- 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 Yusaku Maezawa from Japan as SpaceX's first
privately funded passenger. Their 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's behemoth of a rocket about once a year, 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 blowingly crazy, Elon had to show us it twice because it's so
counterintuitive and so unique. I think it deserves it's own deep dive. Today we'll to cover three topics. First, we'll compare the
reentry of the space shuttle to the reentry 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 in past presentations,
tweets and Reddit AMAs. I think there's actually a
lot of information out there that will help us understand just how exactly the BFS
will reenter and land. Let's get started! - [Technician] Three, two, one,
zero, ignition and liftoff. - [Neil] That's one small step for man. (upbeat, rhythmic music) - [Astronaut] This is
the best of the best one. - 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 these two, let's look at them side by side. The space shuttle's body and
delta wings provided lift, and kept the vehicle in the
upper atmosphere longer, bleeding off speed slowly so as not to overheat the
silica 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 broadside
of the vehicle to aerobrake. Its purpose is basically to scrub off as much speed
as possible, very quickly. When the space shuttle reentered, it 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 'em that. We need to think of
these more as airbrakes at 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 airbrake. 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 how Virgin Galactic
controls SpaceShipTwo's reentry which has that giant tail that flips up that allows it to reenter safely? Or perhaps you're a history buff and you're familiar with the
Soviet Union's MIG 105 Spiral or later the BOR-4, 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
vehicle's 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 it's yaw by utilizing a split aileron to create drag on the
left or the right wing. By deploying what's
essentially an airbrake 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 BFS 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 went 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'd 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 kinda 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 50% rocket
builder, 50% flight simulator and 300% explosion factory. Okay, I know, I know, this
doesn't look right at all. There's six airbrakes down at the bottom, four up at the top, and we
have separate landing gear. This looks kind of nothing like the BFS, but bear with me, this is because I built
this entirely around physics and making sure that those airbrakes were producing the right amount of drag and that the built-in stability control in Kerbal Space Program,
could use the airbrakes to change the amount of drag
and therefore actually control the orientation of the
vehicle though reentry. Airbrakes are the only
things that work like that. Fins don't work like that, or wings and other surfaces don't. This is only using airbrakes. In order to prove that
we're only using airbrakes to maintain our orientation, I turned off 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 airbrakes 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
could 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 of 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. (engine roars) Gear up! And fast forward. Okay, now we're just gonna
coast up to our apoapsis. We're gonna be just shy of 20,000 meters, but it'll be high enough that we get a reenter
through the atmosphere. Once we get to our peak, our
apoapsis, 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 airbrakes and turn off the thrusters, and just let the airbrakes glide us 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 airbrakes and R, 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. 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 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, if we had
fallen straight back down, we would have had 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 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.
(rumbling) Firing 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. Oh, 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. All right so we are in
orbit around Kerbin. We're going to go ahead
and try to land here at Kerbal Space Center. So I'm gonna do a reentry burn and then we're gonna flip belly first. Extend the airbrakes,
and then turn off RCS and let just the airbrakes maintain our belly first orientation. So here we go. All right, there we go. We're starting to glow red
hot, getting kinda spicy. And now that we have some
atmosphere to play with I'm gonna go ahead and turn off RCS, and just let the fins
(buzzing) maintain our orientation. So here we go. All right, the airbrakes seem to be doing their jobs fantastically. Man, I hope we don't overshoot this here. We're still going pretty quick, but there's also still quite a
bit of velocity to scrub off. So hopefully it's doin' okay here. I hope we don't overshoot
this, but I think we're okay. I think we're okay. Now notice the airbrakes
are goin' crazy right now, especially as we kinda slow down as the atmosphere gets
thicker and thicker. They're really gonna have
their work cut out for them. But I think we're gonna be close. Let's see if we can't land somewhere here in Kerbal Space Center. That'll be awesome! Ah, yeah! So it looks like we did
overshoot it a little bit. I'm just gonna do a little
bit of a boost backburn here and see where we end up. See if we can't get this
thing close to the VAB. All right, well we're gonna
miss the VAB this time, unless. (engines firing) I would not wanna see
this flying over my head if I was working. I don't know where we're gonna
land, but we're gonna do it! (landing engines firing) (Tim screams) (Tim laughs maniacally) Good morning everyone! How's work today? Just comin' in for a grasshopper landing. (Tim laughs) Hey we'll go heads-in. 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. (laughs) That was pretty sweet. I'm not gonna lie, that was pretty great. Okay, I'm gonna cut you off there. But if you do wanna see the rest of that, or all of 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 just using airbrakes. Now one thing we don't know for sure yet is how exactly they're going to move those giant fin slash airbrake things? Now Elon did mentioned in the talk that they'll require an
awful lot of force to move, as in the meganewton 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's be strong enough and fast enough. And the consensus is, (gasps) 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. But then again, if anybody knows anything
about motors it'd be Tesla. I wonder if 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
we'll have to 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 in exact thing in 2016, after we saw the first video renderings of what the interplanetary
transportation system would look like, reentering
Mars belly first, and then it did that
maneuver to go tail down. - Besides those fin, 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 over
heat 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 shields about 10 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 100 times before needing to be replaced. PICA-X can handle the
much higher temperatures than the shuttle tiles, which is necessary when trying to reenter 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 reflight? Well, when it comes to mounting
the heat shield to the BFS, according to Elon, "The heat
shield plates will be mounted "directly to the primary tank wall. That's the most mass efficient way to go. "Don't want to build a box in 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 mount,
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 fall off 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 this 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. And 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 Moonliner originally featured at
Disneyland's 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 BFR, it is still evolving, but I think it's getting closer and closer to its final configuration. Now that 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 the 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 BFR or BFS, or
anything space flight related in comments below. I also owe a huge and sincere 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.com/everydayastronaut. Thank you. And now a huge shout out
to to Lukas from kNews 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
everydayastronaut.com/shop. Thanks everybody, that does it for me. I'm Tim Dodd, the Everyday Astronaut! Bringing space down to
Earth for everyday people.
Great content Tim.
Would love to see a deeper dive into PICA-X and what separates it from older One Time Use ablative coatings, like the ones from the Apollo era
If BFR is going to fully replace F9 and FH, I assume it will be delivering LEO payloads as well as payloads to Moon and Mars. Does it mean that the reentry profile would be different depending on where BFS is coming back from?
In other words, if a BFS is coming back from Mars, does it mean that it has a significantly higher/lower speed than LEO orbital velocity, so that it needs a completely different reentry profile?
I wonder if the discussion about BFS using PICA-X is just speculation or informed by sources. I don't think Elon has come out and say PICA-X will be used on BFS, it is hinted at during the IAC 16 presentation but it's not a definite statement, and PICA is not mentioned in IAC 17 or the DearMoon presentation, nor is it mentioned in any of the AMAs.
Tim, as an FYI, at the beginning of your video (approx 2:50), you show a red panel flip up on a sports car.
The panel's purpose isn't to function as an 'air brake' at speed, it's job is to create negative lift (downforce) at high speeds, to keep the car firmly planted on the roadway. It does create some drag while doing this, but that's the aerodynamic price you pay for creating that desired 'downforce' to stabilize the car.
Other than that, looks good! :)
Acronyms, initialisms, abbreviations, contractions, and other phrases which expand to something larger, that I've seen in this thread:
Decronym is a community product of r/SpaceX, implemented by request
10 acronyms in this thread; the most compressed thread commented on today has 117 acronyms.
[Thread #4436 for this sub, first seen 6th Oct 2018, 19:16] [FAQ] [Full list] [Contact] [Source code]
Anyone else think we should call the "wings" on the BFS flippers?
Curious to know how far they are with the aerobrake actuator/hydraulic development. It's arguably one of the hardest parts to develop. I'm guessing for the first hop, the aerobrakes will be fixed in place.
Could a version where all three legs are articulated, and a third airbrake is added at the front; be modelled?
I would like to see the skydiving upper-stage slowly rolling like a bullet; first belly, then top hitting the atmosphere. Then maybe you could put the ablative on the entire vehicle but the layer would be a half (or less) as thick?
"It can potentially be used hundreds of times for Earth orbit reentry with only minor degradation each time — as proven on this flight — and can even withstand the much higher heat of a moon or Mars velocity reentry."
-SpaceX website about PICA-X