Temperature/heat transfer in space

[poont2]

Hello PF,

I was wondering how cold would it be for a human to be in space without any suit or insultation. Assume that human have a oxygen tank, so don't worry about suffocation. What are the main factor? Since there are close to no matter in space, we can ignore convection and conduction. We radiate into space, but at the same time the sun is radiating at us. So how cold would it be if we are naked in space comparing to like the coldest place on Earth and why?

Thank you

 

[Drakkith]

From wikipedia on Space Suit:
The human body can briefly survive the hard vacuum of space unprotected, 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). 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.

 

[poont2]

From wikipedia on Space Suit:
Human flesh expands to about twice its size in such conditions, giving the visual effect of a body builder rather than an overfilled balloon . . .This can be accomplished with a tight-fitting elastic body suit and a helmet for containing breathing gases, known as a Space activity suit.

thx for the reply ,

Twice in size, that's very interesting. I thought we would die really quickly if we expand twice in size in such quick time.

For the SpaceSuit, does it mean that the suit has to be very strong to keep the original shape in close to vacuum space ? And since the suit is kept in original shape , it keep the pressure inside so the human doesn't expand?

Im still interesting in the heat transfer side

 

[Drakkith]

thx for the reply ,

Twice in size, that's very interesting. I thought we would die really quickly if we expand twice in size in such quick time.

For the SpaceSuit, does it mean that the suit has to be very strong to keep the original shape in close to vacuum space ? And since the suit is kept in original shape , it keep the pressure inside so the human doesn't expand?

Im still interesting in the heat transfer side

It needs to be fairly strong, but I wouldn't say very strong. Probably somwhere around half of atmospheric pressure or so. But that's just a guess. Yea, the space suit applies pressure on the body to keep it from bloating.

 

[poont2]

So what about the heat transfer side of the question? ignore all other effect,assuming that the main souce of heat transfer are radiation from sun to body and radiation from body to surround, using the equation of radiation.

using this equation

,

from sun to body
A, Area is limited to the body frontal area and t
T, the temp of the sun is around 5800k,
Tc, body temp

from the body to surround
A, Wouldnt the Area of the surround be infinite?
T, temp of body
Tc, what is the temperature of the surrounding? close to 0 k?

this is the part I am not understanding, i know that there are other start and planet too, but i would the main souce of radiation from the sun? and Wouldnt the Area of the surround be infinite? and what is the temperature of the surrounding? close to 0 k? wouldn't this make the radiation power infinite? what am i missing here?

 

[Drakkith]

You would still use the area of the body. The radiation emitted depends on the surface area of the emitting body.

 

[poont2]

my mistake, so even if i use the surface area of the emitting body. And only a very small percentage of heat from the sun get to the human body because sphere radiate in every direction. Can human body radiate into empty space, or one can only radiate into another matter? if so So how could one explain how cold would it be in space for a human being without any insulation? So exactly around how cold is it?

 

[Drakkith]

You have 2 different effects here. Absorbtion, and emission. Both depend on the surface area. But absorbtion also has to include the incoming intensity of the light. The human body would emit radiation into space and lose heat, but not really that much. I'm not sure what you would feel other than the swelling of your skin lol. I would expect that being in sunlight would cause an increase in temp.

 

[poont2]

interesting answer here =)

http://www.thenakedscientists.com/forum/index.php?topic=28662.0;prev_next=prev"

http://imagine.gsfc.nasa.gov/docs/ask_astro/answers/970603.html"

 

[emkay4597]

So what about the heat transfer side of the question? ignore all other effect,assuming that the main souce of heat transfer are radiation from sun to body and radiation from body to surround, using the equation of radiation.

using this equation

,

from sun to body
A, Area is limited to the body frontal area and t
T, the temp of the sun is around 5800k,
Tc, body temp

from the body to surround
A, Wouldnt the Area of the surround be infinite?
T, temp of body
Tc, what is the temperature of the surrounding? close to 0 k?

this is the part I am not understanding, i know that there are other start and planet too, but i would the main souce of radiation from the sun? and Wouldnt the Area of the surround be infinite? and what is the temperature of the surrounding? close to 0 k? wouldn't this make the radiation power infinite? what am i missing here?

4k i think
edit - er... 3 i mean

 

[Uglybb]

I would suggest the official NASA view (http://imagine.gsfc.nasa.gov/docs/ask_astro/answers/970603.html) is probably correct given the two references they cite are actual experiments on chimpanzees not a best guess scenario.

You could look up the refereneces.

References:

The Effect on the Chimpanzee of Rapid Decompression to a Near Vacuum, Alfred G. Koestler ed., NASA CR-329 (Nov. 1965)

Experimental Animal Decompression to a Near Vacuum Environment, R.W. Bancroft, J.E. Dunn, eds, Report SAM-TR-65-48 (June 1965), USAF School of Aerospace Medicine, Brooks AFB, Texas.