Gravity, the old joke goes, isn't just a good idea; it's the law. In the real-world effort to explore the heavens, there is an even more powerful law at work making it difficult to send spacecraft out of the atmosphere: “There never is enough money for the task at hand.” Surmounting the law of insufficient funding requires as much ingenuity and persistence as blasting out of Earth's gravity will. Fortunately, the scientists and engineers in the U.S. planetary-science community are joining forces with their human-spaceflight comrades—who must deal with the same fiscal physics—to develop concepts for what may be a mutually beneficial roadmap.

Managers in the Human Exploration and Operations (HEO) mission directorate at NASA have decided to focus their efforts on bringing an asteroid closer to Earth—specifically to high-retrograde lunar orbit, 75,000 mi. above the Moon's surface—and leaving it there for a visit by astronauts in an Orion capsule lofted by a heavy-lift Space Launch System (SLS) rocket (illustration). The asteroid-capture mission would provide a near-term deep-space destination for SLS and Orion, and provide a requirements pull for the technology—automated rendezvous, long-term electric propulsion and the like—that would be needed to intercept an asteroid and nudge it toward the Moon.

Learning to operate in cislunar space could also revive hopes for the top-priority major planetary-science mission on the books. Based on “extensive interactions with the broad planetary science community,” the U.S. National Research Council (NRC) set finding and caching samples for return from Mars as its top-priority large mission into the Solar System for the decade that begins this year. Almost as soon as the so-called “decadal” was drafted, NASA changed the game for budget reasons by bailing out on its planned sample-return collaboration with the European Space Agency. But it left open a replay of last year's Mars Science Laboratory (MSL) mission, with launch in 2020, and set up a team to recommend instruments and activities for a rover based on the MSL's Curiosity.

That instrument suite probably will include provisions for finding and storing samples for eventual return to Earth, meeting the decadal-survey objective and perhaps even coming closer to the $2.5 billion price tag the NRC panel recommended (AW&ST Dec. 10, 2012, p. 32). And it could give the SLS/Orion stack another mission as NASA works its way out of Earth orbit with human explorers.

William Gerstenmaier, the associate NASA administrator for HEO, suggests Orion can provide a good way to transport Mars samples through Earth's atmosphere by collecting them from a spacecraft returning from Mars in the same high-retrograde lunar orbit targeted for a captured asteroid. The approach would avoid the need to send an Earth-reentry vehicle all the way to Mars and back. Samples cached in the 2020 rover, baselined to be nuclear-powered and certain to have nuclear heaters even if solar power becomes a better way to go, could be picked up and started on their way to Earth by another rover equipped with an ascent vehicle.

Regardless of whether human and robotic spaceflight can develop a joint approach, protecting Earth, Mars and the Orion crew from alien microbes is one technical hurdle that must be surmounted before a sample-return mission can be run. Doug McCuistion, until recently the head of NASA's Mars Exploration Program, says the best place to look for samples probably is in one of the “special regions” identified as potential sites for past or even present life. Those regions already receive special protection under planetary-protection protocols, so the approach would be to land near one of the special regions and then drive into it with a rover equipped to collect a spectrum of sample types.

Ultimately, those same areas—or areas identified by subjecting Mars samples to the kinds of analyses only available with the range of laboratories on Earth—would be potential landing sites for human explorers. But a lot more must be known about Martian habitability before planners can be sure Mars won't kill human explorers, or be contaminated by them. Special regions may be a no-go for human explorers.

“You can't sterilize a human like you can a robot,” says McCuistion. “The other [contamination] path in a special region is a problem as well, because you certainly don't want to track anything into a human habitat that then infects that habitat. So a special region with a human is challenging.”