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Parameter decomposition Filter of BDS-3 Combined Orbit Determination using inter-satellite link observations

Fri, 03/22/2019 - 19:10

Publication date: Available online 20 March 2019

Source: Advances in Space Research

Author(s): Xiaoying Gong, Dingfa Huang, Shixiang Cai, Letao Zhou, Linguo Yuan, Wei Feng

Abstract

Starting in March 2015, 5 new-generation BDS satellites, including 2 satellites in IGSO and 3 satellites in MEO, have been launched with the Inter Satellite Links (ISLs) on-board and the measurements have been tested. With the ISLs, BDS can achieve Autonomous Navigation (AutoNav) without support of ground facilities. In AutoNav, for lack of the external datum, the residual constellation rotation cannot be observed. This problem will be solved with the support of ground facilities. When ground facilities are available, Combined Orbit Determination (COD) can be achieved by using measurements from the ISLs and ground facilities, which can dramatically improve the precision of orbit determination. Normally, there are two kinds of filters adopted in AutoNav, namely the Parameter Integration Filter (PIF) and the Parameter Decomposition Filter (PDF). The PIF, which is also commonly used in COD due to the one-way property of the L-band satellite-ground measurements, had been prove less efficient than the PDF in AutoNav. As an attempt of improving the solving efficiency for COD, a new PDF is presented and implemented in COD of BDS in this paper. Based on the implement of the COD with simulated observations, the performance of PDF in COD is evaluated by comparing to the PIF in regards to precision and solving efficiency. The results indicate that, given enough observations, the PDF is superior to the PIF in terms of CERR and URE, while inferior to PIF in terms of RERR and PERR. Moreover, the solving efficiency of the PDF is much higher than that of the PIF.

RadioAstron reveals super-compact structures in the bursting H<sub>2</sub>O maser source G25.65+1.05

Fri, 03/22/2019 - 19:10

Publication date: Available online 20 March 2019

Source: Advances in Space Research

Author(s): O.S. Bayandina, N.N. Shakhvorostova, A.V. Alakoz, R.A. Burns, S.E. Kurtz, I.E. Val’tts

Abstract

Water masers are well-known to be variable on a variety of time scales, but only three Galactic H2O masers are known to flare to the level of 105-106 Jy (TB ∼1017 K): Orion KL, W49N, and the recently discovered G25.65+1.05. Recently detected flaring activity of H2O maser in the massive star-forming region G25.65+1.05 gave us a unique opportunity to study the fine structure of H2O maser emission in the bursting state with extremely high space VLBI angular resolution. Observation of the source was carried out with ∼9 Earth diameter space-ground baseline within the framework of the RadioAstron project. H2O maser emission from two spectral features, including the bursting one, was detected in the experiment. Only ∼1% of the bursting H2O maser emission was detected on the space-ground baselines: it indicates the presence of a very compact spatial structure with a size of ∼25 μas, which corresponds to 0.05 AU or ∼5 solar diameters at the distance to the source of 2.08 kpc, and the brightness temperature of ∼3 × 1016 K. Analysis of the flux density as a function of the baseline length for the bursting H2O maser feature in the source shows that most of the emission comes from an extended “halo” structure, while the core of emission is very compact and has an extreme brightness temperature. These results are in agreement with the model of interacting maser clouds considered as the likely explanation of the nature of the burst in the source. Under the assumption of such a model, the beam size of maser emission is reduced while the brightness temperatures similar to the highest observed values are produced.

Solar irradiance, climatic indicators and climate change – An empirical analysis

Fri, 03/22/2019 - 19:10

Publication date: Available online 20 March 2019

Source: Advances in Space Research

Author(s): Asheesh Bhargawa, A.K. Singh

Abstract

Since the Sun is the main source of energy for our planet therefore even a slight change in its output energy can make a huge difference in the climatic conditions of the terrestrial environment. The rate of energy coming from the Sun (solar irradiance) might affect our climate directly by changing the rate of solar heating of the Earth and the atmosphere and indirectly by changing the cloud forming processes. In the present paper, based on stability test of Vector Auto Regressive (VAR) model, we have used the impulse response functions and the variance decomposition method for the analysis of climate variability. We have examined the possible connections among the solar irradiance and some climate indicators, viz., the global temperature anomaly, the global mean sea level, the global sea-ice extent and the global precipitation anomaly occurred during last forty years (1978–2017). In our investigation, we have observed that the impact of solar irradiance on the global surface temperature level in next decade will increase by ∼4.7% while the global mean sea level will increase about 0.67%. In the meantime, we have noticed about 5.3% decrement in the global sea-ice extent for the next decade. In case of the global precipitation anomaly we have not observed any particular trend just because of the variable climatic conditions. We also have studied the effect of CO2 as anthropogenic forcing where we have observed that the global temperature in the next decade will increase by 2.7%; mean sea level will increase by 6.4%. Increasing abundance in CO2 will be responsible for about 0.43% decrease in the sea-ice extent while there will not be any change in the precipitation pattern.

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

Fri, 03/22/2019 - 19:10

Publication date: Available online 19 March 2019

Source: Advances in Space Research

Author(s): N.V. Nunes, N. Bartel, M.F. Bietenholz, M.V. Zakhvatkin, D.A. Litvinov, V.N. Rudenko, L.I. Gurvits, G. Granato, D. Dirkx

Abstract

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 not known and cannot be estimated independently of the gravitational redshift, only the variation of the gravitational redshift is considered for this analysis. We obtain a preliminary measurement of the fractional deviation of the gravitational redshift from prediction of -0.016±0.003stat±0.030syst 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 measurements may be possible with RadioAstron using existing data from dedicated interleaved observations combining uplink and downlink modes of operation.

Robust Foreground Segmentation and Image Registration for Optical Detection of GEO Objects

Fri, 03/22/2019 - 19:10

Publication date: Available online 19 March 2019

Source: Advances in Space Research

Author(s): Huan N. Do, Tat-Jun Chin, Nicholas Moretti, Moriba K. Jah, Matthew Tetlow

Abstract

With the rapid growth in space utilisation, the probability of collisions between space assets and orbital debris also increases substantially. To support the safe utilisation of space and prevent disruptions to satellite-based services, maintaining space situational awareness (SSA) is crucial. A vital first step in achieving SSA is detecting the man-made objects in orbit, such as space-crafts and debris. We focus on the surveillance of Geo-stationary (GEO) orbital band, due to the prevalence of major assets in GEO. Detecting objects in GEO is challenging, due to the objects being significantly distant (hence fainter) and slow moving relative to the observer (e.g., a ground station or an observing satellite). In this paper, we introduce a new detection technique called GP-ICP to detect GEO objects using optical sensors that is applicable for both ground and space-based observations. Our technique is based on mathematically principled methods from computer vision (robust point set registration and line fitting) and machine learning (Gaussian process regression). We demonstrate the superior performance of our technique in detecting objects in GEO.

A Gaussian Random Field Model for De-speckling of Multi-polarized Synthetic Aperture Radar Data

Fri, 03/22/2019 - 19:10

Publication date: Available online 19 March 2019

Source: Advances in Space Research

Author(s): Masoud Mahdianpari, Mahdi Motagh, Vahdi Akbari, Fariba Mohammadimanesh, Bahram Salehi

Abstract

Synthetic Aperture Radar (SAR) data have gained interest for a variety of remote sensing applications, given the capability of SAR sensors to operate independent of solar radiation and day/night conditions. However, the radiometric quality of SAR images is hindered by speckle noise, which affects further image processing and interpretation. As such, speckle reduction is a crucial pre-processing step in many remote sensing studies based on SAR imagery. This study proposed a new adaptive de-speckling method based on a Gaussian Markov Random Field (GMRF) model. The proposed method integrated both pixel-wised and contextual information using a weighted summation technique. As a by-product of the proposed method, a de-speckled pseudo-span image, which was obtained from the least square analysis of the de-speckled multi-polarization channels, was also introduced. Experimental results from the medium resolution, fully polarimetric L-band ALOS PALSAR data demonstrated the effectiveness of the proposed algorithm compared to other well-known de-speckling approaches. The de-speckled images produced by the proposed method maintained the mean value of the original image in homogenous areas, while preserving the edges of features in heterogeneous regions. In particular, the equivalent number of look (ENL) achieved using the proposed method improved by about 15% and 47% compared to the NL-SAR and SARBM3D de-speckling approaches, respectively. Other evaluation indices, such as the mean and variance of the ratio image, also revealed the superiority of the proposed method relative to other de-speckling approaches examined in this study.

Mid latitude ionospheric TEC modeling and the IRI model validation during the recent high solar activity (2013-2015)

Fri, 03/22/2019 - 19:10

Publication date: Available online 19 March 2019

Source: Advances in Space Research

Author(s): Yekoye Asmare Tariku

Abstract

This paper discusses the variability of the modelled Vertical Total Electron Content (VTEC) and performance of the latest versions of the International Reference Ionosphere (IRI) model in the estimation of TEC over the mid-latitude American regions in the recent high solar activity (2013–2015) years. This is conducted by comparing the pattern of the variations of the VTEC obtained from five ground based Global Positioning System (GPS) receivers installed at different mid-latitude American regions and the latest versions of the IRI model (IRI 2007, IRI 2012 and IRI 2016). It has been observed that the measured (GPS-derived) and modelled (IRI 2007, IRI 2012 and IRI 2016) monthly and seasonal diurnal variability of VTEC show the lowest values at around 10:00 UT (04:00 LT) and the highest values at around 20:00 UT (14:00 LT). Moreover, both the measured and modelled VTEC variations generally follow the pattern of the variation of the solar activity, showing enhancement in shifting from 2013 to 2014, and drop again in 2015, with some exceptional months. In the years 2013-2015, the highest measured and modelled seasonal arithmetic mean VTEC values are observed in the March equinox in 2014; while, the lowest measured and modelled VTEC values are observed in the December solstice and June solstice, respectively in 2015. It has also been shown that the IRI 2016 VTEC values are generally larger than those of the IRI 2007 and IRI 2012 VTEC values and tend to respond to variation of the GPS VTEC values better than others, especially in the equinoctial and June solstice months. Moreover, when compared to the IRI 2007 and IRI 2012 versions, the smallest root-mean-square deviations are observed in using the IRI 2016 version, showing that the IRI 2016 version is generally better in capturing the VTEC values with some exceptional months (especially in the December solstice months). Hence, in the December solstice months, the IRI 2007 and IRI 2012 versions are generally better in estimating the VTEC variations as compared to the IRI 2016 version. Moreover, the root-mean-square deviations obtained (either due to overestimations or underestimations) in the IRI 2007 and IRI 2012 versions are very close to each other, proving that the two versions show similar performance in TEC estimation.

Dynamic modeling and modal parameters identification of satellite with large-scale membrane antenna

Fri, 03/22/2019 - 19:10

Publication date: Available online 19 March 2019

Source: Advances in Space Research

Author(s): Liang Fan, Xiang Liu, Guo-ping Cai

Abstract

With the development of antenna technology, membrane antenna has become a research hotspot in aerospace field due to its advantages of light weight, low cost and easy folding. Nevertheless, greater difficulties have been brought to dynamic modeling and identification of the satellite with membrane antenna since its structure is remarkably flexible and complex. In view of the above problems, in this paper, dynamic modeling and on-orbit parameter identification are investigated for satellite systems with large-scale membrane antennas. Firstly, translation, rotation and vibration dynamic equations of the satellite system are developed using the coupling coefficient method. Afterwards observer/Kalman filter identification (OKID) and eigensystem realization algorithms (ERA) are applied to identify the modal parameters of the system. Finally, the validity of proposed methods are verified by numerical simulations. Simulation results indicate that the dynamic model established by this paper coincides well with the software ADAMS when comparing dynamic responses of the satellite, and also reveal that both OKID and ERA can effectively identify natural frequencies and modes of the system.

Studying the properties of interplanetary counterpart of halo-CMEs and their influences on Dst index

Fri, 03/22/2019 - 19:10

Publication date: Available online 19 March 2019

Source: Advances in Space Research

Author(s): A. Goswami

Abstract

The properties of front side halo coronal mass ejections (CMEs) and their interplanetary counterpart (ICME) have been studied here, as well as their relative imprint on Dst index over the period of 1995 to 2015. The results confirm that most of the faster halos are ignited from limb and most of them are associated with flares. The parametric average of interplanetary halos (except velocity and temperature) are found higher in disk associated events than that of limb. The results are also showing that fast and halo CME associated ICMEs are the most promising candidate for producing strong storms if they are exploded within ± 30 degree of the central meridian. About 65% of all front side halo CME associated ICMEs are geoeffective, supporting to the high rate of geoeffectiveness of halo CMEs. A larger fraction (71%) of disk halos are geoeffective. It’s observed that, 92.6% of total Dst associated DS-ICME events have been geoeffective. This value is slightly lower for Dst associated DW-ICMEs. For intermediate events, it has been seen that, 87% of IS-ICMEs are geoeffective. But in the absence of shock intermediate ICMEs are identified as nongeoeffectve ICMEs (however, only one event is present in that group). For LS-ICMEs, it has found that 83% are geoeffective events. Whereas, for LW-ICMEs, 75% are identified as geoeefective. In additions, the intensity of geomagnetic storm depends strongly on Bs and Ey in accordance with threshold limits of the storm producing criteria (more frequently observed in sheath than ejecta). The average values of Bs and Ey are significantly different from moderate to strong magnetic storms.

Effects of different source characteristics on the propagated CR and secondary neutrino spectra: A CRPropa3 simulation

Fri, 03/22/2019 - 19:10

Publication date: Available online 18 March 2019

Source: Advances in Space Research

Author(s): G. Rastegarzadeh, H. Fallahnejad

Abstract

Astrophysical and cosmogenic neutrinos are produced in the interactions of ultra-high energy cosmic rays. Astrophysical neutrinos originate from the interactions of cosmic ray protons with the matter (pp interactions) or photons (γ p interactions) inside their sources and have energies ranging from TeV to 10PeV, while cosmogenic neutrinos are produced during cosmic rays propagation in the intergalactic medium through the interaction with cosmic microwave background (CMB) as well as infrared and optical background (IRB) photons and have energies up to 100EeV. These neutrinos can travel without deflection and reach earth, so the study of this messengers can reveal different characteristics of the cosmic ray sources. In addition to the properties of the sources, the redshift of the sources and the photon background characteristics can also be important in the propagation of cosmic rays. In this paper, first by applying analytical approaches, we calculate the optical depths of UHECR sources (τ) which generate astrophysical neutrinos, and by using the observed fluxes of CR and astrophysical neutrino, we calculate τ0min for different CR source spectral indexes. Then, using CRPropa3 code, we simulate the propagation of UHECRs in the extragalactic medium. Taking a reference case, the propagated CR and neutrino flux are obtained for sources with pure proton mass composition, minimum energy of 0.1 EeV to the maximum rigidity of 200 EV, minimum redshift of zmin=0.0007, maximum redshift of zmax=6 and the Gilmore 2012 IRB background model. Switching the composition to a mixed galactic composition and pure Fe, it is shown that CR and neutrino fluxes are affected by changing the cosmic ray composition. Furthermore, effects of different IRB models and maximum redshift of the sources are investigated. Finally, three source redshift distributions of 3⩽z≤4,4⩽z≤5 and 5⩽z≤6 are considered and the changes in spectra are demonstrated. The study of these changes can help us to understand the nature of UHECR sources.

A novel algorithm for differentiating cloud from snow sheets using Landsat 8 OLI imagery

Fri, 03/22/2019 - 19:10

Publication date: Available online 18 March 2019

Source: Advances in Space Research

Author(s): Tingting Wu, Ling Han, Qing Liu

Abstract

The separation of clouds from snow is fundamentally very challenging because of their similar spectral signature. A new algorithm was proposed to detect clouds from snow in Landsat 8 imagery. Taking the Hetian District region, where there is frequent cloud and snow cover, in northwestern China as one of the typical case areas. The typical case is presented in detail to illustrate the approach produces and results. A band math method for cloud and snow discrimination index (CSDI) was firstly conducted in this paper, fractal digital number-frequency (DN-N) algorithm and hotspot analyses were applied to determine the threshold of the CSDI and eliminate false anomalies. The results showed that an overall accuracy exceeding 95% in areas with very bright land surfaces, which indicate that this algorithm is effective for detecting clouds in specific situations where the ground objects have some reflectance characteristics similar to cloud.

Design and Deployment of a Tetrahedral Formation with Passive Deputy Nanosatellites for Magnetospheric Studies

Fri, 03/22/2019 - 19:10

Publication date: Available online 16 March 2019

Source: Advances in Space Research

Author(s): Michael D. Koptev, Sergey P. Trofimov, Mikhail Yu. Ovchinnikov

Abstract

The problem of designing and deploying a highly elliptical orbit tetrahedral formation of one chief microsatellite and several deputy nanosatellites is examined. Such a formation can be utilized in a number of space science missions, with magnetospheric studies as a main application. To measure the quality of the geometrical configuration in the region of interest, the scalar factor is used which evaluates both the shape and the scale of the formation. To maximize the formation quality, initial orbital elements of all the satellites are optimally selected using the K-60 supercomputing cluster. Several formation deployment schemes are considered, taking into account possible orbit injection errors.

Author Index

Fri, 03/22/2019 - 19:10

Publication date: 15 April 2019

Source: Advances in Space Research, Volume 63, Issue 8

Author(s):

List of Referees

Fri, 03/22/2019 - 19:10

Publication date: 15 April 2019

Source: Advances in Space Research, Volume 63, Issue 8

Author(s):

Retraction: Ionospheric climatology derived from GPS occultation observations made by the ionospheric occultation experiment [Adv. Space Res. 39(5) (2007) 793–802]

Fri, 03/22/2019 - 19:10

Publication date: 15 April 2019

Source: Advances in Space Research, Volume 63, Issue 8

Author(s): P.R. Straus

Investigations on the suitability of PEEK material under space environment conditions and its application in a parabolic space antenna

Fri, 03/22/2019 - 19:10

Publication date: Available online 14 March 2019

Source: Advances in Space Research

Author(s): Sahil Kalra, B.S. Munjal, Vaibhav Raj Singh, Milind Mahajan, Bishakh Bhattacharya

Abstract

Application specific, lightweight yet high strength materials always remain in large demand to the aerospace engineers. Poly-ether-ether-ketone (PEEK) is a unique polymer which has low density, high glass transition temperature, and stability at an ultra-high vacuum condition. In addition, high compliance of PEEK and ease of vacuum forming facilitate the development of complex geometric shapes. In this research, we have investigated the suitability of PEEK material for parabolic antenna structure under space environment conditions. We have carried out rigorous space qualification tests on various categories of PEEK material. With the promising experimental results, we have developed a 450 mm diameter prime focal C-band Antenna. The parabolic antenna is made up of PEEK material, and it is supported on the curved ribs made up of PEEK CA30 material. The developed antenna setup is further installed for far-field radiation testing in a Compact Antenna Test Facility (CATF) in the anechoic chamber. Simultaneously, RF simulations are carried out using CST software. The simulated and measured far-field radiation patterns show close agreements. Thereafter, thermal analysis of the developed antenna and the effect of thermal expansion on radiation far-field are discussed. The developed antenna is very promising to be used in the future space missions.

Least squares orbit estimation including atmospheric density uncertainty consideration

Fri, 03/22/2019 - 19:10

Publication date: Available online 12 March 2019

Source: Advances in Space Research

Author(s): Fabian Schiemenz, Jens Utzmann, Hakan Kayal

Abstract

Density uncertainty is the major driver of unrealistic covariances for objects in low Earth orbits. The analytic propagation of uncertainties in the neutral atmospheric density to resulting uncertainties in the orbital position and velocity has only received little attention in the literature so far.

The main contribution of the paper at hand is the analytic development of an orbital state-vector error variance-covariance matrix that models the propagation of uncertainties in atmospheric density to the orbital state-vector error in the Geocentric Celestial Reference Frame (GCRF). Also extensions of the classical batch weighted least squares (WLS) and the sequential batch weighted least squares algorithms, which allow to incorporate this covariance matrix as process-noise, are presented.

Numerical simulations with three different semi-empirical models are provided to validate the derivations. It is shown that the extension of the WLS-algorithm in combination with the density uncertainty GCRF covariance matrix is able to consistently perform orbit and covariance estimation, which is not the case without density uncertainty consideration in a classical WLS algorithm.

Propagating EUV solar flux uncertainty to atmospheric density uncertainty

Fri, 03/22/2019 - 19:10

Publication date: Available online 11 March 2019

Source: Advances in Space Research

Author(s): Fabian Schiemenz, Jens Utzmann, Hakan Kayal

Abstract

The call for realistic covariances/uncertainties in orbit determination/estimation and propagation is becoming louder. The main reason for unrealistic uncertainties is, in most cases, a disregard of force model uncertainties, i.e. the calculated covariances are based only on the measurement uncertainties. For this reason the covariances are often scaled in practice to avoid misjudgment of orbit knowledge. J. Emmert has recently shown how solar flux uncertainties can be propagated to in-track orbit position errors in the case of long-term orbit propagation. In his method, the density error resulting from solar flux errors is obtained via the underlying atmospheric model. In this paper, a universal analytic approximation of density uncertainty is presented, which is a fast, yet reliable, alternative to the case-based propagation via the atmospheric model. The major benefit of the proposed analytic estimations is that they seamlessly integrate with orbit estimation/propagation. The uncertainty estimate can directly be computed without an additional call to the atmospheric model.

Field Line Random Walk, Field Line Separation, and Particle Transport in Turbulence with Weak Transverse Complexity

Fri, 03/22/2019 - 19:10

Publication date: Available online 11 March 2019

Source: Advances in Space Research

Author(s): A. Shalchi

Abstract

We study the random walk of magnetic field lines as well as field line separation in a magnetized plasma such as the solar wind or the interstellar medium. By doing so we focus on turbulence with small Kubo numbers. For field line random walk this allows us to employ an approach based on a Taylor expansion which is essentially an expansion in the Kubo number. Compared to previous non-linear descriptions, no assumption concerning the field line distribution or diffusivity has to be made. Based on this approach, we compute corrections to the quasi-linear formula allowing us also to test assumptions usually made in non-linear theories of field line random walk. We show that up to the considered order, the assumption of Gaussian statistics does not alter the diffusion coefficient whereas the diffusion approximation provides a correction term which is a factor two too large. We also discuss the separation of two magnetic field lines. We develop a quasi-linear theory for field line separation and introduce a fundamental scale of turbulence describing its transverse structure. Furthermore, we discuss applications of our results in the theory of energetic particle transport. Besides quasi-linear diffusion we also discuss compound sub-diffusion as well as the recovery of diffusion due to transverse complexity. Furthermore, we derive a formula for the perpendicular diffusion coefficient of energetic particles similar compared to the famous Rechester & Rosenbluth result. Applications in astrophysics are also discussed.

A numerical approach to the problem of angles-only initial relative orbit determination in low earth orbit

Fri, 03/22/2019 - 19:10

Publication date: Available online 9 March 2019

Source: Advances in Space Research

Author(s): Jean-Sébastien Ardaens, Gabriella Gaias

Abstract

A practical and effective numerical method is presented, aiming at solving the problem of initial relative orbit determination using solely line-of-sight measurements. The proposed approach exploits the small discrepancies which can be observed between a linear and a more advanced relative motion model. The method consists in systematically performing a series of least-squares adjustments at varying intersatellite distances in the vicinity of a family of collinear solutions coming from the linear theory. The solution presenting the smallest fitting residuals is then selected. The investigations specifically focus on the rendezvous in low Earth near-circular orbit with a noncooperative target. The objective is to determine the relative state of the formation using only bearing observations when the spacecraft are separated by a few dozen kilometers without any a priori additional information. The method is validated with flight data coming from the ARGON (2012) and AVANTI (2016) experiments. Both cases demonstrate that an observation time span of a few maneuver-free orbits is enough to compute a solution which can compete with Two-Line Elements in terms of accuracy.

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