How do they send data back from far outer space?

1.14K views
0

my wifi can’t even reach my bedroom

In: Technology

Your wifi router has a small antenna, probably no more than 10cm long. Your phone’s wifi antenna is even smaller. There’s also a lot of interference from hundreds of other devices that are also using wifi.

Meanwhile, deep space probes are listened to by huge antennas, several meters wide, and they operate on frequencies that have little interference.

Your home wifi is limited by regulation to a very narrow band and very low power so that it does not interfere with other wifi transmitters in the area. You do not have to see further then to cell phones before you get much better range because cell phone operators will work together so neighboring towers and phones do not interfere with each. But in addition to being able to transmit on what frequency band they want at what power they want they also install huge antennas. While your wifi access point have a tiny 6 cm long whip the deep space network uses up to 70 meter wide parabolic antennas. This not only allows them to collect a lot of energy from the signal but also allows them to point it in a single direction. The space probes are similarly using parabolic antennas although smaller in size so that they can concentrate all the signal energy to a narrow beam back to Earth. Another difference is that the bandwidth for deep space communication is much lower then your wifi bandwidth. This is because they transmit each bit for longer times giving the receiver a better chance at receiving it and also sends the same data multiple times so that if the receiver did not catch it correctly the first time they have a chance at getting it right the second time.

The antennas on satellites are what we call “high gain” antennas. Unlike a terrestrial AM or FM radio station which sends its signal out in a nearly 360 degree pattern, a high gain antenna focuses the signal so more energy is radiated to a particular direction in space. These antennas are pointed toward earth so that more of radiated signal is beamed toward us.

Also, on the receiving end, NASA, ESA, etc. have high-gain receiving antennas which are pointed toward the satellites in space. Because they are high gain antennas, radio signals that they pick up are essentially amplified, but they generally only pick up signals which originate from the direction that they’re pointed in. Signals which come in from the side or rear don’t get amplified.

They also use frequencies which are not generally used in terrestrial operations so there is less interference.

In addition to what other people said, they also use really slow speeds. [DSN Now](https://eyes.nasa.gov/dsn/dsn.html) tells me that Earth is currently receiving 160 *bits* per second from Voyager 2. Considering that your wifi probably manages at least 160 megabits per second, Earth has basically a million times more chances to get the correct data.

They use very big antennas, like [this one](https://upload.wikimedia.org/wikipedia/commons/e/e4/Goldstone_DSN_antenna.jpg). It’s 70 metres across. To get an idea of the scale, if you look down to the left, you can see someone’s truck.