WASHINGTON — As NASA gears up a decade-long effort to return samples from Mars, some scientists are worried that the campaign may not leave any funding available for other robotic missions to the planet.

The only future NASA mission to Mars under development is Mars 2020, a rover currently in the final stages of assembly and scheduled to launch in July 2020. The rover, based on the Curiosity rover that has been on Mars for seven years, will cache Martian rock and soil samples for later return to Earth.

While NASA hasn’t formally committed to the additional missions needed to retrieve the samples and return them to Earth, both NASA and the European Space Agency have started planning for them. That approach includes a NASA-led mission to land on Mars, fetch the samples and launch them into orbit around the planet, and an ESA-led mission to grab the sample container in orbit and return it to Earth. Both missions would launch in 2026, returning the samples in 2031.

But as attendees of a meeting last month of the Mars Exploration Program Analysis Group (MEPAG) in Pasadena, California, noted, there are virtually no other Mars robotic missions being developed. The only exception is Escape and Plasma Acceleration and Dynamics Explorers (EscaPADE), a proposed smallsat mission to study the interaction of the solar wind with the Martian atmosphere that NASA selected in June as part of a new planetary science smallsat program. NASA is funding further studies of EscaPADE, but with no guarantee the mission will be approved for development and launch.

That’s led to concerns that Mars sample return is pushing out other research that scientists want to perform at Mars. “Our highest priority is Mars sample return, but we have other priorities as well,” said R. Aileen Yingst, chair of MEPAG, in comments at the beginning of the group’s July 26 meeting. “We should address outstanding science questions in parallel with, or as part of, sample return. Right now, there are no flight opportunities that look forward in that way.”

She noted that in addition to a lack of flagship-class Mars missions like Mars 2020, scientists can’t propose medium-sized New Frontiers missions since such missions, while competed, are limited to only a handful of selected destinations that, for now, excludes Mars. The smaller Discovery program, which also selects missions in a competition, can be used for Mars missions, like the InSight lander. However, she said, “it is problematic to get to Mars under the Discovery cost cap.”

“There is some concern in the community that new data may not be forthcoming any time soon,” she concluded.

Later in the meeting, scientists asked NASA officials in attendance about options to address this, such as flying additional science instruments on the sample return lander and orbiter missions launching in 2026.

Jim Watzin, director of NASA’s Mars Exploration Program, said NASA did consider flying additional science payloads on those missions early in their development. However, he argued that didn’t fit into the “lean” Mars sample return architecture announced nearly two years ago by Thomas Zurbuchen, NASA associate administration for science, which seeks to perform sample return as quickly and as inexpensively as possible.

“That was the right decision,” he said. Those sample return missions face “very, very intense propulsive demands” to get to Mars and back. “Every time I add an extra kilogram of mass to that, it makes the problem harder and harder to implement.”

Some asked about another orbiter to handle communications with the surface and other roles, such as imaging, given the age of existing orbiters. Watzin said that launching the other two parts of the sample return campaign in 2026 means there is a “reasonable probability” that existing orbiters will still be able to operate at least as communications relays.

As for an orbiter to do science, Watzin was more pessimistic. “Unfortunately we live in a world with restricted budgets,” he said, acknowledging the need for a need for a new remote sensing mission to support science and, potentially, future human exploration.

“Do I have a plan today? No,” he said about a new orbiter.