NASA’s near-term plans for Mars exploration are taking shape. On March 9, NASA confirmed it was rescheduling the launch of the InSight Mars lander, originally planned for this March, to May 2018 to provide more time to correct problems with one of its key instruments. That will be followed by the Mars 2020 rover, scheduled to land on Mars in early 2021.

But what comes after Mars 2020? NASA has yet to formally announce a mission that would launch in the next window, in late 2022. However, the agency and the Mars science community are coalescing around the idea of an orbiter, NASA’s first since the MAVEN spacecraft that launched in 2013. Exactly what it will do, though, remains a topic for debate.

“We’ve come to the point in time that we have to start seriously planning and thinking about what we do” after the 2020 rover mission, said Jim Watzin, director of NASA’s Mars Exploration Program, at a March 2 meeting of the Mars Exploration Program Analysis Group (MEPAG) near Washington.

Part of the planning, he said, takes into account NASA’s existing missions, including MAVEN and the Mars Reconnaissance Orbiter (MRO), which marked a decade in Mars orbit in March. Besides their science missions, the spacecraft are designed to serve as telecommunications relays between rovers on the surface and the Earth. By 2022, though, MRO will likely no longer be operational and MAVEN will be nearing the end of its life.

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“Many of the assets that we depend upon for daily operation, and even others depend upon for support, are getting very old,” Watzin said. “An orbiter is the most logical step to do next.”

Besides being a telecommunications relay, scientists envision the 2022 orbiter building upon current science being done from Mars orbit. That includes continuing imaging done by MRO, which has taken medium-resolution images of 95 percent of the planet’s surface and high-resolution — better than one meter per pixel — images of more than 2 percent of the surface. Those images will also be important for planning future Mars missions, both robotic and human.

A report chartered by MEPAG and completed late last year identified other scientific objectives for an orbiter mission, including studying ice deposits and looking for more evidence of present-day liquid water on the surface. Those instruments also could search for resources, like water, to support future human missions.

The MEPAG report offered a baseline set of instruments that could achieve those science and resource goals, including high- and low-resolution cameras, infrared instruments and an atmospheric sounder. “This is not MRO 2,” said Rich Zurek, a Mars scientist at the Jet Propulsion Laboratory who cochaired the MEPAG study, at the meeting. “This is a different system, and it does different things.”

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NASA’s Mars Reconnaissance Orbiter being prepared for its 2005 launch. The $720 million mission has been essential in mapping the Martian surface and serving as a communications relay, but will likely reach the end of its life by 2022. Credit: NASA

A complicating factor is the desire to have the orbiter contribute to a broader effort to return samples from the surface of Mars to the Earth, an effort rated a top priority by planetary scientists in their latest decadal survey. The Mars 2020 rover will collect those samples, but additional missions will be needed to fetch them and send them back to Earth.

“Having an orbiter in place also allows us to now think about how we can support the decadal priority of sample return,” said Watzin. “Obviously, from an infrastructure perspective, that will be critical, but there’s also other orbiter capabilities we can start thinking about.”

One potential role that the MEPAG study considered for the 2022 rover is to perform technology demonstration of capturing a sample return container in Mars orbit. However, the study also argued it could be possible for an orbiter to capture a sample cache launched into Mars orbit and return it to Earth.

Those options would require the use of solar electric propulsion, a technology NASA has already identified as a major priority in its human Mars exploration efforts. A simple demonstration of releasing, then capturing, a prototype sample return container could be done with relatively modest solar electric systems. An Earth-return mission would require the use of a more powerful “exploration” system, similar to that proposed for use on NASA’s Asteroid Redirect Mission.

In the case of a full-fledged sample return mission, the orbiter would remain in orbit for at least five years, carrying out its science and relay roles, while another spacecraft landed on Mars, gathered the samples collected by the 2020 rover, and launched them into Mars orbit. The 2022 orbiter would then collect the sample and use its solar electric propulsion system to slowly spiral out of Mars orbit and return to Earth.

“The advantage of solar electric propulsion is that it’s the one way to come back home,” said Bruce Campbell of the Smithsonian Institution, another co-chair of the MEPAG orbiter study. “You get a tremendous amount of scientific capability while you’re in orbit, moving up and down, but you also have the capability that this mission could grab a sample in orbit and bring it home.”

Solar electric propulsion could also, as Campbell suggested, support the orbiter’s science mission. It would allow the spacecraft to gradually spiral down to a low science orbit. As part of that process, it could stop near the orbits of Phobos and Deimos, the two small moons of Mars, for studies of those bodies, Zurek said.

Solar electric propulsion would also allow the spacecraft to change the inclination of its orbit during its mission, enabling different scientific studies. “You almost get two kinds of missions in the same mission,” he said.

Watzin, while not formally backing using the orbiter as part of a Mars sample return mission, did support the use of solar electric propulsion in some form. “It gives us a lot of things that we can exploit to make it a very productive mission,” he said. That could include reducing the overall mass of the spacecraft, allowing for the use of a smaller rocket. “It’s very attractive all around.”

There are no cost estimates yet for any of these orbiter concepts, or a budget for the 2022 mission. Watzin, though, is conscious of the likely funding pressures such a mission will face, particularly after the flagshipclass 2020 rover. In his presentation, he emphasized using a less-expensive “Discovery-class” spacecraft bus that could, potentially, be upgraded to support solar electric propulsion.

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A slide from a March presentation at the MEPAG meeting illustrates the range in concepts for a 2022 orbiter, from a basic orbiter similar in capabilities to past missions to one using solar electric propulsion that could return Mars samples to Earth.

NASA has requested $10 million for the mission in 2017 to support initial studies. “We’re on track,” Jim Green, director of NASA’s planetary sciences division, said at the MEPAG meeting.

There was a sense of urgency, though, among those at the meeting to start work on the mission as soon as possible in order to keep the mission on track for a 2022 launch. That includes issuing within the next year an announcement of opportunity for orbiter instruments, one of the long-lead items for the mission.

Scientists want to avoid slipping the mission to the next launch window, in 2024. “Obviously, for continuity of telecommunications and other infrastructure assets, the earlier the better,” Campbell said, adding that’s also true for resource studies to support later human missions.

A notional schedule for the orbiter would start initial Phase A studies as soon as late this fiscal year in order to launch the mission in 2022. Time is of the essence, Watzin argued, regardless of the orbiter’s specific mission.

“We’ve got to get started on this,” he said of that schedule. “It’s aggressive, but very, very doable.”