Click here if you are having trouble logging into the forums
Privacy Policy |
Please read our Terms
of Service | Signup and
Troubleshooting FAQ | Problems? PM a Red or a Green Gu.... uh, User
Taqyon
sage
Reged: 06/17/08
Posts: 262
Loc: Cape Town, South Africa
|
|
If I was to be dumped in space on the dark side of earth, would I really be cold? (ignoring all the other factors that has a detrimental effect on my health). There is no way for my body to lose heat through transference, so theoretically I would be nice and cozy while I explosively decompress?
Is cold really such a huge factor for mars explorers? Mars has less than 1% of eath's atmosphere and wearing a heavy jacket protects us from -10 degrees here, so I think our bodies would have plenty of time generating the heat required to stave off the tiny seepage of heat into the thin atmosphere there?
Boots are important, of course.
|
Fish
super member
Reged: 10/13/07
Posts: 160
Loc: Norridgewock, ME
|
|
Good evening,
As you stated I will ignore the other problems associated with flying through space in the buff.
The transfer of energy - heat in this case - can be done in (3) ways:
--> Conduction, direct contact between one item and another. Touching a hot stove burns you by conduction.
--> Convection, by transfer through a current in a fluid or gas. Your meatloaf cooking in the conventional oven heats up from the surrounding air.
--> Radiation. This is why the Sun feels warm on your face or a microwave reheats your leftover meatloaf.
Now then, although conduction and convection require physical contact with other matter, radiation does not. If you survived the decompression, the lack of oxygen, the humiliation . . . you would lose heat through radiation of heat energy.
Is it me or am I feeling a chill?
Regards, Marc
|
HiggsBoson
scholastic sledgehammer
Reged: 02/21/07
Posts: 804
Loc: Kal-li-fornia
|
|
Yes!
--------------------
Michael
ATM: 6" F/9 Newtonian Travel Scope
ATM: 12.5" F/4.5 Real Soon Now...
|
Pess
(Title)
Reged: 09/12/07
Posts: 1910
Loc: Toledo, Ohio
|
|
Quote:
Now then, although conduction and convection require physical contact with other matter, radiation does not. If you survived the decompression, the lack of oxygen, the humiliation . . . you would lose heat through radiation of heat energy.
Which nicely explains why a space suit must insulate from temperature extremes ranging from -100^C (in shade) to +125^C (In direct sunlight).
Pesse (I prefer the see-thru gel suits the Thermions favor.) Mist
|
Kobayashi
sage
Reged: 07/10/08
Posts: 291
|
|
Quote:
. . .you would lose heat through radiation of heat energy.
Yes, but if you're near the earth, you'd also be receiving quite a bit of heat from the earth. Even the dark (night) side of the earth is fairly warm, so it radiates a lot of energy in the infrared. An object there would get somewhat colder than the ground below (because half of the object is facing away and not receiving heat), but not by much. That's how the Space Shuttle controls its temperature, by the way - it has radiators on the inside surface of the cargo bay doors, which is usually pointed towards the earth.
But there's one other heat loss mechanism which I think is significant: evaporation. The human body is mostly water, and when it evaporates from the skin and lungs, it carries away heat. So I would guess your corpse would freeze solid fairly quickly.
--------------------
-- Ken Kobayashi
|
astrotrf
sage
Reged: 09/30/07
Posts: 287
Loc: Rodeo, NM
|
|
Assume, for simplicity, that the Earth fills half of the sky for an orbiting astronaut.
So half of your body would be exposed to the nighttime temperature of the Earth -- say 30 degrees colder than your body temperature. Your body would radiate heat toward Earth at a reasonably slow rate.
The other half of your body would be exposed to the near-absolute-zero temperature of deep space -- hundreds of degrees cooler than your body temperature. Your body would radiate heat toward deep space at a dismayingly fast rate.
Being on the daytime side of Earth isn't going to change this balance significantly.
Deep space is going to win in fairly short order.
--------------------
Terry (astrotrf)
|
Kobayashi
sage
Reged: 07/10/08
Posts: 291
|
|
On rereading my post, I may have inadvertently implied that you wouldn't freeze if it weren't for evaporative cooling. That's not going to be the case.
The point I wanted to make is, the equilibrium temperature of an object in low earth orbit is much closer to the earth's temperature than to the temperature of "deep space." That's because blackbody radiation is proportional to 4th power of temperature.
Consider an object surrounded by surfaces at 300 K in every direction: its equilibrium temperature will be 300 K. Now if you remove half the surfaces so half the sky is completely dark (0 K), it would receive half as much radiation. Its new equilibrium temperature will be the temperature at which it radiates half as much radiation, which would be (1/2)^(1/4)=0.84 times the original temperature, or 252 K. A full 48 K colder than before, admittedly, but still 252 K above "deep space."
--------------------
-- Ken Kobayashi
|
Taqyon
sage
Reged: 06/17/08
Posts: 262
Loc: Cape Town, South Africa
|
|
So you are you guy saying that I would radiate heat away faster than my body can produce it? Would that be infrared heat? Is the rate of radiation the same on earth as it is in space?
I did not realise the earth being so close by would have an effect (very interesting re. the shuttle) - lets move the schenario out into interstellar space.
--------------------
Hein du Plessis
10" Black Diamond Skywatcher Collapsible Dobsonian
Celestron NexImage Webcam
7mm SWA 58° Plössl
(censored)mW Green Laser Pointer
My Pictures
|
Kobayashi
sage
Reged: 07/10/08
Posts: 291
|
|
Post deleted by Kobayashi
--------------------
-- Ken Kobayashi
|
Kobayashi
sage
Reged: 07/10/08
Posts: 291
|
|
Quote:
So you are you guy saying that I would radiate heat away faster than my body can produce it? Would that be infrared heat?
Well, my previous post only addressed what temperature an inert object would reach. But you're right, if you're talking about a live human body, heat production by the body should be considered.
The amount of heat lost to blackbody radiation is given by Stefan-Boltzmann Law. A human body has approximately 1.5 m^2 surface area and 300K temperature, so rate of radiative heat loss is 700 W. Well, a bit less, since the human skin isn't a perfect blackbody - somewhere around 500 W probably. If half the sky is filled with the ground at 300 K (bit warm, but for simplicity), you'd be receiving 250 W from it, so the net heat loss is about 250 W. I think a healthy human being can generate enough heat to compensate, but it would feel very cold.
Although if radiative cooling were your main worry, there's an easy fix: clothing or covering that emits very little infrared. Aluminized mylar would work nicely - in fact that's what most satellites are covered with, which is why they sell that stuff as a "space blanket". (Not only does it reduce radiative cooling, it would also reduce heating from sunlight, so the day/night temperature cycle would be reduced.)
By the way, if it sounds like I've been giving inconsistent answeres, it's because the answer depends on what approximations and assumptions you use - the question is somewhat ambiguous as well. If the exact question is is "Will you freeze to death if you step out of the Shuttle airlock," the answer is "no, you'll die of asphyxiation first, and then your corpse will freeze."
Quote:
Would that be infrared heat? Is the rate of radiation the same on earth as it is in space?
Yes, it would mostly be in the infrared. And yes, the rate of radiation is the same - it only depends on the temperature and qualities of the surface. What's difference is how much heat is received. If you're in a room where all the walls are the same temperature as your body, your body receives as much heat by radiation as it emits. If you're in interstellar space, you'd receive almost none.
--------------------
-- Ken Kobayashi
Edited by Kobayashi (08/05/08 01:48 PM)
|
Qkslvr
Pooh-Bah
Reged: 06/23/06
Posts: 1052
Loc: NE Ohio, US
|
|
Quote:
If you're in a room where all the walls are the same temperature as your body, your body receives as much heat by radiation as it emits. If you're in interstellar space, you'd receive almost none.
Living in Ohio, well it gets cold here. I have noticed that a large patch of skin can tell if it's pointed at a interior or exterior wall in the winter, you can feel the difference.
--------------------
Mike
N8/CG-5/40D
Coming sometime/Maybe FrankenRebel
|
|
5 registered and 1 anonymous users are browsing this forum.
Moderator: llanitedave
Print Thread
|
Forum Permissions
You cannot start new topics
You cannot reply to topics
HTML is disabled
UBBCode is enabled
|
Thread views: 152
|
|
|
|
|
|
|
Previous
Index
Next
Threaded
Edit
Reply
Quote
[Re: 