Understanding Satellite Orbit Types: Molnya, Tundra, and LEO

This tutorial explores various satellite orbit types, focusing on Molnya, Tundra, and Low Earth Orbits (LEO). We’ll delve into how these orbits are used to launch satellites and their specific characteristics.

The path a satellite takes around the Earth is called its orbit. To counteract the Earth’s gravitational pull, satellites are launched with both vertical and forward motion. The inertia generated by the forward motion allows the satellite to maintain its trajectory in a straight line.

Achieving a speed of approximately 25,000 miles per hour is necessary to overcome the Earth’s gravity and place a spacecraft into orbit. Satellites orbit the Earth in either a circular or elliptical path.

Circular vs. Elliptical Orbits

• Circular Orbit: In a circular orbit, the satellite’s altitude remains constant relative to the Earth’s surface.
• Elliptical Orbit: In an elliptical orbit, two key points define the satellite’s position:
  • Apogee: The highest point in the orbit, representing the satellite’s farthest distance from Earth.
  • Perigee: The lowest point in the orbit, representing the satellite’s closest distance to Earth.

Apogee and perigee are measured from the geocenter (center) of the Earth, so the Earth’s radius must be considered when calculating the satellite’s actual distance from the surface.

Classification of Satellite Orbits

Satellite orbits are classified based on their altitude, inclination, and other characteristics. Here are a few common types:

• Geostationary Orbit (GEO):

  • Altitude: Approximately 35,786 km
  • Period: 24 hours
  • Purpose: Provides continuous coverage to a fixed area on Earth.

• Molnya Orbit:

  • Origin: First used by the Soviet Union for television transmission to remote areas.
  • Apogee: Approximately 40,000 km
  • Perigee: Approximately 1,000 km
  • Characteristics: Highly elliptical orbit with a high inclination, providing good coverage of high-latitude regions.

• Tundra Orbit:

  • Apogee: Approximately 46,300 km
  • Perigee: Approximately 25,250 km
  • Characteristics: Similar to Molnya orbits, highly elliptical and inclined, offering enhanced coverage of high-latitude regions.
  • Applications: Molnya and Tundra orbits are suitable for mobile satellite systems and can complement geostationary orbits for improved global coverage.

• Low Earth Orbit (LEO):

  • Altitude: Approximately 500-800 km
  • Applications: Commonly used by radiometers, Earth resources monitoring satellites, data relay satellites, navigation satellites, and low-cost store-and-forward communication systems.