Heat in space

[Lance Kennedy]

I was recently reading a scifi novel involving a version of space opera. Author and title will not be mentioned.
Because I am something of a science geek, I have this habit of observing science fallacies in such stories. The author in this case spoke several times of the deep cold of space, and the difficulty of keeping space vessels and space stations from chilling. I wonder anyone has told him that the problem is actually the reverse.

A ship or station in space is sitting in vacuum. There is a very real problem LOSING heat. Any active vehicle containing humans and the equipment humans need will be generating heat. That heat will build up inside the station. Two of the normal three methods of dumping heat, conduction and convection, cannot work in vacuum. That means that to cool the vehicle can be done only via radiation, which is a less efficient method. Instead of chilling, the real problem is over heating.

The international space station has a system of air conditioning, using ammonia as a refrigerant, for a massive heat pump set up. The ammonia evaporates inside tubes to cool both the living quarters, and the solar cells. The ammonia gas is then compressed again inside a radiator sticking out into space. The radiator gets hot, and radiates that heat out into space.

Any realistic science fiction story involving people operating in space needs to recognise that the problem is over heating , not chilling, and that some kind of heat pump/radiator mechanism will be required.

 

[Expendable]

Well, yes and no. The ISS has two sources of heat - waste heat generated by both people and equipment, and heat it receives from the Sun, a rosy 250°F (121°C). Those parts of the station that are in shadow or when the station is crossing into the twilight zone are a chilling -250°F (-157°C). To keep the temperatures in balance, there is a thick layer of special insulation and the ammonia cooling system.

After the explosion on the Apollo 13 mission, much of the onboard equipment was shut down to preserve power, meaning less heat in the cabin. While it didn't get down to freezing as the movie suggests, they were uncomfortably cold.

The farther out you are from the Sun, the less radiant heat you're receiving from it. And while radiating your heat in the form of infrared radiation is slow, objects in space can eventually drop down to within a few degrees of absolute zero, thanks to background radiation keeping things just a little active. So yes, while vacuum itself is not cold (temperature is a product of matter), objects can be.

 

[Windshadow]

I always wondered why they chose the nasty and dangerous ammonia for a coolant rather that something basically inert like Halon or freon

 

[psikeyhackr]

That is one of the funny things about Star Trek. I think there are at least two episodes where they lost "life support" and behaved as though the ship would be getting unacceptably cold in a matter of hours.

How do thrermos "vacuum" bottles work? Duh!

psik

 

[Lance Kennedy]

Expendable

What you say is correct, but any space ship or space station that is in active use will be generating heat at a level that exceeds passive heat loss.

 

[Expendable]

Really it depends on how they're built.

Interplanetary and interstellar probes rely on radioisotope thermoelectric generators not just to power the equipment but to keep the electronics in a suitable temperature range, despite the insulation they're packed with.

 

[Lance Kennedy]

Loss of heat by radiation depends on both surface area and the colour of the surface. A small probe has a high surface area to volume ratio, and loses more heat. A large space station has the reverse. Not a problem with appropriate design. Like the ISS, any human carrying vessel or station will have some kind of air conditioning system to dump heat into high surface area and black colored radiators.

 

[Prairie_Dog]

I recently read an extensive analyses on radiators and their role in spacecraft design at the Tough SF Blog. It might be of interest to this discussion:

http://toughsf.blogspot.com/2017/07/all-radiators.html?m=0

 

[Lance Kennedy]

Good reference, PD. Thank you.

 

[jason10mm]

Atomic Rockets also discusses this issue extensively, including numerous types of radiators, many of which are quite unconventional and could, theoretically, be working "behind the scenes" to cool many types of soft science space ships (ok, we all know they simply ignore waste heat, but still.... without the need for large radiator arrays.

 

[phil_geo]

I work at an aerospace company, and our interns put together a little payload to include on a high altitude balloon last month. It took a bunch of sensor data as it rose from ground altitude to 100000 feet, and then back down again. The air pressure worked just like you might think - it went from roughly 1 ATMO to essentially zero, and then back up to 1 ATMO on the descent.

But the temperature was really interesting. It went down as the balloon rose, and then as the balloon rose even higher and the atmosphere disappeared, the temp rose up to normal again. The small amount of electronics and a little resistive load were plenty to heat the little payload once all the air was gone. Then as the payload descended, the temp fell, and then rose to normal, forming a "W" type plot like Wonder Woman's symbol. It was a really great way to demonstrate exactly what you guys are talking about.