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NASA NTRS2012

From Concept-to-Flight: An Active Active Fluid Loop Based Thermal Control System for Mars Science Laboratory Rover

The Mars Science Laboratory (MSL) rover, Curiosity, which was launched on November 26, 2011, incorporates a novel active thermal control system to keep the sensitive electronics and science instruments at safe operating and survival temperatures. While the diurnal temperature variations on the Mars surface range from -120 C to +30 C, the sensitive equipment are kept within -40 C to +50 C. The active thermal control system is based on a single-phase mechanically pumped fluid loop (MPFL) system which removes or recovers excess waste heat and manages it to maintain the sensitive equipment inside the rover at safe temperatures. This paper will describe the entire process of developing this active thermal control system for the MSL rover from concept to flight implementation. The development of the rover thermal control system during its architecture, design, fabrication, integration, testing, and launch is described.

heat rejection systems↗
NASA NTRS2013

MARS Science Laboratory Post-Landing Location Estimation Using Post2 Trajectory Simulation

The Mars Science Laboratory (MSL) Curiosity rover landed safely on Mars August 5th, 2012 at 10:32 PDT, Earth Received Time. Immediately following touchdown confirmation, best estimates of position were calculated to assist in determining official MSL locations during entry, descent and landing (EDL). Additionally, estimated balance mass impact locations were provided and used to assess how predicted locations compared to actual locations. For MSL, the Program to Optimize Simulated Trajectories II (POST2) was the primary trajectory simulation tool used to predict and assess EDL performance from cruise stage separation through rover touchdown and descent stage impact. This POST2 simulation was used during MSL operations for EDL trajectory analyses in support of maneuver decisions and imaging MSL during EDL. This paper presents the simulation methodology used and results of pre/post-landing MSL location estimates and associated imagery from Mars Reconnaissance Orbiter s (MRO) High Resolution Imaging Science Experiment (HiRISE) camera. To generate these estimates, the MSL POST2 simulation nominal and Monte Carlo data, flight telemetry from onboard navigation, relay orbiter positions from MRO and Mars Odyssey and HiRISE generated digital elevation models (DEM) were utilized. A comparison of predicted rover and balance mass location estimations against actual locations are also presented.

Davis, J. L.↗
NASA NTRS2013

Potential Applications for Radioisotope Power Systems in Support of Human Exploration Missions

Radioisotope power systems (RPS) for space applications have powered over 27 U.S. space systems, starting with Transit 4A and 4B in 1961, and more recently with the successful landing of the Mars Science Laboratory rover Curiosity in August 2012. RPS enable missions with destinations far from the Sun with faint solar flux, on planetary surfaces with dense or dusty atmospheres, and at places with long eclipse periods where solar array sizes and energy storage mass become impractical. RPS could also provide an enabling capability in support of human exploration activities. It is envisioned that with the higher power needs of most human mission concepts, a high efficiency thermal-to-electric technology would be required such as the Advanced Stirling Radioisotope generator (ASRG). The ASRG should be capable of a four-fold improvement in efficiency over traditional thermoelectric RPS. While it may be impractical to use RPS as a main power source, many other applications could be considered, such as crewed pressurized rovers, in-situ resource production of propellants, back-up habitat power, drilling, any mobile or remote activity from the main base habitat, etc. This paper will identify potential applications and provide concepts that could be a practical extension of the current ASRG design in providing for robust and flexible use of RPS on human exploration missions.

Cataldo, Robert L.↗
NASA NTRS2013

Detection of Organic Constituents Including Chloromethylpropene in the Analyses of the ROCKNEST Drift by Sample Analysis at Mars (SAM)

key challenge in assessing the habitability of martian environments is the detection of organic matter - a requirement of all life as we know it. The Curiosity rover, which landed on August 6, 2012 in Gale Crater of Mars, includes the Sample Analysis at Mars (SAM) instrument suite capable of in situ analysis of gaseous organic components thermally evolved from sediment samples collected, sieved, and delivered by the MSL rover. On Sol 94, SAM received its first solid sample: scooped sediment from Rocknest that was sieved to <150 m particle size. Multiple 10-40 mg portions of the scoop #5 sample were delivered to SAM for analyses. Prior to their introduction, a blank (empty cup) analysis was performed. This blank served 1) to clean the analytical instrument of SAMinternal materials that accumulated in the gas processing system since integration into the rover, and 2) to characterize the background signatures of SAM. Both the blank and the Rocknest samples showed the presence of hydrocarbon components.

Eigenbrode, J. L.↗
NASA NTRS2013

Carbon Isotopic Composition of CO2, Evolved During Perchlorate-Induced Reactions in Mars Analog Materials: Interpreting SAM/MSL Rocknest Data

The Sample Analysis at Mars (SAM) Instrument Suite on the Mars Science Laboratory (MSL) Rover Curiosity made its first solid sample evolved gas analysis of unconsolidated material at aeolian bedform Rocknest in Gale Crater. The magnitude of O2 evolved in each run as well as the chlorinated hydrocarbons detected by SAM gas chromatograph/ mass spectrometer (GCMS) [1] suggest a chlorinated oxidant such as perchlorate in Rocknest materials [2]. Perchlorate induced combustion of organics present in the sample would contribute to the CO2 volatile inventory, possibly overlapping with CO2 from inorganic sources. The resulting carbon and oxygen isotopic composition of CO2 sent to the Tunable Laser Spectrometer (TLS) for analysis would represent mixed sources. This work was undertaken to better understand a) how well the carbon isotopic composition ( 13C) of CO2 from partially combusted products represents their source and b) how the 13C of combusted products can be deconvolved from other carbon sources such as thermal decomposition of carbonate.

Stern, J. C.↗
NASA NTRS2013

A Preliminary Interpretation of the First Results from the REMS Surface Pressure Measurements of the MSL Mission

The Rover Environmental Monitoring Station (REMS) on the Mars Science Laboratory (MSL) Curiosity rover consists of a suite of meteorological instruments that measure pressure, temperature (air and ground), wind (speed and direction), relative humidity, and the UV flux. A description of the instruments is described elsewhere.. Here we focus on interpreting the first 90 sols of REMS operations with a particular emphasis on the pressure data.

Haberle, Robert M.↗
NASA NTRS2013

Reconstruction of the Mars Science Laboratory Parachute Performance and Comparison to the Descent Simulation

The Mars Science Laboratory used a single mortar-deployed disk-gap-band parachute of 21.35 m nominal diameter to assist in the landing of the Curiosity rover on the surface of Mars. The parachute system s performance on Mars has been reconstructed using data from the on-board inertial measurement unit, atmospheric models, and terrestrial measurements of the parachute system. In addition, the parachute performance results were compared against the end-to-end entry, descent, and landing (EDL) simulation created to design, develop, and operate the EDL system. Mortar performance was nominal. The time from mortar fire to suspension lines stretch (deployment) was 1.135 s, and the time from suspension lines stretch to first peak force (inflation) was 0.635 s. These times were slightly shorter than those used in the simulation. The reconstructed aerodynamic portion of the first peak force was 153.8 kN; the median value for this parameter from an 8,000-trial Monte Carlo simulation yielded a value of 175.4 kN - 14% higher than the reconstructed value. Aeroshell dynamics during the parachute phase of EDL were evaluated by examining the aeroshell rotation rate and rotational acceleration. The peak values of these parameters were 69.4 deg/s and 625 deg/sq s, respectively, which were well within the acceptable range. The EDL simulation was successful in predicting the aeroshell dynamics within reasonable bounds. The average total parachute force coefficient for Mach numbers below 0.6 was 0.624, which is close to the pre-flight model nominal drag coefficient of 0.615.

Cruz, Juan R.↗
NASA NTRS2013

Qualification of UHF Antenna for Extreme Martian Thermal Environments

The purpose of this development was to validate the use of the external Rover Ultra High Frequency (RUHF) antenna for space under extreme thermal environments to be encountered during the surface operations of the Mars Science Laboratory (MSL) mission. The antenna must survive all ground operations plus the nominal 670 Martian sol mission that includes summer and winter seasons of the Mars thermal environment.The qualification effort was to verify that the RUHF antenna design and its bonding and packaging processes are adequate to survive the harsh environmental conditions. The RUHF is a quadrifilar helix antenna mounted on the MSL Curiosity rover deck. The main components of the RUHF antenna are the helix structure, feed cables, and hybrid coupler, and the high-power termination load. In the case of MSL rover externally mounted hardware, not only are the expected thermal cycle depths severe, but there are temperature offsets between the Mars summer and winter seasons. The total number of temperature cycles needed to be split into two regimes of summer cycles and winter cycles. The qualification test was designed to demonstrate a survival life of three times more than all expected ground testing, plus a nominal 670 Martian sol missions. Baseline RF tests and a visual inspection were performed prior to the start of the qualification test. Functional RF tests were performed intermittently during chamber breaks over the course of the qualification test. For the RF return loss measurements, the antenna was tested in a controlled environment outside the thermal chamber with a vector network analyzer that was calibrated over the antenna s operational frequency range. A total of 2,010 thermal cycles were performed. Visual inspection showed a dulling of the solder material. This change will not affect the performance of the antenna. No other changes were observed. RF tests were performed on the RUHF helix antenna, hybrid, and load after the 2,010 qualification cycles test. The RF performance of the RUHF antenna, hybrid, and load were almost identical before and after the complete test. Therefore, the developed design of RUHF is qualified for a long-duration MSL mission. The RUHF antenna has not been used for long-duration missions such as MSL in the past. The state-of-the-art technology of the RUHF antenna is used to develop the antennas for MSL mission survivability. This developmental test data provides the confidence in using this RUHF antenna for future NASA missions to Mars.

Ramesham, Rajeshuni↗
NASA NTRS2013

Mars Science Laboratory Cruise Propulsion Maneuvering Operations

Mars Science Laboratory "Curiosity" is NASA's most recent mission to Mars, launched in November 2011, and landed in August 2012. It is a subcompact car-sized nuclear powered rover designed for a long duration mission, with an extensive suite of science instruments. Entry, descent and landing used a unique "skycrane" concept. This report describes the propulsive maneuvering operations during cruise from Earth to Mars, to control attitudes and to target the vehicle for entry. The propulsion subsystem, mission operations, and flight performance are discussed. All trajectory control maneuvers were well within accuracy requirements, and all turns and spin corrections were nominal.

Baker, Raymond S.↗
NASA NTRS2013

Ablator Response Model Development: From Flight Data Back to Fundamental Experiments

The successful Mars atmospheric entry by the Mars Science Laboratory (MSL-Curiosity) combined with the success of the Earth atmospheric entry by the Stardust capsule have established PICA as a major Thermal Protection Systems (TPS) material. We expect that this class of materials will be on the short list selected by NASA for any atmospheric entry missions and that it will be the lead of that list of materials in any planning, feasibility studies or flight readiness studies. In addition to NASAs successes, the Dragon capsule, the successful commercial space vehicle built by SpaceX, uses PICA-X, while the European Space Agency is considering ASTERM for its exploration missions that involve atmospheric entries, both of these materials are of the same family as PICA. In the talk, a high-fidelity model will be detailed and discussed. The model tracks the chemical composition of the gases produced during pyrolysis. As in the conventional models, it uses equilibrium chemistry to determine the recession rate at high temperatures but switches to in-volume finite-rate ablation for lower temperatures. It also tracks the time evolution of the porosity of the material. Progress in implementing this high-fidelity model in a code will be presented. In addition, a set of basic experimental data being supported for model validation will be summarized. The validation process for the model development will be discussed. Preliminary results will be presented for a case where detailed pyrolysis product chemistry is computed. Finally, a wish list for a set of validation experiments will be outlined and discussed.

Mansour, Nagi N.↗
NASA NTRS2014

Cameras Monitor Spacecraft Integrity to Prevent Failures

The Jet Propulsion Laboratory contracted Malin Space Science Systems Inc. to outfit Curiosity with four of its cameras using the latest commercial imaging technology. The company parlayed the knowledge gained under working with NASA to develop an off-the-shelf line of cameras, along with a digital video recorder, designed to help troubleshoot problems that may arise on satellites in space.

Source record↗
NASA NTRS2013

Atmosphere Assessment for MARS Science Laboratory Entry, Descent and Landing Operations

On August 6, 2012, the Mars Science Laboratory rover, Curiosity, successfully landed on the surface of Mars. The Entry, Descent and Landing (EDL) sequence was designed using atmospheric conditions estimated from mesoscale numerical models. The models, developed by two independent organizations (Oregon State University and the Southwest Research Institute), were validated against observations at Mars from three prior years. In the weeks and days before entry, the MSL "Council of Atmospheres" (CoA), a group of atmospheric scientists and modelers, instrument experts and EDL simulation engineers, evaluated the latest Mars data from orbiting assets including the Mars Reconnaissance Orbiter's Mars Color Imager (MARCI) and Mars Climate Sounder (MCS), as well as Mars Odyssey's Thermal Emission Imaging System (THEMIS). The observations were compared to the mesoscale models developed for EDL performance simulation to determine if a spacecraft parameter update was necessary prior to entry. This paper summarizes the daily atmosphere observations and comparison to the performance simulation atmosphere models. Options to modify the atmosphere model in the simulation to compensate for atmosphere effects are also presented. Finally, a summary of the CoA decisions and recommendations to the MSL project in the days leading up to EDL is provided.

Cianciolo, Alicia D.↗
NASA NTRS2013

Modeling the Skills and Practices of Scientists through an “All-Inclusive” Comparative Planetology Student Research Investigation

To effectively prepare the nation's future Science, Technology, Engineering, and Mathematics (STEM) workforce, students in today's classrooms need opportunities to engage in authentic experiences that model skills and practices used by STEM professionals. Relevant, real-world authentic research experiences allow students to behave as scientists as they model the process of science. This enables students to get a true sense of STEM-related professions and also allows them to develop the requisite knowledge, skills, curiosity, and creativity necessary for success in STEM careers. Providing professional development and opportunities to help teachers infuse research in the classroom is one of the primary goals of the Expedition Earth and Beyond (EEAB) program. EEAB, facilitated by the Astromaterials Research and Exploration Science (ARES) Directorate at the NASA Johnson Space Center, is an Earth and planetary science education program designed to inspire, engage, and educate teachers and students in grades 5-12 by getting them actively involved with exploration, discovery, and the process of science. The program combines the expertise of scientists and educators to ensure the professional development provided to classroom teachers is scientifically valid and also recognizes classroom constraints. For many teachers, facilitating research in the classroom can be challenging. In addition to addressing required academic standards and dealing with time constraints, challenges include structuring a research investigation the entire class can successfully complete. To build educator confidence, foster positive classroom research experiences, and enable teachers to help students model the skills and practices of scientists, EEAB has created an "allinclusive" comparative planetology research investigation activity. This activity addresses academic standards while recognizing students (and teachers) potentially lack experience with scientific practices involved in conducting research. Designed as an entry level research engagement investigation, the activity introduces, illustrates, and teaches the skills involved in each step of the research process. Students use astronaut photos, provided through the ARES Crew Earth Observations (CEO) payload on the International Space Station (ISS) as well as remote sensing imagery of other planetary worlds. By including all the necessary tools to complete the investigation, students can focus on gaining experience in the process of science. Additionally, students are able to extend their experience of modeling the skills and practices of scientists through the opportunity to request new data of Earth from the ISS. Professional development offered through in-person and webinar trainings, along with the resources provided, enable educators to gain first-hand experience implementing a structured research investigation in the classroom. Through data and feedback collected from teachers, this type of "all-inclusive" investigation activity aims to become a model that can be utilized for other research topics and STEM disciplines.

Graff, Paige↗
NASA NTRS2013

Spacecraft 3D Augmented Reality Mobile App

The Spacecraft 3D application allows users to learn about and interact with iconic NASA missions in a new and immersive way using common mobile devices. Using Augmented Reality (AR) techniques to project 3D renditions of the mission spacecraft into real-world surroundings, users can interact with and learn about Curiosity, GRAIL, Cassini, and Voyager. Additional updates on future missions, animations, and information will be ongoing. Using a printed AR Target and camera on a mobile device, users can get up close with these robotic explorers, see how some move, and learn about these engineering feats, which are used to expand knowledge and understanding about space. The software receives input from the mobile device's camera to recognize the presence of an AR marker in the camera's field of view. It then displays a 3D rendition of the selected spacecraft in the user's physical surroundings, on the mobile device's screen, while it tracks the device's movement in relation to the physical position of the spacecraft's 3D image on the AR marker.

Hussey, Kevin J.↗
NASA NTRS2013

Detection and Quantification of Nitrogen Compounds in Martian Solid Samples by the Sample Analysis at Mars (SAM) Instrument Suite

The Sample Analysis at Mars (SAM) instrument suite on the Mars Science Laboratory (MSL) Curiosity Rover detected both reduced and oxidized nitrogen-bearing compounds during the pyrolysis of surface materials from three sites at Gale Crater. Preliminary detections of nitrogen species include NO, HCN, ClCN, CH3CN, and TFMA (trifluoro-Nmethyl-acetamide). On Earth, nitrogen is a crucial bio-element, and nitrogen availability controls productivity in many environments. Nitrogen has also recently been detected in the form of CN in inclusions in the Martian meteorite Tissint, and isotopically heavy nitrogen (delta N-15 approx +100per mille) has been measured during stepped combustion experiments in several SNC meteorites. The detection of nitrogen-bearing compounds in Martian regolith would have important implications for the habitability of ancient Mars. However, confirmation of indigenous Martian nitrogen bearing compounds will require ruling out their formation from the terrestrial derivatization reagents (e.g. N-methyl-N-tert-butyldimethylsilyl-trifluoroacetamide, MTBSTFA and dimethylformamide, DMF) carried for SAM's wet chemistry experiment that contribute to the SAM background. The nitrogen species we detect in the SAM solid sample analyses can also be produced during laboratory pyrolysis experiments where these reagents are heated in the presence of perchlorate, a compound that has also been identified by SAM in Mars solid samples. However, this does not preclude a Martian origin for some of these compounds, which are present in nanomolar concentrations in SAM evolved gas analyses. Analysis of SAM data and laboratory breadboard tests are underway to determine whether nitrogen species are present at higher concentrations than can be accounted for by maximum estimates of nitrogen contribution from MTBSTFA and DMF. In addition, methods are currently being developed to use GC Column 6, (functionally similar to a commercial Q-Bond column), to separate and identify unretained compounds such as NO, N2O, and NO2, which are difficult to detect by EGA-MS due to mass interferences at 30, 44 and 46, respectively. Here we present evolved gas analysis-mass spectrometry (EGA-MS) and gas chromatography mass spectrometry (GC-MS) data on the identification and quantification of these nitrogen-bearing compounds, and suggestions for their origins

Stern, Jennifer C.↗
NASA NTRS2013

Characterizing the Phyllosilicates and Amorphous Phases Found by MSL Using Laboratory XRD and EGA Measurements of Natural and Synthetic Materials

The Curiosity Rover landed on the Peace Vallis alluvial fan in Gale crater on August 5, 2012. A primary mission science objective is to search for past habitable environments, and, in particular, to assess the role of past water. Identifying the minerals and mineraloids that result from aqueous alteration at Gale crater is essential for understanding past aqueous processes at the MSL landing site and hence for interpreting the site's potential habitability. X-ray diffraction (XRD) data from the CheMin instrument and evolved gas analyses (EGA) from the SAM instrument have helped the MSL science team identify phases that resulted from aqueous processes: phyllosilicates and amorphous phases were measure in two drill samples (John Klein and Cumberland) obtained from the Sheepbed Member, Yellowknife Bay Fm., which is believed to represent a fluvial-lacustrine environment. A third set of analyses was obtained from scoop samples from the Rocknest sand shadow. Chemical data from the APXS instrument have helped constrain the chemical compositions of these secondary phases and suggest that the phyllosilicate component is Mg-enriched and the amorphous component is Fe-enriched, relatively Si-poor, and S- and H-bearing. To refine the phyllosilicate and amorphous components in the samples measured by MSL, we measured XRD and EGA data for a variety of relevant natural terrestrial phyllosilicates and synthetic mineraloids in laboratory testbeds of the CheMin and SAM instruments. Specifically, Mg-saturated smectites and vermiculites were measured with XRD at low relative humidity to understand the behavior of the 001 reflections under Mars-like conditions. Our laboratory XRD measurements suggest that interlayer cation composition affects the hydration state of swelling clays at low RH and, thus, the 001 peak positions. XRD patterns of synthetic amorphous materials, including allophane, ferrihydrite, and hisingerite were used in full-pattern fitting (FULLPAT) models to help determine the types and abundances of amorphous phases in the martian rocks and sand shadow. These models suggest that the rocks and sand shadow are composed of approx 30% amorphous phases. Sulfate-adsorbed allophane and ferrihydrite were measured by EGA to further understand the speciation of the sulfur present in the amorphous component. These data indicate that sulfate adsorbed onto the surfaces of amorphous phases could explain a portion of the SO2 evolution in the Rocknest SAM data. The additional constraints placed on the mineralogy and chemistry of the aqueous alteration phases through our laboratory measurements can help us better understand the nature of the fluids that affected the different samples and devise a history of aqueous alteration for the Sheepbed Member of the Yellowknife Bay Fm. at Gale crater.

Rampe, Elizabeth B.↗
NASA NTRS2013

The Search for Nitrates on Mars by the Sample Analysis at Mars (SAM) Instrument

Planetary models suggest that nitrogen was abundant in the early Martian atmosphere as N2 but it was lost by sputtering and photochemical loss to space, impact erosion, and chemical oxidation to nitrates. A nitrogen cycle may exist on Mars where nitrates, produced early in Mars' history, may have been later decomposed back into N2 by the current impact flux. Nitrates are a fundamental source of nitrogen for terrestrial microorganisms, and they have evolved metabolic pathways to perform both oxidation and reduction to drive a complete biological nitrogen cycle. Therefore, the characterization of nitrogen in Martian soils is important to assess habitability of the Martian environment, particularly with respect to the presence of nitrates. The only previous mission that was designed to search for soil nitrates was the Phoenix mission but N-containing species were not detected by TEGA or the MECA WCL. Nitrates have been tentatively identified in Nakhla meteorites, and if nitrogen was oxidized on Mars, this has important implications for the habitability potential of Mars. Here we report the results from the Sample Analysis at Mars (SAM) instrument suite aboard the Curiosity rover during the first year of surface operations in Gale Crater. Samples from the Rocknest aeolian deposit and sedimentary rocks (John Klein) were heated to approx 835degC under helium flow and the evolved gases were analyzed by MS and GC-MS. Two and possibly three peaks may be associated with the release of m/z 30 at temperatures ranging from 180degC to 500degC. M/z 30 has been tentatively identified as NO; other plausible contributions include CH2O and an isotopologue of CO, 12C18O. NO, CH2O, and CO may be reaction products of reagents (MTBSTFA/DMF) carried from Earth for the wet chemical derivatization experiments with SAM and/or derived from indigenous soil nitrogenated organics. Laboratory analyses indicate that it is also possible that <550degC evolved NO is produced via reaction of HCl with nitrates arising from the decomposition of perchlorates. All sources of m/z 30 whether it be martian or terrestrial will be considered and their implications for Mars will be discussed.

Navarro-Gonzalez, Rafael↗
NASA NTRS2013

Terrestrial Analogs for Clay Minerals at Yellowknife Bay, Gale Crater, Mars

Sediments of the Sheepbed unit, Gale Crater, were analyzed by the CheMin X-ray diffraction instrument on the Curiosity Rover. The sediments consist of typical basalt minerals (Fe-forsterite, augite, pigeonite, plagioclase), as well as Fe oxide/hydroxides, Fesulfides, amorphous material, and a phyllosilicate. The phyllosilicate has a broad 001 peak at approx 1.0 nm, consistent with a poorly ordered smectite. However, in the absence of diagnostic tests possible on Earth, its identity is not clear. The position of the 06L diffraction band is generally used to distinguish dioctahedral from trioctahedral smectite, but it is beyond CheMin's range of 2 Theta. The measured position of the 02L diffraction band (approx 22.5deg 2 Theta by CheMin), implies that the smectite is trioctahedral. The exact position and shape of the 02L band is determined by the cations in the 'M' sites of the smectite; to constrain those cations, we sought analogs among terrestrial smectites, emphasizing those developed from basaltic precursors. A potential analog for the Sheepbed smectite is 'griffithite,' a variety of trioctahedral smectite in altered basalt of the Topanga formation, Griffith Park, Los Angeles. 'Griffithite' has an 02L diffraction band that is close in position and shape to that of the Sheepbed smectite, although 'griffithite' has a very sharp 001 peak, indicating a high degree of layer ordering not seen in the Sheepbed smectite. A typical chemical formula for 'griffithite,' determined by electron microprobe, is (Ca0.59 Na0.03) (Mg4.28 Fe1.83) (Si6.64 Al1.36) O20 (OH)4, normalized to Si+Al=8. This formula is consistent with a fully trioctahedral Fe-Mg smectite with Ca and Na as interlayer cations. In the Topanga basalt, four types of 'griffithite' are present: fine-grained, filling cracks and vesicles; coarse-grained, filling vesicles; coarse-grained, replacing olivine phenocrysts; and coarse-grained, replacing glassy mesostasis. The fine-grained 'griffithite' formed first, and the last three varieties may be contemporaneous. One sample shows agate (alpha- quartz) that was precipitated between the episodes of deposition of the fine-grained and coarse-grained 'griffithite.' 'Griffithite' is not unique as a possible terrestrial analog - some clay minerals from the Doushantou formation, China, have similar 02L diffraction bands, and many basalts contain smectites in vesicles and as replacements after olivine. Similar trioctahedral smectites occur also in the nakhlite martian meteorites - as veinlets and replacements of olivine. By understanding the formation of these terrestrial clays, we hope to constrain the nature and mechanism of formation of the Sheepbed clay mineral.

Treiman, Allan H↗