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To Freeze or Fry in Space?

Outer space is colder than the North Pole in December! But it can also be hotter than an erupting volcano. On Earth, air helps even out the temperature. But there's no air in space. You can fry on one side while freezing on the other.

For a spacecraft, that spells big trouble!

Some instruments on the spacecraft get hot just doing their jobs and need to get rid of the excess heat. Other spacecraft parts need extra heat to work properly.

Space engineers know all about heating and cooling even tiny spacecraft. The small ones are especially hard to keep comfortable. That's because they have very little space inside for heaters and coolers. They have very little extra electric power for them either.

So how do the engineers solve this problem?

They call on their friends! Their names are Conduction, Convection, and Radiation. These are the ways heat energy moves from place to place.

Conduction

Adding heat energy to matter makes its atoms and molecules jiggle even faster. As they speed up, they bump against their neighbors, and get them jiggling faster too.

Put a cool pan on a hot stove, and soon the pan is hot. If the handle is metal, it will get hot too, as the faster-moving molecules in the metal pass their energy along.

That’s conduction: Matter “conducting” energy throughout itself, through molecules bumping into each other.

Convection

Like conduction, convection happens in matter too, but only in liquids and gases—like water and air. The atoms and molecules in liquids and gases are farther apart than in solids. Because they have more room between them, they are freer to move around. As they heat up and jiggle faster, they move much farther, carrying the heat energy with them.

The atoms and molecules themselves move in currents. For example, a candle flame (which is made of gases so hot they glow) heats the air right around it. The warmed air rises, making a current. Cooler air moves in to replace the warmed air, gets warmed up too, and rises into the current.

Radiation

Radiation moves energy without any help from matter.

We say the Sun’s energy radiates through space to reach Earth. That means it travels in waves and doesn’t need atoms and molecules to move along. Energy that travels by radiation is called electromagnetic radiation. Light is one kind of electromagnetic radiation we can see. But light is just one tiny part of all the kinds of electromagnetic radiation.

Although we can’t see it, the heat we feel on our skin when we stand in the Sun or put our hands over a hot stove is caused by infrared radiation, another type of electromagnetic radiation.

Keeping Cozy in Space

Now, how do engineers keep everything cozy and comfy aboard the spacecraft?

In the past, space engineers put heaters inside the spacecraft near things that needed to be kept warm. Near things that needed to be cooled off they put radiators that send extra heat outside into space. But heaters and radiators are heavy to launch, take up space, and use lots of electricity.

Spacecraft are getting smaller, lighter, and more power-efficient all the time. So these older heating and cooling systems aren’t so good.

These are the three miniature satellites of the Space Technology 5 mission. Designing a heat control system for these three tiny spacecraft was a challenge for thermal engineers.

The Space Technology 8 mission is testing a new miniature spacecraft heat management system, called the Thermal Loop. It uses tiny pipes to conduct heat away from one part of the spacecraft that is getting too warm and deliver it to another part that is getting too cold. It also has special radiators that open out into space to get rid of excess heat. The radiators also have a special coating that can be “tuned” using tiny amounts of electric power to let out more heat or less heat.

This is how the Space Technology 8 Thermal Loop heat management system works. The heat flows from warm instruments (Heat In) to cooler instruments (Evaporators release heat to keep cooler instruments warm). Excess heat flows out into space from the "tunable" Radiators.

The Space Technology 8 Thermal Loop will be flown on a real spacecraft to see how it works in the harsh temperature extremes of space. If all goes as expected, the Thermal Loop will be all ready to use on future missions to Mars . . . and beyond.