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REFERENCE LINKING PLATFORM OF KOREA S&T JOURNALS
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Journal of Astronomy and Space Sciences
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Journal DOI :
The Korean Space Science Society
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Volume & Issues
Volume 25, Issue 4 - Dec 2008
Volume 25, Issue 3 - Sep 2008
Volume 25, Issue 2 - Jun 2008
Volume 25, Issue 1 - Mar 2008
Selecting the target year
Dust Envelopes around Massive Young Stellar Objects
Suh, Kyung-Won ;
Journal of Astronomy and Space Sciences, volume 25, issue 4, 2008, Pages 329~334
DOI : 10.5140/JASS.2008.25.4.329
We investigate the spectral energy distributions (SEDs) of Massive Young Stellar Objects (MYSOs) using the various infrared observational data including the Infrared Space Observatory (ISO) data. We model the dust envelopes around the stars using a radiative transfer model for spherically symmetric geometry. Comparing the model results with the observed SEDs of the two MYSOs (AFGL 4176 and AFGL 2591), we derive the relevant dust shell parameters including the dust opacity, the dust density distribution, and dust temperature distribution. We find that the spherical model can produce the SEDs roughly similar to the observations. We expect that the results would be helpful for making more realistic non-spherical dust envelope models for MYSOs.
Seasonal Characteristics of the Longitudinal Wavenumber-4 Structure in the Equatorial Ionospheric Anomaly
Kim, E. ; Jee, G. ; Kim, Y.H. ;
Journal of Astronomy and Space Sciences, volume 25, issue 4, 2008, Pages 335~346
DOI : 10.5140/JASS.2008.25.4.335
Using the global total electron contents (TEC) measured by the TOPEX satellite from Aug. 1992 to Oct. 2005, we investigate the variations of the longitudinal wavenumber-4 (LW-4) structure in the equatorial anomaly (EA) crests with season, local time, and solar activity. Our study shows that the LW-4 structure in the EA crests (
MLAT in both hemispheres) has clear four peaks at fixed longitude sectors during the daytime for both equinoxes and June solstice. In spite of being called a wavelike structure, however, the magnitudes and spatial intervals of the four peaks are far from being the same or regular. After sunset, the four-peak structure begins to move eastward with gradual weakening in its amplitude during equinoxes and this weakening proceeds much faster during June solstice. Interestingly, the longitudinal variations during December solstice do not show clear four-peak structure. All these features of the LW-4 structure are almost the same for both low and high solar activity conditions although the ion densities are greatly enhanced from low to high solar activities. With the irrelevancy of the magnetic activity in the LW-4, this implies that the large changes of the upper atmospheric ion densities, one of the important factors for ion-neutral interactions, have little effect on the formation of the LW-4 structure. On the other hand, we found that the monthly variation of the LW-4 is remarkably similar to that of the zonal component of wavenumber-3 diurnal tides at low latitudes, which implies that the lower atmospheric tidal forcing, transferred to the upper atmosphere, seems to have a dominant role in producing the LW-4 structure in the EA crests via the E-region dynamo.
Development of a Hardware-In-Loop (HIL) Simulator for Spacecraft Attitude Control Using Momentum Wheels
Kim, Do-Hee ; Park, Sang-Young ; Kim, Jong-Woo ; Choi, Kyu-Hong ;
Journal of Astronomy and Space Sciences, volume 25, issue 4, 2008, Pages 347~360
DOI : 10.5140/JASS.2008.25.4.347
In this paper, a Hardware-In-the-Loop simulator to simulate attitude control of space craft using momentum wheels is developed. The simulator consists of a spherical air bearing system allowing rotation and tilt in all three axes, three momentum wheels for actuation, and an AHRS (Attitude Heading Reference System). The simulator processes various types of data in PC104 and wirelessly communicates with a host PC using TCP/IP protocol. A simple low-cost momentum wheel assembly set and its drive electronics are also developed. Several experiments are performed to test the performance of the momentum wheels. For the control performance test of the simulator, a PID controller is implemented. The results of experimental demonstrations confirm the feasibility and validity of the Hardware-In-the-Loop simulator developed in the current study.
Trajectory Planning of Satellite Formation Flying using Nonlinear Programming and Collocation
Lim, Hyung-Chu ; Bang, Hyo-Choong ;
Journal of Astronomy and Space Sciences, volume 25, issue 4, 2008, Pages 361~374
DOI : 10.5140/JASS.2008.25.4.361
Recently, satellite formation flying has been a topic of significant research interest in aerospace society because it provides potential benefits compared to a large spacecraft. Some techniques have been proposed to design optimal formation trajectories minimizing fuel consumption in the process of formation configuration or reconfiguration. In this study, a method is introduced to build fuel-optimal trajectories minimizing a cost function that combines the total fuel consumption of all satellites and assignment of fuel consumption rate for each satellite. This approach is based on collocation and nonlinear programming to solve constraints for collision avoidance and the final configuration. New constraints of nonlinear equality or inequality are derived for final configuration, and nonlinear inequality constraints are established for collision avoidance. The final configuration constraints are that three or more satellites should form a projected circular orbit and make an equilateral polygon in the horizontal plane. Example scenarios, including these constraints and the cost function, are simulated by the method to generate optimal trajectories for the formation configuration and reconfiguration of multiple satellites.
Earthward Flow Bursts in the Magnetotail Driven by Solar Wind Pressure Impulse
Kim, Khan-Hyuk ; Kwak, Young-Sil ; Lee, Jae-Jin ; Hwang, Jung-A ;
Journal of Astronomy and Space Sciences, volume 25, issue 4, 2008, Pages 375~382
DOI : 10.5140/JASS.2008.25.4.375
On August 31, 2001,
1705 - 1718 UT, Cluster was located near the midnight magnetotail, GSE (x, y, z)
(-19, - 2,2) RE, and observed fast earthward flow bursts in the vicinity of the neutral sheet. They occurred while the tail magnetic field suddenly increased. Using simultaneous measurements in the solar wind, at geosynchronous orbit, and on the ground, it is confirmed that tail magnetic field enhancement is due to an increased solar wind pressure. In the neutral sheet region, strongly enhanced earthward flow bursts perpendicular to the local magnetic field
were observed. Auroral brightenings localized in the pre-midnight sector (
2200 - 2400 MLT) occurred during the interval of the
2 minutes before the onset of auroral brightenings. Our observations suggest that the earthward flow bursts are associated with tail reconnection directly driven by a solar wind pressure impulse and that
caused localized auroral brightenings.
Comparing Directional Parameters of Very Fast Halo CMEs
Rho, Su-Lyun ; Chang, Heon-Young ;
Journal of Astronomy and Space Sciences, volume 25, issue 4, 2008, Pages 383~394
DOI : 10.5140/JASS.2008.25.4.383
We examine geoeffective directional parameters of coronal mass ejections (CMEs). We select 30 front-side halo CMEs from SOHO LASCO CMEs whose speed is larger than 1000km/s and longitude is less than
. These are thought to be the most plausible candidate of geoeffective CMEs. We examine the relation between CMEs directional parameters (Earthward direction, eccentricity,
distance and central angle parameter) and the minimum value of the Dst index. We have found that the Earthward direction parameter has a good correlation with the Dst index, the eccentricity parameter has a much better correlation with the Dst index. The bo distance and central angle parameter has a poor correlation with the Dst index. It's, however, well correlated with the Dst index in very strong geomagnetic storms. Most of CMEs causing very strong storms (Dst
-200nT) are found to have large Earthward direction parameter
, small eccentricity, bo distance and central angle parameters
. These directional parameters are very important parameters that control the geoeffectiveness of very fast front-side halo CMEs.
Long Term Variability of the Sun and Climate Change
Cho, Il-Hyun ; Chang, Heon-Young ;
Journal of Astronomy and Space Sciences, volume 25, issue 4, 2008, Pages 395~404
DOI : 10.5140/JASS.2008.25.4.395
We explore the linkage between the long term variability of the Sun and earth's climate change by analysing periodicities of time series of solar proxies and global temperature anomalies. We apply the power spectral estimation method named as the periodgram to solar proxies and global temperature anomalies. We also decompose global temperature anomalies and reconstructed total solar irradiance into each local variability components by applying the EMD (Empirical Mode Decomposition) and MODWT MRA (Maximal Overlap Discrete Wavelet Multi Resolution Analysis). Powers for solar proxies at low frequencies are lower than those of high frequencies. On the other hand, powers for temperature anomalies show the other way. We fail to decompose components which having lager than 40 year variabilities from EMD, but both residuals are well decomposed respectively. We determine solar induced components from the time series of temperature anomalies and obtain 39% solar contribution on the recent global warming. We discuss the climate system can be approximated with the second order differential equation since the climate sensitivity can only determine the output amplitude of the signal.
Analysis of Wind Vorticity and Divergence in the High-latitude Lower Thermosphere: Dependence on the Interplanetary Magnetic Field (IMF)
Kwak, Young-Sil ; Lee, Jae-Jin ; Ahn, Byung-Ho ; Hwang, Jung-A ; Kim, Khan-Hyuk ; Cho, Kyung-Seok ;
Journal of Astronomy and Space Sciences, volume 25, issue 4, 2008, Pages 405~414
DOI : 10.5140/JASS.2008.25.4.405
To better understand the physical processes that control the high-latitude lower thermospheric dynamics, we analyze the divergence and vorticity of the high-latitude neutral wind field in the lower thermosphere during the southern summertime for different IMF conditions. For this study the National Center for Atmospheric Research Thermosphere-Ionosphere Electrodynamics General Circulation Model (NCAR-TIEG CM) is used. The analysis of the large-scale vorticity and divergence provides basic understanding flow configurations to help elucidate the momentum sources that ulti-mately determine the total wind field in the lower polar thermosphere and provides insight into the relative strengths of the different sources of momentum responsible for driving winds. The mean neutral wind pattern in the high-latitude lower thermosphere is dominated by rotational flow, imparted primarily through the ion drag force, rather than by divergent flow, imparted primarily through Joule and solar heating. The difference vorticity, obtained by subtracting values with zero IMF from those with non-zero IMF, in the high-latitude lower thermosphere is much larger than the difference divergence for all IMF conditions, indicating that a larger response of the thermospheric wind system to enhancement in the momentum input generating the rotational motion with elevated IMF than the corresponding energy input generating the divergent motion. the difference vorticity in the high-latitude lower thermosphere depends on the direction of the IMF. The difference vorticity for negative and positive
shows positive and negative, respectively, at higher magnetic latitudes than
. For negative
, the difference vorticities have positive in the dusk sector and negative in the dawn sector. The difference vorticities for positive
have opposite sign. Negative IMF
has a stronger effect on the vorticity than does positive
Analysis of Forcing Terms Determining the Thermospheric Wind Vortices at High Latitudes
Kwak, Young-Sil ; Ahn, Byung-Ho ; Kim, Khan-Hyuk ;
Journal of Astronomy and Space Sciences, volume 25, issue 4, 2008, Pages 415~424
DOI : 10.5140/JASS.2008.25.4.415
Kwak et al. (2008) found that the mean neutral wind pattern in the high-latitude lower thermosphere is dominated by rotational flow than by divergent flow. As an extension of the our previous work (Kwak et al. 2008), we performed a term analysis of vorticity equation that describes the driving forces for the rotational component of the horizontal wind in order to determine key processes that causes strong rotational flow in the high-latitude lower thermospheric winds. For this study the National Center for Atmospheric Research Thermosphere-Ionosphere Electrodynamics General Circulation Model (NCAR-TIEGCM) is used. The primary forces that determine variations of the vorticity are the ion drag term and the horizontal advection term. Significant contributions, however, can be made by the stretching term. The effects of IMF on the vorticity forces are seen down to around 105-110km.
Comparison of Local Mean Temperature Equations for GPS-based Precipitable Water Vapor Determination
Ha, Ji-Hyun ; Park, Kwan-Dong ;
Journal of Astronomy and Space Sciences, volume 25, issue 4, 2008, Pages 425~434
DOI : 10.5140/JASS.2008.25.4.425
The mean temperature equation is a key factor in calculating GPS meteorological information. A local mean temperature equation should be used to improve accuracy of GPS PWV (Precipitable Water Vapor). In this paper, four local mean temperature equations, HP,
from Ha & Park (2008) were used to analyze the effects of local models in determining GPS PWV. Four different sets of GPS PWVs were compared with radiosonde PWV to validate the accuracies of local models. GPS PWVs of four local models have similar trends compared against radiosonde PWV. The bias and RMS error were the same level: the bias is
and the RMS is
after the bias was removed. Especially, with
models one can obtain accurate PWVs even without surface temperature measurements. And we investigated dry bias of radiosonde measurements depending on sensor types and observation time at Sokcho weather station. After the radiosonde sensor equipment was changed from RS80-15L to GRS DFM-06, dry bias of radiosonde PWV decreased about 18.2% during daytime (KST 09:00), and 16.1% during nighttime (KST 21:00).
Space Radiation Effect on Si Solar Cells
Lee, Jae-Jin ; Kwak, Young-Sil ; Hwang, Jung-A ; Bong, Su-Chang ; Cho, Kyung-Seok ; Jeong, Seong-In ; Kim, Kyung-Hee ; Choi, Han-Woo ; Han, Young-Hwan ; Choi, Yong-Woon ; Seong, Baek-Il ;
Journal of Astronomy and Space Sciences, volume 25, issue 4, 2008, Pages 435~444
DOI : 10.5140/JASS.2008.25.4.435
High energy charged particles are trapped by geomagnetic field in the region named Van Allen Belt. These particles can move to low altitude along magnetic field and threaten even low altitude spacecraft. Space Radiation can cause equipment failures and on occasions can even destroy operations of satellites in orbit. Sun sensors aboard Science and Technology Satellite (STSAT-l) was designed to detect sun light with silicon solar cells which performance was degraded during satellite operation. In this study, we try to identify which particle contribute to the solar cell degradation with ground based radiation facilities. We measured the short circuit current after bombarding electrons and protons on the solar cells same as STSAT-1 sun sensors. Also we estimated particle flux on the STSAT-l orbit with analyzing NOAA POES particle data. Our result clearly shows STSAT-l solar cell degradation was caused by energetic protons which energy is about 700keV to 1.5MeV. Our result can be applied to estimate solar cell conditions of other satellites.
Analysis of SAR Image Quality Degradation due to Pointing and Stability Error of Synthetic Aperture Radar Satellite
Chun, Yong-Sik ; Ra, Sung-Woong ;
Journal of Astronomy and Space Sciences, volume 25, issue 4, 2008, Pages 445~458
DOI : 10.5140/JASS.2008.25.4.445
Image chain analysis of synthetic aperture radar (SAR) satellite is one of the primary activities for satellite design because SAR image quality depends on spacecraft bus performance as well as SAR payload. Especially, satellite pointing and stability error make worst effect on the original SAR image quality which is implemented by SAR payload design. In this research, Image chain analysis S/W was developed in order to analyze the SAR image quality degradation due to satellite pointing and stability error. This S/W consists of orbit model, attitude control model, SAR payload model, clutter model, and SAR processor. SAR raw data, which includes total 25 point targets in the scene of
swath width, was generated and then processed for analysis. High resolution mode (spotlight), of which resolution is 1m, was applied. The results of image chain analysis show that radiometric accuracy is the most degraded due to the pointing error. Therefore, the successful design of attitude control subsystem in spacecraft bus for enhancing the pointing accuracy is most important for image quality.
COMS DATS Implementation and Test
Park, Durk-Jong ; Kim, Su-Jin ; Ahn, Sang-Il ;
Journal of Astronomy and Space Sciences, volume 25, issue 4, 2008, Pages 459~470
DOI : 10.5140/JASS.2008.25.4.459
DATS which is one of three subsystems of IDACS is responsible to receive Sensor Data, LRIT and HRIT in L-Band and transmit LRIT and HRIT in S-Band from/to COMS satellite. This paper shows detailed test procedures used to verify the performance and functionality of DATS after its implementation was completely finished. As a part of efforts to verify key DATS performance, G/T and EIRP were measured by using solar flux density as radio source. Regarding the verification of DATS functionality, RF loop-back test was conducted to validate if there is no BER degradation excepting MODEM/BB implementation loss occurred in the integrated DATS. Integrated with 13m antenna, DATS successfully restored image from received MTSAT-1R broadcasting data, LRIT and HRIT, of which frequencies are all L-Band. S-Band transmission was also verified through test antenna placed away from 13m antenna by measuring real LRIT and HRIT spectrum in S-Band. From those test results, DATS is determined to be fully ready to communicate with COMS in L-Band and S-Band.
Integeation Test of Coms Image Data Acquisition and Control System
Lim, Hyun-Su ; Ahn, Sang-Il ; Park, Durk-Jong ;
Journal of Astronomy and Space Sciences, volume 25, issue 4, 2008, Pages 471~480
DOI : 10.5140/JASS.2008.25.4.471
COMS Image Data Acquisition and Control System (IDACS) plays a key role in real time ground processing of Meteorological and Ocean observation data. Beyond processing, it serves processed image data and additional data to end users through the spacecraft in the internationally recommended format. The IDACS will be installed at three location (MSC, KOSC, and SOC) and automatically operated 24h/365days. After the IDACS subsystem tests and inter -subsystem interface tests had been completed in the first half of 2008, the acceptance test which was a comprehensive test performed as an integrated form to verify function performance and operational requirements. This paper introduces test objective, preparation, and major result of the COMS IDACS acceptance test.
Error Analysis of Reaction Wheel Speed Detection Methods
Oh, Shi-Hwan ; Lee, Hye-Jin ; Lee, Seon-Ho ; Yong, Ki-Lyuk ;
Journal of Astronomy and Space Sciences, volume 25, issue 4, 2008, Pages 481~490
DOI : 10.5140/JASS.2008.25.4.481
Reaction wheel is one of the actuators for spacecraft attitude control, which generates torque by changing an inertial rotor speed inside of the wheel. In order to generate required torque accurately and estimate an accurate angular momentum, wheel speed should be measured as close to the actual speed as possible. In this study, two conventional speed detection methods for high speed motor with digital tacho pulse (Elapsed-time method and Pulse-count method) and their resolutions are analyzed. For satellite attitude maneuvering and control, reaction wheel shall be operated in bi directional and low speed operation is sometimes needed for emergency case. Thus the bias error at low speed with constant acceleration (or deceleration) is also analysed. As a result, the speed detection error of elapsed-time method is largely influenced upon the high-speed clock frequency at high speed and largely effected on the number of tacho pulses used in elapsed time calculation at low speed, respectively.
Development of Path finder Model and Qualified Model of Coarse Sun Sensor Assembly for Low Earth Orbit Satellite
Kim, Yong-Bok ; Jo, Young-Jun ; Yong, Ki-Lyuk ; Woo, Hyung-Je ;
Journal of Astronomy and Space Sciences, volume 25, issue 4, 2008, Pages 491~504
DOI : 10.5140/JASS.2008.25.4.491
CSSA (Coarse Sun Sensor Assembly) is the essential sensor for satellite attitude control. CSSA measures the direction of the sun's rays and determines whether the satellite is in the ellipse. The paper shows the development process and test results of Path-finder & Qualified Model CSSA as the preceding development in order to develop the CSSA for low earth orbit satellite. We needs the definite and precision procedure and lots of experience. This paper shows that we can improve those through the development of Path-finder and Qualified Model CSSA. Therefore, we can obtain the results to meet the functional requirement.