# space marine capabilties



## the_man_with_plan (May 3, 2011)

My friend and i were arguing about how ridiculous space marines are.
here's our hypothetical situation:
so there's this battle barge in orbit above a planet and it is heavily damaged, causing marines to fall out into space. we disagree as to whether these marines(in their armour) could survive the fall. he thinks they could, but i say that's ridiculous. i think that even if he survived the flames of re-entry(doubtful), the impact with the ground would kill the marine. that's why there's drop pods. i think a terminator would probably survive re-entry, but nothing short of a dreadknight actively bracing for impact could(maybe) survive the impact with the ground.

so, who's right? are we both Matt ward level crazy?


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## hailene (Aug 28, 2009)

Well, the drop pod assault would probably be more accurate. And with the droppod surrounding you you're less likely to be killed by enemy fire as you drop.

Anywho, I don't think the Space Marine could handle landing at many hundreds (or possibly thousands, what's the terminial velocity of a man falling down in power armor?) miles per an hour. Their skeleton and organs would go smoosh.


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## Malus Darkblade (Jan 8, 2010)

I think a SM could survive a fall and come out with just a few broken limbs and maybe... *maybe* a broken bolter  

Sigh hailene, why have you lured me into this thread.


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## Giant Fossil Penguin (Apr 11, 2009)

Nothin unprotected can survive a fall from orbit. The heat of re-entry would burn them up- just look what happened to the Shuttle, a system actively designed for re-entry. However, should the falling Astartes manage to pull off a low-velocity re-entry (like Spacecraft One uses), then the impact would, basically, liquify them. Even inside Terminator armour that might survive, the body inside would hit the armour that surrounds them with the same force the armour hits the ground.
The only way to survive a rapid descent is by Drop Pod, with its ablative shell, retros and inbuilt suspension and shock-absorbstion, systems.

GFP


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## Grins1878 (May 10, 2010)

:goodpost: What he said! :grin:


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## Legiomortis (Jun 11, 2011)

As long as the progenoid survives intact its all good, nothing more sacred than the gene seed, or Jack Daniels single barrel, or both.


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## jfvz (Oct 23, 2010)

As mentioned above if we compare it to the space shuttle or that is designed for reentry and a safe landing. (Note: the failures, aka explosions, of the space shuttle have not been relivant to this discussion as they are usually either a heat sheailding issue or an issue with the rockets) Even these purpose build must re-enter within a window of about 2-4 degrees depending on vehicle. any steeper and the craft will burn up even if everything is working perfectally. From memory the temperatures acheived will easially melt steel, hence why the brittle ceramics must be used. 

For an ingame comparison think of a terminator in a hug melta gun beam fully covering the terminator for minutes.

Lets assume that the terminator has been equiped with enough heat sheilding to survive the fall. By doing some rough cals compairing a terminator to a skydiver and assuming a terminator weighs 1000kg (2200 pounds) i found the terminal velocity to be around 800km/h (500miles/h or just under mach 2.4 at sea level). An impact i doubt that even the enhanced spacemarines could survive.

Please forgive me if i went a bit overboard, im an engineering student and like those sorts of calculations :biggrin:


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## hailene (Aug 28, 2009)

Giant Fossil Penguin said:


> Nothin unprotected can survive a fall from orbit. The heat of re-entry would burn them up- just look what happened to the Shuttle, a system actively designed for re-entry. However, should the falling Astartes manage to pull off a low-velocity re-entry (like Spacecraft One uses), then the impact would, basically, liquify them. Even inside Terminator armour that might survive, the body inside would hit the armour that surrounds them with the same force the armour hits the ground.
> The only way to survive a rapid descent is by Drop Pod, with its ablative shell, retros and inbuilt suspension and shock-absorbstion, systems.
> 
> GFP


To be technical, I think Termie armor would survive the reentry. It was designed to run in plasma generators and those things run hot. Really hot.

I agree with the smoosh-ending, though.



Malus Darkblade said:


> I think a SM could survive a fall and come out with just a few broken limbs and maybe... *maybe* a broken bolter
> 
> Sigh hailene, why have you lured me into this thread.


I'm honored you think so well of me that my posting requires you to read it .


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## arlins (Sep 8, 2010)

hailene said:


> I agree with the smoosh-ending, though .


 mmmm.... space marine smoothie , just pop a straw through the eye lens and your good
:grin:


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## Azrell (Jul 16, 2010)

Think of it this way SMs are the ultimate badasses, they can spit acid, eat anything and even gain the memories of people they eat. If they could fall from space and live, they probably would do it just to show people how badass they really are. But they use drop pods, suggesting that as least most of the time badassness ends and being dropped from space.


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## scscofield (May 23, 2011)

The Deathwatch rpg system states on page 261 of it's core book that Space Marines take 1d10+1 damage for every meter they fall. Also states that armor offers no protection from falls. They would be splattered even if they managed to get past reentry :-D


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## Giant Fossil Penguin (Apr 11, 2009)

Maybe think about it in a slightly different way. Take a Main Battle Tank of your choice up into orbit and then let it fall. Oh, and make sure a living crew is inside when you do. What's left of the Tank and crew after impact is what would be left of any armoured Astartes after the same fall.
Termie armour might have been designed to work in plasma cores, the difference, to me, isn't the heat of re-entry, but the energy it would have to absorb on impact and the time in which it would do so. If the impact energy could be absorbed over a long period of time, then the armour might withstand it. But in such a short time period the weakest area wouldn't be able to spread the energy quick enough and once it's breached, it will be game over. Might make for an interesting weapon, though!

GFP


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## NoiseMarine (Jun 8, 2008)

Exactly what Fossil Penguin says, I agree that the armor could survive but that doesn't factor out the G-forces on the body inside of the armor. The terminal velocity culminates in a crash at speeds in excess of 100 mph straight into the ground. Maybe, just maybe they would survive if they crashed into a body of water but even then it's a fat fuckling of a chance.


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## laviathan13089 (Apr 21, 2011)

what about if the battle barge itself was entering the atmosphere due to a decaying orbit (drifting after heavy damage)? do you think the impact would kill all space marines inside? granted a battle barge has a great deal more mass but it also would crate more friction, being such a large object. assuming it doesn't break apart during its fall (possible due to structural design, unknown because of materials used) and the plasma reactor has already died out, and wont go critical (no power for prolonged period or leaked out and doesnt have any catalyst left).


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## Dogbeard (Apr 15, 2011)

Assuming that part of the battle barge remained relatively intact and that they were in that part, I could see Space Marines surviving the crash, yes.


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## NoiseMarine (Jun 8, 2008)

laviathan13089 said:


> what about if the battle barge itself was entering the atmosphere due to a decaying orbit (drifting after heavy damage)? do you think the impact would kill all space marines inside? granted a battle barge has a great deal more mass but it also would crate more friction, being such a large object. assuming it doesn't break apart during its fall (possible due to structural design, unknown because of materials used) and the plasma reactor has already died out, and wont go critical (no power for prolonged period or leaked out and doesnt have any catalyst left).


 Imperial Ships are usually structurally sound enough and big enough to survive a crash relatively intact -unless they've been blown to pieces beforehand. I'd say then, that the Space Marines would be able to survive.


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## Luisjoey (Dec 3, 2010)

if the marines survives the re-entry heat
and the body-landing crash

he would need a good apothecary


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## dtq (Feb 19, 2009)

jfvz said:


> As mentioned above if we compare it to the space shuttle or that is designed for reentry and a safe landing. (Note: the failures, aka explosions, of the space shuttle have not been relivant to this discussion as they are usually either a heat sheailding issue or an issue with the rockets) Even these purpose build must re-enter within a window of about 2-4 degrees depending on vehicle. any steeper and the craft will burn up even if everything is working perfectally. From memory the temperatures acheived will easially melt steel, hence why the brittle ceramics must be used.
> 
> For an ingame comparison think of a terminator in a hug melta gun beam fully covering the terminator for minutes.
> 
> ...


Im no engineering student . But taking that 800km/h and 1000kg mass calculation at point of impact, that gives me a landing force of 246913580 newtons. Now what Im going to try to do is work out that force distributed over the whole estimated front surface of a terminator. to compare that to the force of small arms fire...

OK terminator armour is what 8ft high? by 4ft wide? so if I took a rectangle that size and put a termintor suit on that it would cover what? 60% of the area. so If I work out how many cm2 there is in 60% of a 8x4 rectangle that will give me a surface area to divide the impact by. All highly hypothetical of course.

8'x4' gives me 2.9728 square meters, or 29728 square centimetres, of which 60% is 17836.9 square centimeters so taking the 246913580 newtons and dividing it by the area available= 13842 newtons per square centimeter.

Now Im going to try a bullet calculation, being an american forum Im sure theres gun nuts who can improve this area...

so Im taking a 9mm shell at 7.45g at 920 mph comes out at 6300 newtons total. Taking the area of the main section of the bullet first whilst is 0.636cm2 that gives us 9905 newtons per square centimeter. Of course a bullet doesnt hit back end first, it hits with the point end significantly reducing impact surface to improve pentration etc. so if instead of a 9mm ife we look at say 3mm for the tip hitting first the initial impact area would be 0.07 cm2 that would work out at 90,000 newtons per cm2 FAR in excess of the distributed landing impact on the armour. 

Im pretty certain our 9mm rounds would do nothing to terminator armour, there fore every point of the terminator armour should be able to easily stand impacts in the region of 6x as hard as the skydiving terminator. 

HOWEVER This relies on a even spread of the impact. This is actually not impossible hitting somethign with a lot of give like soil would probably result in rapid compression of the soil before the impact is fully achieved, resulting in
a better overall distribution of the force. If the terminator managed to go head first into a rock and the head part took the full impact then youd be looking at a very different scenario... 

Theres also questions on whether just because one point can take a certain force whether the whole frontal area can stand up to the same force applied all over. Almost certainly that isnt the case! But the forces are FAR below that of 9mm fire, and 9mm fire is far beneath the limits of the suits abilities.

All in all a good bit of skydiving and a relatively soft landing might well preserve the armour suit relatively intact...

Now as for the marine inside the suit. Ive always assumed the marine has no room for movement between himself and the suit. so what we're up against is internal organ movement etc rather than the marine coliding with the armour itself. That said if say the head is able to move and colide with the inside of the helmet hes definetely dead no questions asked.

From that speed to 0 in 0.2 of a second would be a 113g deceleration. I know 30-40g deceleration without any damping is enough to start causing organ movement to be fatal to an average human, mabe space marines can stand 1.5 times that before organs start to move too much etc. so maybe at the outside 60g. However if the terminator suit not only fits over the marine but includes damping systems against shocks - not at all unlikelly and if those systems operate over the whole body area and can reduce the deceleration by 50% or more then it may well be possible that the marine inside could potentially survive.

The maths here is very shakey with a lot of assumptions, based mainly on the initial speed and mass estimates...

I would say its a remote possibility that given an ideal descent and ideal landing, if the suits shock damping is good enough a marine in terminator armour may possibly survive such a descent and landing, over water It would become much more likelly.


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## scscofield (May 23, 2011)

http://www.lpl.arizona.edu/tekton/crater_c.html
​
*Projectile Descriptors*

Projectile Diameter 1 meters Projectile Density 8000 kg/m3​ *Impact Conditions*

Impact Velocity 17 km/sec Impact Angle 90 degrees​ *Target Descriptors*

Target Density 1500 kg/m3 Acceleration of Gravity 9.8 m/sec2 Target Type competent rock or saturated soil​*Results*

The three scaling laws yield the following _transient_ crater diameters (note that diameters are measured at the pre-impact surface. Rim-to-rim diameters are about 1.25 times larger!) Yield Scaling 4.23 x 101	meters Pi Scaling (Preferred method!)	8.93 x 101	meters Gault Scaling 5.63 x 101	meters Crater Formation Time 1.27 seconds 
Using the Pi-scaled transient crater, the _final_ crater is a Simple crater with a rim-to-rim diameter of 1.39 x 102 meters. 
This impactor would strike the target with an energy of 6.05 x 1011 Joules (1.45 x 10-4 MegaTons). 



He would make a 139 meter crater.......


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## jfvz (Oct 23, 2010)

dtq said:


> Im no engineering student . But taking that 800km/h and 1000kg mass calculation at point of impact, that gives me a landing force of 246913580 newtons. Now what Im going to try to do is work out that force distributed over the whole estimated front surface of a terminator. to compare that to the force of small arms fire...


Just one question, what did you use to get this number? you would need to assume some time over which he would come to a stop. I had no idea of it, and thats why i stopped there. 

Also a couple of points:
- Falling into water at those velocities would have very little differance from hitting solid ground due to surface tension. Just look at the footage of plane's wings clipping the water and crashing.
- i may be wrong but i dont think that your comparison is entirly right. Its sort of compairing two different things. The way a bullet works isnt a blunt force it is a burrowing action for lack of a better term. It uses the pressure to part what it wants to go through, also it might be interesting to note that a knife stap generates more pressure than a bullet. Where as a terminator hitting the ground is more like a hammer blow, that deforms the target. Something that i think would be better compaired by the change in kenetic energy (basically movement energy) or momentium (mass times velocity).

Good try its always good to see other people trying to figure out things like these, but remember never just assume that your wrong if some else says something different. Im an engineering student but i am still learning (im only 1st yr), so i could be completely wrong in this and you right.


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## dtq (Feb 19, 2009)

jfvz said:


> Just one question, what did you use to get this number? you would need to assume some time over which he would come to a stop. I had no idea of it, and thats why i stopped there.


Doh I used 800 miles an hour not 800kmh! therefore over calculated the force substantially....

I used this calculator

http://hyperphysics.phy-astr.gsu.edu/hbase/carcr.html

to try to get to the force involved.




jfvz said:


> Also a couple of points:
> - Falling into water at those velocities would have very little differance from hitting solid ground due to surface tension. Just look at the footage of plane's wings clipping the water and crashing.


Yep you're quite right I messed up there. Snow would be far better.



jfvz said:


> - i may be wrong but i dont think that your comparison is entirly right. Its sort of compairing two different things. The way a bullet works isnt a blunt force it is a burrowing action for lack of a better term. It uses the pressure to part what it wants to go through, also it might be interesting to note that a knife stap generates more pressure than a bullet. Where as a terminator hitting the ground is more like a hammer blow, that deforms the target. Something that i think would be better compaired by the change in kenetic energy (basically movement energy) or momentium (mass times velocity).


Not sure on that, but Im 99% certain that Id take a knife would over a 9mm gunshot...



jfvz said:


> Good try its always good to see other people trying to figure out things like these, but remember never just assume that your wrong if some else says something different. Im an engineering student but i am still learning (im only 1st yr), so i could be completely wrong in this and you right.


Just doing what I can, threw it all out by using the wrong figure to start with, but that only alters things in favour of the terminator armour suit at the least surviving.

Now what is interesting after some further reading is that beyond a certain point the distance fallen really doesnt matter, once terminal velocity is reached and air resistance balances with gravity acceleration stops, so the question can a marine survive falling once atmospehric entry has been overcame, is no different to can he survive a parachuteless jump from a plane! Plenty of unarmoured unenhanced humans have survived falls like that and greater. Largelly depending on how they fell and more importantly how they landed.

Ive been looking and people include a skydivers mass in their calculations for terminal velocity. Im not sure why that is as mass isnt supposed to affect falling speed, just the aerodynamics? As far as I can see the terminators mass only really matters when it comes to the hard landing as Ive tried to use in my examples. For the falling part the only thing that should affect the speed is the shape of the terminator and his body position relative to the ground (although atmoshpere density etc would have an affect as well) Apparantly an average human will not hit much more than 125mph no matter how high you drop them from. A terminator is bigger and heavier, but the mass shouldnt affect his falling speed, only how hard he hits the ground. So it would be down to his shape to affect his speed.


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## Malus Darkblade (Jan 8, 2010)

You guys are taking this thread *way* too seriously when it's simply a waste of bandwidth. 

And you can tell who is a troll by the fact that they generally never make another post after their opening one which is usually silly.


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## dtq (Feb 19, 2009)

Malus Darkblade said:


> You guys are taking this thread *way* too seriously when it's simply a waste of bandwidth.
> 
> And you can tell who is a troll by the fact that they generally never make another post after their opening one which is usually silly.


Serious isnt quite the right word. Whether a fiction soldier could survive such a fall or not has no emotional meaning to me at all. Before JFVZ put some maths to it I wouldnt have responded. But once a speed and mass were given it became an interesting mathematical "What if".

Sorry Im an oldschool geek, from before it became trendy. I actually use a calculator for fun at times.


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## Vaz (Mar 19, 2008)

Malus Darkblade said:


> You guys are taking this thread *way* too seriously when it's simply a waste of bandwidth.
> 
> And you can tell who is a troll by the fact that they generally never make another post after their opening one which is usually silly.


Oh you spoke again. Sorry, I thought a bee farted. If you aren't interested in the subject, why post?

You're simply "wasting bandwidth" yet again - and the purpose of a forum is not solely so that the original poster gets an answer, but so that others who read and or participate in the thread can discuss something - regardless of a "troll" or not (I'm sure you know, after all, being one you should be able to spot them a mile off).


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## jfvz (Oct 23, 2010)

dtq said:


> I used this calculator
> 
> http://hyperphysics.phy-astr.gsu.edu/hbase/carcr.html
> 
> ...


I had a look at the calculator but it uses a something we dont actually know, the distance it takes to stop.

The mass wont effect the falling acceleration in a perfect vacume. You said it yourself terminal velocity is acheived when the upwards force of the air resistance = downwards force of gravity, which is given by the mass of the falling object times the gravity. The formula for the terminal velocity is given here: http://en.wikipedia.org/wiki/Terminal_velocity

This formula shows that keeping everything else constant that the terminal velocity is preportional to the square root of the mass. So increasing the mass by a factor of 4 the terminal velocity will increase by the square root of 4, which is 2. But this would not work out exactally as the faster something goes the greater the friction which would lower the max velocity possible.

Oh and for the bullet vs knife, i was more refering to a kevlar vest. Two identical vests, one gets hit with a bullet and it stops it no problem, the other gets stabed with a knife, and it goes straight through it. If they actually get into you then the bullet has a few nasty tricks that make them worse, espically bullets like hollow points. from memory the movie "3 kings" has a fairly easy to understand explination of what a bullet does.

Edit: @ scscofield, where did the 17 km/sec come from there?


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## scscofield (May 23, 2011)

If you play with the drop down menus on the website at the top of the post I made it gives you options. I did a 1meter diameter for him, the 17 km/sec is what the drop down said earth/moon asteroidal impacts.

The Purdue version of that calculator does not give the drop down options but does state this:
This is the velocity of the projectile before it enters the atmosphere. The minimum impact velocity on Earth is 11 km/s. Typical impact velocities are 17 km/s for asteroids and 51 km/s for comets. The maximum Earth impact velocity for objects orbiting the sun is 72 km/s. (http://impact.ese.ic.ac.uk/ImpactEffects/)

They are spiffy little toys to piddle with that and the prior link, pretty much the same calculator other than minor layout changes.

Edit: The purdue calculator results are much more detailed information wise. According to wikipedia from Earth surface outerspace is considered to be 118 km if I remember right from this morning.
EditEdit: http://www.purdue.edu/impactearth zomgcool!


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## the_man_with_plan (May 3, 2011)

Malus Darkblade said:


> You guys are taking this thread *way* too seriously when it's simply a waste of bandwidth.
> 
> And you can tell who is a troll by the fact that they generally never make another post after their opening one which is usually silly.


if I'm a troll then i'm not a very good one, now am I? Trolls are supposed to annoy people and piss them off, but it looks like everyone's having fun answering my question.


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## TheLifeOfReilly (Jun 17, 2011)

Wow thats a lot of scientific ideas you guys are throwing around. My two cents are that seeing how the universe is fictional and ONLY IF the applied physics/mathematical equations of an drop from orbit to Earth are universal (as in being each planet having the same atmosphere, gravitational pull etc. [I honsetly have no idea lol]) that these findings can be proven true. 

Unfortunatly I dont rember reading any of the BL writing from a lone Space Marine tumbling down to earth so I guess we may never know. 

Unless the MKVII or VIII Power Armor is like the Master Chiefs armor LOL where you can endure a Halo dive free fall.


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## TheLifeOfReilly (Jun 17, 2011)

Yet there are 3 special implants in making a Space Marine which would help him endure such a fall.

1) Mucranoid- a waxy substance which shields him from the vaccum (space) and extreme tempreatures (free fall) SPF 40,000 Man 

2) Black Carapace- we all know this one.

3) Ossmodula- if he makes it to Earth this implant would allow for rapid healing (well if hes in 1 piece) and grants him a tough as steel (lol bad analogy as bone is stronger than steel but oh well; on a weight to weight basis however) bone structure . 

I really hope he can land on his feet


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## jfvz (Oct 23, 2010)

@Scscofield: asteroid and comet impacts are a lot faster to begin with because they are already traveling at huge speeds in space. Through it does raise a good point that we probably need to take into account the orbital speed as well.

@TheLifeOfReilly, your right each planet has different atmosphere densities and gravitational feilds. I was just using earth's data as an example because it simplifies the calculations and it would take a lot more work to figure it out for different planets. If we use earth there are already equations that have been "simplified" by putting earth's data into it.

Also i might have had an idea to try and figure out how hot he gets as he falls, through might have 2 play around with it a bit 1st


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## dtq (Feb 19, 2009)

jfvz said:


> I had a look at the calculator but it uses a something we dont actually know, the distance it takes to stop.
> 
> The mass wont effect the falling acceleration in a perfect vacume. You said it yourself terminal velocity is acheived when the upwards force of the air resistance = downwards force of gravity, which is given by the mass of the falling object times the gravity. The formula for the terminal velocity is given here: http://en.wikipedia.org/wiki/Terminal_velocity
> 
> This formula shows that keeping everything else constant that the terminal velocity is preportional to the square root of the mass. So increasing the mass by a factor of 4 the terminal velocity will increase by the square root of 4, which is 2. But this would not work out exactally as the faster something goes the greater the friction which would lower the max velocity possible.


This still goes completely and utterly against everything Ive ever learnt about the equivalence principle, from Galileo to Einstein the principle Ive always been taught is that mass has no effect on the speed or falling time of a falling object. In a vacuum all objects fall at the same speed, in atmosphere aerodynamic drag is the only factor changing the speed. David Scotts hammer and feather drop demonstration on the moon showed that the mass of the items had no impact on acceleration or final speed gravitational acceleration was identical independant of mass.

I can certainly see that the mass has a huge impact upon the force of impact "momentum" mass x velocity but to say that mass itself affects the speed at which an object falls through the atmosphere is surely to go back to Aristotle and "Simplicio"?


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## dtq (Feb 19, 2009)

jfvz said:


> Also i might have had an idea to try and figure out how hot he gets as he falls, through might have 2 play around with it a bit 1st


The more I think about the more Im pretty much certain given the nature of the "fall" that he wouldnt experience any serious temperature increase. Im 99% certain that the heat of atmospheric entry is entirely down to aerodynamic friction which is down to the speed of entering the atmosphere. If the marine in question was falling purely under gravitys pull from the outside edge of gravitational pull Im pretty certain his speed on entering and thus his heat increase would be minor.

Im fairly certain as I think about it that the famous reentry heating is caused by the slowing of an object, friction of the item in question against the molecules of the atmosphere, turning kinetic energy into thermal energy, hence if an item has no great speed to begin with it wouldnt meet as much resistance or heat up as much. This would mean that perhaps terminator armour isnt even required in the first place substantially changing the physics involved.

If we accept the 500mph terminal veloicty you provided, Im absolutely certain that his heating would be negligible, human skydivers without any armour can achieve speeds of 600mph in atmosphere without heating up. I am almost certain that the outer atmosphere has nothing special to it to cause the heating, its just the presence of molecules to hit against that causes the heating, if anything the outer atmosphere would cause less friction than the nearer thicker atmosphere. The reason as far as I can see that a space shuttle or meteorite glows initially is that it slows down as soon as it hits any atmosphere, that process probably happens quite fast and as the item slows down to sub sonic speeds it ceases to heat up.


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## scscofield (May 23, 2011)

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

They are gonna get hot if they fall from orbit

 
*7). ** How fast are orbital debris traveling? *
In low Earth orbit (below 2,000 km), orbital debris circle the Earth at speeds of 7 to 8 km/s. However, the average impact speed of orbital debris with another space object will be approximately 10 km/s. Consequently, collisions with even a small piece of debris will involve considerable energy. ​http://orbitaldebris.jsc.nasa.gov/faqs.html


And they are going to be going fast when they do it. Reentry burnup is because of the orbit speed of a object impacting the air. If they were in a ship in orbit then fell out of said ship they would be traveling at roughly it's orbit speed before they started to fall to the surface. 

​


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## dtq (Feb 19, 2009)

scscofield said:


> http://en.wikipedia.org/wiki/Atmospheric_entry
> 
> They are gonna get hot if they fall from orbit
> 
> ...


Its a good point I hadnt thought about the exact nature of the "orbit" this would have a large impact on the marines speed as you correctly say. If for example the ship was in a retrograde orbit the marine could actually be slowed naturally before reentry. If the ship was in true orbit and the marine continued on at the same speed as the ship was going before he would remain in orbit and never fall...

This all depends on how low a orbit the ship is in. The higher the Orbit the slower the speeds required to maintain an "orbit". The moon orbits the earth at 385,000km amd requires a far slower speed to stay in orbit. I believe a gravitational orbit could be achieved close to 1.5 million km out . However the trip to the earth by gravity's pull could be a long one!

It should be noted that even regular power armour can include movement stabiliser thrusters specifically for zero and low gravity situations. Regardless of whether this marines specific suit is so equipped, those included in the backpack are as far as I know standard equipment. Its not at all impossible a marine could therefore slow his pace from the initial ship destruction to achieve a slower and more controlled reentry.


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## jfvz (Oct 23, 2010)

dtq said:


> This still goes completely and utterly against everything Ive ever learnt about the equivalence principle, from Galileo to Einstein the principle Ive always been taught is that mass has no effect on the speed or falling time of a falling object. In a vacuum all objects fall at the same speed, in atmosphere aerodynamic drag is the only factor changing the speed. David Scotts hammer and feather drop demonstration on the moon showed that the mass of the items had no impact on acceleration or final speed gravitational acceleration was identical independant of mass.
> 
> I can certainly see that the mass has a huge impact upon the force of impact "momentum" mass x velocity but to say that mass itself affects the speed at which an object falls through the atmosphere is surely to go back to Aristotle and "Simplicio"?


Terminal velocity is not the same or dependent on how fast something will initially accelerate. From the formula i referanced before it also takes into account the fluid density (basically how thick the atmosphere is) and in a vacume the terminal velocity would be infinite. Terminal velocity is the point at which the downwards force exurted on the object (remember force = mass times acceleration) equals the upwards force exurted by friction (basically this is dependent on the velocity). So an increase in mass would mean an increase in downward force hence an increase in terminal velocity.

Acceleration is a constant when dealing with gravity. a feather and a truck may fall at the same rate in a vacume but i would much rather get hit by the feather as it exurts a lot less force than the truck. Basically two objects of different mass would start acceleration at the same rate but because of friction thier velocity would "equalise" out at different speeds.

Remember the famous equation force = mass times acceleration), and by rearanging it we get: acceleration = force divided by mass. The force causing the object is the gravitational force minus the frictional force. so if the frictional force is half the gravitation force it would make the total force half of what it would be if there was no frictional force. This means that the accelerate will also be halved due to what we can see from the equation.

From the same equation if the frictional force equals the gravitational force then the total force would be 0. and hence the acceleration is 0. This is the point which terminal velocity is reached.



dtq said:


> The more I think about the more Im pretty much certain given the nature of the "fall" that he wouldnt experience any serious temperature increase. Im 99% certain that the heat of atmospheric entry is entirely down to aerodynamic friction which is down to the speed of entering the atmosphere. If the marine in question was falling purely under gravitys pull from the outside edge of gravitational pull Im pretty certain his speed on entering and thus his heat increase would be minor.
> 
> Im fairly certain as I think about it that the famous reentry heating is caused by the slowing of an object, friction of the item in question against the molecules of the atmosphere, turning kinetic energy into thermal energy, hence if an item has no great speed to begin with it wouldnt meet as much resistance or heat up as much. This would mean that perhaps terminator armour isnt even required in the first place substantially changing the physics involved.
> 
> If we accept the 500mph terminal veloicty you provided, Im absolutely certain that his heating would be negligible, human skydivers without any armour can achieve speeds of 600mph in atmosphere without heating up. I am almost certain that the outer atmosphere has nothing special to it to cause the heating, its just the presence of molecules to hit against that causes the heating, if anything the outer atmosphere would cause less friction than the nearer thicker atmosphere. The reason as far as I can see that a space shuttle or meteorite glows initially is that it slows down as soon as it hits any atmosphere, that process probably happens quite fast and as the item slows down to sub sonic speeds it ceases to heat up.


Basically what i was thinking was using the law of conservation of energy (energy cannot be created or destroyed but changed from one form to another). So the initial energy (kenetic and gravitational potentional energy) will equal the final kenetic energy (worked out from the terminal velocity) + the energy lost due to friction (this is transformed into heat energy). So i know the amount of heat energy being transfered so i can calculate the temp change in an object with known mass and a couple of other things that i can look up easily enough.

Hopefully this allows you to understand the concepts i am using a little better.

edit:


dtq said:


> It should be noted that even regular power armour can include movement stabiliser thrusters specifically for zero and low gravity situations. Regardless of whether this marines specific suit is so equipped, those included in the backpack are as far as I know standard equipment. Its not at all impossible a marine could therefore slow his pace from the initial ship destruction to achieve a slower and more controlled reentry.


The energy required to do this would be massive, why do you think they dont do that for the spaceshuttle or pods that return to earth. You have seen how much fuel it requires to get the space shuttle up (both the small rockets on the side and the big red thing are full of fuel) it would require more fuel to use rockets to slow its decent to a safe level for re-entry and touchdown than to get it up in orbit in the 1st place. It has a lot of wasted energy has heat as it goes through the atmosphere, all it would do is lesson the heat a bit, but then because of the nature of rockets it would just put much of that heat into the armour again.


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## scscofield (May 23, 2011)

Still think it would be a charred splat in a big crater  That is assuming his suit did not cook apart at the seams now that I think about it. The last shuttle we had blow apart was because of a cracked tile. Superheated plasma forced thru the crack and melted the structure away, then the forces put on the whole thing blew it apart. Now that I remember that I'm gonna say the marine would be a pretty shooting star and maybe some small particles would make it to the surface.


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## jfvz (Oct 23, 2010)

scscofield said:


> Still think it would be a charred splat in a big crater  That is assuming his suit did not cook apart at the seams now that I think about it. The last shuttle we had blow apart was because of a cracked tile. Superheated plasma forced thru the crack and melted the structure away, then the forces put on the whole thing blew it apart. Now that I remember that I'm gonna say the marine would be a pretty shooting star and maybe some small particles would make it to the surface.


haha, that i agree with. Think i had been getting to carried away with my maths. Thanks for the wake up :biggrin:


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