Our greenhouse will not only provide food, but it will also provide oxygen to the astronauts after the pods have run out. The only thing is that the astronauts need to be motivated to care for the plants inside. The ceiling will be glass of course so the plants can get there natural bit of sunlight. And sense mars does not have lakes,rivers or oceans, the astronauts will need to collect ice from the polar ice caps and melt it. That is the only water source on that planet. But we only have one problem with this product, plants are used to our planet, our atmosphere. And because of this the plants that we are taking need to evolve into this thin and cold atmosphere. Well, i bet your thinking," why don't they just keep the plants inside the greenhouse?" Well that's the issue. The plants will Create their own Oxygen and stuff inside the greenhouse, But their going to have to adapt to a colder temp than than their used to. And they'll also have to get used to the pressure of the planets atmosphere. They wont have all the gravity pushing down on them.