are not there to provide lift they're, only there to provide more or less, drag, now, they do this by changing their angle, just. Like an air brake and by, adjusting the amount of drag at the top or the bottom of the BFS they. Can change the pitch so you might think isn't, this kind of similar to a Virgin, Galactic control spaceship, twos reentry, which has that giant tail that flips up that allows it to re-enter. Safely, or perhaps you're a history buff and you're familiar with the Soviet Union's MIG 105, spiral, or later, the bore four which, have a variable, dihedral, wing, which changes, their angle of attack during. Descent although, these vehicles do have variable, surfaces, to change their orientation, they. Aren't really dynamic they. Move only to provide different configurations. Either, a more stable reentry, profile, or then, they change to provide more lift and control for the landing phase they, don't actively, go back and forth to continually, adjust the vehicles orientation, maybe the best example I can think of of a vehicle that actually changes its orientation by. Changing, drag would, be the b-2, stealth bomber. The. B-2 bomber actively, changes its yaw by utilizing, a split aileron, to, create drag on the left or the right wing, by, deploying what's essentially, an air brake on one wing or the other the, drag will actually, steer and orient, the vehicle this is honestly about the closest, example I can think of to a vehicle that changes, drag to modify its orientation, in this manner and when. You factor in that belly-first reentry. This dynamic drag, control is one of the reasons why the BF s is more like a skydiver, than an airplane a skydiver, controls, their orientation, by shifting, the amount of drag each limb generates, bend, your legs a little and your head will rise bend your arms and your head will lower one, time I would indoor skydiving.
To Test out a grid fin and, it, was awesome. But. I was really, really, really bad at it but there was an instructor there that was really good at it which was awesome to see instead. Of me going back into an indoor skydiving, place I decided. I just build something in Kerbal space program that Falls and controls, itself like a skydiver. And can land on a dime, okay now full disclosure I just spent about two hours doing a livestream building, and flying and testing, this, kind of little BFS here in Kerbal so, if you want to watch the entire thing for, some reason there's gonna be a link right here all, right welcome to Kerbal space program now if you're not familiar with this game it's basically like 50%, rocket, builder 50%, flight simulator and, 300%. Explosion, Factory okay. I know I know this doesn't look right at all there's like six air breaks down at the bottom for up at the top and. We have like separate landing gear this looks kind of nothing, like, the VF s but bear, with me this is because I built, this entirely, around, physics. And making sure that those air brakes were producing the right amount of drag and that the built-in, stability, control and Kerbal space program could, use the air brakes to change the amount of drag and therefore, you. Know actually, control the orientation of the vehicle through reentry air brakes are the only things that work like that fins don't work like that our, wings and other surfaces don't this. Is only using air brakes in order to prove that we're only using air brakes to maintain our orientation I'm. Actually going, I turned off the, stability of the reaction wheel inside the command module we're gonna turn off the RCS, throughout. Reentry, and even, when we do need it for that flip maneuver to put the tail down we're. Only using 25%. So that's like nothing, now. The only thing I did have to do in order to make this actually work, in Kerbal space program, I did, speed up the air brakes 10 times and that's so that the computer. Has enough control Authority and can actually maintain precise.
Enough Movement to. Actually let it do, everything, it needs to do so that's, the only way I can get this to work but let's, take this out to the pad and see if it works okay, so we're gonna take this thing out of the atmosphere or out of most the atmosphere get it just above 20,000. Meters and, then, we're going to leave a little bit of fuel left over to. Land with so. Let's do this here we go three two one hip-hip. Gear. Up. And fast-forward. Okay, now we're just gonna Coast up to our Apple abscess, we're, gonna be just shy of 20,000. Meters but it'll be high enough that we get it re-enter, through the atmosphere, once, we get to our peak our a flaps is our highest point we're, gonna go ahead and flip belly, first using, the, RCS. The, actual thrusters, then. We're going to deploy the air brakes and turn off the thrusters and just, let the air brakes, Vitus, safely, and point us in the correct orientation here, we go so, I'll hit one, which is going to make it so it wants to fall belly first, so we're controlling from this point once. We're there seven. To deploy the air brakes and our we're turning off the. Thrusters, and now, we. Are just falling. And, changing. Our pitch and fixing, our orientation, using. Only, these, fins these fins are, doing their job phenomenally, but, again I did have to speed them up like crazy in, order to give them the right amount of control Authority so, but this is kind of how it'll work this is a lot more dramatic. I think but in real life the, fins on the BFS, will all move together they'll just be one unit at each of, the four corners, but. Look at this once it's stable, the thing just, Falls. No problem and the beautiful, thing is even. Though we're really high and. Probably. You know if we had fallen straight back down we. Would have had to have a pretty massive burn. We're actually slowing down almost the entire way down so look at us now we're. Scrubbing, off velocity, as that, as, the atmosphere actually gets thicker and thicker and thicker we're, actually slowing down more and more and more that. Is perfect, how cool is that and it's. Stable. Here. We go three, two one, and flip. Gear. Out. Flying. Up the engines to help orientation. Really. Firing up the engines closing. The, top. Fins oh this, is gonna be perfect, oh. Yeah. A. Little. Blue Origin hover there for a second ah. Look. At that with 200, meters per second to spare even and we, hovered for a while I mean that's. Pretty amazing right that's, pretty. Amazing. Okay. We're gonna pop this thing up into orbit now alright, so we are in orbit around kerbin. We're, going to go ahead and try to land here at at, Kerbal Space Center. So I'm gonna do a reentry burn and then we're gonna flip belly first extend. The the air brakes and then, turn off RCS, and let just the air brakes maintain, our belly first orientation, so. Here we go. All. Right there we go we're, starting to glow red-hot getting, kind of spicy and, now that we have some atmosphere to play with I'm gonna go ahead and turn off our CS and just. Let the Finn maintain. Our orientation so. Here we go. All. Right the air brakes seem to be doing their jobs, fantastically. Man. III think, I hope we don't overshoot this, year we're still going pretty quick but there's also still quite a bit of velocity, just to scrub off so hopefully it's doing okay here I hope, we don't overshoot this.
But I I think we're okay I think. We're okay now notice the air brakes are going, crazy right now especially. As we kind of slow down as the atmosphere gets thicker and thicker they're really gonna have their work cut out for them so. But. I think we're gonna be close let's see if we can't land somewhere. Here in Kerrville Space Center that'll be awesome. Yeah. So it looks like we did overshoot, it a little bit I'm gonna just do a little bit of a boost, back burn here and see. Where we end up see. If we can't get this thing closed to the VAB. All. Right well we're gonna miss the vab this time. I. Would. Not want to see this flying over my head if I was working. I don't, know where we're gonna land what we're gonna do it. Ah. Good. Morning everyone I was work today. Just. Coming, in for a grasshopper landing. And. We'll go ahead and say this is the processing, facility that's, where it needed to be we're just trying to park it next to all the extra parts and stuff. But. Look at that, I, was, pretty sweet I'm. Not gonna lie it that was pretty great okay, I'm gonna cut you off there but, if you do want to see the rest of that or all, the other hundreds, of takes of trying to land that thing there. Is a link in the description but let's get back to talking about the BFS. Okay. Okay so that was all just to help illustrate the. Fact that you can control two vectors of a vehicle belly-flopping, by, using, just air brakes now one thing we don't know for sure yet is how exactly, they're, going to move those giant, fin slash air brake things, now Elon did mention in the talk that they'll require an awful lot, of force to move as in. Like the mega Newton scale, of force, that's. A lot people on reddit have already been doing some really deep, dives trying. To figure out what systems, they could actually use. That be strong enough and fast, enough and the consensus, is, who. Really, knows at this point it could be hydraulics. Or it could be electric, motors now. Hydraulics, might, be used but they're pretty slow and awfully, heavy motors. On the other hand can be lightweight but, they might not be able to handle that kind of load and. But. Then again if, anybody knows anything about motors, you'd. Be Tesla. Wonderful. Anyone at SpaceX, knows anyone, over at Tesla. So. My personal bet I think. They'll go with electric motors but, I really have no idea it's just one of those things about the wait and see so a huge, amount of control will be done with the fins but, let's, not forget about the fact that the BFS, will for sure have, some huge, thrusters. To, help maneuver it too as a matter of fact I asked Elon all about this exact, thing in 2016. After we saw the first video renderings, of what the interplanetary, transportation. System would look like re-entering, Mars belly-first, and. Did that maneuver to go tail down. He. Thought never really. We. Must. Respond. Yes. Pretty. Huh. Ten, times cross attack Buster's. Besides. Those Finn wingy, things and, some, massive, control thrusters another. Key piece that will allow the BFS, to do a full-blown, belly, flop through the atmosphere, is the, heat shield the, Space Shuttle used over. 24,000. Individual, and unique silica, tiles to cover the belly of the shuttle the, size of the wings and the amount of lift the shuttle needed to achieve in the upper atmosphere was, largely due to making sure the shuttle didn't overheat the silica tiles. Overwhelming. Them would transfer, the heat from the tiles, to the fuselage, of the orbiter. That's. A really bad thing the BFS on the other hand will use something very similar, to what SpaceX, uses on their dragon, capsules this, is an ablative material, known as pica X or if, you don't like acronyms, and prefer cool sounding words phenolic. Impregnated, carbon. Ablator. Ablative. Heat shields are the ones that purposefully, flake off material as it heats up which, then takes some of the heat with it SpaceX, has had great luck with the heat shields on their Dragon capsule and although, I don't think they've actually reused, a heat shield they did say they could probably reuse heat shield about ten times, before needing to be refurbished and SpaceX. Continues. To advance their pica-x and they, hope to get to the point where it can be used a hundred times, before.
Needing, To be replaced pica-x can handle much higher temperatures, than the shuttle tiles which, is necessary. When trying to re-enter from Mars or the moon not. To mention with, a really, steep reentry profile one that tries to slow down as quickly as possible the heat shield will be pushed to the limits so if, the BFS, will have an ablative heat shield that, needs to be replaced. Isn't. That an even worse refurbishment, process than the Space Shuttle which had thousands. And thousands. Of hours of checks to ensure, that their tiles were okay for every, single reef light well when it comes to mounting the heat shield to the BFS, according, to Elon the heat shield place will be mounted, directly to, the primary tank wall that's, the most massive ficient way to go don't. Want to build a box in a box unlike, the space shuttle a good amount of the fuselage, is uniform, just a giant nine, meter tube so. There could be some really common plates that are easy to, replace, and manufacture. But as the nose tapers, or where there's unique areas like the fins I'm sure, there will need to be more specialized, heat shields in those areas and just like that ugly, little wannabe BFS, I made in Kerbal space program there's. A common, radiator, I mounted, to the belly of the beast they. Were all the same and easy to pop on it. Should be something like this. Ish. Just, like how making hundreds. Of Merlin engines is cheaper than building dozens. Of rocket engines from a manufacturing, standpoint having. A common, heat shield plate that's easily, mountable and replaceable. Should. Help alleviate some of the headaches the Space Shuttle experienced, in its refurbishment, process not, to mention the Space Shuttle tiles were extremely, fragile they. Could follow if you just looked at them wrong and it, was very, important, to make sure that every, single one was literally perfect, before each flight a more, traditional heat, shield is a lot, more resilient, in the sense okay now I hear, you but beyond the fact that it does look like the BFS is beginning to evolve more, and more into the space shuttle the, way it performs reentry is completely. Different, using, different, techniques different technologies, different materials, and an entirely, different reentry. Profile I think. It's really unfair to say it's similar to the space shuttle then I know the, fins on the back do make it look like Tintin's, rocket or the Planet, Express ship, from Futurama but, don't, forget those fins are also the, landing legs and this, in my opinion makes it look more like the TWA, moon liner originally. Featured at Disneyland Tomorrowland, in 1955. I think it's clever to take advantage of the landing gear and make it function as a control surface that's, something I wish was technically, possible on the Falcon 9's landing legs because, it would be super cool but.
Then Again I think they're, doing quite fine with the system as it is like, I mentioned about my last video about the VFR it is, still evolving, but I think it's getting closer and closer to its final configuration, now. They're starting to make some hardware it's, time they start putting it to the test if, all goes well we'll. Start seeing those first little test hops by the end of 2019. That'll, be amazing so. What do you think do, you think that BFS, is just a new Space Shuttle or, do you think it's something entirely. Different let. Me know if you have any other questions about the VFR, or BFS. Or anything. Spaceflight, related and comments below I will humor. Thank you to my patreon, supporters for helping me be able to go out to California and cover this event and all, the other events that I attend as well it's, only possible thanks to my patreon supporters so, if you want access to our exclusive subreddit, or our exclusive discord channel head, on over to patreon comm, slash, everyday astronaut thank, you and now a huge, shout out to lucas from k news for those amazing, animations. He honestly makes some of my favorite, YouTube videos so if you're not subscribed to him be, sure and check out his channel and while you're on the old internet head, on over to my web store I've got a ton of new shirts hats, prints. Of rocket launches mugs lots. Of other fun stuff head, on over to every day astronaut comm, slash, shop thanks everybody that does it for me I'm Tim, Dodd the everyday astronaut, bringing space down to earth for everyday people.