What is LROC: Objectives

As part of its original exploration mission, the Lunar Reconnaissance Orbiter Camera was designed to collect the data necessary to achieve the following measurement objectives:

The Apollo 15 Lunar Module accidentally set down with one leg in a small crater resulting in a tilt of 10°, just 5° below the maximum acceptable angle. Hazards from craters of this size are best detected with meter scale topography and high incidence angle (80°) images - both provided by the LROC NAC.

1. Surface characterization of potential landing sites. LROC provides images of meter- and smaller-scale features that pose a potential threat to landing and obstacles to trafficability. An accurate assessment of the surface characteristics requires 0.5 m/pixel resolution in order to unambiguously identify meter-size objects. In addition, when the Sun is only 10° to 30° above the horizon, features less than 0.5 m high can be identified by their long shadows. The LROC NAC detects blocks with ~1m horizontal scale and heights less than 0.5 m.

2. Mapping of permanently shadowed and sunlit regions. The spin axis of the Moon is tilted by only 1.5° (compared with the Earth's 28.5), potentially leaving some areas near the pole in permanent shadow while allowing others parts in remain in permanent, or near-permanent, illumination. Theory, radar data, and neutron measurements suggest that ice may be present in these permanently shadowed regions. In addition, areas of permanent, or near-permanent, illumination are prime locations for future lunar outposts due to benign thermal conditions and constant solar-power. During each orbit around the Moon, the LROC Wide Angle Camera (WAC) acquires images, at 100 meter per pixel, of the polar regions (80° to 90° north and south latitude). A movie of compiled WAC polar images will graphically illustrate regions of permanent shadow and permanent, or near-permanent, illumination.

3. Meter-scale mapping of polar regions with continuous illumination. During respective summers (although less intense, the Moon has seasons like the Earth), the NAC acquires meter-scale images of both polar regions (above 85.5 latitude) when shadows are minimal. Images collected during the summer are compiled into 1 m/pixel regional mosaics (one for each pole). These high-resolution mosaics provide a basemap for planning future polar exploration.

Spectra of ilmenite (black line) shows a distinctive downturn in reflectance near 500nm. The WAC has the unique ability to acquire measurements in the UV (300, 360 nm) that are well suited to separate ilmenite from basalt.

4. Overlapping observations to enable derivation of meter-scale topography. The LROC NAC collects stereo images that can be used to provide detailed topographic maps of important areas.

5. Global multispectral imaging to map ilmenite and other minerals. Seven filters within the LROC WAC allow scientists to identify concentrations of ilmenite, olivine, and other minerals in the lunar regolith. Understanding the distribution of the economically important mineral ilmenite, in particular, is vital for understanding the distribution of accessible resources on the lunar surface.

6. Global morphology base map. The LROC WAC provides 100 meter per pixel images with Sun angles optimal for morphological mapping (the Sun 15° to 35° above the horizon), except in polar regions where the Sun is always very low on the horizon. The WAC global map improves efforts to characterize terrain based on crater counts, especially on the far side of the Moon, where existing images from earlier missions have high Sun and poor resolution.

7. Characterize regolith properties. The LROC NAC high-resolution images give scientists extremely detailed views of the regolith (soil). Depending on regolith thickness, different sizes of craters have distinctive interior shapes. Mapping the frequency and distribution of these crater mophologies provides accurate estimates of regolith thickness around potential lunar landing sites.

8. Determine current impact hazards. The LROC NAC rephotographs areas seen in Apollo photography so that new impact craters can be identified. At Mars, about 70 craters have been found that formed since the late 1970s when the Viking mission was active at Mars. Cataloging craters formed since Apollo provides a count of the number of small asteroids and comets that have impacted the Moon in the past 40 years; information critical to assessing the rate at which impact craters form and mitigating the hazards to future human spacefarers.

LRO is now in the Extended Mission Directorate mission phase, focused on collecting the data needed to address key lunar science questions, including:

1. Chronology/Bombardment. Determine bombardment history of the Moon as well as timing of basin-forming events and modern processes. Measure lunar landforms at 0.5 - 2.0 meter pixel scales for more than 10,000 targeted sites, and measure mineralogical variation of the Moon via ultraviolet-visible observations at sub-kilometer pixel scales over at least 75% of the surface.

2. Crustal Evolution. Investigate geological processes and their role in the evolution of the lunar crust and shallow lithosphere. This investigation includes imaging of landforms at sub-100 m scale down to meter scale for thousands of targeted regions. Obtain oblique (more than 60° emission angle) imaging of key science targets for the purpose of assessing stratigraphy, at 2 meter pixel scales for an average of at least two targeted regions per month. Also, obtain UV/Visible (400 to 100 meter pixel scales) multi-phase angle imaging over at least 90% of the lunar surface and measure mineralogical variations of the Moon via ultraviolet-visible observations at sub-km pixel scale over a minimum of 75% of the lunar surface.

3. Regolith Evolution. Look for evidence of processes that have shaped the global lunar regolith as they relate to evolution of the crust, verifying physical characteristics of the upper-most regolith layers via their textures, scattering mechanisms and composition. Measure the surface morphology at 0.5 - 2.0 meter pixel scales, and other physical properties at meter pixel scale for specific targets and at 100 meter scale over at least 90% of the lunar surface.

4. Polar Volatiles. Investigate volatile sources, sinks and transfer mechanisms with emphasis on the lunar polar regions, including permanently shadowed regions (PSRs). Measure polar region landforms in PSRs at better than 100 meter horizontal scales. Also, measure reflectivity as a function of phase angle at meter and 100 meter scales near PSRs within 10° of each pole.