GEO-STARIONARY SATELLITE

A geostationary satellite appears stationary for an observation on earth. For a satellite to be Geo-stationary, it must satisfy the following two conditions

1)   Its orbit must lay the equatorial plane of the earth.

2)   Its period and direction of rotation must be same as the period and direction of earth’s rotation about its axis.

The orbit from which the two periods are equal is called a parking orbit or synchronous geostationary orbit or geosynchronous orbit.

                        WEIGHTLESSNESS

Weightlessness: Consider a person getting into a lift to go up a tall building. Suppose the flour is on a weighting scale that displays a weight of the person. Before the lift starts, the scale should read the true weight. But as the lift accelerates upward the scale will displays excess weight corresponding to the value m (g+a). Any time the lift stops and attain a constant upward speed, the scale will give true weight. After taking a view of the city, as the person accelerates downwards, the scale will read reduced weight corresponding to W= m (g-a). So the scale basically measures the relative acceleration due to gravity and due to lift. For a=g, as in free fall, W=0, and the sense of weightlessness arises. Spacecraft in circular orbit around the earth are also in free fall, so everything is weightless. In fact, if the cabin in the spacecraft is accelerating in free space with acceleration g, there is no experiment which can determine whether the experimenter is in such an accelerating spaceship or on the surface of planet of gravitational acceleration g. This is a manifestation of the” principal of equivalence” between gravitational and inertial mass that led Einstein to formulate his gravitational theory of general relativity.

When the weight of a body becomes zero, it is said to be in the state of weightlessness. That a person in a freely falling lifts feels weightlessness has already been discussed in chapter 4. Here we will discuss the same phenomenon in an orbiting spacecraft.

FREE FALL

If a body falling freely under the action of gravity alone negligence of air resistance, the motion is called free fall.

In fact, a body falling in a vacuum or in space is the free fall. One of the examples of free fall could be the body falling on the surface of the moon. This is because the moon has no atmosphere around it. The acceleration of a body in the free fall is equal to acceleration due to gravity “g”. In this condition, the body is in weightlessness. This is because the body feels zero reaction force.