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Old 12-29-2008, 08:26 AM   #1 (permalink)
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My temperature in space/orbit

I was curious about temperatures in space and looked up the question. Turns out because of background radiation it's about 3 Kelvin assuming your not next to a sun. And that's after the object has had a long time to cool off.

But my question is what would my temperature be for the first hour or so, in space? Let's say in orbit on the dark side of earth. Because wouldn't my body heat take a long time to dissipate? Since I'd be in a vacuum.

(Obviously I'd die rather quickly because of the vacuum and dangers of space but this isn't along the vein of survival)
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Old 12-29-2008, 08:59 AM   #2 (permalink)
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Heat loss would only be radiative, in the absence of fluid about you (air or water) there's no medium for conduction and in free fall there's no method for convection.

You also have to account for heat gain from solar radiation. Imagine the hottest day you've ever experienced. That is the heat of the sun fully attenuated by the atmosphere. In space, assuming you were in Earth orbit, you would potentially heat up faster than you'd col down, unless you were in shade.

So the answer to "how long would it take to get to 3K?" is "It depends".
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Old 12-29-2008, 01:01 PM   #3 (permalink)
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Right. Which is why my question specified the dark side of earth, i.e. shade
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Old 12-29-2008, 03:57 PM   #4 (permalink)
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Right. Which is why my question specified the dark side of earth, i.e. shade

But in order to stay on the dark side of the earth, you'd have to not be orbiting (else the orbit would naturally carry you around to the shiny side). In order to remain in Earth's shadow, you would have to provide constant, and very powerful, thrust against the pull of gravity. The heat from the rocket would warm you right up
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Old 12-29-2008, 05:37 PM   #5 (permalink)
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Are you wearing your tinfoil hat at the time or not? It makes a big difference.

Seriously, I'd say a lot depends on what you're wearing, your weight, how hydrated you are and a bunch of other variables like how close to an atmosphere you are, how close to expended rocket fuel you are (and how hot that is), if there's any sources of radio activity, etc.

If you're naked on the dark side of the moon and completely in shade, I'll guess that your core temperature well below 0C in an hour. If you want more specific, I suggest you look for information on liver temperature readings after death. I'm sure that there are studies that you could at least extrapolate a close enough answer.
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Old 12-29-2008, 06:50 PM   #6 (permalink)
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Space is pretty hot. One of the bigger challenges for NASA is keeping objects cool in space, particularly in Low Earth Orbit where satellites and spacecraft are continually exposed to friction and conduction off hot particles with very little radiative cooling ability.

For simple radiative cooling in 'cold' space, the equation would be of the form:

F(T)=F(0)e^(-k*t) Where T is time, F(T) is temperature as a function of Time, e is Eulers number and k is a coefficient of cooling.

Of course, all temperature measurements are in absolute, and K will vary with the emissivity of the particular body in space as well as the units chosen.
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Old 12-29-2008, 07:09 PM   #7 (permalink)
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Yall are being too literal this is hypothetical. Basically I just want to know, barring all other ill effects, if I'd freeze to death in a couple minutes naked in space (outside of the atmosphere completely).

Has there been any experiments done on living tissue exposed to space? (not just vacuum) I'm sure there must be.
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Old 12-29-2008, 07:13 PM   #8 (permalink)
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Quote:
Originally Posted by Zeraph View Post
Yall are being too literal this is hypothetical. Basically I just want to know, barring all other ill effects, if I'd freeze to death in a couple minutes naked in space (outside of the atmosphere completely).

Has there been any experiments done on living tissue exposed to space? (not just vacuum) I'm sure there must be.
I don't see what the point of that experiment would be. It's cold. You'd die.

If you somehow avoided the vacuum problem but were otherwise naked in shadow, yes, you would freeze to death, but probably in less than a couple of minutes. Remember, 35F water will kill you in 5. Naked in Northern Siberia in January will kill you in 5 as well.
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Old 12-29-2008, 07:21 PM   #9 (permalink)
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The vacuum would kill you long before the cold. And the unshielded effects of solar radiation would kill you before that.

Suffice to say, cold would be the least of your worries.
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Old 12-30-2008, 09:37 AM   #10 (permalink)
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Wow, I don't know where to start. I feel like you're all (almost all) talking down to me and not even bothering to read my posts. Yes, I know space is harsh. This is a thought experiment I was hoping we could have some fun in discussing. Instead, for whatever reason, some of you see fit to poopoo all over it.
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Old 12-30-2008, 11:35 AM   #11 (permalink)
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Given the large temperature difference between the human body and 3 K (~310 degrees) you would get pretty cold pretty fast (provided you weren't properly shielded).

I'll do the math when I have more time.
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Old 12-30-2008, 12:49 PM   #12 (permalink)
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So basically what you're asking us is "barring the idea that a tomato is red, what color is the tomato."

No, you would not freeze to death because you would pass out in about 14 seconds, and die of hypoxia long before you froze.

Assuming you could breathe, the alvioli in your lungs would burst due to the pressure differential in the vacuum.

Assuming there was no vacuum, yes, you'd freeze. Quickly. But there /is/ a vacuum and so except perhaps for some harmless frost around the mouth and nose, you wouldn't freeze for a very long time. and since you're somehow maintaining position on the shady side of the earth, you wouldn't have any heating effects either.

Your scenario asks us to remove all of the conditions in outer space, and then asks us to tell you what being in outer space is like. Your question is only answerable if we remove all the current laws of physics from consideration. At that point, since we're in some alternate constructed universe, any answer we give you is both trite and meaningless, since the artificial environment you're insisting we consider is of your own invention and has nothing whatsoever to do with reality.


We aren't poopooing all over your question, but we aren't giving you incorrect answers either.
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Old 12-30-2008, 12:59 PM   #13 (permalink)
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Okay, so assuming the person is in the middle of nowhere, naked, and that 3K is the blackbody temperature of the surrounding universe, with some simplifications one could apply the following equation:

Q = S*A*E_s(T_b^4 - T_s^4)

Where
S is the Stephan Boltzmann constant, 5.67x10^-8 W/m^2-K^4
A is the surface area of the person's naked body, 1.8m^2, roughly
E_s is the emmisivity of human skin, 0.97
T_b is the temperature of the body in K, here ~310K (I have assumed that the body temp is uniform)
T_s is the temperature of space in K, 3K

Q is about 900 Watts. The typical metabolic heat generation for a sleeping person with 1.8m^s worth of skin is 40W/m^2 is 108 W. This means that your net heat loss would be ~800 W.

Assuming the the specific heat of the human body is approximately the same as the specific heat of water, (C_p = 4187 J/kg-K), a 200 lb person (mass = 90 kg), and that we're only concerned with temperatures above 0 C, you could figure out how fast your temperature would be dropping using the following equation:

dT/dt = Q/(mass*C_p)

dT/dt is about 2 thousandths of a degree Celcius per second. So if your body was uniformly 310K, initially you'd be losing a degree every 8 minutes. It would take about 40 minutes of naked stillness to reach stage 3 hypothermia.

There are probably errors in this analysis. And even if error free, it is pretty approximate. If you were behind the earth you'd be getting some heat from the earth, so you'd take a little longer to freeze to death.
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Old 12-30-2008, 01:01 PM   #14 (permalink)
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Yes, some of you are shak...Do you not know what a thought experiment is? This has nothing to do with surviving in space! Einstein imagined riding a beam of light. Guess what? He didn't actually think he could! Nor was his thought experiment actually about saddling a photon and riding it to the rodeo.

Peace, I'm done with this thread.
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Old 12-30-2008, 01:12 PM   #15 (permalink)
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Quote:
Originally Posted by Zeraph View Post
Yes, some of you are shak...Do you not know what a thought experiment is? This has nothing to do with surviving in space! Einstein imagined riding a beam of light. Guess what? He didn't actually think he could! Nor was his thought experiment actually about saddling a photon and riding it to the rodeo.

Peace, I'm done with this thread.
Sorry you felt I wasn't suitably serious. I overlooked the "in the shade" part of your question, for the reasons stated by other posters - in LEO it's not posible to stay in the dark, as you come round the earth quickly.

That said, I think that the calculation given by filtherton is excellent.
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Overhead, the Albatross hangs motionless upon the air,
And deep beneath the rolling waves,
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The Echo of a distant time
Comes willowing across the sand;
And everthing is Green and Submarine

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Old 12-30-2008, 01:17 PM   #16 (permalink)
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Quote:
Originally Posted by Daniel_ View Post
That said, I think that the calculation given by filtherton is excellent.
Thanks.
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Old 12-31-2008, 12:29 PM   #17 (permalink)
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I like it too, filthy, but the one thing that I don't like about it is that it doesn't really calculate the impact of the cold on extremities. Fingers and toes could theoretically freeze solid before death.
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Old 12-31-2008, 02:24 PM   #18 (permalink)
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Jazz, if you want to spring for a workstation for me along with some FEA software I could tell you down to the millisecond when each finger freezes solid. Maybe.
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Old 12-31-2008, 02:39 PM   #19 (permalink)
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How about this? If some crazy cat microwaved a cow carcass up to human body temperature, and chunked that bitch out into space, how long would it take until it reached ambient space temperature? Perhaps that would relieve the difficulties posed in the original question?

props to filthy for whipping out stefan boltzman...I was looking for ye olde T^4 up in here. And if you want some FEA software, see if your school has a license for COMSOL. It would still be a bitch to make up the body when you pull out your mesh.
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Old 12-31-2008, 03:00 PM   #20 (permalink)
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I know it would be a bitch, but it would be the kind of bitch I would happily trade for a workstation.
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Old 12-31-2008, 03:13 PM   #21 (permalink)
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I hear you - I'd love to just get access to some of the parallel machines at one of the unis around the states, and pop onto it using an SSH client. In fact, I may be doing that sometime in the near future if I can convince people to let me. But anywho, the only thing I think you'd need to consider in the above equation is that the calculation of your Q is dependent on the initial temps, with a dependence of T^4. So by the time it drops in half, your driving force has dropped substantially. So your Q is going to drop like T^4, and your time is going to shoot out a bit. I think.

Back to that FEA software.

Shit, my girlfriend is home. Time to run.
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Old 12-31-2008, 03:38 PM   #22 (permalink)
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Way ahead of you, pig. By the time stage 3 hypothermia came around it would take you an extra 30 or so seconds to lose each additional degree.
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