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- The Korean Space Science Society (The Korean Astronomical Society)
- 계간 (Quarterly)
- ISSN : 1225-052x (ISSN : 1225-052x)
1225-052x
- DB구축현황 : 1,253건 (DB Construction : 1,253 Articles)
총 게시글 1,253건
페이지 8/126
71
- Chang, Heon-Young
- Journal of astronomy and space sciences
- 38, n.1
- pp.23-29
- 2021
- 원문 바로보기
Utilizing a new version of the sunspot number and group sunspot number dataset available since 2015, we have statistically studied the relationship between solar activity parameters describing solar cycles and the slope of the linear relationship between the monthly sunspot numbers and the monthly number of active days in percentage (AD). As an effort of evaluating possibilities in use of the number of active days to predict solar activity, it is worthwhile to revisit and extend the analysis performed earlier. In calculating the Pearson's linear correlation coefficient r, the Spearman's rank-order correlation coefficient rs, and the Kendall's τ coefficient with the rejection probability, we have calculated the slope for a given solar cycle in three different ways, namely, by counting the spotless day that occurred during the ascending phase and the descending phase of the solar cycle separately, and during the period corresponding to solar minimum ± 2 years as well. We have found that the maximum solar sunspot number of a given solar cycle and the duration of the ascending phase are hardly correlated with the slope of a linear function of the monthly sunspot numbers and AD. On the other hand, the duration of a solar cycle is found to be marginally correlated with the slope with the rejection probabilities less than a couple of percent. We have also attempted to compare the relation of the monthly sunspot numbers with AD for the even and odd solar cycles. It is inconclusive, however, that the slopes of the linear relationship between the monthly group numbers and AD are subject to the even and odd solar cycles.
72
- Khattab, Elamira Hend
- Journal of astronomy and space sciences
- 38, n.2
- pp.93-103
- 2021
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In this work, the problem of resonance caused by some gravitational potentials due to Mercury and a third body, namely the Sun, together with some non-gravitational perturbations, specifically coronal mass ejections and solar wind in addition to radiation pressure, are investigated. Some simplifying assumptions without loss of accuracy are employed. The considered force model is constructed. Then the Delaunay canonical set is introduced. The Hamiltonian of the problem is obtained then it is expressed in terms of the Deluanay canonical set. The Hamiltonian is re-ordered to adopt it to the perturbation technique used to solve the problem. The Lie transform method is surveyed. The Hamiltonian is doubly averaged. The resonance capture is investigated. Finally, some numerical simulations are illustrated and are analyzed. Many resonant inclinations are revealed.
73
- Woo, Hyung Je
- Journal of astronomy and space sciences
- 38, n.1
- pp.65-82
- 2021
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For the vast majority of geostationary satellites currently in orbit, station keeping activities including orbit determination and maneuver planning and execution are ground-directed and dependent on the availability of ground-based satellite control personnel and facilities. However, a requirement linked to satellite autonomy and survivability in cases of interrupted ground support is often one of the stipulated provisions on the satellite platform design. It is especially important for a geostationary military-purposed satellite to remain within its designated orbital window, in order to provide reliable uninterrupted telecommunications services, in the absence of ground-based resources due to warfare or other disasters. In this paper we investigate factors affecting the robustness of a geostationary satellite's orbit in terms of the maximum duration the satellite's station keeping window can be maintained without ground intervention. By comparing simulations of orbit evolution, given different initial conditions and operations strategies, a variation of parameters study has been performed and we have analyzed which factors the duration is most sensitive to. This also provides valuable insights into which factors may be worth controlling by a military or civilian geostationary satellite operator. Our simulations show that the most beneficial factor for maximizing the time a satellite will remain in the station keeping window is the operational practice of pre-emptively loading East-West station keeping maneuvers for automatic execution on board the satellite should ground control capability be lost. The second most beneficial factor is using short station keeping maneuver cycle durations.
74
- Shin, Jinyoung
- Journal of astronomy and space sciences
- 38, n.4
- pp.217-227
- 2021
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In this study, we describe an analytical process for designing a low Earth orbit constellation for discontinuous regional coverage, to be used for a surveillance and reconnaissance space mission. The objective of this study was to configure a satellite constellation that targeted multiple areas near the Korean Peninsula. The constellation design forms part of a discontinuous regional coverage problem with a minimum revisit time. We first introduced an optimal inclination search algorithm to calculate the orbital inclination that maximizes the geometrical coverage of single or multiple ground targets. The common ground track (CGT) constellation pattern with a repeating period of one nodal day was then used to construct the rest of the orbital elements of the constellation. Combining these results, we present an analytical design process that users can directly apply to their own situation. For Seoul, for example, 39.0° was determined as the optimal orbital inclination, and the maximum and average revisit times were 58.1 min and 27.9 min for a 20-satellite constellation, and 42.5 min and 19.7 min for a 30-satellite CGT constellation, respectively. This study also compares the revisit times of the proposed method with those of a traditional Walker-Delta constellation under three inclination conditions: optimal inclination, restricted inclination by launch trajectories from the Korean Peninsula, and inclination for the sun-synchronous orbit. A comparison showed that the CGT constellation had the shortest revisit times with a non-optimal inclination condition. The results of this analysis can serve as a reference for determining the appropriate constellation pattern for a given inclination condition.
75
- Yang, Tae-Yong
- Journal of astronomy and space sciences
- 38, n.2
- pp.135-143
- 2021
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We report, for the first time, the afternoon (i.e., from noon to sunset time) observations of the northern mid-latitude E-region field-aligned irregularities (FAIs) made by the very high frequency (VHF) coherent backscatter radar operated continuously since 29 December 2009 at Daejeon (36.18°N, 127.14°E, 26.7°N dip latitude) in South Korea. We present the statistical characteristics of the mid-latitude afternoon E-region FAIs based on the continuous radar observations. Echo signal-to-noise ratio (SNR) of the afternoon E-region FAIs is found to be as high as 35 dB, mostly occurring around 100-135 km altitudes. Most spectral widths of the afternoon echoes are close to zero, indicating that the irregularities during the afternoon time are not related to turbulent plasma motions. The occurrence of afternoon E-regional FAI is observed with significant seasonal variation, with a maximum in summer and a minimum in winter. Furthermore, to investigate the afternoon E-region FAIs-Sporadic E (E<sub>s</sub>) relationship, the FAIs have also been compared with E<sub>s</sub> parameters based on observations made from an ionosonde located at Icheon (37.14°N, 127.54°E, 27.7°N dip latitude), which is 100 km north of Daejeon. The virtual height of E<sub>s</sub> (h'E<sub>s</sub>) is mainly in the height range of 105 km to 110 km, which is 5 km to 10 km greater than the bottom of the FAI. There is no relationship between the FAI SNR and the highest frequencies (f<sub>t</sub>E<sub>s</sub>) (or blanket frequencies (f<sub>b</sub>E<sub>s</sub>)). SNR of FAIs, however, is found to be related well with (f<sub>t</sub>E<sub>s</sub>-f<sub>b</sub>E<sub>s</sub>).
76
- Song, Young-Joo
- Journal of astronomy and space sciences
- 38, n.2
- pp.145-155
- 2021
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In this work, preliminary launch opportunities from NARO Space Center to the Sun-Earth Lagrange point are analyzed. Among five different Sun-Earth Lagrange points, L1 and L2 points are selected as suitable candidates for, respectively, solar and astrophysics missions. With high fidelity dynamics models, the L1 and L2 point targeting problem is formulated regarding the location of NARO Space Center and relevant Target Interface Point (TIP) for each different launch date is derived including launch injection energy per unit mass (C3), Right ascension of the injection orbit Apoapsis Vector (RAV) and Declination of the injection orbit Apoapsis Vector (DAV). Potential launch periods to achieve L1 and L2 transfer trajectory are also investigated regarding coasting characteristics from NARO Space Center. The magnitude of the Lagrange Orbit Insertion (LOI) burn, as well as the Orbit Maintenance (OM) maneuver to maintain more than one year of mission orbit around the Lagrange points, is also derived as an example. Even the current work has been made under many assumptions as there are no specific mission goals currently defined yet, so results from the current work could be a good starting point to extend diversities of future Korean deep-space missions.
77
- Kam, Hosik
- Journal of astronomy and space sciences
- 38, n.4
- pp.229-236
- 2021
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We present for the first time the characteristics of upper atmospheric horizontal winds over the Korean Peninsula. Winds and their variability are derived using four-year measurements by the Korea Astronomy and Space Science Institute (KASI) meteor radar. A general characteristic of zonal and meridional winds is that they exhibit distinct diurnal and seasonal variations. Their changes indicate sometimes similar or sometimes different periodicities. Both winds are characterized by either semi-diurnal tides (12 hour period) and/or diurnal tides (24 hour period) from 80-100 km. In terms of annual change, the annual variation is the strongest component in both winds, but semi-annual and ter-annual variations are only detected in zonal winds.
78
- Jang, Uicheol
- Journal of astronomy and space sciences
- 38, n.1
- pp.39-44
- 2021
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In the general accretion disk model theory, the accretion disk surrounding an astronomical object comprises fluid rings obeying Keplerian motion. However, we should consider relativistic and rotational effects as we close in toward the center of accretion disk surrounding spinning compact massive objects such as a black hole or a neutron star. In this study, we explore the geometry of the inner portion of the accretion disk in the context of Mukhopadhyay's pseudo-Newtonian potential approximation for the full general relativity theory. We found that the shape of the accretion disk 'puffs up' or becomes thicker and the luminosity of the disk could exceed the Eddington luminosity near the surface of the compact spinning black hole.
79
- Chae, Jongchul
- Journal of astronomy and space sciences
- 38, n.2
- pp.83-92
- 2021
- 원문 바로보기
The ionization degree of hydrogen is crucial in the physics of the plasma in the solar chromosphere. It specifically limits the range of plasma temperatures that can be determined from the Hα line. Given that the chromosphere greatly deviates from the local thermodynamic equilibrium (LTE) condition, precise determinations of hydrogen ionization require the solving of the full set of non-LTE radiative transfer equations throughout the atmosphere, which is usually a formidable task. In many cases, it is still necessary to obtain a quick estimate of hydrogen ionization without having to solve for the non-LTE radiative transfer. Here, we present a simple method to meet this need. We adopt the assumption that the photoionizing radiation field changes little over time, even if physical conditions change locally. With this assumption, the photoionization rate can be obtained from a published atmosphere model and can be used to determine the degree of hydrogen ionization when the temperature and electron density are specified. The application of our method indicates that in the chromospheric environment, plasma features contain more than 10% neutral hydrogen at temperatures lower than 17,000 K but less than 1% neutral hydrogen at temperatures higher than 23,000 K, implying that the hydrogen temperature determined from the Hα line is physically plausible if it is lower than 20,000 K, but may not be real, if it is higher than 25,000 K. We conclude that our method can be readily exploited to obtain a quick estimate of hydrogen ionization in plasma features in the solar chromosphere.
80
- Salazar-Manzano, Luis E.
- Journal of astronomy and space sciences
- 38, n.1
- pp.1-21
- 2021
- 원문 바로보기
The observation of stellar occultations constitutes one of the most important techniques for determining the dimensions and establishing the physical parameters of small Solar System bodies. The most substantial calculations are obtained from multiple observations of the same event, which turns the observation of stellar occultations into highly collaborative work and groups teams of observers through international networks. The above situation also requires the participation of both professional and amateur observers in these collaborative networks. With the aim of promoting the participation of professional and amateur groups in the collaborative observation of stellar occultations, we present the methodology developed by the Astronomical Observatory of the Technological University of Pereira (OAUTP) for the observations of occultations due small Solar System bodies. We expose the three fundamental phases of the process: the plan to make observations, the capture of the events, and the treatment of the data. We apply our methodology using a fixed station and a mobile station to observe stellar occultations due to MBAs (354) Eleonora (61) Danae (15112) Arlenewolfe (3915) Fukushima (61788) 2000 QP181 (425) Cornelia (257) Silesia (386) Siegena and (41) Daphne, and due to TNOs 1998BU48 and (529823) 2010 PP81. The positive detections for the objects (257) Silesia (386) Siegena and (41) Daphne allow us to derive lower limits in the diameter of the MBAs of 63.1 km, 166.2 km and 158.7 km and offsets in the astrometric position (Δαc cos��c, Δ��c) of 622.30 ± 0.83, 15.23 ± 9.88 mas, 586.06 ± 1.68, 43.03 ± 13.88 mas and -413.44 ± 9.42, 234.05 ± 19.12 mas, respectively.