WASHINGTON A NASA plan to send astronauts to an asteroid was met with skepticism Wednesday when NASA Chief Charlie Bolden presented the idea to top space officials in Congress though their doubts may not be enough to sink the program.

The asteroid mission, unveiled a few weeks ago, would send a NASA probe to capture a small asteroid and drag it to a point near the moon so astronauts riding a new rocket and capsule could visit it, possibly as soon as 2021.

"The goal is [to] remain the world's leader in exploration," Bolden said. But members of the U.S. House science committee took issue with the project's cost and feasibility and questioned why the agency wasn't planning a return to the moon en route to an eventual mission to Mars.

The NASA chief delivered a blunt reply: It's all NASA can afford.

"I need money to go to the moon," Bolden said.

As part of its 2014 budget proposal, the White House wants NASA to spend $105 million next year to begin planning the asteroid mission, which could cost upward of $2.6 billion.

Broadly, the administration envisions sending a probe as soon as 2017 to capture a 25-foot, 500-ton asteroid and tug it near the moon possibly to a spot about 277,000 miles from Earth that would use competing gravitational forces to allow it to "sit" there.

Astronauts flying NASA's new Orion capsule and Space Launch System rocket then would visit it to take samples and possibly set foot on its surface.

In addition to scientific benefits, Bolden said an asteroid trip would serve as a steppingstone for an eventual Mars mission while also teaching NASA engineers how to divert an asteroid in case one ever threatened Earth. He called it "an unprecedented technological challenge."

Lawmakers, however, wanted to know whether NASA would learn more and do more by going back to the moon instead.

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NASA chief: Visiting an asteroid is all we can afford