What are the SpaceX Satellites doing/what is their objective?


Edit: SpaceX Starlink

In: Technology

Ultimately, the end goal, when the entire constellation of StarLink satellites will be online, is for SpaceX to act as an internet service provider, but one that can be accessed from anywhere in the world.

Other satellite internet providers have already existed for many years, however all of those operate in geostationary orbit – which is 35,786 km (22,236 mi) away from the ground.

Because those satellites are so far away, the latency makes the service less than ideal for any real time communications – for example you wouldn’t be able to play a game online without such lag that it’s virtually unplayable.

The major difference with StarLink satellites is that they will operate in low earth orbit, only about 550 km (340 mi) above ground, and they will be able to provide a connection with an even lower latency than what is possible from your local internet service provider.

What exists already and what SpaceX Starlink satellites will do is that you can actually have an internet connection through satellite communication. Most satellites currently operating to provide internet connectivity are in a geostationary orbit (meaning that they stay static in the sky because they follow the rotation of the earth) and have to orbit at about 36000km from the ground.

Some quick math (time = height / speed of light) gives about 120ms (0.12 second) for a light ray sent from Earth to be received by a satellite in a geostationary orbit. Electromagnetic waves travel at the same speed. So when, say, you want to load Google’s search page, your machine has to send data to the satellite that will send back the request to the ground, ultimately to Google’s servers.

This means the time for Google’s servers to receive your request is about twice the 120ms we calculated (because the ray has to go from your machine -> satellite, satellite -> google servers, to make it simple), so 240ms in total.

But then, Google’s servers also has to send you the page you requested. That’s another trip to space, and in total your request will be about 580ms. This is not even accounting from the overhead of the satellite technology and such, for which you could add maybe tens or hundreds of milliseconds for.

For comparison, your average ADSL, 3G or LTE connection will probably give you an average of often 10 to 100 milliseconds for a complete request like that to a nearby server (say in the same country), and most of it is due to overhead of the technology. Fiber net can go even lower.

Why bother with satellite then? Well, for one, you can get coverage where you would never have imagined otherwise. Second, while the latency is absolutely horrible, bandwidth can actually be quite okay, generally about 20mbps (megabits per second, not megabytes) – where many people in rural areas can be stuck to 1Mbps in ADSL or even worse with poor quality mobile reception, which can be barely sufficient to browse the web and check your mails, let alone watch a youtube video in a proper quality. Of course though, this latency makes it a horrible choice for games, especially real time ones which often become unplayable when exceeding 150ms ping-pong latency (imagine figuring out you got shot at in an action game almost half a second after it happened!).

This is where Starlink comes into play. Starlink is about deploying a huge fleet of low-orbit “cheap” and small Starlink satellites, which, as you may have guessed, means much, much better latency. The satellites will be only at a distance from ground of about 550km, and they are willing to go even lower in the future. For our same hypothetical Google request, this comes down to a theoretical 7.5ms! There will be a good amount of overhead to the technology though, so SpaceX is rather estimating about 20ms of latency. This is extremely competitive with other technologies and they are also hoping for a throughput of 1Gbps (1000Mbps) per user, which is what you would get with a typical good fiber connection.

If I had to guess, though, a 1Gbps plan will probably be very expensive and they are likely to have different plans based on available bandwidth. At this point it is purely speculation though, because SpaceX has not communicated on the matter, AFAIK.

Just recently, SpaceX deployed 60 satellites. This is fairly experimental though, and they will need a certain amount of satellites to have a minimal network functional – about half a thousand. Ultimately, these satellites will be able to communicate between each other, which is not yet the case of those deployed satellites. SpaceX is planning for extra launches this year and willing to deploy 12000 satellites by 2020(!). So, of course, reducing the costs of deploying those satellites (which was said to be higher than even just building them) was core of the problem.

Just to add, this is also a gigantic technological challenge. This is much more complicated than communicating with geostationary satellites, because you have to account for those satellites moving in the sky. Meaning that you have to account for the doppler effect (which means that the frequency of waves slightly change depending on the difference of the movement of the receiver object and of the emitter object), among other things.

Here is a good and complete article if you want to learn a bit more: [https://hackaday.com/2019/05/20/everything-we-know-about-spacexs-starlink-network/](https://hackaday.com/2019/05/20/everything-we-know-about-spacexs-starlink-network/)