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This work aims to investigate far-UVC light at 222 nm as a new microbial reduction tool for planetary protection purposes which could potentially be integrated into the spacecraft assembly process. The major advantage of far-UVC (222 nm) compared to traditional germicidal UVC (254 nm) is the potential for application throughout the spacecraft assembly process in the presence of humans without adverse health effects due to the limited penetration of far-UVC light into biological materials. Testing the efficacy of 222-nm light at inactivating hardy bacterial cells and spores isolated from spacecraft and associated surfaces is a necessary step to evaluate this technology. We assessed survival of Bacillus pumilus SAFR-032 and Acinetobacter radioresistens 50v1 exposed to 222-nm light on proxy spacecraft surfaces simulated by drying the bacteria on aluminum coupons. The survival fraction of both bacteria followed a single stage decay function up to 60 mJ/cm2, revealing similar susceptibility of both species to 222-nm light, which was independent of the exposure rate. Irradiation with far-UVC light at 222 nm is an effective method to decontaminate the proxy spacecraft materials tested in this study.

In October 2003, The U.S. National Radio Astronomy Observatory (NRAO) and the U.S. National Research Council (NRC) held a 3-day conference in Washington, DC, on communicating with the public about astronomy. This conference was organized by participants in a December 2002 meeting hosted by Spain’s Instituto de Astrofisica de Canarias in Tenerife on “Communicating Astronomy.” The goals of the 2003 conference, conceived as a working meeting, were “to develop a program to share outreach and education resources among the astronomical community [and] to find ways of communicating with underdeveloped constituencies.” Two important products of the 2003 meeting were: 1. A “Washington charter for communicating astronomy with the public,” a position paper articulating principles of action for funding agencies, professional astronomical societies, individual researchers and universities, laboratories, research organizations, and other institutions with an interest in communicating with the public about astronomy. 2. The appointment of a task group to explore the creation of an electronic archive of informational resources about astronomy. Two options under consideration by the task group are creation of a Web site providing links, categorized and searchable, to astronomy public outreach and education resources and creation of a Web site that would be a searchable database of astronomy information and imagery (either representative or comprehensive). This paper reviews the purpose and proceedings of the conference, reports on outcomes, and provides a status report on post-conference actions. It also reports on a newly organized NASA Astrobiology Institute Working Group on Astrobiology Science Communication.

In this short paper we examine the possible connection between atmospheric parameters measured at low and middle altitudes and geomagnetic storms occurred in 2000 and 2003. For that, from a chain of stations located near the meridian 60°W we compare the storm time values of temperature and wind speed with their standard deviation 2σ obtained from quiet time values. We observed statistically significant variations at several altitudes during the storm recovery phase and after it, both in neutral wind speed and temperature. The results obtained suggest that atmospheric parameters could be affected by geomagnetic storms. Fil: Mansilla, Gustavo Adolfo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Tucumán; Argentina. Universidad Nacional de Tucumán. Facultad de Ciencias Exactas y Tecnología. Departamento de Física. Laboratorio de Ionósfera; Argentina

Geological interpretation, analysis and evaluation of LANDSAT and airborne MSS data, panchromatic and colour infrred photographs and spectral reflectance data for a number of test sites in different mineralized belts in India have led to certain significant results. Lithological discrimination on digitally processed enhanced MSS data products has helped in further subdivisions of major rock groups. Lineament pattern analyses reveals three prominent sets of fractures in Indian Precambrian Shield with predominant ENE-WSW megalineament probably representing earliest deep crustal fractures and subsequent NNW-SSE and NE-SW fractures, associated with polyphase tectonic movements. Correlation of structures and mineralization indicate structural control for most of the mineralized belts with intersecting locii type concentration of ore deposits in some cases. In a few cases control of mineralization is lithology and stratigraphy. Spectral groundtruth and laboratory studies indicate that major rock types have characteristic spectral patterns (signatures) which would be useful for lithological mapping by automatic classification techniques. The work also has led to the improvement of enhanced MSS data products for geological studies.

It is very important to recycle the inedible biomass of higher plants to improve the closure of bioregenerative life support system (BLSS). Processing candidate higher plant residues into the soil-like substrate (SLS) as the plant growth medium is a promising way to achieve. In this study, three different processing techniques of SLSs, using residues of wheat and rice as feedstock, were compared. As for the first traditional technique, SLS1 was obtained by successive conversion of wheat straw by oyster mushrooms and worms. In the other two methods, SLSs were produced with aerobic fermentation (SLS2) or anaerobic fermentation (SLS3) followed by worm conversion. The changes in SLS cellulose, lignin, available elements and pH were measured during the production processes. The maturity was evaluated by the value of C/N. The fertilities were compared in terms of available elements contents and lettuce productivities. The results indicated that the second technique was optimal, whose process cycle was 30 days less than that of SLS1. The total cellulose and lignin degradation of SLS2, achieved 98.6% and 93.1% during the 93-days-processing, and the lettuce productivity reached 12.0 g m−2 day−1.

Human habitation and animal holding experiments in a closed environment, the Closed Ecology Experiment Facilities (CEEF), were carried out. The CEEF were established for collecting experimental data to estimate carbon transfer in the ecosystem around Rokkasho nuclear fuel reprocessing plant. Circulation of O 2 and CO 2 , and supply of food from crops cultivated in the CEEF were conducted for the first time in the habitation experiments. Two humans known as eco-nauts inhabited the CEEF, living and working in the Plant Module (PM) and the Animal and Habitation Module (AHM), for a week three times in 2005. On a fresh weight basis, 82% of their food was supplied from 23 crops including rice and soybean, cultivated and harvested in the PM, in the 2nd and 3rd experiments. For the goats, the animals held in the experiments, all of their feed, consisting of rice straw, soybean plant leaves, and peanut shells and peanut plant leaves, was produced in the PM in the 2nd and 3rd experiments. The O 2 produced in the PM by photosynthesis of the crops was separated by the O 2 separator using molecular sheaves, then accumulated, transferred, and supplied to the AHM atmosphere. The CO 2 produced in the AHM by respiration of the humans and animals was separated by the CO 2 separator using solid amine, then accumulated, transferred, and supplied to the PM atmosphere. The amount of O 2 consumed in the AHM was 46–51% of that produced in the PM, and the amount of CO 2 produced in the AHM was 43–56% of that consumed in the PM. The surplus of O 2 and the shortage of CO 2 was a result of the fact that waste of the goats and the crops and part of the human waste were not processed in these habitation experiments. The estimated amount of carbon ingested by the eco-nauts was 64–92% of that in the harvested edible part of the crops. The estimated amount of carbon ingested by the goats was 36–53% of that in the harvested inedible part of the crops. One week was not enough time for determination of gas exchange especially for humans and animals, because fluctuation of their gas exchange was quite high. The amount of transpired water collected as condensate was 818–938 L d −1 , and it was recycled as replenishing water compensating transpiration loss of nutrient solution. The amount of waste nutrient solution discharged from the PM was 1421–1644 L d −1 . The waste nutrient solutions from rice and other crops were processed through micro filters (MFs) separately. The MF filtrated solutions were processed with reverse osmosis (RO) membrane filter separately and divided into filtrated water and concentrated waste nutrient solution. The concentrated waste nutrient solution from the crops other than rice was processed through an ultra-micro filter (UF) and reused, although that from rice was discharged in 2005. Concentrations of nutritional ions in the UF filtrated solution were determined, the depleted ions were added back, the UF filtrated solution was diluted with the RO membrane filtrated water, and the nutrient solution for the crops other than rice was regenerated. The nutrient solution for rice was newly made each time, using concentrated solution from an external source and the RO membrane filtrated water. Average amounts of water used in the AHM (L d −1 ) were determined as follows: drinking by humans (filtrated water), 1.5; cooking, etc. (filtrated water other than for drinking), 14.3; drinking by goats, 3.8; showering (hot water), 13.2; showering (cold water), 0.1; washing of hand and face and brushing teeth, 4.1; washing of dishes, dish clothes and towels, 36.4; and washing of animal holding tools, 0.3. The waste water was processed by a RO purification system and recycled for toilet flushing and animal pens washing. A circulation experiment for water was started in 2006 and a circulation experiment for waste materials is planned for 2007. In 2006, a single duration of the air circulation experiments was 2 weeks, although the human habitants were changed after 1 week.

This paper based on He + density data gathered between 1000 and 1200 km from ∼1100 orbits of the ISS-b satellite. Its goal is to obtain of the occurrence probability, P , of mid-latitude troughs and subtroughs in He + density as function of local time and season. Mid-latitude He + (H + ) density trough, LIT, is the prominent feature of the upper ionosphere. Other distinct structure of the upper ionosphere as He + (H + ) density subtroughs, located equatoward than LIT, is not so unique and seldom structure, as it was supposed early, since we revealed them in ∼570 cases in ∼1100 orbits. Obtained trough features differ in many respects from qualitative regularities, detected in earlier publications. So, mid-latitude He + troughs are not so frequent by day; they occur more often in summer ( P ≅30%) than in winter ( P =5 to 10%). Subtroughs are also observed by day rather seldom but stable in summer ( P =7 to 12%) and only in exclusive cases in winter. At night the mid-latitude troughs do quite often occur ( P =40 to 60% in winter and 35 to 55% in summer). The subtroughs are more often observed under nighttime conditions ( P ∼30% in winter till 5–10% in summer). It was also further revealed that the occurrence probability of LIT and subtroughs is associated with corresponding variations of the He + density. Our findings might be helpful for the IRI and for theories of trough formation as well.

Accurate forecasts of thermosphere densities, realistic calculation of aerodynamic drag, and propagation of the uncertainty on the predicted orbit positions are required for conjunction analysis and collision avoidance decision making. The main focus of the Committee on Space Research (COSPAR) International Space Weather Action Teams (ISWAT) involved in atmosphere variability studies is satellite drag, and this paper reviews our current capabilities and lists recommendations. The uncertainty in the density of thermosphere models is due to the combined effect of employing simplified or incomplete algorithms, inconsistent and sparse density data, incomplete drivers for upper atmosphere heating processes (proxies for solar and geomagnetic activity), and forecast error of said drivers. When calculating drag, the uncertainty is amplified due to the satellite shape and aerodynamic model. The sources of uncertainty are reviewed in this paper, and possible and promising ways forward are proposed. Data assimilation models/approaches have demonstrated superior skill in reproducing the thermosphere's state and are the most promising way forward. However, data to drive the models is generally lacking, and they require significant computational resources. Substantial progress can only be made by means of setting up a full-blown observing system, including not only density and composition measurements, but equally the necessary model drivers.

Bioregenerative methods are being developed for recycling plant minerals from harvested inedible biomass as part of NASA's Advanced Life Support (ALS) research. Anaerobic processing produces secondary metabolites, a food source for yeast production, while providing a source of water soluble nutrients for plant growth. Since NH4-N is the nitrogen product, processing the effluent through a nitrification reactor was used to convert this to NO3-N, a more acceptable form for plants. Potato (Solanum tuberosum L.) cv. Norland plants were used to test the effects of anaerobically-produced effluent after processing through a yeast reactor or nitrification reactor. These treatments were compared to a mixed-N treatment (75:25, NO3:NH4) or a NO3-N control, both containing only reagent-grade salts. Plant growth and tuber yields were greatest in the NO3-N control and yeast reactor effluent treatments, which is noteworthy, considering the yeast reactor treatment had high organic loading in the nutrient solution and concomitant microbial activity.

The use of controlled environments is subject to problems from contaminants emitted from materials of the system and from plants. Many contaminants are difficult to identify because injurious dosages are very low, there is a lack of information on what compounds injure plants, because species and cultivars differ greatly in their sensitivity to injury and injury symptoms often are not distinctive. Plastics have been shown to emit many different volatile compounds. The compound, di-butyl phthalate, contained in certain flexible plastics, has been shown to be very toxic to plants. Other injuries have been produced by caulking compounds and bonded screening. Paints have been shown to release xylene that is toxic to plants. Steam for humidification can cause problems because of hydroxylamines and other compounds added to steam used for heating to control fungal growth in return lines. Mercury, from broken thermometers is a particular problem in growth chambers because small quantities can collect in cracks and slowly volatilize to slow growth of plants. Plants themselves release large quantities of volatile hydrocarbons, with ethylene being the commonly recognized chemical that can be damaging when allowed to accumulate. People release large quantities of carbon dioxide which can cause variations in the rate of growth of plants. Contaminant problems can be controlled through filtering of the air or ventilation with make-up air, however the potential for problems is always present and careful testing should be undertaken with the particular species and cultivars being grown insure that there are no toxic agents altering growth in each particular controlled environment being utilized.

In this paper, a novel approach based on C1 finite element (FE) interpolation is used to construct a regional ionospheric grid model (RIGM) with high spatio-temporal resolution over Europe. The spatial resolution of the new model is 0.50 for a longitude and latitude and a temporal resolution is 15 minutes. Observations of 38 GPS stations at different days and seasons with different geomagnetic and solar activity conditions are used to evaluate the new method. All stations are used to discretize the whole domain of the problem into separate triangular patches using a Delaunay triangulation algorithm. In this case, GPS stations would be the vertices of the triangular patches. Also, the position of stations in sun-fixed coordinate system with coordinates of latitude and longitude are chosen in order to consider the temporal variations of vertical total electron content (VTEC). To model the behavior of VTEC in each triangular patch, a particular shape function is defined which is fitted to VTEC values at three vertices of each triangle while it satisfies C1 continuity of VTEC at the common edges of the adjacent triangles. The results of the new model are compared with the VTEC of GPS at 4 control stations as well as global ionosphere map (GIM) and NeQuick models. Statistical parameters, including correlation coefficient, root mean square error (RMSE), standard deviation and dVTEC=|VTECGPS - VTECmodel| have been used to evaluate the error of the models. In low geomagnetic activity (KP 4), they are 1.24, 1.68 and 7.62 TECU, respectively. For further analysis, the accuracy of three models in precise point positioning (PPP) has been also evaluated. In PPP method, there is an improvement of about 1 to 16 mm compared to GIM and NeQuick models at coordinate components of control stations in high geomagnetic activity. The results of the analysis performed in this paper show that the FE model has a very high capability and accuracy in regional VTEC modeling in high and low geomagnetic conditions. The regional accuracy of this model is higher than GIM and NeQuick models and therefore can be considered as a new model for the ionosphere.

Monitoring ionospheric scintillation on a global scale requires introducing a network of widely distributed geodetic receivers, which call for a special type of scintillation index due to the low sampling rate of such receivers. ROTI, as a scintillation index with great potential being applied in geodetic receivers globally, lacks extensive verification in the high-latitude region. Taking the phase scintillation index ( σ ϕ ) provided by ionospheric scintillation monitoring receivers as the reference, this paper analyses data collected at 8 high-latitude GNSS stations to validate the performance of ROTI statistically. The data is evaluated against 4 parameters: 1, the detected daily scintillation occurrence rate; 2, the ability to detect the daily occurrence pattern of ionospheric scintillation; 3, the correlation between the detected scintillation and the space weather parameters, including the 10.7 cm solar flux, Ap, the H component of longitudinally asymmetric and polar cap north indices; 4, the overall distribution of the scintillation magnitude. Results reveal that the scintillation occurrence rates, the occurrence patterns of ionospheric scintillations and the correlations provided by ROTI are generally consistent with those given by σ ϕ , particularly in the middle-high-latitude region. However, the analysis on the distribution of σ ϕ for different ranges of ROTI shows ROTI cannot achieve accurate scintillation monitoring at the epoch level in all selected stations. The main outcomes of this paper are of importance in guiding the reasonable application area of ROTI and developing a high-latitude ionospheric scintillation model based on geodetic receivers.

The paper discusses the issues of the disturbances allocations in the ionosphere that are associated with large atmospheric events - tropical cyclones of the 4–5 categories of 2014. On the basis of the characteristic spatio-temporal characteristics of the acoustic-gravity waves from atmospheric disturbances, the method is proposed for the detection of relative disturbances of the electron concentration in the frequency band characteristic of the disturbances. The observation of electron density by Langmuir probes carried out on the ESA Swarm satellites were used as experimental data. In the paper we consider all large 2014 Tropical Cyclones (TC) and discuss the statistics of the identified disturbances from TC in the ionosphere against the background of regular changes in the electron density in quiet geo-heliomagnetic conditions. The obtained results show that the wave mechanism of disturbance transmission from an atmospheric source to ionospheric heights is not the only one.

The paper considers the contactless transportation of space debris by means of an ion beam generated by an active spacecraft electrodynamic engine. The three-dimensional motion of a space debris object relative to its center of mass is studied. Space debris is assumed to be a dynamically symmetric cylindrical rigid body. The aim of the paper is to develop a control of the engine thrust, which ensures the stabilization of spatial oscillations of cylindrical space debris. A simplified mathematical model describing the motion of a dynamically symmetric rigid body in a Keplerian orbit is developed. For the case of a circular orbit, stationary motions relative to the center of mass are found. A feedback control law for the thrust of an electrodynamic engine creating an ion beam, which is aimed at stabilizing the space debris object in a stationary angular position, is proposed. The results of numerical research confirm the effectiveness of this control. The research results can be used in the preparation of space debris removal missions.

In recent years, the research of indoor positioning technology has mainly focused on WI-FI, Bluetooth, ultra-wideband, and pseudo-satellites. Each of these indoor positioning technologies has different advantages, but also has various limitations, especially in indoor areas such as corridors, tunnels, and stairs. Due to the limitations of application scenarios, navigation and positioning accuracy and efficiency, it is difficult to form a satisfactory navigation and positioning solution for indoor special environment. In order to solve the positioning problem of indoor long and narrow areas, a multi-source fusion navigation and positioning algorithm based on pseudo-satellite assistance is proposed in this paper. Under certain map information constraints, it can use the direct arrival signal of a single pseudo-satellite to correct the location information output by mobile phone PDR(Pedestrian Dead Reckoning), and improve the navigation and positioning performance of indoor passageway and corridor areas. To realize the system, it is necessary to ensure that a direct pseudo-satellite signal can be received in any area of the corridor. The position of the pseudo-satellite can be determined according to the captured pseudo-satellite signal, and the pseudo-range change rate can be estimated by calculating the carrier phase change rate. In this paper, we deduce the relationship between the pseudo-range change rate and the change of the mobile phone PDR position, and build an optimization model based on map information constraints, which improves the positioning accuracy of the system for indoor narrow and long areas. A large number of experimental results show that the system has high positioning accuracy in the real indoor long and narrow environment. The average positioning accuracy of the algorithm in indoor environments is better than 0.4 m, and there is no significant change in the performance after a long time of cumulative positioning.

Lightning is a sudden release of electrostatic energy that plays a significant role in the ionospheric-magnetospheric coupling process. A short-term increase in the particle count rates (CR) in the Van Allen Radiation Belt (VAB) is known as the particle bursts. Due to lightning events, the increase in the number of high-energy particles in the inner region of the VAB (L 2) is a fascinating research to implement. This paper tries to determine the number of lightning-induced particles, which can successfully establish a connection between the two regions of the atmosphere (the ionosphere and the magnetosphere). Lightning-generated electromagnetic radiation propagates through the Earth Ionosphere Waveguide (EIWG), where some energy leaks through and scatters particles in the radiation belt. By lowering the pitch angle, some particles precipitate into the ionosphere and cause secondary ionization. This excess particle count caused by lightning strokes is detected using data from the NOAA-15 satellite and data from the World Wide Lightning Location Network (WWLLN) is used to verify the relationship between lightning stroke and particle count. In this paper, we process our work by using lightning locations over a specific region of India and the geographic/geomagnetic conjugate locations. The monthly variation shows a high correlation between the lightning stroke number and the particle counts within the conjugate geomagnetic location, while the correlation with the particle counts within the conjugate geographic location is significantly lower. In the second half of the paper, we use an automated energy filtration method, for the computation of the particle counts induced by maximum energetic lightning (having lightning energy value > 104 J and the particle counts induced by minimum energetic lightning (having lightning energy value 104 J). The results of this analysis demonstrate that the variation of PCs in the conjugate geomagnetic location is more closely related to the maximum energetic lightning variation than the lowest energetic lighting variation. This paper will demonstrate the coupling process between the ionosphere and the magnetosphere based on counting the particles produced by lightning.

In predicting the collision of space debris, the propagated orbital uncertainty may not follow a Gaussian distribution if the initial orbital uncertainty is large or the propagation time is long. In this paper, a Gaussian mixture uncertainty propagation method developed by (Psiaki et al., 2015) is used to calculate the collision probability. The initial Gaussian distribution is fitted by the weighted Gaussian mixture components. The linear matrix inequality is optimized to prevent the covariance matrix of Gaussian mixture components from being too small, and an appropriate number of Gaussian mixture components is used to approximate the initial orbital covariance. At the same time, this paper provides a method to calculate the collision probability of two objects in which a Gaussian mixture is used to represent the distribution of orbital uncertainty. The linear method and the unscented Kalman filter (UKF) method for propagating the Gaussian covariance are analysed. The results of numerical simulations show that compared with the linear covariance propagation method, UKF method, and high-precision Monte Carlo covariance propagation method for space objects with a large initial orbital uncertainty, the Gaussian mixture method can be effectively applied to capture the non-Gaussian characteristics of the predicted nonlinear orbital dynamic uncertainty. Compared with the univariate splitting method, the advantage of this Gaussian mixture method is that it does not need to search for the most nonlinear direction. The accuracy of the collision probability calculation is improved from 1.460 × 10−3 to 1.663 × 10−3. A comparison of the computational burden between the Gaussian mixture algorithm and Vittaldev’s algorithm to achieve the same results is presented. The calculation burden of the Gaussian mixture method is approximately 3 times that of the univariate Gaussian method.

The usage of a satellite cluster of satellite-to-satellite sounding of the ionosphere makes it possible to obtain the global height distribution of an electron density between 200 and 500 km height range in the orbital plane of the cluster. This paper introduces a novel rapid two-dimensional ionospheric radio tomography algorithm that uses total electron content (TEC) data measured between low Earth orbit (LEO) satellites. This algorithm reduces the problem of the ionospheric radio tomography to the rapid filtered back-projection (FBP) algorithm, which was not previously used in the computerized tomography of the ionosphere, and which allows to obtain a high resolution nowcast. Data sets of TEC measurements were simulated via IRI-2016 model and used as an input for the developed algorithm. The reconstructed profiles of the electron density were compared with those profiles from IRI-2016 model to calculate the difference between them. The obtained accuracy is comparable to the accuracy of algebraic reconstruction algorithms (ART), which are classical in the ionospheric radio tomography, and makes it possible to use the developed method to detect local disturbances in the ionosphere that is demonstrated on a test case in this paper.

In this paper, we establish a mathematical model to simulate the dynamic behavior of the high-altitude zero-pressure balloon system during the ground dynamic launching process. The dynamic launching mathematical model includes the solution of the bubble shape and the dynamics model derived by taking the bubble, the membrane bundle, the cable, and the gondola as a whole. The bubble shape is considered as a combination of zero circumferential stress shape at the bottom and fully expanded shape at the top. Under the hypothesis, we use the multiple shooting method and the sequential quadratic programming method together to solve the partially expanded shape in the lower bubble region. Based on bubble shapes, the bubble is modeled as a “spring damping system” and we can establish its dynamic model. The “membrane bundle-cable system” is equivalent to a variable mass rope structure and we solve its dynamic behavior by using the mass particle model. We calculate the swing angle of the gondola by its geometry constraint and force analyses. The Hertz contact model and the Coulomb friction law are used to analyzing the contact between the “membrane bundle-cable system” and the ground or the main boom of the launching vehicle. Based on these dynamic models, we calculate the dynamic launching simulation under three operating conditions of the launching vehicle, which corresponds to three ambient wind speeds. The three operational modes of the launching vehicle are the static operation (2 m/s wind speed), the forward operation to chase the bubble (4 m/s), and the backward operation to increase the gondola releasing angle (0 m/s). We analyze the influence of the wind speed and the launching vehicle action on the force and geometric time history of the dynamic launching system. Furthermore, we discuss the three times typical overload in the dynamic launching system and its influencing factors, which are the opening of the roller, the straightening of the “membrane bundle-cable system” and the releasing of the gondola. The purpose of this paper is to present a set of methods and models for the dynamic launching simulation. It not only calculates the shapes of the bubble and simulates the motion of the quasi rope structure system individually, but also the bubble, the “membrane bundle-cable system” and the gondola are combined to establish a complete set of dynamic models to reflect the main characteristics of the dynamic launching process.

Context Physical and dynamical characterisations of asteroids are used in different fields, such as Solar System formation modelling, Planetary Defence and Resources Prospecting. The vast majority of asteroids are not known in detail - have at best their orbit well defined - and the knowledge on the composition or internal structure is derived by models of reflectivity curves, with limited certainty. Machine learning methods have begun to be used on asteroid datasets, but the major uncertainties about their characteristics are slowing down the applicability. Aims This paper reviews some stakes and challenges of asteroid exploration, and why the introduction of common characterisation factors would be beneficial for the asteroid science community, especially with the application of machine learning methodologies. A preliminary scale to quantify the characterisation of asteroids is proposed, and finally discusses its interests and limitations for machine learning applications. Method The investigated characteristics of asteroids are: size/shape, orbital dynamics, mass/density, spin, internal structure and composition. This paper reviews the current methods used to determine these parameters, and provides a preliminary scale based on the certainty associated with the different measurements. Results Characterisation factors are useful to build datasets that will be used in machine learning algorithms applied to asteroid science. The ratio of currently known asteroids in each defined bin of characterisation factor is estimated. Moreover, a total characterisation factor that yield a preliminary quantification of our knowledge about a specific asteroid (i.e. the sum of all the certainties about its different characteristics) is defined. Finally, characterisation factors for specific applications can be introduced using an adapted weighting system. Next steps This preliminary work provides a baseline for scaling uncertainties of asteroids properties. The next step is to create viable datasets using application specific characterisation factors that would allow the use of advanced machine learning algorithms already available.

This paper discusses the estimation of zonal geomagnetic indices of two super geomagnetic activities of 2015 in the 24th solar cycle. It estimates the zonal geomagnetic indices (Dst, ap, AE) of 17 March and 22 June 2015 super storms with an artificial neural network model. The activities that happened in March and June are considered on the solar wind parameters (B-z , E, P, N, v, T) and zonal geomagnetic indices obtained from NASA coordinated data analysis web. Descriptive values of the variables are indicated, binary correlations of the data are shown with the covariance matrix and the hierarchical cluster of the data are presented by the dendrogram. In the paper, the physical principles govern the artificial neural network model. The model utilizes solar wind parameters as inputs and zonal geomagnetic indices as outputs. The causality principle shapes the models by cause-effect relationship. Back propagation algorithm is specified as Levenberg-Marquardt (trainlm) and 30 neural numbers are used in the artificial neural network. The neural network model estimates the Dst, ap, and AE indices of 17 March and 22 June activities with reliable accuracy. The geomagnetic activity estimation can support interplanetary studies. (C) 2021 COSPAR. Published by Elsevier B.V. All rights reserved.

In a previous paper, Glomsda et al. (2020) revisited the impact of distinct parts of non-tidal loading in the analysis of geodetic Very Long Baseline Interferometry (VLBI). The loading is represented by displacements of the reference positions of the observing VLBI antennas, which are variables of a corresponding Gauss-Markov model for estimating various geodetic target parameters. These displacements were applied at two different levels of the model, the observation and the normal equation level, and quite similar results were obtained for both cases. In this paper, the authors provide a more detailed theoretical discussion of the application of site displacements at the distinct levels, which also comprises the a posteriori application at the solution level. For each case, the respective formulas and implications for the Gauss-Markov model are derived, and equations for assessing the differences between the estimated parameters are established. In this way, the authors aim to create a deeper understanding of the results of the previous paper, which show the capability of the normal equation level to approximate the application of site displacements at the observation level with less effort and prerequisites, and to provide evidence for the claims made in that paper (for VLBI only): (i) the chosen reference frame of the site displacements is basically irrelevant except for the solution level; (ii) the Jacobi matrix does not change substantially; (iii) the loss of temporal resolution of the site displacements is more important than the linear approximation of the functional model at the normal equation level; and (iv) the station coordinate estimates for all three levels strongly depend on the regularizing (datum-) conditions of the model. The theoretical results are substantiated with numerical examples, which consider site displacements generated from non-tidal atmospheric loading by the Earth-System-Modelling group of the Deutsches GeoForschungsZentrum (GFZ). However, the results are valid for site displacements of any source.

The present paper reports magnetospheric-thermospheric-ionospheric interactions, observed during geomagnetically disturbed periods in 2015–2016 from mid-latitude stations located in the US-Pacific longitudes (~120°W geographic). These interactions have been analyzed for a series of Coronal Mass Ejection (CME) and High Speed Solar Wind (HSSW) driven geomagnetic storms during the moderate solar activity periods. The geomagnetically disturbed periods under consideration in this paper have an interesting feature of the occurrences of one or more HSSW events following an intense CME driven intense geomagnetic storm. Correlations were observed between the solar and geomagnetic parameters, hemispherically integrated Joule heating, changes in O/N2 ratio, corresponding changes in neutral wind velocities and mid-latitude Vertical Total Electron Content (VTEC) in most of the cases. Prolonged effects of neutral wind driven equatorward plasma transport process were noticed during the period of the summer solstice (June 23–26, 2015) which was correlated with the hemispherically integrated Joule heating and ionospheric conductivities. The effects of storm onset were observed during March 17–18, 2015. The influences of the ‘super-fountain effect’ in terms of Prompt Penetration Electric Field (PPEF) were seen during the main phases of the geomagnetic storms from these mid-latitude stations. This is correlated with the strength of Equatorial Electrojet (EEJ).

Rain is one of the most dominant factors for satellite communication systems link performance at frequencies above 10 GHz, increasing rapidly at higher frequencies. The prediction of time dynamics of the rain attenuation is required to improve the efficiency of various fade mitigation techniques (FMTs) to reduce signal fading. Fade duration and fade slope statistics are used to describe the dynamic behavior of attenuation experienced by radio communication links. The present study is based on experimental measurements from a Ka band (KaSAT) and Q band (AlphaSAT) beacon receiver at the frequencies 19. 7 GHz and 39. 4 GHz respectively. In this paper, annual and monthly variation of rain attenuation statistics for a temperate location Vigo, Spain is presented. Monthly variation of rain attenuation statistics is much larger than the yearly variation for the present location. This paper also analyzes the fade duration and fade slope statistics for both the bands. The conditional probability density function (PDF) of fade slope shows general symmetry between positive and negative slope values for both Ka and Q bands. All the measured statistics (1st order and 2nd order) are compared with the existing ITU-R and COST-205 models. Predictions of rain attenuation by both the models are close to the measured data. For fade duration statistics, as attenuation threshold increases, performance of both ITU-R and COST-205 models improves for Ka band. For Q band, COST model performs better compared to ITU-R model. Measured probability density function of fade slope fits with the ITU-R model more closely for Q band compared to Ka band.

In the past 25 years, radar altimeters have been designed and operated primarily for ocean observation. However, over the past decade there has been a growing interest for altimetry measurements over inland waters. Studying lakes, reservoirs and rivers water level is of prime importance for the hydrology community to assess the Earth’s global resources of fresh water. Satellite altimetry is key to providing such global and continuous datasets of water surface height. Indeed, much progress has been made in altimeters capability to acquire quality measurements over inland waters. In this paper we present an overview of major technical evolutions of the tracking function of altimeters, from Jason-2/POS3 and SARAL/AltiKa to Jason-3/POS3B and Sentinel-3/SRAL and the improvements brought by the Open-Loop Tracking Command (OLTC) to extend the altimeter observation domain to inland waters. The OLTC is an on-board feature used to set the altimeter waveforms reception window, containing a priori elevation information built from a dedicated database of hydrological targets. This paper focuses on the use of OLTC for acquiring reliable water signal rather than discussing the accuracy of the retrieved height, which constitutes a further step in the altimeter data processing chain. We show how Jason-3 and Sentinel-3 altimetry missions are currently able to observe and monitor about 70,000 hydrological targets over the globe and how it is contributing in building a global dataset of inland waters level, in preparation for future missions such as Sentinel-6 and the Surface Water Ocean Topography mission (SWOT).

The investigation of ocean surface topography variation by low-resolution mode (LRM) altimeters at length scales shorter than 100 km is limited by cm-scale measurement noise. Spectral analysis of along-track altimeter data has been used to highlight the issue and to illustrate that one significant noise source stems from correlation between significant wave height (SWH) and range errors that is inherent to any waveform retracking algorithm. This paper focuses on improved characterization and reduction of these high-rate correlated errors that arise from this altimeter measurement process. Specifically, it addresses the effects of sea-state related errors in high rate (20-Hz) Jason-3 satellite sea level data that may possibly impact both short-scale and longer-scale data via interplay with the sea state bias (SSB) correction. Among the suite of standard corrections used to extract sea surface height (SSH) from the raw altimeter range, the empirical SSB term is designed to remove correlation between range and SWH measurements, but not explicitly short-scale error between the two. In this paper, we report that the efficacy of the SSB correction varies with wavelength and it does not remove all correlated signal at high wavenumbers. Following several recent studies, an independent high-frequency adjustment (HFA) is developed to remove these residual correlated errors. Both SSB and HFA are applied on SSH estimations at the 20-Hz rate, improving both 20-Hz and 1-Hz data. Jason-3 data are used as a test bed. Both corrections and net results are specific to MLE4 Jason-3 waveform retracking. Because the reported updated SSB models provide nearly unbiased continuity from Jason-1 to Jason-3 SSB time-series and the MLE4 retracking algorithm is the standard for these missions, the Jason-3 HFA solution can be applied to earlier Jason data with implications for improving the combined 16-year Jason record. By design, the HFA does not impact wavelengths greater than 200 km which is the acting domain of the SSB correction. Applying both the SSB and HFA corrections leads to a global SSH variance reduction nearing 35% in average. The SSH denoising approach through the computation of an additional HFA term is applicable for any LRM ocean altimeter.

The ionospheric error affects the accuracy of the Global Navigation Satellite Systems observation and precise orbit determination. Usually, only the first order ionospheric error is considered, which can be eliminated by the ionospheric-free linear combination observation. But the remaining higher order ionospheric error will affect the accuracy of observations and their applications. In this paper, the influence of the higher order ionospheric error have been studied by using the International Geomagnetic Reference Field 13 and the Global Ionosphere Maps model produced by the Center for Orbit Determination in Europe. Focus on ionospheric error, the experiment of paper at doy 302 in 2019, which show that the second order ionospheric error impacting BeiDou Navigation Satellite System (BDS) B1I and B3I observation is 6.3569 mm and 11.8484 mm, respectively. Whereas, the third order ionospheric error impacting BDS B1I and B3I observation is 0.1734 mm and 0.3977 mm, respectively. Due to the current measurement accuracy of BDS carrier-phase observation can reach 2 mm, the influence of high order ionospheric error on observation should be considered. For BDS precise orbit determination, the orbit overlapping results are indicated that its orbit accuracy can be improved approximately 5 mm with the higher order ionospheric error correction, which is also in agreement with the results of Satellite Laser Ranging in this work.

Nanosatellites in the swarm initially move along arbitrary unbounded relative trajectories according to the launch initial conditions. Control algorithms developed in the paper are aimed to achieve the required spatial distribution of satellites in the along-track direction. The paper considers a swarm of 3U CubeSats in LEO, their form-factor is suitable for the aerodynamic control since the ratio of the satellite maximum to minimum cross-section areas is 3. Each satellite is provided with the information about the relative motion of neighboring satellites inside a specified communication area. The paper develops the corresponding decentralized control algorithms using the differential drag force. The required attitude control for each satellite is implemented by the active magnetic attitude control system. A set of decentralized control strategies is proposed taking into account the communicational constraints. The performance of these strategies is studied numerically. The swarm separation effect is demonstrated and investigated.

The development of fast and reliable optimization algorithms is required in order to obtain real-time optimal trajectory on-board spacecraft. In addition, the wide spread of small satellites, due to their low costs, is leading to a greater number of satellite formations in space. This paper presents an Improved version of the Magnetic Charged System Search (IMCSS) metaheuristic algorithm to compute time-suboptimal manoeuvres for satellite formation flying. The proposed algorithm exploits some strategies aimed at improving the convergence to the optimum, such as the chaotic local search and the boundary handling technique, and it is able to self-tune its internal parameters and coefficients. Moreover, the inverse dynamics technique and the differential flatness approach, through the B-splines curves, are used to approximate the trajectory. The optimization procedure is applied to the circular J2 relative model developed by Schweighart and Sedwick and to the elliptical relative motion model developed by Yamanaka and Ankersen. The results of this paper show that the convergence is better achieved by using the proposed tools, thus proving the efficiency and reliability of the algorithm in solving some space engineering problems.

The ability to achieve long-endurance station-keeping flights makes stratospheric airships desirable platforms for the provision of communication and surveillance services. To maintain long-endurance flights, it is necessary to consider the problem of energy consumption. In this paper, we discuss long-endurance flight scenarios of stratospheric airships in the presence of thermal effects. The balance between buoyancy and gravity is influenced by thermal effects during the diurnal cycle. We perform a theoretical analysis based on the helium’s mass, pressure differential, and altitude as the main factors. To verify the effectiveness of the control over the pressure differential and the altitude, three long-endurance flight scenarios are proposed and compared. Then, the corresponding optimization problems are constructed to determine the energy-minimum flight. Finally, further efforts are made to reduce energy consumption. The realization and limitations of two strategies for improvement are analyzed. A comparison with other scenarios shows the effectiveness of energy conservation. The study in this paper thus provides a reference for station-keeping applications of stratospheric airships.

This is the first of two companion papers that investigate the operations of distributed satellite systems. This first article presents a survey of conventional methods of operations of spacecraft constellations, investigates its scalability for growing number of spacecraft, and identifies operational paradigm shifts. The second article focuses on the classification of distributed satellite systems and evaluates commercial tools for automated spacecraft operations. The trend of using distributed space systems such as satellite constellation instead of monolithic systems has been growing in the last decade. Recently, a variety of large satellite constellations were announced and the production of some has started. Several of these announced constellations feature more than 1000 satellites. While the “mass production” of satellites is feasible and has already started, there are no effective solutions existing for the “mass operations” of satellites. In some instances, conventional spacecraft operations involve manual control by skilled human operators, following at least a 4-eyes principle. Even when operators batch multiple telecommands together, the scheduling process is still challenging for growing spacecraft numbers. This approach is not (linearly) scalable to large satellite constellations: new operational methods need to be established and the automation level of the constellation increased. To motivate the research activities in this framework and pave the way for automated management of large distributed satellite systems, this paper gives an overview of some conventional methods of spacecraft operations. From this description, the weakness areas in terms of scalability are deduced, identifying potential bottlenecks for the operations of such systems. Following, based on three use case studies, the operational paradigm shifts related to the operation of large distributed satellite systems are identified.

IRASSI is an astronomy mission aimed at observing stellar disks and protoplanetary regions using a constellation of five free-flying telescopes operating around the Sun-Earth/Moon L2 point. In these regions of the cosmos, important chemical/physical phenomena can be observed in the far-infrared, which may advance our current understanding of how pre-biotic conditions in Earth-like planets are formed. The distinguishing aspect of the IRASSI interferometer, however, is its free-flying concept. Rather than relying on a fixed formation configuration and relative position control, IRASSI relies on continuously drifting baselines (e.g., inter-satellite distances) and the knowledge of these baselines during the science observations. However, not all IRASSI targets require the same formation strategy and therefore the planning of the sequence of observation tasks and of the corresponding reconfiguration and science maneuvers has been investigated. The manuscript provides thus an overview of the planning architecture devised for IRASSI, called iSCOUT, composed of different modules: 1) Target Planner Module (TPM), 2) Reconfiguration Module (ReM), 3) Collision- and invisibility Avoidance Module (CAM), 4) Baseline Pattern Module (BPM). The first module (TPM), generates an optimized sequence of targets within a specified window period, taking into account variables such as visibility of the targets at each time step, retargeting time based on the current state, target priority or number of previously observed targets of the same type. The second module, ReM, assigns positions to the telescopes based on the target sequence generated by the TPM. Each translation maneuver is optimized to achieve a specified initial formation configuration, which is both perpendicular to the target direction and three-dimensional. Parameters such as fuel use and fuel-balance as well as ΔV and ΔV-balance are used for optimizing the reconfiguration of the formation. The third module, CAM, ensures that the telescopes following the ReM trajectories do not violate relative proximity restrictions or intervisibility requirements during the reconfiguration. In such an event, the CAM computes a new path in order to avoid collisions and invisibility instances. The last module, BPM, calculates the drifting trajectories that achieve the required patterns in the so-called ‘(U, V)-plane’ during the science observations. (U, V)-plane projection metrics and several operational constraints are used for the optimization of the trajectories. Each module has been individually optimized and the paper describes the main outcomes thereof. Results concerning and end-to-end iSCOUT simulation for the IRASSI mission are presented and future work goals complete the paper.

Constellation is required to be highly stable over several years for a space-based gravitational wave observatory. However, the stability of the constellation can be affected by orbit insertion errors. The effects of orbit insertion errors on the constellation are mainly studied in this paper. Firstly, Monte-Carlo, Unscented Transformation Covariance Analysis Method (UTCAM) and Spherical Simplex Unscented Transformation Covariance Analysis Method (SSUTCAM) are used for simulation. The results indicate that UTCAM and SSUTCAM are highly efficient in calculating, with a relative error of less than 6%. Therefore, it is concluded that because of their accuracy and high efficiency, UTCAM and SSUTCAM can be adequately used in orbit insertion error analysis for a space-based gravitational wave observatory. Secondly, SSUTCAM is used to study the effects of position and velocity errors on the constellation. For the case in this paper, when the position error does not exceed 300 km, and the velocity error does not exceed 4 cm/s, the constellation remains stable.

Over recent times there has been a rise in the number of objects placed into Earth orbit. With various countries licensing a number of large constellations, the orbital population is set to increase dramatically. A significant number of technical advances have facilitated this and, in the UK and elsewhere, this has been matched by the updating of legislation and an increased policy focus on the need for increased space surveillance and tracking. The rise of large constellations coupled with an increasing number of experimental techniques such as active debris removal or on-orbit servicing procedures means that establishing fault will be crucial if litigation is to be successful. In doing this, any legal proceedings will look at both norms of behaviour, deviation from which will point towards fault and the types and standard of evidence that will be required. This paper will outline these problems in detail. It will be proposed that what is required to map out the contours of liability are both codification of the norms for satellite operations and clarity on protocols for evidence gathering in cases where fault may be contested in orbital operations. This discussion will identify that a way in which this could be achieved is by the use of “space law games”. These are simulations, similar to military war games, in which fictional scenarios could highlight some of the key legal issues that might need to be dealt with. The paper will outline some of the ways in which the law games might work and pose questions as to what data and other considerations will be needed to make such simulations meaningful.

The interaction between electromagnetic waves and matter is the working principle of a photon-propelled spacecraft, which extracts momentum from the solar radiation to obtain a propulsive acceleration. An example is offered by solar sails, which use a thin membrane to reflect the impinging photons. The solar radiation momentum may actually be transferred to matter by means of various optical phenomena, such as absorption, emission, or refraction. This paper deals with the novel concept of a refractive sail, through which the Sun’s light is refracted by crossing a film made of polymeric micro-prisms. The main feature of a refractive sail is to give a large transverse component of thrust even when the sail nominal plane is orthogonal to the Sun-spacecraft line. Starting from the recent literature results, this paper proposes a semi-analytical thrust model that estimates the characteristics of the propulsive acceleration vector as a function of the sail attitude angles. Such a mathematical model is then used to analyze a simplified Earth-Mars and Earth-Venus interplanetary transfer within an optimal framework.

Asteroids are coming to be a popular topic in the areas of astrophysical studies and deep space exploration recently. However, surface dynamics of asteroids is still a difficult problem. This paper aims at the motion analysis of surface particles for different asteroids. The dynamical analysis method of particles’ movement is given for three parts: global motion trend, local motion trend and static analysis. A dimensionless parameter ζ is defined to distinguish the predominant term to determine the distribution of effective potential. Three kinds of common asteroids: spheroidal asteroid, spindle-shaped asteroid and dumbbell-shaped asteroid are all discussed for those three parts with different parameter ζ. The motion trend of particles on the surface of each kind of asteroid is given. The static analysis of surface particles for different asteroids is also illustrated. Based on them, some common rules for different shaped asteroids are revealed. This paper could not only provide a reference for asteroid exploration missions but also be meaningful for the research of morphologic evolution of asteroids.

Asteroid mining has the potential to greatly reduce the cost of in-space manufacturing, production of propellant for space transportation and consumables for crewed spacecraft, compared to launching the required resources from the Earth’s deep gravity well. This paper discusses the top-level mission architecture and trajectory design for these resource-return missions, comparing high-thrust trajectories with continuous low-thrust solar-sail trajectories. The paper focuses on maximizing the economic Net Present Value, which takes the time-cost of finance into account and therefore balances the returned resource mass and mission duration. The different propulsion methods are compared in terms of maximum economic return and sets of attainable target asteroids. Results for transporting resources to geostationary orbit show that the orbital parameter hyperspace of suitable target asteroids is considerably larger for solar sails, allowing for more flexibility in selecting potential target asteroids. Also, results show that the Net Present Value that can be realized is larger when employing solar sailing instead of chemical propulsion. In addition, it is demonstrated that a higher Net Present Value can be realized when transporting volatiles to the Lunar Gateway instead of geostationary orbit. The paper provides one more step towards making commercial asteroid mining an economically viable reality by integrating trajectory design, propulsion technology and economic modelling.

Dust detection using remotely sensed measurements has been one of the challenging problems encountered by atmospheric scientists. MODerate Resolution Imaging Spectroradiometer (MODIS) on the Terra (T) and Aqua (A) platforms have been a versatile sensor for well over 21 and 18 years respectively, and have been extremely useful in the retrieval of aerosol information over the entire globe. The MODIS radiances from the Level 1B in general are expected to be within 5% accuracy in the reflective wavelengths and within 1% in the thermal emissive wavelengths. In this paper, we evaluate the sensitivity of previously developed dust detection technique based on thermal emissive wavelengths, which correspond to MODIS bands 20, 29, 31, and 32 respectively. The Thermal Emissive Dust Index (TEDI) performed very comparably to the traditional Aerosol Optical Thickness (AOT) retrievals by MODIS reflective channels. Since the MODIS Thermal Emissive Bands (TEB) are well calibrated on-orbit using a BlackBody (BB) source, the calibration of these long wave infrared bands is quite robust. As A-MODIS continues to perform well beyond its designed lifetime of 6 years, the instrument has undergone various levels of degradation during its mission time. As a consequence, it is imperative to check the impacts of calibration on the higher-level retrievals. In this paper, we rigorously analyze the sensitivity of TEDI due to the impact of calibration by the afore-mentioned TEB. The perturbation of the dominant (linear) calibration term demonstrated the following: first, there was a correlation in the sensitivity of the TEDI due to the uncertainty in the linear calibration term. Based on a perturbation in the linear calibration term for all aforementioned bands over a range of ±5% yielded the TEDI sensitivity to vary from approximately −3.2% to about −3.6%. When considering the uncertainty in each individual band significant changes were observed. The least change was observed for the perturbation in the calibration of band 20 with the TEDI sensitivity and the largest sensitivity in TEDI was observed in the perturbation of band 31 calibration. Thus, in the case of TEDI, noticeable sensitivity due to calibration uncertainty was observed in bands 29, 31, and 32, reiterating the importance of the TEB calibration in these bands. Also, the dust detection scheme based on A-MODIS was successfully transferred to the follow-on sensors such as Suomi (SNPP) and NOAA 20 (N20) VIIRS. The results presented in this paper would be extremely helpful in understanding impacts of calibration on the higher-level products for both current and future missions based on the MODIS heritage. Finally, the work also identifies the importance of radiometric fidelity in maintaining the accuracy of the dust detection. Results presented will show drastic improvement of the Saharan dust detection after the reduction of the electronic crosstalk in the 8.5 µm channel of T-MODIS.

A way to improve the accuracy of the three-body problem model is taking into account the eccentricity of primary attractors. Elliptic Restricted Three-Body Problem (ER3BP) is a model for studying spacecraft trajectory within the three-body problem such that the orbital eccentricity of primaries is reflected in it. As the principal cause of perturbation in the employed dynamical model, the primaries eccentricity changes the structure of orbits compared to the ideal Circular Restricted Three-Body Problem (CR3BP). It also changes the attitude behavior of a spacecraft revolving along periodic orbits in this regime. In this paper, the coupled orbit-attitude dynamics of a spacecraft in the ER3BP are exploited to find precise periodic solutions as the spacecraft is considered to be in planar orbits around Lagrangian points and Distant Retrograde Orbits (DRO). Periodic solutions are repetitious behaviors in which spacecraft whole dynamics are repeated periodically, these periodic behaviors are the main interest of this study because they are beneficial for future mission designs and allow delineation of the system’s governing dynamics. Previous studies laid the foundation for spacecraft stability analysis or studying pitch motion of spacecraft in the ER3BP regime. While in this paper, at first, initial guesses for correction algorithms were derived through verified search methods, then correction algorithms were used to refine calculated orbit-attitude periodic behaviors. Periodic orbits and full periodic solutions are portrayed and compared to previous studies and simpler models. Natural periodic solutions are valuable information eventuate in the longer functional lifetime of spacecraft. Since the problem assumption considered in this paper is much closer to real mission conditions, these results may be the means to use natural bounded motions in the actual operational environment.

The availability of engineering models to estimate the risk from space debris is essential for space missions. According to current research, cumulative flux calculation is mostly carried out based on the equal-width interval discretization. The method discretizes the volume around the Earth into cells defined in earth centered inertial coordinates. The resulting debris flux onto a target object is shown to depend on the chosen size of the cells. To avoid a discretization error, this must be accounted for. In order to present reliable flux predictions for space mission, the algorithm improvement is an ongoing topic for the related research field. The aim of this study was to examine the discretization error during the cumulative flux determination process. Both the effect of interval step length and the orbital boundary are under investigation. Several typical orbits are selected as examples here and the 2018/01/03 TLE (Two Line Element) data published by the US Space Surveillance Network is used as the debris background in this paper. Furthermore, the Interval Distance-Based method for Discretization (IDD) is adopted in this paper. A position-centered flux determination method is introduced based on the IDD method. According to the example analysis, the IDD used in the flux calculation process provides results which are less affected by the interval step-size setup; and the orbital boundary has no effect on the calculation process. In other words, the discretization error is significantly reduced. The position-centered method provided a possible suggestion for the improvement of space debris environment models.

This short paper summarizes the plans for NASA's Space Infrared Telescope Facility (SIRTF) mission and provides a brief overview of NASA's Origins program. SIRTF is a key element of the Origins program, which is a scientific initiative aimed at understanding the origins of galaxies, stars, planets, and - ultimately - of life.

Trajectory optimization of low-thrust perturbed orbit rendezvous is a crucial technology for space missions in low Earth orbits, which is difficult to solve due to its initial value sensitivity, especially when the transfer trajectory has many revolutions. This paper investigated the time-fixed perturbed orbit rendezvous between low-eccentricity orbits and proposed a priori quasi-optimal thrust strategy to simplify the problem into a parametric optimization problem, which significantly reduces the complexity. The optimal trajectory is divided into three stages including transfer to a certain intermediate orbit, thrust-off drifting and transfer from intermediate orbit to the target orbit. In the two transfer stages, the spacecraft is assumed to use a parametric law of thrust. Then, the optimization model can be then obtained using very few unknowns. Finally, a differential evolution algorithm is adopted to solve the simplified optimization model and an analytical correction process is proposed to eliminate the numerical errors. Simulation results and comparisons with previous methods proved this new method's efficiency and high precision for low-eccentricity orbits. The method can be well applied to premilitary analysis and high-precision trajectory optimization of missions such as in-orbit service and active debris removal in low Earth orbits.

In recent years, deep learning (DL) methods have proven their efficiency for various computer vision (CV) tasks such as image classification, natural language processing, and object detection. However, training a DL model is expensive in terms of both complex- ities of the network structure and the amount of labeled data needed. In addition, the imbalance among available labeled data for dif- ferent classes of interest may also adversely affect the model accuracy. This paper addresses these issues using a new convolutional neural network (CNN) based architecture. The proposed network incorporates both spatial and spectral information that combines two sub- networks: spatial-CNN and spectral-CNN. The spectral-CNN extracts spectral information, while spatial-CNN captures spatial infor- mation. Moreover, to make the features more robust, a multiscale spatial CNN architecture is introduced using different kernels. The final feature vector is formed by concatenating the outputs obtained from both spatial-CNN and spectral-CNN. To address the data imbalance problem, a generative adversarial network (GAN) was used to generate data for the underrepresented class. Finally, relatively a shallower network architecture was used to reduce the number of parameters in the network and improve the processing speed. The proposed model was trained and tested on Senitel-2 images for the classification of the debris-covered glacier. The results showed that the proposed method is well-suited for mapping and monitoring debris-covered glaciers at a large scale with high classification accuracy. In addition, we compared the proposed method with conventional machine learning approaches, support vector machine (SVM), random forest (RF) and multilayer perceptron (MLP) 2-s2.0-85131797739

During the satellite’s operations, simulation tools perform an important role in ensuring the space mission success. In this sense, the models implemented in the context of an operational satellite simulator that enables analysis of health status and maintenance during operations shall reflect the current satellite behavior with high fidelity. Moreover, it is complicated to obtain all analytical models of a satellite’s disciplines, considering its aging. This paper proposes an Artificial Neural Network (ANN) to reproduce the battery voltage behavior of a large sun-synchronous remote sensing satellite, the CBERS-4, currently in operation. Using the genetic algorithm to find the best network architecture of ANN, the neural model for this application presented an error of less than 1%, demonstrating its feasibility to obtain a high fidelity model for an operational simulator enabling extend analyses. The paper addresses advanced techniques aligned with the space industry’s future, increasing the ability to analyze a large amount of data and improve the space system’s operation.