Will I Freeze or Burn in Outer Space? A Look at Heat Transfer in Space

[Sakha]

Hello. People always say that the space is 'cold', and I've always heared that on a satellite, the side facing the sun is really hot, while the dark side is very cold. What I don't understand is how can the dark side be cold if the heat it had couldn't escape in any way except radiation, which, to my understanding, is very small.
Image this scenario: I'm orbiting Earth in my new spacecraft , I grab a small oxygen tank that connects to my mask, and jump outside the craft without any special suitn just my breathing mask. Let's ignore all pressure effects and anything else not related to temperature and heat transfer. Will I feel a terrible cold outside? My first thought is that I won't feel cold at all, because as outside is vacuum, the heat from my body can't go anywhere (except the small amount that irradiates).

Thanks

 

[brainstorm]

Hello. People always say that the space is 'cold', and I've always heared that on a satellite, the side facing the sun is really hot, while the dark side is very cold. What I don't understand is how can the dark side be cold if the heat it had couldn't escape in any way except radiation, which, to my understanding, is very small.
Image this scenario: I'm orbiting Earth in my new spacecraft , I grab a small oxygen tank that connects to my mask, and jump outside the craft without any special suitn just my breathing mask. Let's ignore all pressure effects and anything else not related to temperature and heat transfer. Will I feel a terrible cold outside? My first thought is that I won't feel cold at all, because as outside is vacuum, the heat from my body can't go anywhere (except the small amount that irradiates).

Thanks

I believe that there are two factors cooling you in space, as within an atmosphere or other relatively dense medium: 1) convection/conduction and 2) radiation. I lump convection and conduction together as both being transfers of heat as kinetic energy between material substances. Since space is a relative vacuum, I think you may be right that the vacuum may actually insulate you from heat-loss, similar to the way a vacuum thermos prevents thermal transfer through the vacuum wall of the container. The heat lost by radiation in such a thermos is reflected back into you coffee or soup or whatever by the shiny chromed glass inner lining that always seems to shatter for some reason that someone else will have to explain for me (I'm sure it has something to do with pressure-differential).

Anyway, I think you're right that for thermal equilibrium to be achieved between two substances, one of the substances can't be relatively empty space. So maybe Khan was wrong in Star Trek II when he said that "revenge is a dish best served cold and it is very cold in space." Maybe he should have said that the coldness of his revenge was well-preserved in the vacuum thermos of space, but that's not as dramatic - although it may have been more apt for his "genetically superior intellect" lol.

 

[russ_watters]

Radiation is actually a lot more significant than you realize, even at the temp of the body. It isn't that hard to use the Stefan Boltzman equation - give it a try.

 

[brainstorm]

Radiation is actually a lot more significant than you realize, even at the temp of the body. It isn't that hard to use the Stefan Boltzman equation - give it a try.

Are you talking about our "auras?" How is that significant in space, though, provided your space suit is lined with some kind of reflective material?

 

[russ_watters]

Huh? Auras? Anyway, the OP asked how you'd do without a space suit and also how significant is it to the spaceship if it isn't wearing a space suit either.

Here is the equation: http://hyperphysics.phy-astr.gsu.edu/HBASE/thermo/stefan.html

Give it a shot: plug and chug!

 

[brainstorm]

Huh? Auras? Anyway, the OP asked how you'd do without a space suit and also how significant is it to the spaceship if it isn't wearing a space suit either.

After re-reading the OP, you're right. I was thinking the bit about not having a space-suit just referred to air-pressure problems.

Haven't you ever seen those pictures of people's "auras" with special cameras? I assume that these are made by using infrared photography and then superimposing the person's visible-light image over their thermal signature. I guess I should have done more research before assuming, but it just struck me as amusing that you were talking about EM radiation emissions from organic bodies and that these could be photographed and new agists would attribute metaphysical meaning to them.

edit: I just googled it and "Kirlian photography" seems to involve registering the electric or magnetic field of an object through direct contact with a metal plate or something like that. So apparently it is not thermal photography or otherwise registering EM emissions, unless these correspond with the EM fields of the body, which may well be the case, no? Sorry, this has turned into a thread-hijack; although not my intent since I really thought that "aura-photography" was just thermal photography propped up as something mystical.

 

[TheH]

Since a vacuum contains no particles, can it contain any heat? If not, then the heat lost by any object to a vacuum by radiation would be extreme right?

For example, even a 1 meter cube of ice would lose significant heat:
6 * 0.000000056703 * 1 * (273.15^4) = ~1900 watts

 

[brainstorm]

Since a vacuum contains no particles, can it contain any heat? If not, then the heat lost by any object to a vacuum by radiation would be extreme right?

For example, even a 1 meter cube of ice would lose significant heat:
6 * 0.000000056703 * 1 * (273.15^4) = ~1900 watts

So the same object at the same temperature radiates more energy in a vacuum than in pressurized surroundings?

 

[russ_watters]

Since a vacuum contains no particles, can it contain any heat? If not, then the heat lost by any object to a vacuum by radiation would be extreme right?

For example, even a 1 meter cube of ice would lose significant heat:
6 * 0.000000056703 * 1 * (273.15^4) = ~1900 watts

Yep.

Now in reality, you have to be away from/shielded from the sun and nearby planets to radiate that much, but otherwise, yeah, it really is that much.

 

[russ_watters]

So the same object at the same temperature radiates more energy in a vacuum than in pressurized surroundings?

It's not the pressure, it is the absence of other objects to radiate heat back at it.

 

[Sakha]

I will try to derive how much time it would take to an average men to radiate its thermal energy from 37°C to 0°C

Average human body surface area = 1.9m²
average human body specific heat capacity = 3470 J/Kg°C
Average human body emmisivity = .97

Q = CmT
Q = 3470*90kG*37
Q=1.16E7 J

P = A$$\epsilon$$$$\sigma$$T⁴
P = (1.05E-7)(T⁴)

Q= $$\int$$(from 0 to t) (1.05E-7)(T⁴) dt = 1.16E7 J

Q = 1.04x10^-7(t) (273^4) - 1.04x10^-7(0s) (310^4) = 1.16E7

:yuck: Here I think I fail because the time t appears to be independent of the initial temp T (310K)

I'm not quite sure if I know how to integrate something using two variables (time and temperature), that might be why I failed.
Also sorry because of my real messy Latex, its my first time using it.

 

[brainstorm]

I'm not that good with math, but would it help to calculate an amount of watts like with the ice-block example above? I checked my conversion program and watts converts to btu's/minute. So if you have the number of btu's in a human body at 37C, couldn't you just divide that by the btu's/minute rate to get the time to 0C? And, btw, what's the relevance of 0C? Doesn't water freeze and boil at different temperatures depending on air pressure, rendering 0C and 100C arbitary numbers in space?

 

[Sakha]

Watts = joules/second
I think we can't do it the simple way because the power emitted changes with a change in temperature, which changes with time (decreasing by the irradiated heat). I'm pretty sure we need some integral here

 

[hikaru1221]

Your "human body" is like a big stone
$$\epsilon \sigma AT^4dt = -mCdT$$

$$t = -\frac{mC}{\epsilon \sigma A}\int _{37+273}^{273}\frac{dT}{T^4}$$

t is around 4.3 hours!

However human body isn't like stones. We eat, and we store energy. A recommended daily energy intake value for men is about 10^7 J, which is about the same amount of heat you lose if your temperature decreases from 37C to 0C. So if you have a big meal before jumping into the space without suffering from the pressure effect, I think you hardly feel any change, especially when a 90-kg man most likely stores a substantial amount of fat.

Just my 2 cents

 

[Sakha]

Your "human body" is like a big stone
$$\epsilon \sigma AT^4dt = -mCdT$$

$$t = -\frac{mC}{\epsilon \sigma A}\int _{37+273}^{273}\frac{dT}{T^4}$$

t is around 4.3 hours!

However human body isn't like stones. We eat, and we store energy. A recommended daily energy intake value for men is about 10^7 J, which is about the same amount of heat you lose if your temperature decreases from 37C to 0C. So if you have a big meal before jumping into the space without suffering from the pressure effect, I think you hardly feel any change, especially when a 90-kg man most likely stores a substantial amount of fat.

Just my 2 cents

Thanks!
So space is not cold and I won't turn into a block of ice if i go there

 

[brainstorm]

Your "human body" is like a big stone
$$\epsilon \sigma AT^4dt = -mCdT$$

$$t = -\frac{mC}{\epsilon \sigma A}\int _{37+273}^{273}\frac{dT}{T^4}$$

t is around 4.3 hours!

However human body isn't like stones. We eat, and we store energy. A recommended daily energy intake value for men is about 10^7 J, which is about the same amount of heat you lose if your temperature decreases from 37C to 0C. So if you have a big meal before jumping into the space without suffering from the pressure effect, I think you hardly feel any change, especially when a 90-kg man most likely stores a substantial amount of fat.

Just my 2 cents

What would be really useful would be to compare the rate of heat-dissipation to some comparable terrestrial temperature situation, e.g. -40C at sea level.

edit: here is an emissivity calculator online. I can't figure out how to use it. Can it solve this problem?
http://www.pyrometer.com/cgi/pyrometer.cgi

 

[russ_watters]

However human body isn't like stones. We eat, and we store energy. A recommended daily energy intake value for men is about 10^7 J, which is about the same amount of heat you lose if your temperature decreases from 37C to 0C. So if you have a big meal before jumping into the space without suffering from the pressure effect, I think you hardly feel any change, especially when a 90-kg man most likely stores a substantial amount of fat.

Our metabolism doesn't increase substantially after we eat. Humans generate an average of about 150w, so losing 1900 means getting cold very fast.

 

[russ_watters]

Thanks!
So space is not cold and I won't turn into a block of ice if i go there

Yeah, space is cold and you would turn into a block of ice if you go there. That's the whole point of what everyone has been saying (except that one post)! It just takes a while to freeze solid, but the cold could kill you long before you freeze solid. You'd be shivering in seconds and have hypothermia in minutes.

 

[hikaru1221]

What would be really useful would be to compare the rate of heat-dissipation to some comparable terrestrial temperature situation, e.g. -40C at sea level.

Things are different in 2 cases: one in vacuum where the body only emits radiation (and self-generate heat), and the other on the Earth where there are not only radiation from the body, but also conduction, convection (wind speed is a factor), and radiation from the surrounding (and even the sunlight) that the body absorbs.

edit: here is an emissivity calculator online. I can't figure out how to use it. Can it solve this problem?
http://www.pyrometer.com/cgi/pyrometer.cgi

It calculates emissivity, not the heat loss due to radiation. And I don't think it can calculate e for human.

Our metabolism doesn't increase substantially after we eat. Humans generate an average of about 150w, so losing 1900 means getting cold very fast.

Thanks!
So if it's like what you said, i.e. human heat generation rate is about 150W, time taken for our body to decrease from 37C to 35C, at which hypothermia takes place, is about 13min.

 

[brainstorm]

Yeah, space is cold and you would turn into a block of ice if you go there. That's the whole point of what everyone has been saying (except that one post)! It just takes a while to freeze solid, but the cold could kill you long before you freeze solid. You'd be shivering in seconds and have hypothermia in minutes.

The amazing thing, though, is that you don't need any insulation in your space-suit to retain warmth; only reflective material. If there is no cold air surrounding you, the kinetic energy heat inside your suit can't conduct or convey itself outside the suit, right? You could be wearing reflective mylar or some other incredibly light fabric, as long as it could contain the pressure and resist punctures and unfiltered radiation damage, correct?

So if it's like what you said, i.e. human heat generation rate is about 150W, time taken for our body to decrease from 37C to 35C, at which hypothermia takes place, is about 13min.

So, ignoring pressure and radiation exposure, you could run outside to get the mail in your pajamas and make it back inside the spacecraft without endangering your health?

 

[hikaru1221]

So, ignoring pressure and radiation exposure, you could run outside to get the mail in your pajamas and make it back inside the spacecraft without endangering your health?

I think so. Calculations show that it takes about 6min before the body's temperature decreases to 36C, at which we human are still conscious.
However the body cools down way faster due to the pressure effect.

 

[Sakha]

However the body cools down way faster due to the pressure effect.

Can you explain me that?


http://en.wikipedia.org/wiki/Space_suit#Exposure_to_space_without_a_spacesuit"

 

[hikaru1221]

Can you explain me that?http://en.wikipedia.org/wiki/Space_suit#Exposure_to_space_without_a_spacesuit"

In vacuum, water (and some other gases, such as oxygen; but I think it's almost about water) vaporizes at an extremely fast rate. It takes a lot of heat from the body, which is the main reason for the body to cool down tremendously.
However it's not the main reason leading to death. The rapid evaporation of oxygen from the blood leads to hypoxia, and then, brain stops functioning.

 

[brainstorm]

The pressure effect renders the cooling effect meaningless, when taken into account, no? If you can get the bends and get sick and die simply from ascending too fast through the ocean, how deleterious would instant zero-pressure be in how many different ways? However, if you had reflective-material pajamas with an air-tight head-covering and a ventilation tube, I bet you could go outside to sunbathe for a while without risk of hypothermia (provided your pajamas were partially translucent with an spf factor sufficient to block all high-frequency radiation, not just UV).

 

[Sakha]

So, I put out my arm trough my spaceship window. The skin, to my understanding, is airtight, so no water vaporizes. I guess the skin stretches, but beside that, if I only leave it outside for say, 10 seconds, I think my arm would be in good shape after that.

 

[brainstorm]

So, I put out my arm trough my spaceship window. The skin, to my understanding, is airtight, so no water vaporizes. I guess the skin stretches, but beside that, if I only leave it outside for say, 10 seconds, I think my arm would be in good shape after that.

I don't know. Have you ever sucked the air out of a glass bottle and accidentally had it suck your tongue inside? On the other hand, once inside no serious amount of damage seems to result so maybe vacuum isn't as dangerous as sci fi has suggested.

The high-frequency solar radiation concerns me, though, but maybe it's only a problem with extended periods of direct exposure. You might be able to float around in space naked for a few seconds just by holding your breath. lol. I think the best way to test this hypothesis would involve having a new sequel to the Jackass movies made in space and on the moon. Those guys have earned the right to space exploration with their fearless execution of top stunts and nearly pure masochism.

 

[DaveC426913]

So, I put out my arm trough my spaceship window. The skin, to my understanding, is airtight, so no water vaporizes.

No, the skin is largely composed of water, it offgasses water vapour quite nicely.

I discovered this in an astonishing way waiting in the car on a very cold winter night. I was looking at the frost on the inside of the window, and I went to scrape it off with my finger. When my finger was still about an inch from the glass, the glass began to fog up at that point. The fog patch grew and shrunk rapidly and continually, in exactly the way the flame of a candle does.

It was very clear to me that my body is perpetually surrounded by an offgassing aura of water vapour. No wonder we have to drink a litre of water day day just to stay alive!

 

[brainstorm]

The interesting part about this discussion, imo, is wondering how it would feel to your skin to be exposed to no thermal disequilibrium due to lack of (cold) air, yet still be losing heat via radiation emissions from your body. The vacuum would basically insulate you, right? So you wouldn't feel cold like in sub-freezing air.

 

[DaveC426913]

The interesting part about this discussion, imo, is wondering how it would feel to your skin to be exposed to no thermal disequilibrium due to lack of (cold) air, yet still be losing heat via radiation emissions from your body. The vacuum would basically insulate you, right? So you wouldn't feel cold like in sub-freezing air.

Yes you would.

Think of the opposite: you can easily feel heat that is radiated upon you (say, a fireplace through glass, or sunlight through a window), even when there is no convection or conduction.

This radiative heat is always upon you at room temperature. Removing it would make it feel like it's freezing out there.

 

[brainstorm]

Yes you would.

Think of the opposite: you can easily feel heat that is radiated upon you (say, a fireplace through glass, or sunlight through a window), even when there is no convection or conduction.

This radiative heat is always upon you at room temperature. Removing it would make it feel like it's freezing out there.

I'm sure there's a measurable way to answer this. I'm just probably not capable of the math lol. Doesn't air have some kind of specific heat density, or whatever the term is that describes the rate air will draw heat out of warmer matter it comes in contact with?

So, to figure out the rate of total heat loss of an 80kg human in 0C air, you would find the sum of the heat lost to air and the heat radiated due to emissivity. Then you would ADD any heat imparted through ambient radiation. I am wondering how significant ambient radiation is, though, if it would be night-time and you were far away from any heated buildings or other objects. In fact, even if you're standing outside a heated house at night in winter, doesn't the radiation from the house get absorbed by the air long before it reaches you?

Put succinctly, doesn't cold air absorb ambient radiation and express that energy in its kinetic energy, as measured in temperature? Actually, I think I may be wrong because it is possible to use infrared camera to view the temperature of an object in winter, so there must be infrared light reaching the camera through the cold-air. But how would you measure the amount of energy received from ambient radiation?

 

[Naty1]

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

Since the temperature on the outside of the suit varies greatly between sunlight and shadow, the suit is heavily insulated...,

Exposure to space without a spacesuit
The human body can briefly survive the hard vacuum of space unprotected[2], despite contrary depictions in much popular science fiction. Human flesh expands to about twice its size in such conditions, giving the visual effect of a body builder rather than an overfilled balloon. Consciousness is retained for up to 15 seconds as the effects of oxygen starvation set in. No snap freeze effect occurs because all heat must be lost through thermal radiation or the evaporation of liquids, and the blood does not boil because it remains pressurized within the body. The greatest danger is in attempting to hold one's breath before exposure, as the subsequent explosive decompression can damage the lungs. These effects have been confirmed through various accidents (including in very high altitude conditions, outer space and training vacuum chambers).[3][4] Human skin does not need to be protected from vacuum and is gas-tight by itself. Instead it only needs to be mechanically compressed to retain its normal shape. This can be accomplished with a tight-fitting elastic body suit and a helmet for containing breathing gases, known as a Space activity suit.

 

[brainstorm]

Interesting post about bodily effects of outer-space exposure.

Consider that while your body is radiating away heat, the sunlight you would be exposed to would be more direct than even the clearest day at noon on the equator. It is hard to reconcile the idea of such intense sunlight with cold as a result of the body radiating out energy, especially considering the vacuum prevents you from transmitting heat into air molecules. I wonder how dry your skin would become and how quickly. Would you become leathery after a few seconds? I suppose mummification would be the result of too long of exposure, but I suppose the mummified corpse wouldn't last long in sunlight that hot.