Satellite autonomous navigation is an important function of the BeiDou-3 navigation System (BDS-3). Satellite autonomous navigation means that the navigation satellite uses long-term forecast ephemeris and Inter-Satellite Link (ISL) measurements to determinate its own spatial position and time reference without the support of the ground Operation and Control System (OCS) for a long time to ensure that

The impact of nonspherical bodies is complex, even at low velocities where contacting bodies are assumed to be rigid. Models of varying complexity (e.g. finite element methods) can be used to evaluate such impacts, but it is advantageous to use impulsive models such as that by Stronge, which are computationally inexpensive and governed by (fixed) material interaction coefficients. Stronge’s model parameterizes

For precursor solar sail activities a strategy for a controlled deployment of large membranes was developed based on a combination of zig-zag folding and coiling of triangular sail segments spanned between crossed booms. This strategy required four autonomous deployment units that were jettisoned after the deployment is completed. In order to reduce the complexity of the system an adaptation of that

In this study, integrated drought monitoring index (IDMI) was proposed as a tool to assess and monitor the spatio-temporal dynamics of agricultural drought during the northeast monsoon season for the period from 2000 to 2016 in Tamil Nadu state, south-eastern part of Indian peninsula. The IDMI is characterized as the principal component of precipitation condition index (PCI), soil moisture condition

The quality and availability of Uncalibrated Phase Delay (UPD) solutions are crucial to the Precise Point Positioning (PPP) service, and the long-term temporal variability and its contributing factors should be better understood. In this paper, we comprehensively investigate the long-term time-varying characteristics of each UPD product respectively generated by a global and regional network and their

The objective of this study is to investigate cloud attenuation at 30 GHz frequency using ground-based microwave radiometric observations at a tropical location, Kolkata. At higher frequencies and lower elevation angles, cloud attenuation is of major concern at a tropical location. The location experiences high value of liquid water path (LWP), which is responsible for cloud attenuation, during the

The western tropical Atlantic Ocean is a very energetic and highly variable region. It is one of the main contributors to the inter-hemispheric mass and heat transports. This study aim is to give a new picture of the space and time variability of this region using statistical tools applied to five different satellite measurements (Sea Surface Temperature, Sea Surface Salinity, ocean topography, wind

The analysis of the behavior of the critical frequency foF2 during the 24th solar activity cycle (Danilov and Konstantinova, 2020a, c) is prolonged for two more months and the nighttime hours. In addition to the Rz and Ly-α indices used in the aforementioned papers for correction of the F10.7 index during the 24th cycle, the commonly used Mg II index is added. The results confirm the previous conclusions

Hyperspectral resolution image products of a synthetic sensor featuring the high spatial resolution of the space-borne sensor can offer cost-effective means for enhancing our current capabilities in terms of providing an array of images in lieu of designing an expensive system for image acquisition, which can serve the expanding needs of the scientific and user communities for various critical water

Traditional rotary ultrasonic vibration drilling rock (fz < 2A) is an effective drilling rock method, but its feed rate is limited by the ultrasonic vibration amplitude, resulting in lower drilling efficiency. In this paper, based on the requirements of drilling efficiency in the asteroid sampling mission, the process method of rotary ultrasonic vibration assisted drilling rock (fz > 2A) was proposed

The radio occultation (RO) measurements obtained by GOR payload on board the CSES (the first China Seismo-Electromagnetic Satellite) satellite are validated using the observations from five ionosonde stations located at different latitudes and one incoherent scatter radar (ISR) observatory located at mid-latitude. CSES RO peak values (NmF2) and peak heights (hmF2) are compared with the corresponding

Nighttime enhancement in the Vertical Total Electron Content (VTEC) of the ionosphere near equatorial ionization anomaly crest region in the Indian ionospheric sector has been studied during May 2016 to August 2017, a solar minimum period. VTEC data is obtained from a multi-frequency multi-constellation global navigation satellite system (GNSS) receiver installed at Bhopal (23.2°N, 77.4°E & MLAT 14

Considering the height and horizontal separations between stations, we propose a method to regionally model the tropospheric delay. The zenith tropospheric delay (ZTD) is separated into vertically-correlated and horizontally-correlated components, which are to be regionally modeled respectively. A more accurate ZTD is thereby interpolated at the rover station, and enhanced ZTD constraints can be provided

Turbidity is a key indicator of water quality. It has biotic effects due to low penetration of light into the water such as photosynthesis reduction. The seasonal and interannual variability of turbidity in the Eastern Tropical Pacific coast of Mexico were analyzed using ocean color data. The region has an extended continental shelf, with several river discharges and marked seasonal patterns of wind

The radio determination satellite service (RDSS) is an advantageous and unique aspect of the BeiDou Navigation Satellite System (BDS) because other satellite navigation systems do not incorporate the RDSS. Due to the ageing of RDSS equipment, there is a long-term drift in various types of RDSS equipment time delays. There are some differences in the RDSS positioning accuracy with the change in the

The objective of the present paper is to show a method to find orbits near artificial equilibrium points for a satellite equipped with a continuous thrust that allows it to stay near the poles of a celestial body. The physical system includes the presence of a moon of the celestial body under observation, and the perturbation caused by this moon is counteracted by an algorithm to help the satellite

Achieving a soft landing over the surface of small celestial bodies is an essential maneuver in space to advance the status of space exploration, sample collecting and in-situ resource utilization, among other on-orbit tasks. Landing on these bodies is challenging due to the reduced-gravity and airless environment. The correct planning of execution of the trajectory to land on the surface of the body

This paper derives a control solution for mitigation of Parametrically excited vibration of taut cable in cable-truss couple system, which ensures safe and stable regulation for cable towards the desired patterns. The dynamic characteristics with periodic perturbation and the parametrically excited instability of cable are both analyzed; the physical factors of damping influence on the cable are investigated

The retention characteristics of the stratification information is one of the important factors of lunar soil drilling process. A high-accuracy DEM model of lunar soil was established and verified to be accurate both in shear strength indices and elastic-plastic behavior. Then the drilling simulation models of hard tube coring and soft bag coring were established and a “surface slope method” was proposed

In this paper, we propose a tandem tethered balloon scheme as a solution for increasing the operating altitudes of balloons to near-space altitudes of more than 20 km. By adding a middle balloon with a smaller volume than that of the top balloon in the middle weak wind zone, this scheme partially offsets the weight of the tether above the middle balloon, thereby greatly increasing the operating altitude

Radio occultations are commonly used to determine vertical profiles of ionospheric electron density and neutral atmospheric density from measurements of frequency. Previous work has developed expressions for how uncertainties in electron density and neutral density depend on uncertainty in frequency. However, these expressions assume that the relevant density decreases exponentially with increasing

Palaeoclimatic data (thickness variations in the Elatina Formation periglacial varves in the Flinderes Range, South Australia) with a spatial resolution of about one year and a time period of about 1334 years dated to the Marinoan glaciation, 680 Myears ago (late Precambrian), were studied in order to reveal quasiperiodic variations in climate processes in the past. Seven hidden periodicities, i.e

In spacecraft rendezvous, bearings-only navigation generally suffers from a lack of observability in range direction. Therefore, dedicated orbital maneuvers are essential to improve the observability and meet the navigation requirement. This paper proposes a simple one-step guidance method for improving observability. A new cost that quantifies the observability is defined by exploiting a Fisher information

The Indian Regional Navigation Satellite System (IRNSS/NavIC) is fully operational and broadcasting radio signals at L5 (1176.45 MHz) and S-band (2492.028 MHz). When these signals pass through the ionosphere, carrier phase delay, which depends on Total Electron Content (TEC), causes error in positioning. Corrections are applied in the augmented navigation system to minimize the position error due to

Elucidating versatile configurations of spiral folding, and investigating the deployment performance is of relevant interest to extend the applicability of deployable membranes towards large-scale and functional configurations. In this paper we propose new schemes to package flat and curved membranes of finite thickness by using multiple spirals, whose governing equations render folding lines by juxtaposing

Being the very first SAR mode altimeter tandem phase, the Sentinel-3 A/B tandem phase has provided an unprecedented opportunity to better characterize the sensitivity of SAR altimetry retrievals to high-frequency processes, such as long ocean waves. In this paper, we show that for some sea-state conditions, that are still to be precisely characterized, long ocean waves are responsible for high-frequency

Information on the water vapor distribution of the troposphere is useful for weather monitoring and forecast. Water vapor distribution can be estimated from tropospheric delays produced by high-grade Global Navigation Satellite System (GNSS) receivers. This type of techniques is currently used in the data assimilation process of Numerical Weather Prediction (NWP) models, especially, for the limited

This work creates a framework for solving highly non-linear satellite formation control problems by using model-free policy optimisation deep reinforcement learning (DRL) methods. This work considers, believed to be for the first time, DRL methods, such as advantage actor-critic method (A2C) and proximal policy optimisation (PPO), to solve the example satellite formation problem of propellantless planar

The LISA (Laser Interferometer Space Antenna) mission has been selected by the European Space Agency’s Science Programme Committee as the third large-class mission of the Cosmic Vision Programme, addressing the science theme of the Gravitational Universe. With a planned launch date in 2034, LISA will be the first ever space-borne Gravitational Wave observatory, relying on laser interferometry between

The snowline altitude at the end of melting season (SLA-EMS) provides a possibility to rapidly obtain a proxy for their equilibrium line altitude (ELA) which in turn is an indicator for the glacier mass balance. SLA-EMS is also an important parameter for the study of the relationships between climate and cryosphere. High Mountain Asia (HMA) hosts the largest glacier and perennial snow cover concentration

A new orbit-attitude-vibration coupled dynamic model of the tethered solar power satellite (Tethered SPS) is established based on absolute nodal coordinate formulation. The Hamilton’s equation of the system is derived by introducing generalized momentum through Legendre transformation. The correctness of the proposed model is verified by an example. The dynamic characteristics of the Tethered SPS are

An attempt is made to model the three-dimensional global structures and temporal variations of the ionospheric electron density (Ne) using the radio occultation (RO) Ne profile data obtained by the COSMIC/FORMOSAT-3, CHAMP and GRACE missions during the period from July 2006 to June 2017. The modeling technique we adopted is based on the empirical orthogonal function (EOF) analysis of the RO Ne dataset

For precise position services, the real-time precise point positioning (PPP) is a promising technology. The real-time PPP performance is expected to be improved by multi-system combination. The performance of real-time multi-system PPP needs to be periodically investigated, with the increasing number of available satellites and the continuously improved quality of real-time precise products of satellite

Gravitational waves are ripples in space-time predicted by Albert Einstein's general relativity and provide a new way to understand the universe. Space-borne detectors of gravitational waves, extending to very large scales, can effectively detect the middle and low-frequency gravitational wave source with the frequency band of 0.1mHz–1Hz. The test masses are used to make an inertial reference point

By introducing inter-satellite link (ISL), the dependence of the global navigation satellite system (GNSS) on ground infrastructure can be reduced and its performance enhanced via inter-satellite ranging and communication. Owing to platform restrictions, there are usually fewer onboard Ka-band ISL antennas than the number of visible satellites, which poses a problem when optimizing the inter-satellite

All currently considered solar sail designs require the deployment of a thin reflective membrane. This membrane is stowed using some folding technique and sometimes coiled onto a spool. The temperature of the deployed sail membrane is a critical aspect for solar sail design. Depending on the geometry of the imprinted folding lines, sunlight may be reflected inside folding lines which would locally

To meet the urgent needs of emergency observation missions, a well-designed constellation is key to ensuring system performance. This paper presents a multi-objective optimization framework which is well suited for constellation designers to identify key trade-offs and make decisions. Firstly, this work investigates the metrics of responsiveness and coverage simultaneously to approximate to the actual

With the continuous deployment of Low Earth Orbit (LEO) satellites, the estimation of differential code biases (DCBs) based on GNSS observations from LEO has gained increasing attention. Previous studies on LEO-based DCB estimation are usually using the spherical symmetry ionosphere assumption (SSIA), in which a uniform electron density is assumed in a thick shell. In this study, we propose an approach

Doppler, which is an instantaneous GNSS observable signal, has been proven effective in determining velocity and acceleration due to its high availability and accuracy. We propose a real-time triple-frequency cycle slip correction (CSC) method based on Doppler-aided signals because Doppler shift is time-independent and immune to cycle slips. When the sampling interval is less than 1 second, cycle slips

Any vehicle propelled by solid rocket motors (SRMs) must include an attitude control system capable of dealing with the torque generated by thrust misalignment. In order to expand the application of SRMs on CubeSats, an attitude control system utilizing moving mass actuators is discussed. The present research develops an eight-degree-of-freedom simulation model of a 2U CubeSat with two moving mass

It was 100 years ago (on August 7, 1920), that the comprehensive mathematical foundations of climate change research, written by a Serbian researcher, Milutin Milankovitch, were published. A later interpreter and developer of his results, Georg (in Hungarian: György) Bacsák (Pozsony/Pressburg/Bratislava, June 5, 1870 - Fonyód, March 4, 1970) was born 150 years ago and died at the age of one hundred

We have investigated the spatio-temporal evolution of disturbed time post mid-night Equatorial Plasma Bubbles (EPBs) using Canadian Advanced Digital Ionosonde (CADI) located at dip equatorial station, Tirunelveli (8.73°N, 77.7°E, 0.23°N Dip. Lat.), all-sky imager (ASI) observations at low latitude station Panhala (16.48oN, 74.6oE, 11.1oN Dip. Lat.) and Gadanki Ionospheric Radar Interferometer (GIRI)

The D-region ionospheric disturbances due to the tropical cyclone Fani over the Indian Ocean have been analysed using Very Low Frequency (VLF) radio communication signals from three transmitters (VTX, NWC and JJI) received at two low latitude stations (Kolkata-CUB and Cooch Behar-CHB). The cyclone Fani formed from a depression on 26th April, 2019 over the Bay of Bengal (Northeastern part of the Indian

Radial basis function (RBF) interpolation with multi-quadric is developed to perform ionospheric total electron content (TEC) mapping for the Chinese region between 15°N∼40°N and 100°E∼125°E. TEC measurements from the Centre for Orbit Determination in Europe (CODE) covering the solar maximum year 2011 are used to investigate the performance of the proposed RBF interpolation method. The differences

Given recent successes in modelling the transport of cosmic rays (CRs) in the heliosphere from first principles, taking into account the behaviour of heliospheric turbulence quantities and their influence on the transport parameters of these particles in a manner as self-consistent as possible, the question naturally arises as to what insights such a modelling approach can yield when applied to the

In this study, Sq(H) results for Sonmiani geomagnetic observatory (SON), Pakistan are presented first time for solar cycle i.e., Solar Cycle 24. Sonmiani observatory was established in 2008 and was included in the list of INTERMAGNET Magnetic Observatory (IMO) in 2012. The analysis of Sq(H) field is performed to examine diurnal, annual and seasonal behaviour of Sq(H) field at Sonmiani along with Honolulu

A single-receiver integer ambiguity resolution-enabled precise point positioning (PPP-RTK) user experiences a long convergence time when the rather weak single-constellation dual-frequency ionosphere-float model is used. Nowadays, the rapid development of Global Navigation Satellite Systems (GNSS) provides a multitude of available satellites and frequencies that can serve in improving the user’s model

The goal of this study is to examine the capability of the TRMM 3B42 product to detect spatial and temporal patterns in extreme precipitation events over southwestern Iran during the period of 1998–2016. A ground-based gridded precipitation dataset was created using a dense network of surface observations for the evaluation process. Various extreme precipitation indices in the three categories of fixed

Eight proxy records of Northern Fennoscandian summer temperature variability were analyzed for the CE 1700–2000 period. Stable and statistically significant correlation between the summer temperature reconstructions and a quasi 22-year Hale solar cycle was found to be present through the entire study period. The revealed solar–climatic link is a result of the effect of a weak solar cycle signal on

The filtering procedure is usually mandatory for computing the mean dynamic topography (MDT) by combining the mean sea surface (MSS) and geoid due to the inconsistent spectral contents between them. Recently, a rigorous fusion method is proposed to solve this inconsistency problem through the least square method (Becker et al., 2012), where MDT is parameterized by the Lagrange basis functions (LBFs)

In this study we use the CHAMP wind observations from 2002 to 2004 to investigate features of mid-latitude thermospheric winds at low and high geomagnetic activity levels. The winds are observed between the geomagnetic latitudes 40–50° north or south within an altitude range of 370–450 Km and averaged longitudinally. The low geomagnetic activity level wind generally leads eastward in both hemispheres

The Ionosphere PhotoMeter (IPM) is a far ultraviolet nadir-viewing photometer that flew aboard the second-generation, polar-orbiting Chinese meteorological satellite Feng-Yun 3D (FY-3D), which was launched on November 25th, 2017. By observing far ultraviolet night-time OI 135.6 nm emissions, which are produced by the recombination of O+ ions and electrons, the F2 layer peak electron density (NmF2)

The third phase BeiDou Navigation Satellite System (BDS-3) provides a BeiDou Global broadcast Ionospheric delay correction Model (BDGIM) for single-frequency navigation and positioning applications. According to the BDS Interface Control Document (ICD) Signal B1C (Version 1.0), the BDGIM contains nine parameters and was broadcast in December 2018. The BDGIM will gradually replace the BDS-2 ionospheric

This paper proposes a fixed time disturbance observer (FTDO) based fixed time sliding mode control scheme for spacecraft proximity operations in the presence of parameter uncertainties and disturbances. The FTDO is designed to estimate the lumped disturbance which includes kinematic couplings, parameter uncertainties, and disturbances. Based on the observation of lumped disturbance, the fixed time

As evidenced by the Global Exploration Roadmap, international interest exists in a new era of human exploration of the solar system. Such an effort is commencing with the examination of options for maintaining a facility—at times crewed—in an orbit nearby the Moon. Thus, the key objectives in advancing colonization of interplanetary space include positioning and maintaining an inhabited facility in

This paper proposes a novel description of the equations of motion for low-thrust trajectory design in the presence of a third-body perturbation. The framework is formulated using Gauss’ Variational Equations (GVE) with two distinct accelerations: the one produced by the electric engine and the disturbing term of the third-body effect, which is computed using the disturbing potential of the previously

Global navigation satellite systems (GNSSs) play an important role in both military and civilian industries, but most of the existing GNSS carriers are crowded in the L band. Although some modulations, such as binary-offset-carrier (BOC) and its modifications, can reduce the mutual interference of one GNSS signal to others, the exhausted L-band frequencies are still the bottleneck to improve GNSS performance

In a recent study, we developed ultralow-binder-content (UBC) structural materials based on lunar soil simulant and thermoset binders. In the current research, we investigated thermoplastic binders. Compared to thermosets, advanced thermoplastics could be more UV resistant, more durable, more robust, and recyclable. Our main technology is the compaction self-assembly (CSA). By using only ~4 wt% polyetherketoneketone

This paper is aimed at finding the best separation angle between spacecraft for the three-dimensional reconstruction of solar-wind inhomogeneous structures by the CORrelation-Aided Reconstruction(CORAR) method. The analysis is based on the dual-point heliospheric observations from the STEREO HI-1 cameras. We produced synthetic HI-1 white-light images containing artificial blob-like structures in different

Nonlinear propagation of purely stationary large amplitude electromagnetic (EM) solitary waves in a magnetized electron–positron (EP) plasma is studied using a fully relativistic two-fluid hydrodynamic model which accounts for physical regimes of both weakly relativistic (P≪nmc2) and ultrarelativistic (P≫nmc2) random thermal energies. Here, P is the thermal pressure, n the number density and m the