Remember when someone reimagined David Bowie’s “Space Oddity” as “Space Weird Thing,” using only the 1,000 most common words in the English language? xkcd’s Randall Munroe has done the same thing, except this time he’s talking about getting to space in the first place, with a ton of help from Minute Physics. That makes sense, considering that he’s promoting his new book, Thing Explainer: Complicated Stuff in Simple Words. Even better is that the video is ridiculously charming, with explanations about spaceships up-goers like “Actually, it pushes the up-goer away from where the fire comes out. If the fire end points toward space, you are having a bad problem and will not go to space today.”
If you’re good, and lucky, and all the important people say OK, then maybe you can go to space one day. In the meantime, you can watch this video:
Space Weird Thing was a homage to XKCD’s Up Goer Five, which was so much fun it triggered him to write the book.
But cool video all the same.
Agghh… Space is not cold! It’s neither hot nor cold, because it’s a vacuum. Vacuum is an insulator, because there’s no material there to conduct or convect heat to or from an object. Spaceships and spacesuits need cooling systems to avoid overheating when they’re in direct sunlight, which they usually are when they’re in Earth orbit or en route to the Moon, say. The reason the Space Shuttle orbited with its doors open is because its heat radiators were inside them, and that was the only way it could avoid overheating. “Space is cold” is one of the biggest myths about space — particularly the idea that it’s some kind of instant-freeze effect, as a lot of fiction assumes. It only gets cold if you’re in the dark long enough to radiate your heat away. And that’s assuming you’re able to radiate heat away faster than the people and machines inside your ship can generate it — otherwise you’ll overheat. Because if your ship is surrounded by vacuum, you’re basically in a thermos bottle.
@2
It entirely depends if you’re in the sun or the shade. In LEO orbit around the earth, in the sun, the equilibrium temperature of an object is anything from -46 to 266 C depending on the paint used, while in the shade it is consistently around -90 C
See Appendix A in the Countermeasures report here for a full breakdown of the maths as to why.
It’s not instant freeze conditions on either side though. But I think if you’re using the ten hundred most common words … “space is cold” is a pretty good summary. It definitely gets a lot colder quickly as you go out further.
As for the space shuttle … it is primarily built as a really good insulator to protect from re-entry heat.
Entering/Leaving orbit and travelling through space are really different temperature requirements.
@2: Yes, exactly my point. Space is only “cold” (i.e. heat loss is only likely to exceed heat gain) in the shadow of a planet or moon or at a great distance from the Sun, and space is “hot” (i.e. heat gain exceeds heat loss unless you have good heat radiators) if you’re close to the Sun and in direct sunlight, which would usually be the case in Earth orbital or cislunar space. In reality, space is neither hot nor cold, because only substances have a temperature, and space is a vacuum. (Granted, it’s an impure vacuum, but the material in it is too diffuse to be relevant here.) It’s only the objects in space that become hot or cold depending on their circumstances.
And the common myth in fiction is that being exposed to space freezes you instantly, even faster than you’d freeze in Antarctic waters. That makes no sense. You get cold rapidly in the water because there’s a lot of material touching your body and conducting and convecting heat away. In space, you only lose heat by radiation, the least efficient of the three processes. So yes, you would cool down in vacuum eventually, but you’d cool down more slowly than you would in air or water, not nigh-instantaneously as in the myth. If vacuum caused you to freeze instantly, then it would be impossible to keep hot coffee in a thermos.
Yeah, the Expanse series got that rather right in that one character spends some time outside without a suit, and basically gets severe burns on the exposed skin, but she kept her eyes screwed shut so they wouldn’t rupture from the tears and fluid vaporising in the loss of pressure. Skin itself is a fairly strong and a good insulator for a while at least, and it takes a good 10min or so for a person to be completely oxygen starved. They usually aren’t doing much for the last 5 min though. Sudden pressure gains or losses are bad however, we don’t cope well with that.
But anything not in direct sunlight is cold … because unless it has an internal heater, it will cool to the ambient environmental temperature, which is around -100C at 1AU. -100C is considered cold in pretty much any scale from the point of view of humans, who are the ones doing the measurements. Sure, a pure vacuum won’t have a temperature per se as it won’t have anything in it, but Space is an impure vacuum, so we can measure the temperature of the particles in it, the same as we measure the temperature of the Air particles on earth. And we measure air temperature in shaded boxes to prevent the sun from interfering.
@5/Mayhem: I already said that anything not in direct sunlight is “cold,” but I also pointed out that a spaceship operating in the inner Solar System is very, very rarely going to be out of direct sunlight. For instance, in my novel Only Superhuman, terrorists endangered a space habitat in geosynchronous orbit by damaging its heat radiators. At that altitude, it only spent 70 minutes per day in the Earth’s shadow and the other 22 hours and 50 minutes in sunlight. So it needed to get rid of excess heat rather than generating heat to fight the cold. It would never be in shadow long enough to get cold. Even in low Earth orbit, you’d spend more time in sunlight than shadow.
And again, the common misconception is that you’d cool down faster in vacuum than in air, which is getting it backward. Yes, if you were out of direct sunlight in space, you’d eventually get much, much colder than you ever would on Earth. But the key word is “eventually.” It would take longer than it would in air or water.
Anyway, the point is that saying “space is cold,” as if that were the entire story, is a false generalization. It’s no more correct than saying “Earth is cold.” It depends on where and when you’re talking about.
I feel that as the video is only working with the “ten hundred” most common words, that not fully explaining the thermodynamics of a body in a vacuum is understandable.
@7: But they could’ve left out the “space is cold so you need a heater” part altogether. Simplicity is no excuse for perpetuating a falsehood. They could’ve just as easily said “The Sun is hot and there’s not much shade, so you need a way to stay cool,” or something like that.
@8 You have read too many pop culture science books, and not enough real science books. Not only does space (or vacuum in general) *feel* cold to a person, it actually *is* cold. Temperature is not defined by the radiative heat passing through a substance, as you’re suggesting, but as the radiation emitted by that substance (and “space” does emit radiation). Think about it this way: your computer monitor glass is not at several thousand degrees, despite having white light pass through it. The electrons in the LED providing that light *are* technically at that high temperature. That a non-volatile object in space is heated by the sun has nothing to do with the temperature of space. Space is in fact, very, very cold.
@9: For your information, I’m a professional science fiction author with a bachelor’s degree in physics. Don’t make assumptions. And there’s no need to make this personal.
Sure, you can point out certain factoids to justify the phrase “space is cold,” but the video is not talking about how vacuum would feel. It specifically said that spacecraft need heaters, and that is the part that’s wrong. The fact is that, at least when operating in near-Earth space, spacecraft and spacesuits usually need cooling systems.
http://www.space.com/21987-how-nasa-spacesuits-work-infographic.html
http://spaceflight.nasa.gov/shuttle/reference/shutref/orbiter/eclss/atcs.html
http://www.projectrho.com/public_html/rocket/basicdesign.php#radiators
After all, it’s not just about how vacuum “feels.” It’s about heat generation versus heat loss. The people, machines, and engines inside a spacecraft are all going to generate heat of their own, without any extra heaters being necessary. On Earth, that heat will be conducted or convected away by the atmosphere or the ground or the water, so you need to replenish it. In vacuum, though, regardless of how cold it may technically be outside, the rate of heat transfer from the spacecraft is going to be considerably lower than it is when you’re in contact with the ground and the atmosphere. You’re not in contact with any heat sinks, so you need to have your own, in the form of coolant systems and radiator panels.
Now, of course, if you land on a moon or a planet or an asteroid, then you’re going to need a heat source, because the mass of that big solid body is going to serve as a heat sink and you’ll lose heat much faster. Plus, of course, if it rotates, you’re going to spend a fair amount of time out of direct sunlight and will cool off faster still. But the image shown in the video at the point in question was of an Apollo-like space capsule that had just blasted off from the Earth. Now, granted, the Apollo capsules did have heaters, but they only needed them when they lost power, because otherwise the fuel cells themselves generated enough waste heat on their own.
Again, my point is not to say that space never feels cold, because obviously there are circumstances where it can be quite frigid. I’m just refuting the myth that it’s invariably some horribly freezing place, and in particular the inaccurate statement that spacecraft need only heaters rather than cooling systems. A spacecraft can need either one depending on the circumstances.
@CLB
But if you put an insulated object into sunlight, it will get hot on the sun side, and stay cold on the shady side. Which is where the radiators live on a spaceship for obvious reasons. The ambient environment on the shaded side of a craft in orbit is nominally “cold”.
I think the difference is you are basing your assumptions around fancy boxes containing a half dozen ambulatory 100W heaters hanging around Earth, while I’m generally thinking in terms of automated boxes going wandering through the solar system which usually need warming.
At the end of the day, I’ll wait until my copy of Thing Explainer arrives to see if he includes radiators in the designs.
“Near Earth the Sun is hot and there’s not much shade, so you need a way to stay cool” is a pretty good phrase though.
@@@@@9. boquaz
@@@@@ChristopherLBennett is correct. This case is not so much about temperature than it is about heat generation and how to deal with it. And the common misconception that stuff freezes nigh instantaneously in space is something that drives me nuts too. I like that at least they acknowledged that inaccuracy in the commentary for Sunshine.