Satellite Orbit Fundamentals

Understanding the motion of satellites around celestial bodies, such as Earth, involves several key concepts. A satellite's path, known as its orbit, is generally elliptical rather than perfectly circular. Due to this elliptical shape, there are specific points in the orbit where the satellite is closest to the central body it orbits and points where it is farthest away.

Perigee Definition in Satellite Orbit

The term Perigee is used to describe a critical point in a satellite's orbit. Specifically, it is defined as:

• The point in an elliptical orbit where the orbiting body (e.g., a satellite) is at its closest approach to the central body (e.g., Earth).
• It represents the lowest point in the orbit when measured from the gravitational center of the central body.
• At Perigee, due to the increased gravitational pull, the satellite typically achieves its maximum orbital speed.

For satellites orbiting Earth, Perigee signifies the point where the satellite is nearest to Earth's surface.

Apogee in Satellite Orbit

To provide a complete picture of satellite orbits, it's also important to understand the opposing point to Perigee:

• Apogee is the point in an elliptical orbit where the orbiting body is at its farthest distance from the central body.
• It represents the highest point in the orbit relative to the central body.
• At Apogee, the satellite's orbital speed is typically at its minimum.

Orbital Points Summary

Term	Definition
Perigee	The lowest point in a satellite's elliptical orbit, indicating the closest distance to the central body.
Apogee	The highest point in a satellite's elliptical orbit, indicating the farthest distance from the central body.

Analyzing the Satellite Orbit Options

Let's evaluate the given options to identify the correct definition of Perigee with reference to satellite orbit:

• Option 1: "point in an intermediate orbit" - This description is inaccurate. Perigee refers to a specific position within a single orbit, not an "intermediate" orbit.
• Option 2: "highest point in the orbit" - This statement actually describes Apogee, which is the farthest point from the central body in an orbit. Therefore, this option is incorrect for Perigee.
• Option 3: "lowest point in the orbit" - This definition perfectly matches the concept of Perigee. Perigee is indeed the point where the satellite is closest to the central body, making it the lowest point in its elliptical path.
• Option 4: "none of these" - Since Option 3 accurately defines Perigee, this option is incorrect.

Based on the analysis, the definition provided in Option 3 correctly identifies Perigee in the context of a satellite orbit.