# Space Travel Guide ...

 Launching of Artificial Satellite To enable a satellite to orbit around any planet, we have to consider the height from which the satellite must be thrown. Consider yourself, if you throw a stone, it comes to earth after some time, why? It is because of the gravitational attraction of earth and the stone. By the Newton 's law of gravitation, stone and earth would be attracted towards each other by force F = GMm / R2 Where M is mass of earth m is mass of stone R is distance between centre of earth and stone The force exerted on earth by stone is very small to attract or move the earth towards the stone hence, only the stone gets attracted towards earth. Earth also moves but since mass is very large, so, it has very small acceleration which can't be noticed. Then, how to overcome this problem? Since, throwing the satellite from earth's surface will make the satellite to come down to earth's surface due to gravitational pull. Don't worry. The solution also lies in the gravitational pull only. See the Newton 's law of gravitation carefully, you will find that F a 1/ R2 i.e. greater is the distance, lesser the force of attraction. As we have seen earlier that value of g decreases with increase in height and expression is given by gh / g = g ( 1 - 2h / R ) We can say that to put on object into earth's orbit. •  Move the object to suitable height. •  Then, project it with high velocity. Remember, less the height to which object is moved, greater the velocity needed for projecting. As I have talked about the height and velocity relation in last paragraph, I would like to state that the velocity that I was talking about is called as ‘ ORBITAL VELOCITY '.