Precise thermospheric mass density modelling for orbit prediction of low earth orbiters

The steady increase in the number of space objects near the Earth has raised critical security concerns for the low Earth orbit (LEO) space environment where most of the near-Earth satellites missions operate. Orbit prediction (OP) is the foundation of many space missions and applications in LEO, e.g., space situational awareness, re-entry prediction and debris removal. However, the precision of OP is limited due to the accuracy of thermospheric mass density (TMD) prediction. In the past few decades, more atmospheric data sets have been inferred from different techniques such as the Global Navigation Satellite System, satellite laser ranging and two-line-element catalogue. However, accurately predicting TMD is still a challenging task due to the limited knowledge of thermospheric dynamics and the lack of measurements with sufficient temporal and spatial resolution. In this research, a precise OP platform for the analysis and prediction of the orbital motion of satellite and and space debris is developed. It consists of various precise perturbation models of gravitational and non-gravitational forces. This includes the high-order Earth gravitational acceleration with the effect of solid and ocean tides, third-body perturbations from other celestial bodies in the solar system, the general relativity effects, aerodynamic acceleration, direct solar radiation pressure, and Earth's albedo and infrared radiation pressure. Coordinate transformation is established on the precise time systems and the measured Earth orientation parameters. The developed OP platform is validated against the historical precise orbits of LEO satellites. In order to evaluate the most representative classes of empirical TMD models, a comprehensive comparison of 12 models is performed. The vertical variability, horizontal scale and the capability to capture the physics-based features of the selected models are investigated. Various validations against the TMD estimated from on-board accelerometer measurements of the GRACE satellites have been conducted. The performance of these models in the OP of the GRACE-A satellite is assessed under different solar and geomagnetic conditions. Also discussed is the coupling effect between the TMD and ballistic coefficient that measures the impact of atmospheric friction on the space object. The impact of TMD variations on orbit dynamics of LEO objects is an important focus in this thesis, which has not been well-quantified in previous studies. Intra-annual, intra-diurnal and horizontal TMD variations are reproduced using the empirical model DTM-2013. Also evaluated are physics-based variations including the equatorial mass density anomaly (EMA) and midnight mass density maximum (MDM), which exhibit both temporal and spatial variations and are simulated by the Thermosphere Ionosphere Electrodynamics General Circulation Model. The analysis is based on the one-day OP simulation at 400 km. The result show that TMD variations have a dominant impact on the predicted orbits in the along-track direction. Semiannual and semidiurnal TMD variations exert the most significant impact on OP among the intra-annual and intra-diurnal variations, respectively. In addition, both EMA and MDM create weaker but still discernible impacts than other TMD variations. Some recommendations for TMD modelling are also presented. Moreover, precise modelling of TMD during geomagnetic quiet time is performed. This is undertaken using the TMD data inferred from GRACE (500 km), CHAMP (400 km) and GOCE (250 km) satellites during the year of 2002-2013. Three different methods including the Fourier analysis, spherical harmonic (SH) analysis and the artificial neural network (ANN) technique are adopted and compared in order to determine the most suitable methodology for the TMD modelling. Additionally, different combinations of time and coordinate representations are also examined in the TMD modelling. The results reveal that the precision of the low-order Fourier-based model can be improved by up to 10% using the geocentric solar magnetic coordinate. Both the Fourier- and SH-based models have drawbacks in approximating the vertical gradient of TMD. The ANN-based model, however, has the capability in capturing the vertical TMD variability and is not sensitive to the input of time and coordinate

Lower-thermosphere–ionosphere (LTI) quantities: current status of measuring techniques and models

The lower-thermosphere-ionosphere (LTI) system consists of the upper atmosphere and the lower part of the ionosphere and as such comprises a complex system coupled to both the atmosphere below and space above. The atmospheric part of the LTI is dominated by laws of continuum fluid dynamics and chemistry, while the ionosphere is a plasma system controlled by electromagnetic forces driven by the magnetosphere, the solar wind, as well as the wind dynamo. The LTI is hence a domain controlled by many different physical processes. However, systematic in situ measurements within this region are severely lacking, although the LTI is located only 80 to 200 km above the surface of our planet. This paper reviews the current state of the art in measuring the LTI, either in situ or by several different remote-sensing methods. We begin by outlining the open questions within the LTI requiring high-quality in situ measurements, before reviewing directly observable parameters and their most important derivatives. The motivation for this review has arisen from the recent retention of the Daedalus mission as one among three competing mission candidates within the European Space Agency (ESA) Earth Explorer 10 Programme. However, this paper intends to cover the LTI parameters such that it can be used as a background scientific reference for any mission targeting in situ observations of the LTI.Peer reviewe

Forecasting global and multi-level thermospheric neutral density and ionospheric electron content by tuning models against satellite-based accelerometer measurements

Global estimation of thermospheric neutral density (TND) on various altitudes is important for geodetic and space weather applications. This is typically provided by models, however, the quality of these models is limited due to their imperfect structure and the sensitivity of their parameters to the calibration period. Here, we present an ensemble Kalman filter (EnKF)-based calibration and data assimilation (C/DA) technique that updates the model’s states and simultaneously calibrates its key parameters. Its application is demonstrated using the TND estimates from on-board accelerometer measurements, e.g., those of the Gravity Recovery and Climate Experiment (GRACE) mission (at ∼410 km altitude), as observation, and the frequently used empirical model NRLMSISE-00. The C/DA is applied here to re-calibrate the model parameters including those controlling the influence of solar radiation and geomagnetic activity as well as those related to the calculation of exospheric temperature. The resulting model, called here ‘C/DA-NRLMSISE-00’, is then used to now-cast TNDs and individual neutral mass compositions for 3 h, where the model with calibrated parameters is run again during the assimilation period. C/DA-NRLMSISE-00 is also used to forecast the next 21 h, where no new observations are introduced. These forecasts are unique because they are available globally and on various altitudes (300–600 km). To introduce the impact of the thermosphere on estimating ionospheric parameters, the coupled physics-based model TIE-GCM is run by replacing the O2, O1, He and neutral temperature estimates of the C/DA-NRLMSISE-00. Then, the non-assimilated outputs of electron density (Ne) and total electron content (TEC) are validated against independent measurements. Assessing the forecasts of TNDs with those along the Swarm-A (∼467 km), -B (∼521 km), and -C (∼467 km) orbits shows that the root-mean-square error (RMSE) is considerably reduced by 51, 57 and 54%, respectively. We find improvement of 30.92% for forecasting Ne and 26.48% for TEC compared to the radio occulation and global ionosphere maps (GIM), respectively. The presented C/DA approach is recommended for the short-term global multi-level thermosphere and enhanced ionosphere forecasting applications

Geodetic Sciences

Space geodetic techniques, e.g., global navigation satellite systems (GNSS), Very Long Baseline Interferometry (VLBI), satellite gravimetry and altimetry, and GNSS Reflectometry & Radio Occultation, are capable of measuring small changes of the Earth�s shape, rotation, and gravity field, as well as mass changes in the Earth system with an unprecedented accuracy. This book is devoted to presenting recent results and development in space geodetic techniques and sciences, including GNSS, VLBI, gravimetry, geoid, geodetic atmosphere, geodetic geophysics and geodetic mass transport associated with the ocean, hydrology, cryosphere and solid-Earth. This book provides a good reference for geodetic techniques, engineers, scientists as well as user community

Estimating the decay rates of orbital debris through upper-atmosphere density data supplemented with on-board accelerometer measurements

This thesis is focused on research of an accurate method to compute atmospheric density. It presents a comparison between data calculated by MSISE-90 model and ones obtained by the accelerometers on-board of GRACE. It describes a possible new satellite METRIC, which has, as goal, the improve of density data in upper atmoshpere to have better estimate of air drag and, consequently, of satellite operative life.ope

Beyond 100: The Next Century in Geodesy

This open access book contains 30 peer-reviewed papers based on presentations at the 27th General Assembly of the International Union of Geodesy and Geophysics (IUGG). The meeting was held from July 8 to 18, 2019 in Montreal, Canada, with the theme being the celebration of the centennial of the establishment of the IUGG. The centennial was also a good opportunity to look forward to the next century, as reflected in the title of this volume. The papers in this volume represent a cross-section of present activity in geodesy, and highlight the future directions in the field as we begin the second century of the IUGG. During the meeting, the International Association of Geodesy (IAG) organized one Union Symposium, 6 IAG Symposia, 7 Joint Symposia with other associations, and 20 business meetings. In addition, IAG co-sponsored 8 Union Symposia and 15 Joint Symposia. In total, 3952 participants registered, 437 of them with IAG priority. In total, there were 234 symposia and 18 Workshops with 4580 presentations, of which 469 were in IAG-associated symposia. ; This volume will publish papers based on International Association of Geodesy (IAG) -related presentations made at the International Association of Geodesy at the 27th IUGG General Assembly, Montreal, July 2019. It will include papers associated with all of the IAG and joint symposia from the meeting, which span all aspects of modern geodesy, and linkages to earth and environmental sciences. It continues the long-running IAG Symposia Series

Issue Small Satellites

Small satellite is a disruptive technology in space industries. Traditionally, space industries were dominated by satellites which have thousands of kilograms and are bulky and expensive. Small satellites denote a new generation of miniaturized satellites which, by taking advantages of modern technologies (e.g., integrated circuits, digital signal processing, MEMS, and additive manufacturing), can achieve a significant reduction in volume, mass, development time, and cost of satellites. During recent decades, small satellites, including CubeSats, NanoSats, MiniSats, and MicroSats, have undergone rapid developments, and are playing an increasingly larger role in exploration, technology demonstration, scientific research, and education. These miniature satellites provide a low-cost platform for missions, including planetary space exploration, Earth observations, fundamental Earth and space science, and developing precursor science instruments like laser communications and millimeter-wave communications for intersatellite and intrasatellite links, and autonomous movement capabilities. They also allow educators an inexpensive means to engage students in all phases of satellite development, operation, and exploitation through real-world, hands-on research and development experience on rideshare launch opportunities. A number of miniaturized satellites can form spaceborne wireless sensor networks in the space, which are also going to play an important role in Internet of Space (IoS) of the futur