NASA probably will not be able to afford to send a rover to Mars in 2018 with its current budget allocation, and may have to settle for a less capable mission or wait until 2020 to send a rover under its scaled-back plan to explore the red planet.

Orlando Figueroa — a retired NASA executive tapped to head a panel drafting options for the agency as it devises a go-it-alone Mars program — told planetary scientists on the NASA Advisory Council (NAC) Tuesday that the $700-$800 million that will be available for robotic Mars exploration by 2018 under NASA ’s fiscal 2013 budget request will not support a rover.

“A stationary lander may be possible in 2018,” Figueroa says. “A mobile lander, a lander, doesn’t fit the budget we have available, so we need to jump one opportunity to generate enough funds to be able to do it.”

NASA already is “jumping” the 2016 planetary launch window — which comes around every 26 months — after pulling out of its plans to work with the European Space Agency (ESA) on missions in 2016 and 2018 aimed at preparing for a Mars sample-return mission later on. Sample return remains the top priority among U.S. planetary scientists surveyed in the National Research Council’s decadal survey in the field. Congress strongly supports that goal, and a rover would be more useful in meeting it than a stationary lander.

Figueroa says the Mars Program Planning Group (MPPG) that he chairs was established to present options for a new U.S. Mars program that both retains the sample-return goal and draws on funds and expertise held by NASA ’s Human Exploration and Operations (HEO) Mission Directorate, the Office of the Chief Technologist (OCT) and the agency ’s chief scientist , as well as the planetary science organization within the Science Mission Directorate. The MPPG is working with those NASA organizations, as well as the larger U.S. and international planetary science communities to develop options that will fit within the diminished U.S. Mars exploration budget while contributing as much as possible to human knowledge of the planet.

As an alternative to a stationary lander , the funds expected to be available in 2018 probably would support a new orbiter that could help pinpoint potential landing sites for future rovers that could characterize and cache samples for return to Earth eventually. An overarching objective of the MPPG is to develop “pathways” that would ensure samples of the planet ’s surface would be in orbit above it no later than 2033. That year would be particularly advantageous for a Mars-Earth transit, Figueroa says, stressing that the samples could be returned by a robotic spacecraft or human explorers.

Other factors in play are how well new technology is “infused” into exploration plans . One area that Figueroa says is getting a lot of attention from OCT and HEO is laser communications, which would provide broadband links for robotic and human exploration missions.

The NAC Planetary Science Subcommittee met as the House of Representatives took up the Republican-drafted fiscal 2013 appropriations bill that includes NASA . The bill would add $88 million to NASA ’s funding request for Mars exploration in fiscal 2013 (the Senate version would add more than $100 million). But Jim Green, NASA ’s planetary science director, reiterated that “the train has left the station” on working with ESA, which has joined forces with Russia as a replacement for NASA in its ExoMars program.

The White House has threatened a presidential veto of the House bill, based in part on cuts in NASA spending to support development of commercial crew vehicles. In an election year, that kind of jousting could lead to a flat continuing resolution (CR) instead of a new funding bill. Green says there is no guarantee that the Science Mission Directorate would continue to fund Mars exploration at fiscal 2012 levels, and warned that managers could even decide to cut it under a CR below the amount requested for fiscal 2013.

In the meantime, Green says the Mars Science Laboratory remains on track for a landing in the Gale Crater on the night of Aug. 5-6. The mission ’s nuclear-powered Curiosity rover will remain the near-term focus of robotic Mars exploration in the years ahead, provided its untried “sky crane” landing technique works as planned.