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Thermospheric wind measurements obtained from linear non-gravitational accelerations of the Gravity field and steady-state Ocean Circulation Explorer (GOCE) satellite show discrepancies when compared to ground-based measurements. In this paper the cross-wind is derived from both the linear and the angular accelerations using a newly developed iterative algorithm. The two resulting data sets are compared to test the validity of wind derived from angular accelerations and quantify the uncertainty in accelerometer-derived wind data. In general the difference is found to be less than 50 m/s vertically after high-pass filtering, and 100 m/s horizontally. A sensitivity analysis reveals that continuous thrusting is a major source of uncertainty in the torque-derived wind, as are the magnetic properties of the satellite. The energy accommodation coefficient is identified as a particularly promising parameter for improving the consistency of thermospheric cross-wind data sets in the future. The algorithm may be applied to obtain density and cross-wind from other satellite missions that lack accelerometer data, provided the attitude and orbit are known with sufficient accuracy.

The Satellite for Orbital Aerodynamics Research (SOAR) is a 3U CubeSat that has been designed to investigate the aerodynamic performance of different materials at low orbital altitudes. The spacecraft has been developed within the scope of DISCOVERER, a Horizon 2020 project that aims to develop foundational technologies to enable sustainable operations of Earth observation spacecraft in very low Earth orbits (VLEO) i.e., those below 450 km. SOAR features two payloads: i) a set of steerable fins that can expose different materials to the oncoming atmospheric flow developed by The University of Manchester, and ii) a forward-facing ion and neutral mass spectrometer (INMS) that provides in-situ measurements of the atmospheric density, flow composition, and velocity from the Mullard Space Science Laboratory (MSSL) of University College London. These payloads enable characterisation of the aerodynamic performance of different materials at very low altitudes with the aim to advance understanding of the underlying gas-surface interactions in rarefied flow environments. The satellite will also be used to test novel aerodynamic attitude control methods and perform atmospheric characterisation in the VLEO altitude range. SOAR will perform the first in-orbit test of two novel materials that are expected to have atomic oxygen erosion resistance and drag-reducing properties, providing valuable in-orbit validation data for ongoing ground-based experimentation. Such materials hold the promise for extending operations at lower altitudes with benefits particularly for Earth observation and communications satellites that can correspondingly be reduced in size and cost. The platform for SOAR is largely based on GOMX-3 heritage and the spacecraft was assembled, integrated, and tested by GomSpace A/S. The satellite was launched on the SpX-22 commercial resupply service mission to the International Space Station in on 3rd June 2021 was subsequently deployed into orbit on the 14th June 2021. This paper presents the final preparations of SOAR prior to launch and provides an overview of the planned operations of the spacecraft following deployment into orbit. Article signat per 30 autors/res: Nicholas H. Crisp, Alejandro Macario-Rojas, Peter C.E. Roberts, Steve Edmondson, Sarah J. Haigh, Brandon E.A. Holmes, Sabrina Livadiotti, Vitor T.A. Oiko, Katharine L. Smith, Luciana A. Sinpetru, Jonathan Becedas, Valeria Sulliotti-Linner, Simon Christensen, Virginia Hanessian, Thomas K. Jensen, Jens Nielsen, Morten Bisgaard, Yung-An Chan, Georg H. Herdrich, Francesco Romano, Stefanos Fasoulas, Constantin Traub, Daniel Garcia-Almiñana, Silvia Rodriguez-Donaire, Miquel Sureda, Dhiren Kataria, Badia Belkouchi, Alexis Conte, Simon Seminari, Rachel Villain Objectius de Desenvolupament Sostenible::9 - Indústria, Innovació i Infraestructura

The Satellite for Orbital Aerodynamics Research (SOAR) is a CubeSat mission, due to be launched in 2021, to investigate the interaction between different materials and the atmospheric flow regime in very low Earth orbits (VLEO). Improving knowledge of the gas-surface interactions at these altitudes and identification of novel materials that can minimise drag or improve aerodynamic control are important for the design of future spacecraft that can operate in lower altitude orbits. Such satellites may be smaller and cheaper to develop or can provide improved Earth observation data or communications link-budgets and latency. Using precise orbit and attitude determination information and the measured atmospheric flow characteristics the forces and torques experienced by the satellite in orbit can be studied and estimates of the aerodynamic coefficients calculated. This paper presents the scientific concept and design of the SOAR mission. The methodology for recovery of the aerodynamic coefficients from the measured orbit, attitude, and in-situ atmospheric data using a least-squares orbit determination and free-parameter fitting process is described and the experimental uncertainty of the resolved aerodynamic coefficients is estimated. The presented results indicate that the combination of the satellite design and experimental methodology are capable of clearly illustrating the variation of drag and lift coefficient for differing surface incidence angle. The lowest uncertainties for the drag coefficient measurement are found at approximately 300 km, whilst the measurement of lift coefficient improves for reducing orbital altitude to 200 km., Comment: 19 pages, 11 figures. Accepted for publication in Acta Astronautica (2020-12-14)

The German CHAMP, US/German GRACE, and European Space Agency (ESA) GOCE and Swarm Earth Explorer satellites have provided a data set of accelerometer observations allowing the derivation of thermospheric density and wind products for a period spanning more than 15 years. With the advent of highly accurate satellite accelerometer measurements, the neutral density and wind characterization has been significantly improved. These observations provided detailed information on the thermospheric forcing by Solar Extreme Ultraviolet radiation and charged particles, and revealed for the first time the extent of forcing by processes in lower layers of the atmosphere. Because the focus of most of previous research was on relative changes in density, the scale differences between the CHAMP, GRACE, GOCE and Swarm data sets, so far, have been largely ignored. These scale differences originate from errors in the aerodynamic modelling, specifically in the modelling of the gas-surface interactions (GSI) of the satellite. Once detailed 3D geometry models of these satellites are available, the key parameters to describe the satellite aerodynamics can be estimated by cleverly making use of variations in satellite orientation and simultaneous observations by multiple satellites. The first step for obtaining more consistent density and wind data sets consisted of meticulously modelling the satellite outer surface. For this dissertation work, this was done by collecting information from technical drawings and pre-launch pictures, and generating a CAD model of the selected satellites. In the following phase, these geometries were given as input to a rarefied gas-dynamics simulator. The Direct Simulation Monte Carlo approach was used with the SPARTA software to compute the force coefficients under different conditions of satellite speed, atmospheric temperature and local chemical composition. Once all the mission scenarios had been simulated, an aerodynamic data set was generated and applied in the processing of satellite accelerations into thermospheric density and wind data products. To this aim, the Near Real-Time Density Model (NRTDM) software, developed at TU Delft, was used. The data were generated from accelerometer observations and, when necessary, with the help of GPS-based accelerations estimated by a Precise Orbit Determination (POD) technique. Multiple comparisons were performed with empirical and physics-based models. This helped in determining for which conditions the models are performing better, and also which models’ features would need further development. In the second step, the interaction between atmospheric particles and satellite surfaces was investigated. The way in which atmospheric particles collide with the satellite surfaces have a large influence on the satellite aerodynamic forces and, if proper assumptions are not implemented, can produce large discrepancies in the final thermospheric products. Initially, the GSI assumptions were selected in agreement with the fully diffusive reflection mode. This assumption was adopted to exclusively investigate the geometry modelling influence on thermospheric products. Later, to cover also this research area, multiple simulations described different reflection modes. A wide range of GSI parameters was investigated, and more optimal values were found allowing the derivation of new consistent thermospheric products. Within this study, the energy accommodation coefficient, which describes the energy exchange between particles and satellite surfaces, played a crucial role. Although the value of 0.93 is used commonly in the literature, in this study lower values were identified as optimal. Indeed, a value of 0.82 for the GOCE satellite, and a value of 0.85 for the Swarm and CHAMP satellites have been found to provide more consistent thermospheric data. This resulted in new improved thermospheric density and wind data sets, which have been made available to the scientific community. Among the possible applications, these data can be used for data assimilation for improving current atmospheric models. Resolving the problem of deriving the true absolute thermosphere density scale from satellite dynamics measurements improves orbit predictions for the space debris population and its long-term evolution. Moreover, the new capabilities for computing more consistent drag, density and wind, can also be exploited for future missions that are currently in the design phase.

Interest in operating spacecraft in very low Earth orbits (VLEO), those below approximately 450 km, is growing due to the numerous benefits offered by reducing altitude. For remote sensing and Earth observation applications, improvements in resolution can be achieved or smaller instruments used with associated benefits in cost or mission value. Similarly, for communications applications, link-budgets and data latency can be improved by reducing the operational altitude. However, a key challenge to sustainedoperations in lower altitude orbits is to minimise and compensate for the aerodynamic drag that is produced by the interaction with the residual atmosphere. A principal aim of the DISCOVERER project is to identify, develop, and characterise materials thatcan promote specular reflections of the residual atmosphere in VLEO whilst also remaining resistant to the erosive atomic oxygen that is predominant at these altitudes. In combination with geometric design, such materials would be able to reduce the aerodynamic drag experienced by satellites in orbit and would also be able to generate usable aerodynamic lift enabling novel aerodynamic attitude and orbit control. SOAR (Satellite for Orbital Aerodynamics Research) is a 3U CubeSat that has been designed to investigate the aerodynamic performance of different materials in the VLEO environment and provide validation data for further ground-based experiments. To achieve this, the spacecraft features a set of steerable fins that can expose different materials to the oncoming atmospheric flow. A forward-facing ion and neutral mass spectrometer (INMS) provides in-situ measurements of the atmospheric density and flow composition. SOAR is scheduled for launch to the ISS in March 2021. This paper will present the design of the spacecraft, the experimental method that will be used to investigate the aerodynamic properties of materials in orbit, and will provide an update on the status of the spacecraft as it prepares for launch. The DISCOVERER project has received funding from the European Union's Horizon 2020 research and innovation programme under grant agreement No 737183. This publication reflects only the view of the authors. The European Commission is not responsible for any use that may be made of the information it contains

In-situ measurements of the thermospheric wind can be obtained by observing the attitude response of an aerostable spacecraft. In the proposed method, the aerostable spacecraft is left uncontrolled, freely reacting to the aerodynamic torques, and oscillating around its equilibrium attitude. The wind's magnitudeand direction is determined by combining the attitude observations with estimates of the other perturbing torques, atmospheric density, and spacecraft'saerodynamic properties. The spatial resolution of the measurements is proportional to the natural frequency of the attitude's oscillation. Spacecraft with high aerodynamic stiness to inertia ratios operating at low altitudes exhibit higher natural frequencies, making them particularly suited for this method. A one degree-offreedom case is used to present and illustrate the proposedmethod as well as to analyze its performance.

The decay of satellite orbits has been used extensively to obtain thermospheric density measurements. With the introduction of accelerometers in spacecraft, the spatial resolution of these data could be increased. At the same time, the direction of the measured acceleration provides a measure for the direction of the incoming flow, and therefore of the local cross-wind. In this thesis, the angular acceleration of the Gravity field and steady-state Ocean Circulation Explorer (GOCE) satellite, an Earth explorer by the European Space Agency (ESA), is used as a source for such thermospheric wind data for the first time. The goal is to improve aerodynamic parameter estimates and assess the quality of accelerometer-derived wind data by comparing this new data set to that derived from linear accelerations...

The decay of satellite orbits has been used extensively to obtain thermospheric density measurements. With the introduction of accelerometers in spacecraft, the spatial resolution of these data could be increased. At the same time, the direction of the measured acceleration provides a measure for the direction of the incoming flow, and therefore of the local cross-wind. In this thesis, the angular acceleration of the Gravity field and steady-state Ocean Circulation Explorer (GOCE) satellite, an Earth explorer by the European Space Agency (ESA), is used as a source for such thermospheric wind data for the first time. The goal is to improve aerodynamic parameter estimates and assess the quality of accelerometer-derived wind data by comparing this new data set to that derived from linear accelerations...

SOAR (Satellite for Orbital Aerodynamics Research) is a CubeSat mission designed to investigate the interaction betweendifferent materials and the atmospheric flow regime in Very Low Earth Orbits (VLEO) and to demonstrate aerodynamicattitude and orbit control manoeuvres. Improving knowledge of the gas-surface interactions is important for the designof future satellites operating in lower altitude orbits and will enable the identification of materials which can minimisedrag or improve aerodynamic control, a key aim of the Horizon 2020 DISCOVERER project. In order to achieve theseobjectives, SOAR features two payloads: i) a set of steerable fins which provide the ability to expose different materialsor surface finishes to the oncoming flow with varying angle of incidence whilst also providing variable geometry toinvestigate aerostability and aerodynamic control; and ii) an Ion and Neutral Mass Spectrometer with Time-of-Flightcapability which enables accurate measurement of the in-situ flow composition, density, and thermospheric wind velocity.Using precise orbit and attitude determination information and the measured atmospheric flow characteristics the dragand side-force experienced by the satellite in orbit can studied and estimates of the aerodynamic coefficients calculated.This paper first presents the scientific design and operational concept of the SOAR mission, focusing on the stabilityand control strategy which enables the spacecraft to maintain the flow-pointing attitude required by the payloads. Themethodology for recovery of the (relative) aerodynamic coefficients from the measured orbit and in-situ atmosphericdata is then presented. Finally, the uncertainty of the resolved aerodynamic coefficients is estimated statistically usingsimulations.

The solar-wind magnetosphere interaction primarily occurs at altitudes where the dipole component of Earth’s magnetic field is dominating. The disturbances that are created in this interaction propagate along magnetic field lines and interact with the ionosphere–thermosphere system. At ionospheric altitudes, the Earth’s field deviates significantly from a dipole. North–South asymmetries in the magnetic field imply that the magnetosphere–ionosphere–thermosphere (M–I–T) coupling is different in the two hemispheres. In this paper we review the primary differences in the magnetic field at polar latitudes, and the consequences that these have for the M–I–T coupling. We focus on two interhemispheric differences which are thought to have the strongest effects: 1) A difference in the offset between magnetic and geographic poles in the Northern and Southern Hemispheres, and 2) differences in the magnetic field strength at magnetically conjugate regions. These asymmetries lead to differences in plasma convection, neutral winds, total electron content, ion outflow, ionospheric currents and auroral precipitation. publishedVersion

WAVE2004キャンペーンにおけるS310-33ロケット発射時刻(2004年1月17日15:30UT)前後の山川MFレーダーの水平風速・電子密度観測結果を報告する。本キャンペーン期間中の水平風速には、東西成分・南北成分ともに位相が下方へ伝播する1日潮汐が顕著に見られていた。ロケットは、東西風の1日潮汐が西向きに最大で南北風の1日潮汐が北向きに強まっていく時間帯に打ち上げられたことになる。電子密度はロケット打ち上げ時に高度90kmを超えてから急上昇している。ただし中波帯の電波は群遅延の影響を受けるため、MFレーダーで見られている電子密度上昇開始高度は真の高度より高い可能性がある。, Mesospheric and lower thermospheric winds and electron densities observed by the Yamagawa MF radar during the wave 2004 campaign are shown. During this campaign, the diurnal tide with downward phase progression is dominant in both eastward and northward wind velocities. The S310-33 rocket, which was launched at 15:30 UT on 17 January, 2004, goes through the period in which the westward tidal component is maximum and the northward tidal component is growing. The height profile of the electron density observed at the launch time shows steep increase above 90 km altitude, though the height itself might be affected by the group retardation of the MF radio waves., 資料番号: AA0048467006, レポート番号: JAXA-SP-04-007

Приводятся результаты расчета дневного профиля электронной концентрации на основе решения уравнения непрерывности. В расчетах используются экспериментальные значения температур заряженных частиц и данные о скорости движения плазмы на высоте 300 км. В процессе анализа согласованности ионосферных параметров вычисляется вертикальная составляющая скорости движения плазмы, обусловленная термосферным ветром. The results of calculation of daytime electron densityprofile using continuity equation are presented. Experimental data of charged particle temperatures and plasma transport velocity at 300 km are used. At analysis of ionospheric parameters agreement vertical component of plasma velocity, caused by thermospheric wind is calculated.