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At least 307 records · Page 17

The Sun Radio Interferometer Space Experiment (SunRISE) Mission

The Sun Radio Interferometer Space Experiment (SunRISE) will provide an entirely new view on particle acceleration and transport in the inner heliosphere by creating the first low radio frequency interferometer in space to localize heliospheric radio emissions. By imaging and determining the location of decametric-hectometric (DH, 0.1 MHz–23 MHz) solar radio bursts, SunRISE will provide key information on particle acceleration mechanisms associated with coronal mass ejections (CMEs) and the magnetic field topology from active regions into interplanetary space. The SunRISE Observatory will consist of six space vehicles in a passive formation, in orbits designed to keep them within approximately 10 km of each other, and flying in a supersynchronous geosynchronous Earth orbit (GEO). Each space vehicle consists of a Solar DH-GNSS payload and a 6U form factor spacecraft. The SunRISE Observatory together with significant ground-based processing, will enable imaging of the Sun in a portion of the spectrum that is blocked by the ionosphere and cannot be observed from Earth. Key aspects that enable this mission are that only position knowledge of the space vehicles is required, not active control, and that the architecture involves a modest amount of on-board processing coupled with significant ground-based processing for navigation, position determination, and science operations. Mission-enabling advances in software-defined radios, GPS navigation and timing, and small spacecraft technologies, developed and flown on the DARPA High Frequency Research (DHFR) and the Community Initiative for Continuing Earth Radio Occultation (CICERO) have made this mission affordable and low-risk. The SunRISE mission will exploit the multiple spacecraft per aperture (MSPA) capability of NASA’s Deep Space Network (DSN), for more efficient data transfers of larger data volumes, and utilize commercial access to space, in which the SunRISE space vehicles will be carried to their target orbit as secondary payloads in conjunction with a larger host spacecraft intended for GEO.

Neilson, Tim↗

UAVSAR Phased Array Aperture

This paper describes the development of a patch antenna array for an L-band repeat-pass interferometric synthetic aperture radar (InSAR) instrument that is to be flown on an unmanned aerial vehicle (UAV). The antenna operates at a center frequency of 1.2575 GHz and with a bandwidth of 80 MHz, consistent with a number of radar instruments that JPL has previously flown. The antenna is designed to radiate orthogonal linear polarizations in order to facilitate fully-polarimetric measurements. Beam-pointing requirements for repeat-pass SAR interferometry necessitate electronic scanning in azimuth over a range of -20degrees in order to compensate for aircraft yaw. Beam-steering is accomplished by transmit/receive (T/R) modules and a beamforming network implemented in a stripline circuit board. This paper, while providing an overview of phased array architecture, focuses on the electromagnetic design of the antenna tiles and associated interconnects. An important aspect of the design of this antenna is that it has an amplitude taper of 10dB in the elevation direction. This is to reduce multipath reflections from the wing that would otherwise be detrimental to interferometric radar measurements. This taper is provided by coupling networks in the interconnect circuits as opposed to attenuating the output of the T/R modules. Details are given of material choices and fabrication techniques that meet the demanding environmental conditions that the antenna must operate in. Predicted array performance is reported in terms of co-polarized and crosspolarized far-field antenna patterns, and also in terms of active reflection coefficient.

Unmanned Aerial Vehicle (UAV)↗

Optical Design of the EXperiment for Cryogenic Large-Aperture Intensity Mapping (EXCLAIM)

This work describes the optical design of the EXperiment for Cryogenic Large-Aperture Intensity Mapping(EXCLAIM). EXCLAIM is a balloon-borne telescope that will measure integrated line emission from carbonmonoxide (CO) at redshiftsz <1 and ionized carbon ([CII]) at redshiftsz= 2.5−3.5 to probe star forma-tion over cosmic time in cross-correlation with galaxy redshift surveys. The EXCLAIM instrument will observeat frequencies of 420–540 GHz using six microfabricated silicon integrated spectrometers with spectral resolv-ing powerR= 512 coupled to kinetic inductance detectors (KIDs). A completely cryogenic telescope cooledto a temperature below 5 K provides low-background observations between narrow atmospheric lines in thestratosphere. Off-axis reflective optics use a 90-cm primary mirror to provide 4.2′full-width at half-maximum(FWHM) resolution at the center of the EXCLAIM band over a field of view of 22.5′. Illumination of the 1.7 Kcold stop combined with blackened baffling at multiple places in the optical system ensures low (<−40 dB) edgeillumination of the primary to minimize spill onto warmer elements at the top of the dewar.

Thomas Essinger-Hileman↗

Overview of the NASA/JPL UAVSAR and Porting to the Global Hawk

UAVSAR has demonstrated the combined Precisions Autopilot coupled with the L-band electronically steered allow for robust repeat pass radar interferometric collections. Science results in the areas of soil moisture, volcanology, solid earth science, glaciology, and ecosystem system science have been achieved using the UAVSAR platform.

Uninhabited Aerial Vehicle Synthetic Aperture Rada↗

Improved Calibration of Modeled Discharge and Storage Change in the Atchafalaya Floodplain Using SAR Interferometry

This study focuses on the feasibility of using SAR interferometry to support 2D hydrodynamic model calibration and provide water storage change in the floodplain. Two-dimensional (2D) flood inundation modeling has been widely studied using storage cell approaches with the availability of high resolution, remotely sensed floodplain topography. The development of coupled 1D/2D flood modeling has shown improved calculation of 2D floodplain inundation as well as channel water elevation. Most floodplain model results have been validated using remote sensing methods for inundation extent. However, few studies show the quantitative validation of spatial variations in floodplain water elevations in the 2D modeling since most of the gauges are located along main river channels and traditional single track satellite altimetry over the floodplain are limited. Synthetic Aperture Radar (SAR) interferometry recently has been proven to be useful for measuring centimeter-scale water elevation changes over the floodplain. In the current study, we apply the LISFLOOD hydrodynamic model to the central Atchafalaya River Basin, Louisiana, during a 62 day period from 1 April to 1 June 2008 using two different calibration schemes for Manning's n. First, the model is calibrated in terms of water elevations from a single in situ gauge that represents a more traditional approach. Due to the gauge location in the channel, the calibration shows more sensitivity to channel roughness relative to floodplain roughness. Second, the model is calibrated in terms of water elevation changes calculated from ALOS PALSAR interferometry during 46 days of the image acquisition interval from 16 April 2008 to 1 June 2009. Since SAR interferometry receives strongly scatters in floodplain due to double bounce effect as compared to specular scattering of open water, the calibration shows more dependency to floodplain roughness. An iterative approach is used to determine the best-fit Manning's n for the two different calibration approaches. Results suggest similar floodplain roughness but slightly different channel roughness. However, application of SAR interferometry provides a unique view of the floodplain flow gradients, not possible with a single gauge calibration. These gradients, allow improved computation of water storage change over the 46-day simulation period. Overall, the results suggest that the use of 2D SAR water elevation changes in the Atchafalaya basin offers improved understanding and modeling of floodplain hydrodynamics.

Jung, Hahn Chul↗

A System for Measuring the Sway of the Vehicle Assembly Building

A system was developed to measure the sway of the Vehicle Assembly Building (VAB) at Kennedy Space Center. This system was installed in the VAB and gathered more than one total year of data. The building movement was correlated with measurements provided by three wind towers in order to determine the maximum deflection of the building during high-wind events. The VAB owners were in the process of obtaining new platforms for use in assembling very tall rockets when analysis of the VAB showed that a high wind could move the building sufficiently that an upper platform might impact a rocket. The problem arises because safety requires a relatively small gap between the platform and the rocket, while a large enough gap is needed to ensure that stacking tolerances prevent contact between the rocket and the platform. This only leaves an inch or two (approximately 2 to 5 cm) of total clearance, so when the analysis showed that more than a couple of inches of motion could occur in a high wind, there was a potential for damaging the rocket. The KSC Applied Physics Laboratory was asked to install a system in the VAB that could measure the motion of the building in high winds to determine the actual building sway. The motion of the VAB roof under wind load was measured optically, and under analysis, it was determined that a relatively large-aperture optical system would be required to reduce diffraction effects to less than a small fraction of an inch (approximately mm) at a distance of 500 ft (≈150 m). A 10-in. (approximately 250 mm) telescope was placed on the floor of the building, looking at the ceiling. On the ceiling, a flat plate with three white LEDs was mounted in an "L" shape, such that the telescope was essentially looking at three stars. Software was written to track the motion of these three points using an image processing system. This provided a better than 1/10-in. (approximately 2.5-mm) 2D measurement faster than once a second. Data was downloaded once a month for comparison with the wind tower data. The system was fully operational and provided enough data to show that the VAB will only move 1 in. (approximately 2.5 cm) at the ceiling under 70-knot winds. Adjustable platforms are not required.

Youngquist, Robert↗

Two-Phase Fluid Flow Properties of Rough Fractures With Heterogeneous Wettability: Analysis With Lattice Boltzmann Simulations

Fractures are conduits for fluid flow in low-permeability geological formations. Multiphase flow properties of fractures are important in natural processes and in engineering applications such as the evaluation of the sealing capacity of caprocks and productivity of hydrocarbon-bearing tight rocks. Investigations of flow and transport through fractures typically focus on the effects of fracture geometric and mechanical factors such as aperture, roughness, and compressibility. The wettability of the fracture surfaces and its influence on microscale interfacial phenomena and macroscale effective transport properties are seldom studied. In this study, we investigated the effect of heterogeneous wetting properties on the displacement of water by supercritical CO2 through a series of lattice Boltzmann method simulations. The results show the evolution of the CO2 plume within a fracture is controlled by both the roughness of the aperture field and the wetting distribution. We combined these factors into a capillary pressure map that can be related to the macroscopic flow behavior of the fracture. We observed that heterogeneous wetting distributions promote the residual trapping of water where lower capillary pressures allowed for isolated water pockets in higher capillary pressure zones. Analysis of fracture unsteady relative permeability shows the effect of wetting on permeability evolution and provides support for the viscous-coupling relative permeability model. Finally, analysis of the steady-state relative permeability and saturation demonstrates a strong correlation between permeability and the standard deviation of the capillary pressure field. Thus, characterizing the distribution of wetting properties of fractures is crucial to understanding multiphase fracture flow and transport properties.

58 GEOSCIENCES↗

FIRST Mirror Review

As part of a JPL-funded effort to develop lightweight telescope technology suitable for far-infrared astronomy, COI designed and fabricated a spherical, f/1, 2-meter aperture prototype primary mirror using solely graphite/resin composite materials. To assess the performance of this technology, optical metrology of the mirror surface was performed from ambient to an intended operational temperature for IR-telescopes of 70K. Testing was performed horizontally in a cryogenic vacuum chamber at Arnold AFB, Tennessee. The test design had to accommodate requirements for rapid and uniform cooling across the optic, passivation of the ambient vibrational environment, and de-coupling of the mirror from the thermal strain of the test stand. An IR-wavelength phase shifting interferometer (PSI) was the primary instrument used to measure the mirror surface. From an initial surface figure of 2.1 microns RMS at ambient, a modest 3.9 microns of additional RMS surface error was induced at 70K. The thermally induced error was dominated by low-order deformations, of the type that could easily be corrected with secondary or tertiary optics. In addition to exceptional thermal stability, the mirror exhibited no measurable hysteresis between both ambient and cryo measurements.

Dodson, Kelly↗

The radiation from apertures in curved surfaces

The geometrical theory of diffraction is extended to treat the radiation from apertures or slots in convex, perfectly-conducting surfaces. It is assumed that the tangential electric field in the aperture is known so that an equivalent, infinitesimal source can be defined at each point in the aperture. Surface rays emanate from this source which is a caustic of the ray system. A launching coefficient is introduced to describe the excitation of the surface ray modes. If the field radiated from the surface is desired, the ordinary diffraction coefficients are used to determine the field of the rays shed tangentially from the surface rays. The field of the surface ray modes is not the field on the surface; hence if the mutual coupling between slots is of interest, a second coefficient related to the launching coefficient must be employed. In the region adjacent to the shadow boundary, the component of the field directly radiated from the source is presented by Fock-type functions. In the illuminated region the incident radiation from the source (this does not include the diffracted field components) is treated by geometrical optics. This extension of the geometrical theory of diffraction is applied to calculate the radiation from slots on elliptic cylinders, spheres and spheroids.

Pathak, P. H.↗

An analysis of the radiation from apertures in curved surfaces by the geometrical theory of diffraction

In this paper the geometrical theory of diffraction is extended to treat the radiation from apertures of slots in convex perfectly conducting surfaces. It is assumed that the tangential electric field in the aperture is known so that an equivalent infinitesimal source can be defined at each point in the aperture. Surface rays emanate from this source which is a caustic of the ray system. A launching coefficient is introduced to describe the excitation of the surface ray modes. If the field radiated from the surface is desired, the ordinary diffraction coefficients are used to determine the field of the rays shed tangentially from the surface rays. The field of the surface ray modes is not the field on the surface; hence if the mutual coupling between slots is of interest, a second coefficient related to the launching coefficient must be employed. In the region adjacent to the shadow boundary, the component of the field directly radiated from the source is represented by Fock-type functions. In the illuminated region the incident radiation from the source (this does not include the diffracted field components) is treated by geometrical optics. This extension of the geometrical theory of diffraction is applied to calculate the radiation from slots on elliptic cylinders, spheres, and spheroids.

Pathak, P. H.↗

CCAT-prime: Designs and status of the first light 280 GHz MKID array and mod-cam receiver

The CCAT-prime project's first light array will be deployed in Mod-Cam, a single-module testbed and first light cryostat, on the Fred Young Submillimeter Telescope (FYST) in Chile's high Atacama desert in late 2022. FYST is a six-meter aperture telescope being built on Cerro Chajnantor at an elevation of 5600 meters to observe at millimeter and submillimeter wavelengths. 1 Mod-Cam will pave the way for Prime-Cam, the primary first generation instrument, which will house up to seven instrument modules to simultaneously observe the sky and study a diverse set of science goals from monitoring protostars to probing distant galaxy clusters and characterizing the cosmic microwave background (CMB). At least one feedhorn-coupled array of microwave kinetic inductance detectors (MKIDs) centered on 280 GHz will be included in Mod-Cam at first light, with additional instrument modules to be deployed along with Prime-Cam in stages. The first 280 GHz detector array was fabricated by the Quantum Sensors Group at NIST in Boulder, CO and includes 3,456 polarization- sensitive MKIDs. Current mechanical designs allow for up to three hexagonal arrays to be placed in each single instrument module. We present details on this first light detector array, including mechanical designs and cold readout plans, as well as introducing Mod-Cam as both a testbed and predecessor to Prime-Cam.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗

Experiment for Cryogenic Large-Aperture Intensity Mapping: Instrument Design

The EXperiment for Cryogenic Large-Aperture Intensity Mapping (EXCLAIM) is a balloon-borne tele-33scope designed to survey star formation in windows from the present to z=3.5. During this time, the rate of star34formation dropped dramatically, while dark matter continued to cluster. EXCLAIM maps the redshifted emission35of singly-ionized carbon lines and carbon monoxide using intensity mapping, which permits a blind and complete36survey of emitting gas through statistics of cumulative brightness fluctuations. EXCLAIM achieves high sensitivity37using a cryogenic telescope coupled to six integrated spectrometers employing kinetic inductance detectors covering38420540GHz with spectral resolving power R=512and angular resolution⇡40. The spectral resolving power and39cryogenic telescope allow the survey to access dark windows in the spectrum of emission from the upper atmosphere.40EXCLAIM will survey305 deg2in the Sloan Digital Sky Survey Stripe 82 field from a conventional balloon flight41in 2023. EXCLAIM will also map several galactic fields to study carbon monoxide and neutral carbon emission as42tracers of molecular gas. Here, we summarize the design phase of the mission.

Eric R Switzer↗

Integrated-magnetic apparatus

Disclosure is made of an integrated-magnetic apparatus, comprising: winding structure for insulatingly carrying at least two generally flat, laterally offset and spaced apart electrical windings of a power converter around an aperture; a core having a flat exterior face, an interior cavity and an un-gapped core-column that is located within the cavity and that passes through the aperture of the winding structure; flat-sided surface carried by the core and forming an interior chamber that is located adjacent to the flat face of the core and forming a core-column that has a gap and that is located within the chamber; and structure, located around the gapped core-column, for carrying a third electrical winding of the power converter. The first two electrical windings are substantially located within the cavity and are adapted to be transformingly coupled together through the core. The third electrical winding is adapted to be inductively coupled through the gapped core-column to the other electrical windings, and is phased to have the magnetic flux passing through the gapped core-column substantially in the same direction as the magnetic flux passing through the un-gapped core-column and to have substantially the same AC components of flux in the gapped core-column and in the un-gapped core-column.

Bloom, Gordon E.↗

Enabling Affordable Communications for the Burgeoning Deep Space Cubesat Fleet

The low costs of development and launch, coupled with new propulsive technologies, have made CubeSats increasingly popular for use in science investigations beyond geosynchronous orbit. As this deep space CubeSat fleet grows in size, the challenge of trying to provide affordable communications for it grows commensurately. The mass, power, and volume constraints inherent to CubeSats limit the antenna size and transmit power that they can use to close the deep space link. As a consequence, CubeSats need to rely more heavily on ground antennas that are characterized by large aperture, low noise temperatures, and relatively high-power transmitters. Such antennas are not in great abundance, nor are they inexpensive to build. For this reason, NASA’s Deep Space Network has been advocating a three-pronged approach to meeting anticipated CubeSat demand: development of simultaneous, shared-beam multi-spacecraft communications capabilities, development of large-antenna cross-support arrangements with other agencies and universities, and development of less uplink-intensive navigation techniques. This paper focuses on the pursuit of simultaneous, shared-beam multi-spacecraft communications capabilities. While the Multiple Spacecraft per Antenna (MSPA) technique has existed for over a decade, it has generally been limited to supporting downlink for just two in-beam spacecraft at a time. This limitation has largely been a function of the number and cost of available receivers. A relatively new technique that potentially overcomes this limitation is Opportunistic MSPA (OMSPA). Instead of relying on additional receivers, OMSPA makes use of a digital recorder at each ground station that is capable of capturing the intermediate frequency (IF) signals from every spacecraft in the antenna beam within the frequency bands of interest. When CubeSat projects see one or more opportunities for their CubeSat(s) to intercept the traditionally scheduled antenna beam of a “host” spacecraft, they can arrange for the CubeSat(s) to transmit open loop during those opportunities. Via a secure Internet site, the CubeSat mission operators can then retrieve the time- and frequency-relevant portions of the digital recording for subsequent demodulation and decoding, or subscribe to a service that does it for them. This “opportunistic” use of a host spacecraft’s ground antenna beam potentially enables CubeSat projects to make use of large ground antennas for downlink without having to compete with bigger, better-funded missions for antenna time in the formal scheduling process. In so doing, it also potentially enables CubeSat projects to avoid the aperture fees associated with formally scheduled downlink time - fees that factor into the “bottom-line” of competitively-bid NASA missions and that actually get charged to non-NASA missions. Taking advantage of these potential OMSPA benefits, however, will require CubeSat projects to pursue mission designs that ensure at least periodic in-beam operations relative to a “host” spacecraft. In the case of a constellation of CubeSats with inter-spacecraft distances that do not extend outside of the beam-width of the desired ground antenna at the given range, one CubeSat can serve as the “host” and have a formally scheduled downlink while the rest of the CubeSats can downlink essentially for “free” via OMSPA. Deep space CubeSats, of course, will need uplink in addition to downlink. Beyond commanding, this need is driven by the use of two-way ranging and Doppler for navigation. While OMSPA may not directly facilitate uplink, it does have the potential to free up antennas for those spacecraft that periodically require formally scheduled links for commanding and two-way radio metrics. NASA is also exploring the physical feasibility of an in-beam, simultaneous multi-spacecraft uplink technique. As with OMSPA, if successful, it will require little new equipment, further enabling affordable deep space CubeSat communications.

Abraham, Douglas S.↗

Collection of Light From an Optical Fiber With a Numerical Aperture Greater Than One

In an optical fiber having NA greater than 1, light may be internally reflected when it strikes the fiber end at a fiber-air interface. This problem may be overcome by modification of the fiber by reverse tapering the core. Light is redirected by the taper to strike the interface at an angle closer to normal. This allows light to exit the fiber end that would by internally reflected in an untapered fiber of NA greater than 1. The novelty of the present invention lies in the tapering of the fiber core for increased through transmission of light. Prior art devices have made use of fiber tapers to achieve mode control or fiber coupling. The problem of internal reflection has not been addressed as it is one that is not as important in fibers having NA less than 1, which are more common. In chemical sensing it is advantageous to make use of fibers having higher NA due to an increased sensitivity. However the advantages in sensitivity are diminished due to the loss of signal at the fiber-air interface. The present invention overcomes the problem of loss at the interface, thus facilitating the use of high NA fibers for chemical sensing.

Egalon, Claudio O.↗

Simulating Fracture Sealing by Granular LCM Particles in Geothermal Drilling

Lost circulation occurs when the returned fluid is less than what is pumped into the well due to loss of fluid to pores or fractures. A lost-circulation event is a common occurrence in a geothermal well. Typical geothermal reservoirs are often under-pressured and have larger fracture apertures. A severe lost-circulation event is costly and may lead to stuck pipe, well instability, and well abandonment. One typical treatment is adding lost-circulation materials (LCMs) to seal fractures. Conventional LCMs fail to properly seal fractures because their mechanical limit is exceeded at elevated temperatures. In this paper, parametric studies in numerical simulations are conducted to better understand different thermal effects on the sealing mechanisms of LCMs. The computational fluid dynamics (CFDs) and the discrete element method (DEM) are coupled to accurately capture the true physics of sealing by granular materials. Due to computational limits, the traditional Eulerian–Eulerian approach treats solid particles as a group of continuum matter. With the advance of modern computational power, particle bridging is achievable with DEM to track individual particles by modeling their interactive forces between each other. Particle–fluid interactions can be modeled by coupling CFD algorithms. Fracture sealing capability is investigated by studying the effect of four individual properties including fluid viscosity, particle size, friction coefficient, and Young’s modulus. It is found that thermally degraded properties lead to inefficient fracture sealing.

15 GEOTHERMAL ENERGY↗

A New GaAs Laser Radar for Atmospheric Measurements

A special GaAs lidar using fiber coupled diode lasers was constructed for the purpose of measuring the extinction coefficient distribution within a large atmospheric volume at a rate compatible with atmospheric kinematics. The technique is based on taking backscatter signature ratios over spatial increments after the returns are normalized by pulse integration. Essential aspects of the lidar design are beam pulse power, repetition rate, detection system dynamic range and decay linearity. It was necessary to preclude the possibility of eye hazard under any operating conditions, including directly viewing the emitting aperture at close distance with a night-adapted eye. The electronic signal processing and control circuits were built to allow versatile operations. Extinction coefficient measurements were made in fog and clouds using a low-power laboratory version of the lidar, demonstrating feasibility. Data are presented showing range squared corrected backscatter profiles converted to extinction coefficient profiles, temporal signal fluctuations, and solar induced background noise. These results aided in the design of the lidar which is described. Functional tests of this lidar and the implications relevant to the design of a prototype model are discussed. This work was jointly sponsored by Sperry Rand Corporation under its Independent Research and Development program; the Air Force Avionics Laboratory, Wright Field, Dayton, Ohio; and the Naval Ammunition Depot, Crane, Indiana.

Brown, R. T.↗

The Experiment for Cryogenic Large-aperture Intensity Mapping (EXCLAIM)

Submillimeter and far-IR spectroscopy provides insight into galaxy evolution through measurement of atomic and molecular line emission. The EXperiment for Cryogenic Large-Aperture Intensity Mapping (EXCLAIM) is a cryogenic balloon-borne instrument designed to carry out intensity mapping to measure the cumulative redshifted line emission from carbon monoxide and singly-ionized carbon to probe star formation in windows from the present to z=3.5. During this time, the rate of star formation dropped dramatically, while dark matter continued to cluster. Intensity mapping permits a blind and complete survey of emitting gas through statistics of cumulative brightness fluctuations. EXCLAIM achieves high sensitivity using a cryogenic telescope coupled to six integrated spectrometers with spectral resolving power R=512 and employing microwave kinetic inductance detectors. Here we summarize the status of the mission.

Maryam Rahmani↗