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Mars astronaut
Under a plan for the first human Mars mission that NASA is currently studying, astronauts would spend only 30 days on the Red Planet, with the overall mission lasting two years. (credit: NASA)

A long journey but a short stay on Mars

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On one hand, it seems premature for NASA to start planning for the first human mission to Mars. After all, its much nearer-term plans to return humans to the Moon are facing delays, as the 2024 goal of a human landing fades because of a shortfall of funding and a change of presidential administrations. On the other hand, NASA has for decades developed all kinds of architectures for human Mars missions, although for missions that themselves were decades in the future.

Those plans are getting new attention as the time horizon shrinks. Even with a likely delay in human lunar missions, the agency is still looking to send humans to Mars some time in the 2030s. That means those mission concepts for getting people to Mars and back are getting more detailed, while also being increasingly scrutinized.

“The emphasis was to develop a mission concept that can get us there as fast and as soon as possible,” said Rucker.

NASA started dropping hints late last year that its concept for an initial human mission to Mars would be one with a relatively short stay on the planet. At a meeting of the National Academies’ Space Studies Board in November, Jim Watzin, a senior adviser supporting human Mars mission planning at NASA and a former director of the agency’s robotic Mars Exploration Program, described that mission as lasting “on the order of 30 days or so,” with collecting ice cores from below the Martian surface a key objective of that mission (see “The future of Mars exploration, from sample return to human missions,” The Space Review, December 7, 2020).

At a meeting last week of NASA’s Mars Exploration Program Analysis Group (MEPAG), agency officials filled in some of the details of that mission concept. “When we talk about our mission to Mars, our initial trip, it’s about a two-year round trip that includes about a month on the surface,” said Jacob Bleacher, NASA chief exploration scientist.

He and Michelle Rucker of the Johnson Space Center outlined that current concept for an initial human mission during a presentation at the meeting. That includes a four-person crew, Rucker said, using a spacecraft “aggregated” in cislunar space for a mission some time in the 2030s.

“Since this is a shorter mission, we’re looking at trying to do this with relatively minimal infrastructure in place,” she said. “The emphasis was to develop a mission concept that can get us there as fast and as soon as possible.”

That approach is different from past design reference missions, which envisioned long stays on Mars, even for early missions. An example is the Design Reference Architecture (DRA) 5.0 study, completed in 2009, which projected a 500-day stay on the surface of Mars that the agency said allowed for a “very robust” exploration strategy. “Ample time would be provided to plan and re-plan the surface activities, respond to problems, and readdress the scientific questions posed throughout the mission,” the report stated.

The alternative approach makes uses of “opposition-class” trajectories to Mars, which have been studied in the past but usually not as the primary means to get humans to Mars. “It’s a long cruise and a very short stay on the surface,” said Michael Hecht of MIT-Haystack Observatory during a discussion about Mars exploration plans at a meeting last Friday of the Mars panel of the ongoing planetary science decadal survey. “The big appeal is that it’s a much shorter mission. It’s small and it’s fast.”

The overall mission would be shorter—about two years versus the up to three years of earlier concept—but spend more time in transit. That transit time, he said, could be reduced through the use of advanced propulsion, like nuclear thermal propulsion. “Take a long cruise, make it shorter by high-power engines, land, spend 30 days, and get off the surface.”

Rucker said at the MEPAG meeting that NASA is looking at nuclear propulsion systems, including a “hybrid” one that combined conventional chemical propulsion with nuclear electric propulsion, in order to shorten transit times. The mission would also require a lander with about 20 times the payload capacity as the Curiosity and Perseverance rovers, which each weigh about a ton.

“Thirty days is barely enough time to get your land legs,” Hecht said.

Scott Hubbard, a Stanford University professor and former director of NASA’s Ames Research Center, said at the decadal meeting that the presentation two days earlier at MEPAG was the first time he was aware of NASA talking about this mission concept in public in any level of detail. Hecht said earlier in the meeting that the development of the opposition-class architecture was a way to “recover some of that potential lost time” for Mars missions caused by the near-term focus on the Moon.

A human Mars mission that spends only a month on the surface has several implications. One is for science, in the form of a drastically reduced time to explore the surface versus earlier architectures. The DRA 5.0 study, for example, assumed that “it may take the crew a few weeks to acclimate to the partial gravity of Mars after landing.” That is only a minor inconvenience if you’re spending 18 months on the surface; it’s a much bigger obstacle if you’re only spending one month.

Another is the science that can be done in that brief time. Watzin noted last year that retrieving ice cores might be a major goal of the mission, but that got a skeptical reception from members of the Space Studies Board. But Hubbard noted that simply collecting samples could be worthwhile, assuming the astronauts have training to make expecr selections of what samples. “Collecting and returning high-quality samples are among the most scientifically important things they can do,” he said, citing the last decadal survey.

The science could continue after the astronauts depart, in the form of scientific payloads they installed on the surface. Other assets, like communications, needed for the crewed stay on Mars could also be repurposed to support robotic activities, Rucker said.

Another impact of a short-duration stay would be on development of in situ resource utilization (ISRU) technologies to produce oxygen or propellant. While many have trumpeted the importance of ISRU and “living off the land” for long-duration stays, a short mission could simply rely on resources delivered to the surface in advance.

“That has displaced things like ISRU,” said Hecht, who is the principal investigator of the Mars Oxygen In-Situ Resource Utilization Experiment, or MOXIE, on the Perseverance rover, which will test ways to produce oxygen from the Martian atmosphere.

The short stay and limited infrastructure create concerns for scientists. “Thirty days is barely enough time to get your land legs,” Hecht said, particularly given the time needed for initial activities after landing and preparations for departure. “That leaves very limited opportunity for science and maybe even limited opportunity for sample return.”

Such a mission, he continued, could serve as a “trial run” for later, longer missions. “If we just look at this as a one-off, it’s alarming for science.”

“What we’re really trying to do is move as rapidly as we can towards having a large presence on the surface of Mars, getting people there as quickly as we can,” Wooster said.

NASA, though, is not the only organization with ambitions of sending humans to Mars. Another panelist at the decadal survey meeting was Paul Wooster, principal Mars development engineer at SpaceX. He gave a brief overview of SpaceX’s interest in going to Mars, largely covering familiar ground about the company’s plans to use its Starship vehicle for such missions.

SpaceX doesn’t appear to be considering opposition-class missions for short stays on Mars—not surprising, given the company’s long-term goal of establishing a permanent human presence there. “In general, we’re looking at about six months or less” of travel time to Mars, depending on the payload and propellant, he said.

“We’re really optimizing for time,” he said later in the discussion, with SpaceX planning to build a “large number” of vehicles to support eventual Mars missions. “We would want to, as soon as possible, start sending these vehicles to Mars to learn as much as we can about getting there, landing on the surface, and so forth.”

“What we’re really trying to do is move as rapidly as we can towards having a large presence on the surface of Mars, getting people there as quickly as we can and then having a base that is growing,” he said.

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