Internet from Above: The Three Space Highways
A Tale of Three Orbits: GEO, MEO, and LEO
News reports from the space industry are frequently punctuated by the number of payloads carried per mission: "SpaceX Falcon 9 rocket launches 26 Starlink satellites to orbit," or "ISRO's PSLV rocket deploys 19 satellites." This variance in payload capacity is a direct effect of satellite design and, more critically, the chosen orbital destination. The selection of an orbit is a consequential decision, with altitudes varying dramatically—from as low as 250 km to as high as 36,000 km above the Earth's surface. This vast difference is fundamental to how a satellite network is structured and how it operates.
Where our previous post explored the purpose of satellite internet, this one will begin to chart how the technology itself functions. Its architecture is broadly divided into two domains: one on the ground and another in space. The space segment, as the name implies, is the realm of the satellites themselves.
The Space Segment: Satellites Up Close
Satellites are the most capital-intensive component of this celestial network. They are equipped with communication payloads—antennas and transponders—tasked with receiving and transmitting data. Built for endurance, these satellites must withstand the harsh environment of space for their entire service life, which can range from five to twenty years. Given that post-launch repairs are next to impossible, a meticulous deployment plan is crucial. This plan hinges on fundamental choices like the satellite's orbital altitude, which in turn dictates the design of its antennas and overall capabilities.
A Tale of Three Orbits: GEO, MEO, and LEO
Satellites are deployed into specific orbital altitudes, which are broadly categorised into three main types: Geostationary Orbit (GEO), Medium Earth Orbit (MEO), and Low Earth Orbit (LEO).
Geostationary Orbit (GEO)
Perched at a precise altitude of 35,786 km directly above the equator, a GEO satellite's orbital period matches the Earth's rotation. This perfect synchronisation makes it appear stationary from the ground, a fixed point in the sky.
The primary advantage of this high altitude is the immense coverage area. A single GEO satellite can blanket nearly a third of the Earth's surface, making it ideal for broad, regional coverage. A prime example is Viasat's Global Xpress (GX) system, which utilises a fleet of geosynchronous orbit (GEO) satellites for global reach.
GEO satellites often operate as simple "bent-pipes." They receive a signal from a ground station, amplify it, and relay it back down to another location without any data processing. This simplicity means the satellite itself has less complex equipment, with most of the heavy lifting handled by the ground stations.
However, GEO's advantages are also the source of its two major drawbacks: size and latency. To communicate effectively across such vast distances, GEO satellites need large antennas and powerful transmitters, making them bulky—often the size of a school bus. Launching these heavyweights into such a high orbit is a costly affair.
The most significant limitation, however, is propagation latency. The sheer distance results in a noticeable signal delay, making GEO satellites unsuitable for time-sensitive applications like video conferencing, online gaming, or real-time financial transactions where low latency is the benchmark.
Medium Earth Orbit (MEO)
MEO satellites occupy the middle ground, orbiting at altitudes between 2,000 km and 35,786 km. They offer a compromise between the vast coverage of GEO and the low latency of LEO.
Their lower altitude means a smaller coverage area per satellite, necessitating a larger constellation to achieve global service. The O3b constellation, for instance, uses 20 MEO satellites to provide coverage across most of the globe, excluding the polar regions. While their latency is lower than GEO, it is still a significant consideration for real-time applications. These car-sized satellites are still relatively heavy and also expensive to launch.
Low Earth Orbit (LEO)
Flying at altitudes below 2,000 km, LEO satellites are much closer to Earth. This proximity is their defining advantage, resulting in very low latency comparable to that of terrestrial fibre-optic networks. Their smaller size, often no bigger than a large table. They are packed with more advanced technology for on-board processing, where data can be managed and routed directly on the satellite.
Their compact nature also drastically reduces launch costs, as dozens can be deployed in a single mission. The trade-off for this low altitude is a much smaller coverage area. A single LEO satellite's footprint might only cover a large metropolitan area.
To provide continuous global coverage, LEO systems rely on "megaconstellations" comprising hundreds or even thousands of satellites. Starlink, for example, already has over 7,000 satellites in orbit and plans for tens of thousands more. These megaconstellations represent the cutting edge of satellite internet technology, attracting immense interest and investment from both industry and governments.
Given their growing dominance and transformative potential, our focus will shift to these LEO satellite internet constellations in the following posts.