This re-evaluation of NASA's future highlights chronic funding and political issues that have dogged the space agency since the Apollo project.

The first sign of NASA's declining political relevance came almost immediately after Apollo 11, when President Richard Nixon moved to cut funding for the space program, canceling two moon missions. Since then, the space pro- gram's share of the federal budget declined from 4 percent to 0.6 percent.

MARS MISSION

Even so, NASA has attempted to live up to its heritage by continuing to propose ambitious missions, said John Logsdon, the Charles A. Lindbergh chair of aerospace history at the National Air and Space Museum.

Five years ago, it prepared a vision to return to the moon by 2020 and then send humans to Mars. Preliminary design, engineering and mission-planning work is under way.

Just last week, NASA released new photos of several Apollo landing sites -- pictures snapped by a remote device launched last month from Cape Canaveral.

"It was great to see the hardware on the surface, waiting for humans to return," Mark Robinson, a project manager, said Friday. "You can see markings where the astronauts walked."

‘DON'T HAVE MONEY'

Still, many challenges remain.

As the Houston-based manager of the space-shuttle program, John Shannon has had a front-row seat, watching pro- gram managers struggle to develop the next generation of spacecraft with less up-front funding than promised.

"They have a good plan," Shannon said. "Their architecture is good. People say, ‘Ah, they're behind schedule,' or ‘They have these technical difficulties.' They just don't have money.

"We see that on the shuttle side very clearly because we're trying to hand over work force, industrial base, rocket testing, the Vertical Assembly Building [at the Kennedy Space Center in Central Florida], and they just don't have the money to pick those things up," Shannon said. "So now we're trying to scramble to try and keep things mothballed and it's just a mess."

‘COOPERATION'

One realm in which NASA has made significant strides since Apollo is in international relations, according to George Abbey, an assistant to the Apollo program manager and director of the Johnson Space Center from 1996 to 2001.

"We've moved in a direction that's more based on international cooperation, and I think that's taken us in the right direction," Abbey said. ‘‘We started off in Apollo in a competitive program with the Russians. If you look at where we are today, we have pro- grams with the International Space Station, which we're doing with 15 nations."

Abbey said the new pro- gram's rocket development is solely an American effort. To achieve greater goals, he said, NASA must enlist the international coalition that is building the space station.

"Dollars are always going to be a challenge, and if you can utilize their capabilities and complement each other, you can achieve a lot more," he said.

ALDRIN'S VIEW

Aldrin and Collins, among others, argue that NASA should aim higher -- for Mars rather than the moon. Aldrin noted that Russia is planning to launch a soil-sample return mission to the Mars moon Phobos, a potential staging area for human landings on Mars.

"I don't think the American people know that Russia and other nations are actively pursuing things that we've set aside, because we're concentrating on doing what we did 40 years ago," Aldrin said. ‘‘I'm not sure that inviting them to compete, rather than cooperate, with us is productive for anyone."

Contributing to this report were Eric Berger of the Houston Chronicle and former Miami Herald Senior Writer Martin Merzer, who covered the nation's space program from 1986 to 2008.