Remember when we saw those really cool images of Pluto? How did the satellites send those to us all the way from space?

The first spy satellites had actual film cameras onboard, with canisters equipped with parachutes to get the photos back to the ground, but as we advanced, satellites began using digital cameras, on-board computers and radio waves to send data long distances.

Today, the MSL Curiosity rover is on Mars, Juno is almost to Jupiter and Cassini is visiting Saturn… All of these missions are constantly sending data to scientists back on Earth, but how? It’s all thanks to the Deep Space Network.

It became clear really early on in the space program, that scientists needed a way to constantly be able to communicate with their satellites. Unfortunately for them, the Earth rotates, and as it does, satellites appear and disappear. So, 50 years ago, NASA’s JPL began the Deep Space Network.

Three sites were selected to receive data from space, one in California, one in Spain and another in Australia — 120° apart so together they could see the whole sky 24 hours a day. On each site, an array of massive satellite dishes ranging from 24 to 70 meters in diameter were constructed.

This is the most powerful and sensitive communication system in the world. The 70-meter antenna is able to hear quote “a whisper from a billion kilometers” away. Now, because of launch weight restrictions and power limits, broadcast equipment on spacecrafts has to be light, so engineers are forced to use relatively low-powered transmitters — like, 0 watts (that’s way less than the average incandescent light bulb). And it gets weaker as it travels through space.

By the time the signal reaches the dish, it can be “20-billion times less than the power needed to power a digital watch.” When a signal wave hits the dish, it’s reflected to a highly sensitive receiver at the center — and put through a crazy powerful amplifier. The amplifiers are cooled to near absolute zero, to minimize electrical interference from the equipment itself.

So, because of their position on the globe, no matter where the satellites are, at least one DSN dish will be able to hear the broadcast. Signals from near-Earth missions are strong, and can be picked up relatively easily. For deep-space missions, it’s a bit harder.

To strengthen the signal, probes in space use both low and high-gain antennas. Low-gain antennas are like ones used at local radio stations — they spread their power in every direction at once. The tiny microwaves of a high-gain antenna are focused, like a laser, so the signal strength is stronger when it reaches Earth.

If the spacecraft points it’s high-gain antenna at Earth, the DSN can pick it up. The Earth-based antennas also have to move here on the ground. High-gain antennas are extremely directional, because you don’t want to lose at data stream! So, the ability to point directly at what we’re trying to communicate with is super important.

But even if the spacecraft is not pointed at Earth, the DSN can still “see” the low gain signal. According to NASA, this is what makes low-gain antennas useful for things like emergencies.

This Earth-sized marvel of engineering is not only practical for space exploration, but necessary! Without each of these three sites, there would be a time when spacecraft would be on their own, in the dark, in the vastness of space. The Deep Space Network lets them phone home whenever they need to. And you can see this communication happening right now!