Orbits and Satellites: Their Functions and Impact on Modern Life

In the vastness of space, objects move in curved paths around each other because of gravity. Whether it’s a planet like Earth orbiting the Sun or a satellite orbiting our planet, these paths are known as orbits. Satellites of different sizes and purposes circle Earth at various distances, each serving unique roles in communication, observation, and navigation. Understanding these orbits helps us grasp how satellites function and benefit our daily lives.

Understanding Orbits in Space

Definition: An orbit is the curved path that an object in space (such as a star, planet, moon, asteroid or spacecraft) takes around another object due to gravity.

• Orbital Dynamics: Objects of similar mass orbit each other with neither object at the center, whilst small objects orbit around larger objects.
• Solar System Orbits: In our Solar System, the Moon orbits Earth, and Earth orbits the Sun, but that does not mean the larger object remains completely still.
• Gravitational Effects: Because of gravity, Earth is pulled slightly from its centre by the Moon (which is why tides form in our oceans) and our Sun is pulled slightly from its centre by Earth and other planets.
• Orbital Altitude Categories: The height of the orbit, or distance between the satellite and Earth’s surface, determines how quickly the satellite moves around the Earth. 
  • An Earth-orbiting satellite’s motion is mostly controlled by Earth’s gravity.
• Types of Orbits: The orbits can be categorized as High Earth orbit, Medium Earth orbit, or Low Earth orbit based on the height of satellites from the earth.

Low Earth Orbit

Definition: An orbit that is relatively close to Earth’s surface. It is normally at an altitude of less than 1000 km but could be as low as 160 km above Earth.

• Applications of LEO: LEO is commonly used for communication and remote sensing satellite systems, as well as the International Space Station (ISS) and Hubble Space Telescope.
• Orbital Characteristics of LEO: Satellites placed in LEO orbit generally circle the Earth once in 90 minutes.

Middle Earth Orbit

Range: Medium Earth orbit comprises a wide range of orbits anywhere between LEO and GEO.

• The range of this orbit is between 2000 km – 35,780km.

• Characteristics of MEO: It is similar to LEO in that it also does not need to take specific paths around Earth, and it is used by a variety of satellites with many different applications.
• Satellite Applications in MEO: Generally, it takes 12 hours for the satellite to complete one rotation around the Earth.
• Applications: MEO is commonly used for navigation systems, including the U.S. Global Positioning System (GPS).

High Earth Orbit

Range: When a satellite reaches 42,164 kilometers from the Earth’s center (about 36,000 kilometers from the surface), it is said to be in high Earth orbit.

• Applications: Because satellites in this orbit provide a steady view of the same surface, geostationary orbit is particularly useful for weather monitoring and communication (phones, television, radio).
• Geostationary Orbit: At this height, the orbital height of the satellite becomes equal to the Earth’s rotational speed.So, this orbit at this height is called a geosynchronous or Geostationary Orbit.

Geostationary Orbit

A geostationary orbit, also referred to as a geosynchronous equatorial orbit (GEO).

• Location: A geosynchronous orbit is a high Earth orbit that allows satellites to match Earth’s rotation. 
  • Located at 22,236 miles (35,786 kilometers) above Earth’s equator.
• Characteristics: Because the satellite orbits at the same speed that the Earth is turning, the satellite seems to stay in place over a single longitude.

Polar orbit and Sun Synchronous orbit (SSO)

Polar Orbit Characteristics: Satellites in polar orbits usually travel past Earth from north to south rather than from west to east, passing roughly over Earth’s poles.

• Location: Polar orbits are a type of low Earth orbit, as they are at low altitudes between 200 to 1000 km.
• Sun-Synchronous Orbit (SSO) Explanation: Satellites in SSO, traveling over the polar regions, are synchronous with the Sun. 
  • This means they are synchronized to always be in the same ‘fixed’ position relative to the Sun. 
  • This means that the satellite always visits the same spot at the same local time.
  • This means that the satellite will always observe a point on the Earth as if constantly at the same time of the day.
  • It serves a number of applications; for example, it means that scientists and those who use the satellite images can compare how something changes over time.

Transfer orbits and Geostationary Transfer Orbit

Utilizing Transfer Orbits: Transfer orbits are used to get from one orbit to another.

• When satellites are launched from Earth and carried to space with launch vehicles, the satellites are not always placed directly on their final orbit.
• Often, the satellites are instead placed on a transfer orbit: an orbit where, by using relatively little energy from built- in motors, the satellite or spacecraft can move from one orbit to another.

• Advantages of Transfer Orbits: This allows a satellite to reach, for example, a high-altitude orbit like GEO without actually needing the launch vehicle to go all the way to this altitude, which would require more effort.

Lagrange point

Definition of Lagrange Points: Lagrange Points are positions in space where the gravitational forces of a two body system like the Sun and the Earth produce enhanced regions of attraction and repulsion.

• Benefits of Lagrange Points: These can be used by spacecraft to reduce fuel consumption needed to remain in position.
• Origins and Naming of Lagrange Points: Lagrange points are named in honor of Italian-French mathematician Joseph-Louis Lagrange.
• Characteristics: There are five special points where a small mass can orbit in a constant pattern with two larger masses.
• Halo Orbit: It is an orbit around the Lagrange points.

Conclusion

Understanding orbits is fundamental to grasping how satellites function and contribute to our daily lives. 

• From low Earth orbits facilitating communication and research to high Earth orbits like GEO supporting weather monitoring and communication, satellites in different orbits serve diverse applications crucial for modern technology and scientific exploration.

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