PASADENA, Calif. -- Turning the Moon into training ground for human travel to Mars is predicated on a succession of robotic craft, many yet to be defined and funded.

Here at the Jet Propulsion Laboratory (JPL), officials envision a line of robotic probes as precursors to both returning humans to the Moon and eventually sending an expedition to Mars.

Cheney saluted JPLs long legacy of robotic exploration of space, including the new arrival on Mars, the Spirit rover. He said he was taken through Spirits operation center here and added: "But dont worry, I did not touch the controls."

Cheney said President Bush has outlined his vision for a second Great Age of space exploration.

"Our goals are aggressive," the Vice President said. To complete the International Space Station by 2010; send manned flight beyond Earths orbit in 2014; to return to the Moon by 2020; and to use our presence on the Moon as a platform for missions to Mars and beyond."

"These aims are ambitious. Theyre difficult and they are very demanding," Cheney said. "The effort will be repaid many times over in scientific advancement, useful new technologies, the discovery of resources on Earth and beyond, and the discovery of more about ourselves."

Charles Elachi, JPL Director, said the Presidents exploration initiative will equate to "a more robust program" at the laboratory.

Elachi said a critical word of Bushs space agenda is the call for a "sustained" human and robotic exploration. "This is not a quick race to go to the Moon or Mars. It is a long-term exploration program."

"This is not a 100-meter dash. This is a long-term exercise. Every day that you exercise you keep in good health," Elachi said.

As was the case during the early Apollo days, Elachi said, a series of robotic projects will act as trailblazers for human missions. To prepare for a human return to the Moon, a suite of orbiting as well as lunar robotic landing robots are part of the plan.

Elachi said a lunar orbiter mission would take place in 2008, followed by a lander in 2009. These and other robotic vehicles are slated to fly to the Moon, preparing for human return on that cratered body in 2015-2020.

But compared to the Apollo program, all this lunar activity is intended to help shore up the human leap to Mars, Elachi told reporters.

"We dont have a specific date to go to Mars," Elachi remarked. How the technology evolves, as well as the affordability of such an endeavor -- then the time for a humans-to-Mars will become clear, he said.

"Its going to depend, really, on the will of the nation in the long term," the JPL director said.

As it did in the past, JPLs robotic expertise will play a major role in fulfilling Bushs human space exploration agenda. The laboratory led the Ranger, Surveyor, and Lunar Orbiter robotic spacecraft project that gave way to humans setting foot and flag on the Moon.

Asked about the prospect for friction between robotic and human spaceflight factions JPL versus the NASA Johnson Space Center -- Elachi responded to SPACE.com : "This is going to be a common effortnot only between our two centers, but all of NASA. This is going to require talent from all across the agency to work as a seamless team."

Focusing on the 2008 lunar mission, the new NASA budget for 2005 carries study money to begin developing the Moon orbiting craft, Elachi added.

The engineering needed to put humans safely on Mars is far from being a known certainty, said Peter Theisinger, Mars Exploration Rover project manager at JPL.

"Were not prepared to even come close to thinking about that," Theisinger said. Were raising peas in this gardenand thats a watermelon and cantaloupe question," he said.

Theisinger said that robotic spacecraft have already started collecting data helpful for supporting future expeditions to Mars.

For one, Spirits mobility on the red planet is expected to offer engineering data useful for crews visiting Mars, Theisinger said. NASA Mars Odyssey has also begun gleaning data as to the radiation environment at the planet, with future landers to gauge how much radiation reaches the surface.

Europes Mars Express, Theisinger added, like NASAs Mars Odyssey, is equipped to scout out where resources helpful to sustain human explorers are available. By tapping subsurface reservoirs of ice on Mars, that material could be transformed into drinkable water, propellant, and oxygen.

Mars itself "is a big puzzle," Theisinger said, in terms of supporting humans on that faraway world. "It requires a lot of pieces to put it together. Theres a lot of work to do," he said.