WASHINGTON — NASA is emphasizing the science that astronauts will do when they return to the moon in the Artemis program, but agency officials acknowledge that the initial missions might be limited in how many lunar samples they can return.

In presentations at the annual meeting of the Lunar Exploration and Analysis Group (LEAG) here Oct. 29, NASA officials said they were already starting to look for potential landing sites in the south polar region of the moon for the Artemis 3 mission, scheduled to return humans to the moon in 2024.

“We are, no kidding, really starting to plan this mission. This is getting real,” said John Connolly, lunar surface systems lead at the Johnson Space Center, in one presentation before an audience of lunar scientists.

The south pole of the moon is of interest because it may harbor deposits of water ice in permanently shadowed craters. Other regions, Connolly noted, are illuminated most of the time: up to 92% of the year on some ridges, which make them appealing for solar power generation.

The Artemis 3 mission will spend up to six and a half days on the lunar surface as currently planned, he said, which would be longer than any of the Apollo lunar landings a half-century ago. That mission will likely also include an unpressurized rover to allow the astronauts to explore greater distances from the landing site, something he said was based on science requirements. “We heard loud and clear from the science community that you guys want an unpressurized rover on the very first mission,” he said. “Message received.”

That first mission, he said, would largely be geological exploration, augmented by instrumentation brought to the surface on the lander itself, and others “pre-deployed” on robotic precursor landers, such as through NASA’s Commercial Lunar Payload Services (CLPS) program. “It will be a very robust mission from the very beginning.”

One challenge, though, might be regarding the return of lunar samples from that mission. “There will absolutely be samples returned,” Connolly said. “Now, the quantity is really the only question.”

Initial drafts of NASA’s Human Landing System procurement, where the agency will fund the commercial development of human-rated lunar landers and purchase landing services from those companies, called for returning 100 kilograms of samples, including the mass of the sample containers, on the initial mission. The final version, though, reduced that requirement to 35 kilograms: 26 kilograms of samples and nine kilograms for the containers.

“You guys all understand physics,” said Greg Chavers, deputy program manager for the Human Landing System at the Marshall Space Flight Center, in a separate presentation at LEAG. “Getting there quickly with technology we currently have, in 2024, was very challenging. We had no margin on the return mass.”

Chavers said the 35 kilograms of returned samples is a “threshold,” or minimum amount landers have to be capable of in order to qualify for the program. The goal remains 100 kilograms, “and we’ve clearly communicated to the companies that they will be evaluated more favorably on their ability to get to the 100 kilograms.”

Another issue, he said, is how much volume and mass will be available on the Orion spacecraft for samples that would return to Earth with the astronauts. Even if the lander has the ability to carry 100 kilograms of samples, he suggested that there might not be room for them in Orion.

Some attendees seized on a footnote in one chart Chavers presented that stated the Orion capsule “does not have specific storage” for samples. “Sample return mass to Earth via Orion might require mission-by-mission decisions on storage within Orion and possible considerations for different sample return container/bag design,” it stated.

“We haven’t conceded that it’s zero back on Orion yet, we just don’t know what the capability will be,” he said. However, he also said there may be the need to study alternative mechanisms for getting samples back, such as a robotic sample return vehicle delivered to the moon on a CLPS lander.

That did not go over well with some. “It’s getting very complicated,” said Clive Neal, a lunar scientist at the University of Notre Dame, during a discussion that followed Chavers’ presentation.

Chavers said studies of sample return options are ongoing, including meetings at the Johnson Space Center next week on what Orion will be able to accommodate. “The message is: this is just the starting point. It’s not the end.”

The threshold amount of 26 kilograms of samples is only slightly more than the 22 kilograms returned by Apollo 11 during a single two-hour moonwalk. Apollo 17 returned about 110 kilograms collected during three lunar excursions.

“I’m expecting it to evolve,” Neal said later of the sample return capabilities of Artemis. However, he said it emphases the need to train astronauts “to bring the top quality ones back.”