Thermoregulation

Hey Folks! Treading water here with illness. Symptoms are kind of holding at the mild onset stage, which could be a good sign that my body's fending it off. Or, you know, I'm in for a doozy :)

I got the body temperature code hooked up today, along with some stats for the standard human, medium-weight clothes, and an EVA suit. Pretty much all copied exactly from NEO Scavenger. Upon firing it up, it worked...kind of.

Unsurprisingly, the crew froze to death quickly. Or would have, if I had created those states yet. Body temperature dropped from 310K (normal 98.6F) to sub-300 within seconds, until the air pumps had flooded the ship to at least low pressure, and raised the ambient temperature from absolute zero (0.01K) to a sub-freezing 260K. At that stage, the crew continued to lose body head, but in a more controlled fashion.

Wearing clothes seemed to do the trick, with the browncoat outfit slowing a lot of the heat loss, and the EVA suit almost completely insulating the crew. However, that's not really what should be happening.

For one thing, body heat loss in a near vacuum should be slow. You don't freeze to death in the cold of space, because there's no air to carry away your heat. You simply radiate heat at about 100W, which would cause you to freeze to death in hours, not seconds. (And even then, freezing to death is when your core temp reaches 293K or below, so we're talking maybe a handful of degrees lost per hour, not per second.)

NEO Scavenger's code works pretty well at 101.3kPa (atmospheric pressure), and at ranges of 273-315K. You know, Earth-like situations :) Space, on the other hand, ranges from 0-100kPa and 0-300K, and often hotter/higher pressure, depending on the environment.

So I started doing some thinking, to see if there might be a better way to model this. Particularly since the NS code was an arbitrarily complex equation with lots of Earth-specific data.

If you look at today's screenshot, the red curve represents NS body temp, with clothing's "safe" range around 300 on the x-axis. There's a bit not shown here with body rewarming, which happens when the body is at or above the clothing safe range.

What I'm looking for is something more like the black curve: lose body temp below the safe range, gain it above. And the further away from safe, the faster it happens. Furthermore, the air pressure modulates this such that a vacuum has minimal effect, but high pressure works quickly.

Passive rewarming still plays a role here, which I'm thinking has to do with clothing's insulation. Regardless of temperature outside, if you are wearing perfectly-insulated clothes, it'll get hot inside from your body radiating. We just happen to wear clothes that control the amount of heat lost to just keep us comfortable around 293K.

I've already setup this new black equation, but it still has a flaw: the body temp runs away if it's not perfectly balanced in the safe zone. Instead, the body should be able to adapt a bit, which is where that blue graph comes in. If I combine the blue and black graphs, I can probably get a function that tends towards the safe zone when there's a small deviation, but then runs away when outside of that safe range.

Tags: Ostranauts

Comments

ra1's picture
ra1

So do you intend to model calories eaten/used to maintain body temp?

dcfedor's picture
dcfedor

I'm not sure if I'll go that deep. Probably something a bit more in line with NS: a few states for normal, substandard, critical, etc.

Don't get me wrong, I'd love to model all sorts of things. I just know I won't be able to do it all :)

Dan Fedor - Founder, Blue Bottle Games