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NASA NTRS2013

Mars Sample Return Using Commercial Capabilities: ERV Trajectory and Capture Requirements

Mars Sample Return was presented as the highest priority planetary science mission of the next decade [1]. Lemke et al. [2] present a Mars Sample Return mission concept in which the sample is returned directly from the surface of Mars to an Earth orbit. The sample is recovered in Earth Orbit instead of being transferred between spacecraft in Mars Orbit. This paper provides the details of this sample recovery in Earth orbit and presents as such a sub-element of the overall Mars sample return concept given in [2]. We start from the assumption that a Mars Ascent Vehicle (MAV), initially landed on Mars using a modified SpaceX Dragon capsule, has successfully delivered the sample, already contained within an Earth Return Vehicle (ERV), to a parking orbit around Mars. From the parking orbit, the ERV imparts sufficient Delta-V to inject itself into an earthbound trajectory and to be captured into an Earth orbit eventually. We take into account launch window and Delta-V considerations as well as the additional constraint of increased safety margins imposed by planetary protection regulations. We focus on how to overcome two distinct challenges of the sample return that are driven by the issues of planetary protection: (1) the design of an ERV trajectory meeting all the requirements including the need to avoid contamination of Earth's atmosphere; (2) the concept of operations for retrieving the Martian samples in Earth orbit in a safe way. We present an approach to retrieve the samples through a rendezvous between the ERV and a second SpaceX Dragon capsule. The ERV executes a trajectory that brings it from low Mars orbit (LMO) to a Moon-trailing Earth orbit at high inclination with respect to the Earth-Moon plane. After a first burn at Trans-Earth Injection (TEI), the trajectory uses a second burn at perigee during an Earth flyby maneuver to capture the ERV in Earth orbit. The ERV then uses a non-propulsive Moon flyby to come to a near-circular Moon-trailing orbit. To perform the Earth Orbit Rendezvous (EOR), a second Dragon capsule is then launched from Earth and a similar lunar flyby is performed to rendezvous with the ERV. The requirements for rendezvous, close proximity operations and capture of the sample canister are described. A concept of operations for sample retrieval is presented along with design specifications of the ERV, the required modifications to the Dragon capsule, as well as the hardware, software, sensors, actuators, and capture mechanisms used. In our concept, a container is mounted to the front hatch of Dragon, capable of accommodating the sample canister and sealing it from the rest of the capsule. The sample canister is captured using a robotic arm with a magnetic grappling mechanism. Dragon then performs a propulsive maneuver to return to Earth for a controlled re-entry while the ERV (sans sample container) is left in the Moon trailing orbit. Contingency cases and related mitigation strategies are also discussed, including the advantages and disadvantages of performing the ERV rendezvous with a crew.

Faber, Nicolas F.↗
NASA NTRS1973

Moessbauer search for ferric oxide phases in lunar materials and simulated lunar materials

Moessbauer studies were carried out on lunar fines and on simulated lunar glasses containing magnetic-like precipitates with the primary objective of determining how much, if any, ferric oxide is present in the lunar soils. Although unambiguous evidence of lunar Fe(3+) phases was not obtained, an upper limit was estimated from different portions of the Moessbauer spectra to be between 0.1 and 0.4 wt.% (as Fe3O4). A smaller than 62 microns fraction of 15021,118 showed 0.5 wt.% ferromagnetic iron at 300 K in as-returned condition. After heating to 650 C in an evacuated, sealed quartz tube for 1400 hours, the same sample exhibited 1 wt.% ferromagnetic iron at room temperature. An accompanying decrease in excess absorption area near zero velocity was noted. Thus, the result of the vacuum heat treatment was to convert fine grained iron to larger particles, apparently without the oxidation effects commonly reported.

Forester, D. W.↗
NASA NTRS2017

Transmission Electron Microscopy of Plagioclase-Rich Itokawa Grains: Space Weathering Effects and Solar Flare Track Exposure Ages

Limited samples are available for the study of space weathering effects on airless bodies. The grains returned by the Hayabusa mission to asteroid 25143 Itokawa provide the only samples currently available to study space weathering of ordinary chondrite regolith. We have previously studied olivine-rich Itokawa grains and documented their surface alteration and exposure ages based on the observed density of solar flare particle tracks. Here we focus on the rarer Itokawa plagioclase grains, in order to allow comparisons between Itokawa and lunar soil plagioclase grains for which an extensive data set exists.

Keller, Lindsay P.↗
NASA NTRSDate not supplied

Implementing the 3-D woven Mid-Density Carbon Phenolic (3MDCP) Heat Shield for the Mars Sample Return (MSR) Earth Entry Vehicle (EEV)

he Mars Sample Return (MSR)Program will return Martian soil samples to Earth in the early 2030s. Since the biological content of these samples is unknown, and potentially upsetting to Earth’s biosphere, the Earth Entry Vehicle (EEV) is required to be the most reliable entry probe ever devised. Entering Earth’s atmosphere at ~12 km/s, after up to a 6-day in-space free flight phase, the EEV must tolerate the cis-lunar Micro-Meteoroid environment, the near-Earth Orbital debris environment, and then entry heating of over 3,000 W/cm2 and pressures of250 kPa before ballistically impacting Earth’s surface at nearly 45 m/s. To reliably accomplish such a mission, NASA Ames is implementing the 3-D woven Mid-Density Carbon Phenolic (3MDCP) Heat Shield, derived from the prior Heatshield for Extreme Entry Environments(HEEET) material system [1]. 3MDCP development accomplishments to date, along with the future efforts to deliver the flight hardware are presented, along with a discussion of the manufacturing risks and accompanying mitigations achieved.

J C Vander Kam↗
NASA NTRS2022

The VIPER Mission, a Resource-Mapping Mission on Another Celestial Body

The Volatiles Investigation Polar Exploration Rover (VIPER) mission is a lunar polar volatiles prospecting mission developed through NASA’s Science Mission Directorate (SMD) Planetary Science Division with launch in late 2023. VIPER’s mission goals are to (1) characterize the distribution and physical state of lunar polar water and other volatiles in lunar cold traps and regolith and (2)provide the data necessary for NASA to evaluate potential return of In-Situ Resource Utilization (ISRU) from lunar polar regions. VIPER will be optimized for lunar regions that receive prolonged periods of sunlight (short lunar nights). The mission duration will be more than 90 Earth days and result in a traverse distance of up to 20 km. The mission includes a rover-borne payload that can locate surface and near-subsurface volatiles, excavate, and analyze samples of the volatile-bearing regolith, and demonstrate the form, extractability, and usefulness of the materials.

The Volatiles Investigation Polar Exploration Rove↗
NASA NTRS1993

Lunar Science: Using the Moon as a Testbed

The Moon is an excellent test bed for innovative instruments and spacecraft. Excellent science can be done, the Moon has a convenient location, and previous measurements have calibrated many parts of it. I summarize these attributes and give some suggestions for the types of future measurements. The Lunar Scout missions planned by NASA's Office of Exploration will not make all the measurements needed. Thus, test missions to the Moon can also return significant scientific results, making them more than technology demonstrations. The Moon is close to Earth, so cruise time is insignificant, tracking is precise, and some operations can be controlled from Earth, but it is in the deep space environment, allowing full tests of instruments and spacecraft components. The existing database on the Moon allows tests of new instruments against known information. The most precise data come from lunar samples, where detailed analyses of samples from a few places on the Moon provide data on chemical and mineralogical composition and physical properties.

Taylor, G. J.↗
NASA NTRSDate not supplied

Effect of Vacuum on Force Response of an Ultrasonic Penetrator

Introduction: The Apollo astronauts encountered higher than expected resistances when interacting with the lunar soil via the Apollo Lunar Surface Drill (ALSD) and the trenching tool. Reducing the force required to move tools or other mechanical components through regolith will impact many steps of the resource extraction process. Force reduction has been achieved in soil materials by imparting vibration to tooling interfaces such as a vibratory farming cultivator, a percussive scoop, and ultrasonically resonant penetrators. Vibration-assisted tools in granular media reduce interaction forces by fluidizing a volume around the tool, allowing the tool to progress through a dynamic (fluid) medium instead of a static (solid) medium. This work seeks to quantify ultrasonic vibration’s effect on the force response of a penetrator in lunar soil simulant in vacuum sufficient to be within the molecular flow regime of any disturbed gases. Methods: A custom vacuum chamber setup, CUBEvac, was designed and built to facilitate penetration testing in a high vacuum environment, for comparison to penetration behavior in ambient terrestrial environment. A two-stage pumping system (Agilent Triscroll 600 roughing pump, Agilent VHS-6 oil diffusion pump) reached chamber pressures of about 5x10-6 Torr with regolith simulant in place. Figure 1 is a schematic of the heart of the assembly (note the penetration drive mechanisms above the chamber feedthrough and the regolith simulant sample in the bottom are not shown). The penetration actuation stack was comprised of a stepper motor driving a lead screw to move the ultra-sonic probe vertically inside the chamber. Motion was coordinated with an Arduino Uno. GRC-3 lunar simulant was used for this set of experiments. Samples were prepared in a four-liter stain-less steel, cylindrical pot with an internal diameter of approximately 15.56 cm (6.125 in) and a depth of 19.37 cm (7 5/8 in) for testing. The soil was baked out prior to compaction preparation as a measure to reduce soil moisture which interfered with pump down capacity. The soil was not baked again if it was removed from the vacuum chamber, prepped, and immediately returned to the vacuum chamber for pump down. The soil was compacted using a 60 Hz vibration table with a surcharge of 34 kg place on top of the soil in the container. Prepared soil samples weighed approximately 6.5 kg (bulk density 1.895-1.934 g/cm3). Two probe end effectors were tested: A cone penetrometer (static only) with a nominal diameter of 12.7 mm (0.5 in) and a nominal height of 28.6 mm (1.125 in); and a vibrating cylindrical probe measuring 12.7 mm in diameter and 50.8 mm in effective length from the tip (Figure 2). The cylindrical probe vibrated resonantly at 20 kHz with an amplitude 23 μm. The cone penetration tests were conducted to assess potential soil behavior differences in vacuum. The cylinder probe tests were conducted as the primary subject of this investigation to assess force response in vacuum. For each test, a regolith simulant sample was load-ed and compacted in the chamber, which was then evacuated for roughly 18 hours to reach the lowest possible pressure (approximately 5x10-6 Torr for most tests). The probe was then moved to about 10 mm above the soil surface before being pushed to a depth of 50 mm for the cylinder probe tests and to a depth of 100 mm for the cone penetrometer tests, both at a speed of 2 mm/s. The simulant samples were prepared the same for all tests. Ideally, they would respond consistently to probe penetration under ambient and vacuum conditions. This was evaluated by measuring the resistance of representative prepared simulant beds with a standard cone penetrometer in both environments. Results and Discussion: The resistance of the simulant samples in the vacuum tests was consistently lower than in the ambient tests as determined by the cone penetration tests. Thus, the ambient and vacuum results cannot be compared directly; work is underway to de-confound and better correlate the data. Still, figures 3-6 show that probe penetration forces are lower overall in the vacuum environment. In both environments, resonant vibration of the probe provides two useful effects: It reduces the probe penetration force and smooths the force-depth curve, significantly reducing local maxima. These effects have implications for various potential applications, such as astronaut hand-tools, where benefits (reducing astronaut effort) outweigh the cost of the additional energy re-quired to generate vibration. These results demonstrate that resonantly vibrating tools can meaningfully reduce the penetration force required for excavation, probing, and drilling tools in simulated lunar regolith deposits under vacuum levels approaching those that will be experience on the Moon’s surface. Lunar-gravity, ambient environment tests are scheduled soon. The effects of realistic temperatures and temperature gradients and deeper vacuum remain to be tested.

E Rezich↗
NASA NTRS2016

Identifying and Characterizing Impact Melt Outcrops in the Nectaris Basin

The Nectaris Basin is an 820-km diameter, multi-ring impact basin located on the near side of the Moon. Nectaris is a defining stratigraphic horizon based on relationships between ejecta units, giving its name to the Nectarian epoch of lunar history. Lunar basin chronology based on higher resolution LRO imagery and topography, while assigning some important basins like Serenitatis to pre-Nectarian time, were generally consistent with those previously derived. Based on this stratigraphy, at least 11 large basins formed in the time between Nectaris and Imbrium. The absolute age of Nectaris, therefore, is a crucial marker in the lunar time-stratigraphic sequence for understanding the impact flux on the Moon, and by extension, the entire inner solar system. For several decades, workers have attempted to constrain the age of the Nectaris basin through radiometric dating of lunar samples. However, there is little agreement on which samples in our collection represent Nectaris, if any, and what the correct radiometric age of such samples is. The importance of the age of Nectaris goes far beyond assigning a stratigraphic marker to lunar chronology. Several dynamical models use Nectaris as their pin date, so that this date becomes crucial in understanding the time-correlated effects in the rest of the solar system. The importance of the Nectaris basin age, coupled with its nearside, mid-latitude location, make remnants of the impact-melt sheet an attractive target for a future mission, either for in-situ dating or for sample return. We have started exploring this possibility. We have begun a consortium data-analysis effort bringing multiple datasets and analysis methods to bear on these putative impact-melt deposits to characterize their extent, elemental composition and mineralogy, maturity and geologic setting, and to identify potential landing sites that meet both operational safety and science requirements.

Nectaris Basin↗
NASA NTRS1973

Geologic setting of Apollo 16

Prior to the Apollo 16 mission, the materials of the Cayley Plains and the Descartes Mountains were thought to be mostly of volcanic origin. Rock and soil samples from these regions strongly suggest, however, that they may be products of multiring basin forming impacts, although minor local volcanism is not precluded. The smooth planar surfaces may have been formed initially by Imbrium ejecta which flowed into topographic lows at the distal margins of the lineated Fra Mauro ejecta. It is emphasized, however, that the rocks and soils returned from the Apollo 16 site cannot necessarily be considered representative of the lunar crust in the Descartes region from which they were collected.

Hodges, C. A.↗
NASA NTRS2005

A Thorium-rich Mare Basalt Rock Fragment from the Apollo 12 Regolith: A Sample from a Young Procellarum Flow?

In this abstract, we report on the composition, mineralogy and petrography of a basaltic rock fragment, 12032,366-18, found in the Apollo 12 regolith. Age data, collected as part of an investigation by Barra et al., will be presented in detail in. Here, only the age dating result is summarized. This rock fragment garnered our attention because it is significantly enriched in incompatible elements, e.g., 7 ppm thorium, compared to other known lunar basalts. Its mineral- and trace-element chemistry set it apart from other Apollo 12 basalts and indeed from all Apollo and Luna basalts. What makes it potentially very significant is the possibility that it is a sample of a relatively young, thorium-rich basalt flow similar to those inferred to occur in the Procellarum region, especially northwestern Procellarum, on the basis of Lunar Prospector orbital data. Exploiting the lunar regolith for the diversity of rock types that have been delivered to a landing site by impact processes and correlating them to their likely site of origin using remote sensing will be an important part of future missions to the Moon. One such mission is Moonrise, which would collect regolith samples from the South Pole-Aitken Basin, concentrating thousands of rock fragments of 3-20 mm size from the regolith, and returning the samples to Earth.

Jolliff, B. L.↗
NASA NTRS1991

The Geologic Remote Sensing Field Experiment (GRSFE)

Field measurements for the Geologic Remote Sensing Field Experiment (GRSFE) were concentrated in the Lunar Lake area of Nevada. The GRSFE data are meant to be used in a variety of investigations, including tests of multispectral radiative transfer models for scattering and emission from planetary surfaces in support of the Earth Observing System (EOS), Mars Observer, and Magellan Missions. Studies will also be pursued to establish the neotectonic and paleoclimatic history of the arid southwestern United States. The data will also be used to support Mars Rover Sample Return (MRSR) simulation studies.

Dale-Bannister, Mary A.↗
NASA NTRS2010

Permissible Exposure Level for Lunar Dusts: Gaps are Closing

Space faring nations plan to return human explorers to the moon within the next decade. Experience during the Apollo flights suggests that lunar dust will invariably get into the habitat where the finest portion (less than 5 micrometers) could be inhaled by the crew before it is cleared from the atmosphere. NASA is developing a database from which a 6-month, episodic exposure standard for lunar dust can be set. Three kinds of moon dust were prepared from a parent sample of Apollo 14 regolith #14003,96. Our goal was to prepare each type of dust sample with a mean diameter less than 2 m, which is suitable for instillation into the lungs of rats. The three samples were prepared as follows: separation from the parent sample using a fluidized bed, grinding using a jet mill grinder, or grinding with a ball-mill grinder. Grinding simulated restoration of surface activation of dust expected to occur at the surface of the moon on native lunar dust. We used two grinding methods because they seemed to produce different modes of activation. The effects of grinding were preserved by maintaining the dust in ultra-pure nitrogen until immediately before it was placed in suspension for administration to rats. The dust was suspended in physiological saline with 10% Survanta, a lung surfactant. Rats were given intratrachael instillations of the dust suspension at three doses. In addition to the three moon dusts (A, C and E), we instilled the same amount of a negative control (TiO2, B) and a highly-toxic, positive control (quartz, D). These additional mineral dusts were selected because they have well-established and very different permissible exposure levels (PELs). Our goal was to determine where lunar dusts fit between these extremes, and then estimate a PEL for each lunar dust. We evaluated many indices of toxicity to the lung. The figure shows the changes in lactate dehydrogenase (LDH), a marker of cell death, for the five dusts. Benchmark dose software (Version 2.1.2) from the Environmental Protection Agency was used to estimate the 10% effect levels (BMD(sub 10)) using five models. The best-fitting model was used to estimate the optimal BMD(sub 10) (table)

James, John T.↗
NASA NTRS1990

Rationale and requirements for lunar exploration

The moon has had a complex and geologically fascinating history. It is a natural laboratory in which to study planetary processes and is readily accessible, only 2.5 days away. The moon is the only planetary object from which there are samples of known geologic context, and its history is understood well enough to permit the posing and answering of sophisticated scientific questions. The moon also preserves information about the earth's early history and cratering record, and about the sun's history. To retrieve all this information, it is necessary to return to the moon and study it from orbit, establish surface geophysical networks, obtain reconnaissance samples, and perform field work. These ventures will require development of interesting technological systems, such as a robotic field geologist, automated roving vehicles (both pressurized for humans and unpressurized for robotic devices), a host of sampling tools, automated sample-return spacecraft, and all of the associated navigation, communication, and power systems.

Spudis, Paul D.↗
NASA NTRS2017

50th Anniversary of the World's First Extraterrestrial Sample Receiving Laboratory: The Apollo Program's Lunar Receiving Laboratory

The Apollo program's Lunar Receiving Laboratory (LRL), building 37 at NASA's Manned Spaceflight Center (MSC), now Johnson Space Center (JSC), in Houston, TX, was the world's first astronaut and extraterrestrial sample quarantine facility (Fig. 1). It was constructed by Warrior Construction Co. and Warrior-Natkin-National at a cost of $8.1M be-tween August 10, 1966 and June 26, 1967. In 1969, the LRL received and curated the first collection of extra-terrestrial samples returned to Earth; the rock and soil samples of the Apollo 11 mission. This year, the JSC Astromaterials Acquisition and Curation Office (here-after JSC curation) celebrates 50 years since the opening of the LRL and its legacy of laying the foundation for modern curation of extraterrestrial samples.

Calaway, M. J.↗
NASA NTRSDate not supplied

The Oxidation State of Sulfur in Apollo Samples 71035 and 71055

Lunar apatites contain 100s-1000s ppm sulfur [1-3]. This was initially puzzling because lunar basalts are thought to form, including at the time of apatite crystallization, in low oxygen fugacity (fO2) conditions where sulfur exists in its reduced form (S2-), a substitution not previously observed in natural apatite. It has been recently shown, using S-XANES measurements of the oxidation state of sulfur in apatites and proximal mesostasis in the lunar basalts 12039 and 10044, that sulfur is indeed present as S2- in both the mesostasis glass and apatite when measurements were performed far from cracks or pits in the thin section [4]. This observation is consistent with other mineralogical indications of the low fO2 during formation of these samples (~IW-1) such as the presence of Fe-metal, ulvöspinel, ilmenite, fayalite, and silica in the thin sections. In the same study, in addition to clear spectral evidence for the dominance of S2-, analyses of apatite grains in both samples that occurred near cracks or pits in the thin section sometimes revealed non-negligible spectral evidence (e.g., S6+/ΣS > 0.03; [4]) for the presence of S6+. Because S6+ was not observed in the mesostasis glass near the apatite grains measured, or in any phase far from cracks or pits in the studied thin sections, this S6+ was interpreted as either primary S2- in the sulfide altered to S6+ in the thin section, or S6+ of secondary origin, deposited in the fractures of the samples [4, 5]. Whether this is of lunar or terrestrial origin is unknown but has implications for lunar petrogenesis if lunar [e.g., 5], or sample handling and curation if terrestrial. To test between lunar and terrestrial origins for observed S6+ in Apollo-era thin sections, we will measure the oxidation state of sulfur in apatite and associated phases in a specially frozen sample from a boulder sampled at Station 1A during the Apollo 17 mission as part of the NASA Apollo Next Generation Sample Analysis (ANGSA) program. Here, we present “control” measurements of samples 71035 and 71055, using Apollo era thin sections of aliquots of these rocks that were processed upon return to Earth and since stored under N2 atmospheres at room temperature. These will be compared to measurements using newly made thin sections of aliquots of the same rocks (71035 and 71055). In addition, 71036, which has been in cold storage (-20℃) since the return of the Apollo 17 mission to Earth, has been recently made available through the ANGSA program. With 71036 we can test the effect of storage temperature on potential oxidation of S2- to S6+ in the relatively oxidizing and warm conditions of Earth’s surface.

apollo↗
NASA NTRS2004

Lunar and Planetary Science XXXV: Special Session: Oxygen in the Solar System, I

The Special Session: Oxygen in the Solar System, I, included the following reports:Oxygen in the Solar System: Origins of Isotopic and Redox Complexity; The Origin of Oxygen Isotope Variations in the Early Solar System; Solar and Solar-Wind Oxygen Isotopes and the Genesis Mission; Solar 18O/17O and the Setting for Solar Birth; Oxygen Isotopes in Early Solar System Materials: A Perspective Based on Microbeam Analyses of Chondrules from CV Carbonaceous Chondrites; Insight into Primordial Solar System Oxygen Reservoirs from Returned Cometary Samples; Tracing Meteorites to Their Sources Through Asteroid Spectroscopy; Redox Conditions Among the Terrestrial Planets; Redox Complexity in Martian Meteorites: Implications for Oxygen in the Terrestrial Planets; Implications of Sulfur Isotopes for the Evolution of Atmospheric Oxygen; Oxygen in the Outer Solar System; and On the Oxidation States of the Galilean Satellites: Implications for Internal Structures.

Source record↗
NASA NTRS1986

Radioactivities in returned lunar materials and in meteorites

A preliminary C-14 study on lunar soil was carried out with the University of Toronto Iso Trace accelerator mass spectrometer. This accelerator was recommended for C-14 work by Dr. R. Schneider of A.S. and E., who was the field engineer during the assemblage and start-up operation of the accelerator. After the preliminary study using CO2 from 10084,937 soil, which had previously been counted with low-level mini-proportional counters, it became clear that the Toronto accelerator could carry out C-14/C-13/C-12 ratio measurements on 1 gram meteorite and lunar samples and that the C-14 measurements are done with higher precision and better reliability than elsewhere. A collaborative program with the University of Toronto Iso Trace accelerator group, which is expected to be scientifically fruitful. Arrangements have been made for Dr. R.P. Beukens of the Toronto Accelerator Group to extract the carbon compounds from Antarctic meteorite and lunar samples and to convert the compounds to CO2. During the past two years, a uranium-series dating method was developed for polar ice, which method is being applied to ice from the Allan Hills site, Byrd core, and the Beardsmore glacier.

Fireman, E. L.↗
NASA NTRS2017

Boulder Distributions at Legacy Landing Sites: Assessing Regolith Production Rates and Landing Site Hazards

Understanding how the distribution of boulders on the lunar surface changes over time is key to understanding small-scale erosion processes and the rate at which rocks become regolith. Boulders degrade over time, primarily as a result of micrometeorite bombardment so their residence time at the surface can inform the rate at which rocks become regolith or become buried within regolith. Because of the gradual degradation of exposed boulders, we expect that the boulder population around an impact crater will decrease as crater age increases. Boulder distributions around craters of varying ages are needed to understand regolith production rates, and Lunar Reconnaissance Orbiter Camera (LROC) Narrow Angle Camera (NAC) images provide one of the best tools for conducting these studies. Using NAC images to assess how the distribution of boulders varies as a function of crater age provides key constraints for boulder erosion processes. Boulders also represent a potential hazard that must be addressed in the planning of future lunar landings. A boulder under a landing leg can contribute to deck tilt, and boulders can damage spacecraft during landing. Using orbital data to characterize boulder populations at locations where landers have safely touched down (Apollo, Luna, Surveyor, Chang'e-3) provides validation for landed mission hazard avoidance planning. Additionally, counting boulders at legacy landing sites is useful because: 1) LROC has extensive coverage of these sites at high resolutions (approximately 0.5 meters per pixel). 2) Returned samples from craters at these sites have been radiometrically dated, allowing assessment of how boulder distributions vary as a function of crater age. 3) Surface photos at these sites can be used to correlate with remote sensing measurements.

Watkins, R. N.↗