NRLMSISE-00 Model Research Articles

Atmospheric density estimation in very low Earth orbit based on nanosatellite measurement data using machine learning

The atmospheric density in the very low Earth orbit (VLEO), the lower region of the thermosphere is a critical factor for satellite missions on prediction of orbit and lifetime. However, accurately determining atmospheric density remains challenging owing to difficulties in acquiring data within the VLEO. The re-Entry satellite with Gossamer aeroshell and GPS/Iridium (EGG) nanosatellite mission, conducted in 2017, obtained sparse coordinate data through the iridium network and Global Navigation Satellite System (GNSS). Using these data, we developed a methodology based on machine learning and special perturbations to estimate atmospheric density. The originally obtained atmospheric density predicted by NRLMSISE-00 was corrected during trajectory reproduction from GNSS data by special perturbation. The prediction performance of the method was validated using the generated trajectory data. Subsequently, we estimated the density at altitudes of approximately 200 km, particularly in the lower region of the VLEO. Density values that accurately reproduced trajectories of the EGG were 0.5 to 0.64 times greater than that predicted by the NRLMSISE-00 model. This methodology is effective for measuring atmospheric density in the lower VLEO region using GNSS data from low-cost and high-frequency nanosatellite missions. By increasing the availability of accurate atmospheric density data, this methodology enhances our understanding of the atmosphere in the VLEO.

The Feature Analysis and Modeling of Upper Atmospheric Midnight Density Maximum

The features of upper atmospheric midnight density maximum (MDM) around low geographic latitudes are studied based on neutral mass densities data at altitudes 360–480 km, derived from the accelerometer measurements aboard on the three polar orbiting satellites CHAMP (CHAllenging Minisatellite Payload), GRACE-A (Gravity Recovery and Climate Experiment-A), and SWARM-C (The Earth's Magnetic Field and Environment Explorers-C). The MDM appears during the local times from 23:00 to 02:00 LT (Local Time), whose peak locates at the low latitudes within 15∘ and two valleys locate at the middle latitudes between 35∘ and 45∘ on both hemispheres separately. The structure of MDM drifts toward the southern hemisphere overall. The MDM's amplitude decreases with increases in altitude and solar radiation level. The seasonal effect weakens the MDM's amplitudes around the summer and winter solstices, while the amplitudes around the spring and autumn equinoxes are extremely significant due to the slight seasonal difference between both hemispheres. Three atmospheric density models DTM2000 (Drag Temperature Model 2000), NRLMSISE00 (US Naval Research Laboratory Mass Spectrometer and Incoherent Scatter Radar Extended atmosphere model), and JB2008 (Jacchia-Bowman 2008 model) are used to simulate the MDM along these three satellites' orbits, and compared with the observations. It is found that the JB2008 model is failed to describe the MDM, and the other two models underestimate the MDM's amplitudes at altitudes 360 km and 480 km: the simulated amplitudes by the DTM2000 model are 46% and 53% of the observed amplitudes, respectively, and only 33% and 26% for the NRLMSISE00 model. These three models are also failed to depict the MDM's variation with altitude, solar radiation level, and seasonal effects. In order to correct the model prediction, a 6th-order Legendre polynomial of geographic latitude, coupled with arguments of local time and altitude, is designed to fit the MDM signals from the three satellites' observations. In terms of amplitude and phase of the MDM, the fitting results agree with the observations very well, and the correlation coefficient is 0.923. It indicates that this empirical polynomial could be helpful to the density model correction and high accuracy prediction of spacecrafts in low Earth orbits.

Performance analysis of NRLMSIS 2.1 thermospheric mass density model using GRACE-A and SWARM-C observations

Changes in the thermospheric space environment directly affect the movement of Low-Earth-Orbit space targets. The public release of the new generation empirical model NRLMSIS 2.1 provides a new option for estimating thermospheric mass density. This paper analyzes the mass density estimation performance of NRLMSIS 2.1 model using GRACE-A and SWARM-C observations during 2011–2017. First, the results show that compared with the NRLMSISE-00, NRLMSIS 2.1 systematically underestimated mass density by around 10 %. Second, the performance of the models decreased in the middle of most years, which may be due to the lack of a detailed expression of the models for the phenomenon of global density reduction during this period. Third, the biases of the model estimations do not show obvious change characteristics with changing of latitude, but the correlation with satellite observations shows a less downward trend with increasing latitude. Fourth, during the selected periods of 90 space weather events from 2011 to 2017, the estimation performance of NRLMSIS 2.1 faced varying degrees of challenges. Taking satellite observations as references, in extreme cases, the relative deviation of the NRLMSISE-00 model exceed 70 %, while that of NRLMSIS 2.1 is about 50 %. The results indicate that technological iteration and the addition of new data enhance the overall stability of the NRLMSIS 2.1 model.

Retrieval and analysis of thermospheric mass densities below 200 km altitude based on precise orbit data of the re-entry objects SZ-10 MODULE and TIANGONG 1

Atmospheric mass densities in the lower thermosphere below 200 km have not been adequately determined, but they are crucial for re-entry prediction of space objects. In this paper, based on precise orbit data of the re-entry objects SZ-10 MODULE and TIANGONG 1 (COSPAR identifiers 2013-029H and 2011-053A, respectively; NORAD catalog numbers 39193 and 37820, respectively), the semi-major axis decay numerical method and the improved energy balance method are adopted to retrieve thermospheric mass densities below 200 km altitude, and a total of 7044 and 4698 points of valid densities data with one-minute temporal resolution are obtained, respectively. Then the retrieved densities after preprocessing are compared with the NRLMSISE-00 empirical model of the atmosphere. It shows that there is an excellent consistency between these two methods with the Pearson correlation coefficients around 1.00, the retrieved densities of which are also in good agreement with the model with the Pearson correlation coefficients above 0.97 (their systematic biases are about 1.1% and 4.5% with standard deviations of about 14% and 20% for these two objects respectively), but the retrieved densities of the semi-major axis decay numerical method have a smaller systematic bias from the model than the results of the improved energy balance method which is computationally more efficient. In addition, the corresponding retrieved densities and their ratios to the model are further analyzed in terms of latitude and local solar time, and the retrieved densities of these two methods are also in good consistency within about 97%. The maximum mean deviations from the model in both dimensions reach about 12%. It reveals the variations of the thermospheric mass densities below 200 km altitude with latitude and local solar time due to solar activity. Additionally, it also indicates that the NRLMSISE-00 model underestimates the thermospheric densities at high solar activity and overestimates the densities at low solar activity, as compared to the retrieved densities that are regarded as true values.

The Atmospheric Influence on Cosmic-Ray-Induced Ionization and Absorbed Dose Rates

When high-energy particles originating from space penetrate the atmosphere, they may interact with atoms and molecules, initiating air showers composed of secondary and tertiary particles propagating towards the ground. They can cause ionization of the atmosphere and contribute to the radiation dose at low altitudes. This work uses the GEANT-4-based Atmospheric Radiation Interaction Simulator (AtRIS) toolkit to compute these quantities in the Earth’s atmosphere. We take advantage of the unique Planet Specification File (PSF) of the Atmospheric Radiation Interaction Simulator (AtRIS) to investigate the effect of the state of the atmosphere on the resulting induced ionization and absorbed dose rates from the top of the atmosphere (at 100 km) down to the surface. The atmospheric profiles (density, pressure, temperature, and composition) are computed with the NRLMSISE-00 model at various latitudes and for every month of 2014, corresponding to the last maximum of solar activity. The resulting ionization and dose rates present different profiles that vary with latitude in the atmosphere, with the relative difference between equatorial and high latitude ionization rates reaching 68% in the Pfotzer maximum. We obtain differences of up to 59% between the equator and high latitudes observed at commercial flight altitudes for the radiation dose. Both ionization and absorbed dose rates also feature anti-phased seasonal variations in the two hemispheres throughout 2014. Based on these results, we computed global maps of the ionization and dose rates at fixed altitudes in the atmosphere by using precomputed maps of the effective vertical cutoff rigidities and the results of three AtRIS simulations to consider the effect of latitude. While sharing the same general structure as maps created with a single profile, these new maps also show a clear asymmetry in the ionization and absorbed dose rates in the polar regions.

Predicting global thermospheric neutral density during periods with high geomagnetic activity

Estimating global and multi-level Thermosphere Neutral Density (TND) is important for studying coupling processes within the upper atmosphere, and for applications like orbit prediction. Models are applied for predicting TND changes, however, their performance can be improved by accounting for the simplicity of model structure and the sampling limitations of model inputs. In this study, a simultaneous Calibration and Data Assimilation (C/DA) algorithm is applied to integrate freely available CHAMP, GRACE, and Swarm derived TND measurements into the NRLMSISE-00 model. The improved model, called ‘C/DA-NRLMSISE-00’, and its outputs fit to these measured TNDs, are used to produce global TND fields at arbitrary altitudes (with the same vertical coverage as the NRLMSISE-00). Seven periods, between 2003-2020 that are associated with relatively high geomagnetic activity selected to investigate these fields, within which available models represent difficulties to provide reasonable TND estimates. Independent validations are performed with along-track TNDs that were not used within the C/DA framework, as well as with the outputs of other models such as the Jacchia-Bowman 2008 and the High Accuracy Satellite Drag Model. The numerical results indicate an average 52%, 50%, 56%, 25%, 47%, 54%, and 63% improvement in the Root Mean Squared Errors of the short term TND forecasts of C/DA-NRLMSISE00 compared to the along-track TND estimates of GRACE (2003, altitude 490 km), GRACE (2004, altitude 486 km), CHAMP (2008, altitude 343 km), GOCE (2010, altitude 270 km), Swarm-B (2015, altitude 520 km), Swarm-B (2017, altitude 514 km), and Swarm-B (2020, altitude 512 km), respectively.

Performance characterization and kinetic analysis of atmosphere-breathing electric propulsion intake device

An atmosphere-breathing electric propulsion (ABEP) system is designed to capture and compress the rarefied atmosphere through an intake device in very-low-Earth-orbit (VLEO). This study numerically characterizes the intake performance according to the design parameters, including the geometry of the tapered chamber, gas-surface interaction (GSI) models, surface temperature, aspect ratio, and sizing. The design of grid ducts is examined for different gaps, lengths, and yaw angles. The influence of intermolecular collisions is also investigated. The diffuse GSI model is chosen as a realistic model at VLEO due to the adsorption of atomic oxygen. The direct simulation Monte Carlo method is employed to calculate the capture efficiency, compression ratio, particle flow rate, and number density as the four indicators of intake performance. The flow conditions are obtained using the NRLMSISE-00 model, with a target altitude range of 180–220 km. In addition, a comprehensive design is proposed and the related propellant characteristics are investigated using kinetic analysis. Multi-modality is found in the particle velocity distribution, which implies non-equilibrium of the ABEP propellant.

A Novel Method to Derive Exospheric Temperatures from Swarm Thermospheric Densities during Quiet Times

One of the most important parameters in the atmosphere, the neutral temperature, becomes difficult to measure at high altitudes such as the exosphere. Therefore, based on the assumption of static equilibrium and isothermal atmosphere, a new method was developed to derive quiet-time exospheric temperatures using neutral atmospheric densities from 470 km to 550 km, which were obtained from the Swarm satellites. The derived neutral temperatures were obtained at an altitude of approximately 500 km in the low and middle latitudes from mid-April 2014 to early August 2014. The results were evaluated with nighttime temperatures from ground-based Fabry Perot Interferometers at 250 km. The mean deviation between the derived temperatures and FPI was 30.80 K and the standard deviation of the mean was 106.20 K. The diurnal variations of the exospheric temperatures, which tended to reach their maximum in the late afternoon, were in good consistency with the NRL-MSISE00 model simulations. This novel method performs well at low and middle latitudes. The greatest source of uncertainty is the mean molecular mass, which is also not well determined at these high altitudes. Hence, a measurement called “Satellite-tethered Mass Spectrometer Detection” was proposed to address this.

Simulation Calculation of Element Number Density in the Earth’s Atmosphere Based on X-ray Occultation Sounding

The number density profiles of elements N and O in the altitude range of 120–250 km are retrieved by simulation based on X-ray occultation. Based on the parameters of the NICER telescope, the energy spectrum forward model of the Crab Nebula in the energy range of 0.25–8 keV during the occultation is constructed, and the energy spectrum simulation data are obtained by adding noise to the energy spectrum forward model at different tangent point altitudes. The NICER energy band includes the K-shell absorption edges (0.4 keV, 0.53 keV for N, O), and there are significant differences in X-ray cross sections at the K-shell absorption edges, which provides an opportunity to retrieve the atmospheric density of each element. The MCMC algorithm is used to fit the energy spectrum forward model and simulation data, and the density profiles of elements N and O are retrieved. It is found that the retrieved error of O element in the altitude range of 120–140 km is large, which may be related to the low proportion of O in the line of sight and the low signal-to-noise ratio of simulation data. In the altitude range of 140–200 km, the retrieved error of elements N and O is small, but in the altitude range of 200–250 km, the retrieved error of elements N and O becomes larger, and the inconsistency between the retrieved results and NRLMSISE-00 model values increases. This is because the number of absorbed photons is reduced due to the thin atmospheric density at higher altitude, which introduces great uncertainty into the retrieved results. This study lays a foundation for element density retrieval based on X-ray occultation measured data in the future.

Predicting infrasound transmission loss using deep learning

SUMMARY Modelling the spatial distribution of infrasound attenuation (or transmission loss, TL) is key to understanding and interpreting microbarometer data and observations. Such predictions enable the reliable assessment of infrasound source characteristics such as ground pressure levels associated with earthquakes, man-made or volcanic explosion properties, and ocean-generated microbarom wavefields. However, the computational cost inherent in full-waveform modelling tools, such as parabolic equation (PE) codes, often prevents the exploration of a large parameter space, that is variations in wind models, source frequency and source location, when deriving reliable estimates of source or atmospheric properties—in particular for real-time and near-real-time applications. Therefore, many studies rely on analytical regression-based heuristic TL equations that neglect complex vertical wind variations and the range-dependent variation in the atmospheric properties. This introduces significant uncertainties in the predicted TL. In the current contribution, we propose a deep learning approach trained on a large set of simulated wavefields generated using PE simulations and realistic atmospheric winds to predict infrasound ground-level amplitudes up to 1000 km from a ground-based source. Realistic range dependent atmospheric winds are constructed by combining ERA5, NRLMSISE-00 and HWM-14 atmospheric models, and small-scale gravity-wave perturbations computed using the Gardner model. Given a set of wind profiles as input, our new modelling framework provides a fast (0.05 s runtime) and reliable (∼5 dB error on average, compared to PE simulations) estimate of the infrasound TL.

Analysis of Orbital Atmospheric Density from QQ-Satellite Precision Orbits Based on GNSS Observations

Atmospheric drag provides an indirect approach for evaluating atmospheric mass density, which can be derived from the Precise Orbit Determination (POD) of Low Earth Orbit (LEO) satellites. A method was developed to estimate nongravitational acceleration, which includes the drag acceleration of the thermospheric density model and empirical force acceleration in the velocity direction from the centimeter-level reduced-dynamic POD. The main research achievements include the study of atmospheric responses to geomagnetic storms, especially after the launch of the spherical Qiu Qiu (QQ)-Satellite (QQ-Satellite) with the global navigation system satellite (GNSS) receiver onboard tracking the Global Positioning System (GPS) and Beidou System (BDS) data. Using this derivation method, the high-accuracy POD atmospheric density was determined from these data, resulting in better agreement among the QQ-Satellite-derived densities and the NRLMSISE-00 model densities. In addition, the POD-derived density exhibited a more sensitive response to magnetic storms. Improved accuracy of short-term orbit predictions using derived density was one of the aims of this study. Preliminary experiments using densities derived from the QQ-Satellite showed promising and encouraging results in reducing orbit propagation errors within 24 h, especially during periods of geomagnetic activity.

Using 3D Ray Tracing Technology to Study the Disturbance Effect of Rocket Plume on Ionosphere

In this paper, the initial neutral atmospheric parameters, background ionospheric parameters and geomagnetic field parameters of the ionosphere are obtained by NRLMSISE-00 model, IRI-2016 model and IGRF-13 model, respectively. Considering the neutral gas diffusion process, ion chemical reaction and plasma diffusion process, a three-dimensional dynamic model of chemical substances released by rocket plume disturbing the ionosphere is constructed. The influence of the disturbance on the echo path of high frequency radio waves with different incident frequencies is simulated by using three-dimensional digital ray-tracing technology. Using this model, the process of ionospheric disturbance caused by the main chemical substances H2 and H2O in the rocket plume under three different release conditions: fixed-point release at 300 km, vertical path at 250–350 km and parabolic path at 250–350 km, and the influence of the ionospheric cavity on the radio wave propagation of high frequency radio waves at different frequencies are simulated. The main purpose of the article is to focus on the effect of the cavity generated by the rocket exhaust on the propagation of radio waves. It mainly studies the perturbation effect on the ionosphere under different release conditions, considers the neutral gas diffusion process, ion chemical reaction and plasma diffusion process, and establishes the three-dimensional dynamics of the ionospheric electron density and the spatiotemporal distribution of the plume plasma learning model. Finally, the three-dimensional ray-tracing algorithm is used to simulate the propagation path of the radio wave through the disturbance area. We considered three different release conditions, including fixed-point release, vertical path and parabolic path. The ionospheric disturbances produced by these different releases are compared and analyzed, and their effects on the propagation path of radio waves are studied.

Measurement of the vertical atmospheric density profile from the X-ray Earth occultation of the Crab Nebula with Insight-HXMT

Abstract. X-ray Earth occultation sounding (XEOS) is an emerging method for measuring the neutral density in the lower thermosphere. In this paper, the X-ray Earth occultation (XEO) of the Crab Nebula is investigated using the Hard X-ray Modulation Telescope (Insight-HXMT). The pointing observation data on the 30 September 2018 recorded by the low-energy X-ray telescope (LE) of Insight-HXMT are selected and analysed. The extinction light curves and spectra during the X-ray Earth occultation process are extracted. A forward model for the XEO light curve is established, and the theoretical observational signal for light curve is predicted. The atmospheric density model is built with a scale factor to the commonly used Mass Spectrometer Incoherent Scatter Radar Extended model (MSIS) density profile within a certain altitude range. A Bayesian data analysis method is developed for the XEO light curve modelling and the atmospheric density retrieval. The posterior probability distribution of the model parameters is derived through the Markov chain–Monte Carlo (MCMC) algorithm with the NRLMSISE-00 model and the NRLMSIS 2.0 model as basis functions, and the respective best-fit density profiles are retrieved. It is found that in the altitude range of 105–200 km, the retrieved density profile is 88.8 % of the density of NRLMSISE-00 and 109.7 % of the density of NRLMSIS 2.0 by fitting the light curve in the energy range of 1.0–2.5 keV based on the XEOS method. In the altitude range of 95–125 km, the retrieved density profile is 81.0 % of the density of NRLMSISE-00 and 92.3 % of the density of NRLMSIS 2.0 by fitting the light curve in the energy range of 2.5–6.0 keV based on the XEOS method. In the altitude range of 85–110 km, the retrieved density profile is 87.7 % of the density of NRLMSISE-00 and 101.4 % of the density of NRLMSIS 2.0 by fitting the light curve in the energy range of 6.0–10.0 keV based on the XEOS method. Goodness-of-fit testing is carried out for the validation of the results. The measurements of density profiles are compared to the NRLMSISE-00 and NRLMSIS 2.0 model simulations and the previous retrieval results with NASA's Rossi X-ray Timing Explorer (RXTE) satellite. For further confirmation, we also compare the measured density profile to the ones by a standard spectrum retrieval method with an iterative inversion technique. Finally, we find that the retrieved density profile from Insight-HXMT based on the NRLMSISE-00 and NRLMSIS 2.0 models is qualitatively consistent with the previous retrieved results from RXTE. The results of light curve fitting and standard energy spectrum fitting are in good agreement. This research provides a method for the evaluation of the density profiles from MSIS model predictions. This study demonstrates that the XEOS from the X-ray astronomical satellite Insight-HXMT can provide an approach for the study of the upper atmosphere. The Insight-HXMT satellite can join the family of the XEOS. The Insight-HXMT satellite with other X-ray astronomical satellites in orbit can form a space observation network for XEOS in the future.

Orbit-localised thermosphere density prediction using a Kalman filter based calibration of empirical models

Accurate estimation of thermosphere mass density is critical to determining how satellite orbits evolve over time and thus to planning and managing space missions. Empirical thermosphere models are commonly employed for this purpose, but have substantial uncertainties. In this work, a Kalman filter method for calibrating these models along a particular satellite’s trajectory is described. This method was applied to calibrate the NRLMSISE-00, JB2008, and DTM-2020 models with respect to densities measured by the Swarm-C and GOCE satellites. Substantial improvements in root mean squared density residuals were obtained using the technique when compared with either uncalibrated model output or calibration using a linear regression on previous data. Further improvement was obtained by combining estimates from different models using a best linear unbiased estimator method.

New method for Earth neutral atmospheric density retrieval based on energy spectrum fitting during occultation with LE/Insight-HXMT

We propose a new method for retrieving the atmospheric number density profile in the lower thermosphere, based on the X-ray Earth occultation of the Crab Nebula with the Hard X-ray Modulation Telescope (Insight-HXMT) Satellite. The absorption and scattering of X-rays by the atmosphere result in changes in the X-ray energy, and the Earth’s neutral atmospheric number density can be directly retrieved by fitting the observed spectrum and spectrum model at different altitude ranges during the occultation process. The pointing observations from LE/Insight-HXMT on 16 November 2017 are analyzed to obtain high-level data products such as lightcurve, energy spectrum and detector response matrix. The results show that the retrieved results based on the spectrum fitting in the altitude range of 90–200 km are significantly lower than the atmospheric density obtained by the NRLMSISE-00 model, especially in the altitude range of 110–120 km, where the retrieved results are 34.4% lower than the model values. The atmospheric density retrieved by the new method is qualitatively consistent with previous independent X-ray occultation results (Determan et al., 2007; Katsuda et al., 2021), which are also lower than empirical model predictions. In addition, the accuracy of atmospheric density retrieved results decreases with the increase of altitude in the altitude range of 150–200 km, and the accurate quantitative description will be further analyzed after analyzing a large number of X-ray occultation data in the future.

Evaluation of Empirical Atmospheric Models Using Swarm-C Satellite Data

Swarm-C satellite, a new instrument for atmospheric study, has been the focus of many studies to evaluate its usage and accuracy. This paper takes the Swarm-C satellite as a research object to verify the Swarm-C accelerometer’s inversion results. This paper uses the two-row orbital elements density inversion to verify the atmospheric density accuracy results of the Swarm-C satellite accelerometer. After the accuracy of the satellite data is verified, this paper conducts comparative verification and empirical atmospheric model evaluation experiments based on the Swarm-C accelerometer’s inversion results. After comparing with the inversion results of the Swarm-C semi-major axis attenuation method, it is found that the atmospheric density obtained by inversion using the Swarm-C accelerometer is more dynamic and real-time. It shows that with more available data, the Swarm-C satellite could be a new high-quality instrument for related studies along with the well-established satellites. After evaluating the performance of the JB2008 and NRLMSISE-00 empirical atmospheric models using the Swarm-C accelerometer inversion results, it is found that the accuracy and real-time performance of the JB2008 model at the altitude where the Swarm-C satellite is located are better than the NRLMSISE-00 model.

Atmospheric Model Effect on Flight Data Reconstruction: Application to the Early Phase of the IXV Reentry

Recent work on the Intermediate eXperimental Vehicle (IXV) re-entry simulation in hypersonic rarefied regime highlighted several numerical and experimental key aspects for a satisfactory reconstruction of its aerothermodynamic flight data. Indeed, among the investigated sources of discrepancies, the atmospheric model uncertainty on the density estimation appeared as one of the major sources of error for the heat flux calculation. The initial investigation was based on the NRLMSISE-00 model of 2000 which was recently updated in the NRLMSIS 2.0 version of 2020. This last version incorporates major formulation changes and new measurements yielding significantly smaller densities for altitudes below 100 km. The present work therefore focuses on the impact of improving our knowledge of the atmospheric environment to reduce the error related to the numerical reconstruction of the heat flux.

Coupled investigations of ionosphere variations over European and Japanese regions: observations, comparative analysis, and validation of models and facilities

This paper presents the results of a coordinated measurement campaign with ground based and satellite observations over European and Japanese regions during September 5–6, 2017. Two incoherent scatter radars, two satellite missions, International Reference Ionosphere (IRI-2016) empirical model, and Field Line Interhemispheric Plasma (FLIP) physical model were employed to examine the regular behavior of the F2-layer peak height and density and the topside ionosphere electron density, electron, and ion temperatures as well as traveling ionospheric disturbances (TIDs). The daily ionospheric variations over Kharkiv and Shigaraki exhibited similar behavior qualitatively and quantitatively. The results show that none of the empirical IRI-2016 models of F2-layer peak height, topside electron density, and temperature can be preferred for predicting the key qualitative features of variations in ionospheric plasma parameters over Kharkiv and Shigaraki. The likely reason is rapid day to day changes in solar activity and series of moderate enhancements of magnetic activity occurring in the observation period and preceding days. Compared with IRI-2016 model, the FLIP physical model was shown to provide the best agreement with the observations when constrained to follow the observed diurnal variations of F2-layer peak height both over Europe and Japan. This paper presents the first direct comparison of the mid-latitude electron density measured by the Swarm satellite with incoherent scatter radar data and it confirms the high quality of the space-borne data. For the first time, evidence of the possible need to increase the neutral hydrogen density in NRLMSISE-00 model by at least a factor of 2 was obtained for the Asian longitudinal sector. The TIDs, which have predominant periods of about 50 min over Europe and 80 min over Japan, were detected, likely caused by passage of the solar terminator. Such a difference in the periods could indicate regional features and is the topic for further research.

Intake design for an Atmosphere-Breathing Electric Propulsion System (ABEP)

Challenging space missions include those at very low altitudes, where the atmosphere is source of aerodynamic drag on the spacecraft. To extend the lifetime of such missions, an efficient propulsion system is required. One solution is Atmosphere-Breathing Electric Propulsion (ABEP) that collects atmospheric particles to be used as propellant for an electric thruster. The system would minimize the requirement of limited propellant availability and can also be applied to any planetary body with atmosphere, enabling new missions at low altitude ranges for longer times. IRS is developing, within the H2020 DISCOVERER project, an intake and a thruster for an ABEP system. The article describes the design and simulation of the intake, optimized to feed the radio frequency (RF) Helicon-based plasma thruster developed at IRS. The article deals in particular with the design of intakes based on diffuse and specular reflecting materials, which are analysed by the PICLas DSMC-PIC tool. Orbital altitudes h=150−250km and the respective species based on the NRLMSISE-00 model (O, N2, O2, He, Ar, H, N) are investigated for several concepts based on fully diffuse and specular scattering, including hybrid designs. The major focus has been on the intake efficiency defined as ηc=Ṅout∕Ṅin, with Ṅin the incoming particle flux, and Ṅout the one collected by the intake. Finally, two concepts are selected and presented providing the best expected performance for the operation with the selected thruster. The first one is based on fully diffuse accommodation yielding to ηc<0.46 and the second one based on fully specular accommodation yielding to ηc<0.94. Finally, also the influence of misalignment with the flow is analysed, highlighting a strong dependence of ηc in the diffuse-based intake while, for the specular-based intake, this is much lower finally leading to a more resilient design while also relaxing requirements of pointing accuracy for the spacecraft.

Aerodynamic and gravity gradient based attitude control for CubeSats in the presence of environmental and spacecraft uncertainties

In this paper, the problem of controlling the attitude of a CubeSat in low Earth orbit using only the environmental torques is considered. The CubeSat is equipped with a Drag Maneuvering Device (DMD) that enables the spacecraft to modulate its experienced aerodynamic and gravity gradient torques. An adaptive controller is designed to achieve attitude tracking of the spacecraft in the presence of uncertain parameters such as the atmospheric density, drag and lift coefficients, and the time-varying location of the Center of Mass (CoM). The proposed controller also accounts for modeling inaccuracy of the inertia matrix of the spacecraft. A Lyapunov-based analysis is used to prove that the quaternion-based attitude trajectory tracking error is uniformly ultimately bounded. The designed controller is also examined through numerical simulations for a spacecraft with time-varying uncertain drag, lift coefficients and CoM location parameters and the NRLMSISE-00 model for the atmospheric density.