NASA’s newly announced plan to capture an asteroid and re-position it around the moon for an astronaut visit sounds cool, but it’s a side-show on the road to Mars, scientists and long-time space mission managers told Congress.

“To me, the connection between the asteroid retrieval mission, which involves proximity operations with a rock that would fit comfortably in this hearing room, I see no obvious connection between that and any of the technologies and capabilities required for Martian exploration,” Cornell University planetary scientist Steve Squyres told the House Subcommittee on Space on Tuesday.

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A better stepping-stone for human expeditions to Mars is the moon, argued Paul Spudis, senior scientist with the Lunar and Planetary Institute in Houston.

“It has partial gravity like Mars. It has a dust environment that you have to learn to deal with. You can learn how to explore and how to get the most out of the missions,” Spudis said.

NASA planned to follow the space shuttle and International Space Station programs with a return to the moon, but President Obama canceled the project, known as Constellation, in 2010 due to funding shortfalls.

NASA salvaged Constellation’s heavy-lift rocket and deep-space Orion capsule and set about crafting a more flexible exploration initiative that would first send astronauts to an asteroid and eventually to Mars.

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President Obama’s spending plan for NASA for the fiscal year beginning Oct. 1 requests $105 million to begin work on a revamped asteroid mission which combines a robotic precursor spacecraft to fetch a 23- to 33-foot diameter asteroid with a follow-on expedition by astronauts.

NASA has not yet said how much the asteroid-retrieval mission would cost, but expects it would be less than the $2.65 billion estimate made last year by the California Institute of Technology’s Keck Institute for Space Studies.

But for that money, scientists told Congress, NASA may be able to afford a lunar lander -- a key reason for Constellation's fall -- or an upper-stage engine for the heavy-lift Space Launch System to bring it to its full potential.

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Spudis also pointed out that if returning samples from an asteroid was the driver for the mission, scientists already have about 45,000 pieces of near-Earth asteroids at their disposal in the terrestrial meteorite collection.

“The largest one is three meters across and 60 tons. It was found by a farmer digging in a field in Africa and can’t be moved because it’s too heavy. So we actually have an NEO (near-Earth object) right here on the Earth, right now for study,” Spudis said.

“I think we would learn something (by sending astronauts to an asteroid). No space mission is value-less, but in terms of what we’d actually learn compared to a robotic sample return, I don’t think we’d actually learn that much more,” he added.

While NASA officially remains focused on a mission to an asteroid, it also is supporting lunar exploration efforts. On Thursday, the agency will unveil a partnership agreement with privately owned Bigelow Aerospace to look at potential commercial lunar ventures.