Spacecraft In Low Orbit Research Articles

Digital model of the drag force of the Earth’s upper atmosphere for the design of low-orbit spacecraft

A digital model is described for estimating the drag force of the Earth's upper atmosphere acting on a low-orbit spacecraft. Unlike the classical model of aerodynamic force, the digital model is the result of a computer algorithm. This algorithm calculates the field of aerodynamic force values, taking into account changes in the flight altitude, aerodynamic coefficient and the area of the spacecraft midsection over time. The calculations also use a digital model of the dynamic density of the Earth's upper atmosphere. The digital model of the drag force of the Earth's upper atmosphere is useful in the design of low-orbit spacecraft with a low-thrust jet propulsion system (thrust order – millinewtons). On the basis of the calculated values of the aerodynamic force, it is possible to form requirements for the geometry of the spacecraft, attitude modes and arrangement of low-thrust jet engines (for example, electric jet engines). With the accumulation of big data in the form of tabular functions of aerodynamic force from the space of various design and ballistic parameters of low-orbit spacecraft, it is possible to create a machine model (ML-model). It will make forecasts of the values of the design characteristics for the low-orbit spacecraft being developed according to a limited set of initial requirements.

Initial Orbit Determination from Only Heading Measurements

This work introduces the problem of initial orbit determination (IOD) from only heading measurements. Such a problem occurs in practice when estimating the orbit of a spacecraft using visual odometry measurements from an optical camera. After reviewing the problem geometry, a simple solution is developed in the form of an iterative scheme on the parameters describing the orbital hodograph. Numerical results are presented for an example spacecraft in low lunar orbit. The principal intent of this brief study is to communicate the existence of a new class of IOD problem to the community and to encourage the broader study of hodographs and heading-only IOD.

Исследования радиационной стойкости гетероструктурных кремниевых солнечных элементов

The radiation resistance of different types of heterostructural silicon solar cells under irradiation with 1 MeV electrons in the fluence range 2.5•1014 - 1•1015 cm-2 has been studied. Studies have shown that the smallest degradation of the“saturation” currents of the diffusion current flow mechanism from J0d ≤ 5 10-13 to J0d ≤ 3 10-12 A/cm2 and efficiency from 19.2 to 13.6% (AM0, 1367W/m2) were n-α-Si:H/c-p(Ga)/p-α-Si:H and n-µc-Si:H/c-p(Ga)/p-α-Si:H. The results obtained make it possible to evaluate the prospects for the use of heterostructure silicon solar cells for low-orbit spacecraft.

Satellite Attitude Identification and Prediction Based on Neural Network Compensation

This paper proposed a new attitude determination method for low-orbit spacecraft. The attitude prediction accuracy is greatly improved by adding the unmodeled environmental torque to the dynamic equation. Specifically, the environmental torque extraction algorithm based on extended Kalman filter and series extended state observer is introduced, and the unmodeled part of dynamic is identified through the inverse dynamic model. Then, the collected data are analyzed and trained by a backpropagation neural network, resulting in an attitude-torque mapping network with compensation ability. The simulation results show that the proposed feedback attitude prediction algorithm can outperform standard methods and provide a high accurate picture of prediction and reliability with discontinuous measurement.

Оптимізація перельотів між низькими орбітами з суттєвою різницею довгот висхідних вузлів

At present, satellite systems, each comprising hundreds of satellites, are, and are to be, deployed in low orbits. In addition, existing satellite systems are replenished. There has appeared a trend towards the development of modular satellites, which will lead to the development of easy-to-maintain spacecraft consisting of many small structural modules with standardized interface mechanisms. To extend the life of all these systems and reduce their maintenance cost, it is advisable to develop a system for their maintenance. Despite the relatively large number of works on the rendezvous problem, this problem is considered in a somewhat simplified formulation, which is not sufficient for spacecraft servicing in low orbits. As a rule, the consideration is limited to coplanar rendezvous problems in an impulse formulation. In real conditions, rendezvous maneuvers in low orbits are nontrivial. As is known, the orbital parameters of low-orbit spacecraft may differ significantly: the difference in the longitude of ascending nodes (LAN) may reach tens and even hundreds of degrees. Because of this, the energy consumption for an orbital plane change becomes unacceptably high for modern service spacecraft. This energy consumption can be reduced by using the precession of the line of nodes due to the non-centrality of the Earth's gravitational field. A waiting maneuver of a service spacecraft in a well-chosen orbit makes it possible to eliminate the mismatch between the LANs of the service spacecraft’s parking and destination orbits, thus significantly reducing the orbital transfer energy consumption. However, the long wait time of the service spacecraft in its parking orbit significantly increases the total orbital transfer time. The aim of this article is to develop a mathematical model of bicriteria optimization of a transfer of a service spacecraft with a low constant thrust engine between low near-circular orbits with significantly different LANs. This problem is solved by averaging the service spacecraft’s dynamics equations over a fast parameter and using a genetic algorithm of global Pareto optimization. The novelty of the results obtained lies in a formulation of a bicriteria optimization problem and the development of a mathematical model for choosing an optimal service spacecraft parking orbit. The mathematical model developed may be used in planning service spacecraft transfers between low near-circular orbits with significantly different LANs.

Сучасні низькоорбітальні угруповання космічних апаратів дистанційного зондування землі з використанням радарів із синтезованою апертурою

The purpose of this work is to determine the current trends in the development of low-orbit constellations of spacecraft with synthetic aperture radar (SAR), which have a number of significant advantages in Earth remote sensing. It is shown that the demand for Earth remote sensing data and products and services based thereon continues to grow worldwide. The applicability of SAR to Earth remote sensing is considered. The main differences and advantages of image acquisition using SAR spacecraft in comparison with optical spacecraft are shown. The main directions of using low-orbit SAR spacecraft in Earth remote sensing are identified. Land and water surface observation using SAR spacecraft is shown to be one of the most effective remote sensing methods. In particular, it is shown that low-orbit spacecraft constellations can be used to advantage in solving many tasks in the socio-economic sector and tasks aimed at continuous real-time monitoring of various objects. The characteristics of the various Earth remote sensing spacecraft constellations, in particular low-orbit commercial ones, launched into orbit during the past decade are considered. Problems in and prospects for the development of low-orbit SAR spacecraft constellations are elucidated. Existing and planned SAR spacecraft constellations with traditional and mini-satellite platform technologies are overviewed. It is shown that the performance characteristics continue to improve, thus allowing one to get data from any area of the Earth at any time. It is shown that small spacecraft in low and ultralow orbits have significant benefits over traditional spacecraft in power characteristics, but are outperformed by them in the duration of communication sessions and active life. The results obtained make it possible to work out recommendations on the designing of low-orbit constellations of domestic Earth remote sensing spacecraft, in particular on the development of orbit determination models and algorithms and spacecraft dynamics models.

Глобальность радиовидимости низкоорбитальных космических аппаратов

Design optimization of the orbital and target groups of spacecrafts, ground-based control facilities and reception of target information is impossible without taking into account the global visibility of the spacecraft by ground-based means. The estimation of this parameter is traditionally performed using numerical methods for calculating spacecraft flight paths over long time intervals and does not allow us to visualize the relationship between the trajectory parameters and the effectiveness of the systems. The article considers several variants of analytical methods for calculating the global visibility, which allows us to evaluate the capabilities of operational control of the spacecraft and to obtain target information, the load of ground-based means, the volume of transmitted (received) information and the effectiveness of systems. The conclusion of the ratios for calculating the globality coefficient, graphs of its changes for low-orbit spacecraft, and an estimate of the accuracy of the obtained ratios are given. The graphs of global visibility make it easy to determine the optimal characteristics of the space-time structures of the created systems at the initial stage of design. Estimates of the accuracy of the results were obtained using «accurate» spacecraft flight models and confirm the recommendations for the practical application of the research results. The results obtained are of practical interest in the design of any space spacecraft systems in circular orbits.

Analysis of orbit error effect on ultra-high space-ground two-way time comparison

In view of the characteristics of the low-orbit spacecraft's orbit, the influence of the low-orbit spacecraft's orbit error on the time comparison method based on tri-frequency is theoretically analyzed. With the simulation and test, validing the effectiveness of the precise two-way time comparison method, and the accuracy of the method can reach the order of ps-level. Furthermore, with the simulated data, the influence of orbit error on the ultra-high precise space-ground time comparison is analyzed. The results show that the percentage of orbit noise in the total orbit error has a great influence on the accuracy of time comparison. In order to achieve a link accuracy better than ps, the percentage of orbit noise should be kept within 5%.

Influence of space vehicle remote power supply on thermal regimes of solar batteries

The issues of ensuring the functioning of an additional energy-receiving channel for the onboard power supply system of a low-orbit spacecraft are considered. To compensate for the shortage of electricity on board the spacecraft, various options for remote power supply from the system of space power stations transmitting energy to the solar battery by laser radiation during periods of its forced inactivity are possible. Long shadow-sunlight periods of time are a distinctive feature of functioning of low-orbit spacecraft. During these periods the solar battery is idle, and, in addition, even in the daylight portion of the spacecraft's orbit, the energy output from the spacecraft may be reduced to almost zero during the operation of some special systems that require special modes of spacecraft orientation. Reception of energy from a CES with energy flux density higher than that of the solar flux may lead to overheating of the solar battery panel of conventional design, a decrease in its efficiency and even to its failure. Therefore, the analysis of thermal modes of reception and conversion of laser radiation energy which affect the energy efficiency of the solar battery is an important aspect of remote power supply. Relationships of a mathematical model for estimating the available power supply from the solar battery operating in the mode of optimizing control of its power are proposed. The results of approbation of the model for maintaining the safe thermal mode of the solar battery panels during remote power supply of the spacecraft are presented.

Determination of the orientation of the artificial Earth satellite in the case of diffusive scattering of light by its surface

The paper considers the basics of the developed method for determining the orientation of low-orbit and geosynchronous spacecraft based on the results of observations of diffuse light scattering by their surfaces. This scattering can be described by phase functions that depend on the shape of the scattering surface, its orientation relative to the directions to the radiation source, and the receiver. Determining the orientation of the irradiated object in the selected coordinate system is one of the cases of solving the inverse problem. The surfaces of the spacecraft are a superposition of several stereometric surfaces that simultaneously scatter light onto the observer, but are differently oriented towards him, which greatly complicates the solution. The application of the developed method was carried out using the data of colorimetric observations of the American meteorological artificial satellite "NOAA-18", which has a cylindrical shape with two flat solar panels.

A New Space-to-Ground Microwave-Based Two-Way Time Synchronization Method for Next-Generation Space Atomic Clocks

The accuracy of time synchronization can be significantly increased by enhancing the performance of atomic clocks. Future-generation time-frequency loads will be equipped with the latest ultrahigh-precision atomic clocks (with a day stability better than 10−17) and will leverage advantages of the space environment such as microgravity and low interference to operate a new generation of high-performance time-frequency payloads on low-orbit spacecraft. Moreover, using the high-precision time-frequency system of ground stations, low-time-delay high-performance time-frequency transmission networks, which have the potential to achieve ultrahigh-precision time synchronization, will be constructed. By considering full link error terms above the picosecond level, this paper proposes a new space-to-ground microwave two-way time synchronization method for scenarios involving low-orbit spacecraft and ground stations. Using the theoretical principles and practical application scenarios related to this method, a theoretical and simulation verification platform was developed to research the impact of the attitude, phase center calibration, and orbit determination errors on the single-frequency two-way time synchronization method. The effectiveness of this new method was verified. The results showed that when the attitude error is less than 72 arc seconds (0.02°), the phase center calibration error is less than 1 mm, and the precision orbit determination (POD) error is less than 10 cm (three-axis). After disregarding nonlink error terms such as equipment noise, this method can attain a space-to-ground time synchronization accuracy of better than 1.5 ps, and the time deviation (TDEV) of the transfer link is better than 0.7 ps @ 100 s, which results in ultrahigh-precision space-to-ground time synchronization.

Определение статистических параметров флуктуаций коэффициента преломления ионосферы по данным радиолинии передачи информации космос-Земля

The study considers the problem of restoring the covariance function of fluctuations in the refractive index of the ionosphere based on the analysis of random changes in the frequency of the radio signal. To solve the problem, a trans-ionospheric signal of an information transmission radio line is used, radiated from a low-orbit spacecraft and received at a stationary receiving point. A method for estimating ionospheric parameters based on data from one typical communication session is described. To conduct a full-scale experiment, the signal emitted by the P-band radio transmitter of the on-board monitoring and control system of the Aist-2D spacecraft is used during a typical communication session. To receive the signal, ground-based equipment of a bistatic radar complex with a synthesized aperture of the P frequency band is used

Determination of statistical parameters of fluctuations in the refractive index of the ionosphere according to the data of the space-earth information transmission radio line

The study considers the problem of restoring the covariance function of fluctuations in the refractive index of the ionosphere based on the analysis of random changes in the frequency of the radio signal. To solve the problem, a trans-ionospheric signal of an information transmission radio line is used, radiated from a low-orbit spacecraft and received at a stationary receiving point. A method for estimating ionospheric parameters based on data from one typical communication session is described. To conduct a full-scale experiment, the signal emitted by the P-band radio transmitter of the on-board monitoring and control system of the Aist-2D spacecraft is used during a typical communication session. To receive the signal, ground-based equipment of a bistatic radar complex with a synthesized aperture of the P frequency band is used. Keywords: the ionosphere, fluctuations in the refractive index, the radio line of information transmission from the spacecraft, the scale of inhomogeneities and the dispersion of the electron density of the ionosphere.

An analysis of X-ray pulsar navigation accuracy in Earth orbit applications

At present, studies on X-ray signal processing and the navigation filtering algorithm in X-ray pulsar navigation are largely independent; thus, navigation accuracy analysis must be based on the analysis of a sound and complete navigation system. In this study, a navigation system simulation initiated from the numerical generation of the observed signals to navigation filtering solutions was established on the basis of the requirements of the authenticity and integrity of a demonstration of Earth-orbit spacecraft navigation. The influences of the navigation observation time, time delay estimation algorithms, and different pulsar combinations imposed on navigation accuracy were therefore analyzed. The simulation results showed that an optimal observation time existed with the highest navigation accuracy in Earth-orbit applications when three pulsars were observed in parallel, thereby obtaining the optimal observation time and its corresponding navigation accuracy. Using the short time high-accuracy algorithm of time delay estimation, the navigation accuracy of low-orbit spacecraft was greatly improved by 1010 m when the observation time was 60 s. Among three combinations of pulsars analyzed in this study, the pulsar combination of PSR B0531+21, PSR B1821-24, and PSR B1937+21 achieved the highest navigation accuracy on a low orbit, whose result was 560 m. The corresponding simulation results were based on a complete and near-real navigation algorithm, thereby offering a theoretical foundation for determining the navigation accuracy and selecting the orbit and observation time parameters in Earth-orbit pulsar navigation applications.

Relativistic Effects on Satellite–Ground Two–Way Precise Time Synchronization

An ultrahigh precise clock (space optical clock) will be installed onboard a low-orbit spacecraft (a usual expression for a low-orbit satellite operating on an orbit at an altitude of less than 1000 km) in the future, which will be expected to obtain better time-frequency performance in a microgravity environment, and provide the possible realization of ultrahigh precise long-range time synchronization. The advancement of the microwave two-way time synchronization method can offer an effective solution for developing time-frequency transfer technology. In this study, we focus on a method of precise satellite-ground two-way time synchronization and present their key aspects. For reducing the relativistic effects on two-way precise time synchronization, we propose a high-precision correction method. We show the results of tests using simulated data with fully realistic effects such as atmospheric delays, orbit errors, and earth gravity, and demonstrate the satisfactory performance of the methods. The accuracy of the relativistic error correction method is investigated in terms of the spacecraft attitude error, phase center calibration error (the residual error after calibrating phase center offset), and precise orbit determination (POD) error. The results show that the phase center calibration error and POD error contribute greatly to the residual of relativistic correction, at approximately 0.1~0.3 ps, and time synchronization accuracy better than 0.6 ps can be achieved with our proposed methods. In conclusion, the relativistic error correction method is effective, and the satellite-ground two-way precise time synchronization method yields more accurate results. The results of Beidou two-way time synchronization system can only achieve sub-ns accuracy, while the final accuracy obtained by the methods in this paper can improved to ps-level.

Исследование двухсторонних кремниевых солнечных элементов и модулей

The first description of the photoelectric effect in a vertical p-n transition in a silicon crystal dates back to 1941. The development of solar photovoltaic energy began in 1954 after the development of a single-sided planar silicon solar cell in the USA, in which the p-n junction is located parallel to the working illuminated surface. (Research purpose) The research purpose is in conducting an analytical review of the designs and electrophysical characteristics of double-sided solar cells and modules, justifying the leading role of Soviet and Russian scientists in its creation and assessing the prospects for the use of double-sided solar cells and modules in solar photovoltaic energy. (Materials and methods) The first double-sided planar solar cells made of silicon were developed in the USSR in 1969-1970 and were widely used for power supply of low-orbit spacecraft; the first double-sided matrix solar cells with a vertical p-n transition made of silicon were created in the USSR in 1967-1970 and were first used at the Venera-7 interplanetary station in 1970. (Results and discussion) As a result of studies of various types of double-sided matrix solar cells, the following limiting characteristics were obtained: voltage density is 100 volts per square centimeter; linear dependence of the current in the illumination range is up to 10 kilowatts per square centimeter; voltage of one module is of 1000 volts; efficiency at illumination of 10 kilowatts per square meter is of 25 percent; efficiency at monochromatic illumination of 950-1060 nanometers is of 36-42 percent; the maximum voltage of the solar battery is of 32 kilovolts. A global solar power system consisting of three solar power plants measuring 200 by 200 kilometers from double-sided solar modules installed in Australia, Africa and Latin America, and connected by an electric transmission line, will provide year-round and round-the-clock energy supply to the Earth in the amount of 26,000 terawatt-hours per year under the program of transition to carbon-free energy. (Conclusions) During the analysis of the design, manufacturing technologies and characteristics of silicon solar cells with one and two working surfaces, it was revealed that double-sided solar cells have the greatest prospects for development in the solar energy industry.

Multidimensional spatial transformation of streaming video in satellite communication channels

The problem of compression of high-resolution streaming video for transmission over low-speed satellite communication channels of small spacecraft is considered. It has been determined that the specificity of using small spacecraft in low orbits, on the one hand, imposes a number of restrictions on weight and size characteristics and energy consumption, on the other hand, it opens up new opportunities for obtaining high-resolution visual information. Approaches to real-time video data compression are considered, which make it possible to implement a subminiature encoder in the “system-onchip” basis. A coding method based on the complex principles of AV1 coding and multidimensional spatial transformation is proposed. The practical attainability of the developed method and algorithms is shown. The ways of developing the method and creating a video data compression system are proposed.

Global registration by optical radiation of lightning discharges on aboard a low-orbit spacecraft

Registration of the coordinates of lightning by their optical radiation has already been implemented on geostationary spacecraft in the wavelength range of 777.4 nm. However, the algorithms for processing the registered signals, as well as the volumes of information flows, have not yet been sufficiently studied. The choice of the sensor for the global registration of optical radiation of lightning on board a low-orbit spacecraft is substantiated. The prospects of using photodiodes in the difference-ranging method for determining coordinates are shown.The characteristics of lightning detection using matrices and LEDs have been studied. The prospects of using photodiodes in the differential-range-finding method for determining coordinates are shown. It is shown that the registration of optical lightning radiation on board the spacecraft by photodiodes provides the characteristics of detection and false alarms of a higher quality compared with the use of CCD matrices.

Effect of secondary electrons on SGEMP response

It is difficult to effectively shield the system generated electromagnetic pulse (SGEMP), which can significantly affect the performance of important electronic devices and infrastructure, such as low-orbit spacecraft. Numerical simulation is an essential way to study the SGEMP response. However, many previous studies ignored or simplified the effect of secondary electron emission in their models. In this paper, a three-dimensional electromagnetic particle-in-cell numerical simulation model is developed to evaluate the effect of secondary electrons on the SGEMP response of two typical structures (external SGEMP and cavity SGEMP, respectively) under different current densities (0.1–100 A/cm<sup>2</sup>) and different materials (Al, Cu and Au). A right cylinder or cylindrical cavity with a length of 100 mm is used. The photoelectrons produced by the interaction between the X-ray photon and metal are emitted from one end of the system and assumed to be monoenergetic. The photoelectron pulse follows a sine-squared distribution, and its full width at half maximum is 1 ns. Some important parameters of secondary electrons are discussed and summarized, including the emission coefficients of elastically and inelastically backscattered electrons, as well as the probability density functions of emission angles and energies. The results show that ignoring the secondary emission in the simulation model leads the peak electric field to be underestimated by twice-thrice, and the duration of electric field response by more than 10%. The oscillation frequency and the amplitude of the second peak of the tangential magnetic field are also increased, with the secondary electrons considered. Among various types of secondary electrons, backscattered electrons have a dominant effect on the change of SGEMP. The effect of true secondary electrons is about 1/5 of that of backscattered electrons. The effect of secondary electrons on SGEMP response increases with a higher atomic number of the material used in the system, mainly due to higher backscattering emission coefficient and a high ratio of high energy inelastically backscattered electrons. The secondary electrons will influence the response of the external SGEMP only when the space charge effect is strong (high X-ray fluence). While the response of the cavity SGEMP is more easily affected by the secondary electrons even at a relatively low X-ray fluence. This paper helps to better obtain the SGEMP response of a specific device under strong radiation through numerical simulation.

Разработка алгоритма приема и декодирования входного сигнала с применением МПД декодера для абонентских терминалов, работающих с низкоорбитальными космическими аппаратами

The relevance of the topic is determined by the need to increase the speed of data transmission in satellite telecommunication systems through the use of noise-proof coding. The speed of data transmission in a radio channel is actually determined by the level of interference present due to the fact that the radio transmission medium is a public environment and other electronic devices operate in it. The purpose of the article is to develop an algorithm for encoding and decoding the input signal using a multithreshold decoder (MTD) of rigid solutions for subscriber terminals operating with low-orbit spacecraft (NCA), and its comparison with a conventional PC decoder «Messi». The comparison allows us to conclude that the application of the developed algorithm is justified in systems where more stringent requirements are imposed on the probability of an error in the communication channel, while the «Messi» decoder is more appropriate to use in the presence of restrictions on computational complexity