• Journal of Astronomy and Space Sciences
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• v.24 no.4
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• pp.397-408
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• 2007

Diplexer is one of core devices needed to communicate with satellite using single ground antenna by separating uplink and downlink signal. This paper presents the design of the S-band diplexer for LEO TT&C application, especially for KOMPSAT (KOrea Multi-Purpose SATellite). To cope with requirements such as high handling power, low insertion loss, air-cavity resonator with high quality factor was considered as one of design drivers. Design was started with predicting unloaded Q and equivalent circuit from the structure of air-cavity resonator. For the convenience of adjustment, the coupling factor placed between resonators was estimated from COTSEM (Electro-Magnetic) simulator, EESOF $ADS^{TM}$, and expressed with 2-order polynomial regression. To improve the isolation between transmitting part (Tx) and receiving part (Rx), the inductive and capacitive attenuation poles were inserted between $4^{th}\;and\;6^{th}$ resonator respectively. The fabricated diplexer consists of two bandpass filters and each filter has eight resonants. From the measurement, it was shown that major requirements such as 0.5dB of insertion loss, 20dB of return loss and 100dB of isolation were fully satisfied within passband.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.40 no.4
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• pp.354-363
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• 2012

Now there are a lot of expired satellites or space debris around the earth orbit and they threaten the operating satellites and manned space missions. KOMPSAT-2 that scheduled to operate the mission by July, 2013 also has to consider the space debris. This paper introduces the '25 years rules' that must be re-entered within 25 years after the space mission for LEO satellites and describes the removal trajectory design that satisfies the '25 years rules' and minimizes fuel consumption. And this paper suggests monte-carlo simulation for risk analysis that causes the approaching object to the removal trajectory. The result shows that the collision probability of worst case presents 6.0741E-07 and it need to more analysis about precise satellite safety during removal maneuver because there is no information about the object size that approaching to the satellites.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2008.03a
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• pp.283-292
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• 2008

The foremost criterion in the design of a Satellite Launch Vehicle(SLV) is its performance capability to boost the designated payload to the desired mission orbit; it starts from focusing on the SLV configuration to achieve the velocity requirements($}\Delta}V$) for the mission. In this paper we review an analytical approach which is suitable enough for preliminary conceptual design and is used previously to optimize stage configurations for Two Stage to Orbit SLV for Low Earth Orbit(LEO) Missions; we have extended this approach to Three Stage to Orbit SLV and compared different propellant options for the mission. The objective is to minimize the Gross Lift off Weight(GLOW). The primary performance figures of merit were the total inert weight of the SLV and the payload weight that the SLV could lift into LEO, given candidate propulsion systems. The optimization is achieved by configuring the $}\Delta}V$ between stages. A comparison of configurations of single-stage and multi-stage SLVs is made for different propellants. Based upon the optimized stage configurations a comparative performance analysis is made between Liquid and Solid fueled SLV. A 3 degree of freedom trajectory-analysis program is modeled in SIMULINK and used to conduct the performance analysis. Furthermore, a cost analysis is performed on our stage optimized SLVs. The cost estimation relationships(CER) used give us a comparison of development and fabrication costs for the Liquid vs. Solid fueled SLV in man years. The pros and cons of the production, operation ability, performance, responsiveness, logistics, price, shelf life, storage etc of both Solid and Liquid fueled SLVs are discussed. The statistics and data are used from existing or historical(real) SLV stages.

• Journal of Satellite, Information and Communications
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• v.12 no.4
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• pp.67-71
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• 2017

A solar array is main electrical energy source for Low-Earth-Orbit(LEO) satellite. The solar array cannot generate electrical energy during eclipse period, a battery supply electrical energy to the satellite. The electrical power of the solar array is changed in accordance with operating voltage and the solar array has the maximum power point. The solar array regulator makes the solar array supply electrical energy to the satellite and charge the battery. The solar array is connected to the solar array regulator input and the battery is connected to the solar array regulator output. The solar array regulator consists 2 of 3 hot redundant. One solar array regulator contains 3 DC-DC converters, and the solar array regulator operates stably even if the failure occur in one DC-DC converter. In this paper, the solar array regulator, the battery and the solar array operation is analyzed when the failure occur in one DC-DC converter.

• Aerospace Engineering and Technology
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• v.6 no.2
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• pp.79-86
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• 2007

In order to operate Low Earth Orbit(LEO) satellite on space, technical requirements and administrative procedure which are defined by the International Telecommunication Union(ITU) should be followed on satellite development. Main technical requirements to follow are purpose of use, bandwidth, Radio Frequency(RF) intensity, and constraints on new satellite network about existing satellite networks according to frequency spectrum. Such ITU's requirements are reflected and designed on system specification and space to ground interface control document. In order to have a right and protection about using the satellite network on space, the satellite network has to be registered on Master International Frequency Register(MIFR) and procedure for this has to be followed. Coordination with countries raising objection is needed in order to register. And reference and method for coordination are also needed.

• Journal of Aerospace System Engineering
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• v.17 no.4
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• pp.58-66
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• 2023

The latest global issues are the Space economy and low-orbit Space communication. 3GPP announced Release 17 standardization in June 2022, and in this regard, the United States prepared a strategy to enhance the competitiveness of the low-orbit 5G-NTN Space industry, and create an ecosystem at the national level in March 2023. Global smartphone semiconductor manufacturers have announced the development and verification results of standard-based chip technology, and satellite communication operators are launching low-orbit 5G-NTN Space communication services and rate products through convergence between terrestrial communication networks. This study diagnoses the current status of Korea's low-orbit 5G-NTN space communication ecosystem. We present our ecosystem creation strategy in terms of fair competition in the market, the service legal system, and the national R&D governance system.

• Journal of Aerospace System Engineering
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• v.14 no.2
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• pp.50-56
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• 2020

In this study, we investigated whether long short-term memory (LSTM) can be used in the future to predict F10.7 index data; the F10.7 index is a space environment factor affecting atomic oxygen erosion. Based on this, we compared the prediction performances of LSTM, the Autoregressive integrated moving average (ARIMA) model (which is a traditional statistical prediction model), and the similar pattern searching method used for long-term prediction. The LSTM model yielded superior results compared to the other techniques in the prediction period starting from the max/min points, but presented inferior results in the prediction period including the inflection points. It was found that efficient learning was not achieved, owing to the lack of currently available learning data in the prediction period including the maximum points. To overcome this, we proposed a method to increase the size of the learning samples using the sunspot data and to upgrade the LSTM model.

• Aerospace Engineering and Technology
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• v.12 no.2
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• pp.91-98
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• 2013

Computing environment of space explorer including LEO (Low Earth Orbit), GEO (Geosynchronous Earth Orbit) satellite may be considered as the same category of embedded system on the ground. But with comparison with personal computing environment it is widely accepted that the space computing is outdated and behind of state of the art. Especially file system which is nearly essential item in all ground computing environment including personal computer, workstation and server is rarely used in space explorer till lately. In this paper, a study of ESA PUS (Packet Utilization Standard) and CCSDS (Consultative Committee for Space Data Systems) community's activity, international trend, and applicable technical application for applying file system in oder to use these standards for utilizing the file system to deep space explorer is described.

• Journal of Astronomy and Space Sciences
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• v.20 no.1
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• pp.1-10
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• 2003

A precise kinematic orbit determination (P-KOD) procedure for Low Earth Orbiter(LEO) using the GPS ion-free triple differenced carrier phases is presented. Because the triple differenced observables provide only relative information, the first epoch's positions of the orbit should be held fixed. Then, both forward and backward filtering was executed to mitigate the effect of biases of the first epoch's position. p-KOD utilizes the precise GPS orbits and ground stations data from International GPS Service (IGS) so that the only unknown parameters to be solved are positions of the satellite at each epoch. Currently, the 3-D accuracy off-KOD applied to CHAMP (CHAllenging Min-isatellite Payload) shows better than 35 cm compared to the published rapid scientific orbit (RSO) solution from GFZ (GeoForschungsZentrum Potsdam). The data screening for cycle slips is a particularly challenging procedure for LEO, which moves very fast in the middle of the ionospheric layer. It was found that data screening using SNR (signal to noise ratio) generates best results based on the residual analysis using RSO. It is expected that much better accuracy are achievable with refined prescreening procedure and optimized geometry of the satellites and ground stations.

• Aerospace Engineering and Technology
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• v.10 no.1
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• pp.141-148
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• 2011

LEO satellites have many heaters for thermal control, such as bus module heaters, payload heaters and battery internal heaters. Some of these heaters are controlled by thermisters, and others can be controlled by flight software. These heaters are divided into various types of group according to the location, telemetry variables, flight software logic, power distribution, etc. Thus, it is difficult to find out which heaters are included in a certain group and modify heater control logic for a new/other software developers. This document describes about the general/special control logic for satellite heaters and groups/arrays for heaters.