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Synchronous Orbits

Synchronous Orbits

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Synchronous orbits are when a body, like a satellite, orbits the earth in the same direction as the earth rotates. This means that it takes the same amount of time for the satellite to complete one orbit as it does for the earth to do a full rotation. There are different types of synchronous orbits, based on how long it takes for them to complete one orbit.

Geosynchronous orbits

Synchronous orbits that take the same amount of time as the earth to complete one orbit are called high earth orbits. They're about 36000 km above the equator. The altitude is measured relative to the equator because the earth is not perfectly round. Objects in these orbits appear to stay in the same spot in the sky when viewed from earth. This makes them perfect for things like communication.

Geostationary orbits

Geosynchronous orbits are positioned directly over the equator. Satellites in this orbit always have a view of the same part of the earth, making them perfect for weather monitoring and search and rescue systems.

Geostationary and geosynchronous orbits
Geostationary and geosynchronous orbits

To find the radius of orbit of a satellite in a geostationary orbit, we can use the equation:

F_gravity = F_centripetal

where F_gravity is the force of gravity acting on the satellite due to the earth, F_centripetal is the centripetal force required to keep the satellite in orbit, M is the mass of the earth, m is the mass of the satellite, r is the radius of the orbit, and ω is the angular speed.

The force of gravity acting on the satellite due to the earth can be calculated using the equation:

F_gravity = G * M * m / r^2

where G is the gravitational constant, M is the mass of the earth, m is the mass of the satellite, and r is the radius of the orbit.

The centripetal force required to keep the satellite in orbit can be calculated using the equation:

F_centripetal = m * ω^2 * r

where ω is the angular speed of the earth, which can be calculated as:

ω = 2 * π / T

where T is the time period of the earth in seconds.

Since the satellite is in a geostationary orbit, its angular speed is the same as the angular speed of the earth. Therefore, we can substitute the value of ω in the equation for F_centripetal.

Equating F_gravity and F_centripetal, we get:

G * M * m / r^2 = m * ω^2 * r

Simplifying and rearranging, we get:

r = (G * M / ω^2)^1/3

Substituting the values of G, M, and ω, we get:

r = (6.67 * 10^-11 * 5.97 * 10^24 / (2 * π / 86400 s)^2)^1/3

Solving for r, we get:

r = 4.22 * 10^7 m

To find the altitude of the satellite, we need to the radius of the earth the radius of thealtitude = r - 6.37 * 10^6 m

Substituting the value of r, we get:

altitude = 3.58 * 10^7 m

Therefore, the radius of orbit of a satellite in a geostationary orbit is approximately 4.22 * 10^7 m and its altitude is approximately 3.58 * 10^7 m.

Semi-synchronous orbits

Synchronous orbits with a period of half a day and an approximate distance of 20200 km are considered to be in the category of medium earth orbits. These orbits are also known as Molniya orbits, named after the Russian Molniya communication satellites that were first placed in this type of orbit.

The altitude of a Molniya orbit is typically around 20000 km above the earth's surface. This altitude classification is often referred to as the "high earth orbit" or "HEO" range, as it is higher than low earth orbit (LEO) and medium earth orbit (MEO) ranges.

In addition to being useful for geolocation purposes, Molniya orbits are also commonly used for communication and navigation systems in the polar regions, where the curvature of the earth makes it difficult for traditional geostationary satellites to maintain coverage.

Low earth orbits

Low earth orbits (LEO) are orbits that are close to the earth's surface, typically ranging from 160 km to 1000 km in altitude. Satellites in LEO are designed for a variety of applications, including earth observation, remote sensing, and communication.

One of the main advantages of LEO is that the satellites can cover a large area of the earth's surface quickly due to their high angular speed. This makes them ideal for applications that require frequent coverage of a particular location or the entire earth's surface, such as weather monitoring, disaster response, and scientific research.

LEO satellites are also cheaper to launch compared to higher orbit satellites and require less powerful transmitters for communication. Due to their low altitude, LEO satellites experience less signal delay, resulting in better-quality communication.

Most LEO satellites are placed in a polar orbit, which means that they pass over the north and south poles on each orbit. This allows them to cover the entire earth's surface over time. Satellites in polar orbits are also ideal for applications such as remote sensing and mapping, as they provide consistent and comprehensive coverage.

In summary, low earth orbits are used for a wide range of applications, including earth observation, remote sensing, and communication. They are advantageous due to their high angular speed, low launch cost, and comprehensive coverage of the earth's surface.

Medium earth orbits

Medium earth orbits (MEO) are orbits that range from 2000 km to 35786 km in altitude. Satellites in MEO are typically placed in a specific orbit with a tuned radial distance to achieve a specific period and shape for their intended function.

One example of a specialized MEO is the Molniya orbit, which is an elliptical orbit that allows satellites to efficiently observe and monitor high latitude zones. This is because the satellite spends more time in the higher latitudes where the earth's curvature is steeper, allowing for better coverage and resolution.

MEOs are primarily used for navigation and communication systems. In fact, the Global Positioning System (GPS) is a network of satellites in MEO that provide precise geolocation and timing information for navigation purposes. Other navigation and communication systems, such as the Global Navigation Satellite System (GLONASS) and the Galileo satellite navigation system, also use MEO satellites.

Satellites in MEO have a longer orbital period than those in LEO, which means they move more slowly across the sky. This makes them ideal for applications that require longer observation times, such as navigation and communication.

In summary, Medium earth orbits are specialized orbits that range from 2000 km to 35786 km in altitude and are primarily used for navigation and communication systems. They have a longer orbital period than LEO, making them ideal for applications that require longer observation times.

Molniya orbit
Molniya orbit

High earth orbits

Geostationary orbits, also known as high synchronous orbits, are orbits that are 35,786 km above the Earth's surface. Satellites in geostationary orbits have an orbital period that matches the Earth's rotation period, completing one orbit every 24 hours. As a result, they appear to remain fixed in the sky, making them ideal for telecommunications, weather monitoring, and safe-and-rescue beacons.

The lack of atmospheric interference and light pollution in geostationary orbits also makes them ideal for gathering information about the solar system and the universe. There are important telescopes, such as the Hubble Space Telescope, placed in geostationary orbits that have allowed us to thoroughly study the sun, its cycles, and its properties.

Synchronous orbits are classified based on their period of rotation. Objects in synchronous orbits are said to be in high, medium, or low orbits, depending on their altitude with respect to the surface of the earth. Geostationary orbits are considered high synchronous orbits, while medium synchronous orbits are used for navigation and communication systems such as the Indian Regional Navigation Satellite System (IRNSS).

In summary, geostationary orbits are used for telecommunications, weather monitoring, and safe-and-rescue beacons, as well as for gathering information about the solar system and the universe. They have an orbital period that matches the Earth's rotation period, appearing to remain fixed in the sky. Synchronous orbits are classified based on their altitude with respect to the surface of the earth, with geostationary orbits being considered high synchronous orbits.

Synchronous Orbits

What are the 3 types of orbits?

The three types of orbits are geostationary, geosynchronous, and semi-synchronous orbits. However, we also distinguish low earth, medium earth, and high earth orbits.

What is the difference between a sun synchronous and a geosynchronous orbit?

Objects in sun synchronous are located at the altitude of approximately 700 km while geosynchronous orbit is located at the altitude of approximately 35785 km. There is also a time difference in the periods of these orbits, objects in sun synchronous orbits have a period that is around 100 minutes while objects in geosynchronous orbits have a period that is around one Earth day (23 hours, 56 minutes, and 4 seconds).

What do you mean by synchronous orbit?

An object in a synchronous orbit  has the same period as the rotational period of the rotating object that it is orbiting around.

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