• The Bulletin of The Korean Astronomical Society
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• v.39 no.2
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• pp.110.1-110.1
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• 2014

The optics of Space telescope is one of the major parts of space mission used for imaging observation of astronomical targets and the Earth. These kinds of space mission have a bulky and complex opto-mechanics with a long optical tube, but there are attempts have been made to observe a target with a small satellite in many ways. In this paper, we describe an optical design of a reflecting telescope for use in a CubeSat mission. For this design, we adopt the off-axis segmented method of astronomical observation techniques based on the Ritchey-Chr$\acute{e}$tien type telescope. The primary mirror shape is a rectangle with dimensions of $8cm{\times}8cm$, and a secondary mirror has dimensions of $2.4cm{\times}4.1cm$. The focal ratio is 3 which can obtain a $0.3{\times}0.2$ degree diagonal angle in a $1280{\times}800$ CMOS color image sensor with a pixel size of $3{\mu}m{\times}3{\mu}m$. This optical design can capture a ${\sim}4km{\times}{\sim}2.3km$ area of the earth's surface at 700 km altitude operation. Based on this conceptual design, we will keep trying to study more for astronomical observation with Attitude control system.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2008.11a
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• pp.105-108
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• 2008

Nowadays, as there is so much interest in environment, hydrogen peroxide attracts attention as an eco-propellant. Hydrogen peroxide is widely used for mono-propellant of thruster, and oxidizer of bi-propellant rocket. Especially, it is used as mono-propellant of the thruster for attitude control of satellite and military weapons. So, the need of long time storage of hydrogen peroxide appears and storage test is required. In this paper, necessity of storage test of hydrogen peroxide and some conditions and methods are introduced. In addition, the results of storage tests under some condition are compared and analyzed.

• Journal of the Korean Society of Propulsion Engineers
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• v.22 no.1
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• pp.98-106
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• 2018

With the advancement in technology, miniaturization, integration, and weight reduction of satellite components have become possible. In this regard, existing medium and large satellites have been replaced by small satellites. As the demand for small satellites increases, the need for micro-thrusters has emerged for precise attitude and position control. A laser ablation micro-thruster, which generates thrust by using ablation jets that offer a wide range of thrusts and low-impulse thrusts, is considered as an alternative for micro-thrusters in small satellites. The objective of the present study is to introduce configurations of the laser ablation micro-thruster and its research trend.

• International Journal of Control, Automation, and Systems
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• v.5 no.4
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• pp.388-396
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• 2007

This paper describes a multipath estimation method for Global Positioning System (GPS) dual frequency carrier phase measurements. Multipath is a major error source in high precision GPS applications, i.e., carrier phase measurements for precise positioning and attitude determinations. In order to estimate and remove multipath at carrier phase measurements, an array GPS antenna system has been used. The known geometry between the antennas is used to estimate multipath parameters. Dual frequency carrier phase measurements increase the redundancy of measurements, so it can reduce the number of antennas. The unscented Kalman filter (UKF) is recently applied to many areas to overcome some of the limitations of the extended Kalman filter (EKF) such as weakness to severe nonlinearity. This paper uses the UKF for estimating multipath parameters. A series of simulations were performed with GPS antenna arrays located on a straight line with one reflector. The geometry information of the antenna array reduces the number of estimated multipath parameters from four to three. Both the EKF and the UKF are used as estimation algorithms and the results of the EKF and the UKF are compared. When the initial parameters are far from true parameters, the UKF shows better performance than the EKF.

• Journal of Advanced Navigation Technology
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• v.8 no.1
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• pp.49-57
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• 2004

In This paper the embedded linux based embedded control system was used and the tracking antenna system was studied for data link and communication between moving vehicles. A microprocessor based embedded controller is equipped with SA-1110 board and this embedded controller can control the azimuth and the elevation angle of the antenna. The relative position and attitude for pointing are calculated by using the GPS position signals from the moving vehicle. To verify the performance of the designed embedded antenna system, the orbit information of the Arirang satellite(from KARI) is used.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.45 no.4
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• pp.300-309
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• 2017

A spacecraft obtains a reaction momentum required for an orbit correction and an attitude control by exhausting a combustion gas through a small thruster in space. If the exhaust plume collides with spacecraft surfaces, it is very important to predict the exhaust plume behavior of the thruster when designing a satellite, because a generated disturbance force/torque, a heat load and a surface contamination can yield a life shortening and a reduction of the spacecraft function. The purpose of the present study is to ensure the core technology required for the spacecraft design by analyzing numerically the exhaust gas behavior of the 10 N class bipropellant thruster for an attitude control of the spacecraft. To do this, calculation results of chemical equilibrium reaction between a MMH for fuel and a NTO for oxidizer, and continuum region of the nozzle inside are implemented as inlet conditions of the DSMC method for the exhaust plume analysis. From these results, it is possible to predict a nonequilibrium expansion such as a species separation and a backflow in the vicinity of the bipropellant thruster nozzle.

• Journal of the Korean earth science society
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• v.43 no.2
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• pp.239-252
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• 2022

Quality control methods for the first G-band vapor radiometer (GVR) mounted on a weather aircraft in Korea were developed using the GVR Precipitable Water Vapor (PWV). The aircraft attitude information (degree of pitch and roll) was applied to quality control to select the shortest vertical path of the GVR beam. In addition, quality control was applied to remove a GVR PWV ≥20 mm. It was found that the difference between the warm load average power and sky load average power converged to near 0 when the GVR PWV increased to 20 mm or higher. This could be due to the high brightness temperature of the substratus and mesoclouds, which was confirmed by the Communication, Ocean and Meteorological Satellite (COMS) data (cloud type, cloud top height, and cloud amount), cloud combination probe (CCP), and precipitation imaging probe (PIP). The GVR PWV before and after the application of quality control on a cloudy day was quantitatively compared with that of a local data assimilation and prediction system (LDAPS). The Root Mean Square Difference (RMSD) decreased from 2.9 to 1.8 mm and the RMSD with Korea Local Analysis and Precipitation System (KLAPS) decreased from 5.4 to 4.3 mm, showing improved accuracy. In addition, the quality control effectiveness of GVR PWV suggested in this study was verified through comparison with the COMS PWV by using the GVR PWV applied with quality control and the dropsonde PWV.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.44 no.8
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• pp.695-701
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• 2016

Spacecraft propulsion system is a kind of rocket engine that has been developed from the end of 1950s for attitude control and orbit maintenance of satellite. Since the spacecraft propulsion system has to be used for a relatively long time, therefore, stability of propellant and life of thruster could be very important factor for propulsion system design. Recently, green propellant propulsion and all electrical propulsion system have became very important issue, and we also need a development according to well organized plan. In this paper, we will introduce the development status, key technologies and development prospect of spacecraft propulsion system.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.31 no.5
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• pp.117-123
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• 2003

One of the most important elements in satellite attitude control is sensor technology. Generally, inertial sensors introduce drift and noise which cause continuous errors. Absolute reference is needed to eliminate the problem of the inertial sensors. Star trackers are used primarily for such a purpose. There has been relatively less research effort or ground feasibility test experience on star trackers in the domestic side despite the importance of the associated technologies. In this paper, we re-introduce the basic concept of a star tracker and present the S/W simulator for the star tracker. The star simulator may be used ground test of a star tracker for the basic functioning test or the whole spacecraft test with the star tracker assembled.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.31 no.1
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• pp.113-119
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• 2003

During the mission operation time, it is very important to estimate the spacecraft propellant remaining as accurately as possible. This is because the quantity of propellant is related directly to how long the satellite can be operated ín orbit. There are two different methods for spacecraft propellant gauging; the PVT method and the book-keeping method. This paper describes the characteristics and applications of these methods using the flight operation data of KOMPSAT-1. Additionally, propellant consumption rates in delta-V maneuvering and each attitude control submode are analyzed according to spacecraft operation modes. The earth search submode shows the highest propellant consumption rate.