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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 109 records · Page 6
All sourcesNASA NTRSDOE OSTI
NASA NTRS2003

Aircraft engine with inter-turbine engine frame supported counter rotating low pressure turbine rotors

An aircraft gas turbine engine assembly includes an inter-turbine frame axially located between high and low pressure turbines. Low pressure turbine has counter rotating low pressure inner and outer rotors with low pressure inner and outer shafts which are at least in part rotatably disposed co-axially within a high pressure rotor. Inter-turbine frame includes radially spaced apart radially outer first and inner second structural rings disposed co-axially about a centerline and connected by a plurality of circumferentially spaced apart struts. Forward and aft sump members having forward and aft central bores are fixedly joined to axially spaced apart forward and aft portions of the inter-turbine frame. Low pressure inner and outer rotors are rotatably supported by a second turbine frame bearing mounted in aft central bore of aft sump member. A mount for connecting the engine to an aircraft is located on first structural ring.

Seda, Jorge F.↗
NASA NTRS2008

Pion and Kaon Lab Frame Differential Cross Sections for Intermediate Energy Nucleus-Nucleus Collisions

Space radiation transport codes require accurate models for hadron production in intermediate energy nucleus-nucleus collisions. Codes require cross sections to be written in terms of lab frame variables and it is important to be able to verify models against experimental data in the lab frame. Several models are compared to lab frame data. It is found that models based on algebraic parameterizations are unable to describe intermediate energy differential cross section data. However, simple thermal model parameterizations, when appropriately transformed from the center of momentum to the lab frame, are able to account for the data.

Norbury, John W.↗
NASA NTRS2009

Pilotless Frame Synchronization Using LDPC Code Constraints

A method of pilotless frame synchronization has been devised for low- density parity-check (LDPC) codes. In pilotless frame synchronization , there are no pilot symbols; instead, the offset is estimated by ex ploiting selected aspects of the structure of the code. The advantag e of pilotless frame synchronization is that the bandwidth of the sig nal is reduced by an amount associated with elimination of the pilot symbols. The disadvantage is an increase in the amount of receiver data processing needed for frame synchronization.

Jones, Christopher↗
NASA NTRS2010

Space-Frame Lunar Lander

The space-frame lunar lander was originally intended to (1) land on rough lunar terrain, (2) deform itself to conform to the terrain so as to be able to remain there in a stable position and orientation, and (3) if required, further deform itself to perform various functions. In principle, the space-frame lunar lander could be used in the same way on Earth, as might be required, for example, to place meteorological sensors or a radio-communication relay station on an otherwise inaccessible mountain peak. the space-frame lunar lander would include a truss-like structure consisting mostly of a tetrahedral mesh of nodes connected by variable-length struts, the lengths of which would be altered in coordination to impart the desired overall size and shape to the structure. Thrusters (that is, small rocket engines), propellant tanks, a control system, and instrumentation would be mounted in and on the structure (see figure). Once it had landed and deformed itself to the terrain through coordinated variations in the lengths of the struts, the structure could be further deformed into another space-frame structure

Curtis, Steven A.↗
NASA NTRS2010

Enabling IP Header Compression in COTS Routers via Frame Relay on a Simplex Link

NASA is moving toward a networkcentric communications architecture and, in particular, is building toward use of Internet Protocol (IP) in space. The use of IP is motivated by its ubiquitous application in many communications networks and in available commercial off-the-shelf (COTS) technology. The Constellation Program intends to fit two or more voice (over IP) channels on both the forward link to, and the return link from, the Orion Crew Exploration Vehicle (CEV) during all mission phases. Efficient bandwidth utilization of the links is key for voice applications. In Voice over IP (VoIP), the IP packets are limited to small sizes to keep voice latency at a minimum. The common voice codec used in VoIP is G.729. This new algorithm produces voice audio at 8 kbps and in packets of 10-milliseconds duration. Constellation has designed the VoIP communications stack to use the combination of IP/UDP/RTP protocols where IP carries a 20-byte header, UDP (User Datagram Protocol) carries an 8-byte header, and RTP (Real Time Transport Protocol) carries a 12-byte header. The protocol headers total 40 bytes and are equal in length to a 40-byte G.729 payload, doubling the VoIP latency. Since much of the IP/UDP/RTP header information does not change from IP packet to IP packet, IP/UDP/RTP header compression can avoid transmission of much redundant data as well as reduce VoIP latency. The benefits of IP header compression are more pronounced at low data rate links such as the forward and return links during CEV launch. IP/UDP/RTP header compression codecs are well supported by many COTS routers. A common interface to the COTS routers is through frame relay. However, enabling IP header compression over frame relay, according to industry standard (Frame Relay IP Header Compression Agreement FRF.20), requires a duplex link and negotiations between the compressor router and the decompressor router. In Constellation, each forward to and return link from the CEV in space is treated independently as a simplex link. Without negotiation, the COTS routers are prevented from entering into the IP header compression mode, and no IP header compression would be performed. An algorithm is proposed to enable IP header compression in COTS routers on a simplex link with no negotiation or with a one-way messaging. In doing so, COTS routers can enter IP header compression mode without the need to handshake through a bidirectional link as required by FRF.20. This technique would spoof the routers locally and thereby allow the routers to enter into IP header compression mode without having the negotiations between routers actually occur. The spoofing function is conducted by a frame relay adapter (also COTS) with the capability to generate control messages according to the FRF.20 descriptions. Therefore, negotiation is actually performed between the FRF.20 adapter and the connecting COTS router locally and never occurs over the space link. Through understanding of the handshaking protocol described by FRF.20, the necessary FRF.20 negotiations messages can be generated to control the connecting router, not only to turn on IP header compression but also to adjust the compression parameters. The FRF.20 negotiation (or control) message is composed in the FRF.20 adapter by interpreting the incoming router request message. Many of the fields are simply transcribed from request to response while the control field indicating response and type are modified.

Nguyen, Sam P.↗
NASA NTRS2011

Split-screen display system and standardized methods for ultrasound image acquisition and multi-frame data processing

A standardized acquisition methodology assists operators to accurately replicate high resolution B-mode ultrasound images obtained over several spaced-apart examinations utilizing a split-screen display in which the arterial ultrasound image from an earlier examination is displayed on one side of the screen while a real-time "live" ultrasound image from a current examination is displayed next to the earlier image on the opposite side of the screen. By viewing both images, whether simultaneously or alternately, while manually adjusting the ultrasound transducer, an operator is able to bring into view the real-time image that best matches a selected image from the earlier ultrasound examination. Utilizing this methodology, dynamic material properties of arterial structures, such as IMT and diameter, are measured in a standard region over successive image frames. Each frame of the sequence has its echo edge boundaries automatically determined by using the immediately prior frame's true echo edge coordinates as initial boundary conditions. Computerized echo edge recognition and tracking over multiple successive image frames enhances measurement of arterial diameter and IMT and allows for improved vascular dimension measurements, including vascular stiffness and IMT determinations.

Selzer, Robert H.↗
NASA NTRS2010

Global VLBI Observations of Weak Extragalactic Radio Sources: Imaging Candidates to Align the VLBI and Gaia Frames

The space astrometry mission Gaia will construct a dense optical QSO-based celestial reference frame. For consistency between optical and radio positions, it will be important to align the Gaia and VLBI frames (International Celestial Reference Frame) with the highest accuracy. In this respect, it is found that only 10% of the ICRF sources are suitable to establish this link (70 sources), either because most of the ICRF sources are not bright enough at optical wavelengths or because they show extended radio emission which precludes reaching the highest astrometric accuracy. In order to improve the situation, we initiated a multi-step VLBI observational project, dedicated to finding additional suitable radio sources for aligning the two frames. The sample consists of about 450 optically-bright radio sources, typically 20 times weaker than the ICRF sources, which have been selected by cross-correlating optical and radio catalogs. The initial observations, aimed at checking whether these sources are detectable with VLBI, and conducted with the European VLBI Network (EVN) in 2007, showed an excellent 90% detection rate. This paper reports on global VLBI observations carried out in March 2008 to image 105 from the 398 previously detected sources. All sources were successfully imaged, revealing compact VLBI structure for about half of them, which is very promising for the future.

Bourda, Geraldine↗
NASA NTRS2011

Establishing Celestial Reference Frames at Different Ranges of Wavelengths

The current fundamental celestial reference frame is the second realization of the International Celestial Reference Frame (ICRF2) derived from dual frequency VLBI observations at 13/3.6 cm. The ICRF2 catalog includes approximately 3000 compact radio sources, largely quasars, of which 295 defining sources establish the coordinate axes with an accuracy of approximately 10 microarcseconds. More limited catalogs have been developed at 1.2 cm using the VLBA (approximately 300 sources) and at 3.6/0.9 cm using the Deep Space Network (approximately 500 sources), primarily to support spacecraft navigation. Anticipating the prospective Gaia optical catalogue, a set of approximately 400 radio weak but optically bright (V less than or equal to 18) objects is being studied at 13/3.6 cm for the radio-optical frame tie using the high sensitivity of the EVN + VLBA. The Gaia QSO catalog currently has approximately 100,000 defining objects whose morphology and variability are being tabulated. The characteristics, limitations and future development of the various wavelength catalogs will be discussed along with the anticipated radio-optical frame transfer.

Ma, C.↗
NASA NTRS2012

The Lag-Luminosity Relation in the GRB Source-Frame: An Investigation with Swift BAT Bursts

Spectral lag, which is defined as the difference in time of arrival of high and low energy photons, is a common feature in Gamma-ray Bursts (GRBs). Previous investigations have shown a correlation between this lag and the isotropic peak luminosity for long duration bursts. However, most of the previous investigations used lags extracted in the observer-frame only. In this work (based on a sample of 43 Swift long GRBs with known redshifts), we present an analysis of the lag-luminosity relation in the GRB source-frame. Our analysis indicates a higher degree of correlation -0.82+/-0.05 (chance probability of approx 5.5 X 10(exp -5) between the spectral lag and the isotropic peak luminosity, L(sub iso), with a best-fit power-law index of -1.2 +/- 0.2, such that L(sub iso) varies as lag(exp -1.2). In addition, there is an anti-correlation between the source-frame spectral lag and the source-frame peak energy of the burst spectrum, E(sub pk)(1 + z).

Ukwatta, T. N.↗
NASA NTRS2011

The Lag-Luminosity Relation in the GRB Source Frame: An Investigation with Swift BAT Bursts

Spectral lag. which is defined as the difference in time of arrival of high- and low-energy photons. is a common feature in gamma-ray bursts (GRBs). Previous investigations have shown a correlation between this lag and the isotropic peak luminosity for long duration bursts. However. most of the previous investigations used lags extracted in the observer frame only. In this work (based on a sample of 43 Swift long GRBs with known redshifts). we present an analysis of the lag-luminosity relation in the GRB source frame. Our analysis indicates a higher degree of correlation -0.82 +/- 0.05 (chance probability of approx. 5.5 x 10(exp -5) between the spectral lag and the isotropic peak luminosity, L(sub iso). with a best-fitting power-law index of -1.2 +/- 0.2. In addition, there is an anticorrelation between the source-frame spectral lag and the source-frame peak energy of the burst spectrum.

Ukwatta, T. N.↗
NASA NTRS2019

Rest-Frame UV and Optical Emission Line Diagnostics of Ionized Gas Properties: a Test Case in a Star-Forming Knot of a Lensed Galaxy at Z ∼ 1.7

We examine the diagnostic power of rest-frame ultraviolet (UV) nebular emission lines, and compare them to more commonly used rest-frame optical emission lines, using the test case of a single star-forming knot of the bright lensed galaxy RCSGA 032727–132609 at redshift z ∼ 1.7. This galaxy has complete coverage of all the major rest-frame UV and optical emission lines from Magellan/MagE and Keck/NIRSPEC. Using the full suite of diagnostic lines, we infer the physical properties: nebular electron temperature (T(sub e)), electron density (n(sub e)), oxygen abundance (log (O/H), ionization parameter [log (q), and interstellar medium (ISM) pressure (log (P/k)]. We examine the effectiveness of the different UV, optical, and joint UV–optical spectra in constraining the physical conditions. Using UV lines alone we can reliably estimate log (q), but the same is difficult for log (O/H). UV lines yield a higher (∼1.5 dex) log (P/k) than the optical lines, as the former probes a further inner nebular region than the latter. For this comparison, we extend the existing Bayesian inference code IZI, adding to it the capability to infer ISM pressure simultaneously with metallicity and ionization parameter. This work anticipates future rest-frame UV spectral data sets from the James Webb Space Telescope (JWST) at high redshift and from the Extremely Large Telescope (ELT) at moderate redshift.

Acharyya, Ayan↗
NASA NTRS2021

A Comparison of Rest-frame Ultraviolet and Optical Emission-Line Diagnostics in the Lensed Galaxy SDSS J1723+3411 at Redshift z = 1.3293

For the extremely bright lensed galaxy SDSS J1723+3411 at z = 1.3293, we analyze spatially integrated MMT, Keck, and Hubble Space Telescope spectra that fully cover the rest-frame wavelength range of 1400 ̊A to 7200 ̊A. We also analyze near-IR spectra from Gemini that cover Hαfor a portion of the lensed arc. We report fluxes for 42 detected emission lines, and upper limits for an additional22. This galaxy has extreme emission line ratios and high equivalent widths that are characteristic of extreme emission-line galaxies. We compute strong emission line diagnostics from both the rest-frame optical and rest-frame ultraviolet (UV), to constrain physical conditions and test the spectral diagnostics themselves. We tightly determine the nebular physical conditions using the most reliable diagnostics, and then compare to results from other diagnostics. We find disappointing performance from the UV–only diagnostics: they either are unable to measure the metallicity or dramatically under-estimate it; they over-estimate the pressure; and the UV diagnostic of ionization parameter has a strong metallicity dependence in this regime. Based on these results, we suggest that upcoming James Webb Space Telescope(JWST) spectroscopic surveys of galaxies in the reionization epoch should invest the additional integration time to capture the optical [O II] and [O III] emission lines, and not rely solely on the rest-frame UV emission lines. We make available the spectra; they represent one of the highest-quality emission line spectral atlases of star-forming galaxy available beyond the local universe, and will aid planning observations with JWST.

galaxies↗
NASA NTRSDate not supplied

Composable Semantic Frames for Grounding Language in Robot Control Primitives

As robots become increasingly capable of taking on challenging tasks, we want robots to be commanded in intuitive ways. Non-expert users in particular should be able to communicate with robots about task goals. As a result, modes of interaction such as language have gained interest for commanding robots. We present composable semantic frames, which ground commands in robot control primitives by composing high-level commands from lower-level commands. We demonstrate that composable semantic frames allow robots to understand and execute a variety of challenging commands, such as those involving multiple verb meanings, command variations, and compound nouns. The robot quickly processes composable semantic frames and accurately grounds and executes the commanded tasks, demonstrating the power of composable semantic frames for allowing users to intuitively interact with robots.

Emily Sheetz↗
NASA NTRS2023

On More than Two Decades of Celestial Reference Frame VLBI Observations in the Deep South: IVS-CRDS (1995 - 2021)

The International VLBI Service for Geodesy & Astrometry (IVS) regularly provides high-quality data to produce Earth Orientation Parameters (EOP), and for the maintenance and realization of the International Terrestrial and Celestial Reference Frames, ITRF and ICRF. The first iteration of the celestial reference frame (CRF) at radio wavelengths, the ICRF1, was adopted by the International Astronomical Union (IAU) in 1997 to replace the FK5 optical frame. Soon after, the IVS began official operations and in 2009 there was a significant increase in data sufficient to warrant a second iteration of the CRF, ICRF2. The most recent ICRF3, was adopted by the IAU in 2018. However, due to the geographic distribution of observing stations being concentrated in the Northern hemisphere, CRFs are generally weaker in the South due to there being fewer Southern Hemisphere observations. To increase the Southern Hemisphere observations, and the density, precision of the sources, a series of deep South observing sessions was initiated in 1995. This initiative in 2004 became the IVS Celestial Reference Frame Deep South (IVS-CRDS) observing program. This paper covers the evolution of the CRDS observing program for the period 1995 to 2021, details the data products and results, and concludes with a summary of upcoming improvements to this ongoing project.

VLBI↗
NASA NTRS2024

Hierarchical Semantic Frames for Grounding Language in Robot Control Primitives

As robots become increasingly present in human environments, we need robots to be intuitively commanded by and effectively communicate with humans. In particular, non-expert users should be able to communicate task goals with robots. Language emerges as a logical mode of interaction due to its ubiquity in human environments and, more importantly, as the way humans naturally express tasks. Natural language commands present challenges in that robots must reason over ambiguous language probabilistically and reason over commands they may not be able to execute. We present hierarchical semantic frames , which ground commands in robot control primitives through hierarchies that construct high-level commands from lower-level commands. We demonstrate that hierarchical semantic frames allow robots to understand and execute a variety of commands, such as those involving multiple verb meanings, command variations, and compound nouns. The robot quickly processes hierarchical semantic frames and accurately grounds and executes the commanded tasks, demonstrating the power of hierarchical semantic frames for allowing users to intuitively interact with robots.

Emily Sheetz↗
NASA NTRS2024

Improved Mechanical Performance in FDM Cellular Frame Structures through Partial Incorporation of Faces

The utilization of lattice-type cellular architectures has seen a significant increase, owing to their predictable shape and the ability to fabricate templated porous materials through low-cost 3D-printing methods. Frames based on atomic lattice structures such as face-centered cubic (FCC), body-centered cubic (BCC), or simple cubic (SC) have been utilized. In FDM, the mechanical performance has been impeded by stress concentration at the nodes and melt-solidification interfaces arising from layer-by-layer deposition. Adding plates to the frames has resulted in improvements with a concurrent increase in weight and hot-pocket-induced dimensional impact in the closed cells formed. In this paper, we explore compressive performance from the partial addition of plates to the frames of a SC-BCC lattice. Compression testing of both single unit cells and 4 × 4 × 4 lattices in all three axial directions is conducted to examine stress transfer to the nearest neighbor and assess scale-up stress transfer. Our findings reveal that hybrid lattice structure unit cells exhibit significantly improved modulus in the range of 125% to 393%, specific modulus in the range of 13% to 120%, and energy absorption in the range of 17% to 395% over the open lattice. The scaled-up lattice modulus increased by 8% to 400%, specific modulus by 2% to 107%, and energy absorption by 37% to 553% over the lattice frame. Parameters that emerged as key to improved lightweighting.

FDM↗
NASA NTRS2024

Scalability in SLA lattice through lattice orientation and hybrid frame and plate architectures

Lightweighting has been a key goal for engineers and designers, with lattice structures widely explored as the building blocks for structural components. Cellular structure-inspired lattice truss frame designs made of struts, have been extensively studied. All plate-based lattice designs have superior mechanical performance. Limits in scalability occur from formation of closed pockets limiting uv curing in processes like stereolithography (SLA). We examine hybrid frame and plate body-centered cubic-simply cubic (BCC-SC) lattices under compression. Unit cells and scaled up lattice exhibit an increase in yield stress and modulus with the addition of plates. The loading direction on the hybrid frame and plate unit cells affected the magnitude of improvement. Simulations and measurements indicated that the optimal lightweight lattice was determined to be when two plates were placed opposite each other with plates buttressing the struts, inhibiting buckling of the struts aligned with the loading direction. This lattice resulted in 63% improvement in specific modulus, a 137% improvement in specific yield point, and a 360% improvement in specific energy absorption (SEA) and the scaled up 4 × 4 × 4 scaled-up structures, showed a 107%, 148%, and 297% in specific modulus, specific yield point, and SEA, respectively A combined stretching-bending behavior was identified in optimal orientations reflecting the delayed buckling mechanism paired to a rising stress-strain curve past the elastic yield indicating bending resistance. The mass moment of inertia was found to be a key parameter correlating optimum orientation for the same number of plates added to the BCC-SC frame.

Mahan Ghosh↗
NASA NTRS2010

Use of Reference Frames for Interplanetary Navigation at JPL

Navigation of interplanetary spacecraft is typically based on range, Doppler, and differential interferometric measurements made by ground-based telescopes. Acquisition and interpretation of these observations requires accurate knowledge of the terrestrial reference frame and its orientation with respect to the celestial frame. Work is underway at JPL to reprocess historical VLBI and GPS data to improve realizations of the terrestrial and celestial frames. Improvements include minimal constraint alignment, improved tropospheric modeling, better orbit determination, and corrections for antenna phase center patterns.

International Celestial Reference Frame (ICRF)↗