Engineering topics
Burkett, P. J.
Publications and source records attributed to Burkett, P. J..
Development of Genesis Solar Wind Sample Cleanliness Assessment: Initial Report on Sample 60341 Optical Imagery and Elemental Mapping
Since 2005 the Genesis science team has experimented with techniques for removing the contaminant particles and films from the collection surface of the Genesis fragments. A subset of ~40 samples have been designated as "cleaning matrix" samples. These are small samples to which various cleaning approaches are applied and then cleanliness is assessed optically, by TRXRF, SEM, ToF-SIMS, XPS, ellipsometry or other means [1-9]. Most of these sam-ples remain available for allocation, with cleanliness assessment data. This assessment allows evaluation of various cleaning techniques and handling or analytical effects. Cleaning techniques investigated by the Genesis community include acid/base etching, acetate replica peels, ion beam, and CO2 snow jet cleaning [10-16]. JSC provides surface cleaning using UV ozone exposure and ultra-pure water (UPW) [17-20]. The UPW rinse is commonly used to clean samples for handling debris between processing by different researchers. Optical microscopic images of the sample taken before and after UPW cleaning show what has been added or removed during the cleaning process.
Genesis Solar Wind Collector Cleaning Assessment: 60366 Sample Case Study
In order to recognize, localize, characterize and remove particle and thin film surface contamination, a small subset of Genesis mission collector fragments are being subjected to extensive study via various techniques [1-5]. Here we present preliminary results for sample 60336, a Czochralski silicon (Si-CZ) based wafer from the bulk array (B/C).
Investigation of Backside Textures for Genesis Solar Wind Silicon Collectors
Genesis solar wind collectors were comprised of a suite of 15 types of ultrapure materials. The single crystal, pure silicon collectors were fabricated by two methods: float zone (FZ) and Czochralski (CZ). Because of slight differences in bulk purity and surface cleanliness among the fabrication processes and the specific vendor, it is desirable to know which variety of silicon and identity of vendor, so that appropriate reference materials can be used. The Czochralski method results in a bulk composition with slightly higher oxygen, for example. The CZ silicon array wafers that were Genesis-flown were purchased from MEMC Electronics. Most of the Genesis-flown FZ silicon was purchased from Unisil and cleaned by MEMC, although a few FZ wafers were acquired from International Wafer Service (IWS).
Collecting Comet Samples by ER-2 Aircraft: Cosmic Dust Collection During the Draconid Meteor Shower in October 2012
Many tons of dust grains, including samples of asteroids and comets, fall from space into the Earth's atmosphere each day. NASA periodically collects some of these particles from the Earth's stratosphere using sticky collectors mounted on NASA's high-flying aircraft. Sometimes, especially when the Earth experiences a known meteor shower, a special opportunity is presented to associate cosmic dust particles with a known source. NASA JSC's Cosmic Dust Collection Program has made special attempts to collect dust from particular meteor showers and asteroid families when flights can be planned well in advance. However, it has rarely been possible to make collections on very short notice. In 2012, the Draconid meteor shower presented that opportunity. The Draconid meteor shower, originating from Comet 21P/Giacobini-Zinner, has produced both outbursts and storms several times during the last century, but the 2012 event was not predicted to be much of a show. Because of these predictions, the Cosmic Dust team had not targeted a stratospheric collection effort for the Draconids, despite the fact that they have one of the slowest atmospheric entry velocities (23 km/s) of any comet shower, and thus offer significant possibilities of successful dust capture. However, radar measurements obtained by the Canadian Meteor Orbit Radar during the 2012 Draconids shower indicated a meteor storm did occur October 8 with a peak at 16:38 (+/-5 min) UTC for a total duration of approximately 2 hours.
Dividing the Concentrator Target From the Genesis Mission
The Genesis spacecraft, launched in 2001, traveled to a Lagrangian point between the Earth and Sun to collect particles from the solar wind and return them to Earth. However, during the return of the spacecraft in 2004, the parachute failed to open during descent, and the Genesis spacecraft crashed into the Utah desert. Many of the solar wind collectors were broken into smaller pieces, and the field team rapidly collected the capsule and collector pieces for later assessment. On each of the next few days, the team discovered that various collectors had survived intact, including three of four concentrator targets. Within a month, the team had imaged more than 10,000 fragments and packed them for transport to the Astromaterials Acquisition and Curation Office within the ARES Directorate at JSC. Currently, the Genesis samples are curated along with the other extraterrestrial sample collections within ARES. Although they were broken and dirty, the Genesis solar wind collectors still offered the science community the opportunity to better understand our Sun and the solar system as a whole. One of the more highly prized concentrator collectors survived the crash almost completely intact. The Genesis Concentrator was designed to concentrate the solar wind by a factor of at least 20 so that solar oxygen and nitrogen isotopes could be measured. One of these materials was the Diamond-on-Silicon (DoS) concentrator target. Unfortunately, the DoS concentrator broke on impact. Nevertheless, the scientific value of the DoS concentrator target was high. The Genesis Allocation Committee received a request for approximately 1 cm(sup 2) of the DoS specimen taken near the focal point of the concentrator for the analysis of solar wind nitrogen isotopes. The largest fragment, Genesis sample 60000, was designated for this allocation and needed to be precisely cut. The requirement was to subdivide the designated sample in a manner that prevented contamination of the sample and minimized the risk of losing or breaking the precious requested sample fragment. The Genesis curator determined that the use of laser scribing techniques to "cut" a precise line and subsequently cleave the sample (in a controlled break of the sample along that line) was the best method for accomplishing the sample subdivision. However, there were risks, including excess heating of the sample, that could cause some of the implanted solar wind to be lost via thermal diffusion. Accidentally breaking the sample during the handling and cleaving process was an additional risk. Early in fiscal year 2013, to address this delicate, complicated task, the ARES Directorate assembled its top scientists to develop a cutting plan that would ensure success when applied to the actual concentrator target wafer; i.e., to produce an approximately 1 cm(sup 2) piece from the requested area of the wafer. The team, subsequently referred to as the JSC Genesis Tiger Team, spent months researching and testing parameters and techniques related to scribing, cleaving, transporting, handling, and holding (i.e., mounting) the specimen. The investigation required considerable "thinking outside the box," and many, many trials using nonflight wafer analogs. After all preliminary testing, the following method was adopted as the final cutting plan. It was used in two final end-to-end practice runs before being used on the actual flight target wafer. The wafer was oriented on the laser cutting stage with the 100 and 010 directions of the wafer parallel to the corresponding X and Y directions of the cutting stage. The laser was programed to scribe 31 lines of the appropriate length along the Y stage direction. The programed scribe lines were separated by 5 micron in the X direction. The laser parameters were set as follows: (1) The laser power was 0.5 watts; (2) each line consisted of 50 passes, with the Z position being advanced 5 micron per pass; and (3) 30 s would elapse before the next line was scribed to allow for wafer cool down from any possible heating via the laser. The ablated material that "stuck" in the "scribe-cut" was removed from the "cut" using an ultrasonic micro-tool. After all the ablated silicon was removed from the wafer, the wafer was repositioned in exactly the same orientation on the laser stage. The laser was focused using the bottom of the wafer channel, and the 31-line scribing pattern described above was reprogrammed using the Z position of the groove bottom as the starting Z value instead of the top wafer surface, which was used previously. Upon completion of the second set of scribes, the ultrasonic micro-tool was again used to clean out the cut. The wafer was remounted on the stage in exactly the same orientation as before. The laser was again focused on the bottom of the groove. This time, however, the laser was.programed to scribe only one line down the exact center of the channel. The final scribe line consisted of 100 passes with a Z advance of 5 micron per pass and with the laser power set at 0.5 watts. As mentioned above, the final cutting plan was practiced in two end-to-end trials using non-flight, triangular-shaped silicon wafers similar in size and orientation to the actual DOS 60000 target sample. The actual scribing of the triangular-shaped wafers required scribing two lines and cleaving (i.e. scribe-cleave, then scribe-cleave) to obtain the piece requested for allocation. Early in December 2012, after many months of experiments and practicing and perfecting the techniques and procedures, the team successfully subdivided the Genesis DoS 60000 target sample, one of the most scientifically important samples from the Genesis mission (figure 2). On December 17, 2012, the allocated piece of concentrator target sample was delivered to the requesting principal investigator.The cutting plan developed for the subdivision of this sample will be used as the model for subdividing future requested Genesis flight wafers (appropriately modified for different wafer types).
Ultra Pure Water Cleaning Baseline Study on NASA JSC Astromaterial Curation Gloveboxes
Future sample return missions will require strict protocols and procedures for reducing inorganic and organic contamination in isolation containment systems. In 2012, a baseline study was orchestrated to establish the current state of organic cleanliness in gloveboxes used by NASA JSC astromaterials curation labs [1, 2]. As part of this in-depth organic study, the current curatorial technical support procedure (TSP) 23 was used for cleaning the gloveboxes with ultra pure water (UPW) [3-5]. Particle counts and identification were obtained that could be used as a benchmark for future mission designs that require glovebox decontamination. The UPW baseline study demonstrates that TSP 23 works well for gloveboxes that have been thoroughly degreased. However, TSP 23 could be augmented to provide even better glovebox decontamination. JSC 03243 could be used as a starting point for further investigating optimal cleaning techniques and procedures. DuPont Vertrel XF or other chemical substitutes to replace Freon- 113, mechanical scrubbing, and newer technology could be used to enhance glovebox cleanliness in addition to high purity UPW final rinsing. Future sample return missions will significantly benefit from further cleaning studies to reduce inorganic and organic contamination.
Organic Contamination Baseline Study on NASA JSC Astromaterial Curation Gloveboxes
Future planned sample return missions to carbon-rich asteroids and Mars in the next two decades will require strict handling and curation protocols as well as new procedures for reducing organic contamination. After the Apollo program, astromaterial collections have mainly been concerned with inorganic contamination [1-4]. However, future isolation containment systems for astromaterials, possibly nitrogen enriched gloveboxes, must be able to reduce organic and inorganic cross-contamination. In 2012, a baseline study was orchestrated to establish the current state of organic cleanliness in gloveboxes used by NASA JSC astromaterials curation labs that could be used as a benchmark for future mission designs.
Examples of Optical Assessment of Surface Cleanliness of Genesis Samples
Optical microscope assessment of Genesis solar wind collector surfaces is a coordinated part of the effort to obtain an assessed clean subset of flown wafer material for the scientific community. Microscopic survey is typically done at 50X magnification at selected approximately 1 square millimeter areas on the fragment surface. This survey is performed each time a principle investigator (PI) returns a sample to JSC for documentation as part of the established cleaning plan. The cleaning plan encompasses sample handling and analysis by Genesis science team members, and optical survey is done at each step in the process. Sample surface cleaning is performed at JSC (ultrapure water [1] and UV ozone cleaning [2]) and experimentally by other science team members (acid etch [3], acetate replica peels [4], CO2 snow [5], etc.). The documentation of each cleaning method can potentially be assessed with optical observation utilizing Image Pro Plus software [6]. Differences in particle counts can be studied and discussed within analysis groups. Approximately 25 samples have been identified as part of the cleaning matrix effort to date.
Recent Optical and SEM Characterization of Genesis Solar Wind Concentrator Diamond on Silicon Collector
One of the 4 Genesis solar wind concentrator collectors was a silicon substrate coated with diamond-like carbon (DLC) in which to capture solar wind. This material was designed for analysis of solar nitrogen and noble gases [1, 2]. This particular collector fractured during landing, but about 80% of the surface was recovered, including a large piece which was subdivided in 2012 [3, 4, 5]. The optical and SEM imaging and analysis described below supports the subdivision and allocation of the diamond-on-silicon (DOS) concentrator collector.
Laser Subdivision of the Genesis Concentrator Target Sample 60000
The Genesis Allocation Committee received a request for ~ 1 square centimeter of the diamond-like-carbon (DLC) concentrator target for the analysis of solar wind nitrogen isotopes. The target consists of a single crystal float zone (FZ) silicon substrate having a thickness on the order of 550 micrometers with a 1.5-3.0 micrometer-thick coating of DLC on the exposed surface. The solar wind is implanted shallowly in the front side DLC. The original target was a circular quadrant with a radius of 3.1 cm; however, the piece did not survive intact when the spacecraft suffered an anomalous landing upon returning to Earth on September 8, 2004. An estimated 75% of the DLC target was recovered in at least 18 fragments. The largest fragment, Genesis sample 60000, has been designated for this allocation and is the first sample to be subdivided using our laser scribing system Laser subdivision has associated risks including thermal diffusion of the implant if heating occurs and unintended breakage during cleavage. A careful detailed study and considerable subdividing practice using non-flight FZ diamond on silicon, DOS, wafers has considerably reduced the risk of unplanned breakage during the cleaving process. In addition, backside scribing reduces the risk of possible thermal excursions affecting the implanted solar wind, implanted shallowly in the front side DLC.
Toward Lower Organic Environments in Astromaterial Sample Curation for Diverse Collections
Great interest was taken during the frenzied pace of the Apollo lunar sample return to achieve and monitor organic cleanliness. Yet, the first mission resulted in higher organic contamination to samples than desired. But improvements were accomplished by Apollo 12 [1]. Quarantine complicated the goal of achieving organic cleanliness by requiring negative pressure glovebox containment environments, proximity of animal, plant and microbial organic sources, and use of organic sterilants in protocols. A special low organic laboratory was set up at University of California Berkeley (UCB) to cleanly subdivide a subset of samples [2, 3, 4]. Nevertheless, the basic approach of handling rocks and regolith inside of a positive pressure stainless steel glovebox and restrict-ing the tool and container materials allowed in the gloveboxes was established by the last Apollo sample re-turn. In the last 40 years, the collections have grown to encompass Antarctic meteorites, Cosmic Dust, Genesis solar wind, Stardust comet grains and Hayabusa asteroid grains. Each of these collections have unique curation requirements for organic contamination monitor-ing and control. Here is described some changes allowed by improved technology or driven by changes in environmental regulations and economy, concluding with comments on organic witness wafers. Future sample return missions (OSIRIS-Rex; Mars; comets) will require extremely low levels of organic contamination in spacecraft collection and thus similarly low levels in curation. JSC Curation is undertaking a program to document organic baseline levels in current operations and devise ways to reduce those levels.
Using Image Pro Plus Software to Develop Particle Mapping on Genesis Solar Wind Collector Surfaces
The continued success of the Genesis mission science team in analyzing solar wind collector array samples is partially based on close collaboration of the JSC curation team with science team members who develop cleaning techniques and those who assess elemental cleanliness at the levels of detection. The goal of this collaboration is to develop a reservoir of solar wind collectors of known cleanliness to be available to investigators. The heart and driving force behind this effort is Genesis mission PI Don Burnett. While JSC contributes characterization, safe clean storage, and benign collector cleaning with ultrapure water (UPW) and UV ozone, Burnett has coordinated more exotic and rigorous cleaning which is contributed by science team members. He also coordinates cleanliness assessment requiring expertise and instruments not available in curation, such as XPS, TRXRF [1,2] and synchrotron TRXRF. JSC participates by optically documenting the particle distributions as cleaning steps progress. Thus, optical document supplements SEM imaging and analysis, and elemental assessment by TRXRF.
O-6 Optical Property Degradation of the Hubble Space Telescope's Wide Field Camera-2 Pick Off Mirror
Degradation in the performance of optical components can be greatly affected by exposure to the space environment. Many factors can contribute to such degradation including surface contaminants; outgassing; vacuum, UV, and atomic oxygen exposure; temperature cycling; or combinations of parameters. In-situ observations give important clues to degradation processes, but there are relatively few opportunities to correlate those observations with post-flight ground analyses. The return of instruments from the Hubble Space Telescope (HST) after its final servicing mission in May 2009 provided such an opportunity. Among the instruments returned from HST was the Wide-Field Planetary Camera-2 (WFPC-2), which had been exposed to the space environment for 16 years. This work focuses on the identifying the sources of degradation in the performance of the Pick-off mirror (POM) from WFPC-2. Techniques including surface reflectivity measurements, spectroscopic ellipsometry, FTIR (and ATR-FTIR) analyses, SEM/EDS, X-ray photoelectron spectroscopy (XPS) with and without ion milling, and wet and dry physical surface sampling were performed. Destructive and contact analyses took place only after completion of the non-destructive measurements. Spectroscopic ellipsometry was then repeated to determine the extent of contaminant removal by the destructive techniques, providing insight into the nature and extent of polymerization of the contaminant layer.
Higher Magnification Imaging of the Polished Aluminum Collector Returned from the Genesis Mission
The polished aluminum collector (previously referred to as the polished aluminum kidney) was intended for noble gas analysis for the Gene-sis mission. The aluminum collector, fabricated from alloy 6061T, was polished for flight with alumina, then diamond paste. Final cleaning was performed by soak-ing and rinsing with hexane, then isopropanol, and last-ly megasonically energized ultrapure water prior to installation. It was mounted inside the collector canister on the thermal shield at JSC in 2000. The polished aluminum collector was not surveyed microscopically prior to flight.
Technical Tension Between Achieving Particulate and Molecular Organic Environmental Cleanliness: Data from Astromaterial Curation Laboratories
NASA Johnson Space Center operates clean curation facilities for Apollo lunar, Antarctic meteorite, stratospheric cosmic dust, Stardust comet and Genesis solar wind samples. Each of these collections is curated separately due unique requirements. The purpose of this abstract is to highlight the technical tensions between providing particulate cleanliness and molecular cleanliness, illustrated using data from curation laboratories. Strict control of three components are required for curating samples cleanly: a clean environment; clean containers and tools that touch samples; and use of non-shedding materials of cleanable chemistry and smooth surface finish. This abstract focuses on environmental cleanliness and the technical tension between achieving particulate and molecular cleanliness. An environment in which a sample is manipulated or stored can be a room, an enclosed glovebox (or robotic isolation chamber) or an individual sample container.
On the origin of enstatite chondrite chondrules based on their petrography and comparison with experimentally produced chondrules
The recent discovery of several types 3 and 4 enstatite chondrites (EC) in the Antarctic collection increases greatly the ability to compare unaltered, naturally-formed EC chondrules with chondrules produced experimentally from melts of enstatitic chondrule composition. Because these discoveries are so recent we have undertaken the task of characterizing these chondrules for purposes of comparison. We have looked at several new Antarctic E3 chondrites and Qingzhen. They all have numerous chondrules with well defined outlines and readily identifiable textures. All have mostly porphyritic chondrules, but there are differences in the size and kinds of textures. Radial pyroxene, barred/dendritic px, and cryptocrystalline chondrules are present in differing amounts with one exception.