WASHINGTON — NASA would consider sending the first crewed Orion mission to rendezvous with a robotic spacecraft in lunar orbit if it cannot redirect an asteroid to the Moon by 2021, a space agency official told a pair of advisory panels.

When NASA rolled out its asteroid initiative as part of its 2014 budget proposal on April 10, the agency said its goal was to bring an asteroid into orbit around the Moon by 2021 so that the previously scheduled first crewed Orion mission, designated EM-2, could rendezvous with the asteroid.

However, NASA has not yet identified a specific asteroid for this mission. Speaking to the Human Exploration and Operations Committee of the NASA Advisory Council (NAC) April 18, William Gerstenmaier, NASA associate administrator for human exploration and operations, said NASA had identified about 13 asteroids with appropriate sizes and orbits, with one to two new ones being discovered each year, but that further study was needed before selecting a specific target.

“This is one of the things we have to watch,” he said. “I don’t believe I can guarantee today, with the assets and the amount of visibility we get into these targets, that we can find one that we can, with 97 percent probability, capture.”

NASA has developed a notional asteroid capture and redirection mission involving one small asteroid, 2009 BD. In that mission plan, a robotic spacecraft would launch in June 2018, arriving at the asteroid in April 2020. The spacecraft would then start to redirect the asteroid toward the Moon, putting it into a final orbit around the Moon in October 2024.

Gerstenmaier, briefing this mission concept before both the NAC committee and the National Research Council’s (NRC) Committee on Human Spaceflight here April 22, acknowledged that this particular scenario failed to meet the 2021 goal. “This was done as kind of a proof of concept,” he told the NRC committee. “This is not the object we would go to.”

Asked by the NRC committee what NASA would do if it could not find a suitable asteroid, Gerstenmaier said it would still fly the solar-electric propulsion spacecraft to demonstrate its technologies. “I would send that spacecraft on a pretty demanding demonstration mission, which we planned to do anyway,” he said. “Then I would put this spacecraft into this retrograde orbit, and then use Orion to go to that retrograde orbit.”

The asteroid initiative has received a lukewarm reception from many in the space community since the April 10 announcement, failing to win over people already skeptical of human asteroid missions. “I am hard pressed to run into anybody who thinks that going to an asteroid is the right way, primarily, to go on to Mars,” said Scott Pace, director of the Space Policy Institute at the George Washington University here, in a separate presentation to the NRC human spaceflight committee.

Planetary scientist Steve Squyres, chairman of the NAC, told the NRC committee that he endorsed two elements of NASA’s initiative, enhanced efforts to discover and track near-Earth asteroids and a crewed mission to lunar orbit, be it to an asteroid or just a robotic spacecraft. “Even if all you do as your next step in human spaceflight beyond low Earth orbit is to send people to cislunar space for 21 days, it’s worth doing,” he said.

Squyres, who said he was speaking for himself only since the NAC had not yet provided advice to NASA on the asteroid initiative, was undecided on the feasibility of the redirection mission. “I don’t know if this thing can be done or not,” he said. “It needs a really hard, carefully considered look, and then we’ll see.”

Squyres cautioned NASA not to sell such an asteroid mission on the basis of the science it can perform. “It’s not cost-effective,” he said. The money spent on an asteroid redirection mission could instead be spent, he said, on “a small fleet” of robotic spacecraft that could go to multiple asteroids.

He also warned against selling the mission as achieving the goal established by President Barack Obama in his April 2010 speech at NASA’s Kennedy Space Center of sending humans to an asteroid by 2025. That speech, Squyres noted, called for sending crewed missions into deep space beyond the Moon, starting with an asteroid. “I don’t think it was the president’s intent” to satisfy that goal by moving an asteroid to cislunar space, Squyres said.

Squyres said that he has not heard anyone at NASA make the claim that the asteroid capture mission satisfies that presidential goal, but in at least one case a senior NASA official has done so. “The president challenged us to do this back in 2010,” NASA Chief Financial Officer Beth Robinson said in her April 10 presentation on the NASA budget proposal. “He said to do it by 2025, and we now have a plan to do that perhaps as early as 2021.”

Jeff Foust writes about space policy, commercial space, and related topics for SpaceNews. He earned a Ph.D. in planetary sciences from the Massachusetts Institute of Technology and a bachelor’s degree with honors in geophysics and planetary science...