Types of Orbits and their applications

Understanding the various orbit types is critical to understanding how satellites and spacecraft orbit the Earth and other celestial bodies. Each orbit type has a specific purpose depending on its altitude and trajectory, affecting everything from communications to Earth observation.

This article explores the main orbit types: geostationary orbit (GEO), low Earth orbit (LEO), medium Earth orbit (MEO), polar orbit, sun-synchronous orbit (SSO), transfer orbit, and geostationary transfer orbit (GTO).

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But first, let’s understand the science of how objects stay in orbit.

How do objects stay in orbit?

According to Newton’s first law of motion, an object in motion will stay in motion unless acted upon by an outside force. Without gravity, a satellite orbiting the Earth would continue to travel in a straight line into space. However, gravity would pull it back toward Earth, creating a constant tug-of-war between the satellite’s forward momentum and the pull of gravity.

For an object to stay in orbit, its momentum and gravity must be perfectly balanced. If an object’s forward momentum is too high, it will escape Earth’s gravity and drift off into space. Conversely, if momentum is too low, gravity will pull it down, causing it to fall. When these forces are balanced, the object keeps falling toward Earth, but its high sideways velocity ensures that it never actually hits the Earth’s surface.

Now let’s delve deeper into the different types of orbits in space.

Track types and their applications

Geostationary Earth Orbit (GEO)

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Image: ESA

Geostationary orbit (GEO) is a unique and significant orbit in which a satellite appears to remain stationary relative to a point on the Earth’s surface. GEO satellites are located approximately 35,786 km (22,236 miles) above the equator and orbit the Earth from west to east, in line with the Earth’s rotation. This means they complete one orbit in 23 hours, 56 minutes and 4 seconds, the same amount of time it takes the Earth to rotate once on its axis.

To achieve this synchronization, GEO satellites must travel at speeds of approximately 3 kilometers per second. This precise speed ensures that the satellite maintains a fixed position relative to the Earth’s surface, effectively hovering over the same point. This feature is particularly beneficial for communications satellites, weather monitoring systems, and broadcast services.

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Image: ESA

As the name implies, low Earth orbit (LEO) is an orbit relatively close to the Earth’s surface. Typically, LEO is defined as an orbit between 160 km (100 miles) and less than 1,000 km (620 miles) above Earth. To put this in perspective, commercial aircraft typically fly no higher than about 14 km (8.7 miles), and even the lowest LEOs are more than ten times higher than typical aircraft altitudes.

Unlike geostationary orbit (GEO) satellites that must orbit along the Earth’s equator, LEO satellites have the flexibility to follow a variety of orbital paths because their orbital plane can be tilted. This flexibility is one of the reasons why LEO is a popular choice for many satellite missions.

Low Earth orbit’s distance from Earth offers several advantages. It’s the orbit of choice for high-resolution imaging satellites, as the shorter distance to the ground allows for clearer, more detailed pictures. Additionally, the International Space Station (ISS) orbits in low Earth orbit because the shorter distance simplifies travel to and from space, allowing astronauts to complete their journeys more efficiently. Satellites in low Earth orbit travel at 7.8 kilometers per second, which means they orbit the Earth approximately every 90 minutes. Therefore, the ISS orbits the Earth about 16 times per day.

However, the rapid movement of low-Earth orbit satellites across the sky presents challenges to the communications mission. Their fast movement requires ground stations to constantly track them, which can be cumbersome. To address this problem, communications satellites in low-Earth orbit often work as part of large constellations. These constellations consist of multiple satellites that work together to form a network that ensures continuous coverage. By deploying multiple satellites in coordinated orbits, these constellations form a “network” around the Earth that provides widespread and consistent coverage.

Medium Earth Orbit (MEO)

Medium Earth Orbit (MEO) is between Low Earth Orbit (LEO) and Geostationary Earth Orbit (GEO), and is typically between 2,000 km (1,240 mi) and 35,786 km (22,236 mi) above Earth. Satellites in MEO orbits typically take several hours to orbit the Earth, at speeds of 3 to 4 km per second.

MEO is mainly used for navigation satellites, such as those in the Global Positioning System (GPS). These satellites cover a larger area than LEO satellites and provide continuous and accurate position data necessary for global navigation and positioning. Unlike GEO satellites that are fixed to a specific area, MEO satellites can cover different parts of the earth, making them essential for comprehensive navigation systems.

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Polar orbit and Sun-synchronous orbit (SSO)

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Image: ESA

Satellites in polar orbits cross the Earth’s surface from north to south, passing over the poles. These orbits are classified as low Earth orbits and are typically between 200 and 1,000 kilometers (124 and 620 miles) above the Earth. Although satellites in polar orbits do not need to fly directly over the South Pole, deviations of up to 20 to 30 degrees are still considered polar orbits.

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A special variation of a polar orbit is a sun-synchronous orbit (SSO). Satellites in an SSO are unique in that they maintain a fixed position relative to the sun. This synchronization ensures that the satellite always observes the same point on the Earth at the same local solar time. For example, a satellite in an SSO might pass over Paris every day at noon.

This consistent timing is critical for a variety of applications. It allows scientists and analysts to take a series of images of the same location under similar lighting conditions, which is essential for monitoring changes over time. For example, tracking weather patterns, observing natural disasters such as forest fires or floods, and studying long-term environmental issues such as deforestation and sea level rise all benefit from this consistent observation.

Typically, satellites in an SSO are positioned to constantly observe dawn or dusk. By orbiting in this way, they avoid being obscured by the Earth, ensuring continuous data collection. Typically, satellites in an SSO orbit at altitudes between 600 and 800 km (373 and 497 mi) and travel at speeds of about 7.5 km/s at the higher end of that range.

Transfer orbit and geostationary transfer orbit (GTO)

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Image: ESA

Transfer orbits are used to transfer satellites from one orbit to another so that they can be deployed in a designated operational orbit. A common transfer orbit is the geostationary transfer orbit (GTO), which is used to transfer satellites from low earth orbit (LEO) to geostationary orbit (GEO).

After launch, the rocket reaches space along the trajectory shown by the yellow line in the figure. After reaching the predetermined position, the rocket releases the satellite, which then flies along the elliptical path shown by the blue line. This elliptical orbit takes the satellite farther and farther away from the earth. In this orbit, the farthest point from the earth is called the apogee, and the closest point to the earth is called the perigee.

When the satellite reaches the apogee of the geostationary orbit (GEO) at 35,786 km, it fires its engines and enters the circular geostationary orbit (GEO), as shown by the red line in the diagram. Therefore, the GTO is characterized by the blue track, connecting the yellow orbit and the red geostationary orbit.

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in conclusion

Different types of orbits (GEO, LEO, MEO, Polar, SSO, Transfer Orbit, and GTO) play a critical role in space missions and satellite operations. By understanding these orbits, we can gain insight into how satellites provide communications, navigation, and Earth observation services. Each orbit offers unique advantages based on altitude, trajectory, and purpose, highlighting the complex planning required to successfully execute space missions. Mastering these orbital concepts is essential for anyone interested in space and satellite technology, whether for scientific exploration, practical applications, or academic research.

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Category: Optical Illusion