When Neil Armstrong and Buzz Aldrin landed on the moon 40 years ago, it was seen by many as the dawn of a new era of space exploration.
But in the years since that historic moment, NASA hasn't come close to capturing the imagination of the American public in that same way.
It has launched countless space shuttles, two of which met with tragedy. And a few years ago, it sent two rovers to Mars that sent back clear pictures of the Red Planet and took samples of the surface for analysis.
But none of those events generated the same excitement that the 1969 lunar landing did.
Putting a man on Mars was long seen by many as the next logical step. But space science experts say that is still a long ways off, if it happens at all.
James Ryan, professor of physics and space science at the University of New Hampshire, said a manned flight to Mars would be much more costly than sending more rovers and other robotic probing devices.
NASA is still studying the possibility of putting a person — or people — on Mars, Ryan said. But don't expect anyone to set foot on the Red Planet in the next few years.
"The cosmic radiation will kill you," Ryan said. Mars has very little atmosphere to protect living things against cosmic radiation, he noted. Furthermore, if people were to be flown to Mars, they would have to stay inside their space vehicles, or go underground, because the cosmic radiation is so intense, he said.
What the space program needs is a new dream, said Truell Hyde, director of Baylor University's Center for Astrophysics, Space Physics and Engineering Research, also known as CASPER.
Hyde said 40 years ago, NASA promoted a dream of putting a man on the moon, which sparked children to get interested in science and technology. Since then, however, those large goals have slowly faded away.