On 24th May 2018, SpaceX launched a Falcon 9 rocket filled with 60 satellites into space. This marked the beginning of their ambitious new project called “Starlink” which aims to provide high-quality broadband internet to the most isolated parts of the planet, while also providing low latency connectivity to already well-connected cities.
For this mission SpaceX has 12,000 satellites planned for launch over the next decade, dramatically increasing the total amount of spacecraft around Earth’s orbit. This will cost SpaceX billions of dollars, so they must have a good reason for doing so.
Let’s see how this network will work, and how it will compete with existing internet providers
Back in 2015, Elon announced that SpaceX had begun working on a communication satellite network, stating that there is a significant unmet demand for low-cost global broadband capabilities. Around that time, SpaceX opened a new facility in Redmond, Washington to develop and manufacture these new communication satellites.
They had an initial plan to launch the prototype by 2016 but it delayed till 2018 due to several reasons. Finally a successful launch of the two prototypes, Tintin-A and B, which allowed SpaceX to test and refine their satellite design. The company received the approval of FCC to deploy 7,500 satellites in November 2018.
On May 24th, the first batch of production satellites were launched into orbit and people around the world quickly started to spot the train of satellites moving across the night sky.
The working of SpaceX Starlink satellites
As you know these are communication satellites, but SpaceX is not ready to share any sort of information about their mission. But according to the information submitted by the company in FCC, we know that the satellites will contain 5 1.5 kilogram silicon carbide components, which indicates that each satellite will contain 5 individual lasers.
These lasers, like our fibre optic cables here on earth, will use light pulses to transmit information between satellites. Transmitting with light in space offers one massive advantage over transmitting with light here on earth however. The speed of light is not constant in every material, in fact, light travels 47% slower in glass than in a vacuum.
This offers Starlink one huge advantage that will likely be its primary money maker. It provides the potential of lower latency information over a long distance, in simpler terms let’s imagine this as a race between data packets. A user in London wants the new adjusted price of a stock on the NASDAQ from the New York stock exchange.
If this information used a typical route, let’s say through the AC-2 cable which has a return journey of about 12,800 kilometers to make through our optic cable. In a vacuum, light travels at a speed of 299,792,458 meters per second. The speed of travel in glass depends on the refractive index and the refractive index depends on wavelength, but we will take the reduction as 1.47 times slower than the speed of light in a vacuum [203940448 m/s].
This means the data packet will take roughly 0.063 seconds to make the round trip, and thus has a latency of 0.063 seconds, or 62.7 milliseconds.
With the additional steps that add to this latency like the conversion of light signals to electrical signals on either end of the optical cable, traffic queues and the transfer to our final computer terminal, this total time comes out at about 76 milliseconds.
Figuring out the latency for Starlink is a lot more difficult, as we have no real-world measurements to go by, but we can make some educated guesses with the help of Mark Handley, a communications professor at University College London.
The first source of latency for Starlink will be during the up and downlink process, where we need to transfer our information to and from the earth. We know this will be done with phase array antenna, which is a radio antenna that can control the direction of their transmission without moving parts, instead, they use destructive and constructive interference to control the direction of the radio wave.
Each satellite has a cone-beam with an 81-degree range of view. With an orbit of 550 kilometers, each satellite can cover a circular area with a radius of 500 kilometers. At SpaceX’s originally planned orbit this coverage had a radius of 1060 kilometres. Lowering the altitude of a satellite decreases the area it can cover, but also decreases the latency.
This is particularly noticeable for typical communications satellites operating in geostationary orbit at an altitude of about 36,000 kilometres. The time it takes data to travel up to the satellite and back down travelling at the speed of light is around 240 milliseconds 369% slower than our subsea cable.
However, since Starlink is intending to operate at a much lower altitude, the up and downlink theoretical latency could be as low as 3.6 ms. This is why SpaceX needs so many satellites in their constellation in order to provide worldwide coverage.
Each individual Starlink satellite has four phased array antenna. This directional beam was an essential part of SpaceX’s FCC approval application as thousands of satellites broadcasting undirected radio waves would cause significant amounts of interference with other communication methods.
Once that data is received by one Starlink satellite, it can begin to transmit that information between satellites using lasers. In this way, it is hoped to work.
this blog is the short information collected from the following video of “Real engineering”. for detailed information must see the video.