VIPER, NASA’s Moon resource mapper


  • NASA is launching the Volatiles Investigating Polar Exploration Rover, or VIPER, in 2023 to map water on the Moon’s south pole.

  • VIPER’s findings will pave the way for future lunar habitats while also providing insights into the history and origin of water in the solar system.

  • VIPER is different from NASA’s traditional planetary missions — the agency is entrusting a commercial spacecraft to land the rover safely on the Moon.

Why is NASA sending VIPER to the Moon?

NASA wants to land humans on the Moon again — this time to stay. The agency’s Artemis program envisions people sustainably living on the Moon using locally available resources like water. We know from past missions that the lunar poles host at least 600 billion kilograms of water ice, and likely much more. But to be able to use that water, we need to learn about its state and how accessible it is up-close. That’s where NASA’s first robotic lunar rover comes in.

The Volatiles Investigating Polar Exploration Rover, or VIPER, will land on the Moon’s south pole in late 2023. The golf-cart-sized rover will explore the south pole for at least 100 days, venturing into frigid permanently shadowed regions — areas forever deprived of sunlight — to study and map water ice deposits.

VIPER will tell us about the nature of water in permanently shadowed regions for the first time, including where it’s most likely to be found, how easy it is to access, and how much of it is in the form of ice crystals versus being bound to minerals. This will not only inform us how we can extract the water to sustainably live on the Moon but also give us insights into the history and origin of water in the inner solar system, including Earth.

Information about the exact nature of water on the Moon’s poles is so crucial from both a scientific and exploratory standpoint that many other nations are planning missions like VIPER, the earliest one being the joint Japanese-Indian LUPEX rover targeting a post-2023 launch.

VIPER lunar rover
VIPER lunar rover Artist's concept of NASA’s Volatiles Investigating Polar Exploration Rover, or VIPER. VIPER is a mobile robot that will roam around the Moon’s south pole looking for water ice.Image: NASA Ames / Daniel Rutter

How will VIPER map water on the Moon?

NASA has equipped VIPER with three spectrometers — instruments that can identify a material’s composition based on how they emit or absorb light — to collectively detect water ice on the surface and subsurface of permanently shadowed regions.

When exploring a region, VIPER will first use its neutron spectrometer to detect hydrogen — an indirect sign of water — up to 1 meter below the surface. VIPER will scout both inside and outside permanently shadowed regions for locations that show hints of substantial water ice. Once VIPER identifies a potentially water-rich area, typically in a permanently shadowed region, it will use its drill to dig up soil from up to a meter below the surface — the deepest for any robotic mission on another world.

Next, an infrared spectrometer will analyze the soil to determine if the detected hydrogen was part of water ice or hydroxyl (OH) bound to minerals. It will also identify other volatile resources like carbon dioxide, ammonia, and methane. Since volatiles evaporate even at moderately warm temperatures, some of them would escape the soil before the infrared spectrometer can detect them. This is where VIPER’s final instrument, a mass spectrometer, comes in. It will identify escaped volatiles from the soil that pass through it, as well as gases in the environment.

By repeating this entire process at various locations, VIPER will give us a holistic grasp on the exact nature, amount and accessibility of water in various conditions on the Moon’s poles.

Preparing VIPER for the abyss

On top of dealing with the numerous challenges in any Moon mission, NASA is designing VIPER to power through one of the harshest planetary environments in the solar system. With temperatures during major investigations well below -180 degrees Celsius (-292 degrees Fahrenheit), a rocky terrain riddled with steep slopes, a near-horizon Sun causing long, moving shadows that the rover needs to keep avoiding or face a freeze, we’re sending VIPER to lunar hell.

Despite facing much colder temperatures than NASA’s flagship Mars missions, VIPER doesn’t have a nuclear radioisotope for warmth. Instead, the solar-powered rover will rely on its battery and heat pipes to keep itself from freezing. VIPER can survive complete darkness for a little over four Earth days whereas a typical lunar night lasts 14 Earth days. VIPER will thus park at pre-identified high-altitude spots at various points during the mission where nights last only three to four Earth days.

To rove rocky polar terrain, go in and out of craters, and on soils likely different than elsewhere on the Moon, VIPER boasts unprecedented agility in a planetary rover. It can traverse 15-degree inclines with ease, and even 25 to 30-degree slopes if need be. VIPER can drive sideways, diagonally, or move in any direction without changing where it’s facing to keep its solar panels pointed at the Sun. If VIPER gets stuck in fluffy soil, it can lift each of its wheels independently to dig into and sweep along the surface — a bit like swimming — to get out of it. To prevent lunar dust from damaging its wheel system or internals, NASA is wrapping VIPER in multiple protective layers.

VIPER needs to stay connected to Earth during all of its scientific operations — a difficult task because it needs to enter craters to study water ice. To solve this, NASA used extensive mapping data from its Lunar Reconnaissance Orbiter to choose craters and regions with gentle enough slopes that maintain a line of sight to Earth while also meeting all other mission requirements.

Erlanger Crater
Erlanger Crater This image of Erlanger crater near the Moon's north pole was captured by NASA's Lunar Reconnaissance Orbiter. Only the upper rims of the crater, which measures about 10 kilometers wide, ever receive sunlight.Image: NASA/GSFC/Arizona State University

NASA trusts commercial landing for crucial mission

VIPER is different from NASA’s traditional planetary missions. The lander that will deliver VIPER to the Moon’s south pole is not built by NASA, but by a commercial company, Astrobotic, selected via a competitive bidding process as part of the agency’s CLPS program. Astrobotic has selected SpaceX Falcon Heavy to launch its lander, counting on them to not miss the brief, mission-critical launch window in late 2023. The fact that NASA is entrusting a commercial partner with such a crucial mission shows the agency’s growing confidence in building a commercial space ecosystem around lunar exploration.

To reduce mission risks and to maximize the value of future crewed missions depending on VIPER’s findings, NASA is flying versions of VIPER’s instruments on three CLPS commercial landing missions before the rover’s flight to ensure they work as expected.

VIPER’s unprecedented engineering to explore extreme environments will pave the way for future habitats on the Moon. And yet the mission costs just $660 million, minus operating expenses. That’s about three to four times less than what NASA spends on its flagship Mars missions or one SLS rocket launch. VIPER is a sweet planetary deal.

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Acknowledgments: this page was initially written by Jatan Mehta in 2021.