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All sourcesNASA NTRSDOE OSTI
NASA NTRS2015

On-Orbit Quantitative Real-Time Gene Expression Analysis Using the Wetlab-2 System

NASA Ames Research Center's WetLab-2 Project enables on-orbit quantitative Reverse Transcriptase PCR (qRT-PCR) analysis without the need for sample return. The WetLab-2 system is capable of processing sample types ranging from microbial cultures to animal tissues dissected on-orbit. The project developed a RNA preparation module that can lyse cells and extract RNA of sufficient quality and quantity for use as templates in qRT-PCR reactions. Our protocol has the advantage of using non-toxic chemicals and does not require alcohols or other organics. The resulting RNA is dispensed into reaction tubes that contain all lyophilized reagents needed to perform qRT-PCR reactions. System operations require simple and limited crew actions including syringe pushes, valve turns and pipette dispenses. The project selected the Cepheid SmartCycler (TradeMark), a Commercial-Off-The-Shelf (COTS) qRT-PCR unit, because of its advantages including rugged modular design, low power consumption, rapid thermal ramp times and four-color multiplex detection. Single tube multiplex assays can be used to normalize for RNA concentration and integrity, and to study multiple genes of interest in each module. The WetLab-2 system can downlink data from the ISS to the ground after a completed run and uplink new thermal cycling programs. The ability to conduct qRT-PCR and generate results on-orbit is an important step towards utilizing the ISS as a National Laboratory facility. Specifically, the ability to get on-orbit data will provide investigators with the opportunity to adjust experimental parameters in real time without the need for sample return and re-flight. On orbit gene expression analysis can also eliminate the confounding effects on gene expression of reentry stresses and shock acting on live cells and organisms or the concern of RNA degradation of fixed samples and provide on-orbit gene expression benchmarking prior to sample return. Finally, the system can also be used for analysis of air, surface, water, and clinical samples to monitor environmental pathogens and crew health. The validation flight of the WetLab-2 system using E. coli bacteria and mouse liver launched on SpaceX-7 in June 2015 and will remain on the ISS National Laboratory.

ISS tools↗
NASA NTRS1989

Direct determination of the morphology, structure and composition of cometary and interstellar ice analogs in the laboratory

Ices of various kinds (H2O, CO, CO2, CH4, NH3, CH3OH, etc.) comprise a volumetrically significant proportion of objects in the solar system (comets, outer planets, planetary rings, satellites) as well as in interstellar space (astrophysical ices). The refinement of analytical electron microscopy (AEM) procedures for storing, preparing and analyzing ices and other materials at cryogenic temperatures is discussed. These procedures will be essential to the successful analysis of returned comet nucleus samples.

Blake, D. F.↗
NASA NTRS2018

Microscopes on ISS - Present and Future Possibilities

The attached slides are for an invited talk (invitation from Ken Savins at CASIS) to be given July 19 at the "2018 Microgravity Molecular Crystal Growth Workshop". Ken Savins indicated that the protein crystal growth community would benefit from knowing more about what is available on ISS for microscopy. It is especially important that the folks growing protein crystals start to use the microscopes on ISS as diagnostic tools so that when their samples are returned to Earth and the results are unexpected, they are able to determine whether or not the return flight had an impact. In additional to preparing this presentation describing present and possible future LMM capabilities (if it is refurbished), we worked with Rachel A Ormsby (techshot) and Devin Ridgley (HNu Photonics) to add slides and a movie they provided of their capacities. Contact information for the NASA GRC Liquid Crystal Facility (LCF) will be included, and a couple of slides for LCF may be added when the contractor (James Kolibas at ZIN Technology) returns from vacation.

protein crystals↗
NASA NTRSDate not supplied

Hydrogen Peroxide as a Method for Bioburden Reduction in Facilities with Strict Materials Requirements.

The cleanrooms used to curate NASA’s Astromaterials samples are carefully monitored for particulate and inorganic contamination. The clean labs also have a very limited set of acceptable materials and cleaning agents to further minimize the potential for contamination. Labs are cleaned primarily with isopropyl alcohol. Astromaterials samples are handled with tools made of stainless steel (304 or 316), Teflon, or aluminum alloy (6061). Although our current collections are not particularly susceptible to biological alteration or organic contamination, this will not be the case for new collections from the OSIRIS-REx mission, Hayabusa2, and from Mars Sample Return. Therefore, it is necessary to develop and test methods to reduce the bioburden in astromaterials cleanrooms without introducing unwanted contaminants. We will report on the results of three case studies where 7.5 wt% hydrogen peroxide was prepared from a stock solution of ultrapure 30 wt% hydrogen peroxide (JT Baker) using curation-grade ultrapure water. We followed CDC (Center for Disease Control) guidelines for using hydrogen peroxide as a high level disinfectant. This solution was used to clean a glovebox prior to processing Apollo samples, as well as surfaces in the Antarctic meteorite processing lab and Stardust lab after facilities monitoring indicated an unwanted increase in bioburden. In all three instances, the culturable bioburden was significantly reduced after a 30 min. exposure to the 7.5% hydrogen peroxide solution without a corresponding increase in inorganic or organic contamination. We observed 77 to 100% reductions in the bioburden recovery rate. In one case study, we also performed amplicon DNA sequencing on samples collected from the surfaces before and after cleaning. We observed a significant change in microbial community composition after peroxide cleaning. These results suggest that routine cleaning with hydrogen peroxide could be an effective way to control bioburden in astromaterials cleanrooms and other facilities with strict contamination control requirements.

A B Regberg↗
NASA NTRSDate not supplied

Hydrogen Peroxide as a Method for Bioburden Reduction in Facilities with Strict Materials Requirements

The cleanrooms used to curate NASA’s Astromaterials samples are carefully monitored for particulate and inorganic contamination. The clean labs also have a very limited set of acceptable materials and cleaning agents to further minimize the potential for contamination. Labs are cleaned primarily with isopropyl alcohol. Astromaterials samples are handled with tools made of stainless steel (304 or 316), Teflon, or aluminum alloy (6061). Although our current collections are not particularly susceptible to biological alteration or organic contamination, this will not be the case for new collections from the OSIRIS-REx mission, Hayabusa2, and from Mars Sample Return. Therefore, it is necessary to develop and test methods to reduce the bioburden in astromaterials cleanrooms without introducing unwanted contaminants. We will report on the results of three case studies where 7.5 wt% hydrogen peroxide was prepared from a stock solution of ultrapure 30 wt% hydrogen peroxide (JT Baker) using curation-grade ultrapure water. We followed CDC (Center for Disease Control) guidelines for using hydrogen peroxide as a high level disinfectant. This solution was used to clean a glovebox prior to processing Apollo samples, as well as surfaces in the Antarctic meteorite processing lab and Stardust lab after facilities monitoring indicated an unwanted increase in bioburden. In all three instances, the culturable bioburden was significantly reduced after a 30 min. exposure to the 7.5% hydrogen peroxide solution without a corresponding increase in inorganic or organic contamination. We observed 77 to 100% reductions in the bioburden recovery rate. In one case study, we also performed amplicon DNA sequencing on samples collected from the surfaces before and after cleaning. We observed a significant change in microbial community composition after peroxide cleaning. These results suggest that routine cleaning with hydrogen peroxide could be an effective way to control bioburden in astromaterials cleanrooms and other facilities with strict contamination control requirements.

A B Regberg↗
NASA NTRS2011

Expression of Enzymes that Metabolize Medications

INTRODUCTION: Increased exposure to radiation is one physiological stressor associated with spaceflight and it is feasible to conduct ground experiments using known radiation exposures. The health of the liver, especially the activity rate of its metabolic enzymes, determines the concentration of circulating drugs as well as the duration of their efficacy. While radiation is known to alter normal physiological function, how radiation affects liver metabolism of administered medications is unclear. Crew health could be affected if the actions of medications used in spaceflight deviated from expectations formed during terrestrial medication use. This study is an effort to identify liver metabolic enzymes whose expression is altered by spaceflight or by radiation exposures that mimic features of the spaceflight environment. METHODS: Using procedures approved by the Animal Care and Use Committee, mice were exposed to either 137Cs (controls, 50 mGy, 6Gy, or 50 mGy + 6Gy separated by 24 hours) or 13 days of spaceflight on STS 135. Animals were anesthetized and sacrificed at several time points (4 hours, 24 hours or 7 days) after their last radiation exposure, or within 6 hours of return to Earth for the STS 135 animals. Livers were removed immediately and flash-frozen in liquid nitrogen. Tissue was homogenized, RNA extracted, purified and quality-tested. Complementary DNA was prepared from high-quality RNA samples, and used in RT-qPCR experiments to determine relative expression of a wide variety of genes involved in general metabolism and drug metabolism. RESULTS: Results of the ground radiation exposure experiments indicated ~65 genes of the 190 tested were significantly affected by at least one of the radiation doses. Many of the affected genes are involved in the metabolism of drugs with hydrophobic or steroid-like structures, maintenance of redox homeostasis and repair of DNA damage. Most affected genes returned to near control expression levels by 7 days post-treatment. Not all recovered completely by the final time point tested: with 6 Gy exposure, metallothionein expression was 132-fold more than control at the 4 hr time point, and fell at each later time point (11-fold at 24 hrs, and 8-fold at 7 days). In contrast, there were other genes whose expression was altered and remained relatively constant through the 7 day period we tested. One examples is Cyp17a1, which showed a 4-fold elevation at 4 hrs after exposure and remained constant for 7 days after the last treatment. Spaceflight samples evaluated with similar methods and comparisons will be made between the radiation-treated groups and the spaceflight samples. CONCLUSION It seems likely that radiation exposure triggers homeostatic mechanisms, which could include alterations of gene expression. Better understanding of these pathways could aid in optimizing medications doses given to crewmembers who require treatment and eventually, to development of new countermeasures to ameliorate or prevent radiation-induced damage to cells and tissues.

Wotring, V. E.↗
NASA NTRSDate not supplied

New Hayabusa2 and OSIRIS REx Curation Facilities at Nasa Johnson Space Center

Asteroids are made up of rocky material that is left over from the formation of our solar system [1]. This material holds the key to unlocking information about the history of the planets and our sun. Hayabusa2 and OSIRIS-REx are two sample return missions that have collected rocky material from carbonaceous asteroids which are rich in water, carbon, and organic compounds [1]. Hayabusa2 is a spacecraft that collected samples from asteroid Ryugu launched by the Japan Aerospace Exploration Agency (JAXA). Samples were returned to Earth in December 2020 and 10 percent of the collected material is currently housed in a state-of-the-art laboratory at NASA Johnson Space Center (JSC) dedicated to Ryugu material [1]. OSIRIS-REx is a spacecraft launched by NASA that collected samples from asteroid Bennu. The samples are on their journey to Earth and will arrive in September 2023. They will be stored in a separate cleanroom dedicated to Bennu material. From these two missions, scientists will examine dust particles and rocky material to research clues on how the early solar system formed and how life began [2]. Because these samples are so precious and rare, it is important to keep them free from Earth contamination. In September of 2020, a massive construction project began to provide curation facilities to meet the needs of two incoming asteroid collections, Hayabusa2 and OSIRIS-REx. Despite numerous setbacks caused by the coronavirus pandemic, these facilities have been completed in the fall of 2021. Some of these setbacks included strict PPE requirements, keeping safe working distances as well as access to the facilities as NASA was operating under a Stage 3 condition in response to the pandemic. These facilities will provide curation laboratories to safely house the precious asteroid samples as well as facilities to manipulate samples, do sample preparation and process samples into and out of the labs for future studies by the scientific community. The lab suite consists of several different rooms including an initial anteroom (ISO 7), a staging area (ISO 7), two gowning areas (one for OSIRIS-REx and one for Hayabusa2; both ISO 6)), the Haybusa2 Curation Laboratory (ISO 5), the OSIRIS-REx Curation Laboratory (ISO 5), an ultramicrotomy laboratory (ISO 7) and a thin section laboratory (not a cleanroom). To maintain cleanliness levels necessary for these lab spaces quarterly to monthly Balazs organic and inorganic sampling has been conducted on a regular basis before, during and after the construction project to monitor the cleanliness levels in the new labs that will house the asteroid samples. These new facilities feature a Ruuvi (Grafana) monitoring system that measures temperature, humidity, and pressure of the lab suite. This is a small puck shaped sensor that sends signals to the Grafana cloud where the data can be plotted and set up on dashboards within the lab suite. These sensors are easy to set up and install and they run off a cell battery that is good for 3-5 years before needing replacement. This system can deliver text messages and emails to the appropriate personnel when values fall outside of set limits. In addition to the monitoring system, this new lab suite features viewing windows from several different locations and sliding motion censored doors. We have obtained some state-of-the-art equipment to outfit the lab spaces (desiccators, microscopes, ultramicrotome) and are in the process of outfitting the suite with additional items such as: nitrogen gloveboxes, additional desiccators, micromanipulators, etc. The Hayabusa2 samples provided to NASA by JAXA included 23 millimeter sized grains and 4 containers with finer material. OSIRIS-REx is expected to return as much as 400 grams of asteroid Bennu. Samples will be stored in a nitrogen glove box and separated into nitrogen sealed transfer containers. Small Bennu and Ryugu particles will be handled and prepared (e.g., ultra-thin sections for scanning electron microscopy (SEM) or transmission electron microscopy (TEM)) using an Axis Pro micromanipulator and Leica EM UC7 ultramicrotome. Analyzing samples at the atomic scale will provide greater insight to the origins of the solar system and life formation on Earth. All the curation preparation for these sample collections is essential to ongoing research and efforts to understand our solar system, both nowand for future generations.

Curation↗
NASA NTRS2015

SMART: A Propositional Logic-Based Trade Analysis and Risk Assessment Tool for a Complex Mission

This paper introduces a new trade analysis software called the Space Mission Architecture and Risk Analysis Tool (SMART). This tool supports a high-level system trade study on a complex mission, such as a potential Mars Sample Return (MSR) mission, in an intuitive and quantitative manner. In a complex mission, a common approach to increase the probability of success is to have redundancy and prepare backups. Quantitatively evaluating the utility of adding redundancy to a system is important but not straightforward, particularly when the failure of parallel subsystems are correlated.

Ono, Masahiro↗
NASA NTRSDate not supplied

Standardizing A Method to Recreate the Density Profile of the Lunar Surface at Depth

As humanity prepares to return to the moon, it becomes ever more important to understand the geotechnical properties of the body we are visiting. However, with only a small number of samples and few missions that took geotechnical measurements, lunar simulants are essential for developing working technologies to use on the lunar surface. Understanding density related properties can allow us to calculate the shear strength and bearing capacity, which is vital for surface trafficability and building permanent structures. However, testbeds do not exist at a depth that would allow us to be able to accurately test certain equipment and loads in these geotechnical conditions. The goal of this project is to be able to recreate the density profile of the lunar surface at depth using piston compaction, and to evaluate success with geotechnical measurements.

C G Locke↗
NASA NTRS2014

Final Reports of the Stardust ISPE: Seven Probable Interstellar Dust Particles

The Stardust spacecraft carried the first spaceborne collector specifically designed to capture and return a sample of contemporary interstellar dust to terrestrial laboratories for analysis [1]. The collector was exposed to the interstellar dust stream in two periods in 2000 and 2002 with a total exposure of approximately 1.8 10(exp 6) square meters sec. Approximately 85% of the collector consisted of aerogel, and the remainder consisted of Al foils. The Stardust Interstellar Preliminary Examination (ISPE) was a consortiumbased effort to characterize the collection in sufficient detail to enable future investigators to make informed sample requests. Among the questions to be answered were these: How many impacts are consistent in their characteristics with interstellar dust, with interplanetary dust, and with secondary ejecta from impacts on the spacecraft? Are the materials amorphous or crystalline? Are organics detectable? An additional goal of the ISPE was to develop or refine the techniques for preparation, analysis, and curation of these tiny samples, expected to be approximately 1 picogram or smaller, roughly three orders of magnitude smaller in mass than the samples in other small particle collections in NASA's collections - the cometary samples returned by Stardust, and the collection of Interplanetary Dust Particles collected in the stratosphere.

Allen, Carlton↗
NASA NTRSDate not supplied

From Apollo to Artemis: Opening and Processing Lunar Core 73002 for the ANGSA Program

The Apollo mission returned 382 kg of lunar material comprising rock, soil and core samples. Some of these samples were intentionally set aside after their return from the Moon for future study, including samples sealed on the lunar surface, frozen samples and samples stored under Helium. The Apollo Next Generation Sample Analysis (ANGSA) program was established to study thesesamples, in part to help bridge the gap between Apollo and the next generation of lunar science and exploration.Apollo 17 double drive tube core sample 73001/73002 was collected about 50 meters east of Lara Crater from a landslide deposit originating from South Massif. After separating the two halves, the lower drive tube 73001 was immediately sealed in a special vacuum container. Both drive tubes were then placed in an Apollo Lunar Sample Return Container (ALSRC) and returned to Earth under vacuum. Total sample weight and length of 73001/73002 is 1263.0 g and up to 60 cm, with the upper drive 73002 containing 429.7 g and 23 cm of material ( which was then compressed to 18.5 cm during extrusion in the lab). We will present the meticulous methods involved in preparing for, opening and processing lunar core 73002, the upper half of the double drive tube. This includes searching and locating procedures and tools, practicing assembly and extrusion in a mock-up, and finally opening and dissecting the core sample 73002. Challenges (both expected and unexpected) encountered along the way and lessons learned during this project will help pave the way towards improving future lunar sample return missions and advancing insight into the Moon’s history

C. H. Krysher↗
NASA NTRS2015

Low-Latency Teleoperations for Human Exploration and Evolvable Mars Campaign

NASA has been analyzing a number of mission concepts and activities that involve low-latency telerobotic (LLT) operations. One mission concept that will be covered in this presentation is Crew-Assisted Sample Return which involves the crew acquiring samples (1) that have already been delivered to space, and or acquiring samples via LLT from orbit to a planetary surface and then launching the samples to space to be captured in space and then returned to the earth with the crew. Both versions of have key roles for low-latency teleoperations. More broadly, the NASA Evolvable Mars Campaign is exploring a number of other activities that involve LLT, such as: (a) human asteroid missions, (b) PhobosDeimos missions, (c) Mars human landing site reconnaissance and site preparation, and (d) Mars sample handling and analysis. Many of these activities could be conducted from Mars orbit and also with the crew on the Mars surface remotely operating assets elsewhere on the surface, e.g. for exploring Mars special regions and or teleoperating a sample analysis laboratory both of which may help address planetary protection concerns. The operational and technology implications of low-latency teleoperations will be explored, including discussion of relevant items in the NASA Technology Roadmap and also how previously deployed robotic assets from any source could subsequently be used by astronauts via LLT.

crew autonomy↗
NASA NTRS2020

Mars 2020 Rover Adaptive Caching Assembly: Caching Martian Samples for Potential Earth Return

The Adaptive Caching Assembly, part of the Sampling and Caching System on the Mars 2020 Rover, consists of multiple stations that together process sample tubes containing collected Martian material, either rock cores or soil samples, and prepares hermetically-sealed sample tubes for caching on the surface of Mars. There are 7 active degrees-of-freedom, as well as a large number of passive mechanisms within the Adaptive Caching Assembly that must operate in extreme Mars conditions (i.e., temperature and pressure). Hardware cleanliness requirements significantly drove design, assembly, and test operations of the Adaptive Caching Assembly, and were found to adversely affect hardware in some cases such that late design changes and revised cleanliness operations had to be implemented. While Adaptive Caching Assembly hardware was designed to accommodate dust, testing in a representative environment is important to validate functionality is not compromised.

Silverman, Milo↗
NASA NTRS1999

X-Ray Fingerprinting Techniques for Recognizing A Hydrological Role in the Formation of Minerals on the Surface of Mars

Previous work has demonstrated the ability of a miniaturized XRD-XRF instrument to perform in-situ analyses without sample preparation or acquisition. Deployment of this instrument on a Martian rover will allow a large number of rapid qualitative analyses, which will maximize the diversity of samples studied and selected for possible return. As a first step in designing a decision tree for recognizing minerals in complex mixtures, d spacings were plotted against intensity for several mineral groups comprising rock and soil types inferred for the surface of Mars (weathered basalt, playa and hydrothermal deposits, clay-rich soils). In all groups, d spacings cluster in a range from about 1-4 angstroms, which can under certain circumstances obscure patterns for individual phases. However, within the silicate family, minerals containing either bound OH- or molecules of H20 (clays, micas, amphiboles, zeolites) are characterized by a shift of peaks to higher d spacings. Large d spacings (greater than about 7 angstroms) thus act as a first-order filter for distinguishing hydrous from anhydrous silicates. The ability to quickly verify the presence of silicates that have interacted with water has important implications for using mineral chemistry and structure to help decipher the hydrologic and atmospheric history of Mars. This represents a beginning for developing more sophisticated methods of pattern recognition. These will combine XRD and XRF analyses with optical data to rapidly7 discern environmentally diagnostic assemblages without the necessity of identifying every peak individual mineral phase.

Metzger, Ellen P.↗
NASA NTRS2014

Cellulose Acetate Replica Cleaning Study of Genesis Non-Flight Sample 3CZ00327

The Genesis mission collected solar wind and brought it back to Earth in order to provide precise knowledge of solar isotopic and elemental compositions. The ions in the solar wind were stopped in the collectors at depths on the order of 10 to a few hundred nanometers. This shallow implantation layer is critical for scientific analysis of the composition of the solar wind and must be preserved throughout sample handling, cleaning, processing, distribution, preparation and analysis. We are working interactively with the community of scientists analyzing Genesis samples, using our unique laboratory facilities -- and, where needed, our unique cleaning techniques -- to significantly enhance the science return from the Genesis mission. This work is motivated by the need to understand the submicron contamination on the collectors in the Genesis payload as recovered from the crash site in the Utah desert, and -- perhaps more importantly -- how to remove it. That is, we are evaluating the effectiveness of the wet-chemical "cleaning" steps used by various investigators, to enable them to design improved methods of stripping terrestrial contamination from surfaces while still leaving the solar-wind signal intact.

Kuhlman, K. R.↗
NASA NTRS2016

Small Particulate Contamination Survey Of Genesis Flight Sample 61423

The Genesis mission collected solar wind and brought it back to Earth in order to provide precise knowledge of solar isotopic and elemental compositions. The ions in the solar wind stop in the collectors at depths on the order of 10 to a few hundred nanometers. This shallow implantation layer is critical for scientific analysis of the composition of the solar wind and must be preserved throughout sample handling, cleaning, processing, distribution, preparation and analysis. We continue to work with the community of scientists analyzing Genesis samples using our unique laboratory facilities -- and, where needed, our unique cleaning techniques -- to significantly enhance the science return from the Genesis mission. This work is motivated by the need to understand the submicron contamination on the collectors in the Genesis payload as recovered from the crash site in the Utah desert, and -- perhaps more importantly -- how to remove it. We continue to evaluate the effectiveness of the wet-chemical "cleaning" steps used by various investigators, to enable them to design improved methods of stripping spacecraft and terrestrial contamination from surfaces while still leaving the solar-wind signal intact.

Kuhlman, K. R.↗
NASA NTRS2016

Mars 2020 Coring Drill: Prototype Testing and Analysis

The Mars 2020 rover will carry a new subsystem to collect and prepare Martian rocks and regolith (loose, unconsolidated) samples. This includes a rotary percussive coring drill and a set of sample tubes. About 30 of these sample tubes will be deposited at select locations for return on a potential future sample-retrieval mission. In laboratories on Earth, specimens from Mars could be analyzed for evidence of past life on Mars and possible health hazards for future human missions. Hardware and control algorithms for the coring drill are based heavily on testing. Results from testing of prototype hardware are used to refine the design

Kreichbaum, Kristopher↗
NASA NTRS2014

Constraints on Exposure Ages of Lunar and Asteroidal Regolith Particles

Mineral grains in lunar and asteroidal regolith samples provide a unique record of their interaction with the space environment. Exposure to the solar wind results in implantation effects that are preserved in the rims of grains (typically the outermost 100 nm), while impact processes result in the accumulation of vapor-deposited elements, impact melts and adhering grains on particle surfaces. These processes are collectively referred to as space weathering. A critical element in the study of these processes is to determine the rate at which these effects accumulate in the grains during their space exposure. For small particulate samples, one can use the density of solar flare particle tracks to infer the length of time the particle was at the regolith surface (i.e., its exposure age). We have developed a new technique that enables more accurate determination of solar flare particle track densities in mineral grains <50 micron in size that utilizes focused ion beam (FIB) sample preparation combined with transmission electron microscopy (TEM) imaging. We have applied this technique to lunar soil grains from the Apollo 16 site (soil 64501) and most recently to samples from asteroid 25143 Itokawa returned by the Hayabusa mission. Our preliminary results show that the Hayabusa grains have shorter exposure ages compared to typical lunar soil grains. We will use these techniques to re-examine the track density-exposure age calibration from lunar samples reported by Blanford et al. (1975).

Berger, Eve L.↗