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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 NTRS2009

Optical Injection Locking of a VCSEL in an OEO

Optical injection locking has been demonstrated to be effective as a means of stabilizing the wavelength of light emitted by a vertical-cavity surface- emitting laser (VCSEL) that is an active element in the frequency-control loop of an opto-electronic oscillator (OEO) designed to implement an atomic clock based on an electromagnetically- induced-transparency resonance. This particular optical-injection- locking scheme is expected to enable the development of small, low-power, high-stability atomic clocks that would be suitable for use in applications involving precise navigation and/or communication. In one essential aspect of operation of an OEO of the type described above, a microwave modulation signal is coupled into the VCSEL. Heretofore, it has been well known that the wavelength of light emitted by a VCSEL depends on its temperature and drive current, necessitating thorough stabilization of these operational parameters. Recently, it was discovered that the wavelength also depends on the microwave power coupled into the VCSEL. Inasmuch as the microwave power circulating in the frequency-control loop is a dynamic frequency-control variable (and, hence, cannot be stabilized), there arises a need for another means of stabilizing the wavelength. The present optical-injection-locking scheme satisfies the need for a means to stabilize the wavelength against microwave- power fluctuations. It is also expected to afford stabilization against temperature and current fluctuations. In an experiment performed to demonstrate this scheme, wavelength locking was observed when about 200 W of the output power of a commercial tunable diode laser was injected into a commercial VCSEL, designed to operate in the wavelength range of 795+/-3 nm, that was generating about 200 microW of optical power. (The use of relatively high injection power levels is a usual practice in injection locking of VCSELs.)

Strekalov, Dmitry↗
NASA NTRS2009

Dynamic Self-Locking of an OEO Containing a VCSEL

A method of dynamic self-locking has been demonstrated to be effective as a means of stabilizing the wavelength of light emitted by a vertical-cavity surface-emitting laser (VCSEL) that is an active element in the frequency-control loop of an optoelectronic oscillator (OEO) designed to implement an atomic clock based on an electromagnetically- induced-transparency (EIT) resonance. This scheme can be considered an alternative to the one described in Optical Injection Locking of a VCSEL in an OEO (NPO-43454), NASA Tech Briefs, Vol. 33, No. 7 (July 2009), page 33. Both schemes are expected to enable the development of small, low-power, high-stability atomic clocks that would be suitable for use in applications involving precise navigation and/or communication. To recapitulate from the cited prior article: In one essential aspect of operation of an OEO of the type described above, a microwave modulation signal is coupled into the VCSEL. Heretofore, it has been well known that the wavelength of light emitted by a VCSEL depends on its temperature and drive current, necessitating thorough stabilization of these operational parameters. Recently, it was discovered that the wavelength also depends on the microwave power coupled into the VCSEL. This concludes the background information. From the perspective that led to the conception of the optical injection-locking scheme described in the cited prior article, the variation of the VCSEL wavelength with the microwave power circulating in the frequency-control loop is regarded as a disadvantage and optical injection locking is a solution of the problem of stabilizing the wavelength in the presence of uncontrolled fluctuations in the microwave power. The present scheme for dynamic self-locking emerges from a different perspective, in which the dependence of VCSEL wavelength on microwave power is regarded as an advantageous phenomenon that can be exploited as a means of controlling the wavelength. The figure schematically depicts an atomic-clock OEO of the type in question, wherein (1) the light from the VCSEL is used to excite an EIT resonance in selected atoms in a gas cell (e.g., 87Rb atoms in a low-pressure mixture of Ar and Ne) and (2) the power supplied to the VCSEL is modulated by a microwave signal that includes components at beat frequencies among the VCSEL wavelength and modulation sidebands. As the VCSEL wavelength changes, it moves closer to or farther from a nearby absorption spectral line, and the optical power transmitted through the cell (and thus the loop gain) changes accordingly. A change in the loop gain causes a change in the microwave power and, thus, in the VCSEL wavelength. It is possible to choose a set of design and operational parameters (most importantly, the electronic part of the loop gain) such that the OEO stabilizes itself in the sense that an increase in circulating microwave power causes the VCSEL wavelength to change in a direction that results in an increase in optical absorption and thus a decrease in circulating microwave power. Typically, such an appropriate choice of operational parameters involves setting the nominal VCSEL wavelength to a point on the shorter-wavelength wing of an absorption spectral line.

Strekalov, Dmitry↗
NASA NTRS2010

Preliminary Human-in-the-Loop Assessment of Procedures for Very-Closely-Spaced Parallel Runways

Demand in the future air transportation system concept is expected to double or triple by 2025 [1]. Increasing airport arrival rates will help meet the growing demand that could be met with additional runways but the expansion airports is met with environmental challenges for the surrounding communities when using current standards and procedures. Therefore, changes to airport operations can improve airport capacity without adding runways. Building additional runways between current ones, or moving them closer, is a potential solution to meeting the increasing demand, as addressed by the Terminal Area Capacity Enhancing Concept (TACEC). TACEC requires robust technologies and procedures that need to be tested such that operations are not compromised under instrument meteorological conditions. The reduction of runway spacing for independent simultaneous operations dramatically exacerbates the criticality of wake vortex incursion and the calculation of a safe and proper breakout maneuver. The study presented here developed guidelines for such operations by performing a real-time, human-in-the-loop simulation using precision navigation, autopilot-flown approaches, with the pilot monitoring aircraft spacing and the wake vortex safe zone during the approach.

Verma, Savita↗
NASA NTRS2013

Project Morpheus: Morpheus 1.5A Lander Failure Investigation Results

On August 9, 2012 the Morpheus 1.5A vehicle crashed shortly after lift off from the Kennedy Space Center. The loss was limited to the vehicle itself which was pre-declared to be a test failure and not a mishap. The Morpheus project is demonstrating advanced technologies for in space and planetary surface vehicles including: autonomous flight control, landing site hazard identification and safe site selection, relative surface and hazard navigation, precision landing, modular reusable flight software, and high performance, non-toxic, cryogenic liquid Oxygen and liquid Methane integrated main engine and attitude control propulsion system. A comprehensive failure investigation isolated the fault to the Inertial Measurement Unit (IMU) data path to the flight computer. Several improvements have been identified and implemented for the 1.5B and 1.5C vehicles.

Devolites, Jennifer L.↗
NASA NTRS2014

High-Fidelity Flash Lidar Model Development

NASA's Autonomous Landing and Hazard Avoidance Technologies (ALHAT) project is currently developing the critical technologies to safely and precisely navigate and land crew, cargo and robotic spacecraft vehicles on and around planetary bodies. One key element of this project is a high-fidelity Flash Lidar sensor that can generate three-dimensional (3-D) images of the planetary surface. These images are processed with hazard detection and avoidance and hazard relative navigation algorithms, and then are subsequently used by the Guidance, Navigation and Control subsystem to generate an optimal navigation solution. A complex, high-fidelity model of the Flash Lidar was developed in order to evaluate the performance of the sensor and its interaction with the interfacing ALHAT components on vehicles with different configurations and under different flight trajectories. The model contains a parameterized, general approach to Flash Lidar detection and reflects physical attributes such as range and electronic noise sources, and laser pulse temporal and spatial profiles. It also provides the realistic interaction of the laser pulse with terrain features that include varying albedo, boulders, craters slopes and shadows. This paper gives a description of the Flash Lidar model and presents results from the Lidar operating under different scenarios.

Hines, Glenn D.↗
NASA NTRS2016

Coherent Doppler Lidar for Measuring Velocity and Altitude of Space and Aerial Vehicles

A coherent Doppler lidar has been developed to support future NASA missions to planetary bodies. The lidar transmits three laser beams and measures line-of-sight range and velocity along each beam using a frequency modulated continuous wave (FMCW) technique. Accurate altitude and velocity vector data, derived from the line-of-sight measurements, enables the landing vehicle to precisely navigate from several kilometers above the ground to the designated location and execute a gentle touchdown. The same lidar sensor can also benefit terrestrial applications that cannot rely on GPS or require surface-relative altitude and velocity data.

Amzajerdian, Farzin↗
NASA NTRS2018

A Performance-Based Comparison of Deep-Space Navigation using Optical-Communication and Conventional Navigation Techniques: Small Body Missions

Optical communications may be used in future NASA deep-space missions, resulting in much higher data transfer rates. Those optical communication links could also be used for navigation purposes. The performance of deep-space navigation for an asteroid flyby mission using ground-based optical tracking and conventional navigation techniques was investigated in this work. We present the results of variety of asteroid flyby scenarios including low phase and high phase approach angle flybys, one slow flyby in a Trojan tour mission, and also one slow flyby in a Psyche mission. In this task, four different types of observables were simulated, namely ground-based radiometric, spacecraft on-board optical, ground-based optical tracking of spacecraft (astrometry and 2-way range magnitude), and ground-based asteroid astrometry. Different combinations of these four types of observables were compared with currently in-practice ground-based radiometric/on-board optical measurements. The results showed that the ground-based optical tracking is promising and could be a potential candidate for future deep-space navigation. Precise astrometry is not possible for active comets.

McCandless, Sara Elizabeth↗
NASA NTRS2018

A Performance-Based Comparison of Deep-Space Navigation using Optical-Communication and Conventional Navigation Techniques: Small Body Missions

Optical communications may be used in future NASA deep-space missions, resulting in much higher data transfer rates. Those optical communication links could also be used for navigation purposes. The performance of deep-space navigation for an asteroid flyby mission using ground-based optical tracking and conventional navigation techniques was investigated in this work. We present the results of variety of asteroid flyby scenarios including low phase and high phase approach angle flybys, one slow flyby in a Trojan tour mission, and also one slow flyby in a Psyche mission. In this task, four different types of observables were simulated, namely ground-based radiometric, spacecraft on-board optical, ground-based optical tracking of spacecraft (astrometry and 2-way range magnitude), and ground-based asteroid astrometry. Different combinations of these four types of observables were compared with currently in-practice ground-based radiometric/on-board optical measurements. The results showed that the ground-based optical tracking is promising and could be a potential candidate for future deep-space navigation. Precise astrometry is not possible for active comets.

McCandless, Sarah Elizabeth↗
NASA NTRSDate not supplied

Digital Elevation Map Parametric Error Analysis Using Corresponding NAC Images

Future lunar landing systems, particularly those used to land humans on the lunar surface aspart of the ARTEMIS program, will require precision navigation relative to the lunar surface. The most common way to meet these stringent navigation require-ments is through terrain relative navigation (TRN), which localizes a spacecraft by comparing descent im-agery with a predefined map of the surface. The accu-racy achievable using TRN is limited by the accuracy of the reference Digital Elevation Map (DEM). It is therefore critical for future lunar missions that potential errors in DEMs be quantified. This paper describes one of NASA’s current efforts to develop a process for evaluating lunar DEM quality.

Chris R Gnam↗
NASA NTRSDate not supplied

Digital Elevation Map Parametric Error Analysis Pipeline using Corresponding NAC Images

Future lunar landing systems, particularly those used to land humans on the lunar surface as part of the ARTEMIS program, will require precision navigation relative to the lunar surface. The most common way to meet these stringent navigation requirements is through terrain relative navigation (TRN), which localizes a spacecraft by comparing descent imagery with a predefined map of the surface. The accuracy achievable using TRN is limited by the accuracy of the reference Digital Elevation Map (DEM). It is therefore critical for future lunar missions that potential errors in DEMs be quantified. This paper describes one of NASA’s current efforts to develop a process for evaluating lunar DEM quality.

Chris Gnam↗
NASA NTRSDate not supplied

A Structurally-Adaptive Framework for Distributed Airborne Sensing over Real-time Collaborative Information Sharing Networks

The emergence and maturation of wireless communication technologies continue to transform the aviation industry and are enabling new solutions to challenges faced by NASA’s Advanced Air Mobility (AAM) initiative. AAM is leading towards high-density autonomous aircraft operations in areas underserved by traditional aviation, such as over densely populated urban centers. In this paper, we build on concepts from distributed sensing and smart spaces - where sensing, processing, and communication are embedded in an environment, and agents are operating within the space can exploit these capabilities in real-time through collaborative information sharing networks. Building from these concepts, we propose a framework to enable a dynamic, topologically-adaptive, and distributed estimation system for man-rated aviation to address challenges faced by autonomous AAM operations. This paper presents the initial concept of operations and system design for this framework, presents a mathematical formulation for abstraction of the problem, identifies requirements and constraints for operation, and presents algorithmic constructs to demonstrate operation. The initial framework design will focus on supporting precision navigation and independent surveillance supporting conformance monitoring of aircraft in airspace corridors and vertiport airspaces. Preliminary results from this framework shows promise in addressing gaps in current technologies needed to enable future AAM concepts, while promising greater capabilities, performance, robustness, and safety over current aviation systems and operations.

Distributed sensing↗
NASA NTRS2022

On-board Absolute Localization Based on Orbital Imagery for a Future Mars Science Helicopter

Future Mars Rotorcraft require advanced navigationcapabilities to enable all terrain access over long distance flightsthat are executed fully autonomously. A critical component toenable precision navigation during long traverses is the abilityto perform on-board absolute localization to eliminate drift inposition estimates of the on-board odometry algorithm. Inthis paper, we present an approach for on-board map-basedlocalization to provide global reference position based on orbitalor aerial image maps. Our approach builds on a vision-basedlocalization method to localize against a map derived fromHiRISE image products – an ortho-projected image (orthoimage) and a corresponding digital elevation map. The mapis pre-computed using a feature-based approach. Features arestored with their 3D world coordinates, and a descriptor to codethe local image intensity information in the vicinity of the featurelocation. An on-board matching algorithm uses this informationto match visual features in a query image acquired during flight,guided by a pose prior from the on-board range-visual-inertialstate estimator (Range-VIO). Valid matches are then used bya perspective-n-point (PnP) algorithm to estimate the absolutepose of the vehicle in a global frame. We demonstrate andevaluate our approach on simulated data, and data from UASflights.

Balaram, J. Bob↗
NASA NTRSDate not supplied

High-Altitude ADS-B/GPS LPV Flight Tests on a NASA ER-2 Research Airplane

The research presented in this paper describes the conceptual design of a system architecture that integrates Automatic Dependent Surveillance-Broadcast (ADS-B) and Global Positioning System (GPS) Localizer Performance Vertical (LPV) guidance technology onto a unique high-altitude research airplane: a United States Air Force (USAF) / Lockheed Martin (Bethesda, Maryland) Aeronautics U-2S airplane. The design features modern display capabilities to provide air-to-air surveillance and precision navigation, to adhere to Federal Aviation Administration (FAA) certification standards for operations in upper Class E airspace. The National Aeronautics and Space Administration (NASA) variant of the U-2S, now called the Earth Resources (ER-2) airplane, remains unrivaled in the art of sustained high-altitude flight for scientific expeditions. Capable of routinely cruising above flight level (FL) 650 that had been considered, at inception, the domain of only the most elite experimental research aircraft types. Nicknamed the Dragon Lady, this U-2S research testbed is still one of the most advanced aircraft in the world. The exceptional military design of the vehicle, security guidelines, and the performance envelope of the ER-2 posed unique challenges to the integration of modern civilian avionics. ADS-B epitomizes the next generation of surveillance technology, incorporating both air and ground aspects. ADS-B provides air traffic control (ATC) with a more accurate picture of the three-dimensional positioning of aircraft in various phases of flight, including en route, terminal, approach, and ground operations. The airborne surveillance system broadcasts its identification, position, altitude, velocity, and other information. GPS LPV represents a significant advancement in aviation technology, emphasizing the pivotal role that GPS and Performance-Based Navigation concepts will play in the foreseeable future. This technology represents a shift from sensor-based navigation to performance-based navigation, allowing for more flexible and efficient use of airspace. This research described herein is structured as follows: Section II, “Systems Background,” provides a systems background and description of an ADS-B and GPS LPV system equipped on the high-altitude ER-2 research airplane to satisfy the FAA airworthiness requirements for high-altitude flight operations. Section III, “Flight Test System,” describes the flight-test airplane systems. Section IV, “Analysis of GPS SBAS, Safety, and Ground Tests,” provides an overview of the GPS Satellite-Based Augmentation System (SBAS) and an analysis of the GPS LPV metrics, safety, and ground tests. Section V, “High-Altitude Flight Tests,” describes the high-altitude flight tests, including 3 flight-test results, analysis, human factors, and lessons learned. Section VI, the conclusion, draws insights from the lessons learned, discusses the design challenges associated with ADS-B and GPS LPV, and showcases the paramount significance of these pivotal technologies in aircraft surveillance and navigation.

Ricardo A. Arteaga↗
NASA NTRSDate not supplied

Automatic Processing of Intensives at GSFC VLBI Analysis Center

VLBI Intensive (INT) sessions are conducted to determine the change in Earth rotation, which is measured as a correction to UT1. This correction varies unpredictably over time. Because UT1 is used in precise navigation, particularly GNSS, rapid turnaround is very important. The decrease of time elapsed from observations to obtained results can be shortened with the automatic data processing of new INT sessions at the analysis stage.

VLBI↗
NASA NTRSDate not supplied

Enabling Smart Urban Airspaces through Distributed Sensing Technologies

Distributed sensing systems offer potential for enhancing safety and efficiency in urban airspaces and low-altitude metropolitan flight corridors. These systems leverage sensor networks to provide real-time airspace monitoring, situational awareness, and data for decision-making. This paper examines application of distributed sensing and smart airspace concepts to enable advanced urban flight, focusing on critical need applications such as airspace monitoring, corridor surveillance, precision navigation, and hazard avoidance. Benefits such as improved monitoring and increased situational awareness of activity within the urban airspace are considered alongside challenges in system design and implementation. This paper summarizes an ongoing effort to study the feasibility and effectiveness of distributed sensing systems for enabling urban airspace operations. Current research and design considerations are summarized, and a proposed roadmap for future work is presented.

Corey A Ippolito↗