Another way of thinking about it is that the spcecraft is in a giant thermos with walls miles thick. Hot things stay hot, cold things stay cold.
But the fact space has no temperature is key to the explanation for why you get very hot when lit by the sun, and very cold when in shadow,
But that’s not true. If it were, Apollo 13 wouldn’t have cooled off, it would have gotten continually warmer, due to the internal heat source of the astronauts’ body heat.
The capsule was actually shedding heat in the form of infrared radiation, and cooled off. It very much didn’t stay hot.
This is an issue even on Earth. A lot of large buildings, even in northern climates, have to run air conditioning year-round (just less in the winter than in the summer) in order to get rid of all of the waste heat produced by humans, lights, computers, etc.
Well…true but it is the rate of cooling.
It is an energy in/energy out equation. There was little heat being generated inside the capsule (mostly body heat). The engineers assumed there would be other heat sources but those failed in the accident. The capsule was losing heat faster than it was replaced and cooling off. That it took as long as it did is a testament to the engineering of the capsule.
Basically a thermos. A thermos will not keep your stuff hot/cold forever. But heat transfer is slow.
Eventually though, all things will come to thermal equilibrium if no one does an anything to stop that.
That’s really interesting. I did not know that.
Amazon has tried to find a way to utilize waste heat rather than just getting rid of it.
They’re not unique in this (a number of consultants help organizations do this sort of thing) but I thought that particular article was interesting, as it was one company working with an adjacent one.
Well, yes, but saying
doesn’t actually help explain why the Apollo 13 spacecraft had an issue with the astronauts getting cold, while the astronauts on the Moon in other missions had a problem with getting too hot. Again, the Apollo 13 craft didn’t stay at the same temperature. That’s the whole point of this thread.
The thermal balance of the interior of the Apollo spacecraft was designed with the heat generation of the on-board systems in mind. The interior would always leak heat out into space (radiantly), and there would always be some heat leaking into the interior from outside radiant sources (mostly sunlight), and the insulation design was primarily responsible for the interior temperature that resulted from this balance of thermal inflow and outflow. Most of the interior heat was intended to come from the on-board systems.
With the on-board systems turned off, most of the heat energy from the interior was no longer available and the thermal exchange the spacecraft was designed for was no longer appropriate to maintain comfortable conditions. The interior temperature dropped until it stabilized because the heat loss rate through the insulation is a function of the temperature difference between the interior and exterior. At around 40 Fahrenheit internal temperature, the heat exchange balanced again with mostly just the body heat of the crew as the internal heat source.
Plus tasty, tasty neutronium. And Cynthia!
A few thoughts and clarifications or what has gone before.
Space is about 3K, courtesy of the CMB. Not that anything gets anything like that low anywhere near a star. But in principle, if you face an empty bit of sky, unless you are actually colder than 3K, you will be radiating heat out. If the sky isn’t empty, and there is a golly nice sun there, there is a lot of energy to be adsorbed. The CMB is everywhere.
The Apollo spacecraft were designed to get rid of excess heat. Both the CM and LM generated a lot of heat when powered up. All that power that was being generated by the fuel cells in the CM (plus all the losses due to less than 100% efficiency) was being dumped as heat into the spacecraft. Once powered down the CM was placed in a mode it was never designed to operate in. The LM was powered up as much as they could afford (it was run by batteries with a clear limit on energy available), and it was actually actively cooling itself the entire time. LM cooling used sublimation of water to cool glycol circuits that cooled the equipment. This actually uses up water, and as the mission progressed, and the LM was being pushed to operate longer than designed, water for the cooling system could have become a problem. The same cooling mechanism was also used in miniature in the spacesuit backpacks - the PLSS. The Apollo 13 astronauts restricted their drinking to reserve water for the LM cooling system - possibly to bad effect on themselves. A lot of the LM’s systems were not inside the pressurised part of the LM, but in a rack of equipment on the back of the ascent stage. These lived in vacuum, and relied on the circulating coolant to keep cool. They would not heat the interior of the LM. The CM OTOH placed most of the electronics and systems (and it had a lot more) inside.The CM used a set of radiators on the side of the service module to reject heat into space. This system would have been inoperative when the spacecraft was shut down.
Whilst walking on the lunar surface the astronauts would have almost always been in sun. Other than the shadow of the LM there would have been little shade anywhere. Operating on the surface was pretty strenuous. The need too cool space suits became pretty clear very early in the space programme. There is little to no useful way of ejecting heat from a suit other than active cooling and it will heat up quickly if not cooled.
Radiation and adsorption of energy is governed by the emissivity of a material. Emissivity is symmetric. A good radiator is a good absorber, and poor radiator is a poor absorber.
Emissivity depends on a number of things, including wavelength, which makes things tricky, a material may adsorb well at one wavelength and be poor at radiating energy at a different one (which is why chrome door handles get scorchingly hot in the sun). In general black bodies have high emissivity and white and reflective materials have low. The LM was almost totally covered in a layer of protective sheets and foils. All of this was there for a mix of micro-meteorite protection and thermal control. The gold and silver wrap was for thermal control, and the origami like outer shape of the ascent stage of the LM was the outer thermal and meteoroid shield. One notes that this covering had three different colours to effect local control of temperature, with some parts painted black. The actual pressure vessel the astronauts were in was some distance in from this outer layer.
Another factor, though I’m sure a minor one: en route, the craft was almost 100% (spherically) exposed to the 3K background. Upon landing, one hemisphere was occupied by the moon, adding reflected sunlight and thermal radiation from the surface to their heat load.
The 3K background is almost completely irrelevant, when you’re in close proximity to a star. And “close proximity”, in this context, includes nearly everywhere.