The NASA VIPER rover – a precursor mission to human landings in the south polar region of the Moon, and a mission started in 2019 under the Commercial Lunar Payload Services program – has had its landing site selected for its 2023 mission. The rover, known as the Volatiles Investigating Polar Exploration Rover, is now scheduled to land west of Nobile Crater in the lunar south polar region sometime in late 2023 after its launch aboard a SpaceX Falcon Heavy rocket.
This mission, costing $660 million, is one of several that will launch to the Moon in the next two years and is notable for being the first NASA rover to launch as a customer aboard a commercial lander.
The golf cart-sized VIPER rover will be mounted onto a Griffin lunar lander built by Astrobotic, a Pittsburgh-based company developing various lunar spacecraft that can carry payloads into lunar orbit or onto the lunar surface. After landing, VIPER will roll out onto the lunar surface with the help of a pair of ramps mounted on the lander and conduct checkouts before starting its surface mission.
The Griffin/VIPER combination is targeted to land at one of 11 “regions of interest” in the south polar region of the Moon identified in scientific papers as being favorable for hosting permanently shadowed regions (PSRs) with water ice present under the surface, while also being safe for spacecraft to land and generate power through solar panels while outside of the PSRs.
This is in sharp contrast to past lunar rover missions like Lunokhod 1 and 2 and the Lunar Rover driven by astronauts on the Apollo J-class missions, which explored areas of the Moon closer to the equator.
The south polar region of the Moon is now proven to contain water ice, as a result of observations by the Indian Chandrayaan-1 probe in 2008 and a 2009 NASA mission known as LCROSS that found water ice in the ejecta generated by a planned Centaur rocket stage crash into a permanently shadowed crater on the lunar South Pole. Later an instrument on the Lunar Reconnaissance Orbiter called Diviner generated key data that informed scientists about which regions of the Moon would have permanently shadowed regions suitable for water ice to form and remain intact.
The mission team needed to satisfy four criteria: available sunlight for solar power generation, earth visibility for communications, data indicating the presence of water ice in the area, and terrain suitable for rover driving. After extensive study, NASA has announced Nobile Crater as the VIPER landing site. Nobile was one of the 11 “regions of interest” noted above as being identified by scientists as being suitable for exploration in the south polar region of the Moon.
As NASA associate administrator for science Thomas Zurbuchen stated, “Once on the lunar surface, VIPER will provide ground truth measurements for the presence of water and other resources at the Moon’s South Pole, and the areas surrounding Nobile Crater showed the most promise in this scientific pursuit.”
After landing west of Nobile Crater, VIPER is scheduled for a 100-day prime mission to drive around the region. VIPER’s task is to map the region’s water ice deposits and test how accessible the water is, and the nature of the ice, the regolith, and shadowed areas. Though taller and heavier than the Spirit and Opportunity Mars rovers, VIPER’s driving speed is twice as fast as the MER rovers, which will help it cover longer distances more quickly.
The VIPER mission will need to survive brutal extremes of temperature and terrain in the south polar region. Since the Moon doesn’t have any substantial atmosphere, high temperatures can be up to 127 degrees Celsius.
In comparison, lows in the polar regions can get down to -223 degrees Celsius in permanently shadowed regions, one of the coldest areas in the entire solar system. In the polar regions, the Sun is always near the horizon, and the rover will need to avoid long stretches in shadowed areas where it can freeze. Several layers of insulation and heat pipes will help VIPER survive.
VIPER is designed to routinely handle slopes up to 15 degrees, and can even drive on slopes up to 30 degrees if needed, which will be very helpful with the polar terrain, which is pockmarked with craters and can reach elevations of 8000 feet above or below the mean datum level of the Moon. VIPER is designed to survive up to 4 Earth days of total darkness, so it will need to climb up steep slopes to high elevation areas where the night only lasts up to 4 days, compared to 14 Earth days for most of the Moon.
VIPER is equipped with three instruments and a drill. The NSS (Neutron Spectrometer System) is designed to detect areas below the surface that could have ice deposits. Once NSS finds an area where further investigation is warranted, the drill known as TRIDENT (The Regolith and Ice Drill for Exploring New Terrains) will collect soil from up to 1 meter below the surface.
TRIDENT is developed by Honeybee Robotics, using experience from its tools used to drill rock on Mars, starting with the Spirit and Opportunity rovers. Other instruments are developed at the Ames Research Center or the Kennedy Space Center, while the rover hardware is designed at the Johnson Space Center. The mission itself will be managed and commanded from the Ames Research Center in Mountain View, California.
Once TRIDENT gathers its soil cuttings, the MSolo (Mass Spectrometer Observing Lunar Operations) and NIRVSS (Near Infrared Volatiles Spectrometer System) will analyze these cuttings for their composition and concentration of resources. Scientists expect to not only look for water, but also carbon dioxide, ammonia, and methane with these instruments.
The data VIPER gathers will be added to information from other missions to produce the first global map of water resources on another world. In addition, they will inform efforts by Artemis astronauts to use these resources to make rocket fuel, drinking water, and other essentials and make human habitation on the Moon sustainable.
Beginning with the Peregrine-1 lander mission next year, NASA will fly VIPER’s instruments to the lunar surface to test their performance before they fly on the rover itself.
Missions like Peregrine-1, VIPER, other CLPS missions, as well as missions flown by other countries, will start a new era of lunar exploration that is structured to be more sustainable and involve many more commercial and international parties than the previous era of lunar exploration during the Cold War decades of the 1960s and 1970s.