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Advances in Space Research
Journal Prestige (SJR): 0.569
Citation Impact (citeScore): 2
Number of Followers: 403  
 
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ISSN (Print) 0273-1177
Published by Elsevier Homepage  [3160 journals]
  • RadioAstron reveals super-compact structures in the bursting
           H2O maser source G25.65+1.05
    • Abstract: Publication date: Available online 20 March 2019Source: Advances in Space ResearchAuthor(s): O.S. Bayandina, N.N. Shakhvorostova, A.V. Alakoz, R.A. Burns, S.E. Kurtz, I.E. Val’tts 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.
       
  • A Gaussian Random Field Model for De-speckling of Multi-polarized
           Synthetic Aperture Radar Data
    • Abstract: Publication date: Available online 19 March 2019Source: Advances in Space ResearchAuthor(s): Masoud Mahdianpari, Mahdi Motagh, Vahdi Akbari, Fariba Mohammadimanesh, Bahram Salehi 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.
       
  • Dynamic modeling and modal parameters identification of satellite with
           large-scale membrane antenna
    • Abstract: Publication date: Available online 19 March 2019Source: Advances in Space ResearchAuthor(s): Liang Fan, Xiang Liu, Guo-ping Cai 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.
       
  • Robust Foreground Segmentation and Image Registration for Optical
           Detection of GEO Objects
    • Abstract: Publication date: Available online 19 March 2019Source: Advances in Space ResearchAuthor(s): Huan N. Do, Tat-Jun Chin, Nicholas Moretti, Moriba K. Jah, Matthew Tetlow 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.
       
  • Effects of different source characteristics on the propagated CR and
           secondary neutrino spectra: a CRPropa3 simulation
    • Abstract: Publication date: Available online 18 March 2019Source: Advances in Space ResearchAuthor(s): G. Rastegarzadeh, H. Fallahnejad 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 interagalactic 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 0.1EeV to the maximum rigidity of 200EV, 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
    • Abstract: Publication date: Available online 18 March 2019Source: Advances in Space ResearchAuthor(s): Tingting Wu, Ling Han, Qing Liu 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
    • Abstract: Publication date: Available online 16 March 2019Source: Advances in Space ResearchAuthor(s): Michael D. Koptev, Sergey P. Trofimov, Mikhail Yu. Ovchinnikov 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.
       
  • List of Referees
    • Abstract: Publication date: 15 April 2019Source: Advances in Space Research, Volume 63, Issue 8Author(s):
       
  • Penetrating particle ANalyzer (PAN)
    • Abstract: Publication date: 15 April 2019Source: Advances in Space Research, Volume 63, Issue 8Author(s): X. Wu, G. Ambrosi, P. Azzarello, B. Bergmann, B. Bertucci, F. Cadoux, M. Campbell, M. Duranti, M. Ionica, M. Kole, S. Krucker, G. Maehlum, D. Meier, M. Paniccia, L. Pinsky, C. Plainaki, S. Pospisil, T. Stein, P.A. Thonet, N. Tomassetti PAN is a scientific instrument suitable for deep space and interplanetary missions. It can precisely measure and monitor the flux, composition, and direction of highly penetrating particles (>∼100 MeV/nucleon) in deep space, over at least one full solar cycle (11 years). The science program of PAN is multi- and cross-disciplinary, covering cosmic ray physics, solar physics, space weather and space travel. PAN will fill an observation gap of galactic cosmic rays in the GeV region, and provide precise information of the spectrum, composition and emission time of energetic particle originated from the Sun. The precise measurement and monitoring of the energetic particles is also a unique contribution to space weather studies. PAN will map the flux and composition of penetrating particles, which cannot be shielded effectively, precisely and continuously, providing valuable input for the assessment of the related health risk, and for the development of an adequate mitigation strategy. PAN has the potential to become a standard on-board instrument for deep space human travel.PAN is based on the proven detection principle of a magnetic spectrometer, but with novel layout and detection concept. It will adopt advanced particle detection technologies and industrial processes optimized for deep space application. The device will require limited mass (20 kg) and power (20 W) budget. Dipole magnet sectors built from high field permanent magnet Halbach arrays, instrumented in a modular fashion with high resolution silicon strip detectors, allow to reach an energy resolution better than 10% for nuclei from H to Fe at 1 GeV/n. The charge of the particle, from 1 (proton) to 26 (Iron), can be determined by scintillating detectors and silicon strip detectors, with readout ASICs of large dynamic range. Silicon pixel detectors used in a low power setting will maintain the detection capabilities for even the strongest solar events. A fast scintillator with silicon photomultiplier (SiPM) readout will provide timing information to determine the entering direction of the particle, as well as a high rate particle counter. Low noise, low power and high density ASIC will be developed to satisfy the stringent requirement of the position resolution and the power consumption of the tracker.
       
  • Influence of the transport regime on the energetic particle density
           profiles upstream and downstream of interplanetary shocks
    • Abstract: Publication date: 15 April 2019Source: Advances in Space Research, Volume 63, Issue 8Author(s): Giuseppe Prete, Silvia Perri, Gaetano Zimbardo The spatial distribution of energetic particles accelerated at shocks depends on their transport properties. Analyses of energetic particle fluxes measured by spacecraft upstream of interplanetary shock waves have pointed out the presence of spatial profiles different from those expected for normal diffusion. We propose that anomalous, superdiffusive transport can help to interpret the observed energetic particle profiles both upstream and downstream of shock waves. We set up a numerical model to compute the energetic particle profiles on both sides of the shock: particles are injected at the shock and then propagate according to a Gaussian random walk in the case of normal diffusion and according to a Lévy random walk in the case of superdiffusion. The latter is characterized by a nonlinear growth of the mean square displacement of particles and by a power law distribution of free path lengths. A Langevin type equation is solved numerically, and energetic particle spatial profiles are obtained for a steady state configuration. A number of numerical solutions are obtained: in the case of normal diffusion, the well known exponential profile upstream of the shock is recovered. In the case of superdiffusion, varying the power exponent and the scale time characterizing the power law distribution of free path times, it is found that power law upstream profiles and spatially nonconstant downstream profiles are obtained. A preliminary comparison between the obtained numerical results and interplanetary shock observations by the ACE spacecraft is carried out, and good agreement between the energetic particle profiles is found. This shows that the present superdiffusive model can be helpful for interpreting the overall time/space trends of particles accelerated at interplanetary shock waves.
       
  • The cross correlation method response prior to earthquakes using foF2 data
           from various ionospheric stations
    • Abstract: Publication date: 15 April 2019Source: Advances in Space Research, Volume 63, Issue 8Author(s): K. Benghanem, S. Kahlouche, A. Abtout, H. Beldjoudi Considering the non-systematic aspect in detection of seismo-ionospheric precursors; we propose an attempt to characterize the nature of the perturbations in the F2 ionospheric layer prior to earthquakes using cross-correlation method. The effectiveness of cross-correlation method is not questioned; but could the use of more than two observation points undergoing identical influence of solar activity reveal the same perturbations for the same earthquake'The cross-correlation method is known for its ability to eliminate the solar activity effect when two measurements of the critical frequency of the F2 ionospheric layer (foF2) are correlated. As the observation points (ionosonde stations) used have similarity of geographical location they necessarily undergo the same influence of solar activity. Thus only the seismogenic aspect would remain in the cross-correlation coefficients. Therefore we have considered only earthquakes where there are several ionosonde stations satisfying the conditions of use of cross-correlation method. Using several stations should allow determine whether the cross-correlation coefficients vary in the same way for the same event or not.More than Fifty earthquakes from Mediterranean Basin and Japan with magnitude 5 ≤ M ≤ 6.6 and depth not exceeding 40 km are selected according to the availability of critical frequency data of the F2 ionospheric layer. Results vary from one earthquake to another. This is normal because each earthquake has its own characteristics. But the response of the cross-correlation technique is not always the same for the same event. Thus, there are cases where, for the same event, the variation of cross-correlation coefficients has the same behavior for the various pairs of stations considered and other cases where the response is not similar.Neither the magnitude of the earthquake nor the position of the internal station with respect to the epicenter, nor the position of the external stations relative to the internal station, could explain the difference in the behavior of the cross-correlation coefficients during the earthquake preparation process.
       
  • Precursor effect of March 11, 2011 off the coast of Tohoku earthquake on
           high and low latitude ionospheres and its possible disturbing mechanism
    • Abstract: Publication date: 15 April 2019Source: Advances in Space Research, Volume 63, Issue 8Author(s): K.I. Oyama, C.H. Chen, L. Bankov, D. Minakshi, K. Ryu, J.Y. Liu, H. Liu Ionosphere disturbance which was seen prior to an earthquake which occurred on 11 March 2011 off the coast of Tohoku was studied. Ionosphere data which were used are: O+ density acquired with US satellite DMSP, and NmF2, h’F, and fmin obtained by ionosondes. Global Ionosphere Model (GIM) is used as side evidence to compliment findings from DMSP data and ground- based data.Although magnetic disturbance is strong during the earthquake preparation period, global survey of ground based NmF2 shows that special disturbance is limited to earthquake area. Satellite data (DMSP and GIM) analysis shows four important findings before the occurrence of the earthquake; (1) Over geomagnetic equator enhancement of O+ is found, (2) midlatitude trough (MLT) is formed before the earthquake and it moves toward lower latitude as EQ day approaches, (3) O+ enhancement at the equator side edge of the MLT, and (4) no clear difference of O+ behavior between east and west of the epicenter is identified. These four features are connected each other. Night time NmF2 at high latitude ionosonde stations such as Khabarovsk shows 2 days oscillation from 5 March and disappears on 12 March. As the latitude of the station is lower, 2 days oscillation becomes unclear, and the duration of the appearance is shorter.In order to explain both ground – based and satellite data consistently, enhanced east (west) ward dynamo electric field during daytime (nighttime) are proposed. Our speculation is that internal gravity waves of extremely small amplitude due to the ground motion interact with planetary scales waves below 10 km and is amplified. The amplified IGW propagates to the dynamo region, modifies the wind system, or conductivity, which modifies the electric field. Several observational facts which are favor to the generation of IGW are described. Finally, we stress the need of satellite constellation in order to obtain the global morphology of ionosphere disturbance and to identify the mechanism, which at least provides us the material to judge applicability to future earthquake prediction.
       
  • Longitudinal variability of occurrence of ionospheric irregularities over
           the American, African and Indian regions during geomagnetic storms
    • Abstract: Publication date: 15 April 2019Source: Advances in Space Research, Volume 63, Issue 8Author(s): Teshome Dugassa, John Bosco Habarulema, Melessew Nigussie This study presents the longitudinal variabilities of occurrence of ionospheric irregularities over the equatorial/low-latitude region of America, Africa and Indian sectors. Five major geomagnetic storms of the equinoctial months of the year 2012–2013 were analyzed for this study. Total Electron Content (TEC) data obtained from Global Navigation Satellite Systems (GNSS) over American, African and Indian longitudinal sectors were used to derive, the rate of change of TEC index (ROTIave), the ionospheric irregularities proxy. Longitudinal variability of occurrence of irregularities were discussed with respect to the local time when the maximum negative of SYM-H index occurs and polarity of IMF Bz in the dusk hours. Almost all of the storms under investigation inhibited the occurrence of irregularities in Indian sector. Out of five storms, two and three storm periods revealed inhibition in the generation of irregularities over the American and African sectors, respectively. Most of the generation of ionospheric irregularities observed in this study were related to post-midnight local time occurrence of the maximum negative excursion of SYM-H index. There were also cases where irregularities are observed when the minimum value of SYM-H occurred in the pre-midnight and daytime period. It appears that the local time at which minimum SYM-H occur is not a sufficient condition to explain the effect of storms on generation/inhibition of ionospheric irregularities. Significant longitudinal variability in the generation of irregularities were also observed over wide longitudinal ranges (South America, Africa and India) during 09 March 2012 and 17 March 2013 storm events. Difference in longitudinal variation of storm-time electric field were a suggested reason.
       
  • Development of assessment methods of lunar soil simulants with respect to
           chemical composition
    • Abstract: Publication date: 15 April 2019Source: Advances in Space Research, Volume 63, Issue 8Author(s): Byung Chul Chang, Ki Yong Ann The present study concerns a development of assessment tools for lunar soil simulant chemical composition. Prior to developing the methodology, lunar soil was investigated by using the lunar soil samples from Apollo missions then quantifying the average value and standard deviation of the respective oxides. For the assessment methods, the error index and grade index methods were simultaneously developed. As for the error index method, the difference between lunar soil and lunar simulant was summed up, considering the concentration of respective oxides in lunar soil. Thus, a lower value for this index would indicate higher similarity to the lunar soil. To reflect the variation in oxides in lunar soil (i.e., standard deviation), a grade was given to each oxide in the lunar simulant in the grade index method. In the present study, 6 different grades were used to rank the grade score to each grade. The summed value of the grade score is indicative of the similarity of lunar simulant to lunar soil. To demonstrate the feasibility of these methods, the JSC-1 and NU-LHT-1M lunar simulants were taken as examples. It is expected that these assessment method would be useful to rank and evaluate the quality of lunar simulants.
       
  • Flexible airbag cushioning for Martian landing based on discrete element
           method
    • Abstract: Publication date: 15 April 2019Source: Advances in Space Research, Volume 63, Issue 8Author(s): Pan Cao, Xuyan Hou, Yongbin Wang, Meng Li, Xiaoshan Rao, Yuetian Shi With the exploration missions to Mars gradually turning from detection of the surroundings to landing patrol, an airbag cushion system has become a new research area. A large number of researchers have simulated the airbag landing buffering process through numerical calculation methods, and applied the simulation results to optimise the airbag system parameters. According to a summary of previous studies, the researchers have all used a continuous geometry to simulate an impacted surface. Such a model cannot truly reflect the discrete morphological features of the Martian surface, however, and cannot predict the actual airbag cushion characteristics of the Martian subsurface. Based on this problem, this work proposes the use of discrete elements to study the cushioning characteristics of an airbag. This method has certain advantages in simulating the discrete surface of Mars and the dynamic characteristics of discrete surfaces after an impact. At the same time, to simulate the cushioning process of an airbag on the discrete ground, it is necessary to focus on a method of modelling the airbag based on the discrete element theory. We establish a three-dimensional particle-spring equivalent model of an inflatable airbag microelement based on the discrete element idea, and the model parameters are matched based on theory and a simulation. Finally, the discrete element simulation model of a spherical inflatable airbag is established using the discrete element simulation software EDEM, and the reliability of the model is verified by comparing the experimental and simulation values. Based on a theoretical derivation, the physical quantities that affect the airbag acceleration are obtained; these physical quantities are used as variables to perform a multi-condition simulation analysis, and the preliminary variation law between the acceleration and physical quantities is obtained. Further, a multi-ball model for a multi-state simulation analysis is described, along with the simulation results used to predict the cushioning characteristics of the airbag landing in the Martian environment.
       
  • Multi-type multi-objective imaging scheduling method based on improved
           NSGA-III for satellite formation system
    • Abstract: Publication date: 15 April 2019Source: Advances in Space Research, Volume 63, Issue 8Author(s): Ke Wu, Dexin Zhang, Zhonghua Chen, Junli Chen, Xiaowei Shao This paper studies the imaging scheduling issue for China’s L-band differential interferometric synthetic aperture radar (InSAR) satellite formation which can work in different observation modes to satisfy different imaging requests. Previous imaging scheduling mainly focuses on maximizing the total revenue of selected targets but ignores that different types of targets actually have different demands. Therefore, a constraint satisfaction model which classifies targets into three types according to targets’ size and number of observations is established, meanwhile, three objective functions are considered to satisfy demands of different types of targets. Furthermore, an imaging scheduling method based on improved non-dominated sorting genetic algorithm III (NSGA-III) is proposed to obtain a set of well-converged and well-diversified non-dominating solutions. New Niche-Preservation operation with the same penalty value for convergence and diversity performance is adopted in NSGA-III. Numerical comparison simulations on walking fish group (WFG) test suits and three imaging scheduling instances of different size show the superiority of the proposed methodology.
       
  • Safe Mars landing strategy: Towards lidar-based high altitude hazard
           detection
    • Abstract: Publication date: 15 April 2019Source: Advances in Space Research, Volume 63, Issue 8Author(s): Xueming Xiao, Meibao Yao, Hutao Cui, Yuegang Fu This paper presents a high-altitude hazard detection method for Mars landing. Current terminal-triggered methods do not fully support re-targeting maneuvers if all regions are found unsafe. Towards safe landing requirements for future missions, hazard detection should be triggered as soon as possible. We therefore proposed a lidar-based high altitude hazard detection approach, consisting of two main procedures: Terrain reconstruction and Hazard mapping. Morphological filters are first carried out to remove outliers. An interpolation-based terrain reconstruction algorithm is then proposed to model the datum surface of landing region. For hazard mapping, an innovative hazard assessment function is proposed to generate a continuous hazard map that with full hazard information. The new approach is simple but well-performed, and only few parameters are needed. Both synthetic and real data are used to validate the detection performance, and preliminary results show the superiority of the proposed algorithms compared with current plane-based hazard detectors.
       
  • Assessing possible mutual orbit period change by shape deformation of
           Didymos after a kinetic impact in the NASA-led Double Asteroid Redirection
           Test
    • Abstract: Publication date: 15 April 2019Source: Advances in Space Research, Volume 63, Issue 8Author(s): Masatoshi Hirabayashi, Alex B. Davis, Eugene G. Fahnestock, Derek C. Richardson, Patrick Michel, Andrew F. Cheng, Andrew S. Rivkin, Daniel J. Scheeres, Steven R. Chesley, Yang Yu, Shantanu P. Naidu, Stephen R. Schwartz, Lance A.M. Benner, Petr Pravec, Angela M. Stickle, Martin Jutzi, the DART Dynamical and Physical Properties (WG3) analysis group The Asteroid Impact & Deflection Assessment (AIDA) targets binary near-Earth asteroid (65803) Didymos. As part of this mission, the NASA-led Double Asteroid Redirection Test (DART) will make a kinetic impactor collide with the smaller secondary of Didymos to test kinetic impact asteroid deflection technology, while the ESA-led Hera mission will evaluate the efficiency of the deflection by conducting detailed on-site observations. Research has shown that the larger primary of Didymos is spinning close to its critical spin, and the DART-impact-driven ejecta would give kinetic energy to the primary. It has been hypothesized that such an energy input might cause structural deformation of the primary, affecting the mutual orbit period, a critical parameter for assessing the kinetic impact deflection by the DART impactor. A key issue in the previous work was that the secondary was assumed to be spherical, which may not be realistic. Here, we use a second-order inertia-integral mutual dynamics model to analyze the effects of the shapes of the primary and the secondary on the mutual orbit period change of the system. We first compare the second-order model with three mutual dynamics models, including a high-order inertia-integral model that takes into account the detailed shapes of Didymos. The comparison tests show that the second-order model may have an error of ∼10% for computing the mutual orbit period change, compared to the high-order model. We next use the second-order model to analyze how the original shape and shape deformation change the mutual orbit period. The results show that when the secondary is elongated, the mutual orbit period becomes short. Also, shape deformation of the secondary further changes the mutual orbit period. A better understanding of this mechanism allows for detailed assessment of DART’s kinetic impact deflection capability for Didymos.
       
  • Finite time positioning control for a stratospheric airship
    • Abstract: Publication date: 15 April 2019Source: Advances in Space Research, Volume 63, Issue 8Author(s): Yueneng Yang The stratospheric airship provides a unique and promising aerostatic platform for broad applications, which requires fast and robust positioning control to support these tasks. A finite time control scheme is proposed to address the problem of positioning control for stratospheric airships subject to dynamics uncertainty. A nonsingular terminal sliding mode controller is designed for positioning control, which overcomes the problem of asymptotical convergence of sliding mode control and the singularity problem of terminal sliding mode control. Under the framework of nonsingular terminal sliding mode control, a fuzzy logic system is employed to approximate the uncertain dynamics of the stratospheric airship, and the fuzzy logic system approximation-based finite time sliding mode controller is designed. The finite-time convergence of positioning errors and the stability of the closed loop system are guaranteed by Lyapunov theory. Finally, the effectiveness and performances of the proposed controller are demonstrated through experimental simulations. Contrasting simulation results illustrate that the proposed controller decreases chattering effectively and ensures faster convergence compared to sliding mode controller.
       
  • Effect of ionospheric drag on atmospheric density estimation and orbit
           prediction
    • Abstract: Publication date: 15 April 2019Source: Advances in Space Research, Volume 63, Issue 8Author(s): C.J. Capon, B. Smith, M. Brown, R. Abay, R.R. Boyce Accurate prediction of aerodynamic forces in Low Earth Orbit (LEO) remains a key challenge for space situational awareness (SSA) and space traffic management (STM) activities. A neglected aspect of the LEO aerodynamics problem is the force resulting from the charged aerodynamic interaction of LEO objects with the ionosphere, i.e. ionospheric aerodynamics. This work studies the effect accounting for ionospheric drag may have on the motion of LEO objects. This work aims to assess the influence of ionospheric aerodynamics on atmospheric density estimation and orbit prediction capabilities essential to SSA and STM services. The approach taken in this work was to apply Particle-in-Cell (PIC) simulations to develop a surrogate model that describes the variation of a charged drag coefficient (CD,C) as a function of plasma scaling parameters. This surrogate model was then incorporated into an orbit propagator, and the influence of ionospheric drag on body motion is studied for a range of conditions. Results indicate that, when inferring atmospheric neutral density from orbit data, neglecting the contribution of ions without accounting for electrodynamic phenomena, may cause an over-prediction of neutral density ranging between 1% and 45% for the space weather condition considered (F10.7=150,ap=5). Including electrodynamic phenomena was seen to increase this over-prediction for all cases. Objects with thick plasma sheaths were shown to be particularly sensitive to ionospheric drag forces; thick plasma sheaths caused by either a reduction in object scale (rB) or increase in surface potential (ϕ). This result has important implications for modelling space debris populations as thick plasma sheaths may arise at natural floating potentials (-0.75V) when debris fragmentation occurs. For example, accounting ionospheric drag on a spherical debris object with a radius of 0.005 m, area-to-mass ratio of 0.0157 m2/kg and floating potential of -0.75 V in a circular equatorial orbit at 350 km altitude was predicted to cause a change in along-track position of 299 m (and a reduction in semi-major axis of 4 m) over a 24-h period. Results also have important implications for modern satellites, where the trend is toward nano/micro-satellite platforms (e.g. CubeSats) with high-voltage powers systems that may inadvertently cause large artificial surface potentials and therefore enhanced ionospheric aerodynamic forces.
       
  • Low Earth orbit satellite constellation for regional positioning with
           prolonged coverage durations
    • Abstract: Publication date: 15 April 2019Source: Advances in Space Research, Volume 63, Issue 8Author(s): Tomer Shtark, Pini Gurfil Satellite navigation constellations orbit the Earth in medium and geosynchronous orbits. Their high altitude provides wide coverage, which may be redundant if only regional coverage is needed. In this paper, a design scheme for regional navigation satellite constellations in low-Earth orbit is proposed. The design yields long coverage durations, which are characterized by a minimized Geometric Dilution of Precision (GDOP), with respect to a predefined mid-latitude receiver. The proposed constellations are defined for various combinations of the following parameters: Repeat Ground-Track commensurability, receiver latitude, number of satellites, and internal satellite arrangement. Optimal constellations, with respect to the GDOP integral, are searched, design guidelines are set up, and a mathematical model is fitted. The proposed constellations provide GDOP-optimized coverage durations, recurring twice each day. The results include numerical solutions for prograde near-polar constellations in altitudes ranging between 550 and 870 km, with receivers positioned at latitudes from 30° to 60°, and number of satellites ranging from 13 to 36. The average coverage duration varies from 20 to 80 min, with a mean GDOP ranging from 2.5 to 3.
       
  • Coupled rotational and translational modeling of two satellites connected
           by a tether and their robust attitude control using optimal offset
           approach
    • Abstract: Publication date: 15 April 2019Source: Advances in Space Research, Volume 63, Issue 8Author(s): Atefe Darabi, Nima Assadian In this study, the robust sliding mode attitude control of a tethered satellite system using optimal tether offset in the presence of perturbations and uncertainties is investigated. The three main goals of this study are: (1) comprehensive modeling of two satellites connected by a tether considering the coupling between their attitude and position, (2) finding a robust attitude control for both satellites, and (3) reducing the reaction wheels’ power consumption for attitude control utilizing the tether tension. In this regard, the 6 DOF governing equations of the coupled nonlinear rotational and translational dynamics of a two-satellite tethered system in the presence of perturbing forces are derived. Additionally, the offset of the tether attachment points from the center of mass of both satellites is modeled, which results in the coupling of two satellites’ dynamics. The tether tension force acts as external force and moment on each satellite which is used by an optimization method for attitude control of satellites along with their reaction wheels. The simulation results show that the designed sliding mode control stabilizes the attitude of both satellites in the presence of uncertainties and perturbations. Moreover, the optimal offset control saves the energy usage of reaction wheels up to 55 percent.
       
  • Quantifying uncertainties in signal position in non-resolved object
           images: Application to space object observation
    • Abstract: Publication date: 15 April 2019Source: Advances in Space Research, Volume 63, Issue 8Author(s): Francois Sanson, Carolin Frueh Charged Coupled Devices (CCDs) and subsequently Complementary metal-oxide-semiconductor (CMOS) detectors revolutionized scientific imaging. On both the CCD and CMOS detector, the generated images are degraded by inevitable noise. In many applications, such as in astronomy or for satellite tracking, only unresolved object images are available. Strategies to estimate the center of the non-resolved image their results are affected by the detector noise. The uncertainty in the center is classically estimated by running prohibitively costly Monte Carlo simulations, but in this paper, we propose analytic uncertainty estimates of the center position. The expressions that depend on the pixel size, the signal to noise ratio and the extension of the object signal relative to the pixel size are validated against rigorous Monte Carlo simulations with very satisfying results. Numerical tests show that our analytic expression is an efficient substitute to the Monte Carlo simulation thereby reducing computational cost.
       
  • Accurate propagation of debris orbit error via dynamic calibration and its
           cataloguing
    • Abstract: Publication date: 15 April 2019Source: Advances in Space Research, Volume 63, Issue 8Author(s): Bin Li, Jizhang Sang, Hongkang Liu Prediction accuracy of debris location in a perturbing environment is measured by the orbit covariance or uncertainty, which can be propagated with linear or nonlinear models. Linear models decline in propagation accuracy while nonlinear models are computationally intensive, thus not well applied for massive debris orbits needing the high precision. Usually, the debris observations are sparse, resulting in the linearly-propagated covariance over-optimistic. After analyzing with Monte Carlo simulation, the statistical characterizations of propagated orbit errors over past and future time are basically the same in terms of error magnitude, which is theoretically expected. For hundreds of thousands of debris, it only needs an accurate and efficient uncertainty propagation method. This paper proposes a method to dynamically calibrate the linearly-propagated covariance using past observations, including three steps in the estimation of initial orbit covariance, linear propagation of the estimated covariance, and dynamic calibration of the propagated covariance using past observations. Experiments of real data processing show that high-precision propagated errors are achieved, with the accuracy improved by more than 70% after calibration. Besides, to facilitate the catalogue of orbit error, an analytical representation of propagated covariance is proposed, which provides error information of the propagated orbit to users for various needs.
       
  • Space debris positioning based on two-dimensional PVDF piezoelectric film
           sensor
    • Abstract: Publication date: 15 April 2019Source: Advances in Space Research, Volume 63, Issue 8Author(s): E.L. Tang, L. Wang, Y.F. Han In order to determine the positions of debris collision spacecraft accurately, the experiments have been performed to impact orthogonal stacking two-dimensional Polyvinylidene fluoride (PVDF) piezoelectric film at different collision speeds based on the piezoelectric effects of the PVDF film by using two-stage light gas gun loading system and the self-constructed positioning system. The debris source was positioned accurately by PVDF strips sensor and testing system, which has been established to extract piezoelectric signals of the PVDF film during the process of impacting. The visualization of the position for debris impacting spacecraft was achieved through the LABview language programme and signal processing acquired by the signal acquisition system in the experiments. The experimental results show that the positions of the debris impacting source can be realized accurately by the piezoelectric effects of the orthogonal stacking two-dimensional PVDF film, the flight velocity and the incidence angle of the debris can be determined by installing the double-set PVDF film as the targets with a certain spacing.
       
  • Magnetic capture volume derivation and multi-magnetic dipoles
           configuration design for spacecraft soft-docking
    • Abstract: Publication date: 15 April 2019Source: Advances in Space Research, Volume 63, Issue 8Author(s): Yuan-wen Zhang, Le-ping Yang, Yan-wei Zhu, Da-wei Qi, Yi-peng Li Within spacecraft docking operation, electromagnetic coils provide an attractive way to generate required force/torque without propellant consumption and plume contamination. In addition, spacecraft electromagnetic docking has high-precision control capability of continuous, reversible, synchronous and non-contacting. However, the strong nonlinearity of electromagnetic force is still one of the difficult problems of the spacecraft soft-docking. By theoretical deriving and analyzing the magnetic capture volume between magnetic dipoles, this paper put forward a novel control approach for spacecraft electromagnetic soft-docking based on the multi-magnetic dipoles configuration design. And, these theoretical analysis and design are validated by several numerical simulation cases.
       
  • Estimating monthly average temperature by remote sensing in China
    • Abstract: Publication date: 15 April 2019Source: Advances in Space Research, Volume 63, Issue 8Author(s): Long Li, Yong Zha Air temperature is an important parameter affecting biosphere processes, air quality, regional climate, and human health, but is difficult to estimate, especially on a nationwide scale. Remote sensing provides high spatial resolution data that influence air temperature and can help overcome this problem in spatially heterogeneous environments. Generally, the simple linear relationships between air temperature, land surface temperature (LST), and auxiliary data, seldom consider the complex spatial variations in air temperature. The random forest (RF) regression model can characterize the complex temperature distribution by establishing the non-linear relationships among them. The main purpose of this paper is to present an RF regression method to estimate monthly average temperatures in China, using MODIS LST, normalized differential vegetation index (NDVI), night-time light, and a digital elevation model (DEM). Results based on cross-validation show that mean absolute error (MAE) and root mean square error (RMSE) at national level in different months ranged from 1.15 to 1.44 °C (mean ± standard deviation: 1.30 ± 0.10 °C) and from 1.57 to 1.99 °C (1.79 ± 0.13 °C), respectively. Potential sources of error and uncertainty were analyzed and investigated. Results show that regression model performs better in eastern (MAE: 0.68 ± 0.79 °C; RMSE: 0.75 ± 0.81 °C) and central China (MAE: 0.68 ± 0.41 °C; RMSE: 0.74 ± 0.41 °C). The model performance was strongly dependent on elevation, slope, land cover, and satellite data quality. In addition, the percentage increase in mean squared error from RF regression model was used to quantify the importance of variables. Positive importance scores indicated an improvement in accuracy with the assistance of NDVI, night-time lights, and the DEM. LST, and more auxiliary data sources, when integrated into an RF regression model, may be ways in which to improve the modeling of air temperature variations in the future.
       
  • On the variability of tides during a major stratospheric sudden warming in
           September 2002 at Southern hemispheric extra-tropical latitude
    • Abstract: Publication date: 15 April 2019Source: Advances in Space Research, Volume 63, Issue 8Author(s): A. Guharay, P.P. Batista Investigation of the middle atmospheric tidal response to the September 2002 sudden stratospheric warming (SSW) is carried out from a Southern hemispheric extra-tropical location Cachoeira Paulista (22.7°S, 45°W) using meteor radar observations and reanalysis database. Significant diurnal and semidiurnal tidal amplitudes are found in the mesosphere and lower thermosphere (MLT) a few days prior to the warming onset consistent with the high latitude observations. In the troposphere and stratosphere (TS) the tidal amplitudes attain higher value during the main phase of the warming which decrease subsequently. The simultaneous enhancement of the tidal amplitudes in the TS and diminution in the MLT may imply strong dissipation of the upward propagating tides during the SSW at present location. An evident signature of the tide-planetary wave coupling due to nonlinear interactions is found. A preferential modulation of the tidal amplitudes by long/short period planetary waves are observed in the MLT/TS. The migrating diurnal tide (DW1) and nonmigrating semidiurnal tide (SW1) at 10 hPa pressure level show considerable variability during the warming episode.
       
  • Neural network aided fast pointing information determination approach for
           occultation payloads from in-flight measurements: Algorithm design and
           assessment
    • Abstract: Publication date: 15 April 2019Source: Advances in Space Research, Volume 63, Issue 8Author(s): Songyan Zhu, Xiaoying Li, Jian Xu, Tianhai Cheng, Xingying Zhang, Hongmei Wang, Yapeng Wang, Jing Miao Pointing information is decisive to solving precise profile retrieval issues from occultation measurements. Research regarding stratospheric O3 hole in Antarctic and surface O3 pollution would significantly benefit from massive occultation measurements. A neural network aided pointing information determination approach, in terms of tangent heights, is proposed to address issues requiring fast and easy-to-use determined tangent heights. The geometrical triangular iteration (GTI) algorithm in this work is based on N2 absorption microwindows, and several treatments (e.g., tangential stride generator and triangular-net optimization) are adopted. In addition, LSTM is employed to reduce time consumption and increase accuracy. Atmospheric Chemistry Experiment-Fourier Transform Spectrometer (ACE-FTS) in-flight measurements are used to assess this approach. The comparison between the proposed algorithm and eight official products indicates a promising performance. Correlation coefficient for each orbit is greater than 0.99. The processing time is about 16.6 min per orbit with an average cost of ∼0.06. The introduction of LSTM technique demonstrates an approximate 28.49% better result, with less computation time. It costed less than 30 s to determine eight orbit tangent heights. In general, although minor issues remain, this LSTM-aided GTI algorithm is applicable in industry.
       
  • Retraction: Ionospheric climatology derived from GPS occultation
           observations made by the ionospheric occultation experiment [Adv. Space
           Res. 39(5) (2007) 793–802]
    • Abstract: Publication date: 15 April 2019Source: Advances in Space Research, Volume 63, Issue 8Author(s): P.R. Straus
       
  • Investigations on the suitability of PEEK material under space environment
           conditions and its application in a parabolic space antenna
    • Abstract: Publication date: Available online 14 March 2019Source: Advances in Space ResearchAuthor(s): Sahil Kalra, B.S. Munjal, Vaibhav Raj Singh, Milind Mahajan, Bishakh Bhattacharya 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
    • Abstract: Publication date: Available online 12 March 2019Source: Advances in Space ResearchAuthor(s): Fabian Schiemenz, Dr. Jens Utzmann, Dr. Hakan Kayal 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
    • Abstract: Publication date: Available online 11 March 2019Source: Advances in Space ResearchAuthor(s): Fabian Schiemenz, Dr. Jens Utzmann, Dr. Hakan Kayal 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
    • Abstract: Publication date: Available online 11 March 2019Source: Advances in Space ResearchAuthor(s): A. Shalchi 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.
       
  • Detumbling of a Non-cooperative Target with Unknown Inertial Parameters
           Using a Space Robot
    • Abstract: Publication date: Available online 8 March 2019Source: Advances in Space ResearchAuthor(s): Rabindra A. Gangapersaud, Guangjun Liu, Anton H.J. de Ruiter The detumbling of a non-cooperative, tumbling target by a space robot for the purpose of performing on-orbit servicing is a challenging and risky endeavour. The formulation of a detumbling control strategy must respect end-effector force/torque limits of the space robot without prior knowledge of the target’s inertial parameters (mass, inertia tensor, location of center of mass). Prior studies have formulated detumbling strategies with the assumption of accurate knowledge of the target’s inertial parameters. However, obtaining accurate estimates of the target’s inertial parameters is difficult, and parameter uncertainty may lead to instability and violation of the end-effector’s force/torque limits. In this paper, a novel detumbling strategy is presented to detumble targets without prior knowledge of their inertial parameters. Detumbling of the target is achieved by controlling the space robot to follow a reference force/torque that is designed to detumble the target while respecting force/torque limits at the end-effector, without the use of the target’s inertial parameters. To ensure stable detumbling of the target, a robust compensator is designed based on bounds of the target’s unknown inertial parameters. Furthermore, in order to reduce the robust control gains, bounds on the target’s unknown inertial parameters are estimated in real-time once the post-grasping detumbling process starts. Stability proof of the closed-loop system has been provided. Numerical simulations have been conducted, and the results have demonstrated the effectiveness of the proposed method.
       
  • Study of ULF-VLF Wave Propagation in the Near-Earth Environment for
           Earthquake Prediction
    • Abstract: Publication date: Available online 8 March 2019Source: Advances in Space ResearchAuthor(s): Alireza Mahmoudian, Mohammad Javad Kalaee This work presents the study on the electromagnetic wave penetration and propagation into the ionosphere in the frequency range of 100 Hz to 3 kHz and 3 kHz to 10 kHz, corresponding to the Ultra Low Frequency (ULF) and Very Low Frequency (VLF), respectively, for various types of applications including earthquake prediction. The main idea here is to investigate the efficiency of whistler/helicon wave generation in the E-region under different ionospheric conditions by solving Maxwell’s equations and incorporating ionospheric conditions through the Hall, Pedersen, and parallel conductivities. Specifically, the effect of pulse and continuous probing of the lower ionosphere with ULF-VLF signals and the generation of secondary waves and currents due to high conductivities in the E-region is studied. The characteristics and applications of the excited Helicon ULF-VLF waves are discussed. The effect of background ionospheric parameters such as the electron density and ionospheric disturbances due to pre-earthquake conditions and other natural sources including lightning discharges on the excitation and penetration of ULF-VLF waves into the E-region is investigated. The efficiency of this technique in developing a monitoring system to detect and locate seismic activities is discussed.
       
  • LISA Pathfinder mission extension: A feasibility analysis
    • Abstract: Publication date: Available online 6 March 2019Source: Advances in Space ResearchAuthor(s): Diogene A. Dei Tos, Mirco Rasotto, Florian Renk, Francesco Topputo A proposed mission extension for LISA Pathfinder involved redirecting the probe to the Sun–Earth gravitational saddle point. Realistic models for both space and ground segments were used to carry out a number of analyses for trajectory design, orbit determination, and navigation cost. In this work, we present the methods that allow assessing the feasibility of flying general limited-control-authority spacecraft in highly nonlinear dynamics, and in particular of the proposed mission extension in a statistically reliable approach. Solutions for transfers from the Sun–Earth L1 and L2 to the saddle point are shown, which feature very low Δv consumption, from few centimeters per second to 10 m/s. The analysis is then specialized to the case of LISA Pathfinder, for which several solutions are presented. This work gives evidence that LISA Pathfinder might have been able to fly-through the saddle point, provided initial tracking errors within 10 km in each position component and 0.1 m/s in each velocity component. A critical discussion on the opportunistic mission extension is eventually made.
       
  • Characteristics of inter-system biases in Multi-GNSS with precise point
           positioning
    • Abstract: Publication date: Available online 6 March 2019Source: Advances in Space ResearchAuthor(s): Ju Hong, Rui Tu, Yaping Gao, Rui Zhang, Lihong Fan, Pengfei Zhang, Jinhai Liu The impact of inter-system bias (ISB) on integrated precise point positioning (PPP) in multi-GNSS cannot be ignored. Precise orbit/clock products of Multi-GNSS Experiment (MGEX) satellites are diverse and gradually maturing. Analysing short-term and long-term variation characteristics of different types of ISB is thus helpful in understanding their error characteristics. In this study, ISB estimation models were proposed for GPS, GLONASS, BDS, and GALILEO systems with ionosphere-free (IF) combination observations. Then, the characteristics of ISB were mostly analyzed in detail with reverse and forward filtering method. Finally, according to the diurnal variation characteristics of ISB, which were estimated using precise products from several analysis centres, different processing strategies were adopted for ISBs to determine the optional solution strategies. Preliminary results are as follows: (1) The daily mean values of ISB estimated using the same analysis centre products between GPS and GLONASS as well as between GPS and BDS differed, but they were significantly correlated with receiver types. (2) Precise products of the same satellite system exhibited systematic deviations between analysis centres, although they were consistent on the weekly scale; however, the system bias of different satellite systems of the same analysis centres and system bias of different analysis centres all differed. (3) The daily and weekly stability of ISB estimated using different analytical centre products showed similar characteristics. Furthermore, the intra-week daily stability and weekly stability of the ISB of different stations showed good consistency. (4) Considering the strength of the observed model and the stability and reliability of the positioning results, Multi-GNSS PPP with precise products of CODE, GFZ, iGMAS and WHU showed the best performance under constant estimation, 20 min piecewise constant estimation, 1 h piecewise constant estimation and constant estimation strategies, respectively.
       
  • List of Referees
    • Abstract: Publication date: 1 April 2019Source: Advances in Space Research, Volume 63, Issue 7Author(s):
       
  • Variations of geomagnetic cutoff rigidity in the southern hemisphere close
           to 70°W (South-Atlantic Anomaly and Antarctic zones) in the period
           1975–2010
    • Abstract: Publication date: 1 April 2019Source: Advances in Space Research, Volume 63, Issue 7Author(s): E.G. Cordaro, P. Venegas-Aravena, D. Laroze We report the existence of rapid variations in (effective) geomagnetic cutoff rigidity (Rc) between the equatorial and Antarctic zones adjacent to the Andes Mountains, revealed by the variation rate of geomagnetic cutoff rigidity (VRc) in the period 1975–2010. Our analysis is based on empirical records and theoretical models of the variations in cosmic rays and on the structure of geomagnetic fields. These have given us a different view of variations in Rc in time and space along the 70°W meridian, where secular variations in the geomagnetic field are strongly influenced by the proximity of the South Atlantic Magnetic Anomaly (SAMA), one of the most important characteristics of the terrestrial magnetic field that affects our planet, close from the equator to the 50°S parallel and from South America to South Africa. The VRc presents rapid changes in mid-latitudes where SAMA exerts its influence despite the existence of smooth changes in the geomagnetic field. This shows that these changes occur mainly in the spatial configuration, rather than in the temporal evolution of Rc. The analysis was performed using measurements from the Chilean Network of Cosmic Rays and Geomagnetism Observatories, equipped with BF-3 and latest generation He-3 neutron monitors, Fluxgate magnetometers, geomagnetic reference field (IGRF) and Tsyganenko 2001 model (just for completeness).
       
  • Study of VLF wave with relativistic effect in Saturn magnetosphere in the
           presence of parallel A.C. electric field
    • Abstract: Publication date: 1 April 2019Source: Advances in Space Research, Volume 63, Issue 7Author(s): Jyoti Kumari, R.S. Pandey Cassini radio and plasma wave surveys aim to study radio emissions, plasma waves, thermal plasma and dust near Saturn. Using the characteristic solution and dynamics method, the influence of electron beam on the loss cone and bi-Maxwellian distribution of whistler mode waves in the parallel alternating electric field and magnetic field is studied. The dispersion relation and the growth rate of Saturn's magnetic layer were deduced and calculated in detail. Parameter analysis is performed by changing the parameters of the plasma like number density, AC frequency, temperature anisotropy, etc. The influence of AC frequency on Doppler shift and the comparative study of growth rate of oblique and parallel propagating waves are analyzed using generalized distribution function. We found temperature anisotropy AT=1.25 can explain the linear spatiotemporal growth rate of whistler mode waves. It provides the majority of the observed frequency integral power. It can be seen that the effective parameters for the generation of Whistler mode waves are not only temperature anisotropy, but also the relativistic factors discussed in the results and discussion section, and the AC field frequency and width of the loss cone distribution function.
       
  • Performance verification of Lunar Regolith Penetrating Array Radar of
           Chang’E-5 mission
    • Abstract: Publication date: 1 April 2019Source: Advances in Space Research, Volume 63, Issue 7Author(s): Yuxi Li, Wei Lu, Guangyou Fang, Bin Zhou, Shaoxiang Shen Lunar Regolith Penetrating Array Radar (LRPR) is one main payload of the Lander for Chinese Chang’E-5 (CE-5) mission. It is used to support the drilling and sampling device and to detect lunar regolith thickness and structure of the landing site. LRPR will only work in situ under static status, so the antenna array is employed. Since the antenna array is about 90 cm high from the ground, the layout is irregular, and the metal structure of the lander seriously interferes with LRPR, these factors make it very difficult to reconstruct the image of the drilling area, so the performance verification must be carried out. We propose a set of methods to process LRPR’s data and reconstruct image. The verification experiments demonstrate that these methods are suitable for LRPR, the thickness and structure of the lunar regolith from zero to two meters can be clearly mapped, the vertical resolution is a few centimeters, and the electromagnetic properties of the subsurface can be estimated. Therefore, the performance of LRPR meets the requirements, and LRPR can successfully support drilling and sampling.
       
  • Schumann resonance frequency and conductivity in the nighttime ionosphere
           of Mars: A source for lightning
    • Abstract: Publication date: 1 April 2019Source: Advances in Space Research, Volume 63, Issue 7Author(s): S.A. Haider, Jayesh P. Pabari, J. Masoom, Siddhi Y. Shah We have solved the Maxwellian equations of electromagnetic waves which oscillate within the cavity formed in the lower ionosphere of Mars between 0 and 70 km. The electrical conductivity and Schumann Resonance (SR) frequencies are calculated in the lower ionosphere of Mars, in the presence of a major dust storm that occurred in Martian Year (MY) 25 at low latitude region (25°–35°S). It is found that the atmospheric conductivity reduced by one to two orders of magnitude in the presence of a dust storm. It represents a small dust layer at about 25–30 km altitudes where lightning can occur. We also found that the SR frequencies peak at ∼18 km with values 19.9, 34.5 and 48.8 Hz for the modes l = 1, 2 and 3, respectively, in the non-homogeneous medium. Our results indicate that practical or measurable values of SR are dependent on the altitudes.
       
  • A star identification algorithm based on radial and dynamic cyclic
           features of star pattern
    • Abstract: Publication date: 1 April 2019Source: Advances in Space Research, Volume 63, Issue 7Author(s): Xin Wei, Desheng Wen, Zongxi Song, Jiangbo Xi, Weikang Zhang, Gang Liu, Zhixin Li A full-sky star identification algorithm based on radial and dynamic cyclic patterns is presented with the aim of solving the “lost-in-space” problem. The dynamic cyclic pattern match is applied with a maximum cumulate comparison method to identify sensor-catalog pairings in initial match, which substantially eliminates the effects of the star position noise, magnitude noise, and false stars. After initial match pairings of stars are obtained, a chain part extension technique is employed to quickly search for the longest match chain as the final result. Experimental results indicate that the proposed algorithm is highly robust to star position noise, magnitude noise and false stars. In a series of simulations, the identification rate of the algorithm is 97.50% with 2.0 pixels star position noise, 96.90% with 0.4 Mv star magnitude noise and 95.30% with four false stars respectively. Moreover, the algorithm achieves an identification rate of 58.08% when only six stars are in the field of view.
       
  • Optimum parameter matching obtained by experiments for coring drilling
           into lunar simulant
    • Abstract: Publication date: 1 April 2019Source: Advances in Space Research, Volume 63, Issue 7Author(s): Zhen Zhao, Tao Chen, Yong Pang This paper performs a series of ground experiments (on the Earth) to obtain optimum parameter matching for a future core drill on the Moon. Three common stages, I, II, III, are recognized with respect to the cut per revolution (CPR), which is defined as the ratio between the feeding speed and the rotating speed. The optimum matching between the feeding speed and the rotating speed for drills locates at the boundary position between Stage II and Stage III, where the coring rate saturates and the weight on the bit and the driving torque are still low. Further data analysis of the ground experiments reveals that the optimum matching signifies a proportional relation between the maximum conveying rate (MCR) by the groove of the auger and its rotating speed. The kinetic analysis in an ideal condition without gravity, the friction from the auger groove and the pressure at the bit confirm a similar proportion. The correlation between the proportions needs further study to determine whether the optimum matching obtained on the ground can be directly applied to future drills on the Moon.
       
  • Constrained adaptive fault-tolerant attitude tracking control of rigid
           spacecraft
    • Abstract: Publication date: 1 April 2019Source: Advances in Space Research, Volume 63, Issue 7Author(s): Liang Sun A saturated fault-tolerant attitude tracking controller for disturbed rigid spacecraft is derived using nonlinear state feedback control method. The proposed controller achieves the constraints of control inputs by directly using the bounded function instead of the traditional saturation compensator technique, and the active tolerance to the partial loss of actuator effectiveness is also achieved by directly using the known bounds of the actuator faults in the controller. Specifically, compared with the traditional saturated control methods, a continuously bounded nonlinear function in the proposed controller is used to guarantee that the actuator outputs are smoothly bounded under the prescribed constraints. Based on some properties of the attitude tracking dynamics, the proposed controller can ensure the attitude tracking errors converge to small neighborhoods of zero via stability analysis in the Lyapunov framework. Simulation results are presented to illustrate the effectiveness of the control scheme.
       
  • Upwards migration phenomenon on molten lunar regolith: New challenges and
           prospects for ISRU
    • Abstract: Publication date: 1 April 2019Source: Advances in Space Research, Volume 63, Issue 7Author(s): Jesus A. Dominguez, Jonathan Whitlow As part of our research on the feasibility of producing commodities from lunar regolith by thermal-driven processes with minimal terrestrial precursors we need to characterize, reproduce, and understand thermophysical properties of the molten regolith still unforeseen under the lunar vacuum conditions at a scalable sample size. Two unanticipated phenomena, apparently caused by lunar melt’s surface tension under vacuum, have been revealed in our research work, vacuum void formation and upwards migration. In this paper we present our findings and thinkable explanation on the upwards migration phenomenon experimentally observed and consistently replicated as JSC-1A lunar regolith simulant melted at high vacuum. Upwards migration of molten lunar regolith will make future lunar ISRU’s melting processes both challenging as molten bulk material would migrate upwards along the container’s walls, and also promising on new opportunities for alternative ISRU’s sustainable processes as regolith’s upwards migration takes place in uniformed thin-film pattern. Among the potential ISRU’s processes that might use controlled thermal thin-film-based migration without the necessity of terrestrial precursors are production of feedstock for 3D printing, fractional separation of regolith’s component’s (O2, metals, and alloys) via pyrolysis, film coating, purification of valuables solid crystals including silicon, and fabrication of key elements for microfluidic, and MEMS devices. Thermal upwards migration phenomenon on JSC-1A’s melt is formulated and explained by the authors as due to thermal Marangoni effect (also known as thermo-capillarity) in which temperature gradients within the melt’s bulk and along the crucible’s wall yield the surface tension large enough to supersede the gravitational force and yield the experimentally observed upwards thin-film migration. As far as the authors know, upwards thermal migration of molten JSC-1A (or other lunar simulant regolith) under vacuum has not been reported in the literature. A thermal mathematical model accounting for thermal Marangoni effect on molten JSC-1A agrees with what experimentally was observed, the formation of the meniscus on the melt-wall surface interface along with an incipient upwards migration in thin-film pattern along the crucible wall that, according to the model, experiences large temperature gradient, an important factor to trigger the thermal Marangoni effect along with the fact that surface tension of the molten lunar regolith material is temperature dependent.
       
  • Regolith-derived ferrosilicon as a potential feedstock material for
           wire-based additive manufacturing
    • Abstract: Publication date: 1 April 2019Source: Advances in Space Research, Volume 63, Issue 7Author(s): Kevin D. Grossman, Tamil S. Sakthivel, Laurent Sibille, James G. Mantovani, Sudipta Seal Ferrosilicon is a primary metallic alloy produced during the reduction of metal oxides contained in lunar and Martian regolith by a variety of techniques. This study examines the usefulness of ferrosilicon as a candidate feedstock material for wire-based 3D printers designed for in-space manufacturing. Alloys of composition ranging from pure iron to 12 wt% Si were synthesized and their electrical and mechanical properties characterized. The melts were cast into rods for mechanical testing to determine ultimate strength and ductility. It was determined that the samples above 3 wt% Si were too brittle to be pulled into wire and ruptured at low strain values. The 3 wt% Si sample and iron had comparable mechanical properties relative to samples of higher silicon content but with differences in ductility and ultimate strength. Microstructure and compositional studies revealed the differences between the ductile and brittle samples as being the complete ferrite phase presence on the iron and low-Si content samples. This study establishes an upper limit on the Si content at 3 wt% in ferrosilicon materials to be used in wire feedstock in additive manufacturing for in-space applications.
       
  • Evaluation and analysis on positioning performance of BDS/QZSS satellite
           navigation systems in Asian-Pacific region
    • Abstract: Publication date: 1 April 2019Source: Advances in Space Research, Volume 63, Issue 7Author(s): Jinwei Bu, Xiaoqing Zuo, Xiangxin Li, Jun Chang, Xionghao Zhang By using the observation data and products of precise obit and clock offset from Multi-GNSS Experiment (MGEX) of the International GNSS Service (IGS) and GNSS Research Centre, Curtin University in this paper, the positioning performance of BDS/QZSS satellite navigation system has been analyzed and evaluated in aspects of the quantity of visible satellites, DOP value, multipath effect, signal-to-noise ratio, static PPP and kinematic PPP. The analysis results show that compared to BDS single system when the cutoff angle are 30°and 40°, the DOP value of BDS/QZSS combined system has decreased above 20%, and the quantity of visible satellites increased about 16–30% respectively, because of the improved spatial geometric configuration. The magnitude of satellite multipath effect of BDS system shows the trend of MEO > IGSO > GEO, which is consistent with that of QZSS satellite system, as the constellation structure of the two systems is similar. The variation tendencies of signal-to-noise ratio with respect to elevation angle of the two systems are almost the same at all frequencies, showing that at the same elevation angle the signal-to-noise ratio of MEO satellites is higher than that of IGSO satellites, as the higher obit is the lower transmitting power is obtained. For having a specially designed obit, the variation of signal-to-noise ratio of BDS system is more stable. However, the magnitude of signal-to-noise ratio of QZSS system appears the trend of frequency 3 > frequency 2 > frequency 1. The static PPP performance of the BDS/QZSS combination system has been improved more significantly than the BDS single system in E, N and U directions. When the cutoff angle are at 7°, 15° and 30°, the PPP accuracy is increased about 25–34% in U direction, 10–13% and 23–34% in E and N directions respectively. When the elevation angle is large (40°), compared to BDS single system at lower elevation angles (7° and 15°) the PPP accuracy of the BDS/QZSS combination system is improved above 30% in U direction. In kinematic PPP performance, compared to BDS single system, the accuracy, availability and reliability of the BDS/QZSS combination system has been improved too, especially at large elevation angles (30° and 40°), the kinematic PPP accuracy in E and U directions has been improved about 10–50%, and above 50% in U direction. It can be concluded that the combination with QZSS system can improve the positioning accuracy, reliability and stability of BDS system. In the future, with the improvement of the satellite construction of Japan’s QZSS system and the global networking of China’s BDS satellites, the QZSS satellites will contribute greatly to improve the positioning accuracy, reliability, availability and stability of GNSS systems in areas such as cities, mountains, densely-packed buildings and severely covered areas in Asian-Pacific region.
       
  • An assessment of semi-analytical models based on the absorption
           coefficient in retrieving the chlorophyll-a concentration from a reservoir
           
    • Abstract: Publication date: 1 April 2019Source: Advances in Space Research, Volume 63, Issue 7Author(s): Caroline Andrade, Enner Alcântara, Nariane Bernardo, Milton Kampel Monitoring chlorophyll-a (Chl-a) concentrations in inland waters is crucial for water quality management, since Chl-a is a proxy for phytoplankton biomass and, thus, for ecological health of a water environment. Chl-a concentration can be retrieved through the inherent optical properties (IOPs) of a water system, which, in turn, can be remotely sensed obtained. Quasi-analytical algorithm (QAA), originally developed for ocean waters, can also retrieve IOPs for inland waters after re-parameterizations. This study is aimed at assessing the performance of sixteen schemes composed by QAA original and re-parameterized versions followed by models that use absorption coefficients as inputs for estimating Chl-a concentration in Ibitinga reservoir, located at Tietê River cascading system, São Paulo State, Brazil. It was verified that only QAAV5 based schemes were able to obtain reasonable estimates for image data and that by four models tested presented similar and acceptable results for QAAV5 outputs. The best model were applied to a Ocean and Land Colour Instrument (OLCI) image. Light absorption in the reservoir showed to be dominated by colored dissolved organic matter (CDOM), and wide spatial and temporal variability of optical and water quality properties was observed.
       
  • Carrier phase prediction method for GNSS precise positioning in
           challenging environment
    • Abstract: Publication date: 1 April 2019Source: Advances in Space Research, Volume 63, Issue 7Author(s): Zhuo Li, Tisheng Zhang, Farui Qi, Hailiang Tang, Xiaoji Niu Since the signals of global navigation satellite system (GNSS) are blocked frequently in challenging environments, the discontinuous carrier phases seriously affect the application of GNSS precise positioning. To improve the carrier phase continuity, this paper proposes a carrier phase prediction method based on carrier open-loop tracking. In the open-loop tracking mode, the carrier numerically controlled oscillator (NCO) is controlled by the predicted Doppler, but not by the loop filter output. To improve the phase prediction effective time, accurate receiver clock drift estimation is studied in the prediction method. The phase prediction performance is tested on GNSS software receiver. In the phase prediction effective time tests, open-loop processes were set for the tested channel. The test results show that, when some satellite signals are blocked in 15 s, the probability of carrier phase error less than quarter cycles is more than 94%. In the real time kinematic (RTK) positioning tests, some satellite signals are blocked in 10–15 s repeatedly. The test results show that, the carrier phase continuity is basically not affected by the signal interruption, and the RTK can almost keep continuous centimeter-level positioning accuracy without re-fixing the integer ambiguity.
       
  • Correction model of BDS satellite-induced code bias and its impact on
           precise point positioning
    • Abstract: Publication date: 1 April 2019Source: Advances in Space Research, Volume 63, Issue 7Author(s): Jian Chen, Dongjie Yue, Shaolin Zhu, Hao Chen, Zhiqiang Liu, Xingwang Zhao There are code biases on the pseudo-range observations of the Beidou Navigation Satellite System (BDS) that range in size from several decimeters to larger than one meter. These biases can be divided into two categories, which are the code biases in the pseudo-range observations of Inclined Geo-Synchronous Orbit (IGSO) satellites and Medium Earth Orbit (MEO) satellites and the code biases in the pseudo-range observations of Geosynchronous Earth Orbit (GEO) satellites. In view of the code bias of the IGSO/MEO satellites, the code bias correction model is established using the weighted least square curve fitting method. After the correction, the code biases of the IGSO and MEO satellites are clearly mitigated. A methodology of correcting GEO code bias is proposed based on the empirical mode decomposition (EMD)-wavelet transform (WT) coupled model. The accuracies of the GEO multipath combination of the B1, B2 and B3 frequencies are improved by 39.9%, 17.9%, and 29.4%, respectively. Based on the corrections above, the ten days observations of three Multi-GNSS Experiment (MGEX) stations are processed. The results indicate that the convergence time of the precise point positioning (PPP) can be improved remarkably by applying a code bias. The mean convergence time can be improved by 14.67% after the IGSO/MEO code bias correction. By applying the GEO code bias, the mean convergence time can be further improved by 17.42%.
       
  • Land use/land cover classification using time series Landsat 8 images in a
           heavily urbanized area
    • Abstract: Publication date: 1 April 2019Source: Advances in Space Research, Volume 63, Issue 7Author(s): Ziwei Deng, Xiang Zhu, Qingyun He, Lisha Tang It is of great significance to timely, accurately, and effectively monitor land use/cover in city regions for the reasonable development and utilization of urban land resources. The remotely sensed dynamic monitoring of Land use/land cover (LULC) in rapidly developing city regions has increasingly depended on remote-sensing data at high temporal and spatial resolutions. However, due to the influence of revisiting periods and weather, it is difficult to acquire enough time-series images with high quality at both high temporal and spatial resolution from the same sensor. In this paper we used the temporal-spatial fusion model ESTARFM (Enhanced Spatial and Temporal Adaptive Reflectance Fusion Model) to blend Landsat8 and MODIS data and obtain time-series Landsat8 images. Then, land cover information is extracted using an object-based classification method. In this study, the proposed method is validated by a case study of the Changsha City. The results show that the overall accuracy and Kappa coefficient were 94.38% and 0.88, respectively, and the user/producer accuracies of vegetation types were all over 85%. Our approach provides an accurate and efficient technical method for the effective extraction of land use/cover information in the highly heterogeneous regions.
       
  • Effects of variations of geomagnetic field on VLF waves induced by beating
           of two HF waves
    • Abstract: Publication date: 1 April 2019Source: Advances in Space Research, Volume 63, Issue 7Author(s): Guanglin Ma, Lixin Guo, Jutao Yang, Libin Lv, Jing Chen, Tong Xu, Shuji Hao, Jian Wu Beat wave (BW) high frequency (HF) ionospheric heating experiments were conducted to generate very low frequency (VLF) waves. The VLF waves were registered with a VLF receiver located ∼15 km east of the European Incoherent Scatter (EISCAT) heating facility in Tromsø, Norway. A fluxgate magnetometer was used to monitor auroral electrojet current, and ionospheric conditions were measured using a Dynasonde. Correlation coefficients between VLF amplitudes and the deviation of geomagnetic north–south components were calculated. Experimental results show that strong and positive correlation exists the majority of the time, but sometimes no correlation or even a negative correlation occurred. This is consistent with similar past experiments that took place with exclusively AM generation. These results therefore support the conclusion that BW generation of VLF waves is no different than with AM, likely occurring in the D or lower E ionospheric region.
       
  • Simultaneous observations of spread F irregularities over Southeast Asia
           longitude using Sanya VHF radar, GPS and C/NOFS
    • Abstract: Publication date: 1 April 2019Source: Advances in Space Research, Volume 63, Issue 7Author(s): Xing Meng, Hanxian Fang, Libin Weng, Zhendi Liu Through concurrently measurements by Communication/Navigation Outage Forecasting System (C/NOFS), Sanya VHF radar and GPS ionospheric scintillation receiver on 12 March 2010, five plasma bubbles were found and three of them were observed by all those instruments. Two well-developed plumes with strong backscatter echoes were measured by Sanya radar and their corresponding depletions were observed by C/NOFS in Orbit 10317, 10318 and 10319. Broad plasma depletions resulting from merging process were found in orbit of 10318. The occurrence time and geophysical positions of scintillations correlate well with observations implemented by Sanya VHF radar and C/NOFS. Observations from three types of instrument indicate that the spread F irregularities have distinct scale. There were longitudinal differences between Sanya VHF radar and C/NOFS as irregularities measured, and the eastward drift of developed bubbles are responsible for these differences.
       
  • Method of the HF wave absorption evaluation based on GIRO network data
    • Abstract: Publication date: 1 April 2019Source: Advances in Space Research, Volume 63, Issue 7Author(s): N.Y. Zaalov, E.V. Moskaleva, F.V. Shekhovtsov High frequency (HF) communication is strongly dependent on the state of the ionosphere, which specifies the mode structure of the radio wave propagating in ionosphere. Another core factor defining the strength of the HF signal at the receiving site is the ionospheric absorption. Accurate modelling the effect of absorption is an essential part of many studies of the HF propagation in the ionosphere.This paper proposes a method for estimating the absorption. The method is based on analysis of vertical sounding ionograms. The main idea of the approach is to compare the main parameters retrieved from measured and simulated ionograms. The combination of Global Ionospheric Radio Observatory (GIRO, http://giro.uml.edu) data and ionograms modelling allows for developing the empiric absorption model available at near real-time. The ionogram simulation taking into account absorption utilizes the NIM-RT (North Ionospheric Model and Ray Tracing) software. As a result, the proposed technique provides more reliable and accurate evaluation of minimum frequency at which echoes are observed in vertical incidence ionosonde soundings. The values of these frequencies should be used in the following simulation to optimize parameters in the empirical formulae for defining absorption HF wave in ionosphere.The ultimate objective of this work is the designing the method, which allows the simulating of HF radio channel accounting for regular absorption due to UV radiation of the Sun. Eventually it could be considered as some kind of the HF propagation forecasting.
       
  • Ionospheric and geomagnetic Pc5 oscillations as observed by the ionosonde
           and magnetometer at Sodankylä
    • Abstract: Publication date: 1 April 2019Source: Advances in Space Research, Volume 63, Issue 7Author(s): O. Kozyreva, A. Kozlovsky, V. Pilipenko, N. Yagova The study is based on the data of the rapid-run ionosonde at the Sodankylä Geophysical Observatory at auroral latitude (L = 5.25) which routinely performs one-minute sounding since 2007. This dataset allows a unique opportunity for investigating possible effects of ultra-low frequency (ULF, 1–7 mHz) waves in the auroral ionosphere. Suitable observations were made during moderately disturbed geomagnetic conditions typically at recovery of the geomagnetic storms caused by solar wind high-speed streams, in the daytime between 9 and 16 MLT. The ionospheric oscillations corresponding to Pc5 geomagnetic pulsations were found in variations of the virtual height of the F layer and the power of ionosonde reflections from E and F layers. The later are most probably caused by modulation of electron precipitation, which is also manifested in weak (about 0.01–0.06 dB) variations of cosmic noise absorption. The most important and novel result is that the pulsations of power of reflection from E and F layers typically has a spectral maximum at nearly half the periodicity of the Pc5 geomagnetic pulsations, whereas such spectral peak is negligible in the geomagnetic pulsations.
       
  • Adaptive double-saturated control for hovering over an asteroid
    • Abstract: Publication date: 1 April 2019Source: Advances in Space Research, Volume 63, Issue 7Author(s): Bo Zhang, Yuanli Cai, Fei Li Hovering over an irregular-shaped asteroid is particularly challenging due to the large gravitational uncertainties and various external disturbances. An adaptive control scheme considering commanded acceleration and its change-rate saturation for hovering is developed in this paper. Taking full advantage of terminal sliding-mode control theory, first, we convert the double-saturated control problem to a new equivalent system by introducing a special bounded function, in which just control input saturation needs to be considered. Then, a continuous finite-time saturated controller is designed for the new system with the assistance of an constructed auxiliary subsystem. Additionally, an adaptive law is devised for the controller to avoid the requirement of the unknown upper bounds of the disturbances, rendering the control scheme especially suitable to asteroid hovering missions. The finite-time stability of the whole closed-loop system is proved via Lyapunov analysis. Numerical simulation studies are carried out, and the results demonstrate the design features and the desired performance.
       
  • Extrasolar space exploration by a solar sail accelerated via thermal
           desorption of coating
    • Abstract: Publication date: 1 April 2019Source: Advances in Space Research, Volume 63, Issue 7Author(s): Elena Ancona, Roman Ya. Kezerashvili For extrasolar space exploration it might be very convenient to take advantage of space environmental effects such as solar radiation heating to accelerate a solar sail coated by materials that undergo thermal desorption at a particular temperature. Thermal desorption can provide additional thrust as heating liberates atoms, embedded on the surface of the solar sail. We are considering orbital dynamics of a solar sail coated with materials that undergo thermal desorption at a specific temperature, as a result of heating by solar radiation at a particular heliocentric distance, and focus on two scenarios that only differ in the way the sail approaches the Sun. For each scenario once the perihelion is reached, the sail coat undergoes thermal desorption. When the desorption process ends, the sail then escapes the Solar System having the conventional acceleration due to solar radiation pressure. We study the dependence of a cruise speed of a solar sail on perihelion of the orbit where the solar sail is deployed. The following scenarios are considered and analyzed: (1) Hohmann transfer plus thermal desorption. In this scenario the sail would be carried as a payload to the perihelion with a conventional propulsion system by a Hohmann transfer from Earth’s orbit to an orbit very close to the Sun and then be deployed. Our calculations show that the cruise speed of the solar sail varies from 173 km/s to 325 km/s that corresponds to perihelion 0.3 AU and 0.1 AU, respectively. (2) Elliptical transfer plus Slingshot plus thermal desorption. In this scenario the transfer occurs from Earth’s orbit to Jupiter’s orbit; then a Jupiter’s fly-by leads to the orbit close to the Sun, where the sail is deployed and thermal desorption comes active. In this case the cruise speed of the solar sail varies from 187 km/s to 331 km/s depending on the perihelion of the orbit. Our study analyses and compares the different scenarios in which thermal desorption comes beside traditional propulsion systems for extrasolar space exploration.
       
  • Tightly combined GPS/Galileo RTK for short and long baselines: Model and
           performance analysis
    • Abstract: Publication date: 1 April 2019Source: Advances in Space Research, Volume 63, Issue 7Author(s): Mingkui Wu, Wanke Liu, Renpan Wu, Xiaohong Zhang To ensure the compatibility and interoperability with modernized GPS, Galileo satellites are capable of broadcasting navigation signals on carrier phase frequencies that overlap with GPS, i.e., GPS/Galileo L1-E1/L5-E5a. Moreover, the GPS/Galileo L2-E5b signals have different frequencies with wavelength differences smaller than 4.2 mm. Such overlapping and narrowly spaced signals between GPS and Galileo bring the opportunity to use the tightly combined double-differenced (DD) model for precise real-time kinematic (RTK) positioning, resulting in improved performance of ambiguity resolution and positioning with respect to the classical standard or loosely combined DD model. In this paper, we focus on the model and performance assessment of tightly combined GPS/Galileo L1-E1/L2-E5b/L5-E5a RTK for short and long baselines. We first investigate the tightly combined GPS/Galileo DD observational model for both short and long baselines with simultaneously considering the GPS/Galileo overlapping and non-overlapping frequencies. Particularly, we introduce a reparameterization approach to solve the rank deficiency that caused by the correlation between the DISB parameters and the DD ionospheric parameters for both overlapping and non-overlapping frequencies. Then we present performance assessment for the tightly combined GPS/Galileo RTK model with real-time estimation of the differential inter-system bias (DISB) parameters for short and long baselines in terms of ratio value, ambiguity dilution of precision (ADOP), ambiguity conditional number, decorrelation number, search count, empirical success rate, time-to-first-fix (TTFF), and positioning accuracy. Results from both static and kinematic experiments demonstrated that compared to the loosely combined model, the tightly combined model can deliver improved performance of ambiguity resolution and precise positioning with different satellite visibility. For the car-driven short baseline experiment with 10° elevation cut-off angle, the tightly combined model can not only significantly increase the ratio value by approximately 27.5% (from 16.0 to 20.4), but also reduce the ambiguity ADOP, the conditional number, and the search count in LAMBDA by approximately 22.2% (from 0.027 to 0.021 cycles), 14.9% (from 199.2 to 169.6), and 25.4% (from 150.1 to 112.0), respectively. Comparable decorrelation number, empirical success rate, and positioning accuracy are also obtained. For the car-driven long baseline experiment, it is also observed that the ambiguity resolution performance in terms of the ratio value, the decorrelation number, the condition number, and the search count are significantly improved by approximately 18.5% (from 2.7 to 3.2), 22.0% (from 0.186 to 0.227), 55.9% (from 937.6 to 413.7), and 10.3% (from 43.8 to 39.3), respectively. Moreover, comparable ADOP, empirical success rate, and positioning accuracy are obtained as well. Additionally, the TTFF can be reduced (from 54.1 to 51.8 epochs with 10° elevation cut-off angle) as well from the results of static experiments.
       
  • On the practical exploitation of perturbative effects in low Earth orbit
           for space debris mitigation
    • Abstract: Publication date: 1 April 2019Source: Advances in Space Research, Volume 63, Issue 7Author(s): Volker Schaus, Elisa Maria Alessi, Giulia Schettino, Alessandro Rossi, Enrico Stoll This paper presents the results of a numerical evaluation of the natural lifetime reduction in low Earth orbit, due to dynamical perturbations. The study considers two values for the area-to-mass ratio, a nominal ratio which resembles a typical value of spacecraft in orbit today, and an enhanced ratio which covers the surface augmentation. The results were obtained with two orbit propagators, one of a semi-analytical nature and the second one using non-averaged equations of motion. The simulations for both propagators were set up similarly to allow comparison. They both use the solar radiation pressure and the secular terms of the geopotential (J2,J4 and J6). The atmospheric drag was turned on and off in both propagators to alternatively study the eccentricity build up and the residual lifetime. The non-averaging case also covers a validation with the full 6 × 6 geopotential. The results confirm the findings in previous publications, that is, the possibility for de-orbiting from altitudes above the residual atmosphere if a solar sail is deployed at the end-of-life, due to the combined effect of solar radiation pressure and the oblateness of the Earth. At near polar inclinations, shadowing effects can be exploited to the same end. The results obtained with the full, non-averaging propagator revealed additional de-orbiting corridors associated with solar radiation pressure which were not found by previous work on space debris mitigation. The results of both tools are compared for specific initial conditions. For nominal values of area-to-mass ratio, instead, it is confirmed that this resonance effect is negligible.The paper then puts the findings in the perspective of the current satellite catalogue. It identifies space missions which are currently close to a resonance corridor and shows the orbit evolution within the resonances with a significantly shorter residual orbital lifetime. The paper finishes with a discussion on the exploitation of these effects with regards to the long-term simulation of the space debris environment and a flux and collision probability comparison.
       
  • A material experiment for small satellites to characterise the behaviour
           of carbon nanotubes in space – development and ground validation
    • Abstract: Publication date: 1 April 2019Source: Advances in Space Research, Volume 63, Issue 7Author(s): Elisabeth Abbe, Thomas Renger, Maciej Sznajder, Benjamin Klemmed, Elisa Sachse, René Hübner, Tilman Schüler, Yves Bärtling, Benjamin Muchow, Martin Tajmar, Tino Schmiel Over the last years, Carbon Nanotubes (CNT) drew interdisciplinary attention. Regarding space technologies a variety of potential applications were proposed and investigated. However, no complex data on the behaviour and degradation process of carbon nanotubes under space environment exist. Therefore, it is necessary to investigate the performance of these new materials in space environment and to revaluate the application potential of CNTs in space technologies.Hence, CiREX (Carbon Nanotubes – Resistance Experiment) was developed as a part of a student project. It is a small and compact experiment, which is designed for CubeSat class space satellites. These are a class of nanosatellites with a standardized size and shape. The CiREX design, electrical measurements and the satellites interfaces will be discussed in detail. CiREX is the first in-situ space material experiment for CNTs.To evaluate the data obtained from CiREX, ground validation tests are mandatory. As part of an extensive test series the behaviour of CNTs under solar ultra violet light (UV) and vacuum ultraviolet light (VUV) was examined. Single-walled carbon nanotubes (SWNT), multi-walled carbon nanotubes (MWNT) and MWNT/resin composite (ME) were exposed to different light sources. After the exposure, the defect density was investigated with Raman spectroscopy. There is a clear indication that UV and VUV light can increase the defect density of untreated CNTs and influence the electrical behaviour.
       
  • Ionospheric foF2 Disturbance Forecast Using Neural Network
           Improved by a Genetic Algorithm
    • Abstract: Publication date: Available online 6 March 2019Source: Advances in Space ResearchAuthor(s): Jun Zhao, Xiaojun Li, Yi Liu, Xiang Wang, Chen Zhou A single station short-term ionospheric disturbance forecasting model has been developed with a genetic algorithm-based neural network (GA-NN). The genetic algorithm is used to optimize the initial weights of the neural network to avoid the local minimum during NN training. Using this model, the single station predictions of the ionospheric F2 layer critical plasma frequency, foF2, with the time-scale 1∼24 hours in advance in the China region have been investigated. Input parameters of the forecasting GA-NN model include the Beijing time (GMT+8), season information, solar zenith angle, day number, solar activity, geomagnetic activity, neutral winds, geographic coordinates and previous values of foF2. The training dataset in this model are obtained from the ionosonde stations in China. The data coverage is from 1990 to 2004 (more than one solar cycle) except 1995 and 2000. The data of ionospheric disturbances in 1995 (solar minimum) and 2000 (solar maximum) are used as the validation dataset. The prediction results at the different stations show that 1 hour ahead prediction is more accurate than predictions of 3, 6, 12 and 24 hours ahead. Comparisons between the observed and predicted values of foF2 in the low and middle latitudes during the year of solar minimum (1995) and solar maximum (2000) indicate that, the prediction accuracy at middle latitudes are generally better than that at low latitudes. The prediction root-mean-square error (RMSE) in the low solar activity is smaller than that in the high solar activity. The ionospheric disturbances prediction results manifest that the model works well even when the observed values of foF2 are far away from the monthly median value and the ionospheric storm lasts for 18 hours.
       
  • Absolute and Relative Orbit Determination for the CHAMP/GRACE
           Constellation
    • Abstract: Publication date: Available online 4 March 2019Source: Advances in Space ResearchAuthor(s): X. Mao, P.N.A.M. Visser, J. den IJssel Precise orbit determination was investigated for a satellite constellation comprised of two different missions, the CHAllenging Minisatellite Payload (CHAMP) satellite and the Gravity Recovery And Climate Experiment (GRACE) twin satellites. The orbital planes of these two missions aligned closely during March to May 2005, allowing precise baseline determinations between the associated three satellites based on their onboard BlackJack Global Positioning System (GPS) receivers. The GRACE-A/B satellites fly in tandem formation with a baseline of around 220 km, whereas the baselines between CHAMP and the GRACE tandem vary from about 110 to 7500 km during 24-hr orbital arcs centered around the points of closest approaches. A number of factors had to be dealt with for orbit determinations, including the cross-talk between the CHAMP GPS main navigation and occultation antennas, the different levels of non-gravitational accelerations, and the rapidly changing geometry that complicates the fixing of integer ambiguities for the GPS carrier-phase observations.Quality assessments of the orbit solutions were based on comparisons with Satellite Laser Ranging (SLR) observations, best orbit solutions had a precision of typically 1.7-2.3 cm. Consistency checks between reduced-dynamic and kinematic orbit solutions were done. For the GRACE baselines, the reduced-dynamic/kinematic baseline consistency was typically better than 1 cm, with an ambiguity fixing success rate of around 94%. The agreement with the K/Ka-Band Radar Ranging (KBR) measurements was about 0.6 mm. For the CHAMP/GRACE pairs, the reduced-dynamic/kinematic baseline consistency varied from 0.5 to 2.5 cm, where better consistency was obtained for shorter arcs.
       
  • Optimal Control of Approaching Target for Tethered Space Robot based on
           Non-singular Terminal Sliding Mode Method
    • Abstract: Publication date: Available online 28 February 2019Source: Advances in Space ResearchAuthor(s): Yongxin Hu, Panfeng Huang, Zhongjie Meng, Yizhai Zhang, Dongke Wang In the tethered space robot approaching phase, the tether can provide attitude control torque and orbit control force, it can reduce the fuel consumption of the gripper, but there is operation coupling for the tether is not always pass through the centroid of the gripper. And the field of view of the camera is limited, the tracking error of attitude and position can make the target deviate from the camera view field. Aiming to above problems, a position and attitude coordinated control scheme based on non-singular terminal sliding mode method is designed for the approaching task. The dynamic model of tethered space robot based on lumped mass model and elastic rod model are established, respectively. Combining the dynamic model of tethered space robot based on elastic rod model with the relative motion model of the target, a Gaussian pseudo spectral motion planning model is established, the planning model takes into account the constraints of control input and the field of view of gripper. Solving the programming model, the optimal approaching trajectory of the tethered space robot is obtained. Then, a trajectory tracking controller is designed based on non-singular terminal sliding mode method. The simulation results show that the proposed control scheme can realize the accurate position and attitude tracking of the optimal trajectory.
       
  • Improving GLONASS Orbit Quality by Re-estimating Satellite Antenna Offsets
    • Abstract: Publication date: Available online 27 February 2019Source: Advances in Space ResearchAuthor(s): Rolf Dach, Andreja Sušnik, Andrea Grahsl, Arturo Villiger, Stefan Schaer, Daniel Arnold, Lars Prange, Adrian Jäggi Earlier studies performed at the Center for Orbit Determination in Europe (CODE) analysis center have revealed conspicuous signatures for certain GLONASS satellites when comparing their orbits with Satellite Laser Ranging (SLR) measurements. In this study we show that this phenomenon can be significantly reduced when using horizontal satellite antenna offsets that differ from the nominal values used by the International GNSS Service (IGS) for specific intervals and satellites.Analysis of multi-year time series shows instantaneous changes in the satellite antenna offset parameters of several centimeters in the X- and Y-component whereas the Z-component is not affected. In some cases the offsets do not agree with the nominal values during the entire lifetime of the satellite. The magnitude of the deviation may vary between 5 to 15 cm. Using these re-estimated satellite antenna offsets in the orbit determination the residuals with respect to the Satellite Laser Ranging (SLR) measurements are significantly reduced whereas the orbit misclosures for one-day arcs are too noisy to detect a positive or negative impact.It is difficult to reconstruct from the available information what actually caused the observed changes. However, changes in the carrier-to-noise density reported in the observation files in Receiver INdependent EXchange format (RINEX) by several IGS stations suggest an issue with the satellite antennas.
       
  • The North and South Symmetry of the Ionospheric Storms at Magnetic
           Conjugate Points for Low Latitudes during the March 1976 Severe
           Geomagnetic Storms and the Relation between Daily Changes of the Storms
           with Geomagnetic Activity Indices
    • Abstract: Publication date: Available online 27 February 2019Source: Advances in Space ResearchAuthor(s): Erdinç Timoçin In this study, the behavior of the ionospheric storms at magnetic conjugate points for two low-latitude observatories during March 1976 severe geomagnetic storms and the relationship between the ionospheric storms and different geomagnetic indices was investigated. For this purpose, hourly ionospheric critical frequency (foF2) data measured from March 19 to April 17, 1976 at Akita and Brisbane stations were used. These stations are magnetic conjugate pairs. The Kp, Dst, ap, and ap (τ) values are geomagnetic activity indicators for this research. The ap (τ) reflects an integration of the geomagnetic activity over a number of 3-h intervals, giving more weight to the recent past. The ap (τ) values could be better described the magnitude of main phase foF2 deviations using an integration of ap that takes into account the recent history of geomagnetic activity. To investigate the response of ionospheric storms at magnetic conjugate points to the geomagnetic activity changes during the severe geomagnetic storms, the foF2 values in the geomagnetic quiet days were subtracted from all the foF2 values and thus the δfoF2 values were obtained. The cross-correlation coefficient (R) between δfoF2 values of these stations was calculated and it was obtained as 0,93. Besides, the cross-correlation coefficients (R) between δfoF2 values at Brisbane and Akita stations with Kp, Dst, ap, and ap (τ) values were calculated. The best the cross-correlation coefficient between the geomagnetic indices and the δfoF2 values at the Brisbane was obtained as 0,89 for ap(τ=0,5) values. However the best cross-correlation coefficient between the geomagnetic indices and δfoF2 values at the Akita was obtained as 0,87 for ap(τ=0,7) values. Next, the variations depending on local time of δfoF2 values at Brisbane and Akita were investigated for both the main phases and the recovery phases of two severe geomagnetic storms. During the main phases of the geomagnetic storms, the δfoF2 values at both Brisbane and Akita gradually increase with decreasing Dst values. However during the recovery phases of the geomagnetic storms, the mean δfoF2 values (δfoF2¯) at both Brisbane and Akita have positive values during the local nighttime whereas they have negative values during the local daytime. It is presumed that prompt penetrating electric fields (PPEFs) that penetrate into the magnetosphere and the Earth’s ionosphere during the geomagnetic storms are responsible for these results.
       
  • Effect of trapped ion on the shock properties in opposite charged dusty
           plasma
    • Abstract: Publication date: Available online 27 February 2019Source: Advances in Space ResearchAuthor(s): Sultan Z. Alamri The dust acoustic frequency properties and dissipative electrostatic field characteristics in opposite charged viscous dusty fluid plasma having trapped ion have been disused for quasineutrality case. The modified dissipative Burgers equation was analytically derived. The contributions of positive dust parameter, trapped ion, ion temperatures and charge to mass ratio between polarity grains on shock potential and its related electrostatic field have been investigated.
       
  • On the difference between real-time and research simulations with CTIPe
    • Abstract: Publication date: Available online 26 February 2019Source: Advances in Space ResearchAuthor(s): Isabel Fernandez-Gomez, Mariangel Ferdrizzi, Mihail V. Codrescu, Claudia Borries, Martin Fillion, Timothy J. Fuller-Rowell Understanding the thermosphere and ionosphere conditions is crucial for spacecraft operations and many applications using radio signal transmission (e.g in communication and navigation). In this sense, physics based modelling plays an important role, since it can adequately reproduce the complex coupling mechanisms in the magnetosphere-ionosphere-thermosphere (MIT) system. The accuracy of the physics based model results does not only depend on the appropriate implementation of the physical processes, but also on the quality of the input data (forcing). In this study, we analyze the impact of input data uncertainties on the model results. We use the Coupled Thermosphere Ionosphere Plasmasphere electrodynamics model (CTIPe), which requires satellite based solar wind, interplanetary field and hemispheric power data from ACE and TIROS/NOAA missions. To identify the impact of the forcing uncertainties, two model runs are compared against each other. The first run uses the input data that were available in real-time (operational) and the second run uses the best estimate obtained in post-processing (research or historical run). The analysis is performed in a case study on the 20th November 2003 extreme geomagnetic storm, that caused significant perturbations in the MIT system. This paper validates the thermosphere and ionosphere response to this storm over Europe comparing both CTIPe model runs with measurements of Total Electron Content (TEC) and thermosphere neutral density. In general, CTIPe results show a good agreement with measurements. However, the deviations between the model and observations are larger in the ionosphere than in the thermosphere. The comparison of the two model runs reveals that the deviations between model results and measurements are larger for the operational run than the research run. It is evident for the storm analyzed here, that data gaps in the input data are impacting considerably the model performance. The consistency between simulation and measurements allows the interpretation of the physical mechanisms behind the ionosphere perturbations and the changes in neutral composition during this event. Joule heating in the Auroral region, generating meridional winds and large scale surges, is suggested to be the main driver of the positive ionospheric storm over central Europe. In the polar cap and Auroral region, convection processes dominate the thermosphere-ionosphere conditions.This study does not only illustrate the importance of working with a good estimate of the model forcing, but also indicates the necessity of using measurements and models, to get a better understanding of the most likely responsible processes for the observed storm effects.
       
  • Directed Energy Interception of Satellites
    • Abstract: Publication date: Available online 25 February 2019Source: Advances in Space ResearchAuthor(s): Harrison She, Will Hettel, Phillip Lubin High power Earth and orbital-based directed energy (DE) systems pose a potential hazard to Earth orbiting spacecraft. The use of very high power, large aperture DE systems to propel spacecraft is being pursued as the only known, feasible method to achieve relativistic flight in our NASA Starlight and Breakthrough Starshot programs. In addition, other beamed power mission scenarios, such as orbital debris removal and our NASA program using DE for powering high performance ion engine missions, pose similar concerns. It is critical to quantify the probability and rates of interception of the DE beam with the approximately 2000 active Earth orbiting spacecraft. We have modeled the interception of the beam with satellites by using their orbital parameters and computing the likelihood of interception for many of the scenarios of the proposed systems we are working on. We are able to simulate both the absolute interception as well as the distance and angle from the beam to the spacecraft, and have modeled a number of scenarios to obtain general probabilities. We have established that the probability of beam interception of any active satellite, including its orbital position uncertainty, during any of the proposed mission scenarios is low (≈10-4). The outcome of this work gives us the ability to predict when to energize the beam without intercept, as well as the capability to turn off the DE as needed for extended mission scenarios. As additional satellites are launched, our work can be readily extended to accommodate them. Our work can also be used to predict interception of astronomical adaptive optics guide-star lasers as well as more general laser use.
       
  • Time-series Analysis of GPS Measurements for Long-span Bridge Movements
           using Wavelet and Model Prediction Techniques
    • Abstract: Publication date: Available online 23 February 2019Source: Advances in Space ResearchAuthor(s): Mosbeh R. Kaloop, Mosaruf Hussan, Dookie Kim This study aims at assessing the safety behavior of the Incheon long-span bridge using high rate (10Hz) geodetic monitoring global positioning system (GPS). The time series of wavelet spectrum analysis is utilized to assess the dynamic behavior of the bridge. The coefficients and model errors of the time series autoregressive-moving average (ARMA) model are used to evaluate the movement performances of the bridge. The results show that: (i) the accuracy of GPS measurements to extract the dynamic behavior of the bridge is 97.27% when compared with the design results. (ii) the behavior of the bridge is within the safety limits of the bridge design with minimum observed changes for the historical GPS measurements in time and frequency domains, the mean deflection of bridge deck is 8.26 mm and frequency changes of bridge is 0.004 Hz compared with the design results. (iii) the time series analysis of the wavelet spectrum and ARMA model coefficients can be used to detect the significant frequency changes and study the rigidity of the bridge performance, respectively; and the both methods are found to be suitable techniques to estimate the performance changes of the GPS measurements in the time and frequency domains during the monitoring time period.
       
  • Possible evidence for small-scale wave seeding of equatorial plasma
           bubbles
    • Abstract: Publication date: Available online 23 February 2019Source: Advances in Space ResearchAuthor(s): Kangkang Liu, Guozhu Li, Baiqi Ning The small-scale wave-like structure (SSWS) of F region bottomside plasma density was proposed to be an important seeding for equatorial plasma bubble (EPB) generation, and employed in theoretical simulations of EPBs in recent years. The seeding role of SSWS, however, is waiting to be demonstrated by observation. Here we present two cases of SSWS and EPB observed by the Fuke all-sky airglow imager (19.3°N, 109.1°E; dip latitude 14.3°N). For each case, the results show that two large-scale wave-like structures (LSWSs) initially appeared around sunset in the longitude regions separated by 3-4°, but EPB irregularities were only generated in one of the LSWSs where SSWSs were seen riding on LSWS. For the other LSWS, no SSWS and EPB irregularities were seen. Considering that the two LSWSs were situated closely in longitude where the amplitude of pre-reversal enhancement of background eastward electric field should be similar, the observation that EPB was only generated in the longitude with simultaneous LSWS and SSWS could provide supporting evidence for SSWS seeding of EPB.
       
  • Temporal variation and asymmetry of sunspot and solar plage types from
           1930 to 1936
    • Abstract: Publication date: Available online 23 February 2019Source: Advances in Space ResearchAuthor(s): A. Seguí, J.J. Curto, V. de Paula, R. Rodríguez-Gasén, J.M. Vaquero Using the recently converted to digital format heliophysics catalogues of the Ebro Observatory published in the 1930s, we analyse simultaneously the temporal variation and asymmetry of two different solar structures located at different layers of the solar atmosphere: sunspots and solar plages. In particular, we do the research for all the types of sunspots and plages, including the daily and relative frequencies over the solar cycle. The data were catalogued using the sunspot Cortie classification and a solar plage classification scheme proposed by the Ebro Observatory, which group the phenomena by size and shape. For all types of both sunspots and plages, we observe a decrease in their frequency up to the end of solar cycle 16 and an increase over the beginning of solar cycle 17. Furthermore, we note that small sunspot groups are more likely to happen than bigger groups, although single big spots dominate near the solar minimum. The daily frequency of solar plage occurrences shows that there is not a dominance of compact or scattered solar plages. The North-South occurrence distribution of every type in both sunspots and solar plages shows an asymmetry during the solar cycle: in its declining phase, such asymmetry is directed to the north, while in the beginning of a new cycle is directed to the south.
       
  • Comparison of convergence time and positioning accuracy among BDS, GPS and
           BDS/GPS precise point positioning with ambiguity resolution
    • Abstract: Publication date: Available online 23 February 2019Source: Advances in Space ResearchAuthor(s): Xuexi Liu, Weiping Jiang, Zhao Li, Hua Chen, Wen Zhao Precise point positioning (PPP) usually takes about 30 min to obtain centimetre-level accuracy, which greatly limits its application. To address the drawbacks of convergence speed and positioning accuracy, we develop a PPP model with integrated GPS and BDS observations. Based on the method, stations with global coverage are selected to estimate the fractional cycle bias (FCB) of GPS and BDS. The short-term and long-term time series of wide-lane (WL) FCB, and the single day change of narrow-lane (NL) FCB are analysed. It is found that the range of GPS and BDS non-GEO (IGSO and MEO) WL FCB is stable at up to a 30-day-time frame. At times frame of up to 60 days, the stability is reduced a lot. Whether for short-term or long-term, the changes in the BDS GEO WL FCB are large. Moreover, BDS FCB sometimes undergoes a sudden jump. Besides, 17 and 10 stations were used respectively to investigate the convergence speed and positioning errors with six strategies: BDS ambiguity-float PPP (Bfloat), GPS ambiguity-float PPP (Gfloat), BDS/GPS ambiguity-float PPP (BGfloat), BDS ambiguity-fixed PPP (Bfix), GPS ambiguity-fixed (Gfix), and BDS/GPS ambiguity-fixed (BGfix). The average convergence speed of the ambiguity-fixed solution is greatly improved compared with the ambiguity-float solution. In terms of the average convergence time, the Bfloat is the longest and the BGfix is the shortest among these six strategies. Whether for ambiguity-float PPP or ambiguity-fixed PPP, the convergence reduction time in three directions for the combined system is the largest compared with the single BDS. The average RMS value of the Bfix in three directions (easting (E), northing (N), and up (U)) are 2.0 cm, 1.5 cm, and 5.9 cm respectively, while those of the Gfix are 0.8 cm, 0.5 cm, and 1.7 cm. Compared with single system, the BDS/GPS combined ambiguity-fixed system (BGfix) has the fastest convergence speed and the highest accuracy, with average RMS as 0.7 cm, 0.5 cm, and 1.9 cm for the E, N, U components, respectively.
       
  • Sensor-Fault Tolerant Attitude Determination Using Two-Stage Estimator
    • Abstract: Publication date: Available online 22 February 2019Source: Advances in Space ResearchAuthor(s): SooYung Byeon, Sung-Hoon Mok, Hyunwook Woo, Hyochoong Bang Satellite attitude determination accuracy significantly drops when sensor-fault occurs. Hence, a proper mitigation strategy to detect sensor-fault and accurately estimate corresponding fault magnitudes is mandatory for robust and accurate attitude determination. In this paper, a novel sensor-fault tolerant precise attitude estimator is proposed consisting of two stages. In the first stage, sensor-fault is detected, and the associated sensor parameter change is roughly estimated using an interacting multiple-model (IMM) approach. Subsequently, the second stage is triggered. The sensor parameter change is precisely estimated with a new sensor-parameter-augmented filter. This is defined as a selectively augmented extended Kalman filter (SAEKF) in this paper. The conventional augmented extended Kalman filter (AEKF) is computationally more expensive than the proposed SAEKF. The SAEKF augments only the sensor parameters affected by sensor-faults, not the full sensor parameters, into the state vector. This leads to a significant computational time-saving. A transition method from the first stage to the second stage is also investigated. Numerical simulation results demonstrate that the proposed two-stage approach has smaller attitude determination errors than the existing algorithms, ranged from 21.7% to 88.8%, in cases with gyro scale factor error or misalignment.
       
  • Wrinkling analysis for small solar-photon sails: an experimental and
           analytic approach for trajectory design
    • Abstract: Publication date: Available online 22 February 2019Source: Advances in Space ResearchAuthor(s): Tommaso Pino, Christian Circi, Giovanni Vulpetti A good model of solar-radiation pressure induced thrust is one of the key points in sailcraft trajectory design. The sail membrane’s local topographic deformations, i.e. wrinkles and creases, are among the main aspects that such a model should include. We have analyzed the influence of wrinkles/creases, as a whole, by measuring the related deformations on small samples of sail membrane, 2.5 μm thick, consisting of CP1 and physical-vapor-deposition Aluminum. Experimental outcomes from our laboratory facility have been processed, statistically investigated, and inserted into the lightness vector formalism. We have used such formalism for accurate sailcraft trajectory computation via a non-ideal reflection sail thrust model. Finally, we computed the deviations of wrinkled-sail sailcraft final orbital states with respect to the no-wrinkle sail final orbital ones for a circular to circular 2D inward transfer. The radii of the orbits are 1 AU and the semi-major axis of Mercury, respectively. It appears that sail wrinkles and creases are no longer negligible in the sailcraft trajectory design.
       
  • Medium Earth Orbit dynamical survey and its use in passive debris removal
    • Abstract: Publication date: Available online 21 February 2019Source: Advances in Space ResearchAuthor(s): Despoina K. Skoulidou, Aaron J. Rosengren, Kleomenis Tsiganis, George Voyatzis The Medium Earth Orbit (MEO) region hosts satellites for navigation, communication, and geodetic/space environmental science, among which are the Global Navigation Satellites Systems (GNSS). Safe and efficient removal of debris from MEO is problematic due to the high cost for maneuvers needed to directly reach the Earth (reentry orbits) and the relatively crowded GNSS neighborhood (graveyard orbits). Recent studies have highlighted the complicated secular dynamics in the MEO region, but also the possibility of exploiting these dynamics, for designing removal strategies. In this paper, we present our numerical exploration of the long-term dynamics in MEO, performed with the purpose of unveiling the set of reentry and graveyard solutions that could be reached with maneuvers of reasonable ΔV cost. We simulated the dynamics over 120-200 years for an extended grid of millions of fictitious MEO satellites that covered all inclinations from 0 to 90°, using non-averaged equations of motion and a suitable dynamical model that accounted for the principal geopotential terms, 3rd-body perturbations and solar radiation pressure (SRP). We found a sizeable set of usable solutions with reentry times that exceed ∼40 years, mainly around three specific inclination values: 46°, 56°, and 68°; a result compatible with our understanding of MEO secular dynamics. For ΔV⩽300 m/s (i.e., achieved if you start from a typical GNSS orbit and target a disposal orbit with e
       
  • Sea level trend over Malaysian Seas from multi-mission satellite altimetry
           and vertical land motion corrected tidal data
    • Abstract: Publication date: Available online 21 February 2019Source: Advances in Space ResearchAuthor(s): Ami Hassan Md Din, Nur Adilla Zulkifli, Mohammad Hanif Hamden, Wan Anom Wan Aris Rise in sea levels is one of the disastrous effects of climate change. A relatively small increase in sea level could affect natural coastal systems. In a study of long-term changes in sea level and measurements of postglacial rebound, monitoring vertical land motion (VLM) is of crucial interest. This study presents an approach to estimate precise sea level trends based on a combination of multi-sensor techniques in the Malaysian region over 19 years. In this study, satellite altimeters (SALT) were used to derive absolute sea levels (ASLs). Tide gauge (TG) stations along the coast of Malaysia were utilised to derive the rate of relative sea levels using sea level changes and VLMs. To obtain ASL at TGs, VLM at these stations were computed using Global Positioning System (GPS), Persistent Scatterer Interferometric Synthetic Aperture Radar (PS InSAR), and SALT minus TG. The computed VLMs mostly show similarities in signs rather than magnitude. The findings from the multi-sensor techniques showed that regional sea level trends ranged from 2.65 ± 0.86 mm/yr to 6.03 ± 0.79 mm/yr for chosen sub-areas, with an overall mean of 4.47 ± 0.71 mm/yr and overall subsidence. This information is expected to be valuable for a wide variety of climatic applications and for studying environmental issues related to flooding and global warming in Malaysia.
       
  • Estimation of sediment settling velocity in estuarine and coastal waters
           using optical remote sensing data
    • Abstract: Publication date: Available online 21 February 2019Source: Advances in Space ResearchAuthor(s): Hussain J. Nasiha, Palanisamy Shanmugam, R. Sundaravadivelu A robust method has been developed for estimating sediment settling velocity (ws) from high resolution optical remote sensing data in estuarine, coastal and harbor waters. This method estimates settling velocity as a function of the drag coefficient (Cd), Reynolds number (Re), grain size (D50), specific gravity (ΔSG) and grain shape (in terms of the Corey Shape Factor - CSF). These parameters were derived from the particulate inherent optical properties such as backscattering (bbp), beam attenuation (cp), suspended sediment concentration and turbidity using Landsat 8 OLI and HICO data. Preliminary results for the Gulf of Cambay in the eastern Arabian Sea and Yangtze river estuary in the East China Sea, showed that satellite-retrieved settling velocities (m s-1) varied from very low values in clear oceanic waters intermediate values in coastal waters, to very high values in river plumes and sediment-laden coastal waters. The remote sensing retrievals of sediment properties and their settling velocities were generally consistent with field and laboratory results, which indicate that the proposed methodology will have important implications in various coastal engineering, environmental and management studies.
       
 
 
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