Satellite 🛰 are a bodies or object natural existing in orbit in space. Artificial satellites are objects that are intentionally placed into orbit around the Earth or other celestial bodies such as planets or moons.
These satellites are man-made and are launched using rockets. There are currently over 3,000 active artificial satellites orbiting the Earth, serving a variety of purposes such as communication, navigation, Earth observation, weather forecasting, scientific research and exploration, and surveillance. As the number of artificial satellites in orbit increases, the risk of collisions between them also increases.
Thus, satellite operators and space agencies monitor their orbits carefully to avoid collisions and prevent potential debris that could harm other satellites or spacecraft. The study of artificial satellites and their orbits is an important field of study in the science of space engineering and planetary geodesy.
As of March 2, 2023, there are 5,465 active artificial satellites orbiting the Earth , according to Statista. However, please note that the number of satellites in orbit may change over time as new satellites are launched and old ones are decommissioned or destroyed.
- Global Positioning System (GPS)
- Galileo System (Europe)
- Global Satellite Navigation System (GLONASS)
- BeiDou Navigation Satellite System (BDS) (More than 30 Satellites)
- Indian Regional Navigation Satellite System (IRNSS)
- Quazi-Zenith Satellite System (QZSS)
- Weather Satellites
- Communication Satellites
Note that there are currently other satellite positioning systems that are in development or under construction, such as the Australian SBAS and the South Korea KASS, but they have not yet been fully deployed.
Satellite navigation systems such as GPS, GLONASS, Galileo and BeiDou make use of satellites placed in specific orbits to provide global coverage. Here is a list of the common satellite navigation orbits:
- Geostationary orbit (GSO)
- Low Earth orbit (LEO)
- Medium Earth orbit (MEO)
- Highly Elliptical Orbit (HEO)
- Inclined Geosynchronous Orbit (IGSO)
- Polar orbit and Sun-synchronous orbit (SSO)
- Transfer orbits
- Geosynchronous Earth Orbit (GEO): This orbit is used by satellite communication systems, but not for navigation systems. Satellites in GEO orbit at an altitude of approximately 36,000 km and have an orbital period of 24 hours, which keeps them stationary above the same point on Earth.
- Low Earth Orbit (LEO): This orbit is used by some satellite constellations such as the Iridium system. Satellites in LEO orbit at an altitude between 700 to 1500 km and have an orbital period of around 1 to 2 hours. LEO is used for satellite-based systems that require rapid data transmission, such as weather monitoring or earth observation.
- Medium Earth Orbit (MEO): This orbit is used by the GPS, Galileo, and BeiDou systems. Satellites in MEO orbit at an altitude of approximately 20,000 km and have an orbital period of 12 hours.
- Highly Elliptical Orbit (HEO): This is an elongated orbit that is used by some communication satellites and navigation satellites such as Russia’s GLONASS. Satellites in this orbit have a high altitude at apogee (the furthest point) and low altitude at perigee (the closest point), allowing them to provide coverage in high latitudes. Satellites in HEO have an elliptical orbit with an apogee (farthest point from Earth) of around 36,000 km and a perigee (closest point to Earth) of around 500 km.
- Inclined Geosynchronous Orbit (IGSO): This orbit is used by the Indian Regional Navigation Satellite System (IRNSS), which operates in three orbital planes with three satellites in each plane. The satellites in this orbit have an altitude similar to GEO, but their orbits are inclined at an angle of about 29 degrees.
- Polar orbit and Sun-synchronous orbit (SSO): A polar orbit is a type of orbit around the Earth that goes over the North and South Poles. This type of orbit allows satellites to cover the entire planet as it rotates below, making it useful for remote sensing and scientific research. As the Earth rotates beneath the satellite, the satellite can take images of different regions on the Earth’s surface. A Sun-synchronous orbit is a type of polar orbit that is synchronized with the Sun, meaning that the satellite passes over the same point on the Earth’s surface at the same local solar time . This type of orbit is commonly used for Earth observation and remote sensing, because the consistent lighting conditions mean that the images taken by the satellite will have the same lighting and shadow patterns. In a sun-synchronous orbit, a satellite will pass over the equator at the same local solar time on each pass, allowing for consistent illumination of the Earth’s surface. Example of such satellites are:
- Transfer orbits: A transfer orbit refers to an orbital maneuver used to transfer a spacecraft from one orbit to another. One of the most common types of transfer orbits is the Hohmann transfer orbit, which involves moving a spacecraft from one circular orbital path to another by making an elliptical transfer orbit. The spacecraft’s apogee is then transferred to the other orbit. In order to achieve this type of transfer, two main impulses are required – one to leave the initial orbit and one to enter the final orbit. The Hohmann transfer orbit is typically the most energy-efficient way to move a spacecraft between orbits, as it requires minimal energy to make the transfer. In general, transfer orbits are used in space missions to achieve a wide range of objectives, from exploring a planet to delivering a satellite into orbit around the Earth. The type of transfer orbit used in a mission will depend on the specific requirements of the mission, such as the destination, available resources, and overall mission objectives.
- Delta V calculator
- Nano Orbital Transfer System
- NASA’s Cassini spacecraft
Overall, the MEO is the most commonly used orbit for satellite navigation systems as it provides a good balance between coverage and signal strength.
These different types of orbits are not unique to Satellite Navigation systems and can be used by a variety of different satellites for different applications.
How do Artificial Satellites work
More Information ℹ
- Number of satellites in orbit
- UCS Satellite Database
- Space Telescope Science Institute
- Why Satellites are critical for IoT