NASA said Sept. 20 it selected a crater near the lunar south pole as the landing site for a rover called VIPER that will look for water ice at and below the surface. Credit: NASA/Daniel Rutter

WASHINGTON — NASA has selected a crater near the south pole of the moon as the landing site for a robotic rover to search for water ice that could be a resource for future human expeditions.

NASA announced Sept. 20 that its Volatiles Investigating Polar Exploration Rover (VIPER) mission will land near the western edge of Nobile Crater, near the lunar south pole. VIPER is scheduled to arrive there in late 2023, delivered by Astrobotic’s Griffin lunar lander on a mission arranged through NASA’s Commercial Lunar Payload Services program.

Nobile was one of four finalists that emerged from a selection process that originally considered about 15 different regions, agency officials said in a call with reporters. Nobile “maximizes science return and flexibility to help ensure mission success once VIPER is on the moon,” said Lori Glaze, planetary science director at NASA Headquarters.

The project considered several factors when choosing the landing site. The site needed to have good visibility of the Earth, which will be low on the horizon at the south pole, to enable direct-to-Earth communications, as well as good illumination for the solar-powered rover. The site also needed what Anthony Colaprete, lead project scientist for VIPER at the Ames Research Center, called “trafficable terrain” that the rover could navigate, avoiding steep slopes. Finally, scientists wanted a location that had a variety of terrains that might harbor water ice at or just below the surface.

Nobile met all those criteria, he said, from a high elevation that offered good visibility of the Earth to ridgelines that are in sunlight for all but about 50 hours of the two-week lunar night. Those “safe havens” would allow the rover to survive on battery power. In contrast to those illuminated safe havens are permanently shadowed regions in the crater, some 500 to 800 meters across, that the rover can visit to look for water ice deposits.

VIPER is equipped with a suite of instruments, including a drill designed to probe up to a meter below the surface, to detect and quantify water ice. That analysis is of both scientific interest as well as for supporting future human missions that could use the ice for life support and propellant.

NASA picked the VIPER landing site two years in advance because of the intense planning needed to maximize the mission, which will last about 100 Earth days. Colaprete said the project has already developed a “baseline traverse” for the rover running about 25 kilometers with 12 locations it will study in detail.

“The time that we have with a solar-powered rover is limited because of the natural seasons of the polar regions of the moon,” said Daniel Andrews, VIPER project manager. “This entire region will fall into darkness after four months or so. We have a finite amount of time to get this mission done, so we really want to optimize where we go and how we go about doing it.”

Scientists, though, acknowledge that they’ll have to make changes on the fly during the mission based on what the rover finds. “The science team won’t always have days or weeks to think on the data that comes in,” said Darlene Lim, VIPER deputy lead project scientist. “Instead, the science team will have to react and make decisions that enhance the mission on a much faster minute-to-hour timescale.”

NASA is pressing ahead with the selection of the landing site, and the VIPER mission overall, despite having another mission in development that would appear to be able to assist. The Lunar Trailblazer orbiter is designed to map the distribution of ice on the lunar surface at a resolution of 100 meters per pixel, far better than the best estimates of water ice distribution currently available. The spacecraft is scheduled to be ready for launch in late 2022 but won’t fly until early 2025 as part of a NASA rideshare mission whose primarily payload is the IMAP space science spacecraft.

At the briefing, officials said that they didn’t need to fly Lunar Trailblazer first to ensure success for VIPER. “The data that we have are very good at helping us identify those high-probability sites where we might find ice,” said Glaze. “I think we have absolutely sufficient knowledge to fly the VIPER mission right now.”

The lunar science community has been pushing to move up the launch of Lunar Trailblazer, including a recommendation to that effect at a meeting of the Lunar Exploration Analysis Group earlier this month. Glaze, though, said NASA had no plans to accelerate its launch. “At this time, the most reliable launch for Lunar Trailblazer remains on IMAP,” she said. “That will be after the VIPER mission.”

Glaze and others described VIPER as a “ground truthing” mission to see exact what forms ice is in at the south pole of the moon. “We know there’s water ice there, and we know some of it is at the surface and some is below the surface,” Colaprete said. “Exactly where and how much, and how it’s distributed between the surface and subsurface, is a large unknown.” VIPER, he added, will also look for ice in locations where scientists don’t think water ice exists as a test of their hypotheses.

“If we find there’s no water in any place we look,” he added, “that is a fundamental discovery and we will be scratching our heads and rewriting textbooks again.”

Jeff Foust writes about space policy, commercial space, and related topics for SpaceNews. He earned a Ph.D. in planetary sciences from the Massachusetts Institute of Technology and a bachelor’s degree with honors in geophysics and planetary science...