falling from orbit

[lord pickle]

Hello Everyone

So I just finished Halo 4 and it got me thinking about something. Several times in the Halo series Master Chief has fallen from orbit to the ground with nothing but his armor on him. I'm curious about how hard it would be to calculate his speed when he hits the ground. Either the heat of reentry or the fall at the end would damage Master Chief and I don't know which would be more deadly but I am not sure how to go about solving the problems short of doing experiments which would obviously be way to unsafe and expensive to perform. This does sound like a problem for Reel Physics but I am curious to know if there are any people on this forum wise in the ways of physics that can either do the calculation or point me in the right direction to do the calculation.

Thanks
Graeme

 

[Smooth Operator]

Well if we are talking about Earth then it would be a combination of random satellite entry speed and close to human terminal velocity when landing, so in theory if you armor can overcome the entry heat (2000-5000°C) and the final impact (at 200kph or 125mph) you are just dandy.

Also in sci-fi terms he got shields, shields fix all physics holes.

 

[Chimpzy_v1legacy]

Maybe this is a job for the guys from Reel Physics?

Calculate the impact force for a human shaped object weighing around 1400 lbs (635 kg) falling from orbit. Should mix things up a little.

 

[Glaice]

I think the shields would shatter due to the velocity and the armor would slowly disintegrate because I doubt any metal or tech even in the future can protect a human at such extreme temperatures, 2000 to 5000 C would very much cook him from inside the armor, being he even survives that, hitting the ground at such a high speed would break every major bone in his body into pieces.

I believe the helmet's front where one can see would fail as there isn't any known glass to withstand those temperatures, diamond's melting point is 3550 C (6422 F) and boiling point being 4827 C (8720.6 F) thus if it was reinforced with diamond elements, his face will eventually get exposed with even a tiny hole will open and cause agony and death. Not even tungsten's melting point would help even if his armor has such elements because its melting point is 3422 C (6191 F).

Who knows, I don't know of any sort of science fiction armor for standard issue that can withstand temperatures over 150 C. Maybe Dead Space's armor but those can handle the vacuum of space for a short time in its cold atmosphere but it shows it is inefficient in protecting from fire (Surely anyone has gotten burned in DS1 at least once doing the sections with the engines in the military ship and those fire tubes on the Ishimura)

 

[Redingold]

I'm not sure if you can really say which is "more" deadly. Both would absolutely kill an ordinary person. Both are deadly.

I can't see how to approach this question in an accurate way, but here goes with a massive oversimplification of just about everything.

A human with a mass of 65kg sitting on the Earth's surface has about 4GJ of gravitational potential energy, from U = GMm/r. A human sitting in space has at most 0J of gravitational potential energy with respect to the Earth, and such a human will enter the atmosphere at about 11 kilometres per second (that's escape velocity). Thus, over the height of the atmosphere, about 100km, 4GJ of work must be done on a body in order for it to be stationary when it hits the surface. If we assume that at some point the body reaches terminal velocity, which for a human is about 56 metres per second, then just before it hits the ground it has about 97kJ of kinetic energy, from
E = mv[sup]2[/sup]/2. Thus, the vast majority of the energy is expended over the falling, and not when hitting the ground. This energy is lost to the atmosphere as kinetic and thermal energy. Now, let's find the acceleration caused by hitting the ground.

From Newton's approximation for impact depth, we know that the ratio of the thickness of a body to the impact depth is equal to the ratio of the densities of the body and the thing it's impacting. Rock is about 2.65 times denser than a human, so the human will penetrate about 1/2.65 times its thickness. This is an entirely unreasonable assumption and a massive oversimplification, because the human...spreads out upon impact and the calculations (and the ground) get a lot messier. But whatever, this is fun, so let's keep going. So, if a human is about a foot thick, then it impact about 12cm into solid rock when hitting it at terminal velocity. The acceleration is then the velocity squared divided by twice the distance, which is 1330g. This is...extreme, and very much lethal. The deceleration over the atmosphere is then re-entry velocity squared minus terminal velocity squared divided by twice the thickness of the atmosphere (actually, it isn't that at all, it's much lower in the upper atmosphere, and higher in the lower atmosphere), about 62g, which it turns out is less lethal if it's brief. The NHTSA claims that for a sudden impact, the average human can survive 65g (for a women), 75g (for a man) or 50g (for a child). However, for sustained acceleration, anything more than about 5g is lethal. So the deceleration in the atmosphere is also lethal.

I am not gonna work out the thermal effects, but suffice it to say that standard re-entry temperatures are way, way above the point of survivability.

The point is that all the effects are lethal. You wouldn't survive the heat, you wouldn't survive the deceleration, and you most certainly wouldn't survive the impact. That said, if you came in at a sufficiently shallow angle, you can reduce the deceleration to a point where you could survive, with parachutes you can reduce your impact velocity to a survivable level, and with heat shields you can survive the temperature, but if you're just falling straight from space to Earth, you stand no chance.

 

[Eclectic Dreck]

Falling from orbit is remarkably easy. Orbit is maintained by having a certain velocity perpendicular to the pull of gravity. Technically, an orbit is simply moving such that the fall never ends. Increasing this perpendicular velocity results in a wider orbit (though, without any modification, it would simply become elliptical) decreasing it becomes a closer orbit.

Taking gross liberties in assumptions:
1) Master chief can survival the heating that will result from slowing without incident
2) On a planet with significant atmosphere but relatively low gravity (Earth for example) his impact velocity would be appropriately the same as his terminal velocity.

Based on only the roughest calculation, I know that Chief stands at about 2.1 meters tall, and by standard human proportion is approximately .7 meters wide. He, like most people, isn't actually built to be aerodynamic and since we assume lower velocity is better, I'll simply assume he falls such that he presents a maximum cross section. That gives him a total surface cross section of about 1.3 sq meters. I also seem to recall his mass in armor was given as about a half ton. Skipping some tedious math, this gives him a terminal velocity of between 50 and 70 m/s or between 110 and 160 mph.

The wide range is simply because his coefficient of drag is an empirical measurement. A standard person has a coefficient of 1 where a brick is about 2.1 and a bullet (or other aerodynamic object) is 0.3 or less. We can assume he is less aerodynamic than a person (which results in the upper end speed) but more aerodynamic than a brick (the low end estimate of velocity).

Regardless, the velocity is such that his survival chances are suspect regardless of the armor. His survival chances largely hinge on how long it takes him to come to a halt and tiny fractions of a second have a vast impact. Suffice it to say that between his armor (notably the give provided by the otherwise not at all described "gel layer" and a relatively soft and giving surface (say a peaty bog), it is possible that forces could be lowered sufficiently to be survivable at the outer edges of what is possible for a human. Factor in the space magic inherent to the Chief and barely survivable could conceivably become survivable with only minor injuries.

I should point out that we do know that Chief did not hit the ground flat but rather at a fairly extreme angle (as indicated by the torn out section of jungle during the opening of Halo 3). If we assume terminal velocity was being met by this condition, it actually improves his survival chances given a portion of it was scrubbed by interaction with the dirt over the course of several meters rather than over the course of a scant few inches.

Realistically, however, he's a dead man. Only under ideal conditions where he magically survives quite a few other lethal events does a human have even the remote possibility of survival. And magic reinforcement or not, the man still has organs that remain highly susceptible to damage incurred when they slam into muscle and bone.

 

[lord pickle]

Falling from orbit is remarkably easy. Orbit is maintained by having a certain velocity perpendicular to the pull of gravity. Technically, an orbit is simply moving such that the fall never ends. Increasing this perpendicular velocity results in a wider orbit (though, without any modification, it would simply become elliptical) decreasing it becomes a closer orbit.

Taking gross liberties in assumptions:
1) Master chief can survival the heating that will result from slowing without incident
2) On a planet with significant atmosphere but relatively low gravity (Earth for example) his impact velocity would be appropriately the same as his terminal velocity.

Based on only the roughest calculation, I know that Chief stands at about 2.1 meters tall, and by standard human proportion is approximately .7 meters wide. He, like most people, isn't actually built to be aerodynamic and since we assume lower velocity is better, I'll simply assume he falls such that he presents a maximum cross section. That gives him a total surface cross section of about 1.3 sq meters. I also seem to recall his mass in armor was given as about a half ton. Skipping some tedious math, this gives him a terminal velocity of between 50 and 70 m/s or between 110 and 160 mph.

The wide range is simply because his coefficient of drag is an empirical measurement. A standard person has a coefficient of 1 where a brick is about 2.1 and a bullet (or other aerodynamic object) is 0.3 or less. We can assume he is less aerodynamic than a person (which results in the upper end speed) but more aerodynamic than a brick (the low end estimate of velocity).

Say requiem has a lot of gravity. Then does the Chief have enough time to slow to terminal velocity as he falls, or is he going too fast for there to be enough time for him to decelerate to terminal velocity before crashing into the jungle?

Regardless, the velocity is such that his survival chances are suspect regardless of the armor. His survival chances largely hinge on how long it takes him to come to a halt and tiny fractions of a second have a vast impact. Suffice it to say that between his armor (notably the give provided by the otherwise not at all described "gel layer" and a relatively soft and giving surface (say a peaty bog), it is possible that forces could be lowered sufficiently to be survivable at the outer edges of what is possible for a human. Factor in the space magic inherent to the Chief and barely survivable could conceivably become survivable with only minor injuries.

I should point out that we do know that Chief did not hit the ground flat but rather at a fairly extreme angle (as indicated by the torn out section of jungle during the opening of Halo 3). If we assume terminal velocity was being met by this condition, it actually improves his survival chances given a portion of it was scrubbed by interaction with the dirt over the course of several meters rather than over the course of a scant few inches.

Realistically, however, he's a dead man. Only under ideal conditions where he magically survives quite a few other lethal events does a human have even the remote possibility of survival. And magic reinforcement or not, the man still has organs that remain highly susceptible to damage incurred when they slam into muscle and bone.

Say Requiem has a lot of gravity. Then can Master Chief slow down to terminal velocity, or is he going so fast that he hits the ground before the air can slow him down enough?

 

[Eclectic Dreck]

Say Requiem has a lot of gravity. Then can Master Chief slow down to terminal velocity, or is he going so fast that he hits the ground before the air can slow him down enough?

Within tolerances, terminal velocity is more a function of cross sectional area, empirically tested coefficient of drag and air density than gravity. The force attracting the body increases in a linear fashion, by contrast, resistance of air increases by the square. With a sufficiently dense atmosphere and a sufficiently low gravitational force, the fall could readily be survivable of course.

 

[skywolfblue]

I think the shields would shatter due to the velocity and the armor would slowly disintegrate because I doubt any metal or tech even in the future can protect a human at such extreme temperatures, 2000 to 5000 C would very much cook him from inside the armor, being he even survives that, hitting the ground at such a high speed would break every major bone in his body into pieces.

I believe the helmet's front where one can see would fail as there isn't any known glass to withstand those temperatures, diamond's melting point is 3550 C (6422 F) and boiling point being 4827 C (8720.6 F) thus if it was reinforced with diamond elements, his face will eventually get exposed with even a tiny hole will open and cause agony and death. Not even tungsten's melting point would help even if his armor has such elements because its melting point is 3422 C (6191 F).

Who knows, I don't know of any sort of science fiction armor for standard issue that can withstand temperatures over 150 C. Maybe Dead Space's armor but those can handle the vacuum of space for a short time in its cold atmosphere but it shows it is inefficient in protecting from fire (Surely anyone has gotten burned in DS1 at least once doing the sections with the engines in the military ship and those fire tubes on the Ishimura)

This.

In a related note, an interesting oopsie plothole of the halo universe:

In the Halo lore Plasma is extremely effective vs. Shields.

Guess what gets generated in heaploads upon reentry?

His shields should be toasted and his armor burnt to a crisp. But wave the hand, because it's LUCK!

 

[Aaron Sylvester]

Making a suit that can withstand re-entry temperatures is actually no problem, reinforced carbon and silica materials already coat the bottom of the Space Shuttle and can withstand the typical re-entry temperatures of 1200-1300c.

No, the problem is that NO kind of suit is going to be able to keep you alive from thudding into solid ground at terminal velocity. The g-force experienced at the point of impact will literally make the brain squish into the back of the skull and all internal organs will pretty much do the same thing, they won't be able to retain their shape after that and the person will be legally dead.

I haven't played Halo but from what I can tell the suit only expands a few inches out from the body, that's not enough room to "cushion" the fall with gel/soft stuff/anything.

Unless we're talking about a suit that has literally FUSED with the body and tissue/organs/etc are no longer necessary, e.g. Prophet's Nanosuit by the end of Crysis 3. The nanofibers have extended into the body, through muscle and all internal organs (even the heart) have been assimilated into the suit. The wearer eventually becomes nothing more than a semi-organic AI entity but still "human" in the sense that he maintains his identity, personality and memories.

At the end Prophet fell from orbit, landed on an island and easily survived. The suit was fully symbiotic and so integrated into him that it's impossible to say where the suit ended and his body began. He can pretty much take a pile of TNT to the face and survive because g-forces and shocks are no longer a concern

Does the Halo suit do that?

 

[Extra-Ordinary]

Spartans have survived stuff like that before.
It was in one of the books. Don't ask me which one and I barely remember the event as it is so it might have taken place on a planet where the gravity isn't so strong but in any case, there was this time when a bunch of Spartans jumped out of a crashing ship at nigh-subsonic speeds and survived.
Well, some of them survived anyway.

I haven't played Halo but from what I can tell the suit only expands a few inches out from the body, that's not enough room to "cushion" the fall with gel/soft stuff.

That was actually in the book. Like I said, I'm really fuzzy on the specifics, but one thing I do remember is that they over-pressurized the s**t out of their gel-layer to protect themselves. Some of them also managed to hit water. Which I know can hit just as hard as pavement but not if you land in it properly.
How scientifically accurate it is, I'd wager not a lot, but in a Halo universe, apparently it's possible.

 

[Jayemsal]

Making a suit that can withstand re-entry temperatures is actually no problem, reinforced carbon and silica materials already coat the bottom of the Space Shuttle and can withstand the typical re-entry temperatures of 1200-1300c.

No, the problem is that NO kind of suit is going to be able to keep you alive from thudding into solid ground at terminal velocity. The g-force experienced at the point of impact will literally make the brain squish into the back of the skull and all internal organs will pretty much do the same thing, they won't be able to retain their shape after that and the person will be legally dead.

I haven't played Halo but from what I can tell the suit only expands a few inches out from the body, that's not enough room to "cushion" the fall with gel/soft stuff/anything.

Unless we're talking about a suit that has literally FUSED with the body and bones/organs/etc are either no longer necessary, e.g. Prophet's Nanosuit by the end of Crysis 3. The nanofibers have extended into the body, through muscle and all internal organs (even the heart) have been assimilated into the suit. The user becomes nothing more than a brain (again, fused with AI).

At the end Prophet fell from space onto an island and easily survived, at this point the suit is so integrated into him that it's impossible to say where the suit ends and his body begins. He can pretty much take a pile of TNT to the face and survive because g-forces and shocks are no longer a concern.

Does the Halo suit do that?

Absolutely not.

It is power armor, in the same league as Fallout style power armor.

He is no more likely to survive a 200 foot fall, than he is to survive falling from cunting orbit.



To put it simply, you'd have a flattened suit, full of human slushy.

 

[FalloutJack]

zoop

Given the nature of the man who surfed from orbit, if you don't have a chute, you're dead. End of story. It's not a matter of your protective coating. You still hit the inside of IT at terminal velocity, concussive force, you see. Welcome to splattering goo land.

 

[Zantos]

I think the shields would shatter due to the velocity and the armor would slowly disintegrate because I doubt any metal or tech even in the future can protect a human at such extreme temperatures, 2000 to 5000 C would very much cook him from inside the armor, being he even survives that, hitting the ground at such a high speed would break every major bone in his body into pieces.

I believe the helmet's front where one can see would fail as there isn't any known glass to withstand those temperatures, diamond's melting point is 3550 C (6422 F) and boiling point being 4827 C (8720.6 F) thus if it was reinforced with diamond elements, his face will eventually get exposed with even a tiny hole will open and cause agony and death. Not even tungsten's melting point would help even if his armor has such elements because its melting point is 3422 C (6191 F).

Who knows, I don't know of any sort of science fiction armor for standard issue that can withstand temperatures over 150 C. Maybe Dead Space's armor but those can handle the vacuum of space for a short time in its cold atmosphere but it shows it is inefficient in protecting from fire (Surely anyone has gotten burned in DS1 at least once doing the sections with the engines in the military ship and those fire tubes on the Ishimura)

You're forgetting the most important form of armour the chief has, plot armour! With the ability to withstand temperatures of 'however high is convenient' deg C and impact of 'whatever we feel like' N.

Seriously though, I think you're seriously overestimating the temperature, the shuttle's thermal protection system is designed to withstand 3000 deg F (about 1650 deg C) and the chief will probably undergo less aerodynamic heating due to being smaller. That's somewhat more manageable. The impact is more iffy, but "Because we have magical inertial dampeners" has been the mainstay of Sci Fi for far too long for us to get picky about single uses at his point.

 

[McKitten]

How much of a problem heating is will depend completely on the precise descent path. Friction is irrelevant, that produces nowhere near enough heat to cause problems, however compressive heating can. If he's going down a very steep path, decelerating very quickly from orbital velocity to terminal velocity, the compression heat of the air can produce the sort of temperatures that make meteors glow or explode. On the other hand if he's going at a comparatively shallow angle, only slowly breaking as he's hitting denser and denser atmosphere, there's easily enough time to shed the energy without ever being at risk of burning up. Keep in mind that temperature and energy are not the same thing, he'd need to convert a lot of kinetic energy to thermal energy in a very short time to get dangerous temperatures. All while the air rushing by works quite efficiently at dissipating the heat.

Of course, since descent at a steep angle will also lead to uncontrolled flight into terrain at said steep angle, that's not survivable anyway. But at a shallow angle, with a slow descent and soft landing spot, it's survivable. People have fallen from heights were they reached terminal velocity and didn't die. It's a freak accident, but well, someone has to be the luckiest person on earth. (http://en.wikipedia.org/wiki/Vesna_Vulovi&#263

I'm to lazy to do the actual calculation myself but here's how i'd take a rough stab at guesstimating how the fall would be survivable:
1. Calculate the total kinetic energy that needs to be shed. As Redingold did, except for something with the mass of Master Chief, not of a human.
2. Get some ballpark estimate of the effects of convection cooling and compression heating during orbital descent. I'd calculate the energy a shuttle loses during descent and compare that to the temperature it reaches.
3. Get a maximum survivable temperature for Master Chief.
4. Now calculate over how much time the energy has to be spread so the temperature never exceeds that.
5. Calculate at what angle he'd have to descend so it takes at least that long.
6. Profit?

Oh on a final note, soft landing does not mean water. Water is actually extremely hard beyond certain speeds (around 10m/s iirc) because it's not compressible, and above that speed there's no time to push it aside. "Soft" means material that can be compressed easily, but there's not a lot of that in nature, unless you're hitting a hedgerow or something like that.

 

[Bad Jim]

It is possible to make breatheable liquids.

http://en.wikipedia.org/wiki/Liquid_breathing

This is still experimental, but in theory you could fill the suit with the stuff and but reasonably safe as long as the suit doesn't break. It's been proposed as a way to survive high g forces, hitting the ground hard and surviving are just a logical extreme. You would need a very strong suit, but hey, it's the future.

 

[Haunted Serenity]

Here i thought this might be a Kerbal Space Program thread about crap falling from orbit. This is quiet different. A question though. Halo Reach. That bugger gets dropped from orbit plus in Halo 3, Master Cheif seems to alter his descent course after the breakup of the forerunner ship.

 

[xPrometheusx]

Here i thought this might be a Kerbal Space Program thread about crap falling from orbit. This is quiet different. A question though. Halo Reach. That bugger gets dropped from orbit plus in Halo 3, Master Cheif seems to alter his descent course after the breakup of the forerunner ship.

Well at least in Reach you have a space-magic reentry pack on. I figure that had something to do with it, where it could bolster a shield for a short time or some such.

All that said, if a shield can shrug off a shot of plasma (E.G. that stuff the sun's made out of), shouldn't he be able to withstand reentry temperatures, at least? I mean, on impact he'd make a crater a mile wide, no denying that, but does reentry generate enough heat to turn gas to plasma? If not, maybe he can withstand it.

 

[chuckdm]

Well the temperature is not an issue here. The space shuttle has glass, heat tiles, and is considerably MORE aerodynamic than a human. This means it will hit higher speeds, but also higher temperatures, and it has survived (well...usually) for 30+ years and over 100 missions PER SHUTTLE so the materials to handle the heat exist already. Whether those can be used as armor for a powered suit of armor is debatable, though with the aforementioned shield in place, Chief shouldn't need ANY armor, technically. Shields plus striking first in melee renders armor pointless. (FYI I've never played Halo.)

As to speed, we could look at HALO jumps for that. As in, the real world SEALs-do-this-shit-for-fun ones. Jumping from over 50,000 feet puts you about a third of the way up to orbit, and they fall all the way down to as low as 200 feet above the water before they deploy a parachute. In those real HALO jumps, it's the neck snapping from the sudden deceleration (from the parachute) that causes most injury (and death, about 1 time in 20). Accordingly, there's some red bull dude who has jumped from what is technically low orbit (well...I think it was 115,000 feet but they said at that altitude the air is about half hydrogen and half vacuum. sounds like space to me.) about 3 months ago with nothing but an oxygen tank, sealed suit, and a parachute. He survived, landed just fine. The trick was deploying the chute at the right time. Once he mastered that it was relatively easy, as everything else had been done before by someone else.

So really, all Chief needs is some retro-rockets he can fire for less than 30 seconds in his suit and you'd be hard pressed to find a planet with even 3G surface gravity that he couldn't land on. That is, if he can do a series of 10 3-second burns at various points throughout the descent (if done right, these should have the same effect as a parachute) and make the suit out of the same old stuff as the space shuttle, and bingo, totally survivable.

Though again, I haven't ever played Halo. If they're claiming he just freefalls, then no, dude's toast. He MUST have some sort of breaking to survive.

But the heat won't kill him either way.