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Comment by w1zard0f0z | Hacker News Reader

"the air inside Steve blazed about 5,500 degrees Fahrenheit (3,000 degrees Celsius)" 3000 degrees?!:o Is that temperature a typo?

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Yes, that's correct. At 300km, Steve would be situated within the thermosphere [1]

> The highly diluted gas in this layer can reach 2,500 °C (4,530 °F) during the day. Even though the temperature is so high, one would not feel warm in the thermosphere, because it is so near vacuum that there is not enough contact with the few atoms of gas to transfer much heat.

[1] https://en.wikipedia.org/wiki/Thermosphere

Edit: typo

If you were out there during the day you probably warm up a bit though right? with very little in the way of air to draw heat away.

Yes but from the sun, not from the heat in the air molecules. And if you were not shielded from the near vacuum, you’d cool down from the evaporation of sweat on your skin.

This has got me interested now.

At the equator, on the surface of Earth, solar radiation is about 1kW per square meter. According to this¹ wikipedia article 55-60% of solar energy is lost on its way through the atmosphere.

So would ~2kW / square meter at thermosphere height be enough to make you feel warm-hot despite the heat lost to evaporative cooling from sweating?

1. https://en.wikipedia.org/wiki/Space-based_solar_power

Edit: correct highest to height

Sweating would be a lot more effective in a near-vacuum, if we assume you'd wear one of those futuristic mechanical counterpressure space suite.

How come? I thought sweating worked by helping to lead the heat to the air

No, it works by using up heat to change a materials' phase, that is turning it from liquid to gaseous.

... and phase-change is exactly how your freezer works.

Either way, you'd be killed by vacuum exposure.

Indeed, unless you'd have that fancy space suit which is semipermeable.

https://en.wikipedia.org/wiki/Space_activity_suit

One might sweat a couple of liters/hr, and thus might manage 2 kW. But that's not needed. Between bright hot Sun, too hot, and dark cold deep-space sky, too cold, Earth spins, mixing too hot, and too cold, into not too bad. And so can you - the "barbeque roll" thermal management strategy for satellites. And if you're head-on to the Sun, or in shadow (holding an umbrella)... I don't recall whether radiative loss is sufficient to shed basal metabolic rate without sweating or not. If not, you might build yourself some elephant ears, and sleep with them edge-on to the Sun (and Earth). But EVA suits use water sublimation cooling - because people do EVA to strenuously exercise, even in the bright sun.

Science education content, down to kindergarten, mentions Sun heating Earth. But pervasively fails to mention deep-space sky cooling Earth. So a lot of explanatory leverage is left on the table - "Why are nights cold? Especially with clear sky? Especially in the desert? Why are mountains snow-capped? Why is winter colder?" etc. I wish I knew of a forum/community in which to discuss and create such improved content, but I've been failing to find one. :(

But how much can you irradiate to the black space?

The air in this case is what's at high temperature so it wouldn't be drawing anything away at all. You'd still lose heat through infrared radiation. I'm not sure which effect would be greater.

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