Although it has been less than thrilled by NASA’s effective taboo on lunar exploration, Congress has adopted a good-cop approach toward the agency's asteroid-then-Mars human spaceflight plans during the last six years. In hearings, members have suggested that the space agency reconsider its human mission to an asteroid and perhaps work with Europe on some tentative plans to send humans to the surface of the Moon. But NASA hasn’t acquiesced to this gentle cajoling.

During the recent appropriations process in the House, as Ars reported in May, members exercised the power of the purse to more forcefully nudge NASA back toward the Moon as an interim step to Mars. Lawmakers zeroed out funding for the asteroid mission and encouraged NASA to “develop plans to return to the Moon to test capabilities that will be needed for Mars, including habitation modules, lunar prospecting, and landing and ascent vehicles.” After discussions with lawmakers, aides, and officials in the aerospace community since then, it has become clear this is no transient movement. Rather, the Moon-then-Mars plan has bipartisan support.

NASA’s prohibition on lunar exploration dates to 2010, when President Obama set NASA's human exploration program on a course to visit an asteroid by 2025 and then on to Mars in the 2030s. As for the Moon, then the short-term goal of NASA’s human spaceflight program, Obama said, “We’ve been there before.” Now House members see the end of Obama’s presidency looming and have found his go-it-alone approach toward Mars probably will not be supported by the next president—Republican or Democrat.

Although the House language must still go to conference with the Senate, it seems unlikely anyone in that body will fight too hard to save the asteroid mission, Capitol Hill sources told Ars. Even if the administration vetoes the bill, it doesn’t really matter to Congress, because key members of Obama's leadership team, including NASA Administrator Charles Bolden, will probably be gone next year. This year's legislation effectively lays down a marker for negotiations with the new occupant of the White House in 2017.

The key legislators behind the new exploration approach for NASA, California Democrat Mike Honda and Oklahoma Republican Jim Bridenstine, at first blush seem an unlikely pair. Honda consistently ranks among the most liberal House members and Bridenstine among the most conservative. But with this new legislation, they have come together out of a desire for NASA to reconsider the Moon as a pragmatic interim destination before going to Mars.

"There is no better proving ground than the Moon for NASA to test the technologies and techniques needed to successfully meet the goal of sending humans to Mars by the mid 2030s,” Honda told Ars. “I am proud to lead the Congressional effort to ensure that NASA develops a plan to fully take advantage of potential partnerships with commercial industry, academia, and international space agencies to send affordable missions to explore and characterize the lunar surface.”

Some of the Congressional dissatisfaction stems from the asteroid mission proposed by Obama back in 2010. Initially the agency sought to send astronauts into deep space to visit an asteroid in its native environment. However, that proved too costly and challenging, so the mission got de-scoped into bringing an asteroid back to the vicinity of the Moon. Even this proved too much, though, so now the plan is to grab a small boulder off the surface of an asteroid and bring that back to a location near the Moon where astronauts can visit it and technically fulfill the president's asteroid goal.

Legislators have looked at this asteroid mission with increasing skepticism, providing only limited funding in recent budgets. This year NASA asked for a larger chunk of money, $66.7 million, to begin work on developing the robotic spacecraft and other components of the asteroid mission. But with this legislation, Congress has said "no," telling NASA to instead direct those funds toward lunar efforts.

“Experts testifying to the House Science Committee have stated that the Asteroid Redirect Mission will lead to many dead end technologies,” Bridenstine told Ars. “Congress is advising NASA to pivot away from (the asteroid mission) toward focusing more directly on developing technologies beneficial to a Mars mission.”

Although he does not have any major NASA centers in his state of Oklahoma, Bridenstine has expressed an interest in US civil and military space programs, authoring the American Space Renaissance Act to modernize the governance of space. In just his second term as a representative, Bridenstine has established himself as a leading supporter for a strong private space industry. With his proposed renaissance act, he wants to lower the barriers to access to space and provide a pathway for the commercialization of low-Earth orbit and eventually the Moon.

While Honda, the ranking minority member of the House appropriations subcommittee over NASA’s budget, and Bridenstine both believe in Mars as NASA's goal for human exploration, they see the Moon as a more realistic interim step. They found common cause on these issues with the funding committee’s chairman, John Culberson, who also views the lunar surface as a stepping stone to Mars. That politician simply see it as a more feasible, sustainable approach to exploration.

There are three primary lines of argument in favor of the Moon. One is geopolitics. Every one of NASA’s international partners supports a Moon-first strategy, and there is the risk if NASA shoots for Mars that China or Russia might lead development of some type of lunar colony. Then there is commercialism. Planning missions to the Moon would provide additional business opportunities for a thriving commercial space industry that may see Mars as a step too far for its existing business plans. And finally, there is the potential to make deep space exploration more economical. Lunar miners could tap into ice at the Moon's poles to provide hydrogen and oxygen propellants to fuel spacecraft for journeys to Mars.

The counter argument to this from Mars-first advocates is: if we don't go to Mars now, then when? Lawmakers appear to be saying that, absent a vibrant in-space economy that builds outward from Earth in a step-by-step manner, an Apollo-like journey to Mars simply isn't sustainable.

The bill requires NASA to prepare a preliminary report for Congress within 90 days of its enactment that will detail planned and ongoing activities to prospect for resources on the Moon. That report will also outline existing and potential relationships with commercial and international partners.