Orbital decay is the gradual decrease in the altitude and speed of an object in orbit around another object, eventually leading to a collision or re-entry into the atmosphere.
Orbital decay is primarily caused by atmospheric drag, which is the resistance an object experiences as it moves through the Earth's atmosphere. Other factors such as gravitational perturbations from other celestial bodies and solar radiation pressure can also contribute to orbital decay.
The kinetic energy of an orbiting object is directly related to orbital decay. As the object loses speed due to atmospheric drag, its kinetic energy decreases. This decrease in kinetic energy leads to a decrease in the object's orbital altitude, eventually leading to orbital decay.
Mechanical energy is the sum of an object's kinetic energy and potential energy. In the context of orbital decay, mechanical energy refers to the total amount of energy an object has as it orbits another object. As an object experiences orbital decay, its mechanical energy decreases due to the loss of kinetic energy.
Orbital decay can be delayed or prevented by periodically adjusting the orbit of the object, either through propulsive maneuvers or by using aerodynamic devices. However, in most cases, orbital decay is inevitable and eventually, the object will re-enter the atmosphere.