• IEMEK Journal of Embedded Systems and Applications
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• 제14권1호
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• pp.51-61
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• 2019

There are strict evaluation processes before using new processors to satellites. Engineers evaluate processors from various viewpoints including specification, development environment, and cost. From a viewpoint of computation power, manufacturers provide benchmark results with processors, and engineers decide which processors are adequate to their satellites by comparing the benchmark results with requirements of their satellites. However, the benchmark results depends on a test environment of manufacturers, and it is quite difficult to achieve similar performance in a target environment. Therefore, it is necessary to evaluate the processors in the target environment. This paper compares performance of a processor, AT697F/LEON2, in software testbed (STB) with three development boards of XC2V/LEON3, GR712RC/LEON3, and GR740/LEON4. Seven benchmark functions of Dhrystone, Stanford, Coremark, Whetstone, Flops, NBench, and MiBench are selected. Results are analyzed with hardware and software properties: hardware properties of core architecture, number of cores, cache, and memory; and software properties of build options and compilers. Based on the analysis, this paper describes a guideline for choosing processors for next generation satellites.

• Advances in aircraft and spacecraft science
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• 제9권4호
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• pp.279-300
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• 2022

This paper analyzes the possibilities of a new method to using TLE data for detecting satellite maneuvers. The method has a number of advantages over other methods that are designed to detect maneuvers. It allows not only to detect maneuvers, but also to get a more complete picture of the maneuver. In particular, the method makes it possible to estimate the moments of the beginning and end of the maneuver, calculate the changes in the orbital elements, evaluate the tangential and binormal components of the impulse, and finally, calculate the impulse of the satellite obtained as a result of the maneuver. To demonstrate in detail the capabilities of the algorithm, the proposed method was applied to one of LEO satellites - TIANHUI-1 satellite. After the efficiency of the method was proved, this method was applied to the China Space Station - TIANHE-1 (CSS), Starlink-1095 and Starlink-2305 satellites. The maneuvers of the CSS and Starlink-1095 satellite during their close encounter on 1 July, 2021, and the CSS and Starlink-2305 satellite during their close encounter on 21 October, 2021 are analyzed in detail. The minimum distances between the CSS and Starlink satellites at the moments of their maximum approaches are estimated. An estimate of the computation time of this algorithm is given, and the possibility of its use for monitoring maneuvers or other anomalous orbital changes of a large number of satellites in near real-time is shown. It is assumed that on the basis of this method, a service for monitoring satellite maneuvers can be created.

• Journal of Positioning, Navigation, and Timing
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• 제2권2호
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• pp.131-137
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• 2013

In this study, positioning results that combined the code observation information of GPS and GLONASS navigation satellites were analyzed. Especially, the distribution of GLONASS satellites observed in Korea and the combined GPS/GLONASS positioning results were presented. The GNSS data received at two reference stations (GRAS in Europe and KOHG in Goheung, Korea) during a day were processed, and the mean value and root mean square (RMS) value of the position error were calculated. The analysis results indicated that the combined GPS/GLONASS positioning did not show significantly improved performance compared to the GPS-only positioning. This could be due to the inter-system hardware bias for GPS/GLONASS receivers, the selection of transformation parameters between reference coordinate systems, the selection of a confidence level for error analysis, or the number of visible satellites at a specific time.

• Journal of Satellite, Information and Communications
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• 제12권3호
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• pp.93-97
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• 2017

In satellites, even a small error in flight software could cause a failure of missions. Therefore, there are strict development and verification processes for a high reliability of flight software. However, satellites on orbits could meet unexpected situations including hardware malfunction. In this case, it is necessary for flight software to be updated to cope with the unexpected situations and to continue their missions. This paper reviews reprogramming capability of next generation LEO satellites.

• International Journal of Aeronautical and Space Sciences
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• 제17권3호
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• pp.401-408
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• 2016

During daylight, the solar array of low earth orbit satellites harvests electrical power to operate satellites. The power conversion of the solar array is carried out by control of the operation point using the solar array regulator when the solar array faces the sunlight. Thus, the design of the solar array should comply with not only the power requirement of satellite system but also the input voltage requirement of the solar array regulator. In this paper, the design requirements of the solar array for low earth orbit satellites are defined, and the means of satisfying these requirements are described. In addition, the architecture of a multi-distributed interface is suggested to maximize the power harvested from a solar array having high temperature deviation between each panel. The power analysis in this paper shows the optimal number of multi-distributed interfaces with a converter.

• Journal of Positioning, Navigation, and Timing
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• 제5권3호
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• pp.145-156
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• 2016

A variety of methods for indoor positioning systems have been underway to ensure the safety of emergency rescuers who are working in dangerous situations such as fire fighters. However, since most systems display locations of rescue workers in two-dimension (2D)-based maps, it is difficult for a commander located in the outside to recognize locations of rescuers inside the building intuitively. An augmented reality (AR)-based indoor positioning monitoring system can display locations of rescuer inside the building that can be seen by commanders to help intuitive recognition of positioning. To monitor AR-based indoor positioning, it is necessary to have an estimation technique of line of sight vector of observers. In the present study, an estimation technique of a line of sight vector using ultra-wide band tranceiver installed inside the indoor to trace locations is presented.

• International Journal of Aeronautical and Space Sciences
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• 제7권1호
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• pp.84-90
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• 2006

The formation flying of satellites has been identified as an enabling technology for many future space missions. The application of conventional thrusters for formation flying usually results in high cost, limited life-time, and a large weight penalty. Various methods including the use of coulomb forces have been considered as an alternative to the conventional thrusters. In the present investigation, we investigate the feasibility of achieving the desired formation using Coulomb forces. This method has several advantages including low cost, light weight and no contamination. A simple controller based on the relative position and velocity errors between the leader and follower satellites is developed. The proposed controller is applied to circular formations considering the effects of disturbances in initial formation conditions as well as system nonlinearity. Results of the numerical simulation state that the proposed controller is successful in establishing circular formations of leader and follower satellites, for a formation size below 100 m.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 한국추진공학회 2017년도 제48회 춘계학술대회논문집
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• pp.753-756
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• 2017

With the advancement of technology, miniaturization, integration, and weight reduction have become possible, and the existing medium and large satellites have been replaced by small satellites, and the need for a micro thruster has emerged. Laser ablation micro-thruster is a new type thruster using laser ablation. It is emerging as a new candidate in micro-thrusters with wide thrust range and low single impulse thrust. The objective of present study is to introduces the structure, propellant, and research trends of the laser ablation micro-thruster.

• Journal of information and communication convergence engineering
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• 제19권3호
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• pp.131-135
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• 2021

The interference between closely placed co-coverage satellites was analyzed. In general, a satellite network may use different orthogonal polarizations and frequencies to increase the throughput of a satellite. However, when orthogonal linear polarization (horizontal polarization and vertical polarization) or orthogonal circular polarization (left-handed circular polarization and right-handed circular polarization) is used, the signal from one polarization sense to another may be coupled, resulting in cross-polarization interference. This signal-coupling arises due to the finite value of the cross-polarization discrimination of the earth station. In this study, field equations were used to analyze the interference between adjacent satellites using co-frequency. The level of interference was compared to that when two adjacent satellites used the same polarization. The simulation results show that the interference mainly depends on the off-axis co-polar pattern and the cross-polar pattern of the earth station antenna.

• The Journal of Korea Robotics Society
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• 제19권1호
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• pp.71-78
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• 2024

The paper presents a hardware-in-the-loop (HIL) system designed for satellite movement testing in the microgravity environment on the ground with two industrial robots. Especially, the paper deals with the contact between satellites during rendezvous and docking simulations of satellites using a robotic HILS system. For this purpose, the admittance control method plays a core role in preventing damage to the satellite or robot from contact force between satellites. The coordinate frames are transformed into the mass center of the satellite and the admittance control at the level of exponential coordinates is adopted to actively use the properties of Lie groups related to tracking errors. These methods effectively mitigate the risk of robot damage during inter-satellite contact and ensure efficient tracking performance of satellite movements.