Do Spacecraft Really Have To Endure The Hazards of Reentry
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- čas přidán 29. 12. 2023
- An extended answer to a question I keep seeing - can spacecraft avoid the furious heat of reentry by slowing down before reaching the atmosphere, or, but flying above it until slow enough to avoid it.
The footage is from the Artemis 1 mission reentry.
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That reentry footage was terrific.
What if the spacecraft is nuclear powered? Then you could break using less mass/fuel.
@@HansMillingexplain. Nuclear power is just creating something very hot and radioactive. How would that be used to slow down a spacecraft.
@@CheradenZakalwe Nuclear rocket engines are a thing, And they are very efficient, at least when it comes to specific impulse, the few one tested (all on the ground), like NERVA archieved a specific impulse of more then 800s, thats double that of normal hydrogen rocket engine. Ofcourse they still use reaction mass (hydrogen), but the heat for expansion is provided by the nuclear reactor.
@@slome815did you know that the Chinese did experiment with using dense wood like oak as a heat shield and it did work. So, just to summarise some of the options for reentry: a nuclear engine, a lump of wood. I think the KISS principle favours the lump of wood.
I like how it airbrakes once then skips off the atmosphere like a stone and then plunges back down
There’s one solution you’ve missed: Using the mega maid to remove earth’s atmosphere entirely, thus solving the problem of reentry!
But what if she goes from suck to blow?
It doesn't solve anything, just delays the problem. And it is going to be bigger when touching the solid surface. No parachute, no gradual stopping, just very rapid disassembly.
Wouldn’t we need the schwartz for that?
High speed terra firma@@TheBiggreenpig
You think you clever? Where do we get such big hoover to do the job?
That reentry video always gives me a strong sense of relief and appreciation for the safe embrace of earth. Even compared to ending up alone in the middle of the ocean, which is normally considered an exceedingly horrible and deadly situation, it's a warm, protective and comfortable bosom compared to space's sheer hostility to life.
And showed us that the starship is a. tough one
Is reentry really necessary? If I went to space, I would insist on coming back, so yes, it's necessary.
😂
You make watching CZcams more efficient by presenting two videos at the same time.
And then speed up the video playback to 2x to get a 4x overall efficiency improvement.
@@privacyvalued4134 I can't compile all the information even on 0.5x speed
Ah, the TikTok ADHD technique.
@@nukesrus2663 is that a thing ??!!
There was one professor in the early days of Apollo that explained you could use rockets to overcome gravity to slowly deorbit but the amount of fuel was more than what it took to get to orbit. So, a heat shield was more efficient, less cost, less massive. His sketches showed multiple rockets pointing towards earth center and rockets slowing the spacecraft down to match earth’s rotation, then allowing the ship to slowly descend! Fuel requirement was enormous.
or in clear text, the weight of the fuel needed for slow descent is way higher then the weight we are able to decelerate by this method. Or to put it in some illustrative numbers, to use a slowed down re-entry of 50t module you need 75t of fuel, which means the module cant weight 50t since it has the fuel on board that is adding weight that at the end needs more fuel to slow down the module. (the numbers are strictly illustration, not any mathematical/physical equation)
This is a better answer than the “you can’t” Scott has in the video. Tell us what it costs. Obviously heat shields will be around for as long as we have chemical rockets. Maybe in some fictional future we’ll have fuel that doesn’t weigh as much. Note I said Fictional.
What if we give them a giant Ballon full of hydrogen just before reentry?
Just use an orbital Tug System. Its a space structure u dock at or connect to, that tug then de-orbits u by using its own propulsion to slow u down very quickly (so that you dont descend very far into atmosphere before coming to - say - mach 2), you then detach and descend on your own. (That solution I am not going into yet). The tug then accelerates itself back to orbit.
You can argue the practicalities of that if you want, but you can't say its not possible. Its just an engineering problem not a physics problem.. Heck just look at a space elevator, no heat shields required there either.
Incidentally the reverse is also true. build smaller launch systems to get you to a very low earth orbit where the tug picks u up and then lifts you to a much higher orbit. Heck it could take u all the way to the moon, refuel your spacecraft and then de-orbit at the moon and release u a kilometer up so your tiny spacecraft could get the rest of the way. it then speeds back up and returns to earth carrying ships on a return trip.
Although I had seen it before, I appreciate you leaving the re-entry video up as you narrated. The vortex of superheated gases behind the capsule is mesmerizing.
Ah, that is what that is? I already wondered about that.
I just came from the bath room with the same effect.
The thrusters are scary sounding. Keeping the capsule right on the knife edge of catastrophe.
Amazing. Too bad it's fake. Space is fake and the Earth is flat. NASA lied to you. Sorry to tell you.
Talked to a person who worked on the US X-15 rocket plane program (1959-1968). They considered putting the X-15 into orbit, but none of their pilots could fly the re-entry profile on the simulator without burning up. A non pilot member of the program asked if he could try re entry on the simulator, and they let him. He succeeded, and was able to repeat the manuever again and again.
Everyone wanted to know how he was able to succeed where others could not. Simple, he said, he watched the temperature guage. If the X-15 got too hot, he pulled up; when it cooled down he let the plane descend. He did this over and over, and showed that winged reentry from orbit was possible. The X-15's glide ratio was about 4 to 1. Constructed of inconel X alloy. An ablative coating was tried on the X-15, but was found to be unsatisfactory, and actually interferred with the plane's natural ability to disapate heat.
I knew his reasoning for why a winged design wouldn't work was flawed. Heating being a factor of speed and drag would means you don't need to dissipate as much heat should the speed be controlled.
That was an extremely raw simulator I guess considering the computing power at that time. I bet it didnt consider all the variables
This looking very game type things
But in real these types of movement in the entry process can break apart the prob and many factors cannot be performed in a simulator due to the average amount of availability of physics on software 🤔
Neil Armstrong flew the X15. Everyone who did was an engineer. I’d like a source for this story.
This is a very pragmatic way of doing things.
It's good to try outsiders since they are not bound by any concepts.
Sometimes experts get enslaved in their thinking.
Ask the special forces.
I feel like I'm in a capsule returning from the Moon and Scott Manley is on the intercom just rambling on and on about re-entry physics while I'm trying to enjoy this moment.
There is a full length video w/ ambient capsule sounds. It is mesmerizing. I'm surprised Scott didn't link to it. I can't.
um
I know the sounds in the background are the thrusters firing, but I like to think it's just Scott controlling it via keyboard while casually talking about reentry.
@@logarhythmic6859it is lovely to think of it like a KSP video
i feel like he is the type of guy who would totally do that 🤣
Being utterly mesmerized by the parachutes interplay at the moment of splashdown "sparked joy" in this heart. Thanks Scott.
Isn't it interesting that they don't seem to touch each other and instead partially deflate when they get too close to one another. I imagine those vents around the outer edge are forcing some air out to the sides to keep the parachutes apart but that's pure speculation on my part.
@@tissuepaper9962I believe you’re right. The parachute system for soft touchdown after the terminal stages of atmospheric reentry is something I probably know the least about in terms of space hardware but, I believe those vents both around the edge and sometimes on the top do multiple things and one of them is to help provide stability as allowing some of the air through that parachute I believe helps to stabilize it by allowing for a less turbulent stream of air to flow through and this helps to keep the parachute inflated and the flowing air helps to keep it from oscillating violently, preventing the introduction of unnecessary structural stress into the lines and on the stitches of the parachute while being pulled down by the weight of the craft attached. I’m not 100% sure but, I believe that this at least part of their functions.
The inflatable heat shield idea led you to mention the idea of inflatable zeppelins. I kept waiting for you to go to inflatable wings on a space plane. Or, extremely large Kevlar parachutes. At the high altitudes, they could be ver thin and compact before deployment.
DONKEYSMELL
@@thinkingoutloud6741 The high altitude parachute doesn’t really work. There’s not enough air density to keep the parachute reliably inflated. Instead you have a “ballute”, with an enclosed volume and a ram-air scoop to pressurize it.
Fantastic footage and an excellent explanation for what’s going on. Thank you, Scott
A bit of trivia about the L/D ratio for airliners: the B767 has 12 (they discovered it during the Gimli glider incident, go check it out), while the Airbus flock tend to have around 15 (yes, even that monstrosity known as the A380). The B747 and 777 also have around 15, while the original B737 was supposed to have 17 (highly doubt that, but hey). The B787 and B777X are at 20! Except the B767’s, which was actually found out by accident, the rest are all theoretical, so I wouldn’t count on them if were to have a total loss of power on all engines anywhere far from an airport safety cone.
Gliders are on another planet. The first plastic gliders of the 1960s had around 32-35 at relatively low speeds, while more modern ones like the Nimbus 4 have a manufactured-declared L/D of 60+. Recently manufacturers have stopped publishing the “polar curve” of the gliders they make, so we don’t exactly know their design performance with the seams level of detail, but I’d guess is not very far from 50 to 55. The major improvement on previous iterations lies in the speed at which they obtain those L/D ratios, given by the much higher wing loading of modern gliders (55+ kg/sqm vs 30-35kg/sqm for the 1960s ones)
Still not useful for atmospheric reentry
Happy 2024
Easy to determine lift to drag ratio. Put the plane into level flight. You know what the fuel load is so you know the total mass of the aircraft. You also know what the trrust of the engines is because there will be known relationships between fuel consumption, rate ambient pressure, temperature and airspeed etc and thrust. Given that the lift must equal the current mass of the aircraft, lift to drag ratio is easily determined.
@@rogerphelps9939 theoretically you’re absolutely right, and aircraft manufacturers know all of this, but good luck finding those known relationships! I reckon the fuel burn curves of engines and the related thrust ones are among the best kept secrets in the industry, so we’ll have to rely on what the aircraft manufacturers say
Indeed. I am sure engine makers will tell airframe makers only as much as is strictly necessary.@@soffici1
It's called a sailplane
Glider, sailplane… different names for the same object
In the USA there is the “soaring society of America”, in the UK the equivalenti is called “British gliding association”
Scott, this episode was fantastic. I loved that you ran the video through your whole segment. It was a great idea and worked well. Bravo 👌
I am amazed by the 'skipping' of Orion. The calculations to figure that out are truly incredible.
I came to comment the same, I've seen the video before and never even realised it was doing that; though now it seems obvious.
Amazing indeed. Also the little flip manoeuvre it did too.
Totally agree. I thought the same thing. I’m also amazed that the capsule can be “steered”. Apparently the capsule is designed where the center of gravity is slightly offset. This causes the capsule to fall at a slight angle. By rotating it in the direction you want to move it you can steer. Amazing.
@@TraderDan58 that is a pretty common thing with capsule desgins, still pretty cool
Numerical analysis
The Russians worked that out long ago: that's how they'd have brought back a lunar Soyuz. Several Zond probes demonstrated it.
A skipping rock on a pond is one of the best visual analogies to reentry that I ever heard. Really helped me understand and visualize it after that.
I've had a few KSP re-entries like that. Come in too hot and need to spend a few orbits bouncing off the atmosphere while trying not to violently explode. Eventually the "water" has absorbed enough of the energy that the rock can land and sink to the bottom.
@@Knofbath
I was thinking the same thing, so many close calls in that game!
More like shooting a bullet at a flat calm surface of water. At certain angles it’ll bounce off or it’ll penetrate.
@@longsleevethong1457 Both are awful analogies.
Every contact with the atmo is slowing the craft and bringing it lower, it never really skips off anything.
@@Knofbath yeah the issue is that it works best in The Kerbal Space Program, as the Kerbals can go on living forever, without you having to consider caring for their basic needs. E.i. they won't die of starvation, oxygen or water running out or the spacecraft getting full of "Kerbal waste products". In real life going halfway back to the Moon, because you did not slow down enough the first time you entered the atmosphere, isn't really a doable thing.
As you were talking, I was thinking about inflatable or temporary heat shields that spread out and create more surface area. I hadn't heard about that at all. It's super cool that it's already been developed and put into testing. I'm excited to see where that technology goes.
JPAerospace is a leader in alternate ways to achieve orbit. Their design seems to be safer up and down as Scott seemed to suggest. G forces much reduced, and the orbital airship never has to land. That task is given to a more suitable and smaller craft when the Dark Sky Station is built.
Scott, what a great talk. I don't know how many stayed with you, but since I teach an engineering Thermo-Science lab,I was with you every step of the way. Great Job.
It was terrible. I understand reentry and why you can’t stop and then re enter, but I didn’t understand a word Scott said.
I want more of these refutations of common "Why dont they just do X"
I love your content Scott, followed you since the early days of KSP, I remember being hyped every single time you released a "100% reusable space program" video because your solutions to things were so creative.
Why don't they just install a really large parachute very high in the atmosphere during the skipping phase? With arbitrarily large area the parachute can fully stop the rocket to terminal velocity and radiate the heat away faster. It's essentially the same principle as this inflatable heat shield but parachutes are cheaper and simpler.
@@DominikPlaylists Cue the meme "HAHAHAHAHAHAHAH ........... Oh wait, ..you're serious? ........... HAHAHAHAHAHAHA."
Yes, this would be a great series/service!
people with these rejected ideas should try to figure it out for themselves.
@@briankale5977Damn dude, he’s just asking. Do you actually know the mathematical analysis required to shoot down that idea or just have an ego?
I never saw that re-entry footage before - my goodness, how amazing is that?!?!
Thanks for going through the details of re-entry Scott, you answered all my questions on that topic in one short, concise and easy-to-understand video.
I think this footage (original with sound) was a first released to public (if I ain't mistaken).
I was blown away watching that!
Is there a version with telemetry displayed?
That is one of the most complete and informative explanations I have heard on this, well done, I have wondered about the problems involved.
Awesome explanation Scott. The sound(s) are truly amazing (on the original, without commentary)...
Congrats Scott for explaining complex thermoaerodynamics without having to display a single equation on the screen 👏🏻
What’s wrong with equations? The laws of Nature are written in the terms of math(s). Perhaps you do not like that because math is hard. Which is is. But noone promised you Nature chose to make things simple.
I like the equations because they help me understand what's going on especially contemplating the gliding scenario between space and aerodynamics. It makes sense that if you have enormous rockets burning tons of fuel to put a little payload into space and escape Earth, then that little payload must dissipate all that energy somehow to return to Earth.
@@brianjuelpedersen6389 , maybe OP wasn't suggesting "equations are bad" but rather they meant that Scott explained things so well, it was simple enough to understand wherein "utilizing equations" would've made it less understandable for the masses whose strong points are NOT "solving equations" because as you said "Math is hard." It's like the difference in hosting "a discussion with the general public" versus "a technical presentation for a body of professional peers."
Well I definitely missed those equations, I kinda got lost midway through the explanation without any visuals. I'm not saying it should be equations, but at least having some graphs or sketches would have helped a lot.
@blackghost87
This is a video aimed at the laymen masses (such as myself) and thus of more value without equations.
I understood what was being talked about throughout, and I'm not scientifically, or mathematically, minded *at all.*
I'd posit that if you could understand the equations / graphs etc. underpinning what is described in the video, you can easily understand this video *without* them, as you are probably a lot more advanced mathematically / scientifically than the 'average joe'.
I think this is, in essence, what the OP was getting at. The video described the reasoning for re-entry methods in an accessible manner that did *not* require complex maths to be shown (or rather maths that would be complex to an average person).
I remember watching a documentary about the Apollo program, and they went to an aerodynamic expert and asked, "how do we stop our capsule from melting on re-entry." And he told them "make it blunt." The reason being, as Scott said, the bow shock of air formed by a blunt object pushes the super hot air away from the capsule, and actually insulates it from the hot air. Allowing a relatively small ablative heat shield to protect the capsule from the small amount of heat that gets through.
The space shuttle used the same concept, that's why it was all blunt shaped curves on the leading edges. And even then, the heat tiles were essential to insulate the interior of the craft from the extreme heating of re-entry.
Scott has also presented this phenomenon very deeply. I was surprised of his explation: the shape is optimised for a pattern, where the hotest region is some centimeters (cm) from the spacecraft surface ! Not on the surface.
so if I take 1/2 mv2 = 3/2 kT, for mach 24 and O2, I get T = 86,000K ...so I think it's not the air temp, but the air speed. It has much more kinetic energy than thermal energy.
@@DrDeuteronwhen two objects are travelling at different speeds, the interaction becomes heat. The energy has to go somewhere, and typically it becomes heat.
@@patreekotime4578 One of the things I notice as a lay-person (ie.. non-scientific but still technical person), is that when you have any kind of excess energy and you try to convert it to any other kind of energy you get a whole bunch of *Heat* in addition to your net result of energy in the final form you're working toward. I'm sure there are relevant laws and complex formulas (thermodynamics and physics) that can show this and predict and model this accurately.
Just an observation from watching this and other videos on topics like this.
@@patreekotime4578 and what is the conversion between velocity and temperature? I mean how do you get from meters per second to kelvin?
Great video.. I have often wondered about this and this easily answers the questions that I had about it though I had pretty much already come to the same conclusions. This just presents it so well and clarifies some questions I had about confirming it.
One thought that I had was the very idea of engine braking to slow the craft enough for a simple and safe reentry but that idea included having an abundant amount of fuel on board in order to accomplish that goal and that is a very easy one to dispel as being impractical as your video suggests.
Thanks for producing this. It was very well done.
Short answer: it keeps space clean and free of as many bodies as possible.
Long answer: the amount of thrust it would take to actually bring an object back in without a _Dynamic Entry_ is roughly equivalent to half the thrust it took to put something up there but then you have to add thrust to putting the object and its return rocket up there. So for what's basically two tons of refined high-tech terracotta you can cut the price of the trip in half and look ballsy doing it.
yet someone can go into space and fall back to earth with a parachute.
@@Sticklebackthat someone was not in orbit. Being in space and being in orbit are indeed not the same.
given how much energy is avaliable, seems like an opportunity to use it. Thermo'electric or some high pressure turbine generator?
What about landing on a planet or moon with effectively no atmosphere like the earth's moon?
Then you have no choice but to bring extra fuel for deceleration, right?
they aren't orbiting or were ever at a high speed@@Stickleback
Interestingly, I recently finished re-watching Mobile Suit Zeta Gundam (1986), which features inflatable heatshields for various spacecraft entering Earth's atmosphere. For a show about giant robots from the 1980s, they sure did their homework on ballutes.
Old anime were written by massive nerds, of course they were filled with good scifi! Recent stuff has gotten pretty terrible by comparison :/ You dont get these crazy high quality OVAs for example anymore.
Not only old Gundams, even modern Gundams are surprisingly good at the science and laws of physics once you get over big robots - and even big robots have proper inlore explanation. You also have to remember Gundams are the franchise that has multiple entries meant for different ages from little kids to adults.
@@randomnickifyIt would be really interesting to learn that in-lore explanation for giant robot shaped war machines.
In the film 2010, the US-Soviet space ship uses a ballute as a speed brake as it slingshots through the upper atmosphere of Jupiter no
reentry heating was a serious plot point of one episode of the original show
As beautiful as the re-entry footage is, it wouldn't hurt my understanding of the video to show some of the calculations and concepts you're explaining on the screen (maybe in a corner).
Thanks for the interesting vid!
I have always enjoyed your depth of knowledge in these videos ... this one in particular with the step-by-step math included was insightful. Thanks!
This just blows my mind.
I already understand that re-entry is a rough experience to go through but the mathematical knowledge that is understood about it is just beyond me.
The way Scott talks about it, although i don't understand the most of it leaves me in awe of how much understanding there is about the subject.
How much Scott must put in as regards research & actually understanding then making it into such high quality videos is amazing.
A G-Force indicator would be a very fascinating addition to the Falcon 9 telemetry displays of both stages.
I think we will not have to add one as the rocket has at least three of them for inertial navigation.
I thought it displayed acceleration? That's basically the same thing right?
@@gottfriedheumesser1994 the rocket almost certainly has G sensores since they say they limit acceleration to 3G when carrying astronauts by throttling the engines.
@@HashtagBirdyy No they don't display acceleration. They only show altitude speed and time elapsed. I suppose if you wanted to do the math, you could figure it out, but for quick reference G rate display is what I meant.
@@ILikeDoritos456 No modern rocket or spacecraft can work without acceleration and rotation sensors regardless of whether manned or unmanned.
Dude, thanks for being you. This is one of the dopest videos during your commentary I’ve ever seen. I’d have never sought this out but we’ve got you to show us something special while learning the best of human exploration
Ps, I was all about it till they hit the water. Imagine a failure and survive space only to sink into the darkness and being killed by pressure or cold.
@@erdngtn9942they float you know? Capsules? All the Apollo missions landed in the ocean...
I remember trying to watch the reentry video and getting bored and didn't finish it but , just having you talk over it made it so much more enjoyable for my brain to watch , you should do this format more often. It really works. Ty
What a great video Scott and thanks for posting. I really had the sensation I was along for the ride!
Nice to watch the re-entry all the way to the ocean!
One thing missing from this video is an overlay of velocity and altitude. It would be cool to see the initial entry, climb out of the atmosphere, and reentry to final decent as plots in parallel with the video. (there's likely some national security restrictions to include, but just wishing)
Regarding the L/D (Lift to Drag) ratio of space capsules. Apollo had a L/D ratio of 0.52:1 (or ~1:1.92), and a Dragon Capsule has L/D of 0.18:1 (1:5.6). Apollo reentered at 11 km/s, while a Dragon reenters at a 7.5 km/s. Huge differences in amount of kinetic energy, as notes is a factor of mass*velocity^2.
Starship will be the largest (reusable) spacecraft to undergo reentry. It too will reenter at ~7.5 km/s.
or it's just proprietary. but idk.
Coming back from the Moon unless you've got fuel to burn you're going to reenter at 11km/s-ish. From Mars it turns out it's not that much higher, iirc it's less than 13km/s. It's not the craft that matters, it's the trajectory.
@tjthill Trajectory and especially Velocity that matters because the higher the Velocity the narrower the window of reentery and the more likely that the vessel will not survive reentry.
One thing missing is how stands the Dream Chaser space place for reentry. From what Scott said it should be less fiery than the capsule?
@@arthurzettel6618humans suck. Sure, we can send things out of our solar system, but so far, we’ve only ever returned craft as far as….the moon.
I often wondered about that very same question. Thanks for the clear explanation!
Thanks! I had been wondering about this for quite some time.
I love using the ballute mod in ksp. Shoot for a periopsis of around 56 Km, and deploy the ballute as soon as I'm in the atmosphere. It's so much more gentle landing.
KSP does not correspond very well to reality. My son used to play with it a lot and the scaling factors were all wrong.
@@rogerphelps9939 That's why you need to install the Realism Overhaul and Real Solar System mods. There is a community of people trying to get close to reality.
@@rogerphelps9939well kerbin is 1/8 the size of earth and atmosphere out to 70km. It's not meant to be like earth.
periApsis
@@daves6213 perryplatypus
Little bit surprised you didn't mention (unless I missed it) for the second part, the Japanese project back in 2008 to drop paper airplanes from the ISS. It didn't go anywhere, but the paper planes would've enjoyed a relatively low velocity, survivable-to-paper reentry courtesy their large surface area for drag (and some lift) against their very low weight.
Maybe it didn't go anywhere because you can't "drop" things from the ISS. They'll just end up orbiting with all the other space junk.
@@BrandyBalloon actually you can, the ISS is low enough there is a somewhat significant amount of atmospheric drag, so much it has to boost its orbit up on a regular basis
while at the same time securing the guinness world record for longest paper airplane flight (time and distance) for probably the rest of recorded history. very sneak, japan. very sneaky.
@@BrandyBalloon Nothing just stays in orbit forever, all those satellites still experience gravity and they will eventually fall back to earth. There are also varying distances of orbit and things closer to the Earth will of course come down sooner.
@watvannou
It's not the gravity that will pull them down. Well, it will, because that's what gravity does, but it won't technically be gravity doing it. If they were high enough to be put of our atmosphere ENTIRELY, they'd essentially orbit forever, because they're going fast enough to counter Earth's gravity. That's how they orbit in the first place.
No, it's the air resistance that will pull them down. Once they run out of any fuel on board used to boost their orbit and counter the drag from the extremely thin atmosphere in their orbit, the air resistance will eventually cause them to slow down enough to de-orbit. So no, it isn't gravity that will pull them down, it's the air resistance that will slow them enough that they can no longer counter gravity like they normally would.
Just think, if you brought along enough spare fuel that you could decelerate back down without heat re-entry, every ton of that extra fuel you're carrying means 1 ton less of actual payload you can take. If you needed an extra 40 tons of fuel to do this and your payload capacity was like 45 tons, your actual effective payload becomes only 5 tons, and that turns it into an incredibly cost-inefficient vehicle, since your cost/mass ratio goes WAY up.
It's worse as it's not 1 ton but more like 50+ tons of fuel for 1 ton of payload. The Saturn V rocket burned 20 tons a SECOND for its first stage.
I guess you could refuel for reentry; especially if we start living in a world where many space craft are not designed to ever surface after they are launched like ISS.
and you'd still have to carry the goddamned heat shield in case your return rocket didn't light off right...
I have to correct him a little though: It IS possible to slow down on re-entry, we just don't have the technology for it yet. The 40's era rocket technology just doesn't cut it. Possibly in the future we will have more efficient sources of propulsion.
@@DrewReynolds We could just drag a fuel line to space. You know how a hose will extend out when you spin around with the hose in your hand? Just mega size that using earths rotation :P
Amazing footage, and as always Scotts exceptional video composition and delivery. thanks bro. HNY! :)
I WANTED THIS QUESTION TO BE ANSWER FOR SO LONG, THANKS SCOTT FOR THIS. Very interesting and the ratio of lift and drag explained everything
Excellent video. Setting it over the full reentry video, with some tie-ins, was a great idea. I didn't have the patience to watch the full Orion video when it first came out, but had no problem sitting through it this time. The topic of discussion is fun, and is the sort of thing that gets people interested in space and physics, without being too esoteric.
Plus it was sped up...
Scott, You add so much value to the world! Thanks
An informative video with exhilarating visuals~~ thanks so much!
Hi Scott the science is fascinating and the video of the Artemis re-entry was really good thanks for sharing! Happy new year 🎉
Scott talking about rocket science to a backdrop of stunning footage.
I love this format!
Always wondered this. Thanks for answering a question ive had for 30 years.
Good Video. I once read about the aerodynamics of reentry capsules and their testings back in the days. It was great to see the different designs and their 'surprise' that the now normal design would be better than something pointy.
Thank you Scott! I have often considered why we did things the way we do and why not try X- you explained a lot of it in this video.
Hi Scott. The best gliders are now more than 70:1. My own 40 year old glider does 45:1 without even fitting the tip extentions.
Amazing
That's incredible! I did about 250 hours in a wooden/fabric ES-60 Boomerang back in the late 70's and it had a glide ratio of about 32:1. I gave up flying in 1979 but a 70:1 ration would be a dream!
-Modern High performance gliders are a dream, but you can get just as much fun out of an old Ka-8 with a L:D of 25:1.
You are still alone in the air like a bird.
@@BillysFingers
Diamant 18 has that L/D ratio, 60 has been achieved, with boundary layer suction near 80, I have the report by the University of Delft.
Will send a copy to any one interested.
@@arturoeugster7228 I am interested. How can I find that report?
Fascinating footage and great narration.
Now it all makes sense, thanks for explaining it Scott.
Last time I was this early Starliner was still on schedule
😂😂😂
Now it’s just light pollution.
Love the content.
Loved watching the parachutes and their aerodynamic effect on each other.
Scott!? Can you do a video on how parachutes are calculated with regards to size, passtrough vs letting air pass outside it?
In the video you can see the air passing outside the chute interacting with its siblings, was mesmerising to watch
I wonder if they've fixed the parachutes in KSP2 so they don't act like bosons and pile on top of each other.
I was asking a question about this on another channel and they commented back saying you just posted the answer to my question on your channel. So here I am. And thank you for explaining this.
Thank you for covering this question.
I like the inflatable heat shield idea. I was always intrigued by that style of system being deployed by the ship Leonov to aerobrake in Jupiter's atmosphere in 2010: The Year We Make Contact (Space Odyssey II).
Isn't there a design concept for a personal inflatable heat shield for one man escape pod. I saw it on vintage space. Its much easier to shed energy from 75kg of human going at 17500mph than 105 tons of space shuttle bricks. I just feel the deceleration may be too intense if you're very light.
@@dr_jaymz I think I've heard of that too. Talk about an extreme sport...
Holy moly! That’ll be one hell of a ride 😱. “You go first. I’ll watch”. 😂
@@dr_jaymz Not sure if we saw the same one or even if there was more than one but the one I saw was a giant mylar bag with individual cells on one side and several large cans of expanding foam, the idea being they filled the cells to form the parabola and then become the ablative layer for the Astronaut on the other side, which was clear and would look like a hopefully uncooked foam and cellophane packed cut of meat from the supermarket.
that is fascinating. As deadly as the atmosphere can be against us, it is so frikkin thick and it protects us. Just fascinating to listen to. I love to learn stuff. But I am also bewildered because I ain’t no physicist or mathematician. Thank you for re-learning me this concept that I remember learning in high school but here, in a much more detailed manner!
I have absolutely no idea what you talked about. I was too transfixed by the re-entry footage. Amazing!!!
I love the fact that the footage starts to look like an old ‘60s reel from the distortion.
Sick
I can’t believe how complicated and precise the reentry maneuvers are for Orion. You can say what you want about SLS, but the Orion capsule has been pretty damn impressive (and RELATIVELY on-time and on-budget) since the start - which is incredible given its size and complexity vs. the Apollo capsules. It is literally the only spacecraft in the world capable of doing what it’s doing.
Orion is the first vehicle since Apollo that is capable of carrying humans to the moon and back. I agree that is a big deal. And it was done more efficiently and safer then was done with Apollo.
I might have the scale slightly wrong, but if the Earth was the size of a basketball, the safe re-entry corridor is the thickness of a piece of notebook paper.
@@teebob21Someone just watched Apollo 13, huh? They use that same analogy in the movie!
@@brookswoolson909 Well, it's been a hot minute since I watched that movie, but I also worked at NASA between 1989 and 2007. (Mars Global Surveyor, mainly)
@@teebob21 Very cool! I actually just rewatched Apollo 13 the other day, so that’s why it was top of mind. I bet this video is especially poignant for you because of MGS’s aerobraking technique?
Love this one! Thank you for reminding me of some basic physics!
Oh man I've never seen that reentry before that was the full meal deal and it was really cool thank you for sharing
Good video. Good explanations about delta V and what it takes to slow down or stop in space.
Like anything in aviation and space travel, the tricky part is not getting up there but rather figuring out to get back on the ground in one piece!
Scott great work here, I plan to use this video in my physics classes for work and energy unit and my thermodynamics unit. CP
Yyyeesssssss!
I’ve had this question since I first learned about rockets existing - never had a career in any scientific field so never really quested to find the answer but I am ever so grateful to finally get it. Thanks Scott 🙏☺️✌️
Before i watch the video, this is a question i have had for probably 25yrs.
And you are the first person i have seen bring it up other than myself to one other person about a year ago.
So i am curious on what you are about to show me.
On to the video...
Ok, im back...
Thank You Sir. I now understand this even though im not a rocket scientist or engineer and hate hard math :)
Very good explanation.
I had figured some of it out like more weight for reentry fuel so more fuel and weight and kinda zeros out the idea and the slower you come in the harder the drop without powered entry. But i never thought to DIP in and out like skimming a pond to have time to cool off for a minute and then back in again and so forth.
Great video! Thanks for the info and insights
Great talk! As a 1972 Aeronautical Engineer BS degree I knew the conclusions for both including the Blimp or Zeppelin solution. And even looked into it. So the lighter then air embodied rocket would float to a high atmosphere elevation with zero velocity effectively. Heating say hydrogen as the lift gas would help get higher but not significant.
Then collapse the blimp as the hydrogen lift gas and LOX/LH2 is burned would save almost nothing in fuel considering you have to lift the blimp also. So going into orbit is at best a wash but floating to altitude and being in the correct spot and surviving turbulence etc. in the air is a higher risk then flying or rocketing to that starting height.
Blimp would be so large that you would expend energy just to keep it from skipping or it would have to be a lift body that may actually be pushing towards the earth. Lift body means more weight and control surfaces, more weight. Trade off. And the gas inside the blimp couldn't be hydrogen or oxygen. Needs to be something that will not burn or be the oxidizer.
Skylon fly to space with inflatable heat shield for reentry that is discarded or retracted to finish by flying for a landing. Now that is maybe the best combination since the large wings already need to be there to fly at a low mach number early in the climb into space.
I always wondered why nobody made a launch pad in the Andes. You save about 4 km of atmosphere and are at the equator so a launch eastwards will be most beneficial. Add to that the bulging and you can launch from the point furthest away from earth's center, the inactive volcano Chimborazo with about 2 km further out than Everest. You get less distance to space and less gravity to overcome.
*than
Then is for sequence. Than is what you need for comparisons. ‘If it’s cheaper to A than B then be ready for C.’
Hullo, Scott Manley here... makes my day. would love to see a video of you describing the physics of skipping off the atmosphere. great vid and happy new year sir. fly safe
Delightful re-entry video. Thanks.
Thanks for pulling all this together. It fits together what I knew, confirms my understanding, and adds a bit of math - in an enjoyable way.
I guess we'll have to re-enter with a lot of heat until 3010. Maybe we'll have a space elevator running by then!
Love these thought experiments. We should be careful not to say that alternatives are “not possible” when we actually mean not economical or practical. ;)
Or not thought of...yet.
It's certainly possible to use rockets to decelerate.
I've done so multiple times (by accident) when I tremendously overbuilt my rockets on KSP 😂
Economical? Oh gods no. Possible? Definitely.
I would say it like this: Our (chemical rocket) tech is currently barely energetic enough able to have enough energy to get things into space, not to keep it there without using the magic of orbit paths and then get back on earth by using very little energy by using aero braking. When we have more energetic means (fusion, antimatter, Star Wars tech, etc.) then sure, one can spend the energy to slow down in space and come down as slowly as you want. Like in Star Wars, the ships are depicted as having very energetic propulsion systems and the ships are depicted as not orbiting planets, because they don’t need to.
@@GantryG I was curious about a video I watched earlier that talked about SpaceX and Nasa as well as Boeing. Supposedly they have built aircraft that may fly to satellite altitudes up to 350 miles. Is that still within an area that requires aero braking? Maybe they haven't tested them yet.
In the general scheme of things, the resin composite used for ablative heat shields is the same as that of most automotive brake pads. So it's relatively inexpensive compared to other possible approaches of slowing down. Although it may be modified a bit, it's not like some super exotic material either.
Heck, wooden heat shields have been used. These are however only useful as a single use item obviously.
Huh, I heard they used aerogel or something. TLI.
@@OsirusHandle The shuttle used ceramic tiles which were fairly exotic.
@@placeholdername0000 Not significantly ablative AFAIR (or did they have ablative coatings?)
@@DavidEsp1 True, they weren't meant to ablate.
This has answered something I'd wondered about for years! Didn't appreciate how much fuel would be used to slow stuff down
Many thanks for that analysis. It exactly answered (sadly!) various ideas I've toyed with in my idle moments over the years.
I tried that in KSP 1 a few years ago, and I came with the same conclusion, using the heatshield is the best solution.
I recently started playing that. A miscalculation returning from the smaller moon meant I had to use up all the thrusters and push with the jetpacks just to get my orbit down to 65km, it still took dozens of passes to get back. The first few passes completely consumed the ablative part of the heat shield, whatever was left seems to have held up. Is the ablator just a placebo?
@@shanent5793 KSP1 parts are very tolerant to heat. To have a more realistic situation (and probably still not enough to be similar from a real Earth reentry), try to land on Eve.
I remember playing on Real Solar System and good lord, a few Km too low and you exploded, a few too high and you just shot through the atmosphere. Real difficult.
I tried a winged reentry vehicle and it was really difficult to land too.
@@shanent5793 for landing a single capsule on Kerbin, from orbit, essentially yes.
If you want to bring home more than just the capsule or come straight in from an interplanetary trip, whether on Kerbin or somewhere else, that's when you're more likely to need the ablation.
Thats why when i do anything flying in rss i use A LOT of parachutes @@OsirusHandle
What if you attached butter toast to cat, with butter side being side not attached to cat and other side attaches to back of cat. Since cat always lands on legs and toast butter side up either it spins super fast or levitate which both would provide necessary lift (this is joke)
That's debatable.
Landing…fine, but no source of delta V for deceleration. :)
This was an enlightening video. I was trying to come up with some esoteric designs for smoother reentry and the zepplin concept is not far off from what I came up with. I was actually thinking of something like the ships from Arrival, which are zepplin shaped, but are oriented perpendicular to the ground, rather than parallel.
That was one of the coolest videos Ive ever watched! And I always wondered this...
Happy pre new year everyone.
Forgetting all the impracticalities of creating one, would docking with a space elevator then travelling down solve the issue. I have seen videos on how they are impossible to build, it would be great to have one on how the orbital physics would work if one was built. Great video!
A true space elevator is beyond known material science. But an orbital ring with tethers to the planet is merely a very expensive engineering problem.
I always dream of that. I think it would be so cool that once it was built, it could be used forever! But dayam! 26000 miles is a bunch of weight even if you are using fishing line! The day we figure out how to make that elevator is the day we won't need that elevator!
I do wonder how many buttons would be on that elevator, just two? Would there be an emergency stop to slide the door open to take a wiz, since the journey would take days! I guess that elevator would need to get after it cuz 100mph isn't going to cut it!
Funny Willy Wonka's elevator made exploration possible by transforming it into a rocket and now we want to replace a rocket with an actual elevator!
Are there any movies with space elevators? I vaguely remember one of the StarTrek movies, some kind of planet punching drill?
Awesome presentation and explanation!
That re-entry video is really cool.
What I would find most scary if I was riding that would be towards the end, watching those inflated main parachutes hitting each other, wondering if they'd get tangled or otherwise collapse...
Another great video. The best gliders have an LD of 65 or 70. It would be great to see your take on sailplane performance and I'm sure you'd love the experience of flying a Nimbus 4D.
Problem with gliders is you would have to descend way earlier in order to get where you wanted, and you'd have a big chance of overshooting or undershooting the landing by a lot. You obviously need spacecraft to come down somewhere remote and safe, while also being specific. There's also the cost of recovering the craft...the more you're off course, the higher the cost, and not a trivial cost either. So heatshields just makes everything simpler and more predictable. These craft are also a lot heavier, because they need to be structurally strong for space, while maintaining an airtight atmosphere, and withstand things like flexing.
Scott did an excellent job of explaining why its not practical to slam on the breaks and slowly drop back into the atmosphere. However once humanity moves past the whole needing a rocket to get into space issue and can travel up out of earths atmosphere like seen in most scifi movies, then yea you can just fly down to earth at slower speeds. But currently, the way re-entry is done is the most practical method.
Just one slight issue: we don't have enough handwavium to make reactionless thrusters capable of lifting a significant payload into orbit.
@@Runiat "Handwavium". I gotta remember that!!
you mean like a space elevator ?
@@tma2001 Yeah, that's a good example of "handwavium". The only place a space elevator works is at geo-stationary orbit.
@@tma2001 Space elevator is another one of those stupid invention ideas that by the time material science has developed to the state that it can be done, the whole issue with overcoming gravity will already be solved using solid state mechanics..
I always like these videos - and I chuckled a bit when at 0:30 you point out that the spacecraft has 15 times the energy content of TNT!
That certainly sounds more impressive than saying that it has 3.5 times the energy of table sugar, or half again as much energy as bacon grease (sugar and fat have 17 and 37 kJ/g vs. 4 kJ/g of TNT).
Awesome explanation of what is going on during Reentry....all my life watching the Gemini and Apollo missions...I always would say...."just slow down the Reentry speed" and do away with the heat shields.....thank your for putting it in a understandable way....until the next one....👍👍
SpaceX Starship would be a good example for the blunt way to do re-entry, using the biggest surface you have to hand.
Happy New Year🖖 and thanks for your work, time and passion.
A futuristic solution is an orbital spaceport plus a space elevator to get back down to the surface. Maybe in a century or two, if we haven't blown the place up by then . . . sigh.
All the best for 2024, Scott. Fly safe!
Just lie and tell them space elevators make it easier to blow up other places.
Assumingg we ever can figure out how to build a space elevator :/ We could totally do a station in geo synch. orbit though. Will we? Prob. not in the next 40 years unless its a private company cause NASA has a shoestring budget and everything they wanna do has to get the okay of our wonderful congress which never agrees on anything :/
You would still need fuel/propellant to dock with the port and elevator. The atmosphere basically is free propellant, so a bit wasteful not to use it. Maybe your argument is to dock a large spacecraft to a port in an orbit favourable to your incoming trajectory, then switch to a tiny vehicle which is much cheaper to take to the elevator, but you would still need tonnes of fuel to do either.
So atmospheric breaking it is until we have warp drives...
space elevator for big planets like earth is just a pipe dream
any civilization who can build a space elevator , is advanced enough to not need it.
The US just bombed the Nordstream 2 pipeline... So probably No space elevator anytime soon
Great analysis Scott. I'd add one thing. The atmosphere boundary, if you can call it that, isn't exactly uniform. Things which affect the shape and density include the Van Allen Belts (dependent on current magnetic pole position and axial tilt relative to plane of orbit/insertion) large weather systems, ie low pressure regions are rising which push the stratosphere towards the thermosphere which pushes the exosphere, which is what you make make contact with. Then there's solar winds, which push the atmosphere towards the Earth on the sunny side and away on the dark side, such that the exosphere can be over 100km higher on the dark side, depending on the recent strength of the solar wind, which we can't always predict though we are getting better at it. An example of this was when SpaceX lost a large number of Starlink satellites during a launch due to solar wind pushing too much atmosphere in their way during the first few hours after deployment where they don't use their thrusters to avoid damaging each other... I'm going to assume their firmware has been adjusted to shorten that waiting period if they detect delta-v while not operating thrusters!
Yeah, I also found JP aerospace's concept intriguing, even ordered their book "Floating to Space'. Would be great, to watch a whole video about that, Mr. Manley
So, if plasma is what is formed at the front of the vehicle, can you push against it with some EM fields? That way the vehicle stays clear of the plasma and you get the slowing effect.
In theory certainly yes, in practice that would require a Lot of energy to push against it at such high energies and since you already have a plasma formed around the ship trying to use an electromagnetic tether could be a tad.. problematic shall we say.
But yea if someone solved the engineering issues yes
The pushing is quite hard... We do it in fusion reactors (with huge magnets and induced currents and still barely manage to give it the desired ring shape) and Earth does deflect incoming charged particles with its magnetic field, but AFAIK there's no technology to take chaotically forming wildly varying masses of plasma that form near the front of our vehicle and ask them to take a step back.
Not a physicist. Plasma is positively charged. If you have some grid 1m ahead of the ship made from a heat resistant material, and charge it positively, would that not push against the plasma? And i dont think you need to control the plasma. Just push against the whole of the front wave. I presume the net effect would be decelerating...
Wouldn't that be like moving a conductor near a magnet? The magnet induces a current in the conductor and the electrical resistance causes drag. I think that would slow the plasma down which is less desirable than letting it quickly go around the spacecraft
*instead of messing with thousands of tiles which adds weight and complexity why not simply carry dry ice and heat it with the high reentry temperature so that it flows out thru nozzles at the FRONT at high pressure and encases the vehicle in cold CO2 gas for those few minutes of reentry? the cold co2 gas will act as a shield.*
I think this kind of stuff is what KSP teaches in a certain deep way. It lets you try your original thoughts and fail. It makes you *feel* it.
Great video. As an observer of heat shield reentries since the early Apollo days, I learned a lot of specifics in this. And I now know it won't be a hoax if I see a reference to a "Space Zeppelin."
Moving from space faring speeds to earth faring speeds requires a huge change in momentum, and that is only controllable by the input of opposing energy. Either you have to carry that energy yourself, as with a huge fuel cost, or just use the frictional energy that naturally occurs as the space object contacts the atmosphere. Free energy vs costly energy. That's the equation. If you try to slowly work against gravity to gradually dissipate momentum, and spread the frictional energy over a longer span of reentry time, you still need to carry more fuel to control that longer reentry. The easiest way is ultimately just to let atmospheric friction do its thing for "free", just using the cost of heat resistant tiles.
atmospheric entry..... SO HOT RIGHT NOW :O
Very interesting! You talk about the L/D ratio, but those numbers sound very similar to the glide ratio (a GA plane has around 10:1 very good glider has 50:1 etc.); would you say as a rule of thumb they can be treated the same?
It can be proven that these numbers are exactly the same. So not merely a rule of thumb, but a rule.
Lift/drag ratio is glide ratio
awsome vid, love seeing the plasma formed
I have always wondered the same thing... good to know.