Eli5: how does voyager send a message 15 billion miles with ~200watts of power and we struggle with cellphones and satellites signals right here on earth?

Question

Eli5: how does voyager send a message 15 billion miles with ~200watts of power and we struggle with cellphones and satellites signals right here on earth?

In: Engineering

Answer 1

You’re comparing things that aren’t really comparable even though they seem superficially similar. They’re just different systems that are designed to do different things.

Cell towers and cell phones talk to each other using frequencies that can quickly send and receive a lot of data but the drawback is the signal strength drops pretty quickly, and they have limited transmission power. Their antennas transmit equally in all directions which means they don’t transmit strongly in any direction. Cell signals can also be blocked by various structures and even just the terrain. Also, if there are a lot of users connecting to the same towers, that can eat up the bandwidth and slow down data traffic.

The Voyager spacecrafts are sending signals through open space. There’s basically nothing between them and Earth to absorb or block a signals – no atmosphere, no buildings, and no hills or mountains. They communicate with Earth using special high-gain antennas that direct all the signal strength in one narrow beam, and here on Earth, we have giant 70 meter dishes to send and receive signals that are specifically designed to communicate with spacecraft in deep space. In other words, we built a dedicated system called the [Deep Space Network](https://en.wikipedia.org/wiki/NASA_Deep_Space_Network) just to talk to far-away probes, so there are no competing signals.

In short, cell phones and space probes aren’t really comparable because they’re not designed to be. Cell phones are designed to send and receive a lot of data short ranges and to balance the needs of a bunch of users in the same area. They have limited transmission power and signals can be blocked by air, buildings, or land.

Space probes are sending and receiving signals through empty space with nothing in the way to block signals and with dedicated antennas designed to transmit strong signals and to receive weak signals.