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1984년 ~ 2025년까지 1,249 건의 한국우주과학회지를 계간으로 확인하실 수 있습니다.
- The Korean Space Science Society (The Korean Astronomical Society)
- 계간 (Quarterly)
- ISSN : 1225-052x (ISSN : 1225-052x)
1225-052x
- DB구축현황 : 1,249건 (DB Construction : 1,249 Articles)
총 게시글 1,249건
페이지 46/125
451
- Yu, Ji-Woong
- Journal of astronomy and space sciences
- 28, n.4
- pp.273-284
- 2011
- 원문 바로보기
A method of stellar source selection for validating the quality of image is investigated for a low Earth orbit optical remote sensing satellite. Image performance of the optical payload needs to be validated after its launch into orbit. The stellar sources are ideal source points that can be used to validate the quality of optical images. For the image validation, stellar sources should be the brightest as possible in the charge-coupled device dynamic range. The time delayed and integration technique, which is used to observe the ground, is also performed to observe the selected stars. The relations between the incident radiance at aperture and V magnitude of a star are established using Gunn & Stryker's star catalogue of spectrum. Applying this result, an appropriate image performance index is determined, and suitable stars and areas of the sky scene are selected for the optical payload on a remote sensing satellite to observe. The result of this research can be utilized to validate the quality of optical payload of a satellite in orbit.
452
- Chung, Jong-Kyun
- Journal of astronomy and space sciences
- 28, n.4
- pp.305-310
- 2011
- 원문 바로보기
The total electron content (TEC) using global positioning system (GPS) is analyzed to see the characteristics of ionosphere over King Sejong station (KSJ, geographic latitude <TEX>$62^{\circ}13'S$</TEX>, longitude <TEX>$58^{\circ}47'W$</TEX>, corrected geomagnetic latitude <TEX>$48^{\circ}S$</TEX>) in Antarctic. The GPS operational ratio during the observational period between 2005 and 2009 is 90.1%. The annual variation of the daily mean TEC decreases from January 2005 to February 2009, but increase from the June 2009. In summer (December-February), the seasonal mean TEC values have the maximum of 26.2 <TEX>${\pm}$</TEX> 2.4 TEC unit (TECU) in 2005 and the minimum of 16.5 <TEX>${\pm}$</TEX> 2.8 TECU in 2009, and the annual differences decrease from 3.0 TECU (2005-2006) to 1.4 TECU (2008-2009). However, on November 2010, it significantly increases to 22.3 <TEX>${\pm}$</TEX> 2.8 TECU which is up to 5.8 TECU compared with 2009 in summer. In winter (June-August), the seasonal mean TEC slightly decreases from 13.7 <TEX>${\pm}$</TEX> 4.5 TECU in 2005 to 8.9 <TEX>${\pm}$</TEX> 0.6 TECU in 2008, and the annual difference is constantly about 1.6 TECU, and increases to 10.3 <TEX>${\pm}$</TEX> 1.8 TECU in 2009. The annual variations of diurnal amplitude show the seasonal features that are scattered in summer and the enhancements near equinoxes are apparent in the whole years. In contrast, the semidiurnal amplitudes show the disturbed annual peaks in winter and its enhancements near equinoxes are unapparent. The diurnal phases are not constant in winter and show near 12 local time (LT). The semidiurnal phases have a seasonal pattern between 00 LT and 06 LT. Consequently, the KSJ GPS TEC variations show the significant semidiurnal variation in summer from December to February under the solar minimum between 2005 and 2009. The feature is considered as the Weddell Sea anomaly of larger nighttime electron density than a daytime electron density that has been observed around the Antarctica peninsula.
453
- Cheon, Dong-Ik
- Journal of astronomy and space sciences
- 28, n.4
- pp.311-317
- 2011
- 원문 바로보기
Momentum changing actuators like reaction wheels and control moment gyros are generally used for spacecraft attitude control. This type of actuators produces force and torque disturbances. These disturbances must be reduced since they degrade the quality of spacecraft attitude control. Major disturbances are mainly due to static and dynamic imbalances. This paper gives attention to the reduction of the static and dynamic imbalance. Force/torque measurement system is used to measure the disturbance of the test reaction wheel. An identification method for the location and magnitude of the imbalance is suggested, and the corrections of the imbalance are performed using balancing method. Through balancing, the static and dynamic imbalance is remarkably reduced.
454
- Kim, Chun-Hwey
- Journal of astronomy and space sciences
- 28, n.2
- pp.109-116
- 2011
- 원문 바로보기
The first presented BV light curves of BH UMa confirmed Krajci's (2005) result that BH UMa is an RR Lyr star that belongs to the RRc subgroup. The light curves showed a slight asymmetry of D = 0.453 with an amplitude of about <TEX>$0.^m58$</TEX> in B, <TEX>$0.^m47$</TEX> in V, and <TEX>$0.^m11$</TEX> in B-V and with a small hump between <TEX>$0.^p82$</TEX> and <TEX>$0.^p86$</TEX>. We determined nine new times of minimum light and eight times of maximum light. We also analyzed all of the available unanalyzed minimum timings and found for the first time that the period of BH UMa has varied dramatically in at least three independent sinusoidal ways superposed on a secularly downward parabola over 66 years. The secular period decreasing rate was obtained as <TEX>$6.^d684{\times}10^{-8}y^{-1}$</TEX>, corresponding to -0.58 s/century. The semi-amplitude and period for each of the three sinusoidal variations were (<TEX>$0.^d058$</TEX>, <TEX>$14.^y44$</TEX>), (<TEX>$0.^d044$</TEX>, <TEX>$9.^y98$</TEX>), and (<TEX>$0.^d005$</TEX>, <TEX>$0.^y97$</TEX>), respectively. It is uncertain whether the periodicity for the shortest period of <TEX>$0.^y97$</TEX> is real or spurious. The secular period decrease, well consistent with those of the other RRc stars, could be considered as a natural result of the evolution of the BH UMa system. The two possible sinusoidal terms were interpreted as both two light-time effects due to two additional bodies orbiting BH UMa and combinations of random fluctuations in the pulsation period of BH UMa. Two interpretations were shortly discussed with related parameters.
455
- Won, Ji-Hye
- Journal of astronomy and space sciences
- 28, n.4
- pp.291-298
- 2011
- 원문 바로보기
The atmospheric infrared sounder (AIRS) sensor loaded on the Aqua satellite observes the global vertical structure of atmosphere and enables verification of the water vapor distribution over the entire area of South Korea. In this study, we performed a comparative analysis of the accuracy of the total precipitable water (TPW) provided as the AIRS level 2 standard retrieval product by Jet Propulsion Laboratory (JPL) over the South Korean area using the global positioning system (GPS) TPW data. The analysis TPW for the period of one year in 2008 showed that the accuracy of the data produced by the combination of the Advanced Microwave Sounding Unit sensor with the AIRS sensor to correct the effect of clouds (AIRS-X) was higher than that of the AIRS IR-only data (AIRS-I). The annual means of the root mean square error with reference to the GPS data were 5.2 kg/<TEX>$m^2$</TEX> and 4.3 kg/<TEX>$m^2$</TEX> for AIRS-I and AIRS-X, respectively. The accuracy of AIRS-X was higher in summer than in winter while measurement values of AIRS-I and AIRS-X were lower than those of GPS TPW to some extent.
456
- Lee, Ji-Hee
- Journal of astronomy and space sciences
- 28, n.2
- pp.117-122
- 2011
- 원문 바로보기
In this paper, the anisotropic nature of the magnetic turbulence associated with magnetic dipolarizations in the Earth's plasma sheet is examined. Specifically, we determine the power spectral indices for the perpendicular and parallel components of the fluctuating magnetic field with respect to the background magnetic field, and compare them in order to identify possible anisotropic features. For this study, we identify a total of 47 dipolarization events in February 2008 using the magnetic field data observed by the THEMIS A, D and E satellites when they are situated near the neutral sheet in the near-Earth tail. For the identified events, we estimate the spectral indices for the frequency range from 1.3 mHz to 42 mHz. The results show that the degree of anisotropy, as defined by the ratio of the spectral index of the perpendicular components to that of the parallel component, can range from ~0.2 to ~2.6, and there are more events associated with the ratio greater than unity (i.e., the perpendicular index being greater than the parallel index) than those which are anisotropic in the opposite sense. This implies that the dipolarization-associated turbulence of the magnetic field is often anisotropic, to some non-negligible degree. We then discuss how this result differs from what the theory of homogeneous, anisotropic, magnetohydrodynamic turbulence would predict.
457
- Lee, Yong-Sam
- Journal of astronomy and space sciences
- 28, n.2
- pp.143-153
- 2011
- 원문 바로보기
The sundials produced in King Sejong era had the functions of accurate observation instruments and were fabricated in various forms such as Angbuilgu (hemispherical sundial). In this study, we investigated the literature, structural characteristics and principles of Hyeonjuilgu, Cheonpyeongilgu and Jeongnamilgu that were developed in Joseon to have the unique structures. Additionally, the sundials were reviewed in the perspective of technical history by comparing them with the sundials of China. For the restoration of the sundials, we identified the principle in which the light spots and shade of the sun were used, and drew the variations of the altitude and azimuth by the yearly motion of the sun on the Siban on the hemispheric and flat surfaces. Based on these results, we completed the design drawings of the three sundials and proposed the restoration models.
458
- Park, Durk-Jong
- Journal of astronomy and space sciences
- 28, n.4
- pp.299-304
- 2011
- 원문 바로보기
As more satellites are designed to downlink their observed image data through the X-band frequency band, it is inevitable that the occupied bandwidth of a target satellite will overlap with that of other X-band downlink satellites. For sun-synchronized low earth orbit satellites, in particular, it can be expected that two or more satellites be placed within the looking angle of a ground station antenna at the same time. Due to the overlapping in the frequency band, signals transmitted from the adjacent satellites act as interferers, leading to degraded link performance between target satellite and ground station. In this paper, link analysis was initiated by modeling the radiation pattern of ground station antenna through a validated Jet Propulsion Laboratory peak envelope model. From the relative antenna gain depending on the offset angle from center axis of maximum antenna directivity, the ratio of received interference signal level to the target signal level was calculated. As a result, it was found that the degradation increased when the offset angle was within the first point of radiation pattern. For a 7.3 m antenna, serious link degradation began at an offset angle of 0.4 degrees. From this analysis, the link performance of the coming satellite passes can be recognized, which is helpful to establish an operating procedure that will prevent the ground station from receiving corrupted image data in the event of a degraded link.
459
- Park, Jong-Sun
- Journal of astronomy and space sciences
- 28, n.1
- pp.27-36
- 2011
- 원문 바로보기
The present study examines the morning-afternoon asymmetry of the geosynchronous magnetic field strength on the dayside (magnetic local time [MLT] = 06:00~18:00) using observations by the Geostationary Operational Environmental Satellites (GOES) over a period of 9 years from February 1998 to January 2007. During geomagnetically quiet time (Kp < 3), we observed that a peak of the magnetic field strength is skewed toward the earlier local times (11:07~11:37 MLT) with respect to local noon and that the geosynchronous field strength is larger in the morning sector than in the afternoon sector. That is, there is the morning-afternoon asymmetry of the geosynchronous magnetic field strength. Using solar wind data, it is confirmed that the morning-afternoon asymmetry is not associated with the aberration effect due to the orbital motion of the Earth about the Sun. We found that the peak location of the magnetic field strength is shifted toward the earlier local times as the ratio of the magnetic field strength at MLT = 18 (B-dusk) to the magnetic field strength at MLT = 06 (B-dawn) is decreasing. It is also found that the dawn-dusk magnetic field median ratio, B-dusk/B-dawn, is decreasing as the solar wind dynamic pressure is increasing. The morning-afternoon asymmetry of the magnetic field strength appears in Tsyganenko geomagnetic field model (TS-04 model) when the partial ring current is included in TS-04 model. Unlike our observations, however, TS-04 model shows that the peak location of the magnetic field strength is shifted toward local noon as the solar wind dynamic pressure grows in magnitude. This may be due to that the symmetric magnetic field associated with the magnetopause current, strongly affected by the solar wind dynamic pressure, increases. However, the partial ring current is not affected as much as the magnetopause current by the solar wind dynamic pressure in TS-04 model. Thus, our observations suggest that the contribution of the partial ring current at geosynchronous orbit is much larger than that expected from TS-04 model as the solar wind dynamic pressure increases.
460
- Lee, Dae-Hee
- Journal of astronomy and space sciences
- 28, n.3
- pp.225-232
- 2011
- 원문 바로보기
We have designed and manufactured the Earth observation camera (EOC) of multi-purpose infrared imaging system (MIRIS). MIRIS is a main payload of the STSAT-3, which will be launched in late 2012. The main objective of the EOC is to test the operation of Korean IR technology in space, so we have designed the optical and mechanical system of the EOC to fit the IR detector system. We have assembled the flight model (FM) of EOC and performed environment tests successfully. The EOC is now ready to be integrated into the satellite system waiting for operation in space, as planned.