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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 181 records · Page 10
All sourcesNASA NTRSDOE OSTI
NASA NTRS2018

Exploration of Double Clad Fibers for Increased Stability of Bidirectional Free Space Optical Links

Bidirectional, high data rate, low size, weight, and power (SWaP), and low cost free space optical links are needed for space communication applications to send and receive large volumes of data. We are exploring design strategies for optical transceivers to reduce SWaP and cost through increased misalignment tolerance (pointing requirement reduction) and sharing the optical transmit and receive paths (imposing optical symmetry). In applications where the detector is fiber coupled, the fiber numerical aperture is the main driver of the pointing accuracy requirement. Unfortunately, reducing the pointing requirement by increasing the fiber numerical aperture symmetrically causes instability in received power over small environmental changes. This paper explores double clad fibers as a solution to both reduce the power instability and increase the pointing accuracy tolerance. Double clad fibers can transmit a Gaussian beam from a single mode fiber and receive in a multi-mode aperture. Results show that double clad fiber have an improved misalignment tolerance and a higher stability for small changes in temperature when compared to single mode fibers and multimode fibers. Also, double clad fibers are shown to match the performance of an asymmetrical link design with a single mode transmit fiber and a multimode receive fiber.

Double Clad fibers↗
NASA NTRS2018

Exploration of Double Clad Fibers for Increased Stability of Bidirectional Free Space Optical Links

Bidirectional, high data rate, low size, weight, and power (SWaP), and low cost free space optical links are needed for space communication applications to send and receive large volumes of data. We are exploring design strategies for optical transceivers to reduce SWaP and cost through increased misalignment tolerance (pointing requirement reduction) and sharing the optical transmit and receive paths (imposing optical symmetry). In applications where the detector is fiber coupled, the fiber numerical aperture is the main driver of the pointing accuracy requirement. Unfortunately, reducing the pointing requirement by increasing the fiber numerical aperture symmetrically causes instability in received power over small environmental changes. This paper explores double clad fibers as a solution to both reduce the power instability and increase the pointing accuracy tolerance. Double clad fibers can transmit a Gaussian beam from a single mode fiber and receive in a multi-mode aperture. Results show that double clad fiber have an improved misalignment tolerance and a higher stability for small changes in temperature when compared to single mode fibers and multimode fibers. Also, double clad fibers are shown to match the performance of an asymmetrical link design with a single mode transmit fiber and a multimode receive fiber.

Double Clad fibers↗
NASA NTRS2019

System and Method for Training of State-Classifiers

Method and systems are disclosed for training state-classifiers for classification of cognitive state. A set of multimodal signals indicating physiological responses of an operator are sampled over a time period. A depiction of operation by the operator during the time period is displayed. In response to user input selecting a cognitive state for a portion of the time period, the one or more state-classifiers are trained. In training the state-classifiers, the set of multimodal signals sampled in the portion of the time period are used as input to the one or more state-classifiers and the selected one of the set of cognitive states is used as a target result to be indicated by the one or more state-classifiers.

Stephens, Chad L.↗
NASA NTRS2015

The Structure, Anharmonic Vibrational Frequencies, and Intensities of NNHNN+

A semi-global potential energy surface (PES) and quartic force field (QFF) based on fitting high-level electronic structure energies are presented to describe the structures and spectroscopic properties of NNHNN+. The equilibrium structure of NNHNN+ is linear with the proton equidistant between the two nitrogen groups and thus of D(sub ∞h) symmetry. Vibrational second-order perturbation theory (VPT2) calculations based on the QFF fails to describe the proton “rattle” motion, i.e., the antisymmetric proton stretch, due to the very flat nature of PES around the global minimum, but performs properly for other modes with sharper potential wells. Vibrational self-consistent field/virtual state configuration interaction (VSCF/VCI) calculations using a version of MULTIMODE without angular momentum terms successfully describe this motion and predict the fundamental to be at 759 cm(exp -1). This is in good agreement with the value of 746 cm(exp -1) from a fixed-node diffusion Monte Carlo calculation and the experimental Ar-tagged result of 743 cm(exp -1). Other VSCF/VCI energies are in good agreement with other experimentally reported ones. Both double-harmonic intensity and rigorous MULTIMODE intensity calculations show the proton transfer fundamental has a very strong intensity.

Astrochemistry↗
NASA NTRS2020

Measurements of few-mode fiber photonic lanterns in emulated atmospheric conditions for a low earth orbit space to ground optical communication receiver application

Photonic lanterns are being evaluated as a component of a scalable photon counting real-time optical ground receiver for space-to-ground photon-starved communication applications. The function of the lantern as a component of a receiver is to efficiently couple and deliver light from the atmospherically distorted focal spot formed behind a telescope to multiple small-core fiber-coupled single-element super-conducting nanowire detectors. This architecture solution is being compared to a multimode fiber coupled to a multi-element detector array. This paper presents a set of measurements that begins this comparison. This first set of measurements are a comparison of the throughput coupling loss at emulated atmospheric conditions for the case of a 60 cm diameter telescope receiving light from a low earth orbit satellite. The atmospheric conditions are numerically simulated at a range of turbulence levels using a beam propagation method and are physically emulated with a spatial light modulator. The results show that for the same number of output legs as the single-mode fiber lantern, the few-mode fiber lantern increases the power throughput up to 3.92 dB at the worst emulated atmospheric conditions tested of D/r(sub 0)=8.6. Furthermore, the coupling loss of the few-mode fiber lantern approaches the capability of a 30 micron graded index multimode fiber chosen for coupling to a 16 element detector array.

Tedder, Sarah A.↗
NASA NTRS2020

Measurements of Few-Mode Fiber Photonic Lanterns in Emulated Atmospheric Conditions for a Low Earth Orbit Space to Ground Optical Communication Receiver Application

Photonic lanterns are being evaluated as a component of a scalable photon counting real-time optical ground receiver for space-to-ground photon-starved communication applications. The function of the lantern as a component of a receiver is to efficiently couple and deliver light from the atmospherically distorted focal spot formed behind a telescope to multiple small-core fiber-coupled single-element super-conducting nanowire detectors. This architecture solution is being compared to a multimode fiber coupled to a multi-element detector array. This paper presents a set of measurements that begins this comparison. This first set of measurements are a comparison of the throughput coupling loss at emulated atmospheric conditions for the case of a 60 cm diameter telescope receiving light from a low earth orbit satellite. The atmospheric conditions are numerically simulated at a range of turbulence levels using a beam propagation method and are physically emulated with a spatial light modulator. The results show that for the same number of output legs as the single-mode fiber lantern, the few mode fiber lantern increases the power throughput up to 3.92 dB at the worst emulated atmospheric conditions tested of D/r0=8.6. Furthermore, the coupling loss of the few mode fiber lantern approaches the capability of a 30 micron graded index multimode fiber chosen for coupling to a 16 element detector array.

Tedder, Sarah A.↗
NASA NTRS2020

Learning instrument invariant characteristics for generating high-resolution global coral reef maps

Coral reefs are one of the most biologically complex and diverse ecosystems within the shallow marine environment. Unfortunately, these underwater ecosystems are threatened by a number of anthropogenic challenges, including ocean acidification and warming, overfishing, and the continued increase of marine debris in oceans. This requires a comprehensive assessment of the world's coastal environments, including a quantitative analysis on the health and extent of coral reefs and other associated marine species, as a vital Earth Science measurement. However, limitations in observational and technological capabilities inhibit global sustained imaging of the marine environment. Harmonizing multimodal data sets acquired using different remote sensing instruments presents additional challenges, thereby limiting the availability of good quality labeled data for analysis. In this work, we develop a deep learning model for extracting domain invariant features from multimodal remote sensing imagery and creating high-resolution global maps of coral reefs by combining various sources of imagery and limited hand-labeled data available for certain regions. This framework allows us to generate, for the first time, coral reef segmentation maps at 2-meter resolution, which is a significant improvement over the kilometer-scale state-of-the-art maps. Additionally, this framework doubles accuracy and IoU metrics over baselines that do not account for domain invariance.

Domain Adaptation↗
NASA NTRSDate not supplied

Insertion Loss of a Multi-Plane Light Conversion Device with Few Mode Fiber Outputs Under Atmospheric Conditions

A key challenge of photon counting optical communication is delivering light with atmospherically distorted wavefronts from the telescope to detectors efficiently. When using fiber coupled single photon detectors, the efficiency of the transmittance is constrained by the modes supported by the fiber. The number of modes supported by a fiber depends on the size of the core. The larger the core, the more modes supported. However, commercial off the shelf superconducting nanowire single photon detectors (SNSPDs) are currently limited in area, which limits the core size of the fibers that can efficiently couple to the detectors. To increase the amount of light that can be delivered to the detectors, NASA Glenn Research Center is considering many different fiber/detector architectures. This paper compares insertion loss of the fiber device for two different architectures: • a multi-plane light conversion device to split the light from a 30 µm core diameter fiber into 7 separate, 15 µm core diameter few-mode fibers butt-coupled to 7 single-element SNSPDs, and • a 30 µm core diameter multimode fiber butt-coupled to a 16 multi-element, SNSPD array. The measured insertion loss for each fiber device under emulated atmospheric conditions with D/r0 between 2 and 30 is presented. The multi-plane light conversion device shows a consistent ~1 dB loss more than the multimode fiber. Also presented is the measured uneven power splitting of the multiplane light conversion device, especially at lower D/r0. How this uneven power splitting contributes to system loss called blocking loss is discussed.

Fiber↗
NASA NTRSDate not supplied

Insertion Loss of a Multi-Plane Light Conversion Device with Few Mode Fiber Outputs Under Atmospheric Conditions

A key challenge of photon counting optical communication is delivering light with atmospherically distorted wavefronts from the telescope to detectors efficiently. When using fiber coupled single photon detectors, the efficiency of the transmittance is constrained by the modes supported by the fiber. The number of modes supported by a fiber depends on the size of the core. The larger the core, the more modes supported. However, commercial off the shelf superconducting nanowire single photon detectors (SNSPDs) are currently limited in area, which limits the core size of the fibers that can efficiently couple to the detectors. To increase the amount of light that can be delivered to the detectors, NASA Glenn Research Center is considering many different fiber/detector architectures. This paper compares insertion loss of the fiber device for two different architectures: • a multi-plane light conversion device to split the light from a 30 µm core diameter fiber into 7 separate, 15 µm core diameter few-mode fibers butt-coupled to 7 single-element SNSPDs, • and a 30 µm core diameter multimode fiber butt-coupled to a 16 multi-element, SNSPD array. The measured insertion loss for each fiber device under emulated atmospheric conditions with D/r0 between 2 and 30 is presented. The multi-plane light conversion device shows a consistent ~1 dB loss more than the multimode fiber. Also presented is the measured uneven power splitting of the multiplane light conversion device, especially at lower D/r0. How this uneven power splitting contributes to system loss called blocking loss is discussed.

Multi-plane light conversion device↗
NASA NTRSDate not supplied

Concept-based Analysis of Neural Networks via Vision-Language Models

The analysis of vision-based deep neural networks (DNNs) is highly desirable but it is very challenging due to the difficulty of expressing formal specifications for vision tasks and the lack of efficient verification procedures. In this paper, we propose to leverage emerging multimodal, vision-language, foundation models (VLMs) as a lens through which we can reason about vision models. VLMs have been trained on a large body of images accompanied by their textual description, and are thus implicitly aware of high-level, human-understandable concepts describing the images. We describe a logical specification language Con spec designed to facilitate writing specifications in terms of these concepts. To define and formally check Con spec specifications, we build a map between the internal representations of a given vision model and a VLM, leading to an efficient verification procedure of natural-language properties for vision models. We demonstrate our techniques on a ResNet-based classifier trained on the RIVAL-10 dataset using CLIP as the multimodal model.

Large Vision Language Models↗
NASA NTRS1993

Data Compression and VLSI Implementation

An integrated data compression system is proposed to provide adaptive multimode data compression for an advanced multi-instrument spacecraft payload system that has various source data.

VLSI data compression multimode data compression↗
NASA NTRS2015

A Four-Pole Power-Combiner Design for Far-Infrared and Submillimeter Spectroscopy

The far-infrared and submillimeter portions of the electromagnetic spectrum provide a unique view of the astrophysical processes present in the early universe. Micro-Spec (μ-Spec), a high-efficiency direct-detection spectrometer concept working in the 450–1000-micron wavelength range, will enable a wide range of spaceflight missions that would otherwise be challenging due to the large size of current instruments and the required spectral resolution and sensitivity. This paper focuses on the μ-Spec two-dimensional multimode region, where the light of different wavelengths diffracts and converges onto a set of detectors. A two-step optimization process is used to generate geometrical configurations given specific requirements on spectrometer size, operating spectral range, and performance. The canonically employed focal-plane constraints for the power combiner were removed to probe the design space in its entirety. A new four-stigmatic-point optical design solution is identified and explored for use in far-infrared and submillimeter spectroscopy.

electromagnetic spectrum↗
NASA NTRSDate not supplied

Acquisition of and Access to Research Omics Data

Omics data are essential for understanding the myriad and complex effects of space environments on humans. To assure maximum benefit from these kinds of data, the NASA Human Research Program Data Management Plan stipulates that human omics data should be archived within and accessed through the NASA Life Sciences Portal (NLSP). The NLSP has the capability to acquire and provision access to omics (and other kinds of) research results for individual and ad-hoc groups of subjects at the direction of institutional review boards, or other authorizing bodies or individuals, per institutional, program and investigation-specific policies and procedures. However, because some single-subject omics data, like CT scans and other kinds of large, complex biomedical data, could be used to identify heretofore unknown risks to the subject’s health, or, in certain cases, be used to identify a subject, NASA Policy Directive 7170.1 describes various policies regarding the management of and access to “research genetic testing” data, which includes many kinds of omics data. For example, NPD 7170.1 prohibits access to human research genetic data by NASA personnel who make employment decisions for the subjects from whom the data were obtained. To meet the objective of acquiring research omics data for NLSP in compliance with the policies in NPD 7170.1 and other applicable NASA policies, we designed NOMADS (the NLSP Omics Multimodal Acquisition of Data System), a new component that supports the transfer of large research data files, including research genetic testing data, using one of several different transfer mechanisms. The choice of mechanism is made by the submitter of the data, with guiding information from the system, and is likely to often be determined in large part by the nature and source location of the data. For example, for small files where the source data files are not already stored in a cloud storage system, users are likely to prefer to transfer their data to the NLSP via a web browser. Conversely, for large sets of files already organized and stored in a cloud storage system, users may opt for NOMAD’s cloud-to-cloud transfer method. All omics datasets targeted for the NASA Life Sciences Data Archive must pass a variety of quality checks to ensure data integrity and adherence to the standards defined by the LSDA Data Submission Guidelines (DSG) (see https://nlsp.nasa.gov/explore/lsdahome/datasubmit). These include requirements that data are consistent with open standards established by the omics community. Non-compliant data will not be accepted however archivists are available to advise submitters on how to revise data submissions and re-submit until compliance is achieved. Following compliance with the LSDA DSG, omics data next undergo a variety of additional quality checks to ensure the data meet omics community standards. Domain specific Omics data quality control tools and techniques are continually evolving and linked to the advancements in omics assays utilized and thus, the tools and techniques utilized by the LSDA for data quality control and validation will need to be sustained accordingly. All human omics data will be access controlled according to the policies described above, and requiring IRB approval for any additional access grants once the data are acquired (including access for analysis using the NLSP workspace tools).

Omics↗