The real reason Starlink satellites’ laser connection is so important (and it’s not latency)

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star link is the network of satellites to offer the Internet globally owned by SpaceX, Elon Musk’s space launch company. In the first half of 2021, many launches of these satellitesbut then there was a break because decided to add laser communications to the satellites so they could communicate with each other without using ground stations.

Although at first there was a lot of speculation that the reason for these laser communications was to reduce latency is not really the main reason (although it can reduce it). Let’s see the real reason for this technological addition.

How Starlink works

Starlink provides Internet connection via satellite. But unlike traditional satellite connections, which use satellites in geostationary orbit, in this case they are satellites that are at a low altitude: about 500 km in altitude.

This provides great benefits for users at the cost of technical challenges for the constellation manager. Geostationary satellites are fixed in the sky (they actually orbit at the same rate as the Earth rotates on its axis and therefore appear to be stationary). Thanks to this property with a single satellite, it is possible to cover large areas.

The main drawback of geostationary satellites in providing the Internet is that it is a single resource shared among many users (thus the maximum speed is low). Another important problem is that the geostationary orbit is at an altitude of 36,000 km and therefore the signal has a minimum delay of 240 ms, only due to the jump up and down to the satellite: a excessively high latency for many online services.

What is Starlink, how does it work and how much does it cost?

Starlink avoids these problems with much closer satellites, 500 km high, but instead needs a much more numerous constellation: plans are to have up to 30,000 satellitesalthough at the moment there are about 2,000 and they have authorization to reach about 4,000.

Technically having so many satellites is a challenge for their management. But from the user’s point of view, it is very similar to the classic geostationary connections: a terrestrial terminal communicates with the satellites, which are the ones that provide the Internet; Yes indeed, with higher throughput and lower latency.

Another challenge that Starlink has to solve is the need to provide Internet to its users: that is, it is not enough for users to have a connection to the satellites at all times, the satellites have to have an Internet connection to be able to provide it to customers.

The need for ground stations

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Geostationary satellites, being at a high altitude (six times the radius of the Earth) have a fairly large footprint. They can theoretically “see” half of the Earth. And therefore they provide connection to several countries without problem (for this they have several antennas pointing to different areas). However, the Starlink satellites, being lower, only illuminate a small area (radius of 200 to 500 km) that also moves. In this illuminated area there are, obviously, the clients, but there must also be a ground station that provides Internet to the satellite.

So for Starlink satellites to provide global coverage there has to be, apart from a large constellation of satellites, numerous seasons land scattered around the world. And the need for ground stations can be a bottleneck for the actual coverage of the constellation.

How to know when you can see the Starlink satellites pass in your city

However, the new Starlink satellites have a laser link between them. As a result, the need for ground stations is considerably reduced. A user could receive the data from a ground station that is not in the same coverage area of ​​the satellite that provides service, since the data is communicated by laser between several satellites without the need to make ground jumps.

This laser communication is not easy, as the aiming has to be very precise in a fast moving environment. But the good thing is that the bandwidth can be very high and the latency very low.

Starlink latency

Tests currently being carried out by Starlink users indicate latencies of about 40-50 ms, compared to 15 ms for a fiber connection or 20 ms for a mobile connection. Most long-distance communications go over fiber optics, and the latency these long-distance fibers add is considerable. We are talking about thousands of kilometers at a speed of around 200,000 km / s (the speed of light in optical fiber is lower than that of light in a vacuum).

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On the other hand, the laser communications proposed by Starlink would reduce this latency of the fiber connections on Earth. If a user with a fixed connection from Spain tries to access a server in California, their data will have to travel more than 9,000 km at 200,000 km / s. If instead it does it by Starlink with laser connections between satellites, those 9,000 km will be done at 300,000 km/s.

But if we do the previous calculations, it can be seen that the latency of the connections is not determined solely by the speed of the fiber. The difference between traveling 9,000 km in fiber or by laser in free space is just 1.5 ms. The difference between the 15 ms of the fixed connection and the 40-50 ms of Starlink also does not come from the jump of 500 km to the satellite and another 500 km from the satellite to the ground station: we are talking only 3 ms extra (a little more if we take into account that the satellites are not vertical).

The real problem is that many users share a satellite and this shared medium has to be managed. This also happens with mobile phone connections, but in a much more limited scope. Therefore these laser connections will reduce latency but it will not be a panacea. Definitely the main reason it is being deployed is to reduce the need for ground stations.

Images | star link

star link is the network of satellites to offer the Internet globally owned by SpaceX, Elon Musk’s space launch company.…

star link is the network of satellites to offer the Internet globally owned by SpaceX, Elon Musk’s space launch company.…

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