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All sourcesNASA NTRSDOE OSTI
NASA NTRS2003

Neural-Net Based Optical NDE Method for Structural Health Monitoring

This paper answers some performance and calibration questions about a non-destructive-evaluation (NDE) procedure that uses artificial neural networks to detect structural damage or other changes from sub-sampled characteristic patterns. The method shows increasing sensitivity as the number of sub-samples increases from 108 to 6912. The sensitivity of this robust NDE method is not affected by noisy excitations of the first vibration mode. A calibration procedure is proposed and demonstrated where the output of a trained net can be correlated with the outputs of the point sensors used for vibration testing. The calibration procedure is based on controlled changes of fastener torques. A heterodyne interferometer is used as a displacement sensor for a demonstration of the challenges to be handled in using standard point sensors for calibration.

Decker, Arthur J.↗
NASA NTRS1995

TIMED Doppler Interferometer

The Timed Doppler Interferometer (TIDI) will accurately and precisely determine the global vector MLTI (Mesosphere and Lower Thermosphere) wind, temperature, and density profiles. It will measure characteristics of the gravity wave and planetary wave spectra. The tidal characteristics of temperature, density, and wind in the MLTI will be determined. The neutral and ion winds will be measured to characterize the electrodynamical behavior of the MLTI. Oxygen and O2 abundances and nocticulent cloud activity will be measured. This review goes into the calibration and error sources, optical design, mechanisms design, detector design, electronics design, microprocessor and flight software design, and quality assurance and parts.

Killeen, Timothy L.↗
NASA NTRS1993

An Imaging Interferometer for Terrestrial Remote Sensing

A prototype imaging interferometer called DASI (digital array scanned interferometer) is under development at our laboratories. Our objective is to design an instrument for remote sensing of Earth's atmosphere and surface. This paper describes the unusual characteristics of DASIs which make them promising candidates for ground and aircraft-based terrestrial measurements. These characteristics include superior signal-to-noise, design simplicity and compactness, relative to dispersion based imaging spectrometers. Perhaps one of the most notable features of DASIs is their ability to acquire an entire interferogram simultaneously without any moving optical elements. We also describe selected laboratory and ground based field measurements using the prototype DASI. A CCD detector array was placed at the DASI detector plane for wavelength coverage from 0.4 to 1.0 micron. A NICMOS MCT detector was used for coverage from 1.1 to 2.2 micron. The DASI was configured to have a spectral resolution of about 300 1/cm, a spatial field of view of 5 degrees, and a constant number of transverse spatial elements (detector dependent) for each exposure frame. Frame exposure rates were up to 0.6 Hz with the potential to achieve 5 Hz. Image cube measurements of laboratory targets and terrestrial scenes were obtained by multiple frame scanning over the field of view. These data sets reveal the potential science yields from obtaining simultaneous high resolution spatial and spectral information.

Hammer, Philip D.↗
NASA NTRS2008

NASA Tech Briefs, November 2008

Topics covered include: Digital Phase Meter for a Laser Heterodyne Interferometer; Vision System Measures Motions of Robot and External Objects; Advanced Precipitation Radar Antenna to Measure Rainfall From Space; Wide-Band Radar for Measuring Thickness of Sea Ice; Vertical Isolation for Photodiodes in CMOS Imagers; Wide-Band Microwave Receivers Using Photonic Processing; L-Band Transmit/Receive Module for Phase-Stable Array Antennas; Microwave Power Combiner/Switch Utilizing a Faraday Rotator; Compact Low-Loss Planar Magic-T; Using Pipelined XNOR Logic to Reduce SEU Risks in State Machines; Quasi-Optical Transmission Line for 94-GHz Radar; Next Generation Flight Controller Trainer System; Converting from DDOR SASF to APF; Converting from CVF to AAF; Documenting AUTOGEN and APGEN Model Files; Sequence History Update Tool; Extraction and Analysis of Display Data; MRO DKF Post-Processing Tool; Rig Diagnostic Tools; MRO Sequence Checking Tool; Science Activity Planner for the MER Mission; UAVSAR Flight-Planning System; Templates for Deposition of Microscopic Pointed Structures; Adjustable Membrane Mirrors Incorporating G-Elastomers; Hall-Effect Thruster Utilizing Bismuth as Propellant; High-Temperature Crystal-Growth Cartridge Tubes Made by VPS; Quench Crucibles Reinforced with Metal; Deep-Sea Hydrothermal-Vent Sampler; Mars Rocket Propulsion System; Two-Stage Passive Vibration Isolator; Improved Thermal Design of a Compression Mold; Enhanced Pseudo-Waypoint Guidance for Spacecraft Maneuvers; Altimetry Using GPS-Reflection/Occultation Interferometry; Thermally Driven Josephson Effect; Perturbation Effects on a Supercritical C7H16/N2 Mixing Layer; Gold Nanoparticle Labels Amplify Ellipsometric Signals; Phase Matching of Diverse Modes in a WGM Resonator; WGM Resonators for Terahertz-to-Optical Frequency Conversion; Determining Concentration of Nanoparticles from Ellipsometry; Microwave-to-Optical Conversion in WGM Resonators; Four-Pass Coupler for Laser-Diode-Pumped Solid-State Laser; Low-Resolution Raman-Spectroscopy Combustion Thermometry; Temperature Sensors Based on WGM Optical Resonators; Varying the Divergence of Multiple Parallel Laser Beams; Efficient Algorithm for Rectangular Spiral Search; Algorithm-Based Fault Tolerance Integrated with Replication; Targeting and Localization for Mars Rover Operations; Terrain-Adaptive Navigation Architecture; Self-Adjusting Hash Tables for Embedded Flight Applications; Schema for Spacecraft-Command Dictionary; Combined GMSK Communications and PN Ranging; System-Level Integration of Mass Memory; Network-Attached Solid-State Recorder Architecture; Method of Cross-Linking Aerogels Using a One-Pot Reaction Scheme; An Efficient Reachability Analysis Algorithm.

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NASA NTRS2005

NASA Tech Briefs, November 2005

Topics covered include: Laser System for Precise, Unambiguous Range Measurements; Flexible Cryogenic Temperature and Liquid-Level Probes; Precision Cryogenic Dilatometer; Stroboscopic Interferometer for Measuring Mirror Vibrations; Some Improvements in H-PDLCs; Multiple-Bit Differential Detection of OQPSK; Absolute Position Encoders With Vertical Image Binning; Flexible, Carbon-Based Ohmic Contacts for Organic Transistors; GaAs QWIP Array Containing More Than a Million Pixels; AutoChem; Virtual Machine Language; Two-Dimensional Ffowcs Williams/Hawkings Equation Solver; Full Multigrid Flow Solver; Doclet To Synthesize UML; Computing Thermal Effects of Cavitation in Cryogenic Liquids; GUI for Computational Simulation of a Propellant Mixer; Control Program for an Optical-Calibration Robot; SQL-RAMS; Distributing Data from Desktop to Hand-Held Computers; Best-Fit Conic Approximation of Spacecraft Trajectory; Improved Charge-Transfer Fluorescent Dyes; Stability-Augmentation Devices for Miniature Aircraft; Tool Measures Depths of Defects on a Case Tang Joint; Two Heat-Transfer Improvements for Gas Liquefiers; Controlling Force and Depth in Friction Stir Welding; Spill-Resistant Alkali-Metal-Vapor Dispenser; A Methodology for Quantifying Certain Design Requirements During the Design Phase; Measuring Two Key Parameters of H3 Color Centers in Diamond; Improved Compression of Wavelet-Transformed Images; NASA Interactive Forms Type Interface - NIFTI; Predicting Numbers of Problems in Development of Software; Hot-Electron Photon Counters for Detecting Terahertz Photons; Magnetic Variations Associated With Solar Flares; and Artificial Intelligence for Controlling Robotic Aircraft.

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NASA NTRS2005

Laser frequency stabilization for LISA

The requirement on laser frequency noise in the Laser Interferometer Space Antenna (LISA) depends on the velocity and our knowledge of the position of each spacecraft of the interferometer. Currently it is assumed that the lasers must have a pre-stabilized frequency stability of 30Hz/square root of Hz over LISA'S most sensitive frequency band (3 mHz - 30 mHz). The intrinsic frequency stability of even the most stable com- mercial lasers is several orders of magnitude above this level. Therefore it is necessary to stabilize the laser frequency to an ultra-stable frequency reference which meets the LISA requirements. The baseline frequency reference for the LISA lasers are high finesse optical cavities based on ULE spacers. We measured the stability of two ULE spacer cavities with respect to each other. Our current best results show a noise floor at, or below, 30 Hz/square root of Hz above 3 mHz. In this report we describe the experimental layout of the entire experiment and discuss the limiting noise sources.

Mueller, Guido↗
NASA NTRS2016

Flight Phasemeter on the Laser Ranging Interferometer on the GRACE Follow-On Mission

As the first inter-spacecraft laser interferometer, the Laser Ranging Interferometer (LRI) on the GRACE Follow-On Mission will demonstrate interferometry technology relevant to the LISA mission. This paper focuses on the completed LRI Laser Ranging Processor (LRP), which includes heterodyne signal phase tracking at µcycle/vHz precision, differential wavefront sensing, offset frequency phase locking and Pound-Drever-Hall laser stabilization. The LRI design has characteristics that are similar to those for LISA: 1064nm NPRO laser source, science bandwidth in the mHz range, MHz-range intermediate frequency and Doppler shift, detected optical power of tens of picoWatts. Laser frequency stabilization has been demonstrated at a level below 30 Hz/vHz, better than the LISA requirement of 300 Hz/vHz. The LRP has completed all performance testing and environmental qualification and has been delivered to the GRACE Follow-On spacecraft. The LRI is poised to test the LISA techniques of tone-assisted time delay interferometry and arm-locking. GRACE Follow-On launches in 2017.

Bachman, B↗
NASA NTRS2021

Characterizing Deformable Mirrors for the MagAO-X Instrument

The MagAO-X instrument is a new extreme adaptive optics system for high-contrast imaging at visibleand near-infrared wavelengths on the Magellan Clay Telescope. A central component of this system is a 2040-actuatormicroelectromechanical deformable mirror (DM) from Boston Micromachines Corp. that operates at 3.63 kHz forhigh-order wavefront control (the tweeter). Two additional DMs from ALPAO perform the low-order (the woofer)and non-common-path science-arm wavefront correction (the NCPC DM). Prior to integration with the instrument, wecharacterized these devices using a Zygo Verifire Interferometer to measure each DM surface. We present the resultsof the characterization effort here, demonstrating the ability to drive tweeter to a flat of 6.9 nm RMS surface (and 0.56nm RMS surface within its control bandwidth), the woofer to 2.2 nm root mean square (RMS) surface, and the NCPCDM to 2.1 nm RMS surface over the MagAO-X beam footprint on each device. Using focus-diversity phase retrievalon the MagAO-X science cameras to estimate the internal instrument wavefront error (WFE), we further show that theintegrated DMs correct the instrument WFE to 18.7 nm RMS, which, combined with a 11.7% pupil amplitude RMS,produces a Strehl ratio of 0.94 at H↵

Kyle Van Gorkom↗
NASA NTRS2004

An Interferometry Imaging Beauty Contest

We present a formal comparison of the performance of algorithms used for synthesis imaging with optical/infrared long-baseline interferometers. Six different algorithms are evaluated based on their performance with simulated test data. Each set of test data is formated in the interferometry Data Exchange Standard and is designed to simulate a specific problem relevant to long-baseline imaging. The data are calibrated power spectra and bispectra measured with a ctitious array, intended to be typical of existing imaging interferometers. The strengths and limitations of each algorithm are discussed.

aperture synthesis↗
NASA NTRSDate not supplied

Overview of the NASA LISA Laser System Development

NASA Goddard Space Flight Center (GSFC) is developing the Laser System (LS) for the Laser Interferometer Space Antenna (LISA) mission, led by the European Space Agency (ESA) with a launch date of 2035. The LS under development at NASA GSFC consists of the Laser Head (LH), the Frequency Reference System (FRS), and the Power Monitor (PMON) Detector Assemblies. Since late 2017, we have been developing various models to advance the technology readiness level (TRL) for the LH from prototype (TRL4) to a system model demonstration in a relevant environment (TRL6). For the LH and FRS, the models further breakdown into the optical and electronics modules where the LH is made up of the Laser Optical Module (LOM) and the Laser Electronics Module (LEM) and the FRS consists of the FRS Optical Reference Cavity (FRS-O) and the FRS Electronics (FRS-E). The LS development follows the established NASA process in demonstrating the performance requirements [1] through the TRL4 effort and then advancing the form factor and package design to meet relevant environment requirements and qualifying the TRL6 design through rigorous testing and performance verification for space applications. The LOM for the LH is a main oscillator power amplifier (MOPA) with wavelength of 1064 nm and nominal output power of 2 Watt throughout the mission. The low-power, low-noise main oscillator (MO) is a custom micro non-planar ring oscillator (µNPRO) [2] that is phase modulated then amplified by the forward pumped ytterbium-dope fiber power amplifier (PA) stage to meet the output power requirement. The FRS is baselined on the GRACE Follow-On (GFO) [3] approach with updated FRS-E design to work with the LH-LEM. The PMON is located on the Optical Bench Assembly (OBA) [4] that samples a small portion of the LH output signal and provides the feedback signal to the LH-LEM for relative intensity noise (RIN) control. In this paper, we will report on the latest status of the LH testing and system level tests, explain the other subsystems involved in the test campaigns, and discuss the path to bring each LS subsystem to TRL6. We will also present the NASA GSFC roadmap in advancing the LISA LS to TRL6+ and plans for future system level testing as well as the preparation for space flight development to meet the LISA launch date of 2035.

amplifier↗
NASA NTRS2001

Optical metrology for testing an all-composite 2-meter diameter mirror

The Herschel Space Observatory (formerly known as FIRST) consists of a 3.5 m space telescope designed for use in the long IR and sub-milimeter wavebands. To demonstrate the viability of a carbon fiber composite telescope for this application, Composite Optics Incorporated (COI) manufactured a fast (f/1), large (2 m), lightweight (10.1 kg/m squared) demonstration mirror. A key challenge in demonstrating the performance of this novel mirror was to characterize the surface accuracy at cryogenic (70 K) temperatures. A wide variety of optical metrology techniques were investigated and a brief survey of empirical test results and limitations of the various techniques will be presented in this paper. Two complementary infrared (IR)techniques operating at a wavelength of 10.6 microns were chosen for further development: (1) IR Twyman-Green Phase Shifting Interferometry (IR PSI) and (2) IR Shack-Hartmann (IR SH) Wavefront Sensing. Innovative design modifications made to an existing IR PSI to achieve high-resolution, scannable, infrared measurements of the composite mirror are described. The modified interferometer was capable of measuring surface gradients larger than 350 microradians. The design and results of measurements made with a custom-built IR SH Wavefrong Sensor operating at 10.6 microns are also presented. A compact experimental setup permitting simultaneous operation of both the IR PSI and IR SH tools is shown. The advantages and the limitations of the two key IR metrology tools are discussed.

IR metrology phase shifting interferometry Shack-H↗
NASA NTRS2009

Design Enhancements of the Fourier Kelvin Stellar Interferometer to Enable Detection of Earth Twins

During the last few years, considerable effort has been directed towards very large-scale (> $5 billion) missions to detect and characterize Mars-radius to Earth-radius planets around nearby stars; such as the Terrestrial Planet Finder Interferometer and Darwin missions. However, technological issues such as formation flying and control of systematic noise sources will likely prevent these missions from entering Phase A until at least the end of the next decade. Presently more than 350 planets have been discovered by a variety of techniques, and little is known about the majority of them other than their approximate mass. However, a simplified nulling interferometer operating in the near- to mid-infrared (e.g. approx. 5-15 microns), like the enhanced version of the Fourier Kelvin Stellar Interferometer (FKSI), can characterize the atmospheres of a large sample of the known planets - including Earth twins. Many other scientific problems can be addressed with a system like FKSI, including the studies of debris disks, active galactic nuclei, and low mass companions around nearby stars. We report results of a recent engineering study on an enhanced version of FKSI that includes 1-meter primary mirrors, 20-meter boom length, and an advanced sun shield that will provide a 45-degree FOR and 40K operating temperature for all optics including siderostats.

Barry, Richard K.↗
NASA NTRS2013

Control Software for Piezo Stepping Actuators

A control system has been developed for the Space Interferometer Mission (SIM) piezo stepping actuator. Piezo stepping actuators are novel because they offer extreme dynamic range (centimeter stroke with nanometer resolution) with power, thermal, mass, and volume advantages over existing motorized actuation technology. These advantages come with the added benefit of greatly reduced complexity in the support electronics. The piezo stepping actuator consists of three fully redundant sets of piezoelectric transducers (PZTs), two sets of brake PZTs, and one set of extension PZTs. These PZTs are used to grasp and move a runner attached to the optic to be moved. By proper cycling of the two brake and extension PZTs, both forward and backward moves of the runner can be achieved. Each brake can be configured for either a power-on or power-off state. For SIM, the brakes and gate of the mechanism are configured in such a manner that, at the end of the step, the actuator is in a parked or power-off state. The control software uses asynchronous sampling of an optical encoder to monitor the position of the runner. These samples are timed to coincide with the end of the previous move, which may consist of a variable number of steps. This sampling technique linearizes the device by avoiding input saturation of the actuator and makes latencies of the plant vanish. The software also estimates, in real time, the scale factor of the device and a disturbance caused by cycling of the brakes. These estimates are used to actively cancel the brake disturbance. The control system also includes feedback and feedforward elements that regulate the position of the runner to a given reference position. Convergence time for smalland medium-sized reference positions (less than 200 microns) to within 10 nanometers can be achieved in under 10 seconds. Convergence times for large moves (greater than 1 millimeter) are limited by the step rate.

Shields, Joel F.↗
NASA NTRS2019

Transient Astrophysics Probe: White Paper

The Transient Astrophysics Probe (TAP) is a wide-field multi-wavelength transient mission proposed for flight starting in the late 2020s. The mission instruments include unique ``Lobster-eye'' imaging soft X-ray optics that allow an approximately 1600-degrees-squared Field of View (FoV); a high sensitivity, 1-degree-squared FoV soft X-ray telescope; a 1-degree-squared FoV Infrared telescope with bandpass 0.6 to 3 microns; and a set of 8 NaI gamma-ray detectors. TAP's most exciting capability will be the observation of tens per year of X-ray and Infrared counterparts of gravitational waves (GWs) involving stellar-mass black holes and neutron stars detected by LIGO (Laser Interferometer Gravitational-Wave Observatory ) / Virgo / KAGRA (Kamioka (Japan) Gravitational Wave Detector) / LIGO-India, and possibly several per year X-ray counterparts of GWs from supermassive black holes, detected by LISA (Laser Interferometer Space Antenna) and Pulsar Timing Arrays. TAP will also discover hundreds of X-ray transients related to compact objects, including tidal disruption events, supernova shock breakouts, and Gamma-Ray Bursts from the epoch of reionization.

Camp, Jordan↗
NASA NTRS1984

Fuel spray diagnostics

Several laser measurement methods are being studied to provide the capability to make droplet size and velocity measurements under a variety of spray conditions. The droplet sizing interferometer (DSI) promises to be a successful technique because of its capability for rapid data acquisition, compilation and analysis. Its main advantage is the ability to obtain size and velocity measurements in air-fuel mixing studies and hot flows. The existing DSI at NASA Lewis is a two-color, two-component system. Two independent orthogonal measurements of size and velocity components can be made simultaneously. It also uses an off-axis large-angle light scatter detection. The fundamental features of the system are optics, signal processing and data management system. The major component includes a transmitter unit, two receiver units, two signal processors, two data management systems, two Bragg cell systems, two printer/plotters, a laser, power supply and color monitor.

Bosque, M. A.↗
NASA NTRS1998

The Keck Interferometer

The Keck Interferometer is being developed by JPL and CARA as one of the ground-based components of NASA's Origins Program. The interferometer will combine the two 10-m Keck telescopes with four proposed 1.8-m outrigger telescopes located at the periphery of the Keck site on Mauna Kea.

optical↗
NASA NTRS2002

Fabry-Perot Interferometer for Column CO2

Global atmospheric CO2 measurements are essential to resolving significant discrepancies in our understanding of the global carbon budget and, hence, humankind's role in global climate change. The science measurement requirements for CO2 are extremely demanding (precision is less than .3%). No atmospheric chemical species has ever been measured from space with this precision. We are developing a novel application of a Fabry-Perot interferometer to detect spectral absorption of reflected sunlight by CO2 and O2 in the atmosphere. Preliminary design studies indicate that the method will be able to achieve the sensitivity and signal-to-noise detection required to measure column CO2 at the target specification. The objective of this program is to construct a prototype instrument for deployment on an aircraft to test the instrument performance and our ability to retrieve the data in the real atmosphere. To date we have assembled a laboratory bench system to begin testing the optical and electronic components. We are also undertaking some measurements of signal and noise levels for actual sunlight reflecting from the ground in order to evaluate the potential of some components to meet the exacting requirements of this measurement.

Heaps, William S.↗
NASA NTRS2002

Fabry-Perot Interferometer for Column CO2

Global atmospheric CO2 measurements are essential to resolving significant discrepancies in our understanding of the global carbon budget and, hence, humankind's role in global climate change. The science measurement requirements for CO2 are extremely demanding (precision approx. 0.3%). No atmospheric chemical species has ever been measured from space with this precision. We are developing a novel application of a Fabry-Perot interferometer to detect spectral absorption of reflected sunlight by CO2 and O2 in the atmosphere. Preliminary design studies indicate that the method will be able to achieve the sensitivity and signal-to-noise detection required to measure column CO2 at the target specification. The objective of this program is to construct a prototype instrument for deployment on an aircraft to test the instrument performance and our ability to retrieve the data in the real atmosphere. To date we have assembled a laboratory bench system to begin testing the optical and electronic components. We are also measuring signal and noise levels in actual sunlight to evaluate component performance.

Heaps, William S.↗