Why do satellites crash?

Answer 1

Satellites positioned over a specific point are not 'hovering motionless'.

The smaller an orbit is, the shorter its period of revolution, and the larger an orbit is,

the longer its period of revolution. Communications satellites are carefully placed in

an orbit that's just exactly the correct size so that its period is 24 hours. That way,

the satellite appears motionless in the sky, and you don't need a tracking antenna

to follow it. That unique distance happens to be 26,199 miles from the center of the

Earth. In order to revolve completely around a circle that size every 24 hours, the

satellite is moving at roughly 6,860 miles per hour.

Even if the satellite did stop dead in its tracks, it would be in space and take

some time to be attracted towards earth. Once it gained speed (attracted by

the Earth's gravity) and fell into the atmosphere, it would likely burn up, as the

air friction heated it. Heavy metallic fragments might reach the ground.

Answer 2

The geosynchronous satellite appears to stay motionless when viewed from a spot on earth (the ground station), but in reality, the satellite is orbiting at a very high speed relative to the center of earth. The geosynchronous orbit is 42,200 km from the center of the earth. The ground station is about 6,400 km from the center of the earth. The earth is spinning along the polar axis at a great speed -- the ground station is moving at about 0.47 km/s along a circular orbit. In order to appear stationary to a ground station, the satellite will have to keep up to the angular speed of the ground station, or equivalently 3.1 km/s. Its take energy (possibly from an on-board power source) to keep the speed constant. When the satellite speed slows down, the satellite will drop closer to the earth. On the other hand, if the satellite speeds up, the orbit will be elevated, farther away from the earth. When the power source is exhausted, the speed will slow and the satellite will drop its orbit and falls to the earth.

An earthly example will clarify what I just said. Let the string out of a yo-yo. Swing the yo-yo in circles fast in a vertical plane. When the spinning is fast, the string stays taut. However, when the spin slows, the string will slack, and the yo-yo will eventually drop to the ground. The satellite needs a constant supply of energy to stay in orbit.

==========================

Answer 3

A satellite is an artificial man made creation that we launch into orbit around the earth for many different purposes. Some are for weather purposes, some are for data collection, some are for communication, some are even for closer "space exploration" such as the Hubble telescope. Their orbits are maintained by the earths orbit and a small energy source that they have contained on-board. Eventually after a number of years, however, that power source runs out, and the orbit begins to "decay", slightly at first, but when they touch the upper part of our atmosphere "reentry" is imminent. Most of the time we can predict when this will happen; unfortunately not all the time. Their great speed from orbit clashes with our atmosphere, and causes overheating and great pressures on the satellite. Many times they break up before hitting the earth into many small pieces, occasionally one piece may be much larger.

The earth and moon have orbits that do NOT decay as constant magnetic forces are applied by each to the other due to their own makeup of elements and the resulting magnetic fields these apply to each other.