Pair Of Satellites Research Articles

SPIN-ORBIT COUPLING AND CHAOTIC ROTATION FOR COORBITAL BODIES IN QUASI-CIRCULAR ORBITS

Coorbital bodies are observed around the Sun sharing their orbits with the planets, but also in some pairs of satellites around Saturn. The existence of coorbital planets around other stars has also been proposed. For close-in planets and satellites, the rotation slowly evolves due to dissipative tidal effects until some kind of equilibrium is reached. When the orbits are nearly circular, the rotation period is believed to always end synchronous with the orbital period. Here we demonstrate that for coorbital bodies in quasi-circular orbits, stable non-synchronous rotation is possible for a wide range of mass ratios and body shapes. We show the existence of an entirely new family of spin-orbit resonances at the frequencies $n\pm k\nu/2$, where $n$ is the orbital mean motion, $\nu$ the orbital libration frequency, and $k$ an integer. In addition, when the natural rotational libration frequency due to the axial asymmetry, $\sigma$, has the same magnitude as $\nu$, the rotation becomes chaotic. Saturn coorbital satellites are synchronous since $\nu\ll\sigma$, but coorbital exoplanets may present non-synchronous or chaotic rotation. Our results prove that the spin dynamics of a body cannot be dissociated from its orbital environment. We further anticipate that a similar mechanism may affect the rotation of bodies in any mean-motion resonance.

Sub-monthly gravity field recovery from simulated multi-GRACE mission type

Monthly solutions of the current GRACE mission are affected by the aliasing problem. In fact, sub-monthly temporal sampling may reduce the temporal aliasing errors but this will be done at the cost of reduced spatial sampling. Reducing the effects of temporal aliasing can be achieved by setting two pairs of satellites in different orbital planes. In this paper, we investigate the so-called Multi-GRACE constellation to improve temporal and spatial resolution for the GRACE-type mission without deteriorating accuracy. We investigate two scenarios: the Multi-GRACE ΔM that improves the temporal sampling only and the Multi-GRACE ΔΩ that improves the spatial sampling besides the temporal one in time span of only 12 days for the hydrological signal as a time-varying gravity field component. Our findings indicate that the hydrological signal can be submonthly recovered and the aliasing errors can be reduced as well by increasing temporal resolution (sub-month) via the Multi-GRACE ΔΩ constellations.

Use of the Comprehensive Inversion method for Swarm satellite data analysis

An advanced algorithm, known as the “Comprehensive Inversion” (CI), is presented for the analysis of Swarm measurements to generate a consistent set of Level-2 data products to be delivered by the Swarm “Satellite Constellation Application and Research Facility” (SCARF) to the European Space Agency (ESA). This new algorithm improves on a previously developed version in several ways, including the ability to process ground-based observatory data, estimation of rotations describing the alignment of vector magnetometer measurements with a known reference system, and the inclusion of ionospheric induction effects due to an a priori 3-dimensional conductivity model. However, the most substantial improvements entail the application of a mechanism termed “Selective Infinite Variance Weighting” (SIVW), which mitigates the effects of non-zero mean systematic noise and allows for the exploitation of gradient information from the low-altitude Swarm satellite pair to determine small-scale lithospheric fields, and an improvement in the treatment of attitude error due to noise in star-tracking systems over previously established methods. The advanced CI algorithm is validated by applying it to synthetic data from a full simulation of the Swarm mission, where it is found to significantly exceed all mandatory and most target accuracy requirements.

The dynamics of galaxy pairs in a cosmological setting

We use the Millennium Simulation, and an abundance matching framework, to investigate the dynamical behaviour of galaxy pairs embedded in a cosmological context. Our main galaxy-pair sample, selected to have separations r ≤ 250 h−1 kpc, consists of over 1.3 million pairs at redshift z = 0, with stellar masses greater than 1010 Mȯ, probing mass ratios down to 1:1000. We use dark matter halo membership and energy to classify our galaxy pairs. In terms of halo membership, central–satellite pairs tend to be in isolation (in relation to external more massive galaxies), are energetically bound to each other and are also weakly bound to a neighbouring massive galaxy. Satellite–satellite pairs, instead, inhabit regions in close proximity to a more massive galaxy, are energetically unbound and are often bound to that neighbour. We find that 60 per cent of our paired galaxies are bound to both their companion and to a third external object. Moreover, only 9 per cent of our pairs resemble the kind of systems described by idealized binary merger simulations in complete isolation. In sum, we demonstrate the importance of properly connecting galaxy pairs to the rest of the Universe.

Mass‐induced sea level change in the northwestern North Pacific and its contribution to total sea level change

Over the period 2003–2011, the Gravity Recovery and Climate Experiment (GRACE) satellite pair revealed a remarkable variability in mass‐induced sea surface height (MSSH) in the northwestern North Pacific. A significant correlation is found between MSSH and observed total sea surface height (SSH), indicative of the importance of barotropic variability in this region. For the period 2003–2011, MSSH rose at a rate of 6.1 ± 0.7 mm/yr, which has a significant contribution to the SSH rise (8.3 ± 0.7 mm/yr). Analysis of the barotropic vorticity equation based on National Centers for Environmental Prediction/National Center for Atmospheric Research reanalysis product, GRACE, and altimetry data suggests that the MSSH signal is primarily caused by negative wind stress curl associated with an anomalous anticyclonic atmospheric circulation. Regression analysis indicates that trends in MSSH and surface wind are related to the Pacific Decadal Oscillation, whose index had a decreasing trend in the last decade.

Quality assessment of sub-Nyquist recovery from future gravity satellite missions

Drawing on experience from Gravity Recovery and Climate Experiment (GRACE) data analysis, the scientific challenges were already identified in several studies. Any future mission should focus on improvement in both precision and resolution in space and time. For future gravity missions which use high quality sensors, aliasing of high frequency time-variable geophysical signals to the lower frequency signals is one of the most serious problems. The aliasing problem and the spatio-temporal resolution are mainly restricted by two sampling theorems describing the space-time sampling of satellite missions: (i) a Heisenberg-like uncertainty theorem which states that the product of spatial resolution and time resolution is constant, and (ii) the Colombo–Nyquist rule (CNR), which requires the number of satellite revolutions in a repeat period to be at least twice a given maximum spherical harmonic degree. The CNR holds under the assumption of equal ground-track spacing, and limits the spatial resolution of the gravity solution.This study investigates the quality of sub-Nyquist time interval recoveries (when the time intervals are shorter than what is required by the Colombo–Nyquist rule) of different orbit configurations and formation flights, in particular, the dependence of the gravity field accuracy on the measurement duration and ground-track patterns of the satellite formations. It is shown that the fulfillment of the modified CNR, the mission altitude and avoidance of large unobserved gaps by satellite ground-track patterns have the strongest effect on the quality of the recoveries, while the sub-cycle concept does not appear to play an imortant role. It is also found that the modified CNR holds for architectures including two satellite pairs when accounting for the orbital revolutions of both pairs. Moreover, the quality of the solution in the double pair scenario, consisting of a near-polar and an inclined inline pairs, exceeds that of a single near-polar inline pair solution with twice the observations. One important reason is the East–West information of the inclined pair adds to the North–South measurements of the near-polar mission.The simulations of the gravity recoveries of this study are based on a quick-look tool. The tool assumes nominal repeat orbits for satellite missions. Based on the quality assessment of the recoveries and the technical concerns of advanced formation flights as e.g. Pendulum or Cartwheel, a search space for optimal satellite mission scenarios is suggested.

A Comparative Study of Karyomorphology among Three Populations of Garcinia indica (Clusiaceae) (Thomas-Dupetite) Choisy

Garcinia indica is a tree species of the family Clusiaceae. This species is endemically distributed only in Ratnagiri and Sindhudurga district of Maharashtra. Plants collected in particularly Dive Agar and Sawantwadi show morphological variations. Mitotic chromosomes from three different population from the Konkan region were studied using propionic orcein stain. Chromosome numbers 2n = 54 is reported for all the populations. Three populations differed from each other in some aspects. Karyotype analysis showed that Deorukh population from Ratnagiri region showed one pair of satellite and one pair of secondary constrictions while Otawane population from Sawantwadi showed one satellite chromosome but differ in pattern of secondary constriction. Third, Diveagar population from Raigad district showed three pairs of satellite chromosomes and one pair of secondary constriction. So, it can be concluded that, plants from Bapat Garden of Dive Agar and Otawane region can be considered as cytotypes.

Monitoring scan asymmetry of microwave humidity sounding channels using simultaneous all angle collocations (SAACs)

AbstractSimultaneous all angle collocations (SAACs) of microwave humidity sounders (AMSU‐B and MHS) on‐board polar orbiting satellites are used to estimate scan‐dependent biases. This method has distinct advantages over previous methods, such as that the estimated scan‐dependent biases are not influenced by diurnal differences between the edges of the scan and the biases can be estimated for both sides of the scan. We find the results are robust in the sense that biases estimated for one satellite pair can be reproduced by double differencing biases of these satellites with a third satellite. Channel 1 of these instruments shows the least bias for all satellites. Channel 2 has biases greater than 5 K, thus needs to be corrected. Channel 3 has biases of about 2 K and more and they are time varying for some of the satellites. Channel 4 has the largest bias which is about 15 K when the data are averaged for 5 years, but biases of individual months can be as large as 30 K. Channel 5 also has large and time varying biases for two of the AMSU‐Bs. NOAA‐15 (N15) channels are found to be affected the most, mainly due to radio frequency interference (RFI) from onboard data transmitters. Channel 4 of N15 shows the largest and time varying biases, so data of this channel should only be used with caution for climate applications. The two MHS instruments show the best agreement for all channels. Our estimates may be used to correct for scan‐dependent biases of these instruments, or at least used as a guideline for excluding channels with large scan asymmetries from scientific analyses.

Ancient Igneous Intrusions and Early Expansion of the Moon Revealed by GRAIL Gravity Gradiometry

The earliest history of the Moon is poorly preserved in the surface geologic record due to the high flux of impactors, but aspects of that history may be preserved in subsurface structures. Application of gravity gradiometry to observations by the Gravity Recovery and Interior Laboratory (GRAIL) mission results in the identification of a population of linear gravity anomalies with lengths of hundreds of kilometers. Inversion of the gravity anomalies indicates elongated positive-density anomalies that are interpreted to be ancient vertical tabular intrusions or dikes formed by magmatism in combination with extension of the lithosphere. Crosscutting relationships support a pre-Nectarian to Nectarian age, preceding the end of the heavy bombardment of the Moon. The distribution, orientation, and dimensions of the intrusions indicate a globally isotropic extensional stress state arising from an increase in the Moon's radius by 0.6 to 4.9 kilometers early in lunar history, consistent with predictions of thermal models.

Gravity Field of the Moon from the Gravity Recovery and Interior Laboratory (GRAIL) Mission

Spacecraft-to-spacecraft tracking observations from the Gravity Recovery and Interior Laboratory (GRAIL) have been used to construct a gravitational field of the Moon to spherical harmonic degree and order 420. The GRAIL field reveals features not previously resolved, including tectonic structures, volcanic landforms, basin rings, crater central peaks, and numerous simple craters. From degrees 80 through 300, over 98% of the gravitational signature is associated with topography, a result that reflects the preservation of crater relief in highly fractured crust. The remaining 2% represents fine details of subsurface structure not previously resolved. GRAIL elucidates the role of impact bombardment in homogenizing the distribution of shallow density anomalies on terrestrial planetary bodies.

The Crust of the Moon as Seen by GRAIL

High-resolution gravity data obtained from the dual Gravity Recovery and Interior Laboratory (GRAIL) spacecraft show that the bulk density of the Moon's highlands crust is 2550 kilograms per cubic meter, substantially lower than generally assumed. When combined with remote sensing and sample data, this density implies an average crustal porosity of 12% to depths of at least a few kilometers. Lateral variations in crustal porosity correlate with the largest impact basins, whereas lateral variations in crustal density correlate with crustal composition. The low-bulk crustal density allows construction of a global crustal thickness model that satisfies the Apollo seismic constraints, and with an average crustal thickness between 34 and 43 kilometers, the bulk refractory element composition of the Moon is not required to be enriched with respect to that of Earth.

Karyology of nineTrifoliumL. taxa from Turkey

This research comprises a karyologic study of the nine taxa of Trifolium from Turkey. From the Trifolium L. section, Trifolium striatum L. and T. leucanthum Bieb. chromosome numbers were 2n = 14, T. echinatum Bieb. was 2n = 16 and T. phleoides Pourr. ex Willd was 2n = 12. From the Vesicaria Crantz. section, T. resupinatum L. var. resupinatum, T. clusii Godr. and Gren., and T. tomentosum L. all had chromosome numbers of 2n = 16. Chromosome numbers of T. retusum, L. from section Lotoidea, Crantz. and T. glanduliferum Boiss. var. glanduliferum from section Paramesus (C. Presl) Gris. were all found to be 2n = 16. Seven of the 9 taxa contained all pairs of chromosomes and were metacentric; the remaining taxa included 7 were metacentric and only one pair was submetacentric. One pair of satellites was found in T. phleoides. This study reports detailed karyotype analyses from Turkey for the first time in Trifolium.

Application of a Differential Drag Controller to a Full System Simulation

Differential drag control presents an opportunity to control satellites without the use of a fuel-based propulsion system. The relative state of a pair or formation of satellites can be controlled via relative accelerations provided by a differential drag force. The drag acceleration of each vehicle can be altered by changing the area of the vehicle in the direction of motion. In research to date, differential drag controllers have been considered separately from state estimation systems that will be used for orbit determination. This paper examines an integrated system that combines a state estimator with a differential drag controller. A Kalman filter is used to estimate position and velocity elements with realistic levels of measurement noise, as well as measurement biases and atmospheric density. A differential drag controller based on the Hill-Clohessy-Wiltshire equations is presented that takes estimates from the Kalman filter and determines the appropriate control behavior. Modifications are made to the controller to reduce unnecessary actuations due to relative state error. The integrated system is tested with a nonlinear propagation model including the effects of J 2, dynamic modeling errors, and an altitude-varying atmosphere to determine the controller performance in a realistic mission environment.

Leo IV and V – A possible dwarf galaxy pair?

The last few years have seen the discovery of many faint and ultra-faint dwarf spheroidal galaxies around the Milky Way. Among these is a pair of satellites called Leo IV and Leo V. This pair is found at large distances from the Milky Way (154 and 175 kpc respectively). The rather small difference in radial distance, and the fact that they also show a close projected distance on the sky, has led to the idea that we might be seeing a new pair of bound galaxies - like the Magellanic Clouds. In this paper we investigate this speculation by means of a simple integration code (confirming the results with full N-body simulations). As the luminous mass of both faint dwarfs is far too low to allow them to be bound, we simulate the pair assuming extended dark matter haloes. Our results show that the minimum dark matter mass required for the pair to be bound is rather high - ranging from 1.6 x 10^10 Msun to 5.4 x 10^10 Msun (within the virial radii). Computing the mass of dark matter within a commonly adopted radius of 300 pc shows that our models are well within the predicted range of dark matter content for satellites so faint. We therefore conclude that it could be possible that the two galaxies constitute a bound pair.

Radio occultation constellation deployment via impulses along the geomagnetic field

The problem of radio occultation (RO) constellation deployment is examined. Of particular interest here is to study the feasibility of using passively stabilized small satellites. We consider a pair of satellites supplied with a passive magnetic attitude control system. The capsule containing two satellites is launched into a parking orbit and stabilized along the geomagnetic field direction. Then the satellites are pushed apart by a separation spring at some point of orbit. If necessary for braking, one or two thrusters may be placed along the stabilized axis of each satellite. Optimization of the separation point and velocity along with the ΔV required for possible braking thrust is carried out in accordance with some specific demands of RO missions. Atmospheric drag and Earth oblateness are taken into account as perturbations. It is shown that, depending on a mission scenario, the separation with either one braking thrust or no thrusts at all is preferable.

고해상도 위성영상 GeoEye-1과 WorldView-2의 RPC 블록조정모델 정확도 분석

We investigated the accuracy in three dimensional geo-positioning derived by four high resolution satellite images acquired by two different sensors using the vendor-provided rational polynomial coefficients(RPC) based block adjustment in this research. We used two in-track stereo pairs of GeoEye-1 and WorldView-2 satellite and DGPS surveying data. In this experiment, we analyzed accuracies of RPC block adjustment models of two kinds of homogeneous stereo pairs, four kinds of heterogeneous stereo pairs, three 3 triplet image pairs, and one quadruplet image pair separately. The result shows that the accuracies of the models are nearly same. The accuracy without any GCPs reaches about CEP(90) 2.3m and LEP(90) 2.5m and the accuracy with single GCP is about CEP(90) 0.3m and LEP(90) 0.5m.

Surface-Charging Analysis of the Radiation Belt Storm Probe and Magnetospheric MultiScale Spacecraft

The Radiation Belt Storm Probes (RBSPs) are a pair of satellites to be launched in 2012 into 500 × 30 600 km 10°-inclination orbits. The Magnetospheric MultiScale (MMS) mission spacecraft are a set of four satellites to be launched in 2014 into 1300 × 70 000 km (1.2 × 12 Re) 28 °-inclination orbits. The apogee will be boosted to 150 000 km (25 Re) during the mission. The spacecraft of both missions will measure magnetic and electric fields and the charged-particle distribution. As measurements of low-energy plasma and of electric fields are sensitive to surface potentials, stringent requirements for electrostatic cleanliness are imposed on both spacecraft designs. We present a surface-charging analysis of the RBSP and MMS spacecraft designs. The resulting chassis and differential potentials are used to estimate spacecraft-generated effects on the measurements and the risk of arcing.

Karyotypic Variation and Karyomorphology in Iranian Endemic Ecotypes of <i>Plantago ovata</i> Forsk.

Isabgol is an annual herb cultivated as a medicinal plant. In the present study, karyotypic analysis of 12 Iranian endemic Isabgol (Plantago ovata Forsk.) ecotypes was carried out. The chromosome number was 2n=2x=8 with 4m+4st karyotype formula. The mean value of total chromosome length (TL) was 2.86 μm, ranging from 2.44 μm (E4) to 3.26 μm (E12). All ecotypes had 2 pairs of satellites (3S, 4S), varying in size from 0.34 to 0.36 μm. Most of the chromosomal parameters were significantly different among the various ecotypes. In general, karyotypes were symmetrical and fell in the Stebbins 2A category. The scatter diagram of A1 and A2 asymmetry indicated 4 groups of ecotypes while PCA analysis together with cluster analysis and scatter diagram of TL and CI, showed 3 groups, containing 9, 2 and 1 ecotypes, respectively. C-Banding patterns and fluorescence in situ hybridization (FISH) with 45S rDNA probe provided landmarks for chromosome identification in somatic preparations.

Optimization of an Occulter-Based Extrasolar-Planet-Imaging Mission

Anovel approach to extrasolar-planet imaging uses a pair of satellites: a telescope and an occulter, where the latter is placed in the line of sight between the telescope and the star system to be imaged in order to enhance the telescope’s imaging capability. The optimal configuration of this satellite formation around sun–Earth L2 halo orbits is studied. Trajectory optimization of the occultermotion between imaging sessions of different stars is performed using a range of different criteria and methods. Thus, the global optimization problem is transformed into a time-dependent traveling salesman problem. The time-dependent traveling salesman problem is augmentedwith various constraints that arrive from the mission, and this problem is solved by employing simulated annealing and branching algorithms. For a concrete understanding of the feasibility of themission, the performance of an example spacecraft, the Small Missions for Advanced Research in Technology (SMART-1), is analyzed.

Cytogenetical and Molecular Characterization of Five Commercial Varieties in <i>Trichosanthes anguina</i> L.

Five commercial varieties of Trichosanthes anguina (Snake Gourd), namely Turag, Dhaka Green, Super Long Green, Anika and Apurbo, were investigated cytogenetically and at the molecular level for authentic characterization. The variety Super Long Green was found to possess 2n=23 chromosomes and considered as a primary trisomic. 2n=22 chromosomes were found in the other 4 varieties. The total length of the 2n chromosome complement was largest in Anika and smallest in Apurbo. Only one extra large chromosome was found in Turag and Anika suggesting it had either been transferred from different genome or was a case of repeated duplication. No decrease in chromosomal length was found in Turag, a moderate decrease was found in Dhaka Green and Anika, and a sharp decrease in Super Long Green and Apurbo. A pair of satellites was found in Turag. Only a stain specific satellite was found in Dhaka Green. No CMA band was found in Turag and Super Long Green. The other 3 varieties showed distinct CMA banding pattern in respect of number, size, location and percentage of GC-rich area. The 5 varieties showed distinct RAPD bands with 6 different primer combinations. In addition, the Apurbo and Turag varieties showed unique DNA fragments with the primer combinations OPA-3 and OPA-4 respectively. A combination of cluster and karyotytpe analysis clearly indicated that Turag and Apurbo were distinctly related from the other 3 varieties. Therefore, with the help of cytogenetical and RAPD analysis, it was possible to characterize each variety.