SEARCH · Engineering Papers
Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.
Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.
Members of the Space Shuttle Main Engine (SSME) team review some of their memories of working on the SSME and the importance of the SSME to the success of the Shuttle program. There are many views of shuttle launches.
Protein crystal growth rates will be determined for several hyperthermophile proteins.; The growth rates will be assessed using available theoretical models, including kinetic roughening.; If/when kinetic roughening supersaturations are established, determinations of protein crystal quality over a range of supersaturations will also be assessed.; The results of our ground based effort may well address the existence of a correlation between fundamental growth mechanisms and protein crystal quality.
An overview is presented of the space radiation environment and its effects on electrical, electronic, and electromechanical parts. Relevant test standards and guidelines are listed. Test standards and guidelines are necessary to ensure best practices, minimize and bound systematic and random errors, and to ensure comparable results from different testers and vendors. Test standards are by their nature static but exist in a dynamic environment of advancing technology and radiation effects research. New technologies, failure mechanisms, and advancement in our understanding of known failure mechanisms drive the revision or development of test standards. Changes to standards must be weighed against their impact on cost and existing part qualifications. There must be consensus on new best practices. The complexity of some new technologies exceeds the scope of existing test standards and may require development of a guideline specific to the technology. Examples are given to illuminate the value and limitations of key radiation test standards as well as the challenges in keeping these standards up to date.
Helene, (approximately 17.6 kilometers mean radius) is an L4 Trojan co-orbital of Saturn's moon Dione. Its hemisphere features an unusual morphology consisting of broad depressions and a generally smooth surface patterned with streaks and grooves. The streaks appear to be oriented down-gradient, as are the grooves. This pattern suggests intensive mass-wasting as a dominant process on the leading hemisphere. Kilometer-scale impact craters are very sparse on the leading hemisphere other than the degraded kilometer-scale basins defining the overall satellite shape, and many small craters have a diffuse appearance suggesting ongoing mass wasting. Thus mass wasting must dominate surface-modifying processes at present. In fact, the mass wasting appears to have been sufficient in magnitude to narrow the divides between adjacent basins to narrow septa, similar, but in lower relief, to the honeycomb pattern of Hyperion. The prominent groves occur primarily near topographic divides and appear have cut into a broad, slightly lower albedo surface largely conforming to the present topography but elevated a few meters above the smooth surfaces undergoing mass wasting flow. Low ridges and albedo markings on the surface suggest surface flow of materials traveling up to several kilometers. Diffusive mass wasting produces smooth surfaces - such a pattern characterizes most of the low-lying surfaces. The grooves, however, imply that the transport process is advective at those locations where they occur, that is, erosion tends to concentrate along linear pathways separated by divides. In fact, in many places grooves have a fairly regular spacing of 125-160 meters, defining a characteristic erosional scale. Several questions are prompted by the unusual morphology of Helene: 1) What is the nature of the surface materials? 2) Are the transport processes gradual or catastrophic motion from one or a few events? 3) What mechanisms drive mass wasting and groove development? 4) Have the formative processes been active in the recent past? 5) Finally, is the surface accreting or eroding? The smooth character of the leading edge hemisphere of Helene and the dominance of mass wasting suggest that the surface is composed of fine-grained debris, probably dominated by dust-size to small gravel particles. The Lagrangian points of saturnian satellites are locations where planetesimals might have accreted to form co-orbital satellites such as and they may capture ejecta from their master moon. Published models suggest that Helene is a site of net accretion, but we find no extant explanation for the dominance of fine grain sizes for the surface (and probable subsurface) composition of Helene and the other Lagrangian satellites. Observation of the mass wasting tracks on Helene suggests the presence of well-defined streams of debris with low bordering levees that may be depositional features or remnants of the dissected higher surface. Some flows in grazing illumination appear to have a convex cross-section. This mass-flow morphology might be consistent with the occurrence of large-scale flow events, but which might have occurred through rapid emplacement or slow glacier-like creep. On the other hand, small craters appear to have been "softened" by creep-like processes, indicating ongoing mass wasting.
No abstract available
No abstract available
At the Mission Design and Navigation Software Group at the Jet Propulsion Laboratory we make use of finite exponential based defect models to aid in maintenance planning and management for our widely used critical systems. However a number of pragmatic issues arise when applying defect models for a post-release system in continuous use. These include: how to utilize information from problem reports rather than testing to drive defect discovery and removal effort, practical model calibration, and alignment of model assumptions with our environment.
Humans are increasing the amount of carbon dioxide (CO2) in the air through CO2 emissions. This is changing the climate, making life harder for many plants in areas that suffer from heat and drought. However, plants need CO2 to grow, and more CO2 can make them grow better. So will plants overall benefit from increased CO2 level or suffer from it? We wanted to test if the positive effect would offset the negative ones. To do so, we used scientific models to calculate future crop production and water use of four important crops all over the world under different scenarios of CO2 emissions and climate change. Our calculations show that although there will be large reductions in crop yield due to climate change over the next century, some crops will still be able to grow well. This is also because crops can grow with less water when CO2 levels are raised.
Explore the source record for details and available documents.
A new approach to NASA space radiation risk modeling has successfully extended the current NASA probabilistic cancer risk model to an ensemble framework able to consider sub-model parameter uncertainty (e.g. uncertainty in a radiation quality parameter) as well as model-form uncertainty associated with differing theoretical or empirical formalisms (e.g. combined dose-rate and radiation quality effects). Ensemble methodologies are already widely used in weather prediction, modeling of infectious disease outbreaks, and certain terrestrial radiation protection applications to better understand how uncertainty may influence risk decision-making. Applying ensemble methodologies to space radiation risk projections offers the potential to efficiently incorporate emerging research results, allow for the incorporation of future (including international) models, improve uncertainty quantification for underlying sub-models developed against sparse experimental data, and reduce the impact of subjective bias on risk projections. Moreover, risk forecasting across an ensemble of multiple predictive models can provide stakeholders additional information on risk acceptance if current health/medical standards cannot be met or the level of knowledge doesn’t permit a specific risk or exposure limit to be developed for future space exploration missions. In this work, ensemble risk projections implementing multiple sub-models of radiation quality, dose and dose-rate effectiveness factors, excess risk, and latency as ensemble members are presented. Initial consensus methods for ensemble model weights and correlations to account for individual model bias are discussed. In these analyses, the ensemble forecast compares well to results from NASA's current operational cancer risk projection model used to assess permissible exposure limits and permissible mission durations for astronauts. However, a large range of projected risk values are obtained at the upper 95th confidence level where models must extrapolate beyond available biological data sets; closer agreement is seen at the median + one sigma due to the inherent similarities in available models. Future work, including the addition of new models and methods for statistical correlation between predictive members are discussed to define alternate ways of thinking about risk and ‘acceptable’ uncertainty with respect to NASA’s current permissible exposure limits.
The purpose of the Mars Sample Return mission would be to take advantage of the capability to study Mars to the level of detail only possible in Earth laboratories. This paper will attempt to summarize some of the Guidance and Control challenges, even if it succeeds in only scratching the surface.
In this paper, we describe the development of an integrated suite of autonomous, adaptive hardware/software control methods called SMART (System for Mobility and Access to Rough Terrain) that enables mobile robots to explore potentially important science sites currently beyond the reach of conventional rover designs.
The technical challenges confronting development of Alkali Metal Thermal-to Electric Converters (AMTEC) for up to 15 year life on NASA Mars and outer planetary missions are significant, although approaches to solutions are understood by many investigators.
The NASA Resilient Autonomy Project developed a software framework that implemented a Run Time Assurance (RTA) architecture that leveraged ASTM International’s F3269 Industry Standard for safely bounding complex behavior in aircraft. This framework was called the Expandable Variable Autonomy Architecture, or EVAA. EVAA was developed during the height of the Covid-19 lockdown that caused the Resilient Autonomy team to pivot from flight test to distributed simulator testing. EVAA was developed to be platform and mission agnostic where platform specifics were behind a hardware abstraction layer that EVAA called a Coupler. EVAA was able to host multiple safety monitors that could resolve individual safety hazards. EVAA was able to resolve priority conflicts when multiple safety hazards needed to be resolved simultaneously and was able to resolve highly complex situations in a safe manner that could exceed human capabilities.
Explore the source record for details and available documents.
Explore the source record for details and available documents.
Research on migration has become more challenging due to at least four factors: (1) more complex migration traditions; (2) the development of migration economies that engage many types of migrants from ever more social and cultural backgrounds; (3) increasing likelihood of climate change-driven environmental migration; and (4) increasing likelihood of conflict-based migration in some contexts. These developments have shaken economic theories of migration and have encouraged interdisciplinary, methodologically mixed, qualitative and quantitative research and analysis. From a review of the literature, we have gleaned 11 common themes about environmental, economic and conflict migration that we differentiate by process (migration behaviours that are still evolving) and patterns (migration behaviours that have become customary). We then consider how positive and negative dimensions of migration can be captured and represented with close attention to livelihood constellations (multiple economic activities combined by individuals, households and families). Finally, focusing on Somalia and agro-pastoral peoples generally, where recent environmental and conflict migration have been added to decades of economic migration and centuries of seasonal, environmental migration associated with pastoralism, we combine historical and qualitative work to demonstrate the value of a livelihood constellation perspective.
A payload adaptor fitting (PAF) structure has been manufactured at NASA’s Marshall Space Flight Center (MSFC). The PAF structure is essentially a large cone made of carbon/epoxy sandwich structure. The PAF structure contains numerous (about 1000) holes at the top and bottom to secure the carbon/epoxy structure in aluminum rings with bolts. In an effort to obtain higher quality holes, both sides of the PAF structure are covered with an additional, non-structural, ply of woven carbon/epoxy placed at ±45⁰ to the vertical direction. This study evaluated the quality of the holes on sandwich structure both with and without the outer woven carbon/epoxy plies via open hole compression (OHC) strength testing. Results showed a 14% increase in strength of the cloth covered sandwich structure, which did not surpass the 18% added weight due to the outer woven plies.