The Apollo astronauts landed on the Moon and explored it. When they lifted off to return home, they first needed to make lunar orbit, which required a speed of about 5,500 ft/s. The lunar module ascent engine developed a vacuum specific impulse of 310 s. What is the vehicle mass ratio that will allow the engine to achieve the required speed?

(Hint: The quoted value of specific impulse is based on the propellant weight on Earth, so you should use the value of g0 for Earth, not the Moon, in your calculation)