Reaction to NASA’s new plan to capture a small asteroid and transport it to lunar orbit for an up-close astronaut inspection has ranged from cautious to skeptical, suggesting that the space agency has some tough selling to do. 

The asteroid capture mission is the sole highlight in a NASA budget request that otherwise seeks to maintain the status quo in 2014. Funding requested for the agency’s highest-profile programs — commercial crew and cargo, Space Launch System (SLS), Orion deep-space crew capsule and James Webb Space Telescope — fell in line with expectations.

Some prominent lawmakers, among them House Science Committee Chairman Lamar Smith (R-Texas), said they were taken aback by the asteroid capture proposal, formally unveiled April 10, and have been asking pointed questions ever since. That’s perfectly fair.

In contrast, another group of lawmakers — all staunch supporters of SLS — has introduced legislation mandating that the Moon be the focus of NASA’s human exploration program, never mind the fact that there’s no funding available for such an endeavor under any imaginable budget scenario, or that space policy is a presidential prerogative.

What’s ironic about Congress’ skepticism over the asteroid capture mission is that, if nothing else, it provides a destination of sorts for the congressionally mandated SLS, which otherwise is an immensely expensive capability in search of a mission. The same holds true for Orion, a deep-space capsule that was justified in part as a backup to commercial crew taxis for the international space station, a stretch at best.

In a closely related aside, the SLS and Orion factions on Capitol Hill continue to complain that these programs are being shortchanged in favor of NASA’s effort to nurture commercial crew taxis to the space station. These concerns are misplaced: Unlike SLS and Orion, the Commercial Crew Program has a clearly defined and time-urgent mission of restoring independent U.S. crew access to the space station. It is the latter program that continues to be underfunded in appropriations bills, ensuring prolonged dependence on Russia for increasingly expensive crew access to the space station.

The asteroid mission, though it seems a bit far-fetched, has some inherent appeal. It’s certainly novel, with the potential to capture the public’s imagination in a way that was seen this past summer when NASA landed a car-sized rover on the surface of Mars. Moreover, it would leverage investments NASA’s already making, not just in SLS and Orion but also in solar electric propulsion and robotic technologies that could apply to future astronaut travel to deep-space destinations. 

But lawmakers have legitimate questions about this mission that deserve unambiguous answers. To begin with, NASA must clearly explain how it expects to find an asteroid that can be hauled into lunar orbit in time for a visit by the first SLS-Orion crew in a mission currently targeted for 2021. NASA has acknowledged that the asteroid used to develop the capture scenario, 2009 BD, is not suitable for the actual mission because it couldn’t be redirected to lunar orbit until late 2024. 

NASA’s notional backup plan, which would have the first crewed Orion rendezvous not with a captured asteroid but with the spacecraft designed to perform the retrieval mission, probably isn’t worth the investment: There has to be some scientific return to help close the case for this mission. 

Speaking of investment, the $1 billion price tag assigned to the mission — not including SLS and Orion — seems unrealistically low. NASA’s track record for estimating the costs of large, one-of-a-kind missions is not good, and starting ambitious programs only to abandon them because they prove too expensive only hurts the agency and its stakeholders in the long run.

But perhaps NASA’s biggest challenge is demonstrating that this is a serious plan and not merely a technology stunt or — worse — a placeholder designed primarily to blunt critics who correctly note that NASA lacks a realistic, near-term human spaceflight objective beyond the space station. NASA is seeking only $105 million to begin work on the asteroid capture mission in 2014, but that’s too much to spend — in any budget environment, let alone the current one — if NASA cannot make a convincing case that this is real.