LEO satellites are placed in low Earth-centred orbit at an altitude of 2,000km or less. By contrast, most commercial communications satellites are placed in high Geosynchronous Earth Orbit (GEO) slots 35,786km above the Earth's equator that allows satellites to match the Earth's rotation, thus appearing stationary to any point on the ground. Communications satellites placed in LEO require the lowest amount of energy for orbital placement and have high bandwidth and very low latency compared with satellites placed in more distant GEO and Medium Earth Orbit (MEO).
Communication Satellite Orbits Distance and Latency
ms=milliseconds RTT=Round Trip Time
Sources: IDC Canada; Telesat, 2019
The much lower distance from Earth for LEO satellites provides a very fast orbital period, affording a small field of view resulting in a much smaller coverage area and short time to communicate with a fraction of the Earth at a time compared with GEO satellites. To overcome that limitation, a large constellation of LEO satellites is required to maintain permanent connectivity with ground terminals which must also track the LEOs.
Proponents of LEO satellite technology argue the constellations will be able to deliver ubiquitous high-speed broadband Internet access throughout the globe with fiber-optic quality speed and much lower latency.
Telesat's Lightspeed constellation will now comprise 298 satellites, with 78 of the satellites to circle the poles in 1,015km altitude polar orbits and the remaining 220 satellites to follow inclined orbits at 1,325km.
Telesat has a C$3 billion contract with French-Italian aerospace manufacturer, Thales Alenia Space, to build its Lightspeed satellites. The first batch, each with 10-year-lifespans, are planned for launch in early 2023 aboard Jeff Bezos's Blue Origin rockets.
Telesat Planned Lightspeed LEO Constellation and Artist Conception of Lightspeed LEO Satellite