In orbital mechanics, which perturbation most commonly affects Low Earth Orbit satellites?

In orbital mechanics, which perturbation most commonly affects Low Earth Orbit satellites?

• A. Gravitational perturbations from the Moon.
• B. Solar radiation pressure.
• C. Tidal forces from Earth.
• D. Atmospheric drag causing orbital decay.

Answer: (D)

In Low Earth Orbit the satellite still encounters a thin but real layer of Earth's atmosphere. This residual air creates drag that continually removes orbital energy as the craft moves through it. That loss of energy lowers the orbit (a decrease in semi-major axis) and, if uncorrected, leads to orbital decay and eventual reentry. The effect is strongly tied to atmospheric density (which changes with altitude and solar activity), the spacecraft’s cross-sectional area and drag coefficient, and its mass (often summarized by the ballistic coefficient). That’s why even the International Space Station, at roughly 400 km up, requires periodic reboosts to maintain its altitude. Other perturbations do exist, but they are typically less impactful on the short-term evolution of a typical LEO satellite. Gravitational tugs from the Moon and Sun mainly cause slow, long-term changes in orbit orientation and shape rather than immediate energy loss. Solar radiation pressure can alter the orbit—especially for objects with a large area-to-mass ratio—but its effects are generally smaller in the dense, lower part of the atmosphere. Earth’s tidal forces on a single satellite in LEO are negligible compared to atmospheric drag.

In Low Earth Orbit the satellite still encounters a thin but real layer of Earth's atmosphere. This residual air creates drag that continually removes orbital energy as the craft moves through it. That loss of energy lowers the orbit (a decrease in semi-major axis) and, if uncorrected, leads to orbital decay and eventual reentry. The effect is strongly tied to atmospheric density (which changes with altitude and solar activity), the spacecraft’s cross-sectional area and drag coefficient, and its mass (often summarized by the ballistic coefficient). That’s why even the International Space Station, at roughly 400 km up, requires periodic reboosts to maintain its altitude.

Other perturbations do exist, but they are typically less impactful on the short-term evolution of a typical LEO satellite. Gravitational tugs from the Moon and Sun mainly cause slow, long-term changes in orbit orientation and shape rather than immediate energy loss. Solar radiation pressure can alter the orbit—especially for objects with a large area-to-mass ratio—but its effects are generally smaller in the dense, lower part of the atmosphere. Earth’s tidal forces on a single satellite in LEO are negligible compared to atmospheric drag.