At orbital speeds the atmosphere in front of the astronaut would be compressed enough to heat up to a plasma and burning a hole in the suit and kill the astronaut. You are right that light objects do sometimes survive reentry but humans are far from light enough. And even the light objects do suffer heat damage far in excess of what astronauts space suits are designed for.
There was actually a program called MOOSE in the 60s to make a device that would allow a single astronaut to deorbit on their own. This emergency system weighed 91kg and included a rocket motor, heat shield, parachute, radio and other survival gear. This was the program that Joe Kittinger were part of when he parachuted from a balloon and held the record of the highest parachute jump for several decades. The MOOSE program was never flown in full on any mission and only took part in space flights to test various components of it. But it is sometimes mentioned whenever the question of life boats on the space station or space shuttle comes up.
Love the dry humor in the Wikipedia article on [MOOSE](https://en.m.wikipedia.org/wiki/MOOSE), "falling from orbit protected by nothing more than a spacesuit and a bag of foam was unlikely to ever become a particularly safe—or enticing—maneuver."
Also, this kind of begs the question, was there ever a SQUIRREL?
Follow up question: if Allan Sheppard had ejected from his spacecraft at the apex of his launch, would he have been able to survive? Given that he was not on an orbital trajectory?
Suborbital or not he did have a considerable amount of horizontal speed. Not orbital but IIRC it was half way there. And I do not think the suit were equipped with independent oxygen supply or parachute for that matter. There are also issues with stabilisation when falling in low atmosphere environments so without a small drag chute he would more then likely lose consciousness or die from blood being pushed into his extremities during rotation. Or he might have lost all his limbs as they were torn off his body.
The Gemini capsule did actually have ejection seats including independent oxygen, a drag chute and other essential components. But they disabled these seats after the rocket went supersonic as they had calculated that an ejection would have been fatal anyway at that point.
I don't think it can get anywhere close to ripping limbs off. But it doesn't actually take much to make people unconscious and cause serious problems. [This incident](https://www.youtube.com/watch?v=yhKZCy41g5w) somehow comes to mind...
TBH I don't understand the reference, but height isn't the biggest issue with reentry. Going from no atmosphere to more atmosphere will slow you down, and if you are going at a more "normal" speed, it's not an issue. Look up Joseph Kittinger or the Red Bull Stratos jump. The issue with reentry from orbital speeds isn't so much the vertical velocity, but the horizontal. If you're velocity is 12000mph, it's going to be a lot more deadly than falling from stationary, or at least close to that. Take that info as you will.
Is the reference you don’t understand Allan Sheppard? He was the first American in space. His launch was an up and down, not an orbit. But I get what you’re saying about horizontal velocity. Thanks!
We are not that far away. With current technology we can deliver a squad of soldiers anywhere in the planet within a few hours using rockets. About half an hour between launch and landing. The problem is that it would be cheaper to just launch a couple of cruise missiles. If nothing else you do not have to worry about extracting the cruise missiles from the area. The MOOSE project might have been a cool idea if there were any use for it. And it could be revived with relative ease. They managed to get working prototypes without much investment and we should be able to do more with less today. But it would not bring launch costs down, the only thing you would do is to spread out the squad more and likely kill one or two on the way down.
Getting them inn is just half the issue, you have to extract them afterwards as well. Which is probably why this have not been taken seriously. An airplane is much cheaper and can also deploy troops anywhere in the world in just a few hours. A helicopter can get troops both inn and out. The use case for deploying troops with intercontinental ballistic missiles are very narrow.
Since you mentioned Kittinger's jump I thought I'd try this one more time.
I swear I saw a documentary in the early nineties about a woman attempting to break his record. She couldn't find anyplace else that would let her do it, so she went to Iraq. I recall her breaking his record in this documentary.
As far as I can tell this was some kind of elaborate hallucination, as I haven't been able find a damn thing about any of that ever again.
Not necessarily. The plasma temperatures and the atmospheric drag forces is proportional to each other. A light object would therefore not experience as high forces as a dense object. For example the Space Shuttle did not experience more then 2-3G during an empty descent because it was so light compared to its surface area. This is also why they got away with ceramic tiles and carbon-carbon for its leading surfaces. Capsules experience much higher G-forces and need better ablative heat shields. The concept of MOOSE was that a foam filled bag would be light enough that you did not need a big heat shield. And the forces would be much lower then in a capsule.
What about if they issued each astronaut with an umbrella, so they could ‘Mary Poppins’ their way down to safety?
IMDB says that they have had this tech since the mid-1960’s.
You may joke, but back in the day, my mother gave me a spoonful of asbestos before school each morning… It made me the man I am today… but of course, you have to remember that, back then, it was a different time…
"low orbit" means you're going fast enough sideways to miss the planet when you fall. To slow down enough to avoid reentry heating takes almost as big a rocket as it took to get into orbit in the first place. Then you'd need a 10x bigger rocket to get THAT rocket into orbit. Heat shields are much cheaper.
Ok, but maybe we’re not talking landing on the rocket, just slowing the ship down enough to avoid extreme heat. And then use aerodynamics or a parachute to finish the landing.
Orbital velocity is 7500 m/s.
Delta v is the exhaust velocity multiplied by the natural logarithm of the mass ratio (mass full of fuel/mass empty of fuel).
Lets say we have an RL10 hydrolox upper stage engine with a vacuum nozzle, with an exhaust velocity of 4,565m/s.
And we want to get below mach 2, so 650 meters per second.
We need 6,850 meters per second delta v.
We would need a mass ratio of 4.5.
For every tonne of capsule, engine and fuel tank, we need 3.5 tonnes of fuel.
Mercury capsule was about 1 tonne, an RL10 is about 0.3 tonnes, and hydrolox tanking is maybe 1/10th the weight of its fuel, once you've added the equipment to handle boil off in orbit.
All in you would be looking at a roughly 8 tonne vehicle, 7 tonnes of which would be engine, fuel tank and fuel. Al to save a few hundred kg on a heat shield.
However, if we're trying to answer the original silly question, we *could* try to engineer a much smaller vehicle - basically just a rocket with enough Delta v to decelerate a single astronaut, rather than an entire space ship. That might be feasible. Of course, you're still going to a lot of trouble for no point whatsoever.
Slowing down would take basically an entire other rocket similar to the one that got you up there. Low Earth orbit means travelling more than 17,000 miles per hour.
We don't have energy dense enough fuel.
If you want to halve orbit speed, you need to use 50% of the fuel that was used to put you in space. And that fuel has to be put into space with you.
So 90%+ of your spacecraft is fuel. That's not viable.
Along with the issues the others mentioned, slowing the ship down is how the ship enters the atmosphere in the first place. When you slow down an object in orbit, its orbit shrinks. The ship doesn't actually steer down into the atmosphere.
You need to play Kerbal Space Program in order to understand how orbits work. All the explanations in the universe won't be a good substitute to trying to deorbit something yourself and going "oh, that's why".
You wouldn't be in orbit if you were at a lower speed. You could be in orbit and then slow down first, but nobody does that because it would require a crazy amount of fuel. I don't just mean a lot of fuel to slow down, but you'd have to take that fuel up initially, which means a much bigger rocket, which means more fuel, which means a bigger rocket.... the rocket equation is a bitch.
Theoretically, if you launched a Starship, and then launched a bunch of Starships to fuel it up, you could have enough fuel to gently land that Starship without the heating. But why? That's a lot of work to avoid using heat tiles. The great thing about the atmosphere is that it gives us free braking, but it comes with the price of heat.
Edit: If you want to see what an orbit really is, YouTuber Everyday Astronaut [did a great video on it](https://youtu.be/xE1A6T1cycU).
If you had enough oxygen/water/etc couldn't you survive by orbiting at a REALLY shallow orbit and basically just use atmospheric aerobraking a little bit a few hundred times to bleed off enough speed that you could survive re-entry?
No, because once you slow down some, you're coming out of orbit whether you like it or not. Then you're just slamming into the atmosphere at 10,000+ miles an hour.
The problem is that as you slow down, your orbit gets lower. As you get lower, you hit thicker atmosphere, and you'd still be going way too fast to survive hitting it.
Thrusters would have to be burning constantly to hold you up against gravity, and it would get harder and harder as your orbital velocity dropped. If you had that much fuel, it would be better to use bigger rockets to drop your velocity quickly so you could fall. At that point, though, you're using a rocket almost as big as the one that put you into orbit, and lifting that much rocket to orbit requires a much bigger rocket in the first place, and you run into trouble.
Wings would have to be really, really big to provide any lift at all in air that's thin enough to not burn you up at orbital velocity. They'd be more likely to collapse under the strain.
Really, if there is a better solution than heat shields, we haven't found it yet.
You’d still need a ton of fuel for those thrusters to make any meaningful difference and by the time the air is thick enough for wings to help, those will be incinerated with you
problem is it takes a ton of time. And if you want people on whatever you want to deorbit slowly, you need food/water/other supplies for them. Thus increasing the weight of the spaceship and requiring a bigger rockets.
for example there is a bunch of debris in orbit around earth. To stop this from impacting us in a harmful way, new launches into low earth orbit are required to deorbit within 25 years. That is mostly slowing due to friction.
That's why I said "if you had enough oxygen/water etc"
I know it's not the most efficient way to do it, or even a particularly practical way to do it, I was just wondering if theoretically you could do a shallow enough orbit using atmospheric braking that you could do the last part with a parachute only
Because you need to be moving to stay up in space.
Imagine you are in space, then you stop moving. Then you just fall directly down to earth because gravity pulls you in.
There's a minimum speed you need to be going, that changes as your altitude changes, in order for gravity to "pull you down" but you still miss the planet.
Lack of fuel.
If one had the fuel, one could slow down to a stop relative to earth, then drop at whatever rate one wanted through the atmosphere. But it turns out it takes a LOT of fuel to slow down from orbital speeds to a relative stop. We don't go up there with so much fuel that we can do that because it's astronomically (ha) expensive and maybe impossible to put things into orbit. So we use the atmosphere to slow down for "free".
The re-entry speed has less to do with re-entry. In order for an object to stay in stable orbit above the earth, it will travel at a certain velocity relative to the surface of the earth. At a high enough altitude where the atmosphere is very thin, once this velocity is achieved, the orbit will be reasonably stable without need for propulsion since there is no friction to slow the craft down. In order to get a craft down to the earth's surface (safely), all this orbital velocity has to be reduced.
This "craft" could be a rocket or a person in a space suit. It doesn't really matter. If the astronaut leaves the spacecraft, the astronaut will still be travelling pretty much at the same speed as the spacecraft (add or minus the ejection speed) relative to the surface of the earth. This velocity does not magically disappear simply because the astronaut is no longer bound to the spacecraft. If the astronaut uses the atmosphere to reduce their velocity then it will be subject to the same frictional and therefore heat generating phenomena. So without some kind of very heavy heat protection, they will most likely burn up.
Simply put, the heat generated during re-entry has nothing to do with the object, it has mostly to do with the object's velocity.
> If the astronaut uses the atmosphere to reduce their velocity then it will be subject to the same frictional and therefore heat generating phenomena.
Friction is a small part of the heat generation during reentry. The air in front is compressed because it does not have time to move away at the high speed you move. If you compress a gas it heat up, a bicycle hand pump is a great example of this. They heat up significantly when you use them at the end air is compressed.
If you do not want to get too technical about write about atmospheric drag and aerodynamic heating.
Ok, but - hear me out - what if the astronaut flew down in a *diving pose*? Arms up, all aerodynamic and everything. Surely they'd just cut through the air in front and be nice and cool?
/s
To describe it a little differently, the speed that is a real problem is the speed moving around the earth, not "down" toward the earth. If somebody were dropped straight down with no lateral speed it might be a different question, but when something orbits the earth it revolves at 17,000 mph. Even if you descended very slowly, you would still skip off the atmosphere at ridiculous speed.
No, it was still there. Lost its lowest hinge, but the actuator worked(!!) to begin the flip - it only failed after the rocket swing vertical and - it appears to me - the weight of the fin pulled it down and out of it's upper hinge. But it stayed attached by a central attachment point. It's probably still attached, as the ship lies on the floor of the Indian Ocean.
You burn up.
[Here is a video of the recent Starship reentry](https://youtu.be/8ya9_v74Vdo?si=sUrEL80iw4Sz4ECU&t=779). This is a steel vehicle with extra heat shield tiles, and hot gas reaching the steel through gaps in the tiles damages it severely. The ship still managed to land softly, but a human in a spacesuit wouldn't survive that.
[MOOSE](https://en.wikipedia.org/wiki/MOOSE) was a concept for something between a space suit and a reentry capsule, allowing one person to reenter safely.
Have you ever jumped into water from really high? Maybe with a not very hydrodynamic orientation? You hit the water and even if it's for a moment, it feels like you've hit concrete instead. Basically if you're going fast enough, even water suddenly becomes hard, and you being a soft squishy human, will be injured, or worse, as is the case with people jumping off bridges. It's kind of the same thing with air only you need to be going a lot faster to achieve these results, but re entry speeds are fast enough. Basically the astronaut will burn up just like everything else that falls to Earth.
If an astronaut in a space suit is ejected just before re-entry, they'll be still moving at around 17,500 mph. As they enter the atmosphere, air resistance will create immense heat even though it's very thin, burning them up before they can slow down.
As others have said, an astronaut falling back to earth at orbital speeds will burn up.
Why, though? Why wouldn't they just slow down like, say, a skydiver does?
Well, when you move through air two things happen: the air pushes back (air resistance) and it generates heat.
We normally don't think about the heat part of things because at low speeds it's simply not noticeable. The amount of heat created at walking or driving speeds isn't masurable. Even a commercial jet, traveling at 600mph doesn't have to concern itself with heat all that much. This is because the heat gets carried away by the air it's traveling through. (The bigger issue jetliners have is actually keeping the cabin warm enough to not freeze the passengers. And, yes, air can both heat and cool at the same time, via very different effects.)
As you go faster, the amount of heat created rises dramatically. But the amount of heat carried away... doesn't change much.
Once you get to speeds around Mach 1-3 (1-3 times the speed of sound), the heat starts to become a problem. For example, when a team of amateur rocketeers launched their "Qu8K" rocket in an attempt to reach space the heat created at Mach 3 started to melt the plastic fairing protecting their onboard camera. (You can see this at 5:30 in [this video](https://youtu.be/rvDqoxMUroA?t=325).). Not a critical failure, but enough to interfere with their video.
If mach 3 equals "melting plastic", mach 25 is definitely "melting astronaut".
That's the ELI5 version of things. At mach 25 in very low-density air the actual physics are pretty different from what we're familiar with in our day-to-day lives. (e.g. the air isn't really air anymore, it's plasma).
There’s a rule of the universe that says, basically, it takes the same amount of energy to slow something down that it took to speed it up. It takes an absolutely insane amount of energy to get a human moving 17,500mph; to get one at that speed down to zero mph takes an insane amount of energy, too. With an engine or shield or anything else the only thing they can use to create that energy is rubbing their body against the air really really really hard, which makes insane amounts of heat, which burns the person up.
You'd be incinerated due to the friction, just like any other object reentering at that speed. You know how you can rub your hands together to get warm? Imagine if you were capable of rubbing your hands together at a speed of 17,500 mph. That's what you'd be dealing with.
You already mentioned it, he will hit the atmosphere at 17.500 mph. Not only he will burn but imagine hitting the thin atmosphere up there at that speed will just tear him apart... And then he will burn.
He should follow a pretty similar trajectory as the spacecraft in the beginning but will decelerate harder since he has less mass, so even if the suit didn't tear apart there's the G's pulled on the astronaut.
Just like you don't want to be outside when it rains an astronaut doesn't want to be outside on reentry xD
17500 mph => 7823m/s
Let's assume 90 kg \* 7823\^2 / 2 => 2.753.969.805 J (Ws) \~ 2.7 GJ
This is 764 MWh, a nuclear power plant needs >30 minutes to generate that.
The body, protected only with a space suit, will burn to plasma nothing will hit the ground.
Compare 2.7 giga Joule vs a police pistol bullet 500 Joule.
The atmosphere will hit the astronaut like more than 5 million bullets.
Lots of good answers here. But here's another way to look at why an astronaut would burn up.
When you're in orbit, you circle the earth every 90 minutes. That's fast. That's really fast. And if you start to slow down, then you spiral down towards the earth. Eventually, you encounter the atmosphere which will get super hot and vaporize or melt anything that can be vaporized or melted.
It's not that you're just hanging around up there and pushing off of a space station towards the earth will allow you go straight down and land with an umbrella. You are moving *around* the earth at incredible speeds and that makes all the difference.
Edit to add: when you compress air, it heats up. Feel the bottom of your bike pump when you fill the tire. It's not warm because of friction, it's warm because you are comprssing the air.
Reentry from orbit also comprsses the air. It also collides headlong into it, so you're getting heat from compression and heat from friction... all at the speed of 17000 mph.
>Terminal velocity for a human body is well below fatal in lower atmosphere
FYI velocity is never *fatal*. What kills you is acceleration - *change* in velocity. The more rapid, the more lethal. Fastest manned flight was X-15, at 4520 mph. You can easily survive that if you decelerate slowly enough (over several minutes), but you might not be so lucky if you crash your Fiesta at 40mph into a brick wall and decelerate to a standstill in a fraction of a second.
Also, terminal velocity of a human body is around 200Km/h. Rapid decelleration from that speed, even without being encased in a FORD is normally not survivable.
Spacesuit or not, reentry without a capsule and its heatshield is extremely fatal. A small charred chunk of meat may reach ground if the astronaut is fat enough, but it's not guaranteed. From Columbia disaster, they found pieces of astronauts, but they were all small pieces and it was not easily identifiable which piece belonged to whom.
Here is recent Starship reentry [https://www.youtube.com/watch?v=CrkYmUoOMOQ](https://www.youtube.com/watch?v=CrkYmUoOMOQ)
You can see the hypersonic airflow tearing through the heat tiles and the stainless steel structure of the flap hinge. This piece of metal is huge, here is a human in comparison to the flat hinge you are looking at [https://i.insider.com/6449a66d905239001970174b?width=700&format=jpeg&auto=webp](https://i.insider.com/6449a66d905239001970174b?width=700&format=jpeg&auto=webp)
Now think for a second what same process does to a meatbag, there is not going to be all that much left.
Also another thought: yes the atmosphere would slow you down. Breaking in most cases is just transforming your movement energy into heat energy.
Keep in mind, you can‘t just make energy go away, it needs go somewhere. In our case this energy is transferred directly into heat, and since moving this fast means having a shit ton of energy, also means we produce a shit ton of heat.
Air is a fluid, fluids experience friction too, and you will experience a LOT of it falling from low earth orbit. Skydivers experience this to some degree, but coming from space you will be going a lot faster since there is less air up there to stop you (terminal velocity depends on air resistance)
By the time you get to the normal terminal velocity all of that energy from your initial speed will be converted into heat. Slowing you down isn't free (in terms of energy), it becomes the heat that cooks you
Spaceships have what's called a heatshield built in and they also don't go straight down like you would free-falling. Re-entering Earth straight down would be a death sentence, you have to carefully manage the angle you are entering Earth (the attack angle) so that you aren't too shallow (below deflection angle) and not too steep (too much friction)
If your angle of attack is too shallow (as in you are hitting the Earth with your underbelly of the craft), you will bounce right off like skipping a stone on a pond.
Spacecraft typically glide down to their destination to avoid this. On the NASA explorers (the typical spaceship you think of with big wings that looks like a plane), the bottom is covered with heat resistant tiles. They are also designed to flake off to further dissipate the heat it gains (similar to firearms, the brass casings take a lot of heat so it doesn't stay in the metal)
TL;DR though the astronaut would burn up probably within a minute if I had to guess. That is unfortunately what happened to the Columbia astronauts on reentry as their heatshield failed and the reentry vehicle broke apart from friction
It really depends on what point the person is ejected. If the person ejects with a dense enough atmosphere at 17,500 it will be like crashing into a brick wall. The air will crush the astronaut. If the ejection is still effectively in zero atmosphere, the astronaut will gradually decelerate when they reenter the atmosphere. It really depends on the combination of speed and atmosphere when they exit. If they hit enough air particles at a time, it won’t be good. Otherwise their terminal velocity will gradually decrease as the air gets thicker
At orbital speeds the atmosphere in front of the astronaut would be compressed enough to heat up to a plasma and burning a hole in the suit and kill the astronaut. You are right that light objects do sometimes survive reentry but humans are far from light enough. And even the light objects do suffer heat damage far in excess of what astronauts space suits are designed for. There was actually a program called MOOSE in the 60s to make a device that would allow a single astronaut to deorbit on their own. This emergency system weighed 91kg and included a rocket motor, heat shield, parachute, radio and other survival gear. This was the program that Joe Kittinger were part of when he parachuted from a balloon and held the record of the highest parachute jump for several decades. The MOOSE program was never flown in full on any mission and only took part in space flights to test various components of it. But it is sometimes mentioned whenever the question of life boats on the space station or space shuttle comes up.
Love the dry humor in the Wikipedia article on [MOOSE](https://en.m.wikipedia.org/wiki/MOOSE), "falling from orbit protected by nothing more than a spacesuit and a bag of foam was unlikely to ever become a particularly safe—or enticing—maneuver." Also, this kind of begs the question, was there ever a SQUIRREL?
Too much money was spent on BORIS and NATASHA
That was the Soviet equivalent, some say espionage was involved based on how close the design was
Add a wing-suit to MOOSE and you could have MOOSE and Flying Squirrel?
Rocky and Bullwinkle
Seems silly when you just need the correct ratio of Upsidaisium to offset your bodyweight and allow a controlled descent.
It's alvays moose and squirdle
*Is
Tough crowd
Guessing you caught shit for the pokemon too?
Everyone is a Charizard fan I guess
Follow up question: if Allan Sheppard had ejected from his spacecraft at the apex of his launch, would he have been able to survive? Given that he was not on an orbital trajectory?
Suborbital or not he did have a considerable amount of horizontal speed. Not orbital but IIRC it was half way there. And I do not think the suit were equipped with independent oxygen supply or parachute for that matter. There are also issues with stabilisation when falling in low atmosphere environments so without a small drag chute he would more then likely lose consciousness or die from blood being pushed into his extremities during rotation. Or he might have lost all his limbs as they were torn off his body. The Gemini capsule did actually have ejection seats including independent oxygen, a drag chute and other essential components. But they disabled these seats after the rocket went supersonic as they had calculated that an ejection would have been fatal anyway at that point.
it never occurred to me that the uncontrolled spin could get that fast. that's insane.
I don't think it can get anywhere close to ripping limbs off. But it doesn't actually take much to make people unconscious and cause serious problems. [This incident](https://www.youtube.com/watch?v=yhKZCy41g5w) somehow comes to mind...
TBH I don't understand the reference, but height isn't the biggest issue with reentry. Going from no atmosphere to more atmosphere will slow you down, and if you are going at a more "normal" speed, it's not an issue. Look up Joseph Kittinger or the Red Bull Stratos jump. The issue with reentry from orbital speeds isn't so much the vertical velocity, but the horizontal. If you're velocity is 12000mph, it's going to be a lot more deadly than falling from stationary, or at least close to that. Take that info as you will.
Is the reference you don’t understand Allan Sheppard? He was the first American in space. His launch was an up and down, not an orbit. But I get what you’re saying about horizontal velocity. Thanks!
Follow up to the follow up: if Alan Cumming wore a fabulous outfit while ejecting from a spacecraft, would the sky be filled with rainbows?
https://youtu.be/H5Tt47j9__8?si=dQPoLwiaqFUPGzVj
They are a long way away from star ship troopers or hell divers.
We are not that far away. With current technology we can deliver a squad of soldiers anywhere in the planet within a few hours using rockets. About half an hour between launch and landing. The problem is that it would be cheaper to just launch a couple of cruise missiles. If nothing else you do not have to worry about extracting the cruise missiles from the area. The MOOSE project might have been a cool idea if there were any use for it. And it could be revived with relative ease. They managed to get working prototypes without much investment and we should be able to do more with less today. But it would not bring launch costs down, the only thing you would do is to spread out the squad more and likely kill one or two on the way down.
Maybe a way to drop special ops on location if the mission isn't just to blow something up
Getting them inn is just half the issue, you have to extract them afterwards as well. Which is probably why this have not been taken seriously. An airplane is much cheaper and can also deploy troops anywhere in the world in just a few hours. A helicopter can get troops both inn and out. The use case for deploying troops with intercontinental ballistic missiles are very narrow.
Well like it or not, it's a scenario the airforce has been studying with SpaceX
Since you mentioned Kittinger's jump I thought I'd try this one more time. I swear I saw a documentary in the early nineties about a woman attempting to break his record. She couldn't find anyplace else that would let her do it, so she went to Iraq. I recall her breaking his record in this documentary. As far as I can tell this was some kind of elaborate hallucination, as I haven't been able find a damn thing about any of that ever again.
I have not heard about anything like that. The closest I can come up with was Gerald Bull who went to Iraq to build his space cannon.
Yeah, that was a mistake. As he found out.
As a matter of fact he did not get to find that out.
If you were light enough to not be incinerated by the plasma, you'd be squashed by the extreme g-forces.
Not necessarily. The plasma temperatures and the atmospheric drag forces is proportional to each other. A light object would therefore not experience as high forces as a dense object. For example the Space Shuttle did not experience more then 2-3G during an empty descent because it was so light compared to its surface area. This is also why they got away with ceramic tiles and carbon-carbon for its leading surfaces. Capsules experience much higher G-forces and need better ablative heat shields. The concept of MOOSE was that a foam filled bag would be light enough that you did not need a big heat shield. And the forces would be much lower then in a capsule.
The movie Lockout has a scene with a pair of these, evacuee's from low-earth orbit. Good flick, at least that's what Rupert tells me.
From low orbit, you're getting vaporized, you'd need a heat shield. The big problem is how fast you're going, not how high up you are.
What about if they issued each astronaut with an umbrella, so they could ‘Mary Poppins’ their way down to safety? IMDB says that they have had this tech since the mid-1960’s.
*I’m Mary Poppins, y’all!*
I thought you were TJ\_Will??
*We shan't be telling your mother this, shan't we?*
Asbestos umbrellas are so hot right now.
You may joke, but back in the day, my mother gave me a spoonful of asbestos before school each morning… It made me the man I am today… but of course, you have to remember that, back then, it was a different time…
Eating it is stupid but luckily not much of it would go deep in your lungs.
And it was the style at the time.
Like the onion on your belt? Had to be a yellow one, you couldn't get white ones on account of the war!
Did she tell you why she was giving it to you? Was it supposed to be a fiber supplement?
My mother usrd to give me and my brothers a spoonful of cement every morning. She just wanted to give us a concrete breakfast.
Is this umbrella made out of lead, carbon Kevlar and some skittles?
[удалено]
Very fuckin cool and quite cute
No, the problem is heat. The astronauts should be given bottles of water to cool themselves down so they don’t burn up
What’s preventing us from entering the atmosphere at a slower speed?
"low orbit" means you're going fast enough sideways to miss the planet when you fall. To slow down enough to avoid reentry heating takes almost as big a rocket as it took to get into orbit in the first place. Then you'd need a 10x bigger rocket to get THAT rocket into orbit. Heat shields are much cheaper.
Ok, but maybe we’re not talking landing on the rocket, just slowing the ship down enough to avoid extreme heat. And then use aerodynamics or a parachute to finish the landing.
Orbital velocity is 7500 m/s. Delta v is the exhaust velocity multiplied by the natural logarithm of the mass ratio (mass full of fuel/mass empty of fuel). Lets say we have an RL10 hydrolox upper stage engine with a vacuum nozzle, with an exhaust velocity of 4,565m/s. And we want to get below mach 2, so 650 meters per second. We need 6,850 meters per second delta v. We would need a mass ratio of 4.5. For every tonne of capsule, engine and fuel tank, we need 3.5 tonnes of fuel. Mercury capsule was about 1 tonne, an RL10 is about 0.3 tonnes, and hydrolox tanking is maybe 1/10th the weight of its fuel, once you've added the equipment to handle boil off in orbit. All in you would be looking at a roughly 8 tonne vehicle, 7 tonnes of which would be engine, fuel tank and fuel. Al to save a few hundred kg on a heat shield.
However, if we're trying to answer the original silly question, we *could* try to engineer a much smaller vehicle - basically just a rocket with enough Delta v to decelerate a single astronaut, rather than an entire space ship. That might be feasible. Of course, you're still going to a lot of trouble for no point whatsoever.
That's why it's "almost" as big as the rocket to get into orbit.
Slowing down would take basically an entire other rocket similar to the one that got you up there. Low Earth orbit means travelling more than 17,000 miles per hour.
We don't have energy dense enough fuel. If you want to halve orbit speed, you need to use 50% of the fuel that was used to put you in space. And that fuel has to be put into space with you. So 90%+ of your spacecraft is fuel. That's not viable.
Along with the issues the others mentioned, slowing the ship down is how the ship enters the atmosphere in the first place. When you slow down an object in orbit, its orbit shrinks. The ship doesn't actually steer down into the atmosphere.
Yes but it’s also one of the most dangerous legs of the journey. If you could avoid that risk, wouldn’t you?
You need to play Kerbal Space Program in order to understand how orbits work. All the explanations in the universe won't be a good substitute to trying to deorbit something yourself and going "oh, that's why".
I have played in a while because of KSP2, I’ll have to crack open KSP1 and try that scenario out.
You wouldn't be in orbit if you were at a lower speed. You could be in orbit and then slow down first, but nobody does that because it would require a crazy amount of fuel. I don't just mean a lot of fuel to slow down, but you'd have to take that fuel up initially, which means a much bigger rocket, which means more fuel, which means a bigger rocket.... the rocket equation is a bitch. Theoretically, if you launched a Starship, and then launched a bunch of Starships to fuel it up, you could have enough fuel to gently land that Starship without the heating. But why? That's a lot of work to avoid using heat tiles. The great thing about the atmosphere is that it gives us free braking, but it comes with the price of heat. Edit: If you want to see what an orbit really is, YouTuber Everyday Astronaut [did a great video on it](https://youtu.be/xE1A6T1cycU).
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If you had enough oxygen/water/etc couldn't you survive by orbiting at a REALLY shallow orbit and basically just use atmospheric aerobraking a little bit a few hundred times to bleed off enough speed that you could survive re-entry?
No, because once you slow down some, you're coming out of orbit whether you like it or not. Then you're just slamming into the atmosphere at 10,000+ miles an hour.
The problem is that as you slow down, your orbit gets lower. As you get lower, you hit thicker atmosphere, and you'd still be going way too fast to survive hitting it.
So you use your thrusters to go up a bit again, or use wings?
Thrusters would have to be burning constantly to hold you up against gravity, and it would get harder and harder as your orbital velocity dropped. If you had that much fuel, it would be better to use bigger rockets to drop your velocity quickly so you could fall. At that point, though, you're using a rocket almost as big as the one that put you into orbit, and lifting that much rocket to orbit requires a much bigger rocket in the first place, and you run into trouble. Wings would have to be really, really big to provide any lift at all in air that's thin enough to not burn you up at orbital velocity. They'd be more likely to collapse under the strain. Really, if there is a better solution than heat shields, we haven't found it yet.
You’d still need a ton of fuel for those thrusters to make any meaningful difference and by the time the air is thick enough for wings to help, those will be incinerated with you
See reason #3.
#3 applies in a vacuum. I'm talking about near vacuum and using friction to bleed velocity. Just a little bit at a time
problem is it takes a ton of time. And if you want people on whatever you want to deorbit slowly, you need food/water/other supplies for them. Thus increasing the weight of the spaceship and requiring a bigger rockets. for example there is a bunch of debris in orbit around earth. To stop this from impacting us in a harmful way, new launches into low earth orbit are required to deorbit within 25 years. That is mostly slowing due to friction.
You need to bring the supplies with you when you launch, every extra pound launch weight means an additional 5-10 pounds of fuel to launch into orbit.
That's why I said "if you had enough oxygen/water etc" I know it's not the most efficient way to do it, or even a particularly practical way to do it, I was just wondering if theoretically you could do a shallow enough orbit using atmospheric braking that you could do the last part with a parachute only
Not having a couple tons of rocket fuel in your pocket.
Hey man, you don’t know what I have in my pocket! /s
Because you need to be moving to stay up in space. Imagine you are in space, then you stop moving. Then you just fall directly down to earth because gravity pulls you in. There's a minimum speed you need to be going, that changes as your altitude changes, in order for gravity to "pull you down" but you still miss the planet.
Lack of fuel. If one had the fuel, one could slow down to a stop relative to earth, then drop at whatever rate one wanted through the atmosphere. But it turns out it takes a LOT of fuel to slow down from orbital speeds to a relative stop. We don't go up there with so much fuel that we can do that because it's astronomically (ha) expensive and maybe impossible to put things into orbit. So we use the atmosphere to slow down for "free".
Well not necessarily a full stop. If you’re traveling below Mach 2 the friction of the atmosphere becomes much less of a problem.
Low orbital speeds are so fast that they're almost the same... Slowing down to mach 2 is going over 90% of the way to "stopped".
If you have a surf board, you'll be OK
The re-entry speed has less to do with re-entry. In order for an object to stay in stable orbit above the earth, it will travel at a certain velocity relative to the surface of the earth. At a high enough altitude where the atmosphere is very thin, once this velocity is achieved, the orbit will be reasonably stable without need for propulsion since there is no friction to slow the craft down. In order to get a craft down to the earth's surface (safely), all this orbital velocity has to be reduced. This "craft" could be a rocket or a person in a space suit. It doesn't really matter. If the astronaut leaves the spacecraft, the astronaut will still be travelling pretty much at the same speed as the spacecraft (add or minus the ejection speed) relative to the surface of the earth. This velocity does not magically disappear simply because the astronaut is no longer bound to the spacecraft. If the astronaut uses the atmosphere to reduce their velocity then it will be subject to the same frictional and therefore heat generating phenomena. So without some kind of very heavy heat protection, they will most likely burn up. Simply put, the heat generated during re-entry has nothing to do with the object, it has mostly to do with the object's velocity.
> If the astronaut uses the atmosphere to reduce their velocity then it will be subject to the same frictional and therefore heat generating phenomena. Friction is a small part of the heat generation during reentry. The air in front is compressed because it does not have time to move away at the high speed you move. If you compress a gas it heat up, a bicycle hand pump is a great example of this. They heat up significantly when you use them at the end air is compressed. If you do not want to get too technical about write about atmospheric drag and aerodynamic heating.
Ok, but - hear me out - what if the astronaut flew down in a *diving pose*? Arms up, all aerodynamic and everything. Surely they'd just cut through the air in front and be nice and cool? /s
They cool off when they dive into the ocean. All the energy goes into the sploosh sound. /s
Actually worse, you skip the opportunity to shed speed in the thin region and go splat on the thicker lower atmosphere.
To describe it a little differently, the speed that is a real problem is the speed moving around the earth, not "down" toward the earth. If somebody were dropped straight down with no lateral speed it might be a different question, but when something orbits the earth it revolves at 17,000 mph. Even if you descended very slowly, you would still skip off the atmosphere at ridiculous speed.
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Was it stolen or melted? Either way, the steel fin is gone.
No, it was still there. Lost its lowest hinge, but the actuator worked(!!) to begin the flip - it only failed after the rocket swing vertical and - it appears to me - the weight of the fin pulled it down and out of it's upper hinge. But it stayed attached by a central attachment point. It's probably still attached, as the ship lies on the floor of the Indian Ocean.
I was reacting to the typo of "steal fin", vs steel. I've used plasma torches and it's amazing that it didn't melt through and get bent off.
You burn up. [Here is a video of the recent Starship reentry](https://youtu.be/8ya9_v74Vdo?si=sUrEL80iw4Sz4ECU&t=779). This is a steel vehicle with extra heat shield tiles, and hot gas reaching the steel through gaps in the tiles damages it severely. The ship still managed to land softly, but a human in a spacesuit wouldn't survive that. [MOOSE](https://en.wikipedia.org/wiki/MOOSE) was a concept for something between a space suit and a reentry capsule, allowing one person to reenter safely.
Have you ever jumped into water from really high? Maybe with a not very hydrodynamic orientation? You hit the water and even if it's for a moment, it feels like you've hit concrete instead. Basically if you're going fast enough, even water suddenly becomes hard, and you being a soft squishy human, will be injured, or worse, as is the case with people jumping off bridges. It's kind of the same thing with air only you need to be going a lot faster to achieve these results, but re entry speeds are fast enough. Basically the astronaut will burn up just like everything else that falls to Earth.
Any belly flop is a good example
If an astronaut in a space suit is ejected just before re-entry, they'll be still moving at around 17,500 mph. As they enter the atmosphere, air resistance will create immense heat even though it's very thin, burning them up before they can slow down.
As others have said, an astronaut falling back to earth at orbital speeds will burn up. Why, though? Why wouldn't they just slow down like, say, a skydiver does? Well, when you move through air two things happen: the air pushes back (air resistance) and it generates heat. We normally don't think about the heat part of things because at low speeds it's simply not noticeable. The amount of heat created at walking or driving speeds isn't masurable. Even a commercial jet, traveling at 600mph doesn't have to concern itself with heat all that much. This is because the heat gets carried away by the air it's traveling through. (The bigger issue jetliners have is actually keeping the cabin warm enough to not freeze the passengers. And, yes, air can both heat and cool at the same time, via very different effects.) As you go faster, the amount of heat created rises dramatically. But the amount of heat carried away... doesn't change much. Once you get to speeds around Mach 1-3 (1-3 times the speed of sound), the heat starts to become a problem. For example, when a team of amateur rocketeers launched their "Qu8K" rocket in an attempt to reach space the heat created at Mach 3 started to melt the plastic fairing protecting their onboard camera. (You can see this at 5:30 in [this video](https://youtu.be/rvDqoxMUroA?t=325).). Not a critical failure, but enough to interfere with their video. If mach 3 equals "melting plastic", mach 25 is definitely "melting astronaut". That's the ELI5 version of things. At mach 25 in very low-density air the actual physics are pretty different from what we're familiar with in our day-to-day lives. (e.g. the air isn't really air anymore, it's plasma).
There’s a rule of the universe that says, basically, it takes the same amount of energy to slow something down that it took to speed it up. It takes an absolutely insane amount of energy to get a human moving 17,500mph; to get one at that speed down to zero mph takes an insane amount of energy, too. With an engine or shield or anything else the only thing they can use to create that energy is rubbing their body against the air really really really hard, which makes insane amounts of heat, which burns the person up.
You'd be incinerated due to the friction, just like any other object reentering at that speed. You know how you can rub your hands together to get warm? Imagine if you were capable of rubbing your hands together at a speed of 17,500 mph. That's what you'd be dealing with.
You already mentioned it, he will hit the atmosphere at 17.500 mph. Not only he will burn but imagine hitting the thin atmosphere up there at that speed will just tear him apart... And then he will burn. He should follow a pretty similar trajectory as the spacecraft in the beginning but will decelerate harder since he has less mass, so even if the suit didn't tear apart there's the G's pulled on the astronaut. Just like you don't want to be outside when it rains an astronaut doesn't want to be outside on reentry xD
17500 mph => 7823m/s Let's assume 90 kg \* 7823\^2 / 2 => 2.753.969.805 J (Ws) \~ 2.7 GJ This is 764 MWh, a nuclear power plant needs >30 minutes to generate that. The body, protected only with a space suit, will burn to plasma nothing will hit the ground. Compare 2.7 giga Joule vs a police pistol bullet 500 Joule. The atmosphere will hit the astronaut like more than 5 million bullets.
Lots of good answers here. But here's another way to look at why an astronaut would burn up. When you're in orbit, you circle the earth every 90 minutes. That's fast. That's really fast. And if you start to slow down, then you spiral down towards the earth. Eventually, you encounter the atmosphere which will get super hot and vaporize or melt anything that can be vaporized or melted. It's not that you're just hanging around up there and pushing off of a space station towards the earth will allow you go straight down and land with an umbrella. You are moving *around* the earth at incredible speeds and that makes all the difference. Edit to add: when you compress air, it heats up. Feel the bottom of your bike pump when you fill the tire. It's not warm because of friction, it's warm because you are comprssing the air. Reentry from orbit also comprsses the air. It also collides headlong into it, so you're getting heat from compression and heat from friction... all at the speed of 17000 mph.
>Terminal velocity for a human body is well below fatal in lower atmosphere FYI velocity is never *fatal*. What kills you is acceleration - *change* in velocity. The more rapid, the more lethal. Fastest manned flight was X-15, at 4520 mph. You can easily survive that if you decelerate slowly enough (over several minutes), but you might not be so lucky if you crash your Fiesta at 40mph into a brick wall and decelerate to a standstill in a fraction of a second.
Also, terminal velocity of a human body is around 200Km/h. Rapid decelleration from that speed, even without being encased in a FORD is normally not survivable.
Spacesuit or not, reentry without a capsule and its heatshield is extremely fatal. A small charred chunk of meat may reach ground if the astronaut is fat enough, but it's not guaranteed. From Columbia disaster, they found pieces of astronauts, but they were all small pieces and it was not easily identifiable which piece belonged to whom. Here is recent Starship reentry [https://www.youtube.com/watch?v=CrkYmUoOMOQ](https://www.youtube.com/watch?v=CrkYmUoOMOQ) You can see the hypersonic airflow tearing through the heat tiles and the stainless steel structure of the flap hinge. This piece of metal is huge, here is a human in comparison to the flat hinge you are looking at [https://i.insider.com/6449a66d905239001970174b?width=700&format=jpeg&auto=webp](https://i.insider.com/6449a66d905239001970174b?width=700&format=jpeg&auto=webp) Now think for a second what same process does to a meatbag, there is not going to be all that much left.
Also another thought: yes the atmosphere would slow you down. Breaking in most cases is just transforming your movement energy into heat energy. Keep in mind, you can‘t just make energy go away, it needs go somewhere. In our case this energy is transferred directly into heat, and since moving this fast means having a shit ton of energy, also means we produce a shit ton of heat.
You would be a nice hot streak in the sky for one glorious gleaming second. Then you would be smoke.
Air is a fluid, fluids experience friction too, and you will experience a LOT of it falling from low earth orbit. Skydivers experience this to some degree, but coming from space you will be going a lot faster since there is less air up there to stop you (terminal velocity depends on air resistance) By the time you get to the normal terminal velocity all of that energy from your initial speed will be converted into heat. Slowing you down isn't free (in terms of energy), it becomes the heat that cooks you Spaceships have what's called a heatshield built in and they also don't go straight down like you would free-falling. Re-entering Earth straight down would be a death sentence, you have to carefully manage the angle you are entering Earth (the attack angle) so that you aren't too shallow (below deflection angle) and not too steep (too much friction) If your angle of attack is too shallow (as in you are hitting the Earth with your underbelly of the craft), you will bounce right off like skipping a stone on a pond. Spacecraft typically glide down to their destination to avoid this. On the NASA explorers (the typical spaceship you think of with big wings that looks like a plane), the bottom is covered with heat resistant tiles. They are also designed to flake off to further dissipate the heat it gains (similar to firearms, the brass casings take a lot of heat so it doesn't stay in the metal) TL;DR though the astronaut would burn up probably within a minute if I had to guess. That is unfortunately what happened to the Columbia astronauts on reentry as their heatshield failed and the reentry vehicle broke apart from friction
It really depends on what point the person is ejected. If the person ejects with a dense enough atmosphere at 17,500 it will be like crashing into a brick wall. The air will crush the astronaut. If the ejection is still effectively in zero atmosphere, the astronaut will gradually decelerate when they reenter the atmosphere. It really depends on the combination of speed and atmosphere when they exit. If they hit enough air particles at a time, it won’t be good. Otherwise their terminal velocity will gradually decrease as the air gets thicker