Orbits Of Small Satellites Research Articles

A Three-Stage Data-Driven Approach for Determining Reaction Wheels’ Remaining Useful Life Using Long Short-Term Memory

Reaction wheels are widely used in the attitude control system of small satellites. Unfortunately, reaction wheels failure restricts the efficacy of a satellite, and it is one of the many reasons leading to premature abandonment of the satellites. This study observes the measurable system parameter of a faulty reaction wheel induced with incipient fault to estimate the remaining useful life of the reaction wheels. We achieve this goal in three stages, as none of the observable system parameters are directly related to the health of a reaction wheel. In the first stage, we identify the necessary observable system parameter and predict the future of these parameters using sensor acquired data and a long short-term memory recurrent neural network. In the second stage, we estimate the health index parameter using a multivariate long short-term memory network. In the third stage, we predict the remaining useful life of reaction wheels based on historical data of the health index parameter. Normalized root mean squared error is used to evaluate the performance of the various models in each stage. Additionally, three different timespans (short, moderate, and extended in the scale of small satellite orbit times) are simulated and tested for the performance of the proposed methodology regarding the malfunction of reaction wheels. Furthermore, the robustness of the proposed method to missing values, input frequency, and noise is studied. The results show promising performance for the proposed scheme with accuracy in predicting health index parameter around 0.01–0.02 normalized root mean squared error, the accuracy in prediction of RUL of 1%–2.5%, and robustness to various uncertainty factors, as discussed above.

Small Satellite Orbit Determination Methods Based on the Doppler Measurements by Belarusian State University Ground Station

The Doppler measurements of the small satellites (SSs) were carried out using the Belarusian State University ground station. Measurements of a telemetry signal for the several satellite orbits with a limited number of data on one pass were performed. Two methods for orbit determination of an SS are considered. The first method is based on the perturbed circular motion prediction model for the satellite orbit with experimental data from radio signal processing. It does not require additional information from the NORAD database of satellite orbital parameters. Using predicted data of the tracking angles of antenna systems and the Doppler frequency shift of the telemetry radio signal, the ground station of the Belarusian State University received and successfully decoded telemetry packets from unknown SS LUOJIA-1 01. The second method is based on the SGP4 model and requires additional information from the NORAD two-line element (TLE) catalog of the satellite orbital parameters. An unknown SS LUOJIA-1 01 was identified using the NORAD TLE catalog based on a probabilistic estimation of the elevation angle and the Doppler frequency shift of receiving telemetry signals.

Development of methods for ensuring energy balance for the operation of mission equipment of “AIST”-series small satellites under conditions of power limitations

The article examines the issues of determining the light-and-shadow situation and its impact on providing energy balance on the orbits of two small satellites of the AIST series. Ensuring energy balance in the operation of mission equipment becomes particularly relevant in the case of power limitations caused by both the degradation of spacecraft systems and the factors of outer space. The main purpose of the article is to solve the problem of increasing the efficiency of the power supply system of AIST-series small satellites operating under resource constraints. Firstly, modeling of the lighting situation on the orbits of small satellites was carried out. Secondly, the telemetric information of AIST small satellites for the whole period of operation was examined. In addition, the influence of the light-and-shadow conditions on the parameters of the power system of a small satellite was analyzed. As a result, an algorithm for estimating the energy balance, taking into account the influence of the light-and-shadow situation was proposed. Using the proposed algorithm made it possible to take into account the influence of seasonal variations in the light-and-shadow environment on the possibility of ensuring energy balance in the operation of mission equipment

Autonomous navigation algorithm based on AUKF filter about fusion of geomagnetic and sunlight directions

PurposeThe geomagnetic field vector is a function of the satellite’s position. The position and speed of the satellite can be determined by comparing the geomagnetic field vector measured by on board three-axis magnetometer with the standard value of the international geomagnetic field. The geomagnetic model has the disadvantages of uncertainty, low precision and long-term variability. Therefore, accuracy of autonomous navigation using the magnetometer is low. The purpose of this paper is to use the geomagnetic and sunlight information fusion algorithm to improve the orbit accuracy.Design/methodology/approachIn this paper, an autonomous navigation method for low earth orbit satellite is studied by fusing geomagnetic and solar energy information. The algorithm selects the cosine value of the angle between the solar light vector and the geomagnetic vector, and the geomagnetic field intensity as observation. The Adaptive Unscented Kalman Filter (AUKF) filter is used to estimate the speed and position of the satellite, and the simulation research is carried out. This paper also made the same study using the UKF filter for comparison with the AUKF filter.FindingsThe algorithm of adding the sun direction vector information improves the positioning accuracy compared with the simple geomagnetic navigation, and the convergence and stability of the filter are better. The navigation error does not accumulate with time and has engineering application value. It also can be seen that AUKF filtering accuracy is better than UKF filtering accuracy.Research limitations/implicationsGeomagnetic navigation is greatly affected by the accuracy of magnetometer. This paper does not consider the spacecraft’s environmental interference with magnetic sensors.Practical implicationsMagnetometers and solar sensors are common sensors for micro-satellites. Near-Earth satellite orbit has abundant geomagnetic field resources. Therefore, the algorithm will have higher engineering significance in the practical application of low orbit micro-satellites orbit determination.Originality/valueThis paper introduces a satellite autonomous navigation algorithm. The AUKF geomagnetic filter algorithm using sunlight information can obviously improve the navigation accuracy and meet the basic requirements of low orbit small satellite orbit determination.

Optimal small satellite orbit design based on robust multi-objective optimization method

This paper investigates an optimal small satellite orbit design problem subject to the atmospheric drag uncertainty, and the small satellite is assumed to have no orbital control systems due to volume and mass constraints. The optimization objective of maximum target observation time is considered, which is constrained by the priority and minimum observation duration of each target site. Given the adverse impacts of atmospheric drag uncertainty on the designed orbit, the optimal solution is expected to maximize observation duration for given target sites while being less sensitive to substantial variations of atmospheric coefficients involved in atmospheric drag modeling. As a result, a robust orbit design approach is proposed by combining the robust optimization model with multi-objective optimization algorithm. Finally, the Monte Carlo simulation results are provided to demonstrate that the robust orbit solutions are more reliable compared to the nominal orbit solution designed from the traditional single-objective stochastic optimization algorithm.

소형위성의 궤도천이 및 보정을 위한 홀 추력기의 설계

소형 인공위성의 궤도천이 및 보정을 위하여 추력이 약 10 mN이고 비추력이 1500 s인 홀 방식 전기추력기를 설계하였다. 개발된 추력기는 홀 방식의 추력부, 전력공급부 및 연료 공급부로 구성되어 있고, 무게, 소모전력 및 효율은 각각 10 kg, 300 W 및 30%정도이다. 개발된 추력기 시스템에 대한 간략한 소개를 홀 방식의 추력기를 선택하게 된 배경해석과 함께 기술하였다. A small Hall-effect thruster with a thrust range near 10 mN and a specific impulse of about 1500 s has been designed to control or maintain the orbits of small satellites. The thruster system consists of a hall-effect thruster head, a power processing unit and a Xenon (Xe) gas feed system. The total mass, the consumed electric power and the efficiency of the thruster are approximately 10 kg, 300W and 30%, respectively. Analyses results that support the selection of the thruster for small satellites are provided along with a brief description of the thruster system.

The Orbits of Saturn's Small Satellites Derived from Combined Historic andCassiniImaging Observations

We report on the orbits of the small, inner Saturnian satellites, either recovered or newly discovered in recent Cassini imaging observations. The orbits presented here reflect improvements over our previously published values in that the time base of Cassini observations has been extended, and numerical orbital integrations have been performed in those cases in which simple precessing elliptical, inclined orbit solutions were found to be inadequate. Using combined Cassini and Voyager observations, we obtain an eccentricity for Pan 7 times smaller than previously reported because of the predominance of higher quality Cassini data in the fit. The orbit of the small satellite (S/2005 S1 [Daphnis]) discovered by Cassini in the Keeler gap in the outer A ring appears to be circular and coplanar; no external perturbations are apparent. Refined orbits of Atlas, Prometheus, Pandora, Janus, and Epimetheus are based on Cassini , Voyager, Hubble Space Telescope, and Earth-based data and a numerical integration perturbed by all the massive satellites and each other. Atlas is significantly perturbed by Prometheus, and to a lesser extent by Pandora, through high-wavenumber mean-motion resonances. Orbital integrations involving Atlas yield a mass of GMAtlas = (0.44 ± 0.04) × 10-3 km3 s -2, 3 times larger than reported previously (GM is the product of the Newtonian constant of gravitation G and the satellite mass M). Orbital integrations show that Methone is perturbed by Mimas, Pallene is perturbed by Enceladus, and Polydeuces librates around Dione's L5 point with a period of about 791 days. We report on the nature and orbits of bodies sighted in the F ring, two of which may have persisted for a year or more.

B308 超音速マイクロノズル内のPSPによる圧力分布

In recent years, the interest in microdevices and systems has increased rapidly. Gaseous flow through and within such devices is a principal consideration in many applications, and its understanding can be crucial for optimization of performance. Most of the sensors applied to MEMS devices measurement have limited resolution restricted by the sensor size and device geometry. Pressure-sensitive paint (PSP) is one of the options for global distribution measurement in MEMS devices. PSP is a molecular sensor, and has an enough resolution for MEMS. In this paper, we demonstrate the use of PSP for quantitative measurement of pressure distribution in a supersonic micronozzle of the nozzle throat 250μm, such as those that might be employed for flow control and/or small satellite orbit maintenance.

Satellite formation, II

The satellite formation model of Harris and Kaula ( Icarus 24, 516–524, 1975) is extended to include evolution of planetary ring material and elliptic orbital motion. This model is more satisfactory than the previous one in that the formation of the moon begins at a later time in the growth of the earth, and that a significant fraction of the lunar material is processed through a circumterrestrial debris cloud where volatiles might have been lost. Thus the chemical differences between the earth and moon are more plausibly accounted for. Satellites of the outer planets probably formed in large numbers throughout the growth of those planets. Because of rapid inward evolution of the orbits of small satellites, the present satellite systems represent only satellites formed in the last few percent of the growths of their primaries. The rings of Saturn and Uranus are most plausibly explained as the debris of satellites disrupted within the Roche limit. Because such a ring would collapse onto the planet in the course of any significant further accretion by the planet, the rings must have formed very near or even after the conclusion of accretion.