Forty years after the first moonwalk, former Apollo astronauts expressed disappointment Monday that no human has yet set foot on Mars.

"My glass has been half empty for three decades at least," Eugene Cernan said Monday. "But hopefully we can turn that around."

Cernan was one of seven former Apollo astronauts - including Apollo 11's Buzz Aldrin - at a NASA news conference on Monday to commemorate the successful landing of Apollo 11 astronauts on the moon on July 20, 1969.

Cernan said when he completed his moon voyage with Apollo 17 in December 1972, he was sure humans would be back within a decade and would make it to Mars by the end of the century.

At that time, "no one" thought otherwise, said Walt Cunningham, the lunar module pilot for the Apollo 7 mission.

The astronauts at the news conference seemed unanimous in their desire for humans to go to Mars. That would inspire a passion among children to pursue science and do something unique, Cernan argued.

Most children nowadays can't name any astronauts on the space station, he said, and the only real inspiration in recent space science comes from the images and findings of the Hubble telescope.

"Beyond that, unfortunately, science is dull," he said.

Funding, technology hurdles

The astronauts differed, however, in opinions about what it would take to get to Mars.

Cernan said humans should go back to the moon to learn more and develop the technology for travel to Mars - something called for by the Global Exploration Strategy developed by 14 space agencies around the world in 2007.

Aldrin advocated sending astronauts instead on a one-way mission to Mars, as sending them there and supplying them for the rest of their lives would cost far less than a return trip. Some of the astronauts pointed out that the space program is an investment that has paid off in new technologies that have improved our lives.

Cunningham said decision-makers need to recognize the difference between an investment and an expenditure, and be willing to fund space exploration.

He suggested that part of the problem is the U.S. has become a risk-averse society in recent decades.

"There are things worth risking your life for," he added.

Some of the astronauts also criticized the U.S. decision to stop sending spacecraft to the International Space Station.

James Lovell, who flew on the Apollo 8 and Apollo 13 missions, said the station is "almost a white elephant" as little science has come out of it, and much is left to be done.

"Until we can get a return on our investment," he said. "Then it was money wasted."