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DOE OSTI2022

Simple, passive design for large optical trap arrays for single atoms

We present an approach for trapping cold atoms in a two-dimensional (2D) optical trap array generated with a 4f filtering scheme and custom transmission mask without any active device. The approach can be used to generate arrays of bright or dark traps, or both simultaneously with a single wavelength for forming two-species traps. We demonstrate the design by creating a 2D array of 1225 dark trap sites, where single Cs atoms are loaded into regions of near-zero intensity in an approximately Gaussian profile trap. Moreover, we demonstrate a simple solution to the problem of out-of-focus trapped atoms, which occurs due to the Talbot effect in periodic optical lattices. Using a high power yet low cost spectrally and spatially broadband laser, out-of-focus interference is mitigated, leading to near perfect removal of Talbot plane traps.

74 ATOMIC AND MOLECULAR PHYSICS↗

NASA NTRS1999

Interplanetary Microlaser Transponders

The feasibility of an asynchronous (i.e. independently firing) interplanetary laser transponder, capable of ranging between Earth and Mars and using the automated SLR2000 Satellite Laser Ranging (SLR) system as an Earth base station, has been suggested. Since that time, we have received a small amount of discretionary funding to further explore the transponder concept and to develop and test an engineering breadboard. Candidate operational scenarios for acquiring and tracking the opposite laser terminal over interplanetary distances have been developed, and breadboard engineering parameters were chosen to reflect the requirements of an Earth-Mars link Laboratory tests have been devised to simulate the Earth- Mars link between two independent SLR2000 transceivers and to demonstrate the transfer of range and time in single photon mode. The present paper reviews the concept of the asynchronous microlaser transponder, the transponder breadboard design, an operational scenario recently developed for an asteroid rendezvous, and the laboratory test setup. The optical head of the transponder breadboard fits within a cylinder roughly 15 cm in diameter and 32 cm in length and is mounted in a commercial two axis gimbal driven by two computer-controlled stepper motors which allows the receiver optical axis to be centered on a simulated Earth image. The optical head is built around a small optical bench which supports a 14.7 cm diameter refractive telescope, a prototype 2 kHz SLR2000 microlaser transmitter, a quadrant microchannel plate photomultiplier (MCP/PMT), a CCD array camera, spatial and spectral filters, assorted lenses and mirrors, and protective covers and sun shields. The microlaser is end-pumped by a fiber-coupled diode laser array. An annular mirror is employed as a passive transmit/receive (T/R) switch in an aperture-sharing arrangement wherein the transmitted beam passes through the central hole and illuminates only the central 2.5 cm of the common telescope (adequate to achieve a 10 arcsecond full laser beam divergence) while the receiver uses the remainder of the 14.7 cm aperture. Additional electronic instrumentation includes the diode pump array and associated heat sink and current drivers, rubidium frequency standard, timing distribution module, range gate generator, a recently developed all-digital correlation range receiver, and system computer. Acquisition of the opposite transponder terminal requires a search within a three-dimensional volume determined by the initial pointing uncertainty and a maximum 500 microsecond uncertainty in the laser time of fire at the opposite terminal for totally uncorrelated Earth and spacecraft clocks. The angular search is aided by a sensitive CCD array capable of imaging the Earth, Moon, and surrounding stars within the nominal + 0.5 degree cone of uncertainty associated with the initial pointing of a spacecraft body or microwave communications dish.

Degnan, John J.↗

NASA NTRS1991

The pulse-pair algorithm as a robust estimator of turbulent weather spectral parameters using airborne pulse Doppler radar

The pulse pair method for spectrum parameter estimation is commonly used in pulse Doppler weather radar signal processing since it is economical to implement and can be shown to be a maximum likelihood estimator. With the use of airborne weather radar for windshear detection, the turbulent weather and strong ground clutter return spectrum differs from that assumed in its derivation, so the performance robustness of the pulse pair technique must be understood. Here, the effect of radar system pulse to pulse phase jitter and signal spectrum skew on the pulse pair algorithm performance is discussed. Phase jitter effect may be significant when the weather return signal to clutter ratio is very low and clutter rejection filtering is attempted. The analysis can be used to develop design specifications for airborne radar system phase stability. It is also shown that the weather return spectrum skew can cause a significant bias in the pulse pair mean windspeed estimates, and that the poly pulse pair algorithm can reduce this bias. It is suggested that use of a spectrum mode estimator may be more appropriate in characterizing the windspeed within a radar range resolution cell for detection of hazardous windspeed gradients.

Baxa, Ernest G., Jr.↗

NASA NTRSDate not supplied

STAR-X: Survey and Time-domain Astrophysical Research eXplorer

STAR-X is a MIDEX mission proposed to NASA in December 2021. Comprising an X-ray telescope (XRT) provided by GSFC and MIT, a UV telescope (UVT) provided by the University of Colorado, and a spacecraft (SC) provided by Ball Aerospace, STAR-X is designed to conduct time-domain survey and to respond rapidly to transient events discovered by other observatories such as LIGO, Rubin LSST, Roman WFIRST, and SKA. The key features of the XRT are its excellent PSF (2.5 arc-seconds half-power diameter), large effective area (1,800 cm2 at 1 keV), and large field of view (1 deg2), making it more than an order of magnitude more capable and more sensitive than Chandra and Swift/XRT to conduct survey and to find and study transient sources. The UVT has a 30-cm aperture with 5 filters covering the 160nm to 340nm band, providing simultaneous spectral coverage with the XRT and enabling reverberation mapping of accretion disk geometries around black holes. The SC is highly autonomous and is capable of fast slewing, enabling efficient raster scans and time-domain surveys. In particular, in combination with a state-of-the-art mission operations center at the University of Colorado, the SC can respond to targets of opportunity within 2 hours 90% of the time. With its nearly equatorial low-earth orbit, STAR-X’s telescopes will have low particle background, enabling them to have unprecedented sensitivity for measuring faint diffuse emissions from clusters of galaxies. STAR-X is a timely response to Astro2020’s recommendation for a space-based, sustaining time-domain and multi-messenger program.

William W. Zhang↗

NASA NTRS1988

Digital carrier demodulation for the DSN Advanced Receiver

The digital in-phase and quadrature (I and Q) carrier demodulation for the Deep Space Network's (DSN) Advanced Receiver is described and analyzed. The system provides coherent demodulation for a variety of modulation formats including Binary Phase Shift Keying (BPSK), BPSK with a carrier residual, Quadrature Phase Shift Keying (QPSK), Offset-QPSK (OQPSK), and Minimum Shift Keying (MSK). The focus is on the theory and hardware design of the halfband filters which are the integral part of the demodulator. The underlying theory of the filters is summarized, a breadboard hardware design is described, and a VLSI implementation is proposed which significantly decreases the hardware. A second important problem analyzed is DC-offset in the demodulator. This is a serious problem which translates into bias error in the residual carrier phase detector. The dynamic range of the complex mixer is analyzed using a probabilistic approach. It is deduced that the resulting static phase error is less than 0.2 deg when the ratio of carrier power to noise power in the demodulator input bandwidth is -72 dB or higher. Thus, the static phase error is negligible at a carrier power to noise spectral density of 0 dB-Hz for a 15 MHz bandwidth demodulator.

Sadr, R.↗

NASA NTRS1989

A space qualified thermal imaging system using a Pt Si detector array

EDO Corporation, Barnes Engineering Division designed and constructed a high resolution thermal imaging system on contract to Lockheed for use in the SDI Star Lab. This employs a Pt Si CCD array which is sensitive in the spectral range of 3 to 5 microns. Star Lab will be flown in the Shuttle bay and consists basically of a large, reflecting, tracking telescope with associated sensors and electronics. The thermal imaging system is designed to operate in the focal plane of this telescope. The configuration of the system is illustrated. The telescope provides a collimated beam output which is focussed onto the detector array by a silicon objective lens. The detector array subtends a field of view of 1.6 degrees x 1.22 degrees. A beam switching mirror permits bypassing the large telescope to give a field of 4 degrees x 3 degrees. Two 8 position filter wheels are provided, and background radiation is minimized by Narcissus mirrors. The detector is cooled with a Joule-Thompson cryostat fed from a high pressure supply tank. This was selected instead of a more convenient closed-cycle system because of concern with vibration. The latter may couple into the extremely critical Starlab tracking telescope. The electronics produce a digitized video signal for recording. Offset and responsivity correction factors are stored for all pixels and these corrections are made to the digitized output in real time.

Astheimer, Robert W.↗

NASA NTRS2009

Ultra-high Temperature Emittance Measurements for Space and Missile Applications

Advanced modeling and design efforts for many aerospace components require high temperature emittance data. Applications requiring emittance data include propulsion systems, radiators, aeroshells, heatshields/thermal protection systems, and leading edge surfaces. The objective of this work is to provide emittance data at ultra-high temperatures. MSFC has a new instrument for the measurement of emittance at ultra-high temperatures, the Ultra-High Temperature Emissometer System (Ultra-HITEMS). AZ Technology Inc. developed the instrument, designed to provide emittance measurements over the temperature range 700-3500K. The Ultra-HITEMS instrument measures the emittance of samples, heated by lasers, in vacuum, using a blackbody source and a Fourier Transform Spectrometer. Detectors in a Nicolet 6700 FT-IR spectrometer measure emittance over the spectral range of 0.4-25 microns. Emitted energy from the specimen and output from a Mikron M390S blackbody source at the same temperature with matched collection geometry are measured. Integrating emittance over the spectral range yields the total emittance. The ratio provides a direct measure of total hemispherical emittance. Samples are heated using lasers. Optical pyrometry provides temperature data. Optical filters prevent interference from the heating lasers. Data for Inconel 718 show excellent agreement with results from literature and ASTM 835. Measurements taken from levitated spherical specimens provide total hemispherical emittance data; measurements taken from flat specimens mounted in the chamber provide near-normal emittance data. Data from selected characterization studies will be presented. The Ultra-HITEMS technique could advance space and missile technologies by advancing the knowledge base and the technology readiness level for ultra-high temperature materials.

Rogers, Jan↗

NASA NTRS1990

Spacelab qualified infrared imager for microgravity science applications

The Lewis Research Center is developing, under contract, a Spacelab (manned module in the Space Shuttle payload bay) qualified infrared imager for noncontact surface temperature measurement in the Surface Tension Driven Convection Experiment, a microgravity fluid physics experiment. A versatile design philosophy was used in order to provide other experiments with essentially an off the shelf Shuttle qualified instrument, eliminating the duplication of the rigorous development and flight qualification processes. An Inframetrics Model 600 Scanning Infrared Radiometer is being modified to satisfy both experimental and flight requirements, while maintaining the basic performance parameters of the commercial instrument. The modifications include an efficient, low power closed cycle cryogenic cooler to cool the detector, a ruggedized scanner mechanism, 8 bit A/D conversion, Mil-STD components (where possible), size and weight optimization, and the addition of a microprocessor to perform automatic gain control. Features such as detector spectral response, the addition of spectral filters, and target temperature ranges could easily be changed to make this instrument useful as both a qualitative and quantitative diagnostic tool for Spacelab microgravity experiments, in combustion and fluid physics.

Pline, Alexander D.↗

DOE OSTI2026

Startup regime of high-efficiency tapering-enhanced FEL oscillator

In this paper, we present a design of a high-efficiency high-gain free-electron laser oscillator based on the use of a strongly tapered undulator for extracting energy from high-brightness electron beams. We provide an analytical model of the setup followed by numerical simulations for lasing at the wavelength of 13.5 nm. We discuss the optimization of the system in steady state and the conditions necessary for the pass-per-pass buildup of the power from shot noise level. We propose the use of fast phase shifters as a way to accelerate the buildup. Finally, we present time-dependent simulations of the oscillator and discuss the role of spectral filtering. The optimized working point yields a total energy conversion efficiency from the electron beam to output radiation above 1% at the wavelength of 13.5 nm.

Beam dynamics↗

NASA NTRS1992

Spectral analysis for automated exploration and sample acquisition

Future space exploration missions will rely heavily on the use of complex instrument data for determining the geologic, chemical, and elemental character of planetary surfaces. One important instrument is the imaging spectrometer, which collects complete images in multiple discrete wavelengths in the visible and infrared regions of the spectrum. Extensive computational effort is required to extract information from such high-dimensional data. A hierarchical classification scheme allows multispectral data to be analyzed for purposes of mineral classification while limiting the overall computational requirements. The hierarchical classifier exploits the tunability of a new type of imaging spectrometer which is based on an acousto-optic tunable filter. This spectrometer collects a complete image in each wavelength passband without spatial scanning. It may be programmed to scan through a range of wavelengths or to collect only specific bands for data analysis. Spectral classification activities employ artificial neural networks, trained to recognize a number of mineral classes. Analysis of the trained networks has proven useful in determining which subsets of spectral bands should be employed at each step of the hierarchical classifier. The network classifiers are capable of recognizing all mineral types which were included in the training set. In addition, the major components of many mineral mixtures can also be recognized. This capability may prove useful for a system designed to evaluate data in a strange environment where details of the mineral composition are not known in advance.

Eberlein, Susan↗

DOE OSTI2021

On-chip spectrometers using stratified waveguide filters

We present an ultra-compact single-shot spectrometer on silicon platform for sparse spectrum reconstruction. It consists of 32 stratified waveguide filters (SWFs) with diverse transmission spectra for sampling the unknown spectrum of the input signal and a specially designed ultra-compact structure for splitting the incident signal into those 32 filters with low power imbalance. Each SWF has a footprint less than 1 µm × 30,µm, while the 1 × 32 splitter and 32 filters in total occupy an area of about 35 µm × 260 µm, which to the best of our knowledge, is the smallest footprint spectrometer realized on silicon photonic platform. Experimental characteristics of the fabricated spectrometer demonstrate a broad operating bandwidth of 180 nm centered at 1550 nm and narrowband peaks with 0.45 nm Full-Width-Half-Maximum (FWHM) can be clearly resolved. This concept can also be implemented using other material platforms for operation in optical spectral bands of interest for various applications.

42 ENGINEERING↗

DOE OSTI2023

A matched-filter approach to radio variability and transients: searching for orphan afterglows in the VAST Pilot Survey

Radio transient searches using traditional variability metrics struggle to recover sources whose evolution time-scale is significantly longer than the survey cadence. Motivated by the recent observations of slowly evolving radio afterglows at gigahertz frequency, we present the results of a search for radio variables and transients using an alternative matched-filter approach. We designed our matched-filter to recover sources with radio light curves that have a high-significance fit to power-law and smoothly broken power-law functions; light curves following these functions are characteristic of synchrotron transients, including ‘orphan’ gamma-ray burst afterglows, which were the primary targets of our search. Applying this matched-filter approach to data from Variables and Slow Transients Pilot Survey conducted using the Australian SKA Pathfinder, we produced five candidates in our search. Subsequent Australia Telescope Compact Array observations and analysis revealed that: one is likely a synchrotron transient; one is likely a flaring active galactic nucleus, exhibiting a flat-to-steep spectral transition over 4 months; one is associated with a starburst galaxy, with the radio emission originating from either star formation or an underlying slowly evolving transient; and the remaining two are likely extrinsic variables caused by interstellar scintillation. The synchrotron transient, VAST J175036.1–181454, has a multifrequency light curve, peak spectral luminosity, and volumetric rate that is consistent with both an off-axis afterglow and an off-axis tidal disruption event; interpreted as an off-axis afterglow would imply an average inverse beaming factor $\langle f^{-1}_{\text{b}} \rangle = 860^{+1980}_{-710}$, or equivalently, an average jet opening angle of $\langle \theta _{\textrm {j}} \rangle = 3^{+4}_{-1}\,$ deg.

79 ASTRONOMY AND ASTROPHYSICS↗

NASA NTRS2001

Beagle 2: The Next Exobiology Mission to Mars

Beagle 2 is a 60 kg probe (with a 30 kg lander) developed in the United Kingdom for inclusion on the European Space Agency's 2003 Mars Express. Beagle 2 will deliver to the Martian surface a payload which consists of a high percentage of science instruments to landed spacecraft mass. Beagle 2 will be launched in June, 2003 with Mars Express on a Soyuz-Fregat rocket from the Baikonur Cosmodrome in Kazakhstan. Beagle 2 will land on Mars on December 26, 2003 in the Isidis Planitia basin (approximately 10 degrees N and 275 degrees W), a large sedimentary basin that overlies the boundary between ancient highlands and northern plains. Isidis Planitia, the third largest basin on Mars, which is possibly filled with sediment deposited at the bottom of long-standing lakes or seas, offers an ideal environment for preserving traces of life. Beagle 2 was developed to search for organic material and other volatiles on and below the surface of Mars in addition to the study of the inorganic chemistry and mineralogy. Beagle 2 will utilize a mechanical mole and grinder to obtain samples from below the surface, under rocks and inside rocks. A pair of stereo cameras will image the landing site along with a microscope for examination of surface and rock samples. Analyses will include both rock and soil samples at various wavelengths, X-ray spectrometer and Mossbauer spectrometer as well as a search for organics and other light element species (e.g. carbonates and water) and measurement of their isotopic compositions. Beagle 2 has as its focus the goal of establishing whether evidence for life existed in the past on Mars at the Isidis Planitia site or at least establishing if the conditions were ever suitable. Carbonates and organic components were first recognized as existing on Mars when they were found in the Martian meteorite Nakhla. Romanek et al showed the carbonates in ALH84001 were formed at low temperatures. McKay et al noted possible evidence of early life on Mars within the ALH84001 meteorite. Thomas-Keprta et al showed the magnetite biomarkers in ALH84001's carbonates are indistinguishable from those formed by magnetotactic bacteria found on Earth. Gibson et al showed there was significant evidence for liquid water and biogenic products present on Mars across a 3.9 billion year period. A mechanical arm (PAW) operates from the lander and is used for science operations along with sample acquisition. Instruments attached to the PAW include: stereo cameras, Mossbauer instrument, X-ray fluorescence instrument, microscope, environmental sensors, rock corer/grinder, a spoon, mirror, brushes, a mole attachment for acquisition of subsurface to depths of 1 to 2 meters and an illumination device. Each camera has 14 filters which have been optimized for mineralogy composition, dust and water vapor detection. The microscope's camera is designed for viewing the size and shape of dust particles, rock surfaces, microfossils, and characteristics of the samples prior to introduction into the gas analysis package (GAP). The camera has a resolution of 4 microns/pixel, features four color capability (red, green, blue and UV (ultraviolet) fluoresence), a depth of focus of 40 micrometers and translation stage of +3 millimeters. The heart of the Beagle 2's life detection package is the gas analysis package (GAP), which consists of a mass spectrometer with collectors at fixed masses for precise isotopic ratio measurements and voltage scanning for spectral analysis. Primary aim of the GAP is to search for the presence of bulk constituents, individual species, and isotopic fractionations for both extinct and extent life along with studying the low-temperature geochemistry of the hydrogen, carbon, nitrogen and oxygen components on Mars from both the surface and atmosphere. GAP is a magnetic sector mass spectrometer with the range of 1 to 140 amu which can be operated in both the static and dynamic modes. A triple Faraday collector array will be used for C, N and O ratios along with a double Faraday array for H/D. Pulse counting electron multiplier will be utilized for noble gases and selected organics. Anticipated detection limits are at the picomole level for operation in the static mode of operation and high precision isotopic measurements will be made in the dynamic mode. Sample processing and preparation system consists of reaction vessels along with references. Sample ovens capable of being heated are attached to the manifold for sample combustion. Surface, subsurface materials and interior rock specimens will be combusted in pure oxygen gas at various temperature intervals to release organic matter and volatiles. Combustion process will permit detection of all forms and all atoms of carbon present in the samples. A chemical processing system is capable of a variety of conversion reactions. Gases are manipulated either by cryogenic or chemical reactions and passed through the gas handling portion of the vacuum system. There are two modes of operation: quantitative analysis and precise isotopic measurements. Additional information is contained in the original extended abstract.

Gibson, Everett K., Jr.↗

DOE OSTI2025

Broadband Infrared Carbon Nanotube Linear Photodetector Arrays

Carbon nanotubes (CNTs) possess exceptional optoelectronic properties, including broadband absorption and high absorption coefficients, making them promising candidates for photodetector applications. However, conventional designs often rely on single or aligned nanotubes, which restrict device scalability and require complex fabrication techniques. Here, in this work, we address these limitations by utilizing CNT-suspended solutions to fabricate large-area photodetectors based on CNT networks via vacuum filtration and direct laser scribing. CNT networks are uniformly formed onto low-thermal-conductance polymeric filter papers that serve as substrates and mitigate the need for suspended structures, reducing the fabrication complexity and cost. The CNT films are patterned into single devices and 49-pixel linear arrays by using a laser-cutting process, enabling scalable and cost-effective production. The resulting devices operate as bolometers and exhibit broad spectral sensitivity extending from visible to midwave infrared, showing stable operation at room temperature. We further demonstrate proof-of-concept IR imaging using linear arrays.

IR imaging↗

NASA NTRS1992

An atlas of selected calibrated stellar spectra

Five hundred and fifty six stars in the IRAS PSC-2 that are suitable for stellar radiometric standards and are brighter than 1 Jy at 25 microns were identified. In addition, 123 stars that meet all of our criteria for calibration standards, but which lack a luminosity class were identified. An approach to absolute stellar calibration of broadband infrared filters based upon new models of Vega and Sirius due to Kurucz (1992) is presented. A general technique used to assemble continuous wide-band calibrated infrared spectra is described and an absolutely calibrated 1-35 micron spectrum of alpha(Tau) is constructed and the method using new and carefully designed observations is independently validated. The absolute calibration of the IRAS Low Resolution Spectrometer (LRS) database is investigated by comparing the observed spectrum of alpha(Tau) with that assumed in the original LRS calibration scheme. Neglect of the SiO fundamental band in alpha(Tau) has led to the presence of a specious 'emission' feature in all LRS spectra near 8.5 microns, and to an incorrect spectral slope between 8 and 12 microns. Finally, some of the properties of asteroids that effect their utility as calibration objects for the middle and far infrared region are examined. A technique to determine, from IRAS multiwaveband observations, the basic physical parameters needed by various asteroid thermal models that minimize the number of assumptions required is developed.

Walker, Russell G.↗

NASA NTRS2023

2023 Astrophotonics Roadmap: Pathways to Realizing Multi-Functional Integrated Astrophotonic Instruments

Photonic technologies offer numerous functionalities that can be used to realize astrophotonic instruments. The most spectacular example to date is the ESO Gravity instrument at the Very Large Telescope in Chile that combines the light-gathering power of four 8 m telescopes through a complex photonic interferometer. Fully integrated astrophotonic devices stand to offer critical advantages for instrument development, including extreme miniaturization when operating at the diffraction-limit, as well as integration, superior thermal and mechanical stabilization owing to the small footprint, and high replicability offering significant cost savings. Numerous astrophotonic technologies have been developed to address shortcomings of conventional instruments to date, including for example the development of photonic lanterns to convert from multimode inputs to single mode outputs, complex aperiodic fiber Bragg gratings to filter OH emission from the atmosphere, complex beam combiners to enable long baseline interferometry with for example, ESO Gravity, and laser frequency combs for high precision spectral calibration of spectrometers. Despite these successes, the facility implementation of photonic solutions in astronomical instrumentation is currently limited because of (1) low throughputs from coupling to fibers, coupling fibers to chips, propagation and bend losses, device losses, etc, (2) difficulties with scaling to large channel count devices needed for large bandwidths and high resolutions, and (3) efficient integration of photonics with detectors, to name a few. In this roadmap, we identify 24 key areas that need further development. We outline the challenges and advances needed across those areas covering design tools, simulation capabilities, fabrication processes, the need for entirely new components, integration and hybridization and the characterization of devices. To realize these advances the astrophotonics community will have to work cooperatively with industrial partners who have more advanced manufacturing capabilities. With the advances described herein, multi-functional integrated instruments will be realized leading to novel observing capabilities for both ground and space based platforms, enabling new scientific studies and discoveries.

astrophotonics↗

NASA NTRS2008

[The Extrasolar Planetary Imaging Coronagraph]

The Extrasolar Planetary Imaging Coronagraph (EPIC) is a proposed NASA Exoplanet Probe mission to image and characterize extr asolar giant planets in orbits with semi-major axes between 2 and 10 AU. EPIC will provide insights into the physical nature of a variety of planets in other solar systems complimenting radial velocity (RV) and astrometric planet searches. It will detect and characterize the atmospheres of planets identified by radial velocity surveys, deter mine orbital inclinations and masses, characterize the atmospheres around A and F type stars which cannot be found with RV techniques, and observe the inner spatial structure and colors of debris disks. EPIC has a heliocentric Earth trailing drift-away orbit, with a 5 year mission lifetime (5 year goal). The robust mission design is simple and flexible ensuring mission success while minimizing cost and risk. The science payload consists of a heritage optical telescope assembly (OTA), and visible nulling coronagraph (VNC) instrument. The instrument achieves a contrast ratio of 10(exp 9) over a 4.84 arcsecond field-of-view with an unprecedented inner working angle of 0.14 arcseconds over the spectral range of 440-880 nm. The telescope is a 1.65 meter off-axis Cassegrain with an OTA wavefront error of /9, which when coupled to the VNC greatly reduces the requirements on the large scale optics, compressing them to stability requirements within the relatively compact VNC optical chain. The VNC features two integrated modular nullers, a spatial filter array (SFA) and an E2V-L3 photon counting CCD. Direct null control is accomplished from the science focal plane mitigating against complex wavefront and amplitude sensing and control strategies.

Clampin, Mark↗

NASA NTRS2009

Motion Cueing Algorithm Modification for Improved Turbulence Simulation

Atmospheric turbulence cueing produced by flight simulator motion systems has been less than satisfactory because the turbulence profiles have been attenuated by the motion cueing algorithms. Cardullo and Ellor initially addressed this problem by directly porting the turbulence model output to the motion system. Reid and Robinson addressed the problem by employing a parallel aircraft model, which is only stimulated by the turbulence inputs and adding a filter specially designed to pass the higher turbulence frequencies. There have been advances in motion cueing algorithm development at the Man-Machine Systems Laboratory, at SUNY Binghamton. In particular, the system used to generate turbulence cues has been studied. The Reid approach, implemented by Telban and Cardullo, was employed to augment the optimal motion cueing algorithm installed at the NASA LaRC Simulation Laboratory, driving the Visual Motion Simulator. In this implementation, the output of the primary flight channel was added to the output of the turbulence channel and then sent through a non-linear cueing filter. The cueing filter is an adaptive filter; therefore, it is not desirable for the output of the turbulence channel to be augmented by this type of filter. The likelihood of the signal becoming divergent was also an issue in this design. After testing on-site it became apparent that the architecture of the turbulence algorithm was generating unacceptable cues. As mentioned above, this cueing algorithm comprised a filter that was designed to operate at low bandwidth. Therefore, the turbulence was also filtered, augmenting the cues generated by the model. If any filtering is to be done to the turbulence, it will utilize a filter with a much higher bandwidth, above the frequencies produced by the aircraft response to turbulence. The authors have developed an implementation wherein only the signal from the primary flight channel passes through the nonlinear cueing filter. This paper discusses three new algorithms. Testing shows that the new methods provide the pilot with a more realistic sensation of turbulence; the cues are not attenuated by algorithm. Results of offline testing show the credibility of the models. Offline test verification was based primarily on the evaluation of the power spectral density of the outputs and the time response.

Ercole, Anthony V.↗