“With thousands of satellites, each network could beam down tens of terabits per second, filling gaps left by land-based services.
The team estimated each network’s total throughput based on the most recent petitions filed by each company to the FCC. Petitions include technical specifications such as the total number of satellites, the planes and inclination angles at which they will orbit, and the communication capabilities between satellites. Using these data, the team created simulations of each network’s satellite configuration and ran the simulations over a single day, taking “snapshots” every minute of each satellite’s position in the sky. They also recorded its cone of coverage, or the volume of space over which a satellite could communicate in that moment.
The researchers used an atmospheric model to vary the surrounding conditions in the moment, as well as a demand model that estimated the number of users within the satellite’s coverage area, based on a grid map of world population. They also used an algorithm to compute the number of gateways, or ground stations that the satellite would need to relay to in order to reach the most number of users. Finally, they used a link budget model to compute the satellite’s throughput.
“For each of these frozen snapshots, we run a link budget 10,000 times, each time using a different atmospheric condition, like rainy versus cloudy, and we see how the throughput, or data-rate changes,” Pachler explains. “In the end we put this together, see what the minimum throughput is, which is the bottleneck, then over all these different samples we take during the day, we get an average throughput for the entire network.”
Overall, they found that all four networks had comparable throughputs of tens of terabits per second, though each network achieves this through different configurations. For instance, Telesat has fewer satellites in its network (around 1,600), each with advanced capabilities compared to satellites in OneWeb’s network, which plans to compensate with many more satellites (more than 6,000).
SpaceX’s Starlink constellation is the closest to becoming operational, having launched more than 1,000 of its planned 4,400 satellites. In its most recent FCC filing, the company reduced the altitude of the satellites’ orbits, which the team found increased its overall throughput.
The team found that Amazon’s satellite configuration would provide the highest data rates of the four networks, if it were to also build out a disproportionately large number of gateway antennas, which the team estimates to be about 4,000 around the world. “On paper, Amazon has a higher throughput. But these companies are filing new iterations to outdo themselves and get more capable systems. So these are exciting times,” Del Portillo says. “Everyone is talking about these constellations in the space industry. Some people think they will change the world, others think they’ll fail. But there’s a lot of innovation going on.”
This research was funded, in part, by satellite and telecommunications company SES S.A.”