WASHINGTON — NASA plans to redirect a small asteroid into lunar orbit during the next decade as part of a steppingstone approach to landing astronauts on Mars by the 2030s.

Some key leaders in Congress, which must approve funding for the mission, prefer returning to the moon. That plan was scrapped a few years ago by President Obama, who canceled the Constellation Program due to what an independent commission called unsustainable costs.

Here's a look at relevant questions and answers about NASA's asteroid redirect mission, or ARM.

Q: How exactly would the mission work?

A: NASA is exploring two options. The first would identify a small asteroid (about 7 to 10 meters) not far from Earth, use a robotic spacecraft to retrieve it, then drop it into the moon's orbit. An alternative plan would extract a boulder from a larger asteroid and do the same thing.

Once the asteroid is in lunar orbit, a crew of two astronauts would use a deep-space rocket and the Orion crew vehicle NASA is developing to visit the floating rock and dock to the robotic spacecraft still attached to it.

Q: How will NASA find a suitable asteroid?

A: The agency already has identified more than 11,000 asteroids, or "near Earth objects." Three of them, none bigger than a school bus, are being monitored for the mission.

They are believed to have the mass, shape, spin rate and orbit that could prove viable targets for a mission. Three larger ones have been identified as possible candidates for the boulder alternative.

Q: How much will it cost?

A: Estimates range from $1.25 billion to $2.6 billion, not including the cost of developing the deep space rocket and Orion capsule. That would be considerably cheaper than using the moon as a steppingstone to Mars, which would require more infrastructure, notably a lunar lander.

Lack of money has forced NASA to reassess its missions. Unless a more ambitious plan gets broad international buy-in — or Congress decides to approve significantly more money for NASA — an asteroid mission looks like the agency's best option for a deep-space mission for now, said John Logsdon, former director of the Space Policy Institute at George Washington University.

"It's the most interesting mission to undertake, given the current ground rules and current budget," he said.

Q: Are there other advantages of visiting an asteroid?

A: Yes. The most relevant is the opportunity to study the floating space rocks. More information about their composition and how they hurtle through space should help scientists determine how to deflect those that are on a collision course with Earth.

There's also interest in mining asteroids for metals, rare minerals and frozen water, which could be converted into liquid oxygen and liquid hydrogen for rocket fuel that would make a trip to Mars easier and cheaper.

Q: Why is there interest in returning to the moon?

A: The idea leaves some people with a been-there-done-that feeling. But supporters of the proposal say returning to the moon would provide a gateway to the rest of the solar system and enable scientific discoveries valuable to an eventual Mars mission.

It also would give an emerging commercial space industry opportunities to test new technologies and mine for minerals. And it would give the U.S. a chance to partner (read: share costs) with other countries it's been at odds with lately, such as China and Russia.

"There's really no enthusiasm among any of our (international) partners for the ARM," said Cliff Zukin, a Rutgers University political science professor.

Q: What does Congress have to say about this?

A: Lawmakers are split on the asteroid plan. Republican leaders have criticized it as uninspiring and a waste of money, and say it lacks broad support from the scientific community.

Part of that reaction stems from bruised feelings over Obama's decision to abolish the return-to-the-moon Constellation Program — which had been championed by President George W. Bush — without consulting Congress.

Democrats are more supportive, though they're not particularly keen on the asteroid idea either.

Q: What happens next?

A: NASA scientist will continue looking for the best asteroid to use for the mission. The agency also is planning a December test launch from Kennedy Space Center in Florida of an unmanned Orion vehicle atop a United Launch Alliance Delta IV heavy rocket.

Congress, meanwhile, is working on NASA's budget request, which includes about $133 million for the asteroid mission. Space committees in the House and Senate have passed similar spending plans for NASA but have yet to work out a compromise on a final budget.

Contact King at lking@gannett.com; Twitter: @ledgeking

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