Effects of Drag on Orbital Motion (DP IB Physics: HL): Revision Note

Effects of Drag on Orbital Motion

• Satellites in low orbits (<600 km) may be slightly affected by viscous drag, or air resistance

• The effects of drag on the motion of the satellite are usually very small, but over time, it can have a significant effect on the height and speed of the satellite's orbit

Viscous drag can affect the height and speed of a low-orbit satellite as a result of energy dissipation

• The density of the air in the very upper layers of the atmosphere is very low, but not zero

• As a result, satellites travelling through these thin layers of air will experience a small dissipation of kinetic energy into thermal energy

  • This heating is due to the friction between the air particles and the surface of the satellite

As a low-orbit satellite loses energy, it spirals towards the Earth as its orbital radius decreases

• As some of the kinetic energy is dissipated into the surroundings, the satellite's total energy is reduced

  • When a satellite loses energy, its orbital radius decreases

  • However, as the satellite's orbit becomes lower, some of its potential energy is transferred to kinetic energy

• Overall, its speed increases and the effects of air resistance become even greater in its lower orbit resulting in greater dissipation of kinetic energy into thermal energy

• If the overall decrease in potential energy is larger than the overall increase in kinetic energy, the total energy will decrease

$∆E_{total}<0$  if  $∆E_p>∆E_k$