Why did we stop walking on the moon?

Astronaut Gene Cernan has died at the age of 82. One of only three men to go to the moon twice, his 1972 moonwalk as commander of Apollo 17 turned out to be Nasa's last manned voyage to Earth's nearest neighbour.

"We leave as we came and, God willing, as we shall return with peace and hope for all mankind," he said at the time.

However, we did not return at all.

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After Neil Armstrong took his "giant leap for mankind" in 1969, there was a widespread expectation that a permanent human colony would not be far behind, says CNN's Dave Gilbert.

"Throughout the 1970s, children's magazines showed artists' conceptions of the moon bases that would be built," he writes. But the futuristic lunar outpost of popular imagination never materialised. So why did space agencies abandon the moon?

Why don't astronauts walk on the moon anymore?

The cost and danger of sending humans into space, combined with huge leaps in technology that enable us to see further than any human astronaut could hope to travel, has made returning to the moon a low priority for Nasa.

Space agencies have instead opted for the lightest, leanest possible crafts to travel ever-further into space, where they can send back images and information from areas of the universe far beyond the limits incumbent on a manned mission. It has led to the discovery of hundreds of new worlds beyond our own solar system.

In fact, until recently, the focus had evolved so far from manned missions that Nasa lacked the technology to launch one. In 2009, scientist Jeff Hanley told Space magazine: "The amount of rocket energy it takes to accelerate those kinds of payloads away from Earth doesn't exist anymore. It exited in the Apollo era with the Saturn V. Since that time, this nation has retired that capability."

Are there plans for any future space missions?

Nasa might have moved its focus away from future moonwalks, but European, Japanese, Russian and Chinese space agencies have all announced plans for lunar landings. The European Space Agency's "Destination Moon" project aims to put astronauts on the satellite by 2030, with the goal of eventually building a permanent base.

A Nasa spokesman told CNN it could lend a hand with these projects as a "proving ground" for the next frontier - a human landing on Mars.

He said: "Our roadmap for exploration includes the possibility of assisting partners with that kind of exploration, but our investments in human spaceflight are focused on enabling the path to Mars."

Nasa believes humans could reach the red planet by the 2030s, but the main obstacle will be money rather than technology. "Even before Cernan came home from the Moon in 1972, the [US] federal government had begun cutting funding for Nasa from nearly five per cent of the budget to less than 0.5 per cent today," Ars Tecnica reports.