• Journal of Advanced Navigation Technology
• /
• v.2 no.2
• /
• pp.100-106
• /
• 1998

The cone intercept method (CIM) is generally used for attitude determination of a spin-stabilized satellite. The method is popularly used on a transfer orbit, but it is well known that it can also be used for the geosychronous orbit. In this paper, the CIM is applied to the geosynchronous orbit and its performance and limitations will be investigated from the results. The CIM impliments two sensors (Sun and Earth sensors). The Sun sensor finds the angle between the spin-axis and the direction vector to the Sun and the Earth sensor does the angle between the spin-axis and the direction vector to the Earth. By using these two cone angles, the CIM gives the direction of the spin-axis of the satellite.

• Journal of Astronomy and Space Sciences
• /
• v.14 no.1
• /
• pp.136-141
• /
• 1997

To calculate the position and velocity of the artificial satellite precisely, one has to build a mathematical model concerning the perturbations by understanding and analysing the space environment correctly and then quantifying. Due to these space environment model, the total acceleration of the artificial satellite can be expressed as the 2nd order differential equation and we build an orbit propagation algorithm by integrating twice this equation by using the Cowell's method which gives the position and velocity of the artificial satellite at any given time. Perturbations important for the orbits of geostationary spacecraft are the Earth's gravitational potential, the gravitational influences of the sun and moon, and the solar radiation pressure. For precise orbit propagation in Cowell' method, 40 x 40 spherical harmonic coefficients can be applied and the JPL DE403 ephemeris files were used to generate the range from earth to sun and moon and 8th order Runge-Kutta single step method with variable step-size control is used to integrate the the orbit propagation equations.

• Journal of Astronomy and Space Sciences
• /
• v.14 no.2
• /
• pp.381-385
• /
• 1997

A long-term prediction algorithm of geostationary orbit was developed using the analytical method. The perturbation force models include geopotential upto fifth order and degree and luni-solar gravitation, and solar radiation pressure. All of the perturbation effects were analyzed by secular variations, short-period variations, and long-period variations for equinoctial elements such as the semi-major axis, eccentricity vector, inclination vector, and mean longitude of the satellite. Result of the analytical orbit propagator was compared with that of the cowell orbit propagator for the KOREASAT. The comparison indicated that the analytical solution could predict the semi-major axis with an accuracy of better than $pm35$ meters over a period of 3 month.

• Journal of computational fluids engineering
• /
• v.16 no.3
• /
• pp.59-65
• /
• 2011

COMS (Communication, Ocean and Meteorological Satellite) is a geostationary satellite and was developed by KARI for communication, ocean and meteorological observations. COMS was tested under vacuum and very low temperature conditions in order to correlate thermal model and to verify thermal design. The test was performed by using KARI large thermal vacuum chamber. The COMS S/C thermal model was successfully correlated versus the 2 thermal balance test phases. After model correlation, temperatures deviation of all individual units were less than $5^{\circ}C$ and global deviation and standard deviation also satisfied the requirements, less than $2^{\circ}C$ and $3^{\circ}C$. The final flight prediction was performed by using the correlated thermal model.

• Journal of Positioning, Navigation, and Timing
• /
• v.13 no.2
• /
• pp.199-206
• /
• 2024

The GEO-KOMPSAT-2A (GK2A) satellite, which was launched in December 2018, carries weather observation payloads and uses the image navigation and registration system to calibrate the observation images. The calibration system requires accurate orbit prediction data and depends on the accuracy of the orbit determination accuracy. In order to find a possible way to improve the current orbit determination accuracy of the GK2A flight dynamic subsystem module, orbit determination software was developed to independently evaluate the orbit determination accuracy. A comprehensive satellite dynamic model is applied for a batch-type least squares filter. When determining the orbit, thrust firing during station-keeping maneuvers and wheel-off loading maneuvers is taken into account. One month of GK2A ranging data were processed to estimate the satellite position on a daily basis. The orbit determination error was evaluated by comparing estimates during overlapping estimation intervals.

• Aerospace Engineering and Technology
• /
• v.9 no.2
• /
• pp.44-50
• /
• 2010

COMS accommodates multiple payloads; Meteorological Image(MI), Ocean Color Imager(GOCI) and Ka-band communication payloads. In order to improve the quality of MI visible channel, the moon image has been taken into account as backup reference in addition to Albedo monitoring. However, obtaining the moon image by adding special mission schedule is not recommended after IOT, because we may miss chances to obtain meteorological images during the time slots for special imaging. As an alternative solution, an approach extracting moon image from MI FD(Full Disk) image has been proposed when the moon is positioned near to the earth. However, prediction of acquisition time of moon image is somewhat difficult as the moon moves while the MI is scanning type sensor. And the moon can not be seen when it is behind the earth or outside of FD field of view. This paper discusses how effectively the moon can be detected by the MI FD imaging. For that purpose, this paper describes an approach taken to predict the time when the moon image is achievable and then introduces the results obtained from computer simulation.

• Journal of Satellite, Information and Communications
• /
• v.6 no.1
• /
• pp.37-44
• /
• 2011

COMS(Chollian) satellite which was launched on June 26, 2010 has three payloads for Ka-band communications, geostationary ocean color imaging and meteorological imaging. In order to make efficient use of the geostationary satellite, a concept of mission operations has been considered from the beginning of the satellite ground control system development. COMS satellite mission operations are classified by daily, weekly, monthly, and seasonal operations. Daily satellite operations include mission planning, command planning and transmission, telemetry processing and analysis, ranging and orbit determination, ephemeris and event prediction, and wheel off-loading set point parameter calculation. As a weekly operation, North-South station keeping maneuver and East-West station keeping maneuver should be performed on Tuesday and Thursday, respectively. Spacecraft oscillator updating parameter should be calculated and uploaded once a month. Eclipse operations should be performed during a vernal equinox and autumnal equinox season. In this paper, operational validations of the major functions in COMS SGCS are presented for the first three month of in-orbit test operations. All of the major functions have been successfully verified and the COMS SGCS will be used for the mission operations of the COMS satellite for 7 years of mission life time and even more.

• Journal of IKEEE
• /
• v.1 no.1 s.1
• /
• pp.120-137
• /
• 1997

Han's model, which is able to analyze optical communication between earth station and geo-satellite as a function of atmospheric conditions and elevation angles. is presented. In Han's model, atmospheric conditions are roughly classified into six basic types; clear sky, cloud, haze, fog, rain and snow. Data rate satisfying for the BER below $10^{-7}$ is analyzed by Han's model in case of up-link and down-link, respectively. Data rate is more limited by up-link than by down-link because the pointing loss caused by atmosphere on the up-link is greater than the spatial coherence degradation caused by atmosphere on the down-link.

• Journal of Satellite, Information and Communications
• /
• v.8 no.3
• /
• pp.41-46
• /
• 2013

In this paper, we present the compatibility study results including the frequency sharing criteria between new allocation to maritime mobile satellite service and Earth exploration satellite service in the 7/8 GHz. The transmitting Earths station of MMSS in the 8025 - 8400 MHz band would make harmful interference to the receiving Earth station of EESS operating in the same frequency band. In order to ensure the compatibility with EESS, the separation distance is provided as a frequency sharing criteria. The republic of Korea has a plan to launch the geostationary satellite around 2017 and EESS Earth station will be operated in 8025 - 8400 MHz band. Therefore, we calculate the interference levels and separation distance using the system parameters of two Earth station systems. As results of the study, the separation distances for LOS path and Non-LOS path due to the geographical characteristics are shown around 471 km and 200 km, respectively.

• Korean Journal of Remote Sensing
• /
• v.38 no.6_1
• /
• pp.1069-1080
• /
• 2022

The tropospheric ozone is a pollutant that causes a great deal of damage to humans and ecosystems worldwide. In the event that ozone moves downwind from its source, a localized problem becomes a regional and global problem. To enhance ozone monitoring efficiency, geostationary satellites with continuous diurnal observations have been developed. The objective of this study is to derive the Tropospheric Ozone Movement Vector (TOMV) by employing continuous observations of tropospheric ozone from geostationary satellites for the first time in the world. In the absence of Geostationary Environmental Monitoring Satellite (GEMS) tropospheric ozone observation data, the GEOS-Chem model calculated values were used as synthetic data. Comparing TOMV with GEOS-Chem, the TOMV algorithm overestimated wind speed, but it correctly calculated wind direction represented by pollution movement. The ozone influx can also be calculated using the calculated ozone movement speed and direction multiplied by the observed ozone concentration. As an alternative to a backward trajectory method, this approach will provide better forecasting and analysis by monitoring tropospheric ozone inflow characteristics on a continuous basis. However, if the boundary of the ozone distribution is unclear, motion detection may not be accurate. In spite of this, the TOMV method may prove useful for monitoring and forecasting pollution based on geostationary environmental satellites in the future.