Drag refers to the force that occurs when a satellite interacts with the Earth’s outer atmosphere, known as the exosphere. While space is often considered a vacuum, the exosphere contains trace amounts of gas particles and atoms that can exert a significant impact on satellites, especially at lower altitudes.

As a satellite moves through the exosphere, it encounters these sparse gas particles. While individually tiny, the sheer number of encounters adds up to create a cumulative effect on the satellite’s trajectory. The gas particles collide with the satellite, creating resistance, and as a result, the satellite experiences atmospheric drag force in the opposite direction of its orbital motion.

This drag force acts as a decelerating influence on the satellite, gradually reducing its kinetic energy and, consequently, its altitude over time. As a result, the satellite’s orbit begins to decay, causing it to lower its altitude and move closer to Earth’s surface. Without any intervention, the satellite’s orbit would eventually degrade to the point where it re-enters Earth’s atmosphere and burns up, leading to the satellite’s destruction.