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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.

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At least 55 records · Page 3
All sourcesNASA NTRSDOE OSTI
NASA NTRS1994

Dynamic Leg Exercise Improves Tolerance to Lower Body Negative Pressure

These results clearly demonstrate that dynamic leg exercise against the footward force produced by LBNP substantially improves tolerance to LBNP, and that even cyclic ankle flexion without load bearing also increases tolerance. This exercise-induced increase of tolerance was actually an underestimate, because subjects who completed the tolerance test while exercising could have continued for longer periods. Exercise probably increases LBNP tolerance by multiple mechanisms. Tolerance was increased in part by skeletal muscle pumping venous blood from the legs. Rosenhamer and Linnarsson and Rosenhamer also deduced this for subjects cycling during centrifugation, although no measurements of leg volume were made in those studies: they found that male subjects cycling at 98 W could endure 3 Gz centrifugation longer than when they remained relaxed during centrifugation. Skeletal muscle pumping helps maintain cardiac filling pressure by opposing gravity-, centrifugation-, or LBNP-induced accumulation of blood and extravascular fluid in the legs.

Watenpaugh, D. E.↗
NASA NTRS1999

The Design of a Fault-Tolerant COTS-Based Bus Architecture

In this paper, we report our experiences and findings on the design of a fault-tolerant bus architecture comprised of two COTS buses, the IEEE 1394 and the 12C. This fault-tolerant bus is the backbone system bus for the avionics architecture of the X2000 program at the Jet Propulsion Laboratory. COTS buses are attractive because of the availability of low cost commercial products. However, they are not specifically designed for highly reliable applications such as long-life deep-space missions. The X2000 design team has devised a multi-level fault tolerance approach to compensate for this shortcoming of COTS buses. First, the approach enhances the fault tolerance capabilities of the IEEE 1394 and 12 C buses by adding a layer of fault handling hardware and software. Second, algorithms are developed to enable the IEEE 1394 and the 12 C buses assist each other to isolate and recovery from faults. Third, the set of IEEE 1394 and 12 C buses is duplicated to further enhance system reliability. The X2000 design team has paid special attention to guarantee that all fault tolerance provisions will not cause the bus design to deviate from the commercial standard specifications. Otherwise, the economic attractiveness of using COTS will be diminished. The hardware and software design of the X2000 fault-tolerant bus are being implemented and flight hardware will be delivered to the ST4 and Europa Orbiter missions.

Chau, Savio N.↗
NASA NTRS2005

Fault-Tolerant Heat Exchanger

A compact, lightweight heat exchanger has been designed to be fault-tolerant in the sense that a single-point leak would not cause mixing of heat-transfer fluids. This particular heat exchanger is intended to be part of the temperature-regulation system for habitable modules of the International Space Station and to function with water and ammonia as the heat-transfer fluids. The basic fault-tolerant design is adaptable to other heat-transfer fluids and heat exchangers for applications in which mixing of heat-transfer fluids would pose toxic, explosive, or other hazards: Examples could include fuel/air heat exchangers for thermal management on aircraft, process heat exchangers in the cryogenic industry, and heat exchangers used in chemical processing. The reason this heat exchanger can tolerate a single-point leak is that the heat-transfer fluids are everywhere separated by a vented volume and at least two seals. The combination of fault tolerance, compactness, and light weight is implemented in a unique heat-exchanger core configuration: Each fluid passage is entirely surrounded by a vented region bridged by solid structures through which heat is conducted between the fluids. Precise, proprietary fabrication techniques make it possible to manufacture the vented regions and heat-conducting structures with very small dimensions to obtain a very large coefficient of heat transfer between the two fluids. A large heat-transfer coefficient favors compact design by making it possible to use a relatively small core for a given heat-transfer rate. Calculations and experiments have shown that in most respects, the fault-tolerant heat exchanger can be expected to equal or exceed the performance of the non-fault-tolerant heat exchanger that it is intended to supplant (see table). The only significant disadvantages are a slight weight penalty and a small decrease in the mass-specific heat transfer.

Izenson, Michael G.↗
NASA NTRS2012

Fault Tolerance Middleware for a Multi-Core System

Fault Tolerance Middleware (FTM) provides a framework to run on a dedicated core of a multi-core system and handles detection of single-event upsets (SEUs), and the responses to those SEUs, occurring in an application running on multiple cores of the processor. This software was written expressly for a multi-core system and can support different kinds of fault strategies, such as introspection, algorithm-based fault tolerance (ABFT), and triple modular redundancy (TMR). It focuses on providing fault tolerance for the application code, and represents the first step in a plan to eventually include fault tolerance in message passing and the FTM itself. In the multi-core system, the FTM resides on a single, dedicated core, separate from the cores used by the application. This is done in order to isolate the FTM from application faults and to allow it to swap out any application core for a substitute. The structure of the FTM consists of an interface to a fault tolerant strategy module, a responder module, a fault manager module, an error factory, and an error mapper that determines the severity of the error. In the present reference implementation, the only fault tolerant strategy implemented is introspection. The introspection code waits for an application node to send an error notification to it. It then uses the error factory to create an error object, and at this time, a severity level is assigned to the error. The introspection code uses its built-in knowledge base to generate a recommended response to the error. Responses might include ignoring the error, logging it, rolling back the application to a previously saved checkpoint, swapping in a new node to replace a bad one, or restarting the application. The original error and recommended response are passed to the top-level fault manager module, which invokes the response. The responder module also notifies the introspection module of the generated response. This provides additional information to the introspection module that it can use in generating its next response. For example, if the responder triggers an application rollback and errors are still occurring, the introspection module may decide to recommend an application restart.

Some, Raphael R.↗
NASA NTRS2014

Mechanisms of Orthostatic Tolerance Improvement Following Artificial Gravity Exposure Differ Between Men and Women

We recently determined that a short exposure to artificial gravity (AG) improved the orthostatic tolerance limit (OTL) of cardiovascularly deconditioned subjects. We now seek to determine the mechanisms of that improvement in these hypovolemic men and women. Methods. We determined the orthostatic tolerance limit (OTL) of 9 men and 8 women following a 90 min exposure to AG compared to 90 min of head down bed rest (HDBR). In both cases (21 days apart), subjects were made hypovolemic (low salt diet plus 20 mg intravenous furosemide). Orthostatic tolerance was determined from a combination of head up tilt and increasing lower body negative pressure until presyncope. Mean values and correlations with OTL were determined for heart rate, blood pressure, stroke volume, cardiac output and peripheral resistance (Finometer), cerebral artery blood velocity (DWL), partial pressure of carbon dioxide (Novametrics) and body segmental impedance (UFI THRIM) were measured during supine baseline, during OTL to presyncope and during supine recovery Results. Orthostatic tolerance of these hypovolemic subjects was significantly greater on the day of AG exposure than on the HDBR day. Regression of OTL on these variables identified significant relationships on the HDBR day that were not evident on the AG day: resting TPR correlated positively while resting cerebral flow correlated negatively with OTL. On both days, women's resting stroke volume correlated positively with orthostatic tolerance. Higher group mean values of stroke volume and cerebral artery flow and lower values of blood pressure, peripheral vascular and cerebrovascular resistance both at control and during OTL testing were observed on the AG day. Even though regression of OTL on resting stroke volume was significant only in women, presyncopal stroke volume reached the same level on each day of study for both men and women while the OTL test lasted 30% longer in men and 22% longer in women. Cerebral artery flow appeared to follow stroke volume and absolute values of cerebral flow did not correlate with the development of presyncope. Women responded to AG exposure with elevated cerebral flow at resting control and throughout the OTL test, implying a loss of autoregulation in deconditioned (hypovolemic) women following AG exposure. Conclusions. Before countermeasures to space flight cardiovascular deconditioning are established, gender differences in cardiovascular responses to orthostatic stress, in general, and to orthostatic stress following exposure to artificial gravity, in particular, need to be determined. Since, in both men and women, a single, acute bout of AG exposure improved orthostatic tolerance, the feasibility of short exposures to AG during longer spaceflights or prior to entry into a gravity (Earth or Mars) environment, should be explored. Given the known beneficial effects of AG on other organ systems, the present study indicates that the positive effects of AG on cardiac stroke volume make AG a likely candidate for maintaining cardiovascular conditioning.

Evans, J. M.↗
NASA NTRSDate not supplied

Best Practices, Lessons Learned, and Examples on the Application of Damage Tolerance in Space Structures

Damage tolerance is an important consideration in space structures applications. The intent of damage tolerance is to demonstrate that the structure is robust to the presence of flaws over the service life of the space vehicle. Damage tolerance requirements in documents such as those in NASA, AIAA, and ISO can be challenging to implement. The intent of this paper is three-fold: (1) Provide best practices in the application of damage tolerance requirements for space applications, (2) Provide lessons learned for each of class of hardware, (3) Provide examples of challenging situations encountered in the application of damage tolerance. Examples cover additive manufacturing, composite overwrapped pressure vessels, pressurized structures, liquid rocket engines, thermal protection systems, and other classes of hardware. The philosophy and limitations of leak before burst and proof test logic are also discussed. Finally, a discussion on elastic-plastic fracture mechanics with comparisons to test data will be presented.

Best Practices↗
DOE OSTI2025

Drought increases microbial allocation to stress tolerance but with few tradeoffs among community-level traits

Climate change will increase soil drying, altering microbial communities via increasing water stress and decreasing resource availability. The responses of these microbial communities to changing environments could be governed by physiological tradeoffs between high yield, resource acquisition, and stress tolerance (YAS framework). We leveraged a unique field experiment that manipulates both drought and carbon availability across two years and three land uses, and we measured both physiological (with bioassays) and genetic (with metagenomics) microbial traits at the community level to test the following hypotheses: 1. Drought increases microbial allocation to stress tolerance functions, at both physiological and genetic levels. 2. Because microbes are resource-limited under drought, increased carbon will enable greater expression of stress tolerance. 3. All three key life history traits described in the YAS framework will trade off. Drought did increase microbial physiological investment in stress tolerance (measured via trehalose production), but we saw few other changes in microbial communities under drought. Adding carbon to plots increased resource acquisition (measured via enzyme activity and resource acquisition gene abundance) and stress tolerance (trehalose assay), but did so in both drought and average rainfall environments. Here, we found little evidence of trait tradeoffs, as a negative correlation between rRNA copy number and resource acquisition gene abundance was the only significant negative correlation between traits that we found that was consistent across years (for physiological or genetic traits). In summary, we found C addition, and to a lesser extent, drought, altered microbial community function and functional genes. However, resources did not alter drought response in a way that was consistent with theory of life history tradeoffs.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2024

AtDGCR14L contributes to salt-stress tolerance via regulating pre-mRNA splicing in Arabidopsis

In plants, the pre-mRNA alternative splicing has been demonstrated to be a crucial tier that regulates gene expression in response to salt stress. However, the underlying mechanisms remain elusive. Here, in this study, we studied the roles of DIGEORGE-SYNDROME CRITICAL REGION 14-like (AtDGCR14L) in regulating pre-mRNA splicing and salt stress tolerance. We discovered that Arabidopsis AtDGCR14L is required for maintaining plant salt stress tolerance and the constitutively spliced and active isoforms of important stress- and/or abscisic acid (ABA)-responsive genes. We also identified the interaction between AtDGCR14L and splicing factor U1-70k, which needs a highly conserved three amino acid (TWG) motif in DGCR14. Different from wild-type AtDGCR14L, the overexpression of TWG-substituted AtDGCR14L mutant did not change salt stress tolerance or pre-mRNA splicing of stress/ABA-responsive genes. Additionally, SWITCH3A (SWI3A) is a core subunit of the SWI/SUCROSE NONFERMENTING (SWI/SNF) chromatin-remodeling complexes. We found that SWI3A, whose splicing depends on AtDGCR14L, actively enhances salt stress tolerance. These results revealed that AtDGCR14L may play an essential role in crosstalk between plant salt-stress response and pre-mRNA splicing mechanisms. We also unveiled the potential role of SWI3A in controlling salt stress tolerance. The TWG motif in the intrinsically disordered region of AtDGCR14L is highly conserved and crucial for DGCR14 functions.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2025

Combining genome-wide association studies and expression quantitative trait nucleotide mapping with molecular and genetic validations to identify transcriptional networks regulating drought tolerance in Populus

Objectives: (i). To deploy a large-scale experimental drought trial for up to 1000 unique genotypes of Populus equipping the sites with controlled irrigation and drought treatments that are fully automated and monitored. FULLY COMPLETED (ii) To test the hypothesis that a suite of traits identified for drought tolerance in P. nigra can be measured in drought and control treatments in the wide germplasm collection of P. trichocarpa. FULLY COMPLETED (iii) To use established and novel GWAS model approaches to identify gene loci linked to drought tolerance traits on interest in P. trichocarpa. FULLY COMPLETED (iv) To undertake comparative analysis of GWAS results for drought tolerance traits in P. nigra and P. trichocarpa. PARTIALLY COMPLETED – remains active (v) Using RNAseq in P. trichocarpa, in droughted and control treatments to identify cis- and trans-regulated eQTN. FULLY COMPLETED (vi) Validate up to 50 cis-QTNs, from network hubs using transient protoplast assays. FULLY COMPLETED (vii) To establish Agrobacterium-based gene editing protocols in Populus. FULLY COMPLETED (viii) To utilize early leads from previous research to investigate at least 6 candidate genes for drought tolerance in Populus. FULLY COMPLETED (ix) To validate up to 20 candidate genes for drought tolerance in P. trichocarpa refined from the long-list tested in the transient assays for cis-acting hub gene targets. PARTIALLY COMPLETED- remains active.

60 APPLIED LIFE SCIENCES↗
NASA NTRS1972

Sequential behavior and its inherent tolerance to memory faults.

Representation of a memory fault of a sequential machine M by a function mu on the states of M and the result of the fault by an appropriately determined machine M(mu). Given some sequential behavior B, its inherent tolerance to memory faults can then be measured in terms of the minimum memory redundancy required to realize B with a state-assigned machine having fault tolerance type tau and fault tolerance level t. A behavior having maximum inherent tolerance is exhibited, and it is shown that behaviors of the same size can have different inherent tolerance.

Meyer, J. F.↗
NASA NTRS1975

+Gz tolerance in man after 14-day bedrest periods with isometric and isotonic exercise conditioning

The effects of isometric and isotonic exercise training on post-bedrest +Gz tolerance were determined. In general, 14-day bedrest resulted in a significant loss of Gz tolerance, as previously discovered. At 2.1 Gz, neither the isometric nor the isotonic exercises regimens resulted in a significant increase in post-bedrest Gz tolerance. However, following isometric exercise, restoration of about half the tolerance decrement occurred at 3.2 Gz and 3.8 Gz. Possible reasons for this partial restoration of tolerance are put forward.

Greenleaf, J. E.↗
NASA NTRS1975

System applications of the fault tolerant memory

Conventional memory technologies currently employed in aerospace applications contribute at least fifty percent to system unreliability (where the system includes CPU, I/O and memory). A fault tolerant memory performs both error correction and memory replacement at the bit plane level. To determine the effects of system design of using a fault tolerant memory in space applications, analysis was performed to determine tradeable hardware configurations that meet the reliability goals of each program. The candidate configurations, which included redundant elements of the computer system with both conventional and fault tolerant memories, were then traded in terms of selection criteria of cost, weight, volume, and power. These trade studies demonstrated that a fault tolerant memory provided significant advantages in terms of cost, weight, and volume. The memory selected for this analysis was a recently developed five fault tolerant memory.

Murphy, L. J.↗
NASA NTRS1978

Fault-tolerance - The survival attribute of digital systems

Fault-tolerance is the architectural attribute of a digital system that keeps the logic machine doing its specified tasks when its host, the physical system, suffers various kinds of failures of its components. A more general concept of fault-tolerance also includes human mistakes committed during software and hardware implementation and during man/machine interaction among the causes of faults that are to be tolerated by the logic machine. This paper discusses the concept of fault-tolerance, the reasons for its inclusion in digital system architecture, and the methods of its implementation. A chronological view of the evolution of fault-tolerant systems and an outline of some goals for its further development conclude the presentation.

Avizienis, A.↗
NASA NTRS1978

SIFT - Design and analysis of a fault-tolerant computer for aircraft control

SIFT (Software Implemented Fault Tolerance) is an ultrareliable computer for critical aircraft control applications that achieves fault tolerance by the replication of tasks among processing units. The main processing units are off-the-shelf minicomputers, with standard microcomputers serving as the interface to the I/O system. Fault isolation is achieved by using a specially designed redundant bus system to interconnect the processing units. Error detection and analysis and system reconfiguration are performed by software. Iterative tasks are redundantly executed, and the results of each iteration are voted upon before being used. Thus, any single failure in a processing unit or bus can be tolerated with triplication of tasks, and subsequent failures can be tolerated after reconfiguration. Independent execution by separate processors means that the processors need only be loosely synchronized, and a novel fault-tolerant synchronization method is described.

Wensley, J. H.↗
NASA NTRS1982

Effect of resin on impact damage tolerance of graphite/epoxy laminates

Twenty-four different epoxy resin systems were evaluated by a variety of test techniques to identify materials that exhibited improved impact damage tolerance in graphite/epoxy composite laminates. Forty-eight-ply composite panels of five of the material systems were able to sustain 100 m/s impact by a 1.27-cm-diameter aluminum projectile while statically loaded to strains of 0.005. Of the five materials with the highest tolerance to impact, two had elastomeric additives, two had thermoplastic additives, and one had a vinyl modifier; all the five systems used bisphenol A as the base resin. An evaluation of test results shows that the laminate damage tolerance is largely determined by the resin tensile properties, and that improvements in laminate damage tolerance are not necessarily made at the expense of room-temperature mechanical properties. The results also suggest that a resin volume fraction of 40 percent or greater may be required to permit the plastic flow between fibers necessary for improved damage tolerance.

Williams, J. G.↗
NASA NTRS1985

A methodology for testing fault-tolerant software

A methodology for testing fault tolerant software is presented. There are problems associated with testing fault tolerant software because many errors are masked or corrected by voters, limiter, or automatic channel synchronization. This methodology illustrates how the same strategies used for testing fault tolerant hardware can be applied to testing fault tolerant software. For example, one strategy used in testing fault tolerant hardware is to disable the redundancy during testing. A similar testing strategy is proposed for software, namely, to move the major emphasis on testing earlier in the development cycle (before the redundancy is in place) thus reducing the possibility that undetected errors will be masked when limiters and voters are added.

Andrews, D. M.↗
NASA NTRS1985

Fault-tolerant software - Experiment with the sift operating system

Results are presented of an experiment conducted in the NASA Avionics Integrated Research Laboratory (AIRLAB) to investigate the implementation of fault-tolerant software techniques on fault-tolerant computer architectures, in particular the Software Implemented Fault Tolerance (SIFT) computer. The N-version programming and recovery block techniques were implemented on a portion of the SIFT operating system. The results indicate that, to effectively implement fault-tolerant software design techniques, system requirements will be impacted and suggest that retrofitting fault-tolerant software on existing designs will be inefficient and may require system modification.

Brunelle, J. E.↗
NASA NTRS1992

Fault-tolerant wait-free shared objects

A concurrent system consists of processes communicating via shared objects, such as shared variables, queues, etc. The concept of wait-freedom was introduced to cope with process failures: each process that accesses a wait-free object is guaranteed to get a response even if all the other processes crash. However, if a wait-free object 'crashes,' all the processes that access that object are prevented from making progress. In this paper, we introduce the concept of fault-tolerant wait-free objects, and study the problem of implementing them. We give a universal method to construct fault-tolerant wait-free objects, for all types of 'responsive' failures (including one in which faulty objects may 'lie'). In sharp contrast, we prove that many common and interesting types (such as queues, sets, and test&set) have no fault-tolerant wait-free implementations even under the most benign of the 'non-responsive' types of failure. We also introduce several concepts and techniques that are central to the design of fault-tolerant concurrent systems: the concepts of self-implementation and graceful degradation, and techniques to automatically increase the fault-tolerance of implementations. We prove matching lower bounds on the resource complexity of most of our algorithms.

Jayanti, Prasad↗