Forty years after the first humans walked on the moon, Nasa is trying again to reach the Earth's nearest celestial neighbour.
It's not just about retracing 40-year-old footsteps in the lunar dust, though. This time, Nasa wants its moon mission to become an outpost and eventually a Mars mission too, if US Congress and others can be persuaded to part with the necessary money.
The new attempt is well past the idea stage. Two spacecraft have already been launched on scouting missions to map the moon and see whether permanently shaded areas in craters on its south pole really do contain ice, a substance that could make living on the moon vastly easier and that could in theory even be turned into new rocket fuel.
And, with a programme called Constellation now in its third year, Nasa wants to land people on the moon in 2020 and then create an outpost — a "toehold on the frontier", according to John Connolly, head of engineering for the bigger Altair lunar lander.
It might well be that overcoming the Earth's gravity is easier than overcoming the financial constraints of a nation in economic recession.
"Given the current budget, if nothing changes, it's going to be very challenging [to meet the goal of reaching the moon by 2020]", said John Olson, director of Nasa's Exploration Systems Mission Directorate Integration Office.
The current budget plan is uncertain: the Obama administration in May ordered a review of human space-flight programmes that considers the goal of "fitting within the current budget profile for Nasa exploration activities".
Why go back?
There is no more Cold War race spurring the National Aeronautics and Space Administration to outdo the Russians, but the overall reasons to go to the moon and beyond remain the same: inspiration and science.
"The most important attribute we got out of Apollo is it taught us nothing was impossible," Olson said of the first trips to the moon. Monday will mark the 40th anniversary of Apollo 11's lunar landing.
The new program, with aspirations to bring people not just to the moon but also Mars and the asteroids, is "motivating the next generation of students and researchers and engineers and scientists", Olson said.
Nasa also takes pains to point out its economic influences — jobs, spinoffs and money infused in the country's industrial base. The agency is seeking a six percent budget increase to $19.3bn for fiscal 2010, Olson said. Elements of the Constellation program are under way in 11 states.
Larry Taylor is excited by the fact that "scientifically, there's a lot to learn". A former Nasa geologist who worked on the Apollo missions and now a professor at the University of Tennessee in Knoxville, Taylor is interested in questions about the origins of the moon — the history of massive impacts and upwellings of the moon's initially molten interior during the early years of the solar system. Prevailing opinion today holds that the moon was a by-product of a Mars-sized object hitting Earth in the solar system's more turbulent beginnings.
These reasons weigh against the fact that it is expensive to get to the moon.
"You're not going to see any moon mission in my opinion," predicted Charles Pellerin who, as Nasa's former director of astrophysics, led the Hubble Space Telescope project. "The price to go back to the moon is probably at least a doubling of Nasa's budget."
He prefers robotic exploration to human exploration. And if he controlled Nasa's purse strings, he would spend the budget to study the science behind the Earth's climate, the origins of life, and new physics informed by investigation of the universe's distant past. The Hubble showed visible light from far away — and therefore long ago — but he would like to see the same views in X-ray, gamma ray and infrared light.
"There are phenomena throughout the universe that have physics you can't even conceive of on the Earth," Pellerin said. "Quasars release more energy in one second than the sun does in 30,000 years. How's that work?"
How do we get there?
Of course, a lot of people get more excited about humans exploring than about astrophysics, and it is for them that Nasa likes to send people into space. So how does the new and improved moon programme work?
The same way the old one did, in part. "The physics of moving around the solar system hasn't changed," Connolly said. But there are many significant differences from the grander aspirations.
"We designed the transportation system so we could fly folks to Mars eventually," Connolly said. That means the system can lift more mass into space, whether to build a lunar outpost or to head to Mars.
To lift more weight, there are two rockets, Ares I and V, instead of Apollo's one rocket. The smaller Ares I is designed to carry the crew — as many as six, four of whom can land on the moon. The more powerful Ares V...
