How engineers protect satellites from extreme temperatures

HostMost of us know that if you leave a phone out on a garden table in the middle of summer, it'll stop working pretty fast. But we're sending machines worth millions of dollars into a place where the sun hits twice as hard and there's no shade to hide under. How do you stop a satellite from just melting the moment it leaves our world?

GuestIt's a massive puzzle because space doesn't behave the way we expect it to. Down here on earth, if you get too hot, you can stand in front of a fan. The fan moves air over your skin, and that air carries the heat away. But in the deep void of space, there's no air. There's nothing to carry the heat off. You're basically stuck in the biggest thermos ever made. If the sun is beating down on one side of the craft, that heat just stays there and builds up. It has nowhere to go. So, the first thing we have to do is find a way to stop that heat from getting inside the box in the first place.

HostSo that's why they all look like they have been wrapped in shiny gold gift wrap. I always thought that was just a thick blanket to keep them warm because space is so cold.

GuestWell, it's a blanket, but it works the opposite way from the one on your bed. Your blanket at home is meant to trap your body heat so you stay cozy. The gold stuff on a satellite, which is really just many layers of very thin plastic coated in metal, is there to act like a mirror. Its job is to bounce the sun's stinging heat back into the void before it can ever touch the actual body of the craft. We call it multi-layer padding. If you looked at it up close, it's like twenty sheets of kitchen foil stacked together, but with tiny gaps between them. Those gaps are key. Since heat struggles to jump across empty space, having all those layers means the sun's energy gets stuck on the outside and eventually just bounces away.

HostBut surely they have some kind of internal cooling system for the parts inside that are working hard. Why not just put a small fan in there to blow the heat around and keep the computers from getting scorched?

GuestA fan would be a total waste of weight. Think about it. A fan only works because it pushes air molecules. In a vacuum, the blades would just be spinning in nothing. There's no air to move, so no heat would go anywhere. In fact, the motor of the fan would make the satellite even hotter. Instead, we have to move heat through solid paths. We use things called heat pipes. Imagine a long straw filled with a little bit of fluid. One end of the straw touches the hot computer parts, and the other end goes out to the skin of the satellite. The fluid hits the hot end, turns into steam, and rushes to the cold end. There, it turns back into a liquid and flows back to start over. It's a way to move heat from the inside to the outside without needing any moving parts or air at all.

HostI keep focusing on the heat, but everyone says space is freezing. I would think the cold would be the bigger threat to the gear inside.

GuestIt's a common thought, but for most satellites, staying cool is actually a much bigger headache than staying warm. The electronics inside the craft make their own heat just by being turned on. It's like a laptop that never gets a break. If we didn't find a way to spit that heat out, the whole thing would cook itself from the inside. That said, the cold is still dangerous because of the swings. A satellite can go from boiling hot in the sun to hundreds of degrees below zero the second it slips into the shadow of the earth.

HostThat sounds like it would make the metal parts very brittle. Does that constant change back and forth cause things to snap?

GuestIt can. Most materials grow when they get hot and shrink when they get cold. If one side of your satellite is growing while the other side is shrinking, the whole frame starts to twist and pull. To stop that, we use special materials that barely change size at all when they get hot. We also use these things called radiators, which are big white panels that always face away from the sun. They act like a release valve, constantly bleeding off that extra heat into the dark. We even have little shutters on them, almost like the blinds on a window.

HostWait, so the satellite actually opens and closes its own windows to stay at the right temperature?

GuestPretty much. These shutters use metal strips that bend when they get hot and straighten out when they get cold. When the satellite gets too warm, the strips bend and open the slats to let heat escape into the dark. When it gets too cold, they snap shut to hold onto whatever heat the computers are making. It's all done with physics, so we don't have to worry about a computer program crashing and letting the craft freeze or fry. We even use little heaters that look like stickers to keep the most sensitive parts from getting too chilled during those long stays in the shadow of the earth.

HostThe metal strips that bend on their own are the same thing that tells an old toaster when to pop up the bread.

GuestIt's exactly that kind of simple logic that keeps a billion dollar machine alive for twenty years in the harshest place we have ever gone.

HostThe next time I shut the blinds to keep the afternoon sun out of the living room, I'll think about those satellites doing the same thing above our heads.