| Satellite Telemetry | ||
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| Non-Terestrial Services | The mobile phone network is referred to as a Terestrial or land based system. Satellites by contrast are referred to as "non-terestrial". The first satellite was launched by the Russians in 1956 and numbers increased year on year. However in each of the last few years the number of satellites in orbit at the end of teh year has been double that of what it was at the start of the year. |
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| GeoStationary Satellites | If a satellite is sent far enough away from the earth, there is a radius at which the satellite will orbit the earth at the same rate as the earth is turning. The satellite is then referred to as "geo-stationary" or "geo-synchronous" and they typically orbit at a radious of 36000km. Dish antennae on the satellite will have a fixed and predictable foot-print, which enables the operators to know exactly which parts of the globe the satellite will cover. The size of the footprint means that only a small fleet of satellites is required in order to achieve global coverage. The downside of this approach is that it takes a long time for radio signals to travel out to the satellite and back - a round trip time of about 0.5 sec. This makes the sending of packetised data more complex, as the protocol which is responsible for breaking transmitted data into packets and re-assembling them at the other end, must be capable of accommodating the long delays. The long distance means high power levels are required: a power of 1mW (a candle power) can be made to reach the satellite if it is passed through a 60dB gain dish antenna (3.7m diameter). But as the dish size is reduced, the power must go up - if the dish size halves, the power must go up 4 times. |
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| Low Earth Orbiting (LEO) Satellites | Satellites tend to have a fixed life and this is governed by how much fuel they can carry: fuel is burned to make small changes to the satellite's orbit to keep it in the correct position. When the fuel runs out, the satellite is brought out of orbit and allowed to burn up as it re-enters the atmosphere. Geo-stationary satellites are large. Firstly so they can carry enough equipment to give them the capacity to run cost effectively and secondly so they can carry enough fuel. If satellites are kept in a lower orbit they can be smaller, cheaper and easier to build and deploy. But at the lower altitudes they rotate at a different rate to the earth, so the satellite's footprint is not only smaller, it is continually changing. A much larger fleet of satellites is required in order to achieve global coverage. Many early networks were premised on requiring 30 to 60 satellites but, as the application shifts more and more towards high speed Internet services, the size of the required fleet has increased to bwteeen 600 and 4000 satellites. |
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| Iridium | Iridium is probably the best known and longest lived of the satellite services. If you want dependable, reliable, robust satellite connectivity, Iririum is the first point of call. But, even though the Iridium fleet is being progressively updated, it suffers from low throughput and high end user charges. The latter being a dis-incentive to many users. Adding an Iridium Edge modem to a YDOC unit makes for a simple satellite RTU and there are hundreds of these units running around the world. On the environmental monitoring front, Iridium services are suitable for sites with low sensor count and infrequent data transmissions - for example for water leve monitoring stations. But sending 15 minute data from an automatic weather station starts to push the limits of affordability. |
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| Starlink | Starlink is the best known of the new breed of competitors to Iridium. The main aim of Starlink has been to provide high speed internet access to customers who are unable to obtain satisfactory data speeds over terestrial services. And Starlink have been very successful in this regard. Stalink had over 2000 satellites in operation in mid 2024. It has had the advantage that in SpaceX, it has its own fleet of rockets with which to launch the satellites. When Starlink purchased and promptly closed the competing Swarm satellite system, they saw an opportunity to add low speed data services to their network. All subsequent satellites were subsequently fitted with modified cellular base stations and the standards for 4G (and 5G) services were updated to allow for satellite (non terestrial) services. Starlink have tested SMS messaging over the system and have set a commercial launch date. This will be followed by their narrow band data service. Unfortunately Starlink have targetted the extremely low end of this market - the same market targetted by LoraWan, that is for low volume, low speed data from battery powered devices. The Starlink Cat M1 service will not allow direct two way connectivity to nodes, which takes away one of the biggest features of the ground based service. To get the same functionality offered by LTE-M and NB IoT, users will have to wait until Stalink launch their "Direct to cell" service, which will allow holders of compatible handsets to make voice calls via the satellite service. Because vocie calls in a 4G/5G environment are really data calls, the same functionality will enable modems to be used for data transmission. YDOC have been testing a direct to satellite modem and hope to offer a direct to cell option soon after the service is launched. |
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| Amazon - Project Kuiper |
Amazon has been late to market with their competing system. But as Amazon, like Starlink, have developed their own launch capacity, they will be able to increase their fleet dramatically over the coming years. One reason for the delays has been the issus with getting Amazon's launch rockets working properly. Geoff Bozos of Amazon hopes to be able to compete head to head with Elon Musk's Starlink once Amazon has enough satellites in operation. |
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| European LEO | If you don't trust the US based technology duopoly, then there are alternatives coming to the fore. In Europe there are private and public systems under development: OneWeb: purchased from bankruptcy by Bharti Global (India) and the UK government and then received funding from the French. It was subsequently purchased by EutelSat and is now at the stage of having to repalce the 650 satelite fleet. The first 100 replacement satellites will launch in 2026 IRIS: a consortium with SpaceRise, SES, EutelSat and Hispasat which is planning a mix of Low orbit and geo-syncrhonous satellites. A key goal is to provide a "resiliant" communications infrastructure for government and private customers - one which is independent of the US owned systems. You can expect a concerted effort from the Europeans to attract southern hemisphere clients: after all, it gives them a way of filling the satellites data channels for the half of the day when they are not flying over Europe. | |
| China and LEO | The Chinese government has a plan to launch two LEO networks with a total satellite count of 13000. As they have done in so many fields, the Chinese will compete on cost. This will make their service very attractive in developing countries. The question for countries like Australia, will be whether using a Chinese satellite provider constitutes a risk to data security or not. |
