De-orbit maneuvers are done to lower the perigee of the orbit to 60 miles (or less). Calculate the minimum change in velocity (delta V) required for the Space Shuttle to decrease its altitude to 60 miles if its orbiting with an apogee of 236 miles and a perigee of 220 miles above the surface of earth. Use the rule of thumb that below an altitude of 500 miles, for every two fee per second (fps) change in the orbiting space craft's velocity its altitude will change by 1 mile. Put your answer in feet per second.