A balloon filled with helium gas is to be used to lift a military vehicle that weighs 2570 pounds. As learned in class, the density of helium is about one-seventh the density of air. Assuming the average density of helium to be 0.011 lbm/ft3, what is the minimum diameter of the balloon required to lift the vehicle? Neglect the mass of ropes and harnesses, and consider standard atmospheric pressure conditions.