KUALA LUMPUR, Malaysia (AP)--Neil Armstrong said Tuesday that a manned mission to Mars will not happen for at least 20 years--but the effort might be easier than what it took to send him to the moon in 1969.

The first man to walk on the moon noted that scientists must develop better onboard spacecraft technology and stronger protection shields from harmful space radiation before a manned flight to the Red Planet can be accomplished.

"It will certainly be 20 years or more before that happens," Armstrong said during a global leadership forum.

"It will be expensive, it will take a lot of energy and a complex spacecraft. But I suspect that even though the various questions are difficult and many, they are not as difficult and many as those we faced when we started the Apollo (space program) in 1961."

Armstrong, 75, who seldom appears at public functions or grants interviews, commanded NASA's Apollo 11 mission in 1969. He left the space program in 1971 to teach aeronautical engineering at the University of Cincinnati.

The current U.S. space initiative envisions returning astronauts to the moon within 15 years and then launching manned flights to Mars and beyond at an unspecified date. The initiative will cost hundreds of billions of dollars.

Armstrong said setting foot on the moon was "a wonderful feeling," especially because he believed there was only a 50 percent chance of a successful lunar landing.

"I was elated, ecstatic and extremely surprised that we were successful," Armstrong said, responding to an audience member's question about how he and fellow astronaut Buzz Aldrin felt during their first moments on the moon.

"We would have loved the opportunity to take some time to enjoy it, but we had the inevitable checklist and experiments that had to go on. So it was back to business, back to work as soon as we congratulated each other."