Airlocks are for losers

[Vestnik]

Re: Airlocks are for losers

 

Bah. Forget biology. Be a full-conversion cyborg' date=' or upload your brain and leave the meat behind completely. That'll make this whole vacuum thing much easier to deal with.[/quote']

 

I was thinking of some sort of organism that had naturally evolved for such an environment (however incredibly unlikely that would be).

[Maur]

Re: Airlocks are for losers

 

I think everyone is overestimating the cooling problem. Remember you are going to be losing H2O as well as O2 and CO2. The water outgassing from every sweat gland should provide enough cooling for the four minutes it takes anoxia to set in.

 

Perspiration requires that conduction or convection is the method used to draw heat away from the body. You can't do either in the vacuum of space, so that leaves radiation as the only way to get rid of heat mass.

[Comic]

Re: Airlocks are for losers

 

Perspiration requires that conduction or convection is the method used to draw heat away from the body. You can't do either in the vacuum of space' date=' so that leaves radiation as the only way to get rid of heat mass.[/quote']

Sublimation works in a vacuum. Evaporation, too. Simple physical disconnection, as well.

[theltemes]

Re: Airlocks are for losers

 

Sublimation works in a vacuum. Evaporation' date=' too. Simple physical disconnection, as well.[/quote']

 

Yep. That's why you'll eventually end up as freeze-dried jerky if you spend too much time in an evacuated environment.

[Cancer]

Re: Airlocks are for losers

 

I'm not sure that the cooling problem is a short-term enough problem to concern someone pushed out an air lock.

 

The power emitted by radiation, L, is

 

L = (Area) * (Stefan-Boltzmann constant) * (T^4)

 

where T is the temperture in Kelvin.

 

Choosing a 70-inch tall, 200 pound person, and the Body Surface Area formula from here, I get 1.65 square meters for area. The S-B constant is 5.67e-8 Watts/m^2/K^4, and T = 37 C = 310 K, so L is 864 Watts for that person.

 

The emissivity of the body matters there; strictly speaking that simple relation assumes an emissivity of 1. I think that's OK for a butt-nekkid solid at blackbody at 310 K, but I don't know that for certain, and certainly simple suits (like the reflective metal-foil types) would drop that power output substantially.

 

Adding more specs (male, 35 years old) to our subject person, and taking the metabolic rate formula from Wikipedia (the Mifflin-St Jeor Equation), I get a basal metabolic rate of 752 Watts for that body.

 

Looks like lots depends on what you assume for your suit, but with the heat capacity of water being about 4000 J/kg/degree, my guess is that thermal problems aren't going to kill you as fast as other things.

[Maur]

Re: Airlocks are for losers

 

Well, that assumes you are on the dark side from the sun... Go to the sunny side of space and you now have to also get rid of all that incoming heat as well.

[keithcurtis]

Re: Airlocks are for losers

 

Only if you are solid and compact. If you are hollow or spread out that doesn't apply.

 

Since those equalities can exist regardless of size, I figured them to be superfluous.

 

Keith "Simplest terms" Curtis

[Clonus]

Re: Airlocks are for losers

 

Since those equalities can exist regardless of size, I figured them to be superfluous.

 

Keith "Simplest terms" Curtis

 

Except you still have to contain enough actual air to support an intelligent organism. A hollow human sized organism would sacrifice too much function for that to be possible.

[Cancer]

Re: Airlocks are for losers

 

Well' date=' that assumes you are on the dark side from the sun... Go to the sunny side of space and you now have to also get rid of all that incoming heat as well.[/quote']

Well, that's 1360 W/m^2, and reflectivity ALWAYS applies there, in addition to the chance of being in shade; further, it can never be true that more than half your area will be exposed to the Sun. If you aren't wearing black, then call your albedo 50%, and say a projected 1/3 of your area is exposed ... and now the solar heating is on the same order as, perhaps somewhat smaller than, your thermal losses. So, that puts it as a term of the same order as the first one ... maybe it makes things a factor of two worse in terms of heat loss. I don't think that changes the conclusion. Yes, it's a problem, but it's a problem that operates slower than other problems you're likely to have.

[Vestnik]

Re: Airlocks are for losers

 

Except you still have to contain enough actual air to support an intelligent organism. A hollow human sized organism would sacrifice too much function for that to be possible.

 

I assume it would be possible for an organism to manufacture oxygen. From something.

 

I think the ultimate problem is that to maintain any sophisticated organism you're going to need "food," some source of energy and raw materials, of which there is not a lot in space.

[Zeropoint]

Re: Airlocks are for losers

 

Barring nuclear processes, you can't MAKE oxygen; you can only extract it from chemical compounds that contain it. The amount of energy required to do this depends on the compound that you're getting it from; there are even compounds that release energy as they decompose and produce oxygen, such as whatever is in "oxygen candles".

 

The reason that we, and other air-breathing organisms and mechanisms need oxygen is essentially for burning our fuel to produce energy. If you have to supply energy to break down a compound to get the oxygen, that energy has to come out of what you get by burning your fuel (metabolizing your food) using that oxygen. The usefulness of this process is going to depend very heavily on the relative chemical energy of the oxygen source compound and your metabolic byproducts, and depending on what you're eating, may not be beneficial at all.

 

An organism could also use solar power to extract oxygen, like plants do. However, if you're going to do that, why not just use the solar power directly?

[McCoy]

Re: Airlocks are for losers

 

Perspiration requires that conduction or convection is the method used to draw heat away from the body. You can't do either in the vacuum of space' date=' so that leaves radiation as the only way to get rid of heat mass.[/quote']

 

Sublimation works in a vacuum. Evaporation' date=' too. Simple physical disconnection, as well.[/quote']

What Comic said. As the water is sucked out from every pore it undergoes a state change from liquid to vapor, sucking half a calorie of heat out of the body for every gram of water you lose.

[keithcurtis]

Re: Airlocks are for losers

 

Except you still have to contain enough actual air to support an intelligent organism. A hollow human sized organism would sacrifice too much function for that to be possible.

 

Since the quote originally referred to maximizing the surface area for the purpose of photosynthesis, I had assumed we were speaking of a decidedly non-human physiology. I was merely pointing out that in contrast to the statement I originally referenced, increasing size does not automatically increase surface area relative to the organism.

 

Keith "nothing more" Curtis

[input.jack]

Re: Airlocks are for losers

 

Kudos to Cancer for his excellent answers.

 

Question: Ive heard that a huge problem with being uninsulated in space is that, while you float in the middle of nowhere your heat reguklation is as previously stated, if you come in contact with a large metallic object (like a space station youre trying to get itno), the heat transferance from your body to the object can kill you.

 

Is that true?

[Cancer]

Re: Airlocks are for losers

 

I'm not sure how. Temperature is an absolute scale, in the sense that you can tell the heat content of things by the black-body radiation they give off. Energy flow by conduction scales as temperature difference and by contact area, so the only way heat flow would kill you is if you got a good, full-body contact with something really hot or really cold. I admit you can burn yourself fatally with fairly modest temperature differences (scalding sets in fast, e.g.), though.

 

Electrical potentials are another thing. In principle you could have substantial electric charges built up on objects in space, and grabbing a nice metal hull which happens to have a big charge on it might be lethal. I'd have to look stuff up and push numbers around to decide whether that was a serious concern, but the experiences of human space efforts so far suggest it isn't. Otherwise there'd be something more made of docking with ISS, for example, and bleeding off charge and electrical potential differences early in the docking process.

[Clonus]

Re: Airlocks are for losers

 

Since the quote originally referred to maximizing the surface area for the purpose of photosynthesis' date=' [/quote']

 

And containing enough air. The photosynthesis is just to maximise how long your oxygen supply lasts.