Ethan Martin
Ethan is a senior at the University of Pittsburgh studying Mechanical Engineering
Starting in 2019 Elon Musk and Starlink sent 60 satellites into low orbit as the start to his mission of bringing fast and reliable internet to all reaches of the world. Starlink satellites move at 27,000 Kilometers per hour at an altitude of 550 km to create a 20 ms latency which is critical for smooth internet connection. These table-sized satellites were launched using SpaceX Falcon 9 rocket from an Air Force base in Florida. Since this launch, over 6,000 additional satellites have been sent into low orbit and Starlink plans to send anywhere from 12,000 to 34,000 more satellites soon.
In addition to the satellites orbiting 550 km above the Earth’s Surface, Starlink uses a receiving dish called Dishy Mcflatface, or Dishy for short. Dishy is attached to your home, boat, or vehicle and will send and receive data at over 100 Mb/s. Due to the large number of satellites orbiting the Earth, Dishy must switch between satellites every 4 minutes or so. This is because the satellites move in and out of the field of view due to their extremely high speeds. Unlike traditional satellites which propagate signals in a wide fan that can cover entire land masses, Starlink’s send waves in much smaller radii. This coupled with the low altitudes means each satellite will constantly be changing its service area and is why Starlink requires so many. Normal TV satellite dishes can only receive signal and cannot send. Dishy, however, can both send and receive signals.
Dishy is quite an impressive satellite dish and is composed of many different layers and components. It homes an aluminum backplate with a massive printed circuit board (PCB). Additionally, it has 640 small microchips, 20 large microchips, a main central processing unit (CPU), a GPS module, and 1280 antennas. In 6 layers, these antennas are arranged in a hexagonal honeycombed pattern, most of which are in the PCB. From these small microchips, copper wire feeds to the antenna stack where a 12 GHz signal is sent in sinusoidal fashion every 8 picoseconds. In the antenna patch, an electric field is created due to the oscillation of voltage. As the voltage flips between positive and negative, a positive and negative pole is formed between the top and bottom of the patch. This created the electric field, and due to the constant flow of electrons, a magnetic field is also produced in the perpendicular direction. The two oscillating fields produce electromagnetic waves traveling outwards in an expanding shell fashion. These waves are then amplified together in order to reach the satellites in low orbit. This occurs in each of the 1280 antennas. Having just one antenna, which is approximately 1 centimeter in diameter, is very weak and alone cannot travel the required distance. Beamforming occurs when all 1280 antennas work in synchronization due to zones of constructive interference forming. With the combination of all the antennas, the power is about 3500 times the power of a single antenna.
For Dishy to then receive the signal from Starklink satellites, the antenna must switch off the 12 GHz signal. The incoming electromagnetic waves from the satellite influence the electrons within the copper patch. This creates an oscillating flow of electrons which is coupled to the feed line to be sent to the front-end module chip. Here the signal is amplified. Because there are thousands of electromagnetic waves from thousands of different sources around the world, Dishy is designed with very specific dimensions so that they can only receive certain frequencies and block the rest.
A challenge that Starlink had to face was being able to accurately send information from Dishy to a moving satellite and in transmittable form. In order for Dishy to accurately send information to low orbit, they use phase array beam steering. By feeding the signals at phase shifts from each antenna, this allows them to propagate outwards with constructive interference at an angled path. Each time the phase changes, so does the angle of the signal being sent out. This allows Dishy to constantly change the phase of the electromagnetic waves and accurately hit the satellites in low orbit. In order to send information from Dishy to the satellite, a 6-bit binary value is assigned to each permutation of amplitude and phase of the electromagnetic waves sent from Dishy. There are 64 different permutations which are arranged in a graph called a constellation diagram. The distance from the origin to the point on the graph is denoted by the amplitude and the angle from the x-axis is the phase. Each 6-bit permutation is called a symbol and this technique of sending 6-bit symbols is called Quadrature amplitude modulation (QAM). The frequency is still 12 GHz or once every 83 picoseconds. Each signal will last 10 nanoseconds, which means there will be 120 wavelengths per symbol before the next one is sent. This is plenty of time for the satellites to capture the information and make sense of it. Within one second over 90 million symbols can be sent which results in about 540 million bits per second. Because Dishy cannot send and receive at the same time, about 74 milliseconds for every second are used for sending data from Dishy to the satellite and 26 ms for receiving data from the satellite. To reduce the latency, the upload and download is varied within the second to avoid grouping.
As Starlink adds additional satellites into orbit the capabilities will continue to grow. This technology offers to opportunity to truly connect the entire world, even remote locations that were otherwise left without the internet. This also offers an interesting opportunity for maritime travel and mobile homes to connect to the internet as they are traveling. The possibilities will only continue to grow as Starlink expands.
Some potential issues involve the massive number of satellites orbiting the Earth every day. With thousands of satellites comes the issue of having to steer them and ensure they will not collide with each other. Also, their lifespan is approximately 5 years, which means at the end of their life they will burn up in the atmosphere and need to be replaced. Because the satellites contain aluminum, when they burn up they will produce aluminum oxide, known as alumina, which is known to deplete the ozone. This can have very negative environmental effects as well as high costs. Additionally, astronomers are angry with the mass amounts of light pollution from the satellite mega-constellation. Only time will tell how Starlink will respond to the critics and how the environment will be affected.
