• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.38C no.12
• /
• pp.1159-1169
• /
• 2013

EQM Model Digital transponder applying the Korean's own designing and manufacturing technology has gone through a series of trials and errors during the development. In particular, lack of thermal designs expedience for the vacuum causes variety of errors in designing, assembling transponder and setting up the test at the first thermal vacuum test (TVAC). Since the first TVAC test could not accomplished its aims successfully, so the second TVAC should be performed as make up test with revised Digital transponder. In this paper, the defects that identified in the first TVAC are analyzed and applied solutions and its results at the second TVAC are presented. Using the lessons from the first and second TVAC, we will be able to make more reliable digital transponders in the next phase of project. In addition it also be useful as a reference when we design another satellite payloads.

• Korean Journal of Optics and Photonics
• /
• v.13 no.1
• /
• pp.1-8
• /
• 2002

Optical payloads for earth-observation satellites become bigger as the required resolution becomes finer. For example, the diameter of the primary mirror of IKONOS, which has ground sampling distances of 1m/4m in panchromatic/multi spectral bands, is about 700mm. As the size of optical payload becomes bigger, the light-weighting of the mirrors becomes more significant. This paper presents the FEM results of the following four mirror types of 300 m diameter under gravity release and temperature changes: flat back mirror, single arch mirror, double arch mirror, and honeycomb sandwich mirror. Furthermore, this paper extends the FEM results to larger mirrors up to the diameter of 1m based on a general scaling law and Valenete\`s equation.

• Journal of the Korean Society for Aeronautical & Space Sciences
• /
• v.33 no.5
• /
• pp.34-40
• /
• 2005

Most analyses and researches on Micro Aerial Vehicle(MAV) have focused upon propulsion, automatic control, aerodynamic configuration in low Reynolds number region, and miniaturization of telemetric parts. In the present study, a structural concept for MAV is designed by using the composite material suitable for light flight structures. In order to study the load path and stress state of the MAV, the load and structural analyses are simultaneously performed by the aeroelasticity module of MSC/NASTRAN. The stability derivatives of the MAV are obtained for three symmetric, two antisymmetric, and four unsymmetric maneuvering conditions. Although the aerodynamic theory in MSC/NASTRAN could not be proper for MAV analysis, it provides an traditional and effective tool for trim and load analyses and may be corrected with the results by more accurate theory or test. The results show that the inertial load due to payloads has a more effect on stress rather than the aerodynamic load.

• Journal of the Korean Society for Aeronautical & Space Sciences
• /
• v.46 no.6
• /
• pp.519-526
• /
• 2018

In order to analyze space resources, it had to be brought to earth. However, using laser-induced breakdown spectroscopy(LIBS) and Raman spectroscopy, it is possible to analyze qualitative and quantitative analysis of space minerals in real time. LIBS is a spectroscopic method in which a high energy laser is concentrated on a material surface to generate a plasma, and the emitted light is acquired through a spectroscope to analyze the atomic composition. Raman spectroscopy is a spectroscopic method that analyzes the molecular structure by measuring scattered light. These two spectroscopic methods are complementary spectroscopic methods for analyzing the atoms and molecules of unknown minerals and have an advantage as space payloads. In this study, data were analyzed qualitatively by using principal component analysis(PCA). In addition, a mixture of two minerals was prepared and a quantitative analysis was performed to predict the concentration of the material.

• Korean Journal of Remote Sensing
• /
• v.33 no.5_1
• /
• pp.521-535
• /
• 2017

Since satellites, including payloads, are limited in how they can respond to problems after launch, the functionality of the satellite should be verified sufficiently by EGSE (Electrical Ground Support Equipment). In addition, considering the trend that the development period of the satellite is shortening and the development of the EGSE must precede the development of the engineering model of electronic equipment, early securing of EGSE is necessary to comply with the development schedule of the entire satellite. In this paper, we propose a method for early securing highly reliable EGSE by devising a scenario based operating payload packet analyzer, which is a part of the EGSE, through functional modularization and external parameterization, and show the result of applying the implemented payload packet analyzer to real satellite program.

• Proceedings of the KSRS Conference
• /
• 2005.10a
• /
• pp.87-90
• /
• 2005

The FORMOSAT-3/COSMIC mission is a micro satellite mission to deploy a constellation of six micro satellites at low Earth orbits. The final mission orbit is of an altitude of 750-800 lan. It is a collaborative Taiwan-USA science experiment. Each satellite consists of three science payloads in which the GPS occultation experiment (GOX) payload will collect the GPS signals for the studies of meteorology, climate, space weather, and geodesy. The GOX onboard FORMOSAT -3 is designed as a GPS receiver with 4 antennas. The fore and aft limb antennas are installed on the front and back sides, respectively, and as well as the two precise orbit determination (POD) antennas. The precise orbit information is needed for both the occultation inversion and geodetic research. However, the instrument associated errors, such as the antenna phase center offset and even the different cable delay due to the geometric configuration of fore- and aft-positions of the POD antennas produce error on the orbit. Thus, the focus of this study is to investigate the impact of POD antenna parameter on the determination of precise satellite orbit. Furthermore, the effect of the accuracy of the determined satellite orbit on the retrieved atmospheric and ionospheric parameters is also examined. The CHAMP data, the FORMOSAT-3 satellite and orbit parameters, the Bernese 5.0 software, and the occultation data processing system are used in this work. The results show that 8 cm error on the POD antenna phase center can result in ~8 cm bias on the determined orbit and subsequently cause 0.2 K deviation on the retrieved atmospheric temperature at altitudes above 10 lan.

• Bulletin of the Korean Space Science Society
• /
• 2011.04a
• /
• pp.24.4-24.4
• /
• 2011

Frozen orbit concept is very useful in designing particular mission orbits including the Sun-synchronous and minimum altitude variation orbits. In this work, variety of frozen and Sun-synchronous orbit conditions around the Moon is investigated and analyzed. The first two zonal harmonics of the Moon, J2 and J3, are considered to determine mean orbital elements to be a frozen orbit. To check the long-term behavior of a frozen orbit, formerly developed YonSei Precise Lunar Orbit Propagator (YSPLOP) is used. First, frozen orbit solutions without conditions to be the Sun-synchronous orbit is investigated. Various mean semi-major axes having between ranges from 1,788 km to 1,938 km with inclinations from 30 deg to 150 deg are considered. It is found that a polar orbit (90 deg of inclination) having 100 km of altitude requires the orbital eccentricity of about 0.01975 for a frozen orbit. Also, mean apolune and perilune altitudes for this case is about 136.301 km and 63.694 km, respectively. Second, frozen orbit solutions with additional condition to be the Sun-synchronous orbit is investigated. It is discovered that orbital inclinations are increased from 138.223 deg to 171.553 deg when mean altitude ranged from 50 km to 200 km. For the most usual mission altitude at the Moon (100 km), the Sun-synchronous orbit condition is satisfied with the eccentricity of 0.01124 and 145.235 deg of inclination. For this case, mean apolune and perilune altitudes are found to be about 120.677 km and 79.323 km, respectively. The results analyzed in this work could be useful to design a preliminary mapping orbit as well as to estimate basic on-board payloads' system requirements, for a future Korea's lunar orbiter mission. Other detailed perturbative effects should be considered in the further study, to analyze more accurate frozen orbit conditions at the Moon.

• Proceedings of the Korea Society of Information Technology Applications Conference
• /
• 2005.11a
• /
• pp.161-164
• /
• 2005

As the power of influence of the Internet grows steadily, attacks against the Internet can cause enormous monetary damages nowadays. A worm can not only replicate itself like a virus but also propagate itself across the Internet. So it infects vulnerable hosts in the Internet and then downgrades the overall performance of the Internet or makes the Internet not to work. To response this, worm detection and prevention technologies are developed. The worm detection technologies are classified into two categories, host based detection and network based detection. Host based detection methods are a method which checks the files that worms make, a method which checks the integrity of the file systems and so on. Network based detection methods are a misuse detection method which compares traffic payloads with worm signatures and anomaly detection methods which check inbound/outbound scan rates, ICMP host/port unreachable message rates, and TCP RST packet rates. However, single detection methods like the aforementioned can't response worms' attacks effectively because worms attack the Internet in the distributed fashion. In this paper, we propose a design of distributed worm detection system to overcome the inefficiency. Existing distributed network intrusion detection systems cooperate with each other only with their own information. Unlike this, in our proposed system, a worm detection system on a network in which worms select targets and a worm detection system on a network in which worms propagate themselves cooperate with each other with the direction-aware information in terms of worm's lifecycle. The direction-aware information includes the moving direction of worms and the service port attacked by worms. In this way, we can not only reduce false positive rate of the system but also prevent worms from propagating themselves across the Internet through dispersing the confirmed worm signature.

• Journal of the Korea Institute of Information Security & Cryptology
• /
• v.30 no.4
• /
• pp.669-677
• /
• 2020

As the number of Internet users exploded, attacks on the web increased. In addition, the attack patterns have been diversified to bypass existing defense techniques. Traditional web firewalls are difficult to detect attacks of unknown patterns.Therefore, the method of detecting abnormal behavior by artificial intelligence has been studied as an alternative. Specifically, attempts have been made to apply natural language processing techniques because the type of script or query being exploited consists of text. However, because there are many unknown words in scripts and queries, natural language processing requires a different approach. In this paper, we propose a new classification model which uses byte pair encoding (BPE) technology to learn the embedding vector, that is often used for web attack payloads, and uses an attention mechanism-based Bi-GRU neural network to extract a set of tokens that learn their order and importance. For major web attacks such as SQL injection, cross-site scripting, and command injection attacks, the accuracy of the proposed classification method is about 0.9990 and its accuracy outperforms the model suggested in the previous study.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.38 no.3
• /
• pp.289-294
• /
• 2014

Industrial manipulators are usually heavy given the payloads they carry. Therefore, they require high-capacity servomotors and speed reducers, which leads to high costs. However, if manipulator weight could be compensated for using a counterbalance mechanism, the motors' and speed reducers' capacities could be minimized substantially. However, it is usually difficult to assure durability and reliability with the conventional wire-based counterbalance mechanism. Therefore, a more robust gear- and roller-based counterbalance mechanism is proposed in this study. A manipulator was developed using this mechanism; this manipulator maintains its performance even when using motors and reducers of lower capacities. The results of various simulations and experiments verified that the proposed mechanism provides the torque required to compensate for gravitational torque in any configuration and minimizes the torque required for supporting a large payload.