To the people asking how you can "Bounce" of the atmosphere, think of it this way: Imagine the top of the atmosphere as the surface of a lake. If you hit it slow enough, you'll glide into the water. But hit too hard, and the object bounces, but eventually falls into the water. The pain from a "Belly Flop" would be what the craft would experience hitting the atmosphere, but the spacecraft would hit thousands of times harder. Hope this helps!
Why would that description help? Apollo craft returning from the moon could skip off the atmosphere because they were coming in MUCH faster than an object in a LEO (Low Earth Orbit). Objects in a LEO won't ever "skip off" unless they are trying to and aren't going very deep into the atmosphere (and thrusting at the same time- search WaveRider for more). They just don't have the energy. Once anything gets below 100 km altitude, it is coming in. You can use a huge deorbit burn and hit that 100 km line very steep and burn yourself up, or use a more modest deorbit burn (but one that will still take your perigee close to ~100 km, maybe ~150, I forget) and burn energy off more gradually, thereby not baking your spacecraft and not decelerating so quickly your aorta rips loose.
Love this, the bouncy atmosphere analogy was excellent for painting a mental picture of the forces at play here. I was able to imagine the concept of our atmosphere in relation to the point at which it becomes normal space and the transition of a physical object between the two with surprising clarity. Nailed it Hank.
+Bill Smith it's not... same way that you can skip rocks on water, if the angle is too shallow, you can skip off. if you point right at the ground(90 degrees), geo sync orbit you can surely enter the atmosphere at whatever speed. If you arent orbiting at the same speed as the atmosphere, just think that atmosphere is making 1 revolution per day at oh, 300 miles up. so it will be moving even if you aren't.
+Bill Smith I think this needs some clarification. He said if you go too slow it won't penetrate the atmosphere and would bounce off. Does that mean if you came to a stop you could just sit on the atmosphere? This doesn't make sense to me seeing how the atmosphere would be so thin at that altitude you would fall through it eventually reaching terminal velocity, which would decrease as you get lower. Which begs the question, why don't space craft do that?
+Dave Akers someone who actually knows feel free to correct me, but I think when they mean that if the shuttle comes in too slow, think of too slow in the context of spaceships. Sure, if it were possible, I'm sure you could slow to the speed of a car and go through the atmosphere as if it were nothing, but it would take forever to reach the ground that way and be horribly inefficient. But like he said, when you're traveling at speeds necessary for space travel and orbit, if you're flying through vacuum and suddenly hit an atmosphere at the wrong angle. .....bad stuff is going to happen. Just like the rock skipping over water analogy, yeah, if you threw a rock over water the right way, it bounces, but that doesn't mean that if you hold a rock inches over the surface of the water and slowly insert it into the water, it will bounce. It's all about the speed....and this case, the angle too. Like the host said, the atmosphere just doesn't have the time to get out of the way
It's hard to conceptualize because we're ALWAYS moving through an atmosphere so it seems like nothing to us, but we're also moving very slowly through said atmosphere. But atmosphere is matter....it's something you have to push through. when you're travelling through space, you're moving through pretty much nothing. So imagine travelling through nothing at a very fast speed and suddenly hitting...something. You're going to feel it as soon as the spacecraft hits that matter. Now imagine going so fast that that matter (atmosphere) literally doesn't have time to get pushed out of the way. It's like hitting a brick wall. It's like the same thing as if you jumped off a high diving board and into the water...you feel that impact even though it's just water. If you next to that water and slowly moved your hand into the water, you barely feel anything. Speed is the difference.
Looking forward to the next one. Seeing first hand the ablative shields at the Air and Space Museum in D.C. really puts the kind of amazing heat spacecraft must endure during reentry into perspective. Great topic.
Kenneth Oppel's Starclimber mentioned needing to re-enter the atmosphere at a specific angle to not bounce off, if I recall correctly. It sounded logical enough at the time. I didn't realize it was based on actual facts. I love when fiction writers maintain internal consistency using real world physics or facts.
It won't be, because it's a misconception. A spacecraft reenters because it's lost enough velocity that it can no longer orbit. In order to "skip off", which is something that's often said but never with much to explain what happens next (presumably the spacecraft flying back out into orbit, else it wouldn't be called "skipping off" at all, but just a prolonged reentry at a dynamically shallowing angle)... anyway, in order to "skip off", the atmosphere would have to add quite a bit of kinetic energy to the spacecraft. Something like half a kilometer per second of velocity most likely. The trouble is that the atmosphere can only really act with the force of drag, which is a form of friction, which can only resist movement, not add to it. Instead, too shallow a reentry simply never enters dense enough atmosphere to be slowed down sufficiently to fully de-orbit. Its path is still elliptical (or hyperbolic in the case of interplanetary reentry), just modified slightly to reduce apogee by the friction with the low-density upper atmosphere. Indeed, such maneuvers are sometimes done deliberately, called Aerobraking if used to bleed off velocity for a more efficient transfer from a high orbit to a low one, or Aerocapture if used to transfer from a hyperbolic orbit to a closed orbit at the end of an interplanetary journey. Done unintentionally, however, it can mean the spacecraft might have to stay in orbit longer than supplies or power reserves can allow (many days in the case of a return from the moon, which is when this strange myth got its start, presumably in a wildly inaccurate public service video meant to convey a sense of daring and danger to the Apollo program), so it's generally not desired unless it's planned. In the case of a deorbit from low earth orbit however, like the space shuttle uses, it's extremely unlikely that too little velocity would be bled off for a successful deorbit. At worst it might start to gain altitude part way through the de-orbit, but then continue losing speed and go back down again. Even if it did go back up into what is considered empty space, it would be back to its perigee in about an hour and a half... enough time that everyone would have to go to the bathroom perhaps, but they wouldn't starve to death. It would also however, no longer be in position to land at the planned coordinates due to the continued rotation of the Earth, which could also be tricky. It's also worth noting that at the angle of attack used during shuttle reentry, thanks to its far greater apparent cross-sectional area in relation to its mass, the Space Shuttle was actually far, far more "blunt" than a capsule-style reentry vehicle, which at hypersonic velocities is actually quite well streamlined thanks to the shockwave formed just ahead of it, that forms an ideal surface at all velocities. It's this much-increased drag, along with the ability to create aerodynamic lift, that allowed the shuttle to enter at such a shallow angle, not some magical barrier it would "bounce off of" if it weren't streamlined.
Angle of Attack is the specific angle between the chord of the wing (a line between the leading edge and trailing edge of the wing) and the relative airflow... The Angle you are talking about would be sink rate.
That episode gave me flashbacks to the movie Apollo 13, I think the part with "like a rock off a lake" was changed from Apollo 13's "skipping a rock off a pond"
I like it better when Caitlin host, she's got that cute nerdy lab assistant in chemistry class vibe. Hank reminds me of the guy that's always talking about how fast he finished his home work, while trying to look cool with his messenger bag full of note books.
I may be quoting Kerbal Space Program again, but how about bouncing off the atmosphere several times to loose more and more of your orbital velocity and then finally plunging down? Why do spacecraft have to go through the entire ordeal in one sitting? If the whole goal of reentry is to bleed off the kinetic energy you used to get into space in the first place, why not bleed it off through a lengthier amount of time?
I think this is why. In the video Hank mentioned that you need a lot of speed (kinetic energy) to puncture through the Earth's atmosphere so if you tried that you may just end up orbiting around the Earth instead of going down to the surface.
Sand Dry I thought about that too, but if you consider that each time you brushed the atmosphere, a small bit of your kinetic energy would be lost, then at some point you're bound to fall to the ground. This is after all why big spacecraft like the ISS have to make periodic burns in their engines to keep afloat. Otherwise the tiny friction with the sparse air molecules in its path slows it down and reduces its orbital speed gradually. So if the ISS is worried about "reentrying" by mistake, why not purposefully reentrying in such a way?
alot of it has to do with the time it would take to do something to that degree, also if you were trying to land on a runway like the shuttle then its much easier and safer to do it in the same setting. Not that NASA (or at the very least KSP players) don't do what you are referring to the technical name being "Aerobraking,"
talksfor lifetwo yeah, my guess too is that such process would take a much longer amount of time. Possibly an _unreasonable_ amount of time which would offset all possible advantages
I see what you mean,but that only works if you are returning froom the moon or some other planet,and you want to safely kill all that velocity.The"curiosity"rover used multiple flyby maneuvers to safely slow down and land on Mars. But if you are planing to land on the specific spot(which you have to),the retro burn from LEO has to be done at the exact time. The angle of attack also has to be precise. "Bouncing" is to unpedictable and dangerous if you are not planing to land in the middle of nowhere. "If the whole goal of reentry is to bleed off the kinetic energy you used to get into space in the first place, why not bleed it off through a lengthier amount of time?" They do exactly that. They just dont "bounce".
The imperial system isn't "imprecise" dumb fuck. If you are making that claim then you obviously don't understand it.Weight, distance, speed, etc. can be measured just as precisely in both systems...the only difference is what exact numbers will represent their values.1 kilometer is exactly 1 km, 1 mile is exactly 1 mile.They are equally precise.And why does the whole world have to think and do everything exactly the same?Just because youre too insecure to accept that other people don't all like what you like?
That's completely true? An object like a SPACE SHUTTLE can smash/bounce off of our atmosphere? -MIND BLOWN- ( just an average person but love watching scishow, assumes atmosphere as air...remember-far from genius) keep up the good work!
With practice humans can remain conscious at well over 6 G's, and, for short periods (seconds, not minutes) even at more than 12 G's. Red Bull Air Race pilots will sometimes pull 12 G's while maneuvering during the race and are occasionally disqualified for exceeding the 12 G safety limit of the aircraft. It's called over G-ing the airplane, and it is a good way to bend very expensive components. Fortunately for the Air Race pilot who accidentally over G's his plane, the wings don't fall off until you top at least 15 G's in those particular aircraft. (More common aircraft like a Cessna Skyhawk will come apart at around 6 G's, and commercial airliners won't tolerate even that many.) While the pilots do wear G-suits these days, that wasn't always the case. They pulled just as many G's then as they do today, and, when you're flying 200+ miles an hour 50 feet off the ground while engaging in low-level aerobatics, blacking out becomes very obvious to everyone very quickly!
Gunslinger454 Also John Glenn reached 9Gs during ascent on the Atlas rocket, reaching orbit in a little over 5 minutes, making the Mercury-Atlas astronauts the fastest to reach orbit.
So, the bouncing of the atmosphere thing is really hard for me to grasp. Would the craft just bounce around forever? What would happen after the initial bounce off?
I presume after the initial bounce off it would go back out to space, and after a while, stop bouncing. Think of it like a paddle ball, as you put less momentum into the bounce, the ball stops hitting the paddle.
coolguyman16 Ok correct me if I'm wrong. Space shuttles need to maintain a certain speed to remain in orbit. So if they drop out of orbit and are no longer moving fast enough to reenter the atmosphere what would happen? I might be wrong, but I'd assume that at this point the shuttle would also not be moving fast enough to escape earths gravity, and that's where my confusion is coming from. So I based on that assumption, which may be wrong, this hypothetical shuttle is just stuck there? It can't escape earth gravity, but it also can't get through the atmosphere. I'm just trying to explain my understanding and confusion that comes from it, so if anyone could clarify I'd be really happy with that.
Morgan A It isn't that you need to maintain a speed to remain in orbit - Orbit is actually a state of free-fall. Since the craft is in space, it's just a matter of reaching the lateral speed necessary to 'miss' the Earth while falling towards it, creating the orbit. Once that's reached, there's no 'maintaining' to do, you're just falling in a circle in space around a large object like Earth. The mechanics of getting out of orbit are actually a little weird as well, for that reason, since closer orbits are actually -faster-, so accelerating in the direction you're orbiting actually can take you downward towards the surface in certain circumstances, while slowing down can take you further away from the planet's surface. It's weird and counter-intuitive in a way, but that's space for you.
No,the craft would temporarily"bounce"but then the true problem begins,because your vertical velocity woud spike as you re enter the atmosphere at a steep angle. Not to mention that if you do survive the g forces,and the heat,that will be much more intense,you WILL miss the landing site,so good luck with that "little"problem. I tell you,sometimes being an astronaut,is not fun.
Morgan A It would come around once again to reenter. It wouldn't simply accidentally escape the Earth's gravity, that takes an enormous amount of energy. Its orbit already intersects the atmosphere, so one more orbit later it would begin to slow down again.
have you seen those videos where they extract all the air off a metal barrel and the barrel is squished by what seems like an invisible hand? That's just how _dense_ our atmosphere is.
Arturo Gutierrez I knew it was that thick... (It's that basics on how vacuums work) But I did not know it was thick enough and had a such defined horizon that on contact it would be like belly flopping into a pool.
***** The game is much more interesting with it. Aero braking suddenly becomes much more dangerous if your approach is to deep in the atmosphere. Roughly speaking,newer go below 20km with your periapse and you should be fine.
Eric Nash It is not the atmosphere that is dense,its the speed that is the problem. At around 28.000km/h even a "near" vacuum has an effect on the craft. That will be one of the problems that we will have to solve if we ever manage to build something that will almost reach the speed of light. At that speed even the vacum of space is deadly(non ionizing radiation becomes ionizing). Not to mention that if you where to hit an object the size of a grain of sand,it would hit with a force of a nuclear explosion.
I always wondered, How is it that there are so many people support ufo theories but no one ever explained how these objects could possibly travel so fast in our atmosphere without sonic boom etc.
+NI Bojczuk Simple, they found a way to nullify friction between atmosphere and skin of their ship. For any decent civilization that posses a planetary landing craft, that would be the ultimate goal : how to land something regardless of the type and density of the atmosphere you land in. One step in the right direction are superconductors. You project some sort of a magnetic field forward, along the axis of travel, repelling the different atoms, creating like a funnel of vacuum, in which your ship can accelerate. Another type of design I can think of is some sort of a permeable ship skin, that absorbs all income molecules of air and converts them into fuel or whatever. Having an anti gravity engine, you can simulate any type of gravity you want, that means you can nullify inertia, so all the bombardment of air molecules your ship would sustain , you can nullify thanks to your engines.
Sans the Moral Compass Atoms don't have a charge. Electrons and protons have charges. Atoms are neutral. Superconductors make an enormous difference. Too bad we can't produce a stable one at room temperature, yet
I have an engineering degree and worked at Lockheed Martin as a satellite engineer, and I needed this channel to explain "re-entry" to me. God, I feel dumb... I'm literally doing the math right now to see how fast I would hit the atmosphere if I just "pushed off" of a geo-stationary satellite (aside from needing enough oxygen to travel 23k miles).
the part about bouncing off is some nonsense. I'm not sure what they were trying to say, but slowing down in the orbit will definitely not prevent you from penetrating the atmosphere. the main reason the spacecrafts don't slow down more before descent is the cost of fuel. It's much cheaper to burn off the speed in the atmosphere using heat shields, than burn tons of fuel in the orbit.
How did "rocket science" become the measuring stick for difficulty? I realize it's just an idiom and I'm also not trying to downplay rocket science at all...but it is by no means the most difficult or rigorous field of study in today's world. I cannot say what is, but I could certainly propose a few: neuroscience, bioengineering, theoretical physics... hopefully you see my point.
The reason is that the idiom didn't come from today's world. It came back from a time where neuroscience and bioengineering didn't exist. It came from a time where rocket science WAS theoretical physics. It just stuck around like a lot of other idioms.
I think it is because in rocket science you not only have to do complex math, you have to be _really_ sure your calculations are correct, otherwise you or someone else may die in horrible ways. So perhaps we say that not just because the rocket equations and orbital parameters are complicated. But because there's also *a lot* more in stake compared to other sciences if someone makes a mistake. I think it is a matter of "practical" difficulty more than theoretical difficulty.
Ya, I was just talking to Dr. Roger McNamara (head of the Orion Abort System) about all this yesterday. It's pretty damn awesome. Who's excited to see Orion launch?
Oh Hank, dear Hank, could you make a video explaining how the atmosphere could be so dense that you'd bounce off of it?? It seems to be very complicated and VERY interesting!
"The jets fired at what looked like treetop height, slamming us down into our couches. I smiled, which is hard to do with ten gravities pulling at you, thinking about the expression on the colonel's face at that moment. "
Very interesting!!! I think you guys have already done this but Warp Theory is interesting. As is out ability to protect astronauts (and potential space citizens) from solar radiation
No space craft designed would be able to 'skip' off the atmosphere, the terminal velocity is just to high. However, if a spaceship could use the atmosphere as a trampoline, the ship could use a lot less fuel for certain maneuvers.
What if you slow down to nearly zero km/h or m/s would you just fall to the earth due to gravity and penetrate the atmosphere gently? Like is there no way to ease into it, like you go so slow that you are not hitting the the molecules fast enough to burn up
Sometimes I experience some of those symptoms during re-entry to wakefulness in the morning. Dizziness... blurred vision... passing out for another hour or so.
7.7k m/s sounds slow when it comes to space travel, but when you consider a huge man-made object crossing 77 football fields in 1 second... thats pretty damn fast.
2:06 I don't understand the part about if you go too slow the atmosphere is too dense. Its not some physical shield. If you are going slow enough the air has plenty of time to move out of the way.
What happens if the angle is too shallow and you skip on the surface ? Surely you will not have escape velocity or you would not the in a condition to skip in the first place. Would you keep on skipping untill you slow down enough for the angle to be steep enough for reantry ?
So some commenters before me asked a variation of the question, but what I want to know is WHY it bounces off? Every time I watch or read about re entry they always talk about bouncing off anndd... they move onto the rest of the talk not actually saying why? If you slowed down the space craft and had it float towards Earth what exactly is stopping it from coming back?
Would it be practical to have a separate re-entry vessel for longer trips. For example if we were to travel to the moon, if in the return trip a new ship is launched. The astronauts would then transfer into this spacecraft then return to earth.
so if you can bounce off the atmosphere does that mean you can also stand on it? or at least have a boat on it. i know you probably can't but i'm having trouble understanding how the atmosphere works so that you can bounce off it.
This is the equivalent of sending a person in a plane, making them fly, but not teaching them how to get back down, Then you included a how to book in the cockpit
wait, didn't that spaceX plane enter slowly by rotating it's wings and entering more like a leaf or something similar or is that one of those that didn't fully leave the atmosphere so it never had to fully re enter?
If you slow down to an almost complete stop (in relation to our atmosphere) before or just at the Karman line. (A rock set on, not thrown into a pond will go straight in). Then let gravity and maybe some propulsion lower the craft into the atmosphere at a much slower rate. Then once enough in the atmosphere the craft behave like a plane.
This is a very big fuel waste. Where would you get all this fuel to decelerate that much? You need to bring it up with you and that means you need even more fuel to get all that stuff in orbit in the first place. Or as my physics prof said: "In rocket science, every gram is a bitch." (actual words)
I'm confused what you're trying to say about the atmosphere being too dense to penetrate without going really fast. I mean, it's air. If you dropped something in at suborbital velocity it wouldn't just bounce, it would fall through the air and reach the ground. Spacecraft entering at orbital velocity but *at the wrong angle* can sort of "skip" off like a rock, but it's not like you can't enter the atmosphere without going super fast. It's just that it would take a lot more fuel to slow down to a safer speed from your orbital velocity.
My physics teacher said that "deceleration" isn't the accurate word. Slowing down, speeding up, any change at all is acceleration, just positive or negative. The term deceleration now bothers me to no end.
+Helen Wang Think of deceleration as a word referring to "acceleration in the direction *opposite* to direction of velocity." Therefore, deceleration is still a relevant word. It's just easier to teach physics by referring to deceleration as negative acceleration (for the equations). I hope my perspective helps alleviate your frustration. ;)
Deceleration is a real word, and it's exactly what they said it means. You could say "negative acceleration" but the word "acceleration" usually refers to a positive change in velocity.
I've heard of this "Bouncing off the atmosphere" before, usually star trek. Didn't know it was a real thing, and really not sure how it's possible. By that logic, I could slowly approach a planet, and then "sit" on it's atmosphere, no?
If you are going slow enough you don't bounce. Or you could think of airplanes as craft that bounce their way around the globe. As a completely unanalogous analogy, think of a stone on a pond. Fast enough and it skips, slow enough and it sinks.
so why cant they just thrust in the reverse of their velocity to slow down enough where the orbit would intersect the karman line, and at that point do exactly what hank said and just skip along the atmosphere until friction slows it enough that it can just sink through the atmosphere?
Is it possible to come down in an orbit? 1st orbit the planet then into the atmosphere while dropping speed till they become avient? How long would that take?
What about the technique from the Silvervogel concept, where the bomber would decelerate and reenter the atmosphere by literally bouncing off of that 'wall' repeatedly until it slows down enough to pass through slowly.
![Lil Uzi Vert - We Good [Official Audio]](http://i.ytimg.com/vi/DrSfBULAsek/mqdefault.jpg)
love the animation of the shuttle hitting the air wall.
love that totally incorrect animation
watching this to improve my Kerbal survival rate
+ThatMrTC Agreed. This video should be integrated into KSP 1.1 tutorials
Lol
To the people asking how you can "Bounce" of the atmosphere, think of it this way: Imagine the top of the atmosphere as the surface of a lake. If you hit it slow enough, you'll glide into the water. But hit too hard, and the object bounces, but eventually falls into the water. The pain from a "Belly Flop" would be what the craft would experience hitting the atmosphere, but the spacecraft would hit thousands of times harder. Hope this helps!
Why would that description help? Apollo craft returning from the moon could skip off the atmosphere because they were coming in MUCH faster than an object in a LEO (Low Earth Orbit). Objects in a LEO won't ever "skip off" unless they are trying to and aren't going very deep into the atmosphere (and thrusting at the same time- search WaveRider for more). They just don't have the energy. Once anything gets below 100 km altitude, it is coming in. You can use a huge deorbit burn and hit that 100 km line very steep and burn yourself up, or use a more modest deorbit burn (but one that will still take your perigee close to ~100 km, maybe ~150, I forget) and burn energy off more gradually, thereby not baking your spacecraft and not decelerating so quickly your aorta rips loose.
ahgflyguy it's an analogy.
It helps.
Anonymous Mystery that's what I'm saying How does too slow result in a bounce?
New American Fishkeeper he said going too slow would result in bounce how?
Love this, the bouncy atmosphere analogy was excellent for painting a mental picture of the forces at play here. I was able to imagine the concept of our atmosphere in relation to the point at which it becomes normal space and the transition of a physical object between the two with surprising clarity. Nailed it Hank.
This is awesome! I had no idea that the atmosphere was so think that shuttles and *bounce off of it*!
+Bill Smith it's not... same way that you can skip rocks on water, if the angle is too shallow, you can skip off. if you point right at the ground(90 degrees), geo sync orbit you can surely enter the atmosphere at whatever speed. If you arent orbiting at the same speed as the atmosphere, just think that atmosphere is making 1 revolution per day at oh, 300 miles up. so it will be moving even if you aren't.
+Bill Smith I think this needs some clarification. He said if you go too slow it won't penetrate the atmosphere and would bounce off. Does that mean if you came to a stop you could just sit on the atmosphere? This doesn't make sense to me seeing how the atmosphere would be so thin at that altitude you would fall through it eventually reaching terminal velocity, which would decrease as you get lower. Which begs the question, why don't space craft do that?
+Dave Akers someone who actually knows feel free to correct me, but I think when they mean that if the shuttle comes in too slow, think of too slow in the context of spaceships. Sure, if it were possible, I'm sure you could slow to the speed of a car and go through the atmosphere as if it were nothing, but it would take forever to reach the ground that way and be horribly inefficient. But like he said, when you're traveling at speeds necessary for space travel and orbit, if you're flying through vacuum and suddenly hit an atmosphere at the wrong angle. .....bad stuff is going to happen. Just like the rock skipping over water analogy, yeah, if you threw a rock over water the right way, it bounces, but that doesn't mean that if you hold a rock inches over the surface of the water and slowly insert it into the water, it will bounce. It's all about the speed....and this case, the angle too. Like the host said, the atmosphere just doesn't have the time to get out of the way
it will only bounce if it's moving. If it's still, gravity will take over and it will fall. it need some speed to maintain an orbit
It's hard to conceptualize because we're ALWAYS moving through an atmosphere so it seems like nothing to us, but we're also moving very slowly through said atmosphere. But atmosphere is matter....it's something you have to push through. when you're travelling through space, you're moving through pretty much nothing. So imagine travelling through nothing at a very fast speed and suddenly hitting...something. You're going to feel it as soon as the spacecraft hits that matter. Now imagine going so fast that that matter (atmosphere) literally doesn't have time to get pushed out of the way. It's like hitting a brick wall. It's like the same thing as if you jumped off a high diving board and into the water...you feel that impact even though it's just water. If you next to that water and slowly moved your hand into the water, you barely feel anything. Speed is the difference.
Looking forward to the next one. Seeing first hand the ablative shields at the Air and Space Museum in D.C. really puts the kind of amazing heat spacecraft must endure during reentry into perspective. Great topic.
Kenneth Oppel's Starclimber mentioned needing to re-enter the atmosphere at a specific angle to not bounce off, if I recall correctly. It sounded logical enough at the time. I didn't realize it was based on actual facts. I love when fiction writers maintain internal consistency using real world physics or facts.
The "skip off the atmosphere like a rock" thing really should get explained better.
It won't be, because it's a misconception. A spacecraft reenters because it's lost enough velocity that it can no longer orbit. In order to "skip off", which is something that's often said but never with much to explain what happens next (presumably the spacecraft flying back out into orbit, else it wouldn't be called "skipping off" at all, but just a prolonged reentry at a dynamically shallowing angle)... anyway, in order to "skip off", the atmosphere would have to add quite a bit of kinetic energy to the spacecraft. Something like half a kilometer per second of velocity most likely. The trouble is that the atmosphere can only really act with the force of drag, which is a form of friction, which can only resist movement, not add to it.
Instead, too shallow a reentry simply never enters dense enough atmosphere to be slowed down sufficiently to fully de-orbit. Its path is still elliptical (or hyperbolic in the case of interplanetary reentry), just modified slightly to reduce apogee by the friction with the low-density upper atmosphere.
Indeed, such maneuvers are sometimes done deliberately, called Aerobraking if used to bleed off velocity for a more efficient transfer from a high orbit to a low one, or Aerocapture if used to transfer from a hyperbolic orbit to a closed orbit at the end of an interplanetary journey. Done unintentionally, however, it can mean the spacecraft might have to stay in orbit longer than supplies or power reserves can allow (many days in the case of a return from the moon, which is when this strange myth got its start, presumably in a wildly inaccurate public service video meant to convey a sense of daring and danger to the Apollo program), so it's generally not desired unless it's planned.
In the case of a deorbit from low earth orbit however, like the space shuttle uses, it's extremely unlikely that too little velocity would be bled off for a successful deorbit. At worst it might start to gain altitude part way through the de-orbit, but then continue losing speed and go back down again. Even if it did go back up into what is considered empty space, it would be back to its perigee in about an hour and a half... enough time that everyone would have to go to the bathroom perhaps, but they wouldn't starve to death. It would also however, no longer be in position to land at the planned coordinates due to the continued rotation of the Earth, which could also be tricky.
It's also worth noting that at the angle of attack used during shuttle reentry, thanks to its far greater apparent cross-sectional area in relation to its mass, the Space Shuttle was actually far, far more "blunt" than a capsule-style reentry vehicle, which at hypersonic velocities is actually quite well streamlined thanks to the shockwave formed just ahead of it, that forms an ideal surface at all velocities. It's this much-increased drag, along with the ability to create aerodynamic lift, that allowed the shuttle to enter at such a shallow angle, not some magical barrier it would "bounce off of" if it weren't streamlined.
Firro Seranel thanks a ton for your well written explanation . It helped me and hopefully many others
You're welcome!
I'd like to thank you too
Great explanation! Sucked I had to read an entire 5 paragraph essay in a RUclips comment section....
I'll keep this in mind while playing KSP.
Deadly re-entry for life.
KSP Best game EVER! Nuff said.
I never knew it was this difficult to go back from space to earth!
Angle of Attack is the specific angle between the chord of the wing (a line between the leading edge and trailing edge of the wing) and the relative airflow... The Angle you are talking about would be sink rate.
Teased the episode out, can’t wait for the next one.
That episode gave me flashbacks to the movie Apollo 13, I think the part with "like a rock off a lake" was changed from Apollo 13's "skipping a rock off a pond"
this stuff is so cool. I'm 21 and I've never heard about these things before. thank you!
Yes, it *is* rocket science.
uncleanunicorn Literally.
lol, why yes it is. pseudo science lemons.
When I saw "Space Camp" as a kid, I thought the "reentry windows" were physical holes in the earth's atmosphere.
XD
G
reminds me of spaceballs and their airlocks
@@coolguy284_2 Spoiler alert: the code is 12345
I like it better when Caitlin host, she's got that cute nerdy lab assistant in chemistry class vibe. Hank reminds me of the guy that's always talking about how fast he finished his home work, while trying to look cool with his messenger bag full of note books.
Simp
I may be quoting Kerbal Space Program again, but how about bouncing off the atmosphere several times to loose more and more of your orbital velocity and then finally plunging down? Why do spacecraft have to go through the entire ordeal in one sitting? If the whole goal of reentry is to bleed off the kinetic energy you used to get into space in the first place, why not bleed it off through a lengthier amount of time?
I think this is why.
In the video Hank mentioned that you need a lot of speed (kinetic energy) to puncture through the Earth's atmosphere so if you tried that you may just end up orbiting around the Earth instead of going down to the surface.
Sand Dry I thought about that too, but if you consider that each time you brushed the atmosphere, a small bit of your kinetic energy would be lost, then at some point you're bound to fall to the ground.
This is after all why big spacecraft like the ISS have to make periodic burns in their engines to keep afloat. Otherwise the tiny friction with the sparse air molecules in its path slows it down and reduces its orbital speed gradually.
So if the ISS is worried about "reentrying" by mistake, why not purposefully reentrying in such a way?
alot of it has to do with the time it would take to do something to that degree, also if you were trying to land on a runway like the shuttle then its much easier and safer to do it in the same setting. Not that NASA (or at the very least KSP players) don't do what you are referring to the technical name being "Aerobraking,"
talksfor lifetwo yeah, my guess too is that such process would take a much longer amount of time. Possibly an _unreasonable_ amount of time which would offset all possible advantages
I see what you mean,but that only works if you are returning froom the moon or some other planet,and you want to safely kill all that velocity.The"curiosity"rover used multiple flyby maneuvers to safely slow down and land on Mars.
But if you are planing to land on the specific spot(which you have to),the retro burn from LEO has to be done at the exact time.
The angle of attack also has to be precise.
"Bouncing" is to unpedictable and dangerous if you are not planing to land in the middle of nowhere.
"If the whole goal of reentry is to bleed off the kinetic energy you used to get into space in the first place, why not bleed it off through a lengthier amount of time?"
They do exactly that.
They just dont "bounce".
This is why we need the space elevator!!! Kickstarter anyone?
we need a carbon nanotube kickstarter first
I appreciate Apollo 13 so much more now
Yay, metric system!
It is annoying how 400 million people use the stupid imprecise imperial system. Use tens, not twelves and stuff.
The imperial system isn't "imprecise" dumb fuck. If you are making that claim then you obviously don't understand it.Weight, distance, speed, etc. can be measured just as precisely in both systems...the only difference is what exact numbers will represent their values.1 kilometer is exactly 1 km, 1 mile is exactly 1 mile.They are equally precise.And why does the whole world have to think and do everything exactly the same?Just because youre too insecure to accept that other people don't all like what you like?
plathhs I hate the metric system!
Americans prefer the Imperial system. Go USA 🇺🇸
yay well i use metric system
That's completely true? An object like a SPACE SHUTTLE can smash/bounce off of our atmosphere? -MIND BLOWN- ( just an average person but love watching scishow, assumes atmosphere as air...remember-far from genius) keep up the good work!
that was your most exciting episode yet!
With practice humans can remain conscious at well over 6 G's, and, for short periods (seconds, not minutes) even at more than 12 G's. Red Bull Air Race pilots will sometimes pull 12 G's while maneuvering during the race and are occasionally disqualified for exceeding the 12 G safety limit of the aircraft. It's called over G-ing the airplane, and it is a good way to bend very expensive components. Fortunately for the Air Race pilot who accidentally over G's his plane, the wings don't fall off until you top at least 15 G's in those particular aircraft. (More common aircraft like a Cessna Skyhawk will come apart at around 6 G's, and commercial airliners won't tolerate even that many.) While the pilots do wear G-suits these days, that wasn't always the case. They pulled just as many G's then as they do today, and, when you're flying 200+ miles an hour 50 feet off the ground while engaging in low-level aerobatics, blacking out becomes very obvious to everyone very quickly!
Gunslinger454... dat heavy skience
Gunslinger454 Also John Glenn reached 9Gs during ascent on the Atlas rocket, reaching orbit in a little over 5 minutes, making the Mercury-Atlas astronauts the fastest to reach orbit.
So, the bouncing of the atmosphere thing is really hard for me to grasp. Would the craft just bounce around forever? What would happen after the initial bounce off?
I presume after the initial bounce off it would go back out to space, and after a while, stop bouncing. Think of it like a paddle ball, as you put less momentum into the bounce, the ball stops hitting the paddle.
coolguyman16 Ok correct me if I'm wrong. Space shuttles need to maintain a certain speed to remain in orbit. So if they drop out of orbit and are no longer moving fast enough to reenter the atmosphere what would happen? I might be wrong, but I'd assume that at this point the shuttle would also not be moving fast enough to escape earths gravity, and that's where my confusion is coming from. So I based on that assumption, which may be wrong, this hypothetical shuttle is just stuck there? It can't escape earth gravity, but it also can't get through the atmosphere. I'm just trying to explain my understanding and confusion that comes from it, so if anyone could clarify I'd be really happy with that.
Morgan A It isn't that you need to maintain a speed to remain in orbit - Orbit is actually a state of free-fall. Since the craft is in space, it's just a matter of reaching the lateral speed necessary to 'miss' the Earth while falling towards it, creating the orbit. Once that's reached, there's no 'maintaining' to do, you're just falling in a circle in space around a large object like Earth. The mechanics of getting out of orbit are actually a little weird as well, for that reason, since closer orbits are actually -faster-, so accelerating in the direction you're orbiting actually can take you downward towards the surface in certain circumstances, while slowing down can take you further away from the planet's surface. It's weird and counter-intuitive in a way, but that's space for you.
No,the craft would temporarily"bounce"but then the true problem begins,because your vertical velocity woud spike as you re enter the atmosphere at a steep angle.
Not to mention that if you do survive the g forces,and the heat,that will be much more intense,you WILL miss the landing site,so good luck with that "little"problem.
I tell you,sometimes being an astronaut,is not fun.
Morgan A It would come around once again to reenter. It wouldn't simply accidentally escape the Earth's gravity, that takes an enormous amount of energy. Its orbit already intersects the atmosphere, so one more orbit later it would begin to slow down again.
Looking forward for the next week!
This is why I'm scared of going to space. I want to but I kinda don't want anything to go wrong.
+Kid Kirby
I guess you could say you don't have...
(•_•)
( •_•)>⌐■-■
(⌐■_■)
The right stuff.
Ikr! So many things can go wrong in space!
***** yeah. That's true
+Kid Kirby
I feel like my mercury program reference went un-noticed D:
Lucky for you, 'you' dont need to. many others will step up
Wow that's really cool I never knew the atmosphere was that dense.
*(In reference to the statement made by the host at **2:27** - **2:34**)*
have you seen those videos where they extract all the air off a metal barrel and the barrel is squished by what seems like an invisible hand? That's just how _dense_ our atmosphere is.
think of it this way doing a belly flp dive into water 1000 feet up..It would be like running into a brick wall at over 100mph
Not really. It's just that they're coming in too fast.
drive 50mph and stick your hand out the window....now imagine that but 200x faster.
Arturo Gutierrez I knew it was that thick... (It's that basics on how vacuums work)
But I did not know it was thick enough and had a such defined horizon that on contact it would be like belly flopping into a pool.
I wonder how long Hank's been waiting to use the "It is Rocket Science" line.
Now I want to install Deadly Re-entry for my copy of KSP
You are in for a deadly treat
***** The game is much more interesting with it.
Aero braking suddenly becomes much more dangerous if your approach is to deep in the atmosphere.
Roughly speaking,newer go below 20km with your periapse and you should be fine.
Assuming you already have FAR installed, yes?
I never would have thought that the atmosphere was so dense that it could deflect an aircraft like that.
Well, it IS going from "pretty much nothing" to "air" in a short amount of time.
Eric Nash It is not the atmosphere that is dense,its the speed that is the problem.
At around 28.000km/h even a "near" vacuum has an effect on the craft.
That will be one of the problems that we will have to solve if we ever manage to build something that will almost reach the speed of light.
At that speed even the vacum of space is deadly(non ionizing radiation becomes ionizing).
Not to mention that if you where to hit an object the size of a grain of sand,it would hit with a force of a nuclear explosion.
Atmospheric re-entry is the coolest part of space travel.
I always wondered, How is it that there are so many people support ufo theories but no one ever explained how these objects could possibly travel so fast in our atmosphere without sonic boom etc.
Or melting/burning/exploding.
+NI Bojczuk Simple, they found a way to nullify friction between atmosphere and skin of their ship. For any decent civilization that posses a planetary landing craft, that would be the ultimate goal : how to land something regardless of the type and density of the atmosphere you land in.
One step in the right direction are superconductors. You project some sort of a magnetic field forward, along the axis of travel, repelling the different atoms, creating like a funnel of vacuum, in which your ship can accelerate.
Another type of design I can think of is some sort of a permeable ship skin, that absorbs all income molecules of air and converts them into fuel or whatever. Having an anti gravity engine, you can simulate any type of gravity you want, that means you can nullify inertia, so all the bombardment of air molecules your ship would sustain , you can nullify thanks to your engines.
+Zamolxes77 too complex....... i think some kind of warp drive is better for this theory.... you know, moving space not the craft
+Zamolxes77 What about those atoms that have the same charge? I don't think superconductors make a difference.
Sans the Moral Compass Atoms don't have a charge. Electrons and protons have charges. Atoms are neutral.
Superconductors make an enormous difference. Too bad we can't produce a stable one at room temperature, yet
I have an engineering degree and worked at Lockheed Martin as a satellite engineer, and I needed this channel to explain "re-entry" to me. God, I feel dumb... I'm literally doing the math right now to see how fast I would hit the atmosphere if I just "pushed off" of a geo-stationary satellite (aside from needing enough oxygen to travel 23k miles).
Definitely need to expand on the whole "bouncing off the atmosphere" part.
Awesome video Hank!
i always get happy when i stargaze on clear night sky this world is crazy beautiful.
"...and that is what we are going to explore next week on SciShow Space." Screw you to Hank. SCIENCE ME NOW!
Apollo astronaut John Young was once asked what is the most dangerous part of any spaceflight. He replied, "the part between launch and splashdown".
SCREW HEAD MATH. I use Kerbal Space Program for all the calculations and simulations I need for re-entry ;)
Make sure you have Ferram and Deadly Reentry, just to be sure your calculations and simulations are correct!
SciShow Space is awesome !
Looking forward to next week :D
fascinating episode.
the part about bouncing off is some nonsense. I'm not sure what they were trying to say, but slowing down in the orbit will definitely not prevent you from penetrating the atmosphere. the main reason the spacecrafts don't slow down more before descent is the cost of fuel. It's much cheaper to burn off the speed in the atmosphere using heat shields, than burn tons of fuel in the orbit.
How did "rocket science" become the measuring stick for difficulty? I realize it's just an idiom and I'm also not trying to downplay rocket science at all...but it is by no means the most difficult or rigorous field of study in today's world. I cannot say what is, but I could certainly propose a few: neuroscience, bioengineering, theoretical physics... hopefully you see my point.
Yeah see your point, but sayings like that are not accurate like if you are outside to long you can catch a cold. They are sayings, not facts
The reason is that the idiom didn't come from today's world. It came back from a time where neuroscience and bioengineering didn't exist. It came from a time where rocket science WAS theoretical physics. It just stuck around like a lot of other idioms.
Relatability. Use your brain.
I think it is because in rocket science you not only have to do complex math, you have to be _really_ sure your calculations are correct, otherwise you or someone else may die in horrible ways.
So perhaps we say that not just because the rocket equations and orbital parameters are complicated. But because there's also *a lot* more in stake compared to other sciences if someone makes a mistake. I think it is a matter of "practical" difficulty more than theoretical difficulty.
Taking candy from a baby isn't easy at all. Little shits fight for that as if their lives depended on it.
Ya, I was just talking to Dr. Roger McNamara (head of the Orion Abort System) about all this yesterday. It's pretty damn awesome. Who's excited to see Orion launch?
This video came out on my birthday almost two years ago :)
Amazing.
Oh Hank, dear Hank, could you make a video explaining how the atmosphere could be so dense that you'd bounce off of it?? It seems to be very complicated and VERY interesting!
One word: _SPEEEEEEEEEEEEEEED_
Like rocks on a lake: Shallow angle, it skips off
Steep angle, it sinks right in
"The jets fired at what looked like treetop height, slamming us down into our couches. I smiled, which is hard to do with ten gravities pulling at you, thinking about the expression on the colonel's face at that moment. "
Very interesting!!! I think you guys have already done this but Warp Theory is interesting. As is out ability to protect astronauts (and potential space citizens) from solar radiation
No space craft designed would be able to 'skip' off the atmosphere, the terminal velocity is just to high. However, if a spaceship could use the atmosphere as a trampoline, the ship could use a lot less fuel for certain maneuvers.
I really liked this one Hank
For whatever reason I just can't imagine anything bouncing off the atmosphere
What if you slow down to nearly zero km/h or m/s would you just fall to the earth due to gravity and penetrate the atmosphere gently? Like is there no way to ease into it, like you go so slow that you are not hitting the the molecules fast enough to burn up
Sometimes I experience some of those symptoms during re-entry to wakefulness in the morning. Dizziness... blurred vision... passing out for another hour or so.
Maybe it's because you're one of those little white creatures that wander in the woods. ;-)
CanadianRM4 Now that does explain a lot. :)
Great video!
good job guys
I'm coming home, coming home, tell the world that I'm coming home
Could you do an episode on how torpedoes work, and can you talk about how they boil the water in front of them to create Supercavitation. Thx
7.7k m/s sounds slow when it comes to space travel, but when you consider a huge man-made object crossing 77 football fields in 1 second... thats pretty damn fast.
2:06 I don't understand the part about if you go too slow the atmosphere is too dense. Its not some physical shield. If you are going slow enough the air has plenty of time to move out of the way.
Really liked this video its just awesome. Cheers from Sint Maarten
What happens if the angle is too shallow and you skip on the surface ?
Surely you will not have escape velocity or you would not the in a condition to skip in the first place.
Would you keep on skipping untill you slow down enough for the angle to be steep enough for reantry ?
Great vid my friend!
awsome episode :)
How come this is the first I'm hearing about the Russian 10 G thing.?
So some commenters before me asked a variation of the question, but what I want to know is WHY it bounces off?
Every time I watch or read about re entry they always talk about bouncing off anndd... they move onto the rest of the talk not actually saying why?
If you slowed down the space craft and had it float towards Earth what exactly is stopping it from coming back?
I had a run in with a few Gs, I could only handle about 5 of them before I had to turn around and walk away.
Would it be practical to have a separate re-entry vessel for longer trips. For example if we were to travel to the moon, if in the return trip a new ship is launched. The astronauts would then transfer into this spacecraft then return to earth.
Hank is back!
Man, I never thought it was so complicated! >.
so if you can bounce off the atmosphere does that mean you can also stand on it?
or at least have a boat on it.
i know you probably can't but i'm having trouble understanding how the atmosphere works so that you can bounce off it.
Very cool
This is the equivalent of sending a person in a plane, making them fly, but not teaching them how to get back down,
Then you included a how to book in the cockpit
1:30 Even if it IS designed to deal with those temperatures it can still burn up, as Columbia discovered.
Millennia ago the people did see these chunks of material entering the atmosphere and a lot more of it.
What they thought of the sightings made us.
wait, didn't that spaceX plane enter slowly by rotating it's wings and entering more like a leaf or something similar or is that one of those that didn't fully leave the atmosphere so it never had to fully re enter?
I have an idea for melting it. It's a giant space station that is roughly the size of our moon. Like the death star except not to explode things.
Please make more videos about what Curiosity is doing on Mars.
If you slow down to an almost complete stop (in relation to our atmosphere) before or just at the Karman line. (A rock set on, not thrown into a pond will go straight in). Then let gravity and maybe some propulsion lower the craft into the atmosphere at a much slower rate. Then once enough in the atmosphere the craft behave like a plane.
That won't work. The moment you start decelerating, the craft starts to lose altitude. There wouldn't be enough time to get to almost a complete stop.
This is a very big fuel waste. Where would you get all this fuel to decelerate that much? You need to bring it up with you and that means you need even more fuel to get all that stuff in orbit in the first place.
Or as my physics prof said: "In rocket science, every gram is a bitch." (actual words)
Good timing for the video. China is going to test a re entry capsule from lunar orbit and NASA is going to test Orion's heat shield :-)
This was a fucking insane episode
I'm confused what you're trying to say about the atmosphere being too dense to penetrate without going really fast. I mean, it's air. If you dropped something in at suborbital velocity it wouldn't just bounce, it would fall through the air and reach the ground. Spacecraft entering at orbital velocity but *at the wrong angle* can sort of "skip" off like a rock, but it's not like you can't enter the atmosphere without going super fast. It's just that it would take a lot more fuel to slow down to a safer speed from your orbital velocity.
FYI, the shuttle's name is "ENDEAVOUR". It uses the British (correct) spelling as she's named for a British ship.
Imagining the guys at the Space Agency skipping their astronauts off the atmosphere
My physics teacher said that "deceleration" isn't the accurate word. Slowing down, speeding up, any change at all is acceleration, just positive or negative. The term deceleration now bothers me to no end.
+Helen Wang Think of deceleration as a word referring to "acceleration in the direction *opposite* to direction of velocity."
Therefore, deceleration is still a relevant word.
It's just easier to teach physics by referring to deceleration as negative acceleration (for the equations).
I hope my perspective helps alleviate your frustration. ;)
Deceleration is a real word, and it's exactly what they said it means. You could say "negative acceleration" but the word "acceleration" usually refers to a positive change in velocity.
I know m/s second is SI units but don't you think km/h or even mph is more relatable to most people?
this may sound dumb but is there a such thing of up down or left or right in space?
I've heard of this "Bouncing off the atmosphere" before, usually star trek. Didn't know it was a real thing, and really not sure how it's possible. By that logic, I could slowly approach a planet, and then "sit" on it's atmosphere, no?
If you are going slow enough you don't bounce. Or you could think of airplanes as craft that bounce their way around the globe.
As a completely unanalogous analogy, think of a stone on a pond. Fast enough and it skips, slow enough and it sinks.
Does a skipping stone float?
No.
Could you stand on the atmosphere? If you can’t enter unless your going fast enough would it be dense enough to stand on
It would be truly amazing if they could utilize the heat generated via the compression of air into some sort of energy to aid in the next take off.
so why cant they just thrust in the reverse of their velocity to slow down enough where the orbit would intersect the karman line, and at that point do exactly what hank said and just skip along the atmosphere until friction slows it enough that it can just sink through the atmosphere?
Is it possible to come down in an orbit? 1st orbit the planet then into the atmosphere while dropping speed till they become avient? How long would that take?
Formula 1 drivers encounter around 7 Gs while have to stay beyond focused for hours on end and that is why the are the worlds best athletes.
The space shuttle: a flying brick with heat shield...
Hank,"that we will cover next week ." Me."RRAAAAA"
What if re-entry is slow enough for the molecules of air to displace around the craft ? Perfect re-entry ?
could you please talk about the delta IV rocket/orion launch on dec4?
What about the technique from the Silvervogel concept, where the bomber would decelerate and reenter the atmosphere by literally bouncing off of that 'wall' repeatedly until it slows down enough to pass through slowly.
Like a rock skipping across a lake? Sounds pretty cool.
It was, the forces on the plane and the pilot though. It would do this so many times that it would have the possibility of landing in Japan.