A 4.4times 10^{10};{rm kg} asteroid is heading directly toward the center of the earth at a steady 15 km/s. To save the planet, astronauts strap a giant rocket to the asteroid perpendicular to its direction of travel. The rocket generates 5.0times 10^{9};{rm N} of thrust. The rocket is fired when the asteroid is 4.0times 10^{6}; {rm km}away from earth. You can ignore the rotational motion of the earth and asteroid around the sun.