They can stay on the moon only around for 3 days because of the fuel but they need around 6 months to reach Mars. Now they are working on the Propellant depot project to be able to reach the moon and stay there longer. Why did not they use the Mars Mission technic? They can use the Mars Mission scenario for the moon mission and they can stay on the moon longer and no need for the propellant depot. Is there a difference between the Mars-Moon Mission propulsion systems?