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At least 235 records · Page 13

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NASA NTRS1981

Design aspects of a solar array drive for spot, with a high platform stability objective

A solar array drive mechanism (MEGS) for the SPOT platform, which is a prototype of a multimission platform, is described. High-resolution cameras and other optical instruments are carried by the platform, requiring excellent platform stability in order to obtain high-quality pictures. Therefore, a severe requirement for the MEGS is the low level of disturbing torques it may generate considering the 0.6 times 10 to the minus 3 power deg/sec stability required. The mechanical design aspects aiming at reducing the mean friction torque, and therefore its fluctuations, are described as well as the method of compensation of the motor imperfections. It was concluded, however, that this is not sufficient to reach the stability requirement.

Cabillic, J.↗

NASA NTRSDate not supplied

TPSAS-NF1676L-34417-DND

A boron nitride nanotube (BNNT), an electrically-insulating counterpart of a carbon nanotube (CNT), is a great nanofiller candidate for ferroelectric polymeric nanocomposites due to BNNT?s exceptional properties in piezoelectricity, thermal stability, mechanical strength, and radiation shielding capability. Fast and high-yield polar crystallization of polyvinylidene fluoride (PVDF) was accomplished by incorporating BNNTs as a nucleating agent. As-fabricated BNNT-PVDF nanocomposites were characterized by Fourier-transform infrared spectroscopy (FTIR), wide-angle X-ray diffraction (XRD), and differential scanning calorimetry (DSC) to identify and quantify chain conformations. Besides, piezoelectric constants, d33 of BNNT-PVDF nanocomposites were measured and compared with that of a mechanically drawn beta phase polar PVDF. The polar transformation due to BNNT incorporation has a great advantage over conventional beta or gamma transformation methods that require (1) mechanical drawing often resulting in defects or (2) high-temperature annealing for an extended time. In addition to the fast polar crystallization, BNNTs had a role of reinforcement of the polymer matrix. The improved Young?s modulus and electromechanical coupling coefficient of BNNT-PVDF nanocomposites indicated potential applications in energy harvesting under harsh environments such as large deformation, wide temperature cycles, and high radiation.

Dongwon Lee↗

NASA NTRS1975

Power processing system for a 200 watt communication satellite transmitter

A power processing system (PPS) for a communication satellite, high power (200W RF) multi-stage depressed collector, 12 GHz, traveling wave tube, is described. The PPS converts spacecraft bus power at a nominal voltage of 76 Vdc to the levels necessary for operating a ten-collector coupled cavity TWT requiring approximately 500 watts of input power. Regulated voltages of up to -11.3K Vdc are provided along with command, protection and telemetry signal conditioning circuits. Power processor interface requirements are set forth and a block diagram illustrating the basic approach utilized is presented. Overall performance, design characteristics and unique features are discussed. Thermal and mechanical interface requirements impacting on PPS design are described as well as the thermal control technique utilized for the overall PPS/TWT assembly.

Farber, B. F.↗

NASA NTRS2011

The Hyperspectral Thermal Emission Spectrometer (HyTES): Preliminary Results

The Hyperspectral Thermal Emission Spectrometer (HyTES) is being developed as part of the risk reduction activities associated with the Hyperspectral Infrared Imager (HyspIRI). HyspIRI is one of the Tier 2 Decadal Survey Missions. HyTES will provide information on how to place the filters on the HyspIRI Thermal Infrared Instrument (TIR) as well as provide antecedent science data. The pushbroom design has 512 spatial pixels over a 50-degree field of view and 256 spectral channels between 7.5 micrometers to 12 micrometers. HyTES includes many key enabling state-of-the-art technologies including a high performance convex diffraction grating, a quantum well infrared photodetector (QWIP) focal plane array, and a compact Dyson-inspired optical design. The Dyson optical design allows for a very compact and optically fast system (F/1.6). It also minimizes cooling requirements due to the fact it has a single monolithic prism-like grating design which allows baffling for stray light suppression. The monolithic configuration eases mechanical tolerancing requirements which are a concern since the complete optical assembly is operated at cryogenic temperatures ((is) approximately 100K). The QWIP allows for optimum spatial and spectral uniformity and provides adequate responsivity or D-star to allow 200mK noise equivalent temperature difference (NEDT) operation across the LWIR passband. Assembly of the system is nearly complete. After completion, alignment results will be presented which show low keystone and smile distortion. This is required to minimize spatial-spectral mixing between adjacent spectral channels and spatial positions. Predictions show the system will have adequate signal to noise for laboratory calibration targets.

Moon Mineralogical Mapper (M3).↗

NASA NTRS2013

Coarse-Grain Bandwidth Estimation Scheme for Large-Scale Network

A large-scale network that supports a large number of users can have an aggregate data rate of hundreds of Mbps at any time. High-fidelity simulation of a large-scale network might be too complicated and memory-intensive for typical commercial-off-the-shelf (COTS) tools. Unlike a large commercial wide-area-network (WAN) that shares diverse network resources among diverse users and has a complex topology that requires routing mechanism and flow control, the ground communication links of a space network operate under the assumption of a guaranteed dedicated bandwidth allocation between specific sparse endpoints in a star-like topology. This work solved the network design problem of estimating the bandwidths of a ground network architecture option that offer different service classes to meet the latency requirements of different user data types. In this work, a top-down analysis and simulation approach was created to size the bandwidths of a store-and-forward network for a given network topology, a mission traffic scenario, and a set of data types with different latency requirements. These techniques were used to estimate the WAN bandwidths of the ground links for different architecture options of the proposed Integrated Space Communication and Navigation (SCaN) Network. A new analytical approach, called the "leveling scheme," was developed to model the store-and-forward mechanism of the network data flow. The term "leveling" refers to the spreading of data across a longer time horizon without violating the corresponding latency requirement of the data type. Two versions of the leveling scheme were developed: 1. A straightforward version that simply spreads the data of each data type across the time horizon and doesn't take into account the interactions among data types within a pass, or between data types across overlapping passes at a network node, and is inherently sub-optimal. 2. Two-state Markov leveling scheme that takes into account the second order behavior of the store-and-forward mechanism, and the interactions among data types within a pass. The novelty of this approach lies in the modeling of the store-and-forward mechanism of each network node. The term store-and-forward refers to the data traffic regulation technique in which data is sent to an intermediate network node where they are temporarily stored and sent at a later time to the destination node or to another intermediate node. Store-and-forward can be applied to both space-based networks that have intermittent connectivity, and ground-based networks with deterministic connectivity. For groundbased networks, the store-and-forward mechanism is used to regulate the network data flow and link resource utilization such that the user data types can be delivered to their destination nodes without violating their respective latency requirements.

Cheung, Kar-Ming↗

NASA NTRS2002

Candidate Coatings and Dry Traction Drives for Planetary Vehicles

Robert Fusaro and Fred Oswald of the Mechanical Components Branch discussed 'Candidate Coatings and Dry Traction Drives for Planetary Vehicles'. Vehicles to be designed for exploration of planets and moons of the solar system will require reliable mechanical drives to operate efficiently. Long-term operation of these drives will be challenging because of extreme operating conditions. These extreme conditions include: very high and/or very cold temperatures, wide temperature ranges, dust, vacuum or low-pressure atmospheres, and corrosive environments. Most drives used on Earth involve oil-lubricated gears. However, due to the extreme conditions on planetary surfaces, it may not be advisable or even possible to use oil lubrication. Unfortunately, solid lubricants do not work well when applied to gears because of the high contact stress conditions and large sliding motion between the teeth, which cause wear and limit life. We believe traction drives will provide an attractive alternative to gear drives. Traction drives are composed of rollers that provide geometry more conducive to solid lubrication. Minimal slip occurs in this contact geometry and thus there is very low wear to the solid lubricant. The challenge for these solid-lubricated drives is finding materials or coatings that provide the required long-life while also providing high traction. We seek materials that provide low wear with high friction.

Fusaro, Robert↗

NASA NTRS1985

Long-delayed radio echoes - Mechanisms and observations

Experiments carried out in Alaska with the object of observing long-delayed radio echoes (LDE) are described. The results are subjected to critical sonogram analysis, together with data form previous experiments carried out at Stanford and elsewhere. It is concluded that, although strong supporting evidence for sporadic LDE phenomena has accumulated over the late 50 years, and a variety of plausible mechanisms have been proposed, stringent analysis of records such as those discussed in the paper almost invariably reveal alternative possible explanations for them. Further detailed experimentation is required on mechanisms, for which the phenomenon seems best established, e.g., round-the-world echoes and other forms of guided propagation.

Vidmar, R. J.↗

NASA NTRS1995

17-4 PH and 15-5 PH

17-4 PH and 15-5 PH are extremely useful and versatile precipitation-hardening stainless steels. Armco 17-4 PH is well suited for the magnetic particle inspection requirements of Aerospace Material Specification. Armco 15-5 PH and 17-4 PH are produced in billet, plate, bar, and wire. Also, 15-5 PH is able to meet the stringent mechanical properties required in the aerospace and nuclear industries. Both products are easy to heat treat and machine, making them very useful in many applications.

Johnson, Howard T.↗

NASA NTRSDate not supplied

Investigation of Additive Manufactured GRCop-42 Alloy Developed by Directed Energy Deposition Methods

GRCop is an alloy family constructed of copper, chromium, and niobium and was developed by NASA for high heat flux applications. GRCop-alloys were specifically formulated for the requirements in channel-cooled main combustion chambers allowing for repeat use in high heat flux environments[1]. GRCop-84 was evolved using additive manufacturing techniques under a NASA development program. To further increase thermal conductivity while maintaining material strength characteristics, the percentage of alloying elements were cut in half and GRCop-42 was developed. In recent years, NASA has successfully additively manufactured GRCop-42 with comparable material characteristics to extrudedGRCop-42 using a Laser Powder Bed Fusion (L-PBF) process. Benefits of this process include fabrication of intricate internal cooling channels as well as a decrease in manufacturing time. However, there are some large disadvantages in using this process. The nature of the powder bed process imposes a strict volume constraint as well as an excessive amount of material inventory required. A Directed Energy Deposition (DED) process addresses these limitations while also speeding up the manufacturing process. With little data on how DED performs with GRCop-42, an investigation into the mechanical properties was conducted. More specifically, Blown Powder Directed Energy Deposition (BPD), was used to compare material properties to that of the L-PBF manufactured GRCop-42. The DED manufactured material was found to have less than 0.1% porosity. Tensile tests concluded that the DED manufactured GRCop-42 had lower tensile strengths at room temperature. The results point towards a process capable of producing fully dense parts capable of meeting mechanical strength requirements with some possible refinement of printing parameters.

GRCop-42↗

NASA NTRS1973

SUMC/MPOS/HAL interface study

The implementation of the HAL/S language on the IBM-360, and in particular the mechanization of its real time, I/O, and error control statements within the OS-360 environment is described. The objectives are twofold: (1) An analysis and general description of HAL/S real time, I/O, and error control statements and the structure required to mechanize these statements. The emphasis is on describing the logical functions performed upon execution of each HAL statement rather than defining whether it is accomplished by the compiler or operating system. (2) An identification of the OS-360 facilities required during execution of HAL/S code as implemented for the current HAL/S-360 compiler; and an evaluation of the aspects involved with interfacing HAL/S with the SUMC operating system utilizing either the HAL/S-360 compiler or by designing a new HAL/S-SUMC compiler.

Saponaro, J. A.↗

NASA NTRS2012

Launch Pad Closeout Operations for the Mars Science Laboratory's Heat Rejection System

The Mars Science Laboratory (MSL) rover was launched on an Atlas V on November 26, 2011. Preparations were carried out prior to launch in order to closeout the spacecraft's complex heat rejection system (HRS), which consists of two mechanically pumped CFC-11 fluid loops. The first HRS loop, onboard the Curiosity rover, was fully integrated, filled with CFC-11, and successfully operated prior to launch pad operations; however, the second thermal loop, called the cruise HRS loop, required final mechanical and thermal integration activities to occur while on the launch pad in order to accommodate the last minute installation of the rover's Multi-Mission Radioisotope Thermoelectric Generator (MMRTG) power source. In order to prevent overheating of propellant tanks and critical avionics equipment buried deep within the spacecraft's aeroshell, the MMRTG needed to be pre-cooled using a separate non-flight mechanically pumped fluid loop prior to and during the final closeout and subsequent startup of the flight loop. This paper outlines the various steps that took place to safely install the MMRTG while carefully transitioning from the pre-cooling operation to the final startup and operation of the flight cruise HRS loop. Temperature data of the launch pad thermal transition from the ground support loop activity to the final flight loop operation is presented. Some background development of the ground support loop and lessons learned are also discussed. This successful launch pad integration activity required a close-knit coordination between NASA KSC, JPL, the Department of Energy, Idaho National Labs, Pratt and Whitney Rocketdyne Inc., Teledyne Technologies Inc., ULA, and Advanced Thermal Sciences Corp.

thermal↗

NASA NTRS2016

Mechanical Testing of MLCCs

Cracking of multilayer ceramic capacitors, MLCCs, remains a serious problem for space systems. This problem increases substantially for large size capacitors and in cases when manual soldering is involved or the system experiences mechanical shock or vibration. In any case, a fracture occurs when the sum of external and internal mechanical stresses exceeds the strength of the part. To reduce the probability of cracking, the level of stress should be reduced, e.g. by optimizing the assembly workmanship and rules for board design, and the strength of the parts increased by selecting the most mechanically robust capacitors. The latter might possibly be achieved by selecting MLCCs based on the in-situ measurements of mechanical characteristics using four types of tests: flexural strength, hardness, fracture toughness, and flex bend testing. Note that military specifications MIL-PRF-123 and MIL-PRF-55681 do not have requirements for mechanical testing of the parts. However, specifications for automotive industry components employ two types of mechanical tests: beam load (break strength) test per AEC-Q200-003 and board flex test per AEC-Q200-005. A recent military specification for thin dielectric capacitors, MIL-PRF-32535, has one mechanical test, board flex testing, that is similar to AEC-Q200-005. The purpose of this report was assessment of the efficiency of different mechanical tests for selection robust capacitors and comparison of mechanical characteristics of Base Metal Electrode (BME) and Precious Metal Electrode (PME) capacitors. The report has three parts related to the first three mechanical tests mentioned above.

Precious Metal Electrode (PME) capacitors↗

NASA NTRS2005

A Formal Approach to Requirements-Based Programming

No significant general-purpose method is currently available to mechanically transform system requirements into a provably equivalent model. The widespread use of such a method represents a necessary step toward high-dependability system engineering for numerous application domains. Current tools and methods that start with a formal model of a system and mechanically produce a provably equivalent implementation are valuable but not sufficient. The "gap" unfilled by such tools and methods is that the formal models cannot be proven to be equivalent to the requirements. We offer a method for mechanically transforming requirements into a provably equivalent formal model that can be used as the basis for code generation and other transformations. This method is unique in offering full mathematical tractability while using notations and techniques that are well known and well trusted. Finally, we describe further application areas we are investigating for use of the approach.

Hinchey, Michael G.↗

DOE OSTI2022

A critical assessment of solutions to the galaxy diversity problem

Galactic rotation curves exhibit a diverse range of inner slopes. Observational data indicates that explaining this diversity may require a mechanism that correlates a galaxy's surface brightness with the central-most region of its dark matter halo. Here, in this work, we compare several concrete models that capture the relevant physics required to explain the galaxy diversity problem. We focus specifically on a Self-Interacting Dark Matter (SIDM) model with an isothermal core and two Cold Dark Matter (CDM) models with/without baryonic feedback. In contrast to the CDM case, the SIDM model can lead to the formation of an isothermal core in the halo, and is also mostly insensitive to baryonic feedback processes, which act on longer time-scales. Using rotation curves from 90 galaxies in the Spitzer Photometry & Accurate Rotation Curves (SPARC) catalog, we perform a comprehensive model comparison that addresses issues of statistical methodology from prior works. The best-fit halo models that we recover are consistent with standard CDM concentration-mass and abundance matching relations. We find that both the SIDM and feedback-affected CDM models are better than a CDM model with no feedback in explaining the rotation curves of low and high surface brightness galaxies in the sample. However, when compared to each other, there is no strong statistical preference for either the SIDM or the feedback-affected CDM halo model as the source of galaxy diversity in the SPARC catalog.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2020

Microwave ignition of energetic material housed within a gun

The systems and methods for microwave ignition of energetic material housed within a gun (e.g., primers and/or propellants) allow for the use of insensitive energetic materials and/or insensitive gas-generating materials in place of sensitive energetic materials relied upon by mechanical ignition systems. In some embodiments, the use of insensitive energetic materials and/or insensitive gas-generating materials increase the safety and reliability of guns that would otherwise need to depend on sensitive energetic material required by mechanical or laser ignition mechanisms. Additionally, in some embodiments, the systems and methods provide greater versatility with respect to the variety of energetic materials that may be employed within guns.

42 ENGINEERING↗

NASA NTRS2003

Material Properties Analysis of Structural Members in Pumpkin Balloons

The efficient design, service-life qualification, and reliability predictions for lightweight aerospace structures require careful mechanical properties analysis of candidate structural materials. The demand for high-quality laboratory data is particularly acute when the candidate material or the structural design has little history. The pumpkin-shaped super-pressure balloon presents both challenges. Its design utilizes load members (tendons) extending from apex to base around the gas envelope to achieve a lightweight structure. The candidate tendon material is highly weight-efficient braided HM cord. Previous mechanical properties studies of Zylon have focused on fiber and yarn, and industrial use of the material in tensile applications is limited. For high-performance polymers, a carefully plamed and executed properties analysis scheme is required to ensure the data are relevant to the desired application. Because no directly-applicable testing standard was available, a protocol was developed based on guidelines fiom professional and industry organizations. Due to the liquid-crystalline nature of the polymer, the cord is very stiff, creeps very little, and does not yield. Therefore, the key material property for this application is the breaking strength. The pretension load and gauge length were found to have negligible effect on the measured breaking strength over the ranges investigated. Strain rate was found to have no effect on breaking strength, within the range of rates suggested by the standards organizations. However, at the lower rate more similar to ULDB operations, the strength was reduced. The breaking strength increased when the experiment temperature was decreased from ambient to 183K which is the lowest temperature ULDB is expected to experience. The measured strength under all test conditions was well below that resulting from direct scale-up of fiber strength based on the manufacturers data. This expected result is due to the effects of the braiding process and material ageing.

Sterling, W. J.↗

DOE OSTI2023

Motility of Synthetic Cells from Engineered Lipids

Synthetic cells are artificial systems that resemble natural cells. Significant efforts have been made over the years to construct synthetic protocells that can mimic biological mechanisms and perform various complex processes. These include compartmentalization, metabolism, energy supply, communication, and gene reproduction. Cell motility is also of great importance, as nature uses elegant mechanisms for intracellular trafficking, immune response, and embryogenesis. In this review, we discuss the motility of synthetic cells made from lipid vesicles and relevant molecular mechanisms. Synthetic cell motion may be classified into surface-based or solution-based depending on whether it involves interactions with surfaces or movement in fluids. Collective migration behaviors have also been demonstrated. The swarm motion requires additional mechanisms for intercellular signaling and directional motility that enable communication and coordination among the synthetic vesicles. In addition, intracellular trafficking for molecular transport has been reconstituted in minimal cells with the help of DNA nanotechnology. These efforts demonstrate synthetic cells that can move, detect, respond, and interact. Finally, we envision that new developments in protocell motility will enhance our understanding of biological processes and be instrumental in bioengineering and therapeutic applications.

59 BASIC BIOLOGICAL SCIENCES↗

NASA NTRS1972

Selection of a surface tension propellant management system for the Viking 75 Orbiter.

Discussion of the propellant management system requirements derived for the Viking 75 mission, and review of a series of surface tension propellant management system design concepts. The chosen concept is identified and its mission operation described. The ullage bubble and bulk liquid positioning characteristics are presented, along with propellant dynamic considerations entailed by thrust initiation/termination. Pressurization design considerations, required to assure minimum disturbance to the bulk propellant, are introduced as well as those of the tank ullage vent. Design provisions to assure liquid communication between tank ends are discussed. Results of a preliminary design study are presented, including mechanical testing requirements to assure structural integrity, propellant compatibility, and proper installation.

Dowdy, M. W.↗