Types of Satellites and Applications

• Communications Satellite.
• Remote Sensing Satellite.
• Navigation Satellite.
• Geocentric Orbit type staellies – LEO, MEO, HEO.
• Global Positioning System (GPS)
• Geostationary Satellites (GEOs)
• Drone Satellite.
• Ground Satellite.

Used for global communications coverage, satellite mega-constellations are present in the outer atmosphere of the planet and are connected to each other through the technology of inter-satellite communication.

History. The Iridium satellite constellation was conceived in the early 1990s as a way to reach high Earth latitudes with reliable satellite communication services. Early calculations showed that 77 satellites would be needed, hence the name Iridium, after the metal with atomic number 77.

But a constellation of many satellites can stay in low Earth orbit while ensuring that one or several of its members is in range of ground-based transmitters and receivers at all times. That means the constellation can talk to, or keep an eye on, the same places on Earth at all times.

Examples of passive satellite sensors are those aboard the Landsat, SPOT, Pléiades, EROS, GeoEye, and WorldView satellites. Active sensors provide their own source of energy to illuminate the objects and measure the observations.

Companies are placing satellites into orbit at an unprecedented frequency to build ‘mega-constellations’ of communications satellites in Low Earth Orbit (LEO). In two years, the number of active and defunct satellites in LEO has increased by over 50%, to about 5000 (as of 30 March 2021).

The GPS constellation calls for 24 satellites to be distributed equally among six orbital planes….Navigational satellite constellations.

A satellite constellation is a group of artificial satellites working together as a system.

To accomplish this, each of the 31 satellites emits signals that enable receivers through a combination of signals from at least four satellites, to determine their location and time. GPS satellites carry atomic clocks that provide extremely accurate time.

Unlike GEO satellites, LEO satellites also fly at a much faster pace because of their proximity to Earth. Because GEO satellites orbit at such a high altitude, however, there is a longer communication time lag (latency) as the signals travel to and from these satellites.