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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 361 records · Page 20
All sourcesNASA NTRSDOE OSTI
NASA NTRS2001

Considerations and Architectures for Inter-Satellite Communications in Distributed Spacecraft Systems

This paper will identify the important characteristics and requirements necessary for inter-satellite communications in distributed spacecraft systems and present analysis results focusing on architectural and protocol comparisons. Emerging spacecraft systems plan to deploy multiple satellites in various "distributed" configurations ranging from close proximity formation flying to widely separated constellations. Distributed spacecraft configurations provide advantages for science exploration and operations since many activities useful for missions may be better served by distributing them between spacecraft. For example, many scientific observations can be enhanced through spatially separated platforms, such as for deep space interferometry. operating multiple distributed spacecraft as a mission requires coordination that may be best provided through inter-satellite communications. For example, several future distributed spacecraft systems envision autonomous operations requiring relative navigational calculations and coordinated attitude and position corrections. To conduct these operations, data must be exchanged between spacecraft. Direct cross-links between satellites provides an efficient and practical method for transferring data and commands. Unlike existing "bent-pipe" relay networks supporting space missions, no standard or widely-used method exists for cross-link communications. Consequently, to support these future missions, the characteristics necessary for inter-satellite communications need to be examined. At first glance, all of the missions look extremely different. Some missions call for tens to hundreds of nano-satellites in constant communications in close proximity to each other. Other missions call for a handful of satellites communicating very slowly over thousands to hundreds of thousands of kilometers. The paper will first classify distributed spacecraft missions to help guide the evaluation and definition of cross-link architectures and approaches. Based on this general classification, the paper will examine general physical layer parameters, such as frequency bands and data rates, necessary to support the missions. The paper will also identify classes of communication architectures that may be employed, ranging from fully distributed to centralized topologies. Numerous factors, such as number of spacecraft, must be evaluated when attempting to pick a communications architecture. Also important is the stability of the formation from a communications standpoint. For example, do all of the spacecraft require equal bandwidth and are spacecraft allowed to enter and leave a formation? The type of science mission being attempted may also heavily influence the communications architecture. In addition, the paper will assess various parameters and characteristics typically associated with the data link layer. The paper will analyze the performance of various multiple access techniques given the operational scenario, requirements, and communication topologies envisioned for missions. This assessment will also include a survey of existing standards and their applicability for distributed spacecraft systems. An important consideration includes the interoperability of the lower layers (physical and data link) examined in this paper with the higher layer protocols(network) envisioned for future space internetworking. Finally, the paper will define a suggested path, including preliminary recommendations, for defining and developing a standard for intersatellite communications based on the classes of distributed spacecraft missions and analysis results.

Edwards, Bernard↗
NASA NTRS2016

Recent Experiments Conducted with the Wide-Field Imaging Interferometry Testbed (WIIT)

The Wide-field Imaging Interferometry Testbed (WIIT) was developed at NASA's Goddard Space Flight Center to demonstrate and explore the practical limitations inherent in wide field-of-view double Fourier (spatio-spectral) interferometry. The testbed delivers high-quality interferometric data and is capable of observing spatially and spectrally complex hyperspectral test scenes. Although WIIT operates at visible wavelengths, by design the data are representative of those from a space-based far-infrared observatory. We used WIIT to observe a calibrated, independently characterized test scene of modest spatial and spectral complexity, and an astronomically realistic test scene of much greater spatial and spectral complexity. This paper describes the experimental setup, summarizes the performance of the testbed, and presents representative data.

Leisawitz, David T.↗
NASA NTRS2017

Community Exoplanet Follow-up Program

During the Kepler mission, our team provided the community with the highest resolution images available anywhere of exoplanet host stars. Using speckle interferometry on the 3.5-m WIYN, and 8-m Gemini telescopes, thousands of observations have been obtained reaching the diffraction limit of the telescope. From these public data available at the NASA Exoplanet Archive, numerous publications have resulted and many scientific results have been obtained for exoplanets including the fact that high-resolution imaging is critical to fully characterize the planet host stars and the planets themselves (e.g., planet radius and incident flux). Exoplanet host star observations have also occurred (and continue) for K2 mission candidates with archival data available as well. Observational programs for TESS candidates, WFIRST program stars, and Zodiacal light candidates are currently on-going. Availability to propose or obtain such observations are possible through 1) collaboration with our team, 2) successfully proposing to WIYN or GEMINI for telescope time, or 3) using publically available archival data. This poster will highlight the observational program, how time is allocated and how our queue observational program works, and new features and observational modes that are available now.

Exoplanet↗
NASA NTRS2020

TOI 564 b and TOI 905 b: Grazing and Fully Transiting Hot Jupiters Discovered by TESS

We report the discovery and confirmation of two new hot Jupiters discovered by the Transiting Exoplanet Survey Satellite(TESS): TOI 564 b and TOI 905 b. The transits of these two planets were initially observed by TESS with orbital periods of 1.651 and 3.739 days, respectively. We conducted follow-up observations of each system from the ground, including photometry in multiple filters, speckle interferometry, and radial velocity measurements. For TOI 564 b, our global fitting revealed a classical hot Jupiter with a mass of-+1.4630.0960.10MJand a radius of-+1.020.290.71RJ. Also a classical hot Jupiter, TOI 905 b has a mass of-+0.6670.0410.042MJand radius of-+1.1710.0510.053RJ. Both planets orbit Sun-like, moderately bright, mid-G dwarf stars with V11. While TOI 905 b fully transits its star, we found that TOI 564 b has a very high transit impact parameter of-+0.9940.0490.083, making it one of only∼20 known systems to exhibit a grazing transit and one of the brightest host stars among them. Therefore, TOI 564 b is one of the most attractive systems to search for additional nontransiting, smaller planets by exploiting the sensitivity of grazing transits to small changes in inclination and transit duration over a timescale of several years.

Exoplanet astronomy↗
NASA NTRS1987

Meteor observation by the Kyoto meteor radar

The Kyoto Meteor Radar is a monostatic coherent pulsed Doppler radar operating on the frequency of 31.57 MH. The system is computer controlled and uses radio interferometry for echo height determination. The antenna, an improvement, can be directed either to the north or the east. The system has been continuously collecting data on winds at meteor heights by radar observation. The meteor echo rate was also measured, the echo rate distribution with height and the daily variation in height integrated echo rate are discussed. Investigations of atmospheric tides are being pursued by cooperative observations. A novel approach to the study of gravity waves was attempted using the meteor radar which is able to detect the horizontal propagation of the waves by observing the changing phase through the region illuminated by the radar.

Kato, Susumu↗
DOE OSTI2021

Entanglement Enabled Intensity Interferometry of different wavelengths of light

Highlights: • We use quantum entanglement to erase the color of photons for a new imaging method. • Can achieve higher resolution imaging by accessing hidden phase information. • We detail practical experimental designs to implement our theoretical protocols. We propose methods to perform intensity interferometry of photons having two different wavelengths. Distinguishable particles typically cannot interfere with each other, but we overcome that obstacle by processing the particles via entanglement and projection so that they lead to the same final state at the detection apparatus. Specifically, we discuss how quasi-phase-matched nonlinear crystals can be used to convert a quantum superposition of light of different wavelengths onto a common wavelength, while preserving the phase information essential for their meaningful interference. We thereby gain access to a host of new observables, which can probe subtle frequency correlations and entanglement. Further, we generalize the van Cittert–Zernike formula for the intensity interferometry of extended sources, demonstrate how our proposal supports enhanced resolution of sources with different spectral character, and suggest potential applications.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
NASA NTRS1987

Short baseline phase delay interferometry

The high precision of the phase delay data type allows angular navigation accuracy on relatively short baselines to compete with the angular accuracy achieved with long baseline group delay measurements. Differential phase delay observations of close quasar pairs on both a 5.9-km baseline (DSS 12-DSS 13) and a 253-km baseline (DSS 13-Owens Valley Radio Observatory) have been performed to study the potential navigational precision and accuracy of the short baseline interferometry. As a first step toward demonstration of a connected element system at Goldstone, the DSS 12-DSS 13 baseline was operated coherently, distributing a common frequency reference via a recently installed fiber optic cable. The observed phase delay residuals of about 10 psec or less on both baselines appear to be dominated by short term troposphere fluctuations, and correspond to navigational accuracies of well below 50 nrad for the 253-km baseline. Additional experiments will be required to probe the full range of systematic errors.

Edwards, C. D.↗
NASA NTRS2008

Interferometry on a Balloon; Paving the Way for Space-based Interferometers

Astronomical studies at infrared wavelengths have dramatically improved our understanding of the universe, and observations with Spitzer, the upcoming Herschel mission, and SOFIA will continue to provide exciting new discoveries. The relatively low angular resolution of these missions, however, is insufficient to resolve the physical scale on which mid-to-far-infrared emission arises, resulting in source and structure ambiguities that limit our ability to answer key science questions. Interferometry enables high angular resolution at these wavelengths- a powerful tool for scientific discovery. We will build the Balloon Experimental Twin Telescope for Infrared Interferometry (BETTII), an eight-meter baseline Michelson stellar interferometer to fly on a high-altitude balloon. BETTII's spectral-spatial capability, provided by an instrument using double-Fourier techniques, will address key questions about the nature of disks in young star clusters and active galactic nuclei and the envelopes of evolved stars. BETTII will also lay the technological groundwork for future space interferometers.

Rinehart, Stephen A.↗
NASA NTRS2003

Nonlinear Observers for Gyro Calibration

High precision estimation and control algorithms, to achieve unprecedented levels of pointing accuracy, will be required to support future formation flying missions such as interferometry missions. Achieving high pointing accuracy requires precise knowledge of the spacecraft rotation rate. Typically, the rotation rate is measured by a gyro. The measured rates can be corrupted by errors in alignment and scale factor, gyro biases, and noise. In this work, we present nonlinear observers for gyro calibration. Nonlinear observers are superior to extended or pseudo-linear Kalman filter type approaches for large errors and global stability. Three nonlinear gyro calibration observers are developed. The first observer estimates a constant gyro bias. The second observer estimates scale factor errors. The third observer estimates the gyro alignment for three orthogonal gyros. The convergence properties of all three observers are discussed. Additionally, all three observers are coupled with a nonlinear control algorithm. The stability of each of the resulting closed loop systems is analyzed. The observers are then combined, and the gyro calibration parameters are estimated simultaneously. The stability of the combined observers is addressed, as well as the stability of the resulting closed loop systems. Simulated test results are presented for each scenario. Finally, the nonlinear observers are compared to a pseudo-linear Kalman filter.

Thienel, Julie↗
NASA NTRS2002

Keck interferometer update

The Keck Interferometer is a NASA-funded joint development between JPL and the W. M. Keck Observatory. The first phase of the project combines the two 10-m Keck Telescopes for high sensitivity near-infrared fringe visibility measurements, nulling interferometry at 10 pm to measure the quantity of exozodiacal emission around nearby stars, and differential-phase measurements to detect hot Jupiters by their direct emission. First fringes with the interferometer were obtained in March 200 1 using the two Kecks with their A 0 systems. Subsequent engineering work been focusedtoward the visibility mode in the areas of improving sensitivity, increasing automation, and adding functionality, in preparation for the high-precision modes. Recently four shared-risk teams were selected by NASA to participate in early science observations, and initial shared-risk science observations have begun.

Keck↗
NASA NTRS1988

Speckle interferometry of asteroids. IV - Reconstructed images of 4 Vesta

The images of 4 Vesta obtained by means of speckle interferometric observations on November 16 and 17, 1983, support a 5-hr 20.5-min rotational period. The 4 Vesta visible light curve was approximately matched by the placing of circular 'spots' with 135-km diameter over the three dark and three bright features, followed by the assigning of albedos of 0 to the dark spots and 2 to the bright. The light curve is found to be primarily defined by albedo structure, rather than shape; this results in one maximum and one minimum/rotation, rather than the two of each that would be associated with 4 Vesta's triaxial ellipsoid morphology.

Drummond, J.↗
NASA NTRS1993

Navigation of space VLBI missions: Radioastron and VSOP

In the mid-1990s, Russian and Japanese space agencies will each place into highly elliptic earth orbit a radio telescope consisting of a large antenna and radio astronomy receivers. Very long baseline interferometry (VLBI) techniques will be used to obtain high resolution images of radio sources observed by the space and ground based antennas. Stringent navigation accuracy requirements are imposed on the space VLBI missions by the need to transfer an ultra-stable ground reference frequency standard to the spacecraft and by the demands of the VLBI correlation process. Orbit determination for the mission will be the joint responsibility of navigation centers in the U.S., Russia, and Japan with orbit estimates based on combining tracking data from NASA, Russian, and Japanese sites. This paper describes the operational plans, the inter-agency coordination, and data exchange between the navigation centers required for space VLBI navigation.

Ellis, Jordan↗
NASA NTRS2018

Conceptual Ideas for Radio Telescope on the Far Side of the Moon

A radio telescope on the far-side of the Moon has tremendous advantages compared to Earth-based telescopes because it could observe the universe at wavelengths that are hitherto poorly explored by humans so far and the Moon acts as a physical shield that isolates the telescope from the radio interference and noises from Earth. This paper presents a novel concept for building a radio telescope on the far-side of the Moon. The main idea is to shape a suitable existing lunar crater (1 − 50km in diameter) on the far-side of the Moon into a spherical reflecting dish. The proposed Lunar Crater Radio Telescope (LCRT) would be able to observe the universe in the 5 − 100m wavelength band (i.e., 3 − 60MHz radio frequency band). The key innovations of this concept are: (1) LCRT would be the largest filled-aperture radio telescope in the Solar System. (2) LCRT could potentially make tremendous scientific discoveries in fields of cosmology and extrasolar planets by observing the universe in the 5−100m λ band(i.e., 3−60MHz ν band) that has been hitherto poorly explored. (3) It would require only a few robots from Earth and autonomously modify an existing lunar crater to build the LCRT; thereby significantly reducing launch weight and cost compared to all previous lunar surface telescope mission concepts. (4) Furthermore, the Earth based robots are not consumed during construction of LCRT. Therefore, they could create a network of LCRTs to (i) observe different regions of the universe, and (ii) enable lunar Very-Long-Baseline Interferometry (VLBI) astronomy. We envisage that this concept would unlock the potential for groundbreaking scientific discoveries in radio astronomy.

Rahmani, Amir↗
NASA NTRS2023

First Observations With A Gnss Antenna to Radio Telescope Interferometer

We describe the design of a radio interferometer composed of a Global Navigation Satellite Systems (GNSS) antenna and a Very Long Baseline Interferometry radio telescope. Our eventual goal is to use this interferometer for geodetic applications including local tie measurements. The GNSS element of the interferometer uses a unique software-defined receiving system and modified commercial geodetic-quality GNSS antenna. We ran three observing sessions in 2022 between a 25 m radio telescope in Fort Davis, Texas (FD-VLBA), a transportable GNSS antenna placed within 100 m, and a GNSS antenna placed at a distance of about 9 km. We have detected a strong interferometric response with a Signal-to-Noise Ratio (SNR) of over 1,000 from Global Positioning System and Galileo satellites. We also observed natural radio sources including Galactic supernova remnants and Active Galactic Nuclei located as far as one gigaparsec, thus extending the range of sources that can be referenced to a GNSS antenna by 18 orders of magnitude. These detections represent the first observations made with a GNSS antenna to radio telescope interferometer. We have developed a novel technique based on a Precise Point Positioning solution of the recorded GNSS signal that allows us to extend integration time at 1.5 GHz to at least 20 min without any noticeable SNR degradation when a rubidium frequency standard is used.

Geodesy↗
NASA NTRS2004

Space Interferometry Mission Science Overview

Conclusions: SIM is on track for a launch in 2010. Project 'Phase C' start in October 2005. SIM is a flexibly-pointed instrument Astrometric capability (wide angle) a) 4 pas parallax precision on targets down to V = 20 = Stellar and Galactic astrophysics; and b) 1 pas single measurement accuracy. Sensitive to terrestrial-mass planets around the nearest stars New proposal opportunities are: a) AO-2 for new (large) Key projects - 2005; and b) General Observer program, for smaller proposals - 2006.

planet searching↗