Lesson 1 – How did understanding forces send a rover to Mars? We learned that an unbalanced force of 900,000 N from a booster rocket accelerates the rocket carrying the rover upward. Then smaller rockets in the second stage fire to keep the rocket on course as it is traveling at constant velocity. Next as the spacecraft approaches Mars, gravitational attraction begins to accelerate it toward the surface. Then the rover detaches and parachutes slowly to its fall. Finally a big ball inflates over the rover to protect it for impact.