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Results for “Very Long Baseline Array Interferometric (VLBI)”

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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8 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS2006

Use of Very Long Baseline Array Interferometric Data for Spacecraft Navigation

The main VLBI technique that is used at JPL is known as the Delta Differential One-way Ranging ((Delta)DOR). Two DSN antennas simultaneously track a source, and alternate between sources. The signals recorded at the antennas from each source are correlated to obtain the delay in arrival to the two antennas, and the delays are differenced to remove common-source errors. An alternative technique is to use carrier phase differences between antennas. This is routinely done by the Very Large Baseline Array (VLBA) as part of source imaging. The VLBA capabilities are used for scientific research, but also have the potential to be used for navigation. Two main experiments were performed with the VLBA and JPL spacecraft. This paper describes and analyzes these experiments and discusses the possible uses of VLBA tracking for spacecraft navigation.

Very Large Baseline Array (VLBA)↗
NASA NTRS2012

The Potential for a Ka-band (32 GHz) Worldwide VLBI Network

Ka-band (32 GHz, 9mm) Very Long Baseline Interferometric (VLBI) networking has now begun and has tremendous potential for expansion over the next few years. Ka-band VLBI astrometry from NASA's Deep Space Network has already developed a catalog of 470 observable sources with highly accurate positions. Now, several antennas worldwide are planning or are considering adding Ka-band VLBI capability. Thus, there is now an opportunity to create a worldwide Ka-band network with potential for high resolution imaging and astrometry. With baselines approaching a Giga-lambda, a Ka-band network would be able to probe source structure at the nano-radian (200 as) level ( 100X better than Hubble) and thus gain insight into the astrophysics of the most compact regions of emission in active galactic nuclei. We discuss the advantages of Ka-band, show the known sources and candidates, simulate projected baseline (uv) coverage, and discuss potential radio frequency feeds. The combination of these elements demonstrates the feasibility of a worldwide Ka network within the next few years!

quasar↗
NASA NTRS1982

VLBI observations of the nucleus and jet of M87

The nucleus and jet of M87 was mapped with an eight-station very long baseline interferometric array at 18 cm wavelength with high dynamic range. It was found that the nucleus of M87 consists of a core-jet structure with a peak brightness temperature greater than 10 to the 10th K. Emission is shown to extend for more than 50 milli-arcsec with a brightness temperature exceeding 10 to the 8th K along a position angle of 288 degrees, which precisely matches the position angle of the 20'' radio/optical/X-ray jet. In addition, the nucleus contains a significant structure of lower brightness at approximately the same position angle, although no counterjet is observed. By invoking relativistic beaming in order to enhance the jet and diminish the counterjet, it is shown that the jet must be aligned within about 60 degrees to our line of sight, and its flow velocity must exceed about 60% of the speed of light. The knots embedded in the 20'' jet contain no bright compact structures, and the sizes of the innermost knot (knot D) is between 0.1-0.3''.

Reid, M. J.↗
NASA NTRS1983

Very-long-baseline radio interferometry - The Mark III system for geodesy, astrometry, and aperture synthesis

Up to 112 megabit/sec from each radio telescope of an interferometric array can be recorded and processed by the Mark III VLBI system. Sample results are given for baseline lengths between three antennas in the U.S. and three in Europe, as well as for the arc lengths between the positions of six extragalactic radio sources. No significant change is detected in any of these quantities. Signals of a given polarization or of pairs of orthogonal polarizations may be recorded in up to 28 contiguous bands, each nearly 2 MHz wide, for mapping the brightness distribution of compact radio sources. The demonstrated ability to record large bandwidths, and to link many large radio telescopes, allows compact sources with flux densities below 1 millijansky to be detected and studied.

Rogers, A. E. E.↗
NASA NTRSDate not supplied

Ultra-Low Noise Laser and Optical Frequency Comb-Based Timing System for the Event Horizon Explorer (EHE) Mission

Very Long Baseline Interferometry (VLBI) requires a highly stable time reference and synchronization system to maintain coherence between observations recorded independently at multiple stations – for example, the array of ground-based radio telescopes that comprise the Event Horizon Telescope (EHT). Instability in the time reference or inaccuracy in the synchronization impacts phase conference and reduces the performance of the VLBI system. For space-based telescopes like the Event Horizon Explorer (EHE) mission, the precision timing system must meet the size, weight, and power (SWaP) constraints of the spacecraft platform and be capable of operating in the space environment. The EHE mission is a proposed extension to the EHT that can improve the angular and time resolution of observations by enabling longer interferometric baselines than are possible on the Earth and sampling a wide range of Fourier spatial frequencies throughout the orbital motion. In this effort, we demonstrate the performance of one option for the EHE mission: the use of a space-qualified, ultra-low noise laser developed as part of the Laser Interferometer Space Antenna (LISA) mission as the timing reference, and an optical frequency comb to transfer the stability of this laser to the microwave regime for instrumentation use. We describe the implementation of the microwave down-conversion, in which the LISA cavity-stabilized laser is locked to a self-referenced optical frequency comb to divide the optical frequency down to 100 MHz. The phase noise of the 100 MHz signal is measured and validated using a phase noise analyzer that is referenced to a separate laboratory ultra-stable laser system. We present the results of this experiment, which demonstrates that the performance of this system meets the EHE requirement: a relative frequency error of 1e-14 from 1 to 30 seconds.

Hannah Tomio↗
NASA NTRS1995

Radio interferometer observations of solar wind turbulence from the orbit of Helios to the solar corona

We report observations of Very Long Baseline Interferometer (VLBI) phase scintillations due to turbulence in the solar wind. The observations were made at 5.00 and 8.42 GHz with the Very Long Baseline Array (VLBA) on three dates in 1991 July and August. We observed the sources 0851 + 202 and 0735 + 178 at solar elongations ranging from 2.66 deg to 13.29 deg; the closest approach of the line of sight to the Sun ranged from 10 to 49.8 solar radii. We have also included previously unpublished 5 GHz VLBI phase scintillation measurements from 1989. These measurements probe solar wind density fluctuations on spatial scales from about 200 km to 2000 km. Our measurements are in quite good agreement with the Coles & Harmon model for the radio phase structure function, which was largely determined from observations on both shorter and larger spatial scales. Departures from the Coles & Harmon functions are attributable to day-to-day variations in the solar wind conditions. Phase scintillations at the greatest solar elongations are in very good agreement with extrapolated estimates from direct measurements made with the Helios spacecraft at slightly larger heliocentric distances. Thus there is a consistency between the in-situ spacecraft and radio sensing measurements of density turbulence. All of the VLBI data are consistent with a Kolmogorov spectrum for the density fluctuations, although at the closest elongations there may be excess power at small spatial scales. An advantage of interferometric techniques over other radio propagation measurements is that they provide a measure of the anisotropy of the irregularities. Our observations at closest approach (10 solar radii) show weak evidence for anisotropic, field-aligned density irregularities with an axial ratio of order 2. This degree of anisotropy would appear to be less than that measured at similar solar elongations but on smaller spatial scales by Armstrong and colleagues. Finally, a combination of the radio propagation data and in situ Helios measurements is used to determine the heliocentric distance dependence of the normalization coefficient of the density power spectrum, C(sup 2)(sub N). Modeling C(sup2)(sub N) varies as (R/solar radii)(sup -Kappa), we find Kappa = 3.72 +/- 0.30. Subject to a number of assumptions, this result is consistent with the conclusion of D. A. Roberts that turbulence within 0.28 astronomical units adheres to a WKB formula for turbulence amplitude as a function of heliocentric distance.

Spangler, Steven R.↗
NASA NTRS2023

Radioastron Discovery of A Mini-Cocoon Around the Restarted Parsec-Scale Jet in 3C 84

We present RadioAstron space-based very long baseline interferometry (VLBI) observations of the nearby radio galaxy 3C 84 (NGC 1275) at the centre of the Perseus cluster. The observations were carried out during a perigee passage of the Spektr-R spacecraft on September 21–22, 2013 and involved a global array of 24 ground radio telescopes observing at 5 GHz and 22 GHz, together with the Space Radio Telescope (SRT). Furthermore, the Very Long Baseline Array (VLBA) and the phased Very Large Array (VLA) observed the source quasi-simultaneously at 15 GHz and 43 GHz. Fringes between the ground array and the SRT were detected on baseline lengths up to 8.1 times the Earth’s diameter, providing unprecedented resolution for 3C 84 at these wavelengths. We note that the corresponding fringe spacing is 125 μas at 5 GHz and 27 μas at 22 GHz. Our space-VLBI images reveal a previously unseen sub-structure inside the compact ∼1 pc long jet that was ejected about ten years earlier. In the 5 GHz image, we detected, for the first time, low-intensity emission from a cocoon-like structure around the restarted jet. Our results suggest that the increased power of the young jet is inflating a bubble of hot plasma as it carves its way through the ambient medium of the central region of the galaxy. Here, we estimate the minimum energy stored in the mini-cocoon, along with its pressure, volume, expansion speed, and the ratio of heavy particles to relativistic electrons, as well as the density of the ambient medium. About half of the energy delivered by the jet is dumped into the mini-cocoon and the quasi-spherical shape of the bubble suggests that this energy may be transferred to a significantly larger volume of the interstellar medium than what would be accomplished by the well-collimated jet on its own. The pressure of the hot mini-cocoon also provides a natural explanation for the almost cylindrical jet profile seen in the 22 GHz RadioAstron image.

galaxies: jets↗
DOE OSTI2026

Locating the missing large-scale emission in the jet of M87* with short EHT baselines

In very-long baseline interferometric arrays, nearly co-located stations probe the largest scales and typically cannot resolve the observed source. In the absence of a large-scale structure, closure phases constructed with these stations are zero and, since they are independent of station-based errors, they can be used to probe data issues. Here, we show how these trivial closure phases become nonzero with a brightness distribution on smaller scales than their short baseline would suggest. When applied to sources that are made up of a bright compact and large-scale diffuse component, the trivial closure phases directly measure the centroid relative to the compact source and higher-order image moments. We present a technique to measure these image moments with minimal model assumptions and validate it on synthetic Event Horizon Telescope (EHT) data. We then apply this technique to 2017 and 2018 EHT observations of M87* and find a weak preference for extended emission in the direction of the large-scale jet. We also apply it to 2021 EHT data and measure the source centroid about 1 mas northwest of the compact ring, which is consistent with the jet observed at lower frequencies.

79 ASTRONOMY AND ASTROPHYSICS↗