“We are cutting the metal for the 2016 mission,” Dordain says. “It's not yet a reality, but close to a reality.”

In Washington, the MPPG reported last week that NASA may be able to return samples from Mars without significant international cooperation, in part by eliminating stovepipes in the way it organizes for scientific and human space missions. Set up after the Obama administration dropped its plans to collaborate on ExoMars, the planning group found lower-cost—but less-capable—sample-return missions still are possible, particularly if NASA's space science and human exploration organizations work together more closely, using the agency's Office of the Chief Technologist to develop hardware that serves the needs of both.

“Sending a mission to go to Mars and return a sample looks a lot like sending a crew to Mars and returning them safely,” says John Grunsfeld, a former space shuttle mission specialist who is the associate administrator for science.

Headed by retired NASA “Mars czar” Orlando Figueroa, agency and outside scientists and engineers on the MPPG spent five months developing options for a U.S.-only mission that follows the sample-return priority set in the “decadal survey” of planetary scientists run by the National Research Council last year.

Briefing the NRC's Committee on Astrobiology and Planetary Science (CAPS) Sept. 25, Figueroa presented robotic Mars options that could fly in the planetary launch windows in 2018, 2020 and 2022. With U.S. spending for the next mission to Mars limited to a Discovery-class mission capped at $800 million, Figueroa said there is probably not enough funding to land another rover on Mars in the 2018 window to identify and cache samples for eventual return to Earth.

Congress may not agree, however. Both houses added back $100 million for Mars exploration in fiscal 2013 spending measures that are still pending, although superseded by continuing resolutions. At that level, some of the options presented by the MPPG could be affordable under the fairly rigorous cost estimates included in the MPPG report.

“Basically we're getting what the decadal survey wanted in terms of science, and now the cost numbers have been looked at much more carefully,” says Arizona State University geological sciences Prof. Philip R. Christensen, who is chairman of the CAPS panel that Figueroa briefed. “We know MSL [the Mars Science Laboratory] worked, so we can rely on build-to-print MSL elements, so I think the $1.5-1.7-billion estimate is far closer, far more accurate, and will do exactly the science that the decadal survey was asking for.”

Based on the $800 million cost cap the MPPG used, Figueroa left the impression that a rover in 2018 could supplement the aging “infrastructure” of Mars orbiters able to relay commands and data. The planning group lists four orbiter options of increasing complexity that could be flown within the $800 million constraint. They include a $200 million single-purpose relay satellite launched to Mars as a secondary payload, and a combined science and relay orbiter based on the Mars Reconnaissance Orbiter and the upcoming Mars Atmosphere and Volatile Evolution (Maven) mission that could probably stay under the cost cap if launched on private contractor SpaceX's Falcon 9. Other options were a $500 million solar-electric-propulsion sample-return orbiter built with commercial components and piggybacked on the launcher for a lander, and an orbiter that would conduct research while waiting for sample deliveries from the surface, at a cost of $700 million plus a Falcon 9 launch.

Sample-return also would require a Mars ascent vehicle that possibly could be carried by the most expensive rover option the planning group identified. Designated Rover D, the vehicle would be a solar-powered version of the nuclear-powered MSL to save money. It would carry an ascent rocket along with a robotic arm to collect samples. Other rover options are a solar-powered version of Rover D without the ascent vehicle, designated Rover C, and two solar-powered rovers—A and B—based on the twin Mars Exploration Rovers Spirit and Opportunity, both with the guided-entry capability that put Curiosity down in Gale Crater, and distinguished from each other by the level of heritage hardware incorporated in their mechanical systems.