The Gruithuisen region in northern Oceanus Procellarum on the Moon contains three distinctive domes interpreted as nonmare volcanic features of Imbrian age. A 4 d extravehicular activity (EVA), four-astronaut sortie mission to explore these enigmatic features and the surrounding terrain provides the opportunity to address key outstanding lunar science questions. The landing site is on the mare south of Gruithuisen 3 (36.22°N, 40.60°W). From this site, diverse geologic terrains and features are accessible, including highlands, dome material, mare basalts, multiple craters, small rilles, and a negative topographic feature of unknown origin. Preliminary mission planning is based on Clementine multispectral data, Lunar Prospector geochemical estimates, and high-resolution (0.5 m/pixel) stereo images from the Lunar Reconnaissance Orbiter Narrow Angle Camera. Science objectives for the mission include: (1) determining the nature of the domes, (2) identifying and measuring the distribution of any potassium, rare earth elements, and phosphorus (KREEP)- and thorium-rich materials, (3) collecting samples for age dating of key units to investigate the evolution of the region, and (4) deploying a passive seismic grid as part of a global lunar network. Satisfying the science objectives requires 7 h, ~20 km round-trip EVAs, and significant time driving on slopes up to ~15°.

The motivation for this study was to create lunar surface exploration scenarios that would support current science needs, as captured in the Lunar Exploration Analysis Group (LEAG) Roadmap for Lunar Exploration. A science-driven capability to meet those needs required enhanced capability, relative to the Apollo J missions, to provide a broader field context for (1) improved interpretation of samples and measurements; (2) greater flexibility in the selection and nature of activities at field stations; as well as (3) greater potential for breakthrough science. Here, we offer advanced regional-scale (hundreds of kilometers) surface exploration scenarios, essentially design reference missions, for three high-priority targets representing the broadest differences in the nature and distribution of geological features. South Pole–Aitken Basin is the largest and oldest confirmed lunar impact basin. Covering most of the farside southern hemisphere and >2000 km in diameter, it contains extraordinarily diverse features and geochemical anomalies that are widely scattered and thus would require several regional-scale missions. Tsiolkovsky is an anomaly among farside craters: It is mare-filled in the thickest portion of farside crust, young, and has well-preserved impact structures, yet it is surrounded by the ancient Tsiolkovsky-Stark Basin. Aristarchus Plateau is a tectonically uplifted plateau associated with the formation of Imbrium Basin, and it is found on a concentric ring of basin. Features encompassing the entire range of mare volcanism activity in style and age are found either on the relatively compact plateau or within hundreds of kilometers in surrounding western Oceanus Procellarum. Our regional-scale architecture would allow science objectives for study of Aristarchus Plateau or Tsiolkovsky to be addressed from one landing site conveniently located on the target, while South Pole–Aitken Basin would require several missions to achieve such objectives. We describe the geological context and resulting investigations, as well as the required tools, instruments, and activities. We assumed, as initially instructed, science need–driven capabilities at least a generation beyond the Apollo J missions, i.e., the availability of a minimum of two pressurized rovers capable of hundreds of kilometers driving range at average speeds of 10–15 kph (without recharge), four crew, and 700 kg of science payload. The implications of such science-conducive architecture in the context of other architectures under consideration are discussed.

The volcanic processes that formed Vallis Schröteri are not well understood. Vallis Schröteri, located on the Aristarchus Plateau, is the largest rille on the Moon, and it displays three key morphologic components: the Cobra Head, the 155-km-long primary rille, and the 240-km-long inner rille. Observations of terrestrial eruptions are applied here to help explain the morphologic relationships observed for Vallis Schröteri. The Cobra Head, a 10-km-wide source vent surrounded by a 35-km-diameter and 900-m-high low shield, might have been constructed from flows, spatter, and pyroclastic deposits erupted during lava fountain events, similar to the early stages of the vent at Pu‘u ‘Ō‘ō in Hawaii and the final morphology of Bandera crater, a cinder cone in New Mexico. The vent fed an initial sheet flow controlled by pre-eruption topography. A channel formed within this sheet flow was the foundation for the primary rille, which deepened through construction and thermomechanical erosion by lava. The inner rille is confined to the flat floor of the primary rille and is characterized by tight gooseneck meanders. This rille crosscuts the distal scarp of the primary rille and extends toward Oceanus Procellarum. This enigmatic relationship can be explained through backup, overflow, and diversion of the lava into a new rille that eroded into the margin of the primary rille. Similar backup, overflow, and redirection of the lava flow were observed during the 1984 Mauna Loa eruption in Hawaii. Analysis of the final morphology of lunar rilles provides key information about lunar volcanic processes and insight into the local stratigraphy.