In space, a rocket accelerates by burning its fuel and ejecting the burned gases. The operation of the rocket follows the conservation of linear momentum. The ejected gases from the rocket have momentum in the opposite direction to that of the rocket's motion. Here, the mass of the expelled gases is equal to the mass lost by the rocket. Dividing both the sides by dt and rearranging the equation, the expression for the acceleration of the rocket is obtained. The acceleration of the rocket continuously increases as the mass of the rocket decreases for a constant velocity. The product of mass and acceleration is the force for the flight, which depends on the velocity of the expelled gases and the combustion rate. Rearranging the equation for force and integrating the equation for the rocket's velocity with initial and final limits, the ideal rocket equation is derived. The rocket achieves maximum velocity when the ratio mi over m is made as large as possible such that the fuel primarily constitutes the initial mass of the rocket.