Pair Of Satellites Research Articles

Phase-Space Areas of the Body Motion in the Solar System Deduced from the Bohr-Sommerfeld Atomic Theory and Approximate Invariance of Their Ratios for the Pairs of Planets and Satellites

Energy-time and momentum-position phase spaces defined by the electron orbits in the hydrogen-like atom exhibit special properties of equivalence. It is demonstrated that equivalence of the same kind can be obtained for the phase-space areas defined by the orbit pairs of planets, or satellites, which compose the solar system. In the choice of the examined areas it is useful to be guided by the Bohr-Sommerfeld atomic theory.

Intersatellite calibration of AMSU-A observations for weather and climate applications

[1] Long-term observations from the Advanced Microwave Sounding Unit-A (AMSU-A) onboard polar-orbiting satellites NOAA 15, 16, 17, and 18 and European Meteorological Operational satellite program-A (MetOp-A) were intercalibrated using their overlap observations. Simultaneous nadir overpasses (SNOs) and global ocean mean differences between these satellites were used to characterize calibration errors and to obtain calibration coefficients. Calibration errors were found manifesting themselves as certain scatter or temporal patterns of intersatellite biases, such as well-defined seasonal cycles in the Arctic and Antarctic SNO difference time series or a unique pattern closely correlated to the instrument temperature variability induced by Solar Beta Angle (SBA) variations in global ocean mean difference time series. Analyses of these patterns revealed five different types of biases that need to be removed from existing prelaunch-calibrated AMSU-A observations, which include relatively stable intersatellite biases between most satellite pairs, bias drifts on NOAA 16 and channel 7 of MetOp-A, sun-heating-induced instrument temperature variability in radiances, scene temperature dependency in biases due to inaccurate calibration nonlinearity, and biases due to channel frequency shift from its prelaunch measurement in certain satellite channels. Level-1c time-dependent calibration offsets and nonlinear coefficients were introduced and determined from SNO and global ocean mean temperature regressions to remove or minimize the first four types of biases. Channel frequency shift in NOAA 15 channel 6 was obtained from the radiative transfer model simulation experiments. The new calibration coefficients and channel frequency values have significantly reduced the five different types of biases and resulted in more consistent multisatellite radiance observations for intercalibrated satellite channels. The intercalibrated AMSU-A observations have been merged with its precursor, the intercalibrated microwave sounding unit (MSU), to generate the NOAA/Center for Satellite Applications and Research (STAR) version 2.0 upper-air temperature climate data record (CDR) for climate trend and variability monitoring from 1979 to the present. The intercalibrated AMSU-A radiance data are expected to further improve accuracies of numerical weather prediction and consistencies in climate reanalysis and CDR developments.

Expected improvements in determining continental hydrology, ice mass variations, ocean bottom pressure signals, and earthquakes using two pairs of dedicated satellites for temporal gravity recovery

[1] The Gravity Recovery and Climate Experiment mission has demonstrated the ability to quantify global mass variations at large spatial scales with monthly to sub-monthly temporal resolution. Future missions of this type taking advantage of improved measurement technologies will be limited by temporal aliasing errors. We suggest the addition of a second pair of satellites to reduce these errors. Using an optimized mission architecture consisting of a polar pair of satellites coupled with a lower inclined pair of satellites (72°), both in 13-day repeating orbits, we quantify the expected scientific improvements that having two pairs of satellites will provide over one pair. Numerical simulations to spherical harmonic degree 100 are run over one full year. Analysis using empirical orthogonal functions reveals that two satellite pairs determine annual mass variations in small basins which are undetected using one pair of satellites. Averaging kernels are used to show that two satellite pairs offer an 80% reduction in the level of error in determining mass variations in 53 hydrological basins and 12 Greenland basins over the year. After standard GRACE post-processing techniques have been applied to the one-pair solutions, it is seen that two satellite pairs (with no post-processing) still offer a 25%–75% improvement in determining the mass variations. Spatiospectral localization analysis is used to show increased spatial resolution and higher signal-to-noise ratios in recovering hydrology in the Amazon River basin, ocean bottom pressure signals in the Southeast Pacific basin, and a simulated earthquake signal representative of the 2010 Maule, Chile earthquake.

Precise CCD positions of Galilean satellite-pairs

In this paper, we present 526 precise CCD positions of Galilean satellite-pairs of Jupiter, which have been extracted from 441 CCD frames captured by a 1-m telescope at the Yunnan Observatory from 2002 to 2010. The four Galilean satellites (Io, Europa, Ganymede and Callisto) are used to calibrate the CCD field of view by comparing their pixel positions with their theoretical positions computed from two modern ephemerides of the Galilean satellites, L2 and JUP230, which have been developed by the Institut de Mechanique Celeste et de Calcul des Ephemerides and the Jet Propulsion Laboratory, respectively. In this paper, we focus on the relative position of a pair of satellites with short separation (less than 85 arcsec) for good internal precision. The mean (O − C) (observed minus computed) values of all these satellite-pairs in right ascension and declination are found to be no larger than 6 mas and 2 mas, respectively, for each ephemeris. The estimated precision for one single observation is better than 30 mas in each direction.

Cytological and molecular characterization of Vicia barbazitae Ten. & Guss.

Vicia barbazitae, a taxon belonging to section Vicia of subgenus Vicia, was recovered and analysed by cytological, karyological and molecular methods with the aim of both proposing a general characterisation of this species and studying the relationships among the species of section Vicia . Phylogenetic relationships among the species of the section Vicia and those of the sections Microcarinae, Wiggersia and Atossa were also analysed. Automated karyotype analysis has been determined after Feulgen's reaction; chromosome banding was performed by sequence-specific fluorochrome staining. Fluorescent chromosome banding showed CMA(+)/DAPI(-) NOR-associated heterochromatin in the satellite pair. Karyomorphological parameters, based on symmetry indices, the dendrogram of linkage distance constructed on 37 chromosome parameters, as well as the molecular data based on internal transcribed spacer sequences provided information about phylogenetic position of this species inside the section Vicia and among the species belonging to the sections Microcarinae, Wiggersia, Atossa and Vicia. From our karyological and molecular results, it emerges that V. barbazitae can be considered a natural member of section Vicia.

Design considerations for a dedicated gravity recovery satellite mission consisting of two pairs of satellites

Future satellite missions dedicated to measuring time-variable gravity will need to address the concern of temporal aliasing errors; i.e., errors due to high-frequency mass variations. These errors have been shown to be a limiting error source for future missions with improved sensors. One method of reducing them is to fly multiple satellite pairs, thus increasing the sampling frequency of the mission. While one could imagine a system architecture consisting of dozens of satellite pairs, this paper explores the more economically feasible option of optimizing the orbits of two pairs of satellites. While the search space for this problem is infinite by nature, steps have been made to reduce it via proper assumptions regarding some parameters and a large number of numerical simulations exploring appropriate ranges for other parameters. A search space originally consisting of 15 variables is reduced to two variables with the utmost impact on mission performance: the repeat period of both pairs of satellites (shown to be near-optimal when they are equal to each other), as well as the inclination of one of the satellite pairs (the other pair is assumed to be in a polar orbit). To arrive at this conclusion, we assume circular orbits, repeat groundtracks for both pairs of satellites, a 100-km inter-satellite separation distance, and a minimum allowable operational satellite altitude of 290 km based on a projected 10-year mission lifetime. Given the scientific objectives of determining time-variable hydrology, ice mass variations, and ocean bottom pressure signals with higher spatial resolution, we find that an optimal architecture consists of a polar pair of satellites coupled with a pair inclined at 72°, both in 13-day repeating orbits. This architecture provides a 67% reduction in error over one pair of satellites, in addition to reducing the longitudinal striping to such a level that minimal post-processing is required, permitting a substantial increase in the spatial resolution of the gravity field products. It should be emphasized that given different sets of scientific objectives for the mission, or a different minimum allowable satellite altitude, different architectures might be selected.

Estimating low resolution gravity fields at short time intervals to reduce temporal aliasing errors

The Gravity Recovery and Climate Experiment (GRACE) satellite mission has been estimating temporal changes in the Earth’s gravitational field since its launch in 2002. While it is not yet fully resolved what the limiting source of error is for GRACE, studies on future missions have shown that temporal aliasing errors due to undersampling signals of interest (such as hydrological variations) and errors in atmospheric, ocean, and tide models will be a limiting source of error for missions taking advantage of improved technologies (flying drag-free with a laser interferometer). This paper explores the option of reducing the effects of temporal aliasing errors by directly estimating low degree and order gravity fields at short time intervals, ultimately resulting in data products with improved spatial resolution. Three potential architectures are considered: a single pair of polar orbiting satellites, two pairs of polar orbiting satellites, and a polar orbiting pair of satellites coupled with a lower inclined pair of satellites. Results show that improvements in spatial resolution are obtained when one estimates a low resolution gravity field every two days for the case of a single pair of satellites, and every day for the case of two polar pairs of satellites. However, the spatial resolution for these cases is still lower than that provided by simply destriping and smoothing the solutions via standard GRACE post-processing techniques. Alternately, estimating daily gravity fields for the case of a polar pair of satellites coupled with a lower inclined pair results in solutions with superior spatial resolution than that offered by simply destriping and smoothing the solutions.

Astrometric results of observations at Russian observatories of mutual occultations and eclipses of Jupiter’s Galilean satellites in 2009

In 2009, in five Russian observatories photometric observations of Jupiter’s Galilean satellites during their mutual occultations and eclipses were carried out. Based on these observations, an original method was used to ascertain astrometric results such as the difference between the coordinates of pairs of satellites. Fifty-three phenomena were successfully observed. A total of 94 light curves of satellites were measured. The error in the coordinates of satellites due to random errors in photometry, calculated on all data obtained, was 0.041″ in right ascension and 0.046″ in declination. The discrepancies between the theory and observations in these coordinates was found to be 0.060″ and 0.057″, respectively. The results were uploaded to the common database for all observations of natural satellites of planets at the Natural Satellites Data Center (NSDC), which is available online at http://www.sai.msu.ru/neb/nss/index.htm. For the first time in the practice of photometric observations of satellites in epochs of mutual occultations and eclipses a new method of observation was tested, which eliminates from astrometric results the major systematic errors caused by an inaccurate account of the background level. The tests were conducted in the Terskol Observatory and the observatory of the Crimean laboratory of the Sternberg State Astronomical Institute of the Moscow State University. The application of the new method showed that the elimination of the background level at these observatories was carried out correctly.

Measurement of drag and its cancellation

The design of drag cancellation missions of the future will take advantage of the technology experience of the past. The importance of data for modeling of the atmosphere led to at least six types of measurement: (a) balloon flights, (b) missile-launched falling spheres, (c) the ‘cannonball’ satellites of Ken Champion with accelerometers for low-altitude drag measurement (late 1960s and early 1970s), (d) the Agena flight of LOGACS (1967), a Bell MESA accelerometer mounted on a rotating platform to spectrally shift low-frequency errors in the accelerometer, (e) a series of French low-level accelerometers (e.g. CACTUS, 1975), and (f) correction of differential accelerations for drag errors in measuring gravity gradient on a pair of satellites (GRACE, 2002). The independent invention of the drag-free satellite concept by Pugh and Lange (1964) to cancel external disturbance added implementation opportunities. Its first flight application was for ephemeris prediction improvement with the DISCOS flight (1972)—still the only extended free test mass flight. Then successful flights for reduced disturbance environment for science measurement with gyros on GP-B (2004) and for improved accuracy in geodesy and ocean studies (GOCE, 2009) each using accelerometer measurements to control the drag-canceling thrust. LISA, DECIGO, BBO and other gravity wave-measuring satellite systems will push the cancellation of drag to new levels.

Lithium ion conduction mechanism in LiInI 4 studied by single crystal 7Li NMR

Conduction mechanism of Li + cation in a stoichiometric LiInI 4 was studied experimentally. In general, the interpretations of the 7Li NMR powder spectrum and its temperature dependence are not straightforward because of a broadening due to not only dipole–dipole interactions but quadrupole effect ( 7Li, I = 3/2). In this NMR experiment on LiInI 4, the quadrupole effect and the dipole–dipole interactions could be discussed separately using a single crystal. Since LiInI 4 belongs to a monoclinic crystal, two pairs of satellite transitions ( Δm = 3/2 ↔ 1/2 and − 3/2 ↔ − 1/2 ) as well as a central transition ( Δm = − 1/2 ↔ 1/2) were observed for 7Li NMR due to the first order quadrupole effect. Above 380 K, however, these two satellite pairs merged into one pair associated with the motional narrowing phenomenon. This finding directly suggests a site exchange of the Li + between two crystallographically equivalent sites. The exchange rate ( k ex) was estimated using a spectrum simulation of the coalescence phenomena and, furthermore, the bulk ionic conductivities were calculated as a function of temperature which agreed well to those from the complex impedance method. The site exchange phenomenon especially appeared on the single crystal NMR spectra was proved to be a good technique to evaluate ionic conductivity and its mechanism in solid.

Aluminum doped silicon carbide thin films prepared by hot-wire CVD: Investigation of defects with electron spin resonance

Al-doped p-type μc-SiC:H is prepared in a wide range of HWCVD preparation parameters like Al-doping ratio, deposition pressure, substrate and filament temperatures. We investigate the structural and electrical properties, and focus on identification of paramagnetic defect states by electron spin resonance (ESR). Nominally undoped μc-SiC:H is of a high n-type conductivity (σ D = 10 − 6 –10 − 1 S/cm) and shows a narrow central ESR line (g ≈ 2.003, peak-to-peak linewidth ∆H pp ≈ 4 G) with two pairs of satellites and a spin density N S = 10 19 cm − 3 . Al-doping results in the compensation of dark conductivity to as low as σ D = 10 − 11 S/cm and at higher doping concentrations to effective p-type material. Increase of Al-doping results in reduction of crystallinity ( I C IR ), ESR line shifts to g ≈ 2.01 and becomes as broad as ∆H pp ≈ 30 G, not unlike to the resonance of singly occupied paramagnetic valence band tail states in a-Si:H. ESR spectrum of highly crystalline Al-doped μc-SiC:H however has a g-value very close to undoped μc-SiC:H. Electron spin density in compensated material decreases to 5 × 10 17 cm − 3 before it increases again for the highly doped material.

A record-high ocean bottom pressure in the South Pacific observed by GRACE

In late 2009 to early 2010, the Gravity Recovery and Climate Experiment (GRACE) satellite pair observed a record increase in ocean bottom pressure (OBP) over a large mid-latitude region of the South East Pacific. Its magnitude is substantially larger than other oceanic events in the Southern Hemisphere found in the entire GRACE data records (2003-2010) on multi-month time scales. The OBP data help to understand the nature of a similar signal in sea surface height (SSH) anomaly observed by altimetry: the SSH increase is mainly due to mass convergence. Analysis of the barotropic vorticity equation using scatterometer data, atmospheric reanalysis product, and GRACE and altimeter an atmospheric reanalysis product observations suggests that the observed OBP/SSH signal was primarily caused by wind stress curl associated with a strong and persistent anticyclone in late 2009 in combination with effects of planetary vorticity gradient, bottom topography, and friction

Comparing galactic satellite properties in hydrodynamical and N-body simulations

In this work, we examine the different properties of galactic satellites in hydrodynamical and pure dark matter simulations. We use three pairs of simulations (collisional and collision-less) starting from identical initial conditions. We concentrate our analysis on pairs of satellites in the hydro and Nbody runs that form from the same Lagrangian region. We look at the radial positions, mass loss as a function of time and orbital parameters of these "twin" satellites. We confirm an overall higher radial density of satellites in the hydrodynamical runs, but find that trends in the mass loss and radial position of these satellites in the inner and outer region of the parent halo differ from the pure dark matter case. In the outskirts of the halo (~70% of the virial radius) satellites experience a stronger mass loss and higher dynamical friction in pure dark matter runs. The situation is reversed in the central region of the halo, where hydrodynamical satellites have smaller apocenter distances and suffer higher mass stripping. We partially ascribe this bimodal behaviour to the delayed infall time for hydro satellites, which on average cross the virial radius of the parent halo 0.7 Gyrs after their dark matter twins. Finally, we briefly discuss the implications of the different set of satellite orbital parameters and mass loss rates in hydrodynamical simulations within the context of thin discs heating and destruction.

Formation flying control implementation for highly elliptical orbits

The Tschauner-Hempel equations are widely used to correct the separation distance drifts between a pair of satellites within a constellation in highly elliptical orbits [1]. This set of equations was discretized in the true anomaly angle [1] to be used in a digital steady-state hierarchical controller [2]. This controller [2] performed the drift correction between a pair of satellites within the constellation. The objective of a discretized system is to develop a simple algorithm to be implemented in the computer onboard the satellite. The main advantage of the discrete systems is that the computational time can be reduced by selecting a suitable sampling interval. For this digital system, the amount of data will depend on the sampling interval in the true anomaly angle [3]. The purpose of this paper is to implement the discrete Tschauner-Hempel equations and the steady-state hierarchical controller in the computer onboard the satellite. This set of equations is expressed in the true anomaly angle in which a relation will be formulated between the time and the true anomaly angle domains.

Fluorescent Karyotype Analysis in Four Varieties of Solanum melongena L.

Four varieties of Solanum melongena L., namely local variety-Islampuri, BARI Begun-3 (Tarapuri, Claimed as F1 hybrid between local and BARI Begun-1 F1 hybrid), BARI Begun-1 (Uttara) and BARI Begun-5 (Nayantara), were cytogenetically investigated to characterize individual karyotypes. Although each variety was found to possess 2n=24 chromosomes, the karyotype formulae differed sharply among them. Heteromorphicity in respect of centromeric position revealed the occurence of minute deletion. Each variety possesed distinct CMA- and DAPI-banding karyotypes. Reversible chromosome banding i.e. CMA positive-DAPI negative was found in BARI Begun-5 (Nayantara). The overall karyotypic features indicated that BARI Begun-5 was totally different from the other 3 varieties. In BARI Begun-1, a pair of satellites was found in CMA-stained metaphase plates. It was not observed in orcein and DAPI staining revealed stain-specificity of the satellited portions. The karyotype analysis did not support the suggestion that BARI Begun-3 is a hybrid between local (Islampuri) and BARI Begun-1 (Uttara).

On the scarcity of Magellanic Cloud like satellites

We have used H alpha narrow-band imaging to search for star-forming satellite galaxies around 143 luminous spiral galaxies, with the goal of quantifying the frequency of occurrence of satellites resembling the Magellanic Clouds, around galaxies comparable to the Milky Way. For two-thirds of the central galaxies, no star-forming satellites are found, down to luminosities and star-formation rates well below those of the Magellanic Clouds. A total of 62 satellites is found, associated with 47 of the central galaxies searched. The R-band magnitude difference between central galaxies and their satellites has a median value of 4.6 mag, and a maximum of 10.2 mag. The mean projected separation of the satellites from their central galaxies is 81 kpc, or 98 kpc for systems beyond 30 Mpc. Thus star-forming satellites are quite rare, and the Milky Way is unusual both for the luminosity and the proximity of its two brightest satellites. We also find that the Clouds themselves are unusual in that they appear to form a bound binary pair; such close satellite pairs, of any luminosity, are also extremely rare in our survey.

Multiple Shooting Method for Initial Satellite Orbit Determination

After a satellite has been launched, the determination of its initial orbit is one of the primary tasks to be accomplished by mission control: e.g., in order to prepare for high-precision orbit determination or orbital transfers. For this purpose, tracking measurements are acquired by ground stations, which are the basis for the determination of the unknown orbit parameters. In this paper, the orbit determination problem is formulated as a least-squares parameter estimation problem, and a newly developed multiple shooting method is presented for its solution. For the generation of initial guesses, the method incorporates a so-called analytical projection, which is specifically tailored to the available measurement data. Original tracking data of the launch and early orbit phases of the Artemis satellite and the second pair of Cluster-II satellites are used for tests of the method. Both scenarios constitute challenging benchmark problems, because the satellites were launched into orbits significantly different from the expected ones. A comparison to the widely employed single shooting method reveals that the newly developed method significantly improves the convergence behavior.

Paramagnetic states in µc‐SiC:H thin films prepared by Hot‐Wire CVD at low temperatures

AbstractThe relationship between the structure, electrical conductivity and paramagnetic states in microcrystalline hydrogenated silicon carbide (µc‐SiC:H) prepared by HWCVD is investigated. The study includes undoped and Al‐doped (p ‐type) µc‐SiC:H of different crystalline volume fraction (ICIR). High densities of paramagnetic states are observed in undoped material over a wide range of crystallinity whereas the conductivity increases by 10 orders of magnitude up to 10‐2 S/cm as the material becomes more crystalline. This dramatic increase of the conductivity attributed to unintentional n ‐type doping has a clear effect on the ESR spectrum which changes from a broad featureless resonance in the low crystallinity material to a sharp line with a pair of distinct satellites in highly crystalline n ‐type µc‐SiC:H. Al‐doping results in compensation and then effective p ‐type doping in µc‐SiC:H at higher doping concentration. Al‐doping seems to hinder the crystalline growth in p ‐type µc‐SiC:H. For ICIR ≤ 20% the spin resonance signature is a broad (peak‐to‐peak linewidth ΔHpp ≈ 30 G) featureless slightly asymmetric line at g ≈ 2.01. The nature and behavior of the ESR spectra in different types of µc‐SiC:H are investigated with respect to the Fermi level position and crystalline volume fraction (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

C-banded karyotypes of Allium (Alliaceae) sect. Sacculiferum in Korea

C-banded karyotypes of eight taxa of Korean Allium sect. Sacculiferum were examined by means of Giemsa techniques. Each of the taxa had their own characteristic bands. Most of the bands on the somatic metaphase chromosomes were mainly located on the short arm, intercalary region and medium sized chromosomes. In addition, the heterochromatic bands were usually facultative, recognized as two spots, and all investigated taxa had a pair of satellites of heterochromatin. The similarities of total length and number of bands revealed that three varieties of A. thunbergii G. Don have a closer cytological relationship than the others. The C-banding patterns of A. longistylum and A. linearifolium were examined for the first time in this study, and the former was clearly distinguished from the others by the distribution and number of its bands. The proportion of heterochromatic bands suggested that A. thunbergii var. thunbergii is the most primitive, and A. sacculiferum the most advonced, within the section.

Deployment procedure for the Tetrahedron Constellation

The NASA Benchmark Tetrahedron Constellation is a four-satellite formation that requires a nominal separation distance at every apogee point. The deployment procedure of a tetrahedron constellation is complex and depends on the separation distance between any pair of satellites within the constellation. In this paper, the deployment procedure of the tetrahedron constellation will be divided into two stages: the deployment from a circular parking orbit to an elliptical orbit, and the correction of the separation distance between pairs of satellites within the constellation. The solution of this problem will be implemented with a combination of Hohmann transfer maneuvers and the digital linear quadratic regulator control scheme showing a minimum consumption of fuel. In summary, the combination of these two techniques will provide a different approach to the deployment procedure of the NASA benchmark tetrahedron constellation.