Orbital Decay
Orbital decay refers to the progressive decline in the height of an orbiting body with respect to the central mass. In the case of man-made satellites, it is often the degredation in altitude of the orbiting installation.
Factors Affecting Orbital Decay
1. Atmospheric drag accounts for a large amount of orbital decay for satellites and other spacecraft that are in low earth orbit. Installations in these orbits are close enough to the Earth to still experience the resistive effects of the atmosphere. While these effects are often small, their prolonged effects over time result in a reduced velocity for the orbiting body and thus a decline in orbital altitude. If allowed to continue without interference, the orbit will decay to a point where the satellite crashes into the Earth.
2. Interactions with particles and forces in space can further degrade an orbit. If a satellite orbiting Earth comes into contact or collision with debris in such a way that lowers its orbital velocity, its orbit will decay.
3.
Tidal effects can also affect
orbital decay. If
the orbiting body is of great enough mass to create a ‘tidal bulge’ on
the
central body, momentum will be taken from the orbiting mass and
transferred to
that of the central mass. This effect, however, does not play a factor
in the
orbits of man-made satellites as their mass is far to small to have any
impact
on Earth.