Navigation support for the RadioAstron mission

Zakhvatkin, M. V.; Ponomarev, Yu. N.; Stepanyants, V. A.; Тучин, А. Г.; Zaslavskiy, G. S.

doi:10.1134/s0010952514050128

Cited by 13 publications

(8 citation statements)

References 5 publications

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“…The satellite telemetry and science data are received and recorded at tracking stations in Puschino (Andreyanov et al 2014) and Green Bank (Ford et al 2014) and later transferred for correlation at one of the RadioAstron correlation facilities. Accurate reconstruction of the orbit and of the momentary state vector of the Spektr-R spacecraft is achieved by combining together radiometric range and radial velocity measurements made at the satellite control stations in Bear Lakes and Ussurijsk (Russia), Doppler measurements obtained at each of the tracking stations, and laser ranging and optical astrometric measurements of the spacecraft position in the sky Zakhvatkin et al 2014). The accuracy can be further enhanced by simultaneous VLBI measurements performed on the narrow-band downlink signal from the spacecraft (Duev et al 2012).…”

Section: Imaging With Radioastronmentioning

confidence: 99%

RadioAstron space VLBI imaging of polarized radio emission in the high-redshift quasar 0642+449 at 1.6 GHz

Lobanov

Gómez

Bruni

et al. 2015

A&A

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Context. Polarization of radio emission in extragalactic jets at a sub-milliarcsecond angular resolution holds important clues for understanding the structure of the magnetic field in the inner regions of the jets and in close vicinity of the supermassive black holes in the centers of active galaxies. Aims. Space VLBI observations provide a unique tool for polarimetric imaging at a sub-milliarcsecond angular resolution and studying the properties of magnetic field in active galactic nuclei on scales of less than 10 4 gravitational radii. Methods. A space VLBI observation of high-redshift quasar TXS 0642+449 (OH 471), made at a wavelength of 18 cm (frequency of 1.6 GHz) as part of the early science programme (ESP) of the RadioAstron mission, is used here to test the polarimetric performance of the orbiting Space Radio Telescope (SRT) employed by the mission, to establish a methodology for making full Stokes polarimetry with space VLBI at 1.6 GHz, and to study the polarized emission in the target object on sub-milliarcsecond scales. Results. Polarization leakage of the SRT at 18 cm is found to be within 9% in amplitude, demonstrating the feasibility of high fidelity polarization imaging with RadioAstron at this wavelength. A polarimetric image of 0642+449 with a resolution of 0.8 mas (signifying an ∼4 times improvement over ground VLBI observations at the same wavelength) is obtained. The image shows a compact corejet structure with low (≈2%) polarization and predominantly transverse magnetic field in the nuclear region. The VLBI data also uncover a complex structure of the nuclear region, with two prominent features possibly corresponding to the jet base and a strong recollimation shock. The maximum brightness temperature at the jet base can be as high as 4 × 10 13 K.

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Section: Imaging With Radioastronmentioning

confidence: 99%

RadioAstron space VLBI imaging of polarized radio emission in the high-redshift quasar 0642+449 at 1.6 GHz

Lobanov

Gómez

Bruni

et al. 2015

A&A

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“…HALCA and Astro-G used circular near-Earth orbits, providing (u, v) coverage of satisfactory quality for imaging observations [32,33]. Radioastron mission had a high elliptical near-Earth (HEO) orbit with an apogee of ≈ 330,000 km, which made it possible to achieve the highest angular resolution of 8 µas at the shortest wavelength of the mission (λ = 1.3 cm) [34,35].…”

Section: Orbital Configurationsmentioning

confidence: 99%

Analysis of Orbital Configurations for Millimetron Space Observatory

Rudnitskiy,

Mzhelskiy,

Shchurov

et al. 2021

Preprint

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In this contribution a primary feasibility study of different orbital configurations for Millimetron space observatory is presented. Priority factors and limitations were considered by which it is possible to assess the capabilities of a particular orbit. It included technical and scientific capabilities of each orbit regarding the fuel costs, satellite observability, the quality of very long baseline interferometric (VLBI) imaging observations and source visibilities.

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“…To look for a possible violation using measured fractional frequency shifts, the state parameters for the spacecraft must be known with sufficient accuracy to isolate the gravitational redshift from other effects, particularly the much larger non-relativistic Doppler effect. Orbit determination for the RadioAstron mission is done using a variety of sources of data, among them the same frequency observations made at the PU and GB ground stations 6 used in this analysis (Zakhvatkin et al, 2013(Zakhvatkin et al, , 2018. The position and velocity of the spacecraft are determined using a least-squares minimization in which no violation is assumed.…”

Section: Feasibility Of Determining the Violation Parametermentioning

confidence: 99%

The gravitational redshift monitored with RadioAstron from near Earth up to 350,000 km

Nunes

Bartel

Bietenholz

et al. 2020

Advances in Space Research

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We report on our efforts to test the Einstein Equivalence Principle by measuring the gravitational redshift with the VLBI spacecraft RadioAstron, in an eccentric orbit around Earth with geocentric distances as small as ∼ 7,000 km and up to 350,000 km. The spacecraft and its ground stations are each equipped with stable hydrogen maser frequency standards, and measurements of the redshifted downlink carrier frequencies were obtained at both 8.4 and 15 GHz between 2012 and 2017. Over the course of the ∼ 9 d orbit, the gravitational redshift between the spacecraft and the ground stations varies between 6.8 × 10 −10 and 0.6 × 10 −10 . Since the clock offset between the masers is difficult to estimate independently of the gravitational redshift, only the variation of the gravitational redshift is considered for this analysis. We obtain a preliminary estimate of the fractional deviation of the gravi- tational redshift from prediction of = −0.016 ± 0.003 stat ± 0.030 syst with the systematic uncertainty likely being dominated by unmodelled effects including the error in accounting for the non-relativistic Doppler shift. This result is consistent with zero within the uncertainties. For the first time, the gravitational redshift has been probed over such large distances in the vicinity of Earth. About three orders of magnitude more accurate estimates may be possible with RadioAstron using existing data from dedicated interleaved observations combining uplink and downlink modes of operation.

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Navigation support for the RadioAstron mission

Cited by 13 publications

References 5 publications

RadioAstron space VLBI imaging of polarized radio emission in the high-redshift quasar 0642+449 at 1.6 GHz

RadioAstron space VLBI imaging of polarized radio emission in the high-redshift quasar 0642+449 at 1.6 GHz

Analysis of Orbital Configurations for Millimetron Space Observatory

The gravitational redshift monitored with RadioAstron from near Earth up to 350,000 km

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Navigation support for the RadioAstron mission

Cited by 13 publications

References 5 publications

RadioAstron space VLBI imaging of polarized radio emission in the high-redshift quasar 0642+449 at 1.6 GHz

RadioAstron space VLBI imaging of polarized radio emission in the high-redshift quasar 0642+449 at 1.6 GHz

Analysis of Orbital Configurations for Millimetron Space Observatory

The gravitational redshift monitored with RadioAstron from near Earth up to 350,000 km

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Product

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The gravitational redshift monitored with RadioAstron from near Earth up to 350,000 km