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Dr David Maddison describes S TARLINK WARM TA SHIELD R Global Wireless Internet from SpaceX Starlink, owned by SpaceX, provides affordable satellite internet anywhere in the world. Remote connectivity for Internet of Things (IoT) devices located just about anywhere can also be via Starlink or another subsidiary, Swarm, while Starshield is aimed at government users. M ost people in developed or even developing countries can now receive mobile, wireless internet data via their smartphones or other devices when near a city or town, or along a major transport route. Internet connectivity outside such areas via satellite tends to be expensive and slow. Starlink is owned by SpaceX and enables regular users to (relatively) affordably get satellite internet anywhere in the world, no matter whether they be at sea on a yacht or ship, on an aircraft, in Antarctica, in a mobile home, a remote area, or on an outback expedition. Low latency Apart from relative affordability, Starlink aims to have low latency, ie, keeping the round trip time for a packet of internet data as low as possible. A finite amount of time is required for a radio wave to travel between transmitter and receiver at the speed of light (about 3 × 108m/s). There are also delays due to signal processing and internet switching time. The realistic round-trip time for a geostationary satellite orbiting at 35,786km is around 600ms or more when including switching overhead, which is excessive for two-way live audio or video, gaming or other interactive applications. Starlink achieves low latency by having satellites in low Earth orbit of about 550km, giving a latency of about 20ms, comparable with wired networks. However, because the satellites are orbiting at such a low altitude, a very large number are required to give global coverage. Another stated objective of Starlink is to provide internet connectivity in developing countries, some of which have little wired or wireless phone or internet infrastructure. According to the UN, about 57% of the world’s population lacks internet access. SpaceX Image source from SpaceX (CC BY-NC 2.0): www.flickr.com/photos/spacex/49422067976/in/photostream/ 14 Silicon Chip Australia's electronics magazine SpaceX, or Space Exploration Technologies Corp, is largely owned by the Elon Musk Trust (47.4% equity, 78.3% voting control). SpaceX builds the Starlink, Swarm and Starshield satellites and their delivery systems, such as the Falcon 9 rocket. As of December 2022, Starlink had one million customers, including in Australia and New Zealand. siliconchip.com.au Satellite constellation & orbit A satellite constellation is a group of satellites working together as an integrated system. A well-known example is the GPS satellite constellation. Starlink, Swarm and Starshield all form satellite constellations too. Due to the low latency requirement of Starlink, the satellites need to be in low Earth orbit. Because of this, the visibility of an individual satellite to any given area on Earth is quite limited. Therefore, a large number of satellites are required for complete Earth coverage. Fig.1 shows the comparative Earth coverage for three common satellite orbital altitudes: geosynchronous orbit (GEO), medium Earth orbit (MEO) and low Earth orbit (LEO). Starlink satellites will be placed in LEO. Fig.2 and Table 1 show further orbital characteristics for GEO, MEO and LEO. GEO MEO LEO Fig.1: a representation of three common orbit types and comparative ground coverage areas: geosynchronous orbit (GEO), medium Earth orbit (MEO) and low Earth orbit (LEO). Land surface visible to a satellite We can calculate the amount of the Earth’s surface visible to a satellite at a certain altitude as follows. If the altitude above the Earth’s surface is d and the radius of the Earth is R (nominally 6378km at the equator), then the fraction of the surface visible to the satellite is given by the formula f = d ÷ 2 × (R + d). We use this formula to calculate the areas visible to a satellite for various orbits in Table 1. For practical reasons, a satellite will not be visible all the way to the horizon due to mountains, trees etc. Also, the signal will be degraded by extensive travel through the atmosphere. So in practice, a certain elevation angle is defined below which no attempt is made to communicate with the satellite from an Earth station, as illustrated in Fig.3. The red disc shows the absolute horizon, while the yellow one represents the minimum coverage at the designed elevation angle, which is smaller than the horizon. Therefore, the coverage a satellite can achieve is less than we calculated with the above formula. Starlink orbital altitude As with any large satellite program, there will be several different versions of satellites. For Starlink, there are presently V1, V1.5 (Figs.4 & 5), V2 and V2 mini satellites. So siliconchip.com.au Fig.2: a not-to-scale representation of features of several orbital altitudes. RTT is the round-trip time for a radio signal. The Van Allen radiation belts are best avoided. The radius listed is from the centre of the Earth, while the height is from the surface of the Earth. Source: https://w.wiki/6H8X Table 1 – Characteristics of various satellite orbits Geosynchronous orbit (GEO) Medium Earth orbit (MEO) Low Earth orbit (LEO) 2000-35,786km (20,500km typical) 160-2000km (500km typical) GPS (20,180km) Starlink (550km) Latency at 600ms typical altitude (round trip) 400ms 20ms Proportion of 42.4% Earth’s surface visible 38.1% 4.0% 10-15; more for redundancy At least 32, but in practice, hundreds Slow; each satellite is visible for 1-3 hours Fast; each satellite is visible for 5-15 minutes Fewer satellites than LEO, lower latency than GEO; smaller antenna systems; better signal strength above 72° latitude Low latency, low signal loss, low power Earth stations, potentially lower cost due to mass production Altitude 35,790km typical Examples GOES, Inmarsat, Intelsat Min. number Three; four for of satellites some overlap. for full Earth coverage Antenna No tracking tracking speed needed required Advantages Few satellites required, no tracking, no handover, always connected, simple management, no complicated orbits Australia's electronics magazine June 2023  15 Table 1 – Characteristics of various satellite orbits (continued) Geosynchronous orbit (GEO) Disadvantages Weak signals, poor coverage above 72° latitude, high latency Typical >15 years satellite life Network Low complexity Medium Earth orbit (MEO) Low Earth orbit (LEO) Antenna tracking required, satellite handover needed, more satellites than GEO, more exposure to Van Allen Belt radiation than GEO or LEO Small service area, antenna tracking needed, frequent satellite handover, large Doppler shifts, short orbital life due to atmospheric drag 10-15 years 3-7 years Medium High far, only V1 and V1.5 satellites have been launched; V1.5 satellites are still being launched. Starlink V1 satellites are inserted into various ‘shells’ in orbits of altitudes between 540km and 570km, shown in Table 2. A satellite orbital shell is a series of satellites sharing the same circular orbit at a certain altitude. Satellite deployment timeline SpaceX is constantly launching Starlink satellites, but the following satellites have been launched at the time of writing. They launched two “Tintin” test satellites in 2018. In 2019, a further series of 60 V0.9 ‘production design’ satellites were launched. SpaceX launched operational v1.0 satellites from November 2019 through to May 2021. Usually, 60 were launched at a time (some launches had fewer), over 29 launches, for a total of 1675. Of those, around 183 are no longer working. Starlink V1.5 satellites started to be launched in June 2021 through to at least January 2023. There have been 40 launches of V1.5 satellites, each launch carrying up to 54 satellites, for a total of 1881 so far, of which 52 are no longer operational. For a complete, up-to-date list of Starlink satellite data, see https:// planet4589.org/space/con/star/stats. html There were also four Starshield V1.5 launches on the 13th of January 2022 and another four on the 19th of June 2022, for unknown US government agencies. Coverage area With the first orbital shell at 53.0°, Starlink initially provided coverage to areas below about 55° latitude, which covers a vast majority of the world’s population. Later launches at other orbital inclinations covered higher latitudes. The 53.2° shell extended the number of customers covered in the mid and low latitudes. The 70.0° shell expanded coverage to Alaska and northern Europe (and presumably equivalent latitudes in the southern hemisphere). These earlier Starlink launches were in ‘equatorial orbits’, so they did not cover polar regions – see Fig.6. Four launches of 46 satellites each for the 97.6° shell occurred in July and August 2022, adding coverage for polar regions. This includes Antarctica plus areas of northern Alaska, northern Canada, Finland, Norway and Sweden not previously covered. High-level Starlink architecture Starlink consists of three main components: satellites, ground stations Fig.3: satellite visibility at zero elevation (red) and designed elevation (yellow), showing the difference between the theoretical and actual coverage. Original source: www. frontiersin.org/articles/10.3389/ frcmn.2021.643095/full and user terminals. The ground stations are the connection to the terrestrial internet and can also act as a means for Starlink satellites to communicate with each other. The number of ground stations needed is minimised by later (V1.5+) satellites that can communicate with each other via inter-satellite laser links. When a user connects to a satellite via their user terminal, the satellite either relays the signal directly to a Starlink ground station connected to the internet, or to another Starlink satellite via laser and then onto a ground station. This inter-satellite relay is necessary for users at higher latitudes where the satellites have access to few or no ground stations. Laser communication between satellites V1.5 satellites can communicate with each other via inter-satellite laser links. This reduces latency, as a signal travelling via laser will travel about 30-40% faster than between switching equipment on the ground connected via coaxial cable or optical fibre. Also, due to the shorter distance between satellites compared to cables on the ground or undersea, overall latency is reduced by up to 50%. Laser connections between satellites are necessary for the Starlink satellites Table 2 – orbital shells and numbers of Starlink V1 and V1.5 satellites (4408 in total) Inclination 16 Orbital altitude Orbital planes Eventual satellites/plane Total satellites Shell 1 53.0° 550km 72 22 1584 Shell 2 70.0° 570km 36 20 720 Shell 3 97.6° 560km 6 (polar) 58 348 Shell 4 53.2° 540km 72 22 1584 Shell 5 97.6° 560km 4 (polar) 43 172 Silicon Chip Australia's electronics magazine Laser comms. All All siliconchip.com.au Fig.4: an artist’s concept of a Starlink V1 satellite. Source: https://w.wiki/6H8Y in polar orbit, as they won’t have access to many or any ground stations. Geographic availability of Starlink Starlink can be used everywhere on the surface of the Earth; however, under International Telecommunication Union (ITU) regulations and international treaties, each country and its telecommunications regulators must grant rights to use satellite communications such as Starlink. This means that Starlink has to set up operations in each country in which it does business. Australia and New Zealand provided rapid regulatory approval for Starlink in April 2021, the 6th and 5th countries to do so after the USA, Canada, the UK and Germany. Fig.7 shows Starlink availability by country. Starlink equipment is programmed only to work at or near your residential address if on a residential plan, or other areas on an RV plan. Fig.5: a rendering of Starlink V1.5 (left) and V1 (right) satellites. V2.0 satellites have five times as much surface area for Earth-facing antennas and are much more capable. Source: www.teslarati.com/ spacex-elon-musknext-gen-starlinksatellite-details/ Number of satellites in orbit To appreciate the enormousness of the Starlink project, it is important to consider the number of satellites already in orbit. According to the United Nations Office for Outer Space Affairs (UNOOSA) searchable index at www. unoosa.org/oosa/osoindex/search-ng. jspx, as of 3rd January 2023, 14281 objects had been launched into space since Sputnik 1 in 1957. Of those, 8734 are classified as still ‘in orbit’ although not necessarily functional. Of the 8734 objects classified as ‘in orbit’, 3568 were labelled Starlink and 5166 were not. This means that nearly 41% of orbiting objects are associated with Starlink. Still, that number will increase dramatically as the entire constellation is rolled out. So, in a few years, a large majority of all artificial satellites could be part of Starlink! According to a web page that keeps a tally of Starlink satellites at https:// planet4589.org/space/con/star/stats. html, as of 20th January 2023, 3389 Starlink satellites are currently operational. Fig.6: the incomplete global coverage provided by earlier Starlink satellite launches in equatorial orbits (left) compared to the complete global coverage after later launches into polar orbit (right). Starlink satellite features Some features of the Starlink satellites not already mentioned include: • a flat design for easier and higher density packing into Falcon 9 rockets • a star tracker for guidance siliconchip.com.au Fig.7: the availability of Starlink services. Green means approved and activated, blue means activated and grey is unknown. Source: https://w.wiki/6H8Z Australia's electronics magazine June 2023  17 • each satellite has four phased-­ array antennas and two parabolic antennas (see www.starlink.com/ technology). The current lineup of Starlink ground station antennas for users is shown in Fig.8. Aviation antennas An aviation application for Starlink with an aerospace-certified antenna, shown in Fig.9, is to be released in 2023. Link speeds will be 350Mbps with no data volume restrictions and latency as low as 20ms. While internet connectivity is already available in some aircraft, it is slow and can be expensive. Starlink will enable high-bandwidth or low-­ latency activities on aircraft, such as video calls, streaming high-definition video, online gaming etc. Devices on the plane will access the Starlink internet via a standard WiFi connection. For those interested in costs, at the time of writing, there is a onetime hardware cost of US$150,000 (~$210,000) and monthly service fees with unlimited data are US$12,50025,000 (~$18,000-$35,000). Initial certification is being obtained for the following business and regional aircraft types: ERJ-135, ERJ-145, G650, G550, Falcon 2000, G450, Challenger 300, Challenger 350, Global Express, Global 5000, Global 6000, and Global 7500, with more applications being developed for larger commercial jets. How Starlink antennas work Unlike an antenna pointed at a geostationary satellite, which needs a clear view in only one direction, Starlink antennas need to be unobstructed from horizon to horizon, as the LEO satellites can be anywhere in the sky. When setting up a Starlink antenna, a phone app will guide your placement to confirm a good signal. Starlink antennas are motorised and Frequencies used by Starlink satellites According to www.elonx.net/starlink-compendium/, the following frequencies are used by Starlink: ● Satellite to user terminals: 10.7–12.7GHz, 37.5–42.5GHz ● Satellite to gateway: 17.8–18.6GHz. 18.8–19.3GHz, 37.5–42.5GHz ● Terminals to satellites: 14.0–14.5GHz, 47.2–50.2GHz, 50.4–51.4GHz ● Gateways to satellites: 27.5–29.1GHz, 29.5–30.0GHz, 47.2–50.2GHz, 50.4–51.4GHz ● Tracking, telemetry and control (downlink): 12.15–12.25GHz, 18.55–18.60GHz, 37.5–37.75GHz ● Tracking, telemetry and control (uplink): 13.85–14.00GHz, 47.2– 47.45GHz self-aligning, but once the antenna is pointed in the optimal direction, it does not need to move much more by itself. That is because, apart from antenna motors used for basic alignment, the antenna can electronically steer its beam using a phased array. New versions of Starlink antennas intended for rooftop RV mounting or aircraft are not mechanically steered at all; they are electronically steered only. Hacking antennas Starlink antennas are not designed to be disassembled by users. An attempt to do so might void the warranty if it causes damage, but some hackers have done so. Various people disassembled their antennas, either to see what was inside or to repurpose stationary antennas for mobile (car) or lightweight expedition (on foot) use. While a mobile antenna is now available, that was not always the case. Antenna teardown There is very little officially published information about the construction of the Starlink ground station antennas. What we know is only what has been discovered by hackers – see Figs.10, 11 & 12. The Starlink antenna is a remarkably complicated device and arguably Fig.8: a standard Starlink antenna for regular residential users (left), with a 100° field of view. The high-performance antenna (middle) is for businesses and enterprises as it can connect to more satellites, is more tolerant of extreme environments and has a 140° field of view. The flat high-performance antenna (right) is intended for mobile applications such as motor homes and boats, also with a 140° field of view. Source: Starlink. 18 Silicon Chip Australia's electronics magazine the most critical part of the ground equipment. If you watch the teardown videos, you will see that it is an engineering masterpiece. It has a lot of electronics in it, including an ARM processor, RAM chips and many custom ICs. Presumably, these are all to drive the phased array. Teardown videos include: ● Starlink Teardown: DISHY DESTROYED! https://youtu.be/iOmdQnIlnRo ● TSP #181 - Starlink Dish Phased Array Design, Architecture & RF In-depth Analysis https://youtu.be/h6MfM8EFkGg ● Starlink Dish TEARDOWN! - Part 1 - SpaceX BugBounty is open during the Starlink Public Beta https://youtu.be/QudtSo5tpLk ● Starlink Dish TEARDOWN! - Part 2 - Serial console and login prompt. Can you guess Dishy’s password? https://youtu.be/38_KTq8j0Nw ● Starlink RECTANGLE Teardown Details - Working on trimming Rectangle dish to make a low-power panel https://youtu.be/AlvIWF0AXI0 There is also a good article on this at siliconchip.au/link/abjf Mobile phone service In August 2022, Starlink partnered with T-mobile in the United States to provide cellular phone service via V2 Starlink satellites, to begin testing in 2023. Unlike other satellite phone systems, this will use standard mobile devices. The service will initially support text messaging and voice calls. The total bandwidth available per satellite will be 2-4Mb/s, which equates to 1000-2000 simultaneous voice calls or millions of text messages across a cell. The intention is to use this service in remote areas with no existing cellular service or in emergencies. It will be initially offered in the USA only, but T-mobile will siliconchip.com.au Fig.9: a rectangular Starlink antenna facing up is visible toward the front of the aircraft. Source: Starlink. Figs.10 & 11: part of a Starlink antenna PCB. The PCB traces are curved to provide constant lengths for all traces (and RF signals don’t like sharp corners). Source: https://youtu.be/AlvIWF0AXI0 eventually partner with providers in other countries. The technological challenges in providing satellite connectivity to a standard mobile phone are significant. Firstly, by the time the phone signal travels around 550km or more, it will be very weak. With the satellite moving at around 27,000km/h, there will be a significant Doppler shift to account for. The phone will be electronically locked onto using a phased array antenna, which can steer the satellite beam to the phone’s location as the satellite moves in its orbit. According to Elon Musk, these are the most advanced phased-array antennas in the world. The satellites used for this service will be very large at 7m long, with a mass of 1.25 tonnes each, and the antenna will be 5 × 5m but folded for launch. They are too big for the SpaceX Falcon 9 rocket, so they will be launched on a SpaceX Starship rocket. SpaceX has also proposed a miniature version of the V2 satellite, which will fit on the Falcon 9. Each V2 satellite will represent one mobile phone cell covering an area of nearly 17,000km2. There will eventually be 30,000 V2 satellites (see Table 3), enough to cover the Earth’s entire surface of around 510 million km2! Until the whole constellation of V2 satellites is up, cell phone connectivity will only be when V2 satellites are visible to the user. Tesla cars will also be able to connect to Starlink cellular service in T-mobile coverage areas or other areas with other providers as they become available. Besides cellular coverage, V2 satellites will also provide internet connectivity through conventional ground or air stations. Collision avoidance and satellite lifespan Starlink satellites, indeed all satellites these days, need to be able to manoeuvre to avoid collisions with other satellites and adjust their orbit. They also need to be able to deorbit at the end of their life to prevent excessive debris from accumulating in orbit. Starlink satellites are equipped with Hall-effect thrusters (HETs), electric ion engines that use krypton gas as the propellant to effect the required manoeuvres. Even if the thruster malfunctions at the end of a satellite’s life, its orbit will decay due to atmospheric drag within about four years, and it will re-enter the Earth’s atmosphere and incinerate. Table 3 – proposed orbital shells & numbers of Starlink V2 satellites (29,988 total) Fig.12: part of the phased array ‘sandwich’ on the non-component side of the antenna PCB. Source: https:// youtu.be/AlvIWF0AXI0 siliconchip.com.au Inclination Altitude Orbital planes Satellites/plane Total satellites 53.0° 340km 48 110 5280 46.0° 345km 48 110 5280 38.0° 350km 48 110 5280 96.9° 360km 30 120 3600 53.0° 525km 28 120 3360 43.0° 530km 28 120 3360 33.0° 535km 28 120 3360 148.0° 604km 12 12 144 115.7° 614km 18 18 324 Australia's electronics magazine June 2023  19 Fig.13: Starlink satellites can lower their profile to avoid collisions. Source: https://astronomy.com/ news/2022/02/spacex-defendsstarlink-over-collision-concerns Avoiding collisions with the large number of satellites now in space is vital to avoid the Kessler syndrome. This is a phenomenon where a satellite collision generates a large amount of debris. That debris creates more collisions and debris, leading to a cascading effect, rendering orbital space unusable. Starlink uses an AI-based autonomous collision avoidance system with tracking data from the US Space Force 18th Space Defense Squadron (see siliconchip.au/link/abjg). Suppose a Starlink satellite is expected to come very close to another object and cannot manoeuvre out of the way. In that case, it can lower its solar panel to present a lower profile and less chance of collision, as shown in Fig.13. A major loss of Starlink satellites Starlink satellites are deployed at a much lower altitude than they operate at. This is for initial testing; if the satellite is entirely non-functional, the orbit will quickly decay at the lower altitude, preventing orbital debris from 20 Silicon Chip Fig.14: a 2019 photo taken at the Cerro Tololo Inter-American Observatory (CTIO) in Chile after the launch of the second batch of Starlink satellites. This 333-second exposure contains 19 streaks from satellites. Source: https://noirlab. edu/public/images/iotw1946a/ accumulating. If the satellite tests OK, its orbit is raised. On the 4th of February 2022, while 49 V1.5 satellites (Group 4-7) were deployed into low orbit, there was a major geomagnetic storm. This caused increased atmospheric drag, and 38 of the satellites deorbited, leaving only 11 to raise their orbits. configuration just after launch is changed to a ‘shark fin’ configuration for the solar panel when on-orbit, with the panel pointing away from Earth (see Fig.15). • They are also testing a roll manoeuvre during orbit raising to minimise reflections (see Fig.16). Interference with astronomy Naturally, Starlink has been a target for hackers. We do not recommend you do this but we present this as a matter of interest. A group has published “Glitched on Earth by Humans: A From the outset of the Starlink project, with its thousands of satellites, astronomers have had concerns about interference with their observations. Fig.14 is a very early example of image interference due to the second batch of Starlink satellites being launched in November 2019. Mitigation strategies include: • A ‘visor’ called VisorSat to cover radio antennas and other parts of the satellite. It is transparent to radio waves but stops light reflections (see Fig.17). • A light-absorbing coating on the satellite (‘DarkSat’); however, this makes the satellite get too hot, so the preference is for the visor. • The high-reflection ‘open book’ Australia's electronics magazine Hacking Starlink! Fig.15: the shark fin configuration reduces the amount of sunlight reflected towards the Earth. Source: https://astronomynow.com/2020/05/05/ spacex-to-debut-satellite-dimmingsunshade-on-next-starlink-launch/ siliconchip.com.au Black-Box Security Evaluation of the SpaceX Starlink User Terminal” at https://github.com/KULeuven-COSIC/ Starlink-FI that enables execution of arbitrary code on a Starlink User Terminal – see Fig.18. This has no stated purpose except for experimentation. We expect by now that the exploited security deficiencies have already been patched. This doesn’t bother Starlink; in fact, they encourage it under the “Bug Bounty Program”. Starlink will pay US$25,000 ($35,500) to anyone who finds a bug in their network. If you want to have a go, see siliconchip.au/ link/abjh Also, a group at The University of Texas at Austin devised a way to use Starlink signals as a GPS alternative. See siliconchip.au/link/abji Swarm Swarm (https://swarm.space/) offers low-bandwidth IoT (Internet of Things) global connectivity via dedicated SpaceBEE satellites (see Fig.19) – BEE stands for ‘basic electronic elements’. Swarm Technologies became a subsidiary of SpaceX in July 2021. Interestingly, the venture capital arm of the US CIA (Central Intelligence Agency), In-Q-Tel, lists Swarm as one of their start-ups (see https://www.iqt.org/ portfolio/). The satellites used for Swarm are thought to be the smallest commercially active satellites at ¼U (11 × 11 × 2.8cm), with a mass of about 400g. ¼U is a Cubesat designation referring to the size relative to a standard 1U cube of 10 × 10 × 10cm, although, strictly speaking, the Swarm satellite slightly exceeds the Cubesat standard. For more information, see our article on Cubesats in the January 2018 issue (siliconchip.au/Article/10930). The Swarm satellites are classed as ‘picosatellites’. They are in a sun-­ synchronous orbit at 450-550km with an intended constellation size of 150. A sun-synchronous orbit is a special kind of polar orbit (travelling roughly north-south) in which a satellite visits the same spot on the Earth’s surface at the same time each day. You can check when the next Swarm satellite comes into your area at https://kube.tools. swarm.space/pass-checker/ Solar panels and batteries power the SpaceBEEs, and the antenna unfolds when the satellite is deployed. siliconchip.com.au ORIENTATIONAL ROLL ARRAY MITIGATION DURING ORBIT RAISE The rolling satellite makes sunlight bounce off the smaller ‘knife edge’ of the array, reducing reflection. Fig.16: detail of the shark fin configuration. Source: same as Fig.14. VISORSAT ANTENNAE MITIGATION ON STATION On station, sun shade blocks sunlight from antennas, preventing reflection. Fig.17: the visor was added to later Starlink satellites to reduce the amount of light reflected at the Earth. Source: same as Fig.15. Fig.18: a “Modchip” board (red) and interface added to a Starlink antenna panel. Source: https:// github.com/KULeuvenCOSIC/Starlink-FI Fig.19: a Swarm SpaceBEE satellite, the tiniest satellite in commercial use. Australia's electronics magazine June 2023  21 IIoT gateway satellite mounted on rear of panel Wind speed & direction sensor Temp, humidity & barometric pressure sensor 12W solar panel Multiple mount points on base & rear Fig.20: an example of a commercial remote ModuSense Weather Station with built-in Swarm connectivity. Source: www.freewave.com/ products/modusense-weather-station/ Fig.21: the Swarm asset tracker fitted to an asset. Source: https://swarm.space/ swarm-announces-new-asset-tracking-product/ All satellites in orbit have to be able to be tracked for collision avoidance and orbital planning purposes. There were concerns about the trackability of these satellites due to their small size, but that was addressed by: • Incorporating a passive ‘Van Atta array’ radar retro-reflector, increasing their radar return strength. • The satellite has a GPS and sends its location when requested. • The 1m-long antenna improves visibility to ground-based tracking radars and other sensors (eg, by the US Space Surveillance Network). One of the main attractions of Swarm, apart from its global accessibility, is its low cost. Swarm devices and data plans are easily within reach of typical hobbyists and are also suitable for professional users. According to the Swarm website, a typical data plan costs US$5 ($7) per month per device and “provides 750 data packets per device per month (up to 192 bytes per packet or 144kB per month), including up to 60 downlink (2-way) data packets, AES256-GCM encryption for secure transmission, annual contract with no setup or hidden fees and data delivered via a REST API or Webhook to any cloud service”. That amount of data should be sufficient for hourly readings from a remote weather station, like the one shown in Fig.20. Devices available to connect to Swarm include an asset tracker (US$99/$140) to globally track assets with “one GPS acquisition every two hours with one transmission per twohour window” and “motion detection enabled”. The data rate is 1kbps (oneway) and the frequencies used are 137138MHz (downlink) and 148-150MHz (uplink). The device weighs 227g and the battery lasts 40+ days on internal power, or it can be connected to external power. Data can be accessed from the Swarm Hive – see Fig.21. Another Swarm device is the M138 Fig.22: a SparkFun M138 modem breakout board. The M138 is the device in the centre with “Swarm” written on it. Source: www. electronics-lab.com/sparkfuns-swarm-m138modem-satellite-transceiver-breakout-board/ 22 Silicon Chip Australia's electronics magazine modem, designed to be embedded in a third-party IoT device with data delivered via a REST API or Webhook to any cloud service. These cost US$89 ($125) with a minimum purchase of 25. For fewer units, the SparkFun M138 Modem breakout board can be purchased for US$149.95 ($215; www. sparkfun.com/products/19236) or a later version for US$199.95 ($285; www.sparkfun.com/products/21287) – see Fig.22. The M138 comes in a Mini PCB Express card form factor weighing 9.6g and includes a GNSS receiver for GPS and other navigational systems. Data is sent to the modem as a hexadecimal ASCII string, and two-letter NMEA-like (National Marine Electronics Association) commands are sent over a 3.3V serial (UART) link. The M138 modem is incorporated in the asset tracker mentioned above. Applications for the M138 modem with the breakout board include reading remote sensors such as for weather monitoring, remote equipment monitoring, asset tracking and environmental monitoring – see Fig.23. Finally, the US$449 ($637) Swarm Eval Kit (Fig.24) “is designed to provide the developer with an easy-to-use platform, with the included FeatherS2 – ESP32 board + OLED, a USB-C port and I2C port for sensors. FeatherWing add-on modules can provide a suite of additional capabilities”. “The Eval Kit includes a tripod, solar panel, batteries, and integrated VHF and GPS antenna. A live readout of RF background noise helps you siliconchip.com.au Fig.23: a mountaintop sensor array connected to Swarm. Source: https://swarm.space/ achieve the best possible link quality”. Devices can be connected via WiFi (AP or STA mode), USB, or serial interfaces, and data can be managed via the Swarm Cloud and REST API. The data rate is 1kbps with a maximum packet size of 192 bytes, and it supports AES256 GCM encryption. The command format is two-letter NMEA. The kit comes with an M138 modem described above and weighs 2.6kg. Starshield Starshield (www.spacex.com/ starshield/) is a derivative of Starlink specifically for US government and military use. According to the SpaceX website, Starshield’s initial focus is on Earth observation, communications and hosted payloads. Earth observation involves launching satellites with sensing payloads and delivering processed data directly to the end user (a government agency). This includes global communication with Starshield equipment, having an even higher level of security than Starlink, which is already end-to-end encrypted. Hosted payloads involve building appropriate satellite buses to suit customer needs. A satellite bus is the basic structural element of a spacecraft with equipment such as command and data handling, comms, power, propulsion, thermal control, attitude control and guidance. There is room to install a customer’s specialised payload, such as a sensor array to suit a specific mission. siliconchip.com.au This is less expensive than building a dedicated satellite from scratch. The spacecraft bus will be based on existing Starlink V1.5 and V2.0 satellites with a much greater solar array area. If desired, Starshield satellites can be made interoperable with Starlink via inter-satellite laser communications. Starlink applications can be rapidly developed because of SpaceX’s delivery systems, their manufacturing of the satellites and their ability to rapidly deploy large numbers of satellites in a single launch. Similar satellite systems AST SpaceMobile ast-science.com AST is launching a cellular broadband service in LEO that will allow the use of standard unmodified smartphones via a satellite with an enormous 64.4m2 phased array antenna. Its prototype BlueWalker 3 satellite launched in November 2022, orbits at 508-527km and has a field of view of 777,000km2. AST SpaceMobile eventually plans to deploy a constellation of 243 BlueBird satellites in orbits between 725740km in late 2023. The BlueBird satellites are similar to the prototype BlueWalker 3; later versions will have an even larger antenna array. Their partners are AT&T, Vodafone, Orange and Rakuten Mobile. BlueWalker 3 was launched as a ‘rideshare’ on a SpaceX Falcon 9 along with Starlink satellites. Globalstar www.globalstar.com/en-ap Globalstar offers a constellation of LEO satellites at 1400km altitude for Fig.24: the Swarm Eval Kit. Documentation can be found at https://swarm. space/documentationswarm/ and www.sparkfun. com/products/19236 under the “documents” tab. Australia's electronics magazine June 2023  23 Notes on accuracy and timeliness We have done our best to provide the most accurate and up-to-date information, but precise information on specific details of Starlink satellites and their numbers in orbit are either not published or are subject to variation as the commercial plans of SpaceX change with time. Remember that Starlink, Swarm and Starshield are systems that are being built even as you read this, and plans are constantly evolving. voice telephony with special phones and low-speed data. There are 24 2nd-generation satellites in the constellation. Users of the iPhone 14 in the USA and Canada can send emergency messages via this satellite system. Hughes Network Systems hughes.com Hughes Network Systems is a US provider of broadband internet services worldwide, mostly in remote areas. They also offer ‘cellular backhaul’ services via geostationary satellites (connections between parts of mobile networks) and internet services on aircraft. Their cellular backhaul services are via satellite because wires or traditional microwave links to a remote site are too expensive. Since geostationary satellites are used, there is the problem of high latency, meaning the system is unsuitable for videoconferencing and gaming, and there is a significant delay in voice communications. Inmarsat www.inmarsat.com Inmarsat uses 14 satellites in GEO orbit and offers a range of services and coverage options, including connectivity for 160,000 ships and 17,000 aircraft, plus government agencies and large businesses. Their services include tracking, high-speed internet, distress and safety services. A special phone or other terminal equipment is required to connect to Inmarsat. Malaysia Airlines Flight 370 that mysteriously disappeared used Inmarsat’s satellite phone service, and the analysis of that data determined it flew into the southern Indian Ocean. Iridium www.iridium.com Iridium uses 66 active satellites in polar LEO with a 100-minute orbital period in six orbital planes, 30° apart at an altitude of 780km. Communication is via dedicated equipment by Iridium or third parties (www.iridium. com/products/) and includes options for text, data, SOS, voice and others. The frequencies used are 1616.0MHz to 1626.5MHz, while gateway uplink is 29.1-29.3GHz, gateway downlink is 24 Silicon Chip 19.1-19.6GHz and inter-satellite links are at 22.55-23.55GHz. Kuiper Systems LLC www.aboutamazon.com/news/tag/project-kuiper Kuiper Systems is a subsidiary of Amazon. Its objective is to provide accessible and affordable satellite broadband internet to “unserved and underserved communities around the world”. It is building a constellation of 3276 satellites in LEO, with the prototype satellites to be launched in early 2023. The satellites will orbit between 590630km. Lynk Global lynk.world Lynk wants to create a “cell tower in space” so standard mobile phones can connect to its satellites in LEO at 500km. It will focus on providing coverage to people in ‘third-world’ countries so they can use cheap, affordable phones. They will also cover areas of the world where there is no mobile signal coverage or coverage is down due to a natural disaster. Lynk is currently in a testing phase and will need 1000 satellites for full broadband coverage, which it expects to achieve by 2025, and ultimately a full constellation of 5000 satellites. O3b www.ses.com O3b uses a constellation of 20 satellites in medium Earth orbit (MEO), 8000km above the surface, for relatively low latency. The idea is to provide internet connectivity to rural and remote areas at altitudes between 50°N and 50°S (covering 96% of Earth’s population) for mobile network operators, telcos, enterprises and government. Examples include telemedicine, electronic banking and virtual classrooms in places like American Samoa, Brazil, Chad, East Timor and Papua New Guinea. 4G+ mobile phone services can be offered in places like the Cook Islands by providing backhaul services. They can also provide internet connectivity at sea, such as on cruise ships. For the next generation of services, O3b is also launching mPower Australia's electronics magazine satellites for government, military and various enterprises and will have 11 satellites in MEO, each of which can produce 5,000 digitally-formed beams directed to various users. OneWeb oneweb.net OneWeb is in the process of launching a 648-­satellite constellation into LEO (1200km) to provide global broadband internet services by the end of 2023. Customers are intended to be government, military, telcos and remote communities, not individuals. Orbcomm orbcomm.com/en/partners/connectivity/satellite Orbcomm offers a constellation of Isat Data Pro satellites in GEO orbit and ORBCOMM OG2 in LEO for satellite IoT (Internet of Things) connectivity. Project Loon is a now-defunct proposal to use high-altitude balloons at 18-25km to create a wide-area wireless network. Manoeuvring to stay on station was by adjusting buoyancy to find winds in the correct direction. Links • Find naked eye visibility of Starlink satellites in your area at https:// findstarlink.com/ Note that Starlink satellites are less visible now than they used to be due to measures taken to minimise the disturbance to astronomers. An App is also available for Android and iOS devices. • See the present location of the Starlink constellation, as well as OneWeb and GPS constellations, at https:// satellitemap.space/ • There is an interactive map to determine availability at your service address at www.starlink.com/map While the availability of the satellite service is global, there still needs to be ground-level national agreements and billing arrangements. • There is a video of an Australian review of the Starlink system for travel in an RV titled “The Truth About Starlink RV! Is It Worth It?” at https:// youtu.be/d29jURzZGe0 • A video of the ‘satellite train’ shortly after launch, before the satellites were put in their final orbits, titled “Starlink Satellites train seen in the sky” at https://youtu.be/ihVuz8uM1qU • A very interesting and simple project to receive Starlink beacon (tracking) signals with a Raspberry Pi computer, a software-defined radio and a satellite antenna receiver (LNB): siliconchip.au/link/abjm SC siliconchip.com.au