space-science managers and the scientists they serve want to use the newly announced Curiosity 2.0 rover to collect samples for eventual analysis on Earth.
But with U.S. federal spending teetering on the “fiscal cliff,” the space agency's White House overseers are not ready to commit to a mission that is pointless without an expensive follow-on to develop a way to get the samples back.
Instead,is setting up a “science definition team” to decide how to use the proposed Curiosity-derived rover when it reaches the surface of Mars in 2020. The instruments that will ride on the big rover will be chosen in an open competition based on that team's work, starting with an announcement of opportunity next summer. Like Curiosity, the new rover will again use the “sky crane” technique to touch down.
Mars Sample Return (MSR) remains the top priority of the planetary scientists polled by the National Research Council for its latest decadal survey on the subject. A pickup committee of experts NASA pulled together after the U.S. bailed out of a joint sample-return effort with Europe last year reiterated that goal this fall. But in announcing the agency's decision to spend $1.5 billion—give or take $200 million—to launch another rover to the surface of Mars in 2020, NASA'S science chief was careful to keep his options open.
“The science definition team is going to have to weigh what science do we want to get done; how much mass and power do we have available; what can we get to the surface and where do we want to go,” says Associate Administrator John Grunsfeld. “[The team] may decide that they want caching [or] they may decide that they would rather use that weight and volume for additional in-situ science to go to some really interesting place that would emerge from what we discover in the next six months to eight months on Curiosity.”
NASA's plan to build another Curiosity-class rover, announced Dec. 4 in San Francisco at the American Geophysical Union Fall Meeting, follows a decision to place an astrobiology instrument on the European Space Agency's (ESA) planned 2018 rover mission to drill deeper than ever below the Martian surface. The Mars Organics Molecule Analyzer (MOMA), will use gas chromatograph mass spectrometry and laser desorption mass spectrometry to analyze samples retrieved from as much as two meters below the surface by ESA's ExoMars drill. It also reestablishes some of the coordination with ESA in Mars exploration lost when NASA pulled out of ExoMars for budget reasons, and the European agency turned to Russia for launches and other help (AW&ST Feb. 20, p. 33).
Coupled with Curiosity's findings as it explores the rock layers in the central mountain that rises from the floor of Gale Crater, and detailed data collected from the Mars Odyssey orbiter, Mars Reconnaissance Orbiter (MRO) and ESA's Mars Express orbiter, results from the U.S. instrument on ExoMars should help guide the 2020 mission to a likely site for evidence of life on Mars, says Scott Hubbard, a Stanford University professor who was NASA's first “Mars czar,” and has written a memoir—“Exploring Mars”—based on that experience.
“In principle, you get below the irradiated top meter or so, down to some material that is more pristine, that hasn't been disturbed by radiation or the surface environment or what they call gardening, where meteorites hit and churn up the soil,” Hubbard says.
Grunsfeld also stresses that NASA is providing its Electra radios for ESA's 2016 ExoMars orbiter, which would be able to act as a relay for the 2020 U.S. rover in case the MRO spacecraft playing that role for Curiosity goes down.
“It allowed us to reengage with the Europeans on ExoMars,” he says of the decision to launch another lander. “They're very good partners.”
Before their Mars-exploration split, NASA and ESA were working together to cache promising samples for later return to Earth, where the full array of scientific hardware and expertise can be brought to bear on finding evidence of life—past or present. After the split, NASA's Mars Program Planning Group concluded NASA could bring back samples on its own, and noted that a new rover using “build-to-print” components from Curiosity “will do exactly the science that the decadal survey was asking for” (AW&ST Oct. 1, p. 36).
Gunsfeld says continuing analysis shows NASA has the spare parts, plans and knowledge to create a new rover on the Curiosity pattern, including a spare radioisotope thermoelectric generator and an engineering model that can be converted to the backup. Jim Green, director of NASA's Planetary Science Division, says NASA's Energy Department alottment of plutonium-238 fuel is adequate for the rover's RTG.
The agency also has a supply of flight-qualified spare actuators that can be used to to move the wheels, arm joints and other elements of a new rover. Theand its Curiosity suppliers still are running inventory to see what other parts are available.
Ultimately, the configuration of the new rover will be based on recommendations generated by the science definition team being set up by Michael A. Meyer, lead scientist for NASA's Mars Exploration Program, Green says. As NASA draws on its human spaceflight and space-technology efforts for the rover project, the panel will be pulled from scientists and engineers working on human exploration and exploration-enabling technology as well as planetary science, he says.
Even the power source is on the table, with solar power a possibility if the mission requirements call for it. Some Pu-238 still would be needed for heaters to keep the rover electronics warm during the Martian nights, and a caching rover still would need in-situ science instruments like those on Curiosity to select the samples to be cached.
Curiosity is the largest payload ever landed on Mars. Its sky crane landing technique, lowering the rover to a wheels-down landing on cables played out from a platform hovering on retro rockets above the surface, was untried until its Aug. 6 success inside the equatorial Gale Crater. Grunsfeld and Green say that approach will also be used on the second rover, maintaining the skills at JPL that enabled the success with Curiosity.
But the entry, descent and landing that worked so well on Curiosity won't be duplicated. Some changes likely will be made to take advantage of lessons learned and accommodate more mission mass. Grunsfeld notes the heat shield that protected Curiosity during atmospheric entry was “very conservative, very thick,” and analysis shows there might not have been a need for so much shielding. While there might be weight savings with a thinner shield, Grunsfeld says mission planners also must decide “is that a cost-driver?”
While NASA says the 2020 mission will fit into the budget profile carried in NASA's fiscal 2013 budget for Mars exploration, the mission is contingent on the funds actually being appropriated by Congress. And Grunsfeld says the same budget profile fell short of the funding needed to support a launch in 2018, when the planetary alignment would be particularly favorable for a trip to Mars.