From Mars is Our Planet of Destiny in der SPIEGEL:

SPIEGEL: Mr. Puttkamer, the first person set foot on the moon exactly 40 years ago. Why does NASA want to return to that barren, lifeless place?

Puttkamer: The Apollo astronauts were only able to spend a couple of days up there -- that was just a quick visit. When we fly there again in 2019-2020, we'll stay much longer. The four-person team will gain experience for the real long-term goal -- the journey to Mars. We want to build a lunar station where people could live for weeks or even months, as preparation for the larger Mars project.

SPIEGEL: So NASA is not preparing to populate the moon?

Puttkamer: No, the lunar station won't be capable of continuous operation 365 days a year, since we'll need to supply it constantly with air, water and food from Earth, and that would be insanely expensive. But the living conditions on Mars are actually very different. There are many natural resources there, and our probe just recently discovered traces that could originate from liquid water. It's also been known for a long time that water in solid form -- in other words, ice -- exists there in large quantities.

SPIEGEL: Will America fly to the moon alone again?

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Puttkamer: Certainly not -- and especially not when we want to reach more distant destinations. The age of going it alone is over. The Apollo project took place during the Cold War, when we were involved in a dramatic race with the Soviets. But a lot has changed since then. We've moved away from that competitive way of thinking, and everyone is invited to take part in future missions. It functions that way already on the International Space Station, where 16 countries work together in an exemplary way. We've created a kind of United Nations in space.

SPIEGEL: Yet the United States is going to build the new moon rockets alone again.

Puttkamer: Unfortunately it can't be done any other way. After our shuttle fleet is withdrawn from service next year, we're going to need a new space carrier of our own as quickly as possible. To that end, we needed to commission industry to develop the new Ares rocket and the accompanying Orion spaceship as soon as possible. Then there's also the Altair lunar lander. But in any case, the European Space Agency is already very interested in helping with the construction of infrastructure on the moon later. Our Russian partners would definitely participate as well. And I personally would be very happy to also see Germany involved."...