WASHINGTON — NASA’s plan to retrieve an asteroid for astronauts to explore in lunar space by 2025 caused a big stir at the Small Bodies Assessment Group (SBAG) here July 30 when an asteroid expert delivered a withering critique of the mission and warned that it could bring NASA’s entire Planetary Science Division to ruin.

“If you get behind this in any way, it’s going to irreparably damage small-body exploration, and I think there’s implications to the broader Planetary Science Division,” Richard Binzel, an astronomer and asteroid specialist from the Massachusetts Institute of Technology, told the group.

Calling the Asteroid Redirect Mission (ARM) the White House hatched in 2013 to satisfy U.S. President Barack Obama’s 2010 challenge to send astronauts to an asteroid by 2025 a “one-and-done stunt,” Binzel warned SBAG members that embracing ARM meant risking their credibility in the eyes the lawmakers who control NASA’s purse strings. SBAG and the science community at large, he said, should “just say no” to the mission.

The NASA-charted group represents the interests of scientists who study objects as small as interplanetary dust and as large as tiny moons, such as Mars’ two natural satellites, Phobos and Deimos. A 10-person SBAG steering committee is responsible for distilling the larger group’s discussions into reports — but not recommendations — for NASA’s Planetary Science Division.

The latest such report, presented in draft form July 30, stopped short of Binzel’s outright condemnation of the mission but reiterated the cautious position SBAG adopted not long after NASA unveiled ARM in April 2013: that it is not a scientifically sound way to collect an asteroid sample and therefore “support of ARM with planetary science resources is not appropriate.”

The report explains which type of asteroids small-bodies scientists would most prefer to sample, and how a team of small-bodies experts could be integrated with ARM operations to reap the maximum scientific benefit from a mission that, while not conceived by or for scientists, fits squarely in SBAG’s wheelhouse.

When it comes to details about ARM — its cost, its exact launch date, the asteroid it will target — NASA has been tight lipped, other than to say that a new robotic spacecraft will retrieve the asteroid, and that astronauts aboard the Space Launch System-launched Orion crew capsule the agency is building will visit it around the middle of next decade.

But NASA still has to choose between a robotic retrieval of a 10-meter-diameter, free-flying asteroid, and plucking a similar boulder-sized sample off a much larger asteroid. NASA is postponing the choice until December, and further details about the chosen architecture will not be worked out until an ARM mission concept review scheduled for February.

However, Brian Muirhead, pre-program manager for ARM at NASA’s Jet Propulsion Laboratory in Pasadena, California, offered some new details about the robotic retrieval portion of ARM at the July 30 SBAG meeting.

The notional ARM missions Muirhead briefed to SBAG assume the robotic retrieval craft will launch on a United Launch Alliance Delta 4 Heavy rocket in 2019. It is a powerful but pricey launch vehicle. NASA is paying $375 million for the Delta 4 Heavy it ordered in 2011 for this December’s launch of an uncrewed Orion on an Earth-orbiting test flight. The cost of a Delta 4 Heavy is not included in NASA’s preliminary $1.25 billion estimate for building an asteroid-capture spacecraft.

Muirhead also identified six potential target asteroids retrievable between 2023 and 2025, including three small space rocks that would be brought back whole and three large asteroids from which a boulder-sized sample might be retrieved.

Dan Leone is a SpaceNews staff writer, covering NASA, NOAA and a growing number of entrepreneurial space companies. He earned a bachelor’s degree in public communications from the American University in Washington.