Every week we are all learning more about the Starlink technology and as it becomes more clear, more questions develop that remain to be answered.
Starlink is a satellite-based internet connection provider. But, unlike the traditional satellite solutions from Hughes and Galaxy, it does not use geostationary orbit spacecraft. With geostationary satellites, they are single satellites that are positioned high up in the Clarke Belt over the equator. At about 35,000 kilometres high and speeding along at extraordinary speeds, they complete an full orbit of the earth in 24 hours. The earth also takes 24 hours to complete a full rotation, therefore, to us on the ground, they appear to be geostationary, or fixed in one exact point in space.
With the Starlink services, they make use of an array of satellites flying along at much lower altitudes. In fact, since May 2019, the September 3, 2020 launch was the 12th in a series of launches to place into orbit over 700 internet beaming satellites, and more are coming every month. SpaceX is the business that launches these Starlink satellites, typically 60 per launch. Company founder and CEO of SpaceX and Starlink is Elon Musk, and he has said that there need to be between 500 and 800 satellites in orbit before service can begin to roll out.
The Starlink satellites are not geostationary. They are much closer to earth orbiting between 400 and 700 kilometres high. They are in a polar orbit travelling north-south and complete a full circumnavigation in about 90 minutes. So, for full-time coverage of any one home, you must have an array of satellites trailing one another. It is similar to the way Tarzan, the King of the Jungle, swings through the trees. He moves from one vine to the next. For us to connect to the Starlink satellites, we will connect to one satellite after another as they rise up over the horizon, climb high above us, and then descend downward to fall out of sight. It is only with this constant stream of satellites flying past our homes relaying our connection one to another in a continuous and seamless stream that this connection appears to be contiguous and uninterrupted.
SpaceX’s Starlink megaconstellation is already the largest fleet of satellites in the world, but hundreds more will be launched in the coming months as the company works to fulfill its initial network of 1,440 satellites. To that end, company representatives have said that roughly six of the flat-panel satellites are built each day at its facilities in Washington state, and they estimate that 60-satellite Starlink missions could launch every two to three weeks.
The U.S. Federal Communications Commission granted SpaceX approval to launch as many as 12,000 Starlink satellites to Low Earth Orbit (LEO), providing customers with high-speed, low-latency internet.
SpaceX originally planned a constellation consisting of 4,425 satellites at altitudes around 1,200 km, which would later be supplemented by a set of 7,518 satellites located in orbits at an altitude of about 320 km. The FCC granted a license to SpaceX to operate the first 4,425 satellites in March 2018, which triggered an important countdown. The FCC requires satellite companies to deploy half of the planned number of satellites within 6 years of receiving the initial authorization. On top of that, the FCC requires all satellites to be in orbit within 9 years. If companies fail to meet these deadlines, they’ll be allowed to operate only as many satellites as had been deployed before the deadline.
In November 2018, SpaceX also received permission from the FCC to launch and operate the remaining 7,518 satellites. At the same time, SpaceX asked for the previous license to be modified. Instead of operating all 4,425 satellites at an altitude around 1,100 km, the company now plans to operate only 2,825 satellites there, while adding 1,584 satellites that would orbit at 550 km. As currently planned, the complete constellation would consist of 11,924 satellites in total:
- 1,584 satellites positioned at altitude of 550 km, split into 72 orbital planes with 22 satellites each, with 53° inclination (these satellites will be deployed first)
- 2,825 satellites positioned between 1,110 km and 1,325 km, split into several different planes with different inclinations (see table below)
- 7,518 satellites positioned at an altitude of 320 km (these will most likely be the last ones to be deployed)
But, how does this all work with imperfect weather? And, more specifically, how will Starlink overcome the serious issue of rain fade?
Rain fade is the deterioration of the microwave RF signal levels caused by rain precipitation on either end of the satellite link. Typically, Ku, Ka, and V band links are affected most (all frequencies above 11 GHz) and can occur at the user terminal locations or the gateway end of the link.
Well, most of us are still in the dark about this technology and as we capture small bits of information and struggle to piece it all together to gain deeper insights, we understand it more clearly. As you may expect, there are many skeptics that argue the pros and cons of this internet from space strategy. Some Wall Street pundits have strongly stated that it will not work. They say that it is a foolish endeavour. However, betting against Elon Musk has proven to be a mistake time and time again. So, only time will tell.
Now, we are learning small bits of information about Starlink’s spectrum usage. We now know that they will operate in at least three bands of spectrum.
As we understand it, these satellites will be in orbits at altitudes between 340 km and 1,300 km and will eventually be interconnected using lasers (the first generation will not yet utilize lasers) and their signal will cover the entire Earth surface in the Ku (12–18 GHz), Ka (26.5–40 GHz) and V (40–75 GHz) bands.
All of these three bands are negatively affected by rain fade. This means that Starlink will face severe rain fade outages. So, it will take some creative engineering alchemy to overcome the unimaginable physics of Mother Nature.
The V and Ku bands will be used by the network’s users, while the V and Ka bands will be used to connect to gateways and for tracking, telemetry, and control purposes. The 7,518 satellites located in very low Earth orbit will use V-band for all purposes. Here is a breakdown of the specific frequency bands used by Starlink:
- Transmissions from satellite to user terminals: 10.7 – 12.7 GHz and 37.5 – 42.5 GHz
- Satellite to gateway transmissions: 17.8 – 18.6 GHz and 18.8 – 19.3 GHz and 37.5 – 42.5 GHz
- Transmissions from terminals to satellites: 14.0 – 14.5 GHz and 47.2 – 50.2 GHz and 50.4 – 51.4 GHz
- Transmissions from gateways to satellites: 27.5 – 29.1 GHz and 29.5 – 30.0 GHz and 47.2 – 50.2 GHz and 50.4 – 51.4 GHz
- Tracking, telemetry and control (downlink): 12.15 – 12.25 GHz and 18.55 – 18.60 GHz and 37.5 – 37.75 GHz
- Tracking, telemetry and control (uplink): 13.85 – 14.00 GHz and 47.2 – 47.45 GHz
Satellites will communicate either directly with user terminals or with gateways, which will be typically located near major Internet nodes. As of November 2019, SpaceX was authorized to operate six Ku gateways located in different places around the US. These test gateways will operate in Ku band and SpaceX will use them “to deliver broadband data between the first-generation satellites of its NGSO system and terrestrial Internet exchange points”. Reddit user daedalus_j managed to photograph these antennas near North Bend. They are located next to Level 3 Communications, a Tier 1 network who have huge interconnections to the internet.
These antennas appear to be used as gateway connections to / from the in-orbit satellites. They seem to be very small size for this task and at these frequencies. At these frequencies, a 5.6 metre antenna or larger upwards to 30 metres would be used at a gateway location. Below is a photograph of a classic Ka-band uplink that I built in Toronto over 20 years ago. However, the larger the antenna, the narrower the beamwidth, which restricts the view to more than one satellite at a time. With LEOs, the gateways may need to see multiple satellites simultaneously, so smaller antennas will permit these multiple wider look angles.
With larger amplifiers (2500 watts or more) and uplink power control (UPC), as well as superior AGC (automatic gain control) on the satellites themselves, the link from earth to satellite can be maintained with perhaps 20+ dB of uplink power control. This is done on the ground by dynamically controlling the amplifier power output to punch through the rainfall (10 dB). This capability will help to punch through most normal rain fade concerns, but not all downpours can be overcome. In addition, it is common to use a variable gain pre-amplifer onboard the satellite receiver to dynamically adjust their receive sensitivity (10 dB). It is akin to a hearing aid to help you hear better.
It is this combination of UPC and AGC that can extend service connections during weather impairment. With a combined gain advantage of about 20+ dB of signal adjustment, perhaps 95% of all rain fade can be overcome. That leaves about 5% of the time when service outages are to be expected. Unless of course, the Starlink engineers have dreamed up some new technology to overcome this serious impediment to performance.
In the photograph below, of a classic Ka-Band uplink gateway, the two small 1.2 metre antennas hidden by the cars and in front of the larger 5.6 metre uplinks are used with radiometers to measure the noise temperature of the ‘Big Bang’. It resonates at about 30 degrees Kelvin. As clouds pass by, they raise the noise temperature and these measuring devices indicate to the pool of amplifiers to power up to increase transmit signal strength to keep the satellites at near saturation. We never want to over-saturate the satellites for fear of burning out their front-end receive circuits, so it is maintained at about 97% saturation. When we run out of ground-based UPC, then the onboard satellite AGC takes over and increases gain at the space-end of the link. But, excessive AGC increases noise in the connection so it needs to be used judiciously.
So, for now, rain fade can be anticipated. But, I would not be surprised as we learn more technical details that the Starlink team has some brilliant strategy to overcome it. Maybe they will throttle the data rates to maintain the connections? Or, they will tune-in multiple satellites simultaneously to keep the connection alive by looking through the rain at various angles? Or, they have designed even more gain control than anyone has seen work before? I would not put it past them to have a solution built on one or more strategies in concatenation. I anticipate a unique and very clever solution to this age old rain fade issue. Time will tell as details leak out.
SRC00CHY. (2020). Starlink Compendium. ELONX.net. Retrieved on September 6, 2020 from, https://www.elonx.net/starlink-compendium/
Thompson, A. (2020). SpaceX launches 60 Starlink internet satellites, sticks rocket landing. Space.com. Retrieved on September 6, 2020 from, https://www.space.com/spacex-starlink-11-satellites-launch-september-2020.html
About the Author:
Michael Martin has more than 35 years of experience in systems design for applications that use broadband networks, optical fibre, wireless, and digital communications technologies. He is a business and technology consultant. He offers his services on a contracting basis. Over the past 15 years with IBM, he has worked in the GBS Global Center of Competency for Energy and Utilities and the GTS Global Center of Excellence for Energy and Utilities. He is a founding partner and President of MICAN Communications and before that was President of Comlink Systems Limited and Ensat Broadcast Services, Inc., both divisions of Cygnal Technologies Corporation (CYN: TSX). Martin currently serves on the Board of Directors for TeraGo Inc (TGO: TSX) and previously served on the Board of Directors for Avante Logixx Inc. (XX: TSX.V). He has served as a Member, SCC ISO-IEC JTC 1/SC-41 – Internet of Things and related technologies, ISO – International Organization for Standardization, and as a member of the NIST SP 500-325 Fog Computing Conceptual Model, National Institute of Standards and Technology. He served on the Board of Governors of the University of Ontario Institute of Technology (UOIT) [now OntarioTech University] and on the Board of Advisers of five different Colleges in Ontario. For 16 years he served on the Board of the Society of Motion Picture and Television Engineers (SMPTE), Toronto Section. He holds three master’s degrees, in business (MBA), communication (MA), and education (MEd). As well, he has three undergraduate diplomas and five certifications in business, computer programming, internetworking, project management, media, photography, and communication technology. He has earned 20 badges in next generation MOOC continuous education in IoT, Cloud, AI and Cognitive systems, Blockchain, Agile, Big Data, Design Thinking, Security, and more.