Modern rockets do not use gunpowders, but are propelled into space by a variety of fuels. The fuels burn inside the combustion chamber and produce hot gases which, expand and shoot out of the chamber through a nozzle at the back of the rocket. The jet of gases rushing out of the nozzle pushes the rocket in the opposite direction, in the same manner as you push a boat in the opposite direction while stepping out of it. This reaction force propels the rocket forward.

Overcoming gravity is the biggest problem in getting into space. A rocket overcomes gravity by producing thrust (a pushing force). The extra thrust accelerates the spacecraft. It makes the spacecraft go faster and faster until it reaches the velocity needed for its journey.

NOTE : Did you know that to launch a satellite into an orbit around the earth, a rocket must reach a speed of about 18,000 miles per hour.?