Lunar slopes have distinct patterned regolith textures, but their formation mechanism remains enigmatic. We mapped the distribution of these "elephant hide" texture (EHT) occurrences in and out of shadow near the south pole (90 degrees S to 88 degrees S) at a scale of 1:25,000 and 1:20,000 to test if permanently shadowed regions (PSRs) have unique regolith properties relative to nonshadowed areas (polar and equatorial). We recorded the presence or absence of EHT occurrences in grid-map cells (5 and 1 Orbiter ShadowCam images of permanently and temporarily shadowed terrain. We find that diffuse lighting does not interfere with the ability to identify textures. We observed that EHT has a similar likelihood to occur on shallow slopes <= 5 degrees in both illuminated and permanently shadowed terrain, with no difference in texture morphology across temperature boundaries or from PSR to PSR. This suggests that regolith properties in PSRs that are relevant to EHT formation are not significantly different from those of the illuminated surface. We also observed variations of EHT across the same slopes and EHT on near-horizontal surfaces (<= 3 degrees) within similar to 500 m of the foot of slopes. This suggests that patterned regolith textures are formed by down-slope transport of loose regolith, likely driven by both episodic and continuous disturbances.
Polishing is a critical process in fabricating space-telescope mirrors because it determines the surface figure and consequently optical performance. Deterministic polishing relies on the tool influence function (TIF), which describes the spatial materialremoval profile. At nanometric removal depths, the TIF becomes highly sensitive to process conditions, limiting the accuracy of analytic models such as Preston's equation. In this study, we propose a deep learning-based approach to predict TIF depth for polishing a Silicon Carbide (SiC) mirror surface. To mitigate data scarcity, we augment 231 experimental measurements with Gaussian noise consistent with the repeatability observed in repeated trials (approximate to 20 nm peak-to-peak). The resulting model achieves a validation mean absolute error (MAE) of 4.24 nm and a test MAE of 3.99 nm; on nine additional experimental cases, the MAE is 6.75 nm. These results indicate that the proposed augmentation improves robustness to experimental variability and supports the development of a data-driven, automated polishing workflow.
Here, we have statistically investigated the averaged occurrence rate of sunspots during active days to test whether it is uniform across solar cycles, motivated by an intriguing observation that weak solar cycles tend to be preceded by solar minimum with numerous spotless days. The occurrence rate of sunspot in a particular month is defined by a ratio of the monthly sunspot number to the number of active days in the corresponding month. The cycle with a large number of spotless days becomes weak owing to either a small number of active days during solar cycle or a lower occurrence rate per day during active days of solar cycle, or even both. More specifically speaking, we have attempted to examine whether the averaged occurrence rate of sunspots during weak solar cycles differs from that of strong ones, and, if so, determine in what part of solar cycle the occurrence rate contributes to such changes in sunspot number. As a result, we find that the occurrence rate of sunspot averaged over the period from maximum of (i - 1)-th solar cycle to maximum of i-th solar cycle is negatively correlated with the number of spotless days, and is correlated with sunspot numbers. It is found that the averaged occurrence rate appears to more significantly correlate with the sunspot number when the sun is relatively more active compared to the period when the sun is relatively less active. It is also found that the averaged occurrence rate of sunspot does not correlate with length of solar cycle, nor length of ascending phase. Finally, we conclude by pointing out implications of our findings.
This study investigates high-latitude ionospheric mesoscale irregularities associated with energetic particle precipitation and magnetosphere-ionosphere-thermosphere coupling processes within the auroral oval using ground-based Global Navigation Satellite Systems (GNSS) total electron content (TEC) measurements. This scale size is much larger than those associated with GNSS scintillations, which range from sub-kilometers (small scales) to > 10 km (large scales). Analyzing 15 yr of data from 2010 to 2024, we characterize, for the first time, the climatology of enhanced intensity of ionospheric mesoscale irregularities at high latitudes. The observed intensity of irregularities in GNSS TEC fluctuations can serve as a proxy for the dynamic behavior of the auroral oval which varies with magnetic local time, longitude, latitude, season, solar activity cycle, geomagnetic disturbances, and hemisphere. The spatial distribution of the irregularity is oval-shaped and therefore this pat- tern is named as “irregularity oval”; the morphology of the irregularity oval is generally aligned well with the known variations of auroral oval established by using other technologies. While the primary goal has been to document systematically these irregularity longterm observations, future work will focus on the development of a novel GNSS TEC-based “irregularity oval” model.
Exploration of the lunar poles is accelerating as multiple missions target these regions, with growing interest in studying the environment within permanently shadowed regions (PSRs)—areas at the poles that never receive direct sunlight. To prepare for these exploration activities within PSRs, we determined radiance levels in PSRs of various sizes and derived a conversion factor from ShadowCam radiance units to luminance, which is more suitable for evaluating human factors, as luminance accounts for the wavelength range to which humans are sensitive. Notably, during lunar summer, many PSRs reach luminance levels comparable to those of well-lit buildings for several Earth days each month, while peak winter lighting is typically up to six times dimmer, except in regions where regional shadows predominate and further decrease illumination. As a result, we do not expect artificial light to be needed for missions visiting PSRs during the summer peak lighting period, except for close inspection of samples. In contrast, in winter, diminished ambient lighting may require supplemental illumination for many tasks
The Shackleton crater permanently shadowed region (PSR) exhibits high 1,064 nm reflectance and S-band radar circular polarization ratios (CPR), which previous studies interpreted as indicating the presence of water-ice or frost. In the absence of photogeologic evidence, alternative hypotheses offered for the reflective properties of the Shackleton crater PSR (mass wasting, presence of pure anorthosite, and interior blockiness) were not confirmed. ShadowCam has acquired high signalto- noise ratio stereo images of Shackleton crater; we use these images, derived digital terrain models, and M3 data to show that episodic mass wasting is active inside Shackleton, arising from the instability of steep wall slopes. We conclude that the relatively high reflectance within the Shackleton PSR results from continued exposure of plagioclase-rich material and not from water-ice or frost. In addition, mass wasting also excavates small blocks that collect on the wall and floor, mainly responsible for the enhanced radar CPR signature.
Cosmic ray neutron monitors (NMs) are ground-based detectors that measure secondary neutrons produced by primary cosmic ray particles in the energy range of approximately 500 MeV to several GeV. South Korea operates two NMs: one at Jang Bogo Station in Antarctica and another recently relocated from Daejeon to Mt. Gamak in Geochang, now managed by the Korea Astronomy and Space Science Institute (KASI). Mt. Gamak is geographically comparable to the former Daejeon site, located approximately 100 km to the southeast. The NM at Mt. Gamak’s altitude is approximately 925 meters, which is about four times higher than that of the Daejeon site. In addition, the average atmospheric pressure at Mt. Gamak was 915.9 hPa, about 85 hPa lower than that of Daejeon. The barometric coefficient was approximately –0.7101%/hPa. As a result, the NM at Mt. Gamak records more than twice the count rate observed at the Daejeon site. Given these conditions, the Mt. Gamak NM is expected to play a crucial role in cosmic ray research and in monitoring the solar and space environment in the mid-latitude region.
Two main components of polar motion are Chandler wobble and annual wobble. Annual wobble is obviously caused by the seasonal perturbations on the Earth – such was suspected as well as readily confirmed in unison. Unlike annual wobble the cause of Chandler wobble has long been controversial, and finally solid proof came out with recent polar motion reconstruction using fluid spheres excitation data. In this study, certain characteristics of two main oscillatory components of polar motion are investigated once again. First, with two kinds of datasets; (i) the polar motion time series and (ii) the Earth’s fluid sphere excitation time series, the cause of the main oscillatory polar motion including Chandler wobble is investigated. Formerly such investigations have been mostly done in the frequency domain only. We attempted to construct of polar motion time series from excitation through a new procedure using Fourier transform and its inverse. Secondly, the minor effect of earthquakes on Chandler wobble has been also assessed by the same method with a simple empirical model for post seismic relaxation. Then we compared the constructed polar motion with the observed polar motion. Contrary to several former claims, the role of geomagnetic jerk as another driving force of Chandler wobble is declined. Reliable estimates of the period and quality factor of Chandler wobble are attained.
The tip of the Antarctic Peninsula is widely recognized as one of the most active regions for gravity wave activity. Situated in this dynamic area, the King Sejong Station (KSS: 62.22°S, 58.78°W) serves as an ideal location for investigating gravity wave activity in the mesosphere and lower thermosphere (MLT) region. The Korea Polar Research Institute (KOPRI) has been operating a meteor radar (MR) and an airglow all-sky camera (ASC) at KSS for over a decade, enabling studies on gravity wave activity and MLT dynamics. To enhance these observational capabilities, a new optical instrument, the Advanced Mesospheric Temperature Mapper (AMTM), was installed in January 2023. The KSS-AMTM provides hydroxyl (OH) airglow intensities at approximately 87 km altitude as well as two-dimensional temperature maps at a high temporal resolution. This study presents a brief overview of the observational features and operation of the instrument, alongside initial results obtained over 28 clear nights from February to October 2023. As part of the initial validation, observed mesopause temperatures were compared with data from meteor radar and the Microwave Limb Sounder onboard the Aura satellite.
The electron density profiles produced from the ionospheric sounding system are traditionally estimated by the inversion procedure based on the image analysis of the observed ionograms. Jang Bogo Vertical Incidence Pulsed Ionospheric Radar (VIPIR) with Dynasonde (hereafter, JVD), however, uses the three-dimensional electron density inversion approach named “NeXtYZ” to produce ionospheric density, ion velocity, and tilt of the ionization in the bottomside ionosphere based on the list of detected radio echoes with their physical parameters. Sometimes, the resulting density profiles can be erroneous, not reflecting real ionosphere, probably due to severely disturbed ionosphere in the polar region. In this study, the automatic classification procedure of the estimated electron density profiles is developed to filter out unusable data for the 5-year period from 2017 to 2021. The ionograms are classified into four categories: ‘Unavailable’, ‘Sporadic E’, ‘Needs Reprocessing’, and ‘Available’. It is found that approximately 50% of ionograms are evaluated to be reasonable with proper electron density profiles and about 35% of them tend to be affected by sporadic-E like structures, blocking the F-region ionosphere to be observed. It should be noted that the sporadic-E like structures in the polar ionosphere seems to be main obstacles for the ionospheric sounding observation of the F-region ionosphere. Only less than 10% of ionograms are classified as a reprocessing type which needs to be reprocessed. Finally, no echoes are recognized by Dynasonde analysis for about 5% of ionograms. The reprocessing and/or unavailable types might be associated with auroral precipitations that disturbs the ionosphere in the polar region.
The mission-assisting anisotropic magnetoresistive sensor (MAMS) module is one of the components supporting the operation of the lunar surface magnetometer (LSMAG), one of the Korean candidate payloads for the Commercial Lunar Payload Services (CLPS) program. LSMAG uses fluxgate magnetometers (FGMs), which have a 0.2 nT resolution and ± 2,000 nT measurement range. For the scientific analysis of LSMAG data, four types of additional mission-assisting functions are required: strong magnetic field measurement, lander noise detection, offset calibration signal generation, and attitude information provision. To perform these functions, the MAMS module utilizes anisotropic magnetoresistive (AMR) sensors (HMC1001/1002), an accelerometer (ADXL355), and an artificial magnetic field generating circuit. The AMR sensors have a larger measurement range than FGMs. Therefore, these sensors are suitable for measuring strong magnetic fields and the lander’s noise signal, making them applicable for noise-removal techniques. The MAMS module also includes an accelerometer (ADXL355) to measure the attitude of the LSMAG boom and features an artificial field-generating function to determine the sensor offset. The MAMS module passed functional and space environmental tests to verify its performance. The AMR sensors have a 20 nT resolution and ± 80,000 nT range, while the accelerometer has a 6 mg resolution and ± 2 g range under Earth conditions. This module includes its own microcontroller unit and supports a wide input voltage range and standard RS485 universal asynchronous receiver/transmitter (UART) communication. We expect the MAMS module to not only play an essential role in supporting LSMAG data calibration and operation, but also to be used in various future space science exploration missions.
The advent of low Earth orbit (LEO) mega satellite constellations to accelerate high-speed internet worldwide represents a new technological advancement. However, this development raises concerns regarding militarization, orbital debris, environmental protection, and their effects on space tourism. Despite these challenges, existing space law treaties have not addressed these issues. This article highlights the gaps in current treaties and emphasizes the need for advancements to mitigate emerging challenges and ensure long-term solutions. This study explores the legal challenges associated with possible smashes flanked by existing satellites in orbit and newly launched satellites as part of mega-constellations, which could jeopardize mission safety and threaten the sustainability of space activities. It also analyzes the significant issues related to space debris, particularly given the anticipated increase in satellite constellations in LEO over the coming decades. The increase in small satellites with shorter lifespans is likely to contribute to greater debris generation. Finally, these findings suggest the need for a suitable international legal structure to facilitate the efficient deployment and operation of satellite techniques.
This study examined the variations of solar, interplanetary, and geomagnetic (SIG) parameters from 1974 to 2024 to assess the changes in the solar cycle. Eleven SIG parameters were analyzed, including the sunspot number (SSN), solar magnetic field, 10.7 cm solar radio flux, total solar irradiance, and Ap index. This study also aimed to predict Solar Cycle 25 using the seasonal autoregressive integrated moving average (SARIMA) statistical forecasting model. The results showed that consistent with previous studies, all SIG parameters exhibited a strong correlation with the SSN. The change in SSN strongly influences the variations in all SIG parameters, even though some exhibit time-lagged responses. The cross-correlation analysis revealed a high correlation coefficient of 0.9678 between the SSN and the 10.7 cm solar radio flux without delay. Most SIG parameters showed a general weakening trend toward Solar Cycles 22–24. This suggests that solar activity is waning over time. In particular, the solar polar magnetic field (SPMF) showed a large decrease in the solar minimum 23/24, and specifically, the SPMF at the south pole weakened more rapidly than at the north pole. Hence, the SPMF is changing asymmetrically between the north and south poles. This weakening of the solar magnetic field suggests an increase in galactic cosmic rays within the heliosphere, exposing the Earth to higher levels of cosmic rays. Finally, forecasts for Solar Cycle 25 using the SARIMA model predict that the SSN will continue to decline after the solar maximum in 2024, with the predicted minimum SSN of 9.42 in October 2028, and will likely enter a solar minimum period around 2030.
Space debris poses significant threats to spacecraft and human activities in space. Accurate modeling of space debris is crucial for understanding and mitigating these risks, ensuring the sustainability of the space environment. This paper discusses the importance of space debris modeling in the space environment, highlighting its critical role in safeguarding assets in orbit. Two primary methods of space debris modeling, namely the 1D and 3D approaches, are discussed in detail, and their respective strengths and limitations are elucidated. Furthermore, a comprehensive review of existing models, including the space debris evolutionary model (MOCAT, SOLEM, DAMAGE, LEODEEM & GEODEEM, DELTA, and LEGEND) and engineering models (MOCAT-MC, NEODEEM, MASTER, ORDEM), are presented. These models offer valuable insights into the dynamics and characteristics of space debris populations, aiding in formulating effective debris mitigation strategies and orbital capacity problems for reducing the possibilities of Kessler’s syndrome. Additionally, the paper provides insights into the ongoing development of the Korean space debris model, focusing on its methodology and space debris cataloging techniques for modeling space debris environments.
This paper presents ground calibration and orthogonality correction methods for the tri-axis fluxgate magnetometer (FGM), named as adaptive in-phase magnetometer (AIMAG), aboard the CAS500-3 satellite. The orthogonality errors of the FGM among the axes can lead to significant inaccuracies in magnetic field measurements. In this study, we employed Helmholtz coils and an autocollimator to apply controlled magnetic fields and adjust the magnetometer’s alignment. By deriving the correction matrix, we could transfer the sensor axes to the ideal orthogonal coordinate system. We validated the correction method by analyzing the sensor’s output under various magnetic field conditions. This correction method is expected to enhance the in-flight magnetic field measurements of the CAS500-3 satellite.
The advent of “space tourism” has induced outer space law to respond and adapt to this dramatic growth because of the principled contribution of private entities in these activities. This article discusses the main legal aspects of licensing, supervision, liability, registration, and health side effects, and how these reveal the influence of space tourism. Because of the moral participation of private individuals in these activities, “space tourism” demands that outer space law be modified and adaptable. Although many issues of ship, crew, and passenger certification have not been defined in international law, these would be evaluated to show that domestic legislative interests may drive the law before it reaches international law. Air and adventure tourism laws are also evaluated. Space are not likely to remain limited to professionally trained individuals and wealthy astronauts. The potential for public access to space raises complex legal, health-related, and ethical questions on the inadequacy of the current international legal instruments addressing the utilization and exploration of outer space. Furthermore, this study is designed to evaluate the role of human presence in spaceflights, accidents that occurred to participants of space missions, and other risks spaceflights may induce on humans. In addition, this study focuses on analyzing existing legal regulations related to astronauts’ health and life protection during spaceflight and how states can address emerging challenges to astronauts’ safety. The existing global legal framework regulating aviation and space operations is unsuitable for the widespread commercial entry into space. This is because it was designed when drafters did not envisage such endeavors to this extent. The insufficient legal clarity should be addressed rapidly to set applicable standards to promote such activities. To conclude, this article compares national space regulations and elaborates on the drawbacks of the current international space regulations.
The ShadowCam instrument on the Danuri spacecraft provides high-resolution views of shadowed portions of the Moon, which are illuminated by naturally scattered light from nearby sunlit terrain. The sensitive time-delay integration detector captures high signal-to-noise observations within the permanently shadowed regions and areas in shadow for part of the year. We characterized the geometric properties of the images, enabling accurate placement of observations within the lunar cartographic framework. This work describes the internal and external orientation parameters using laboratory observations and images collected during the cruise and commissioning phase of the mission. We identified a radial distortion in the cross-track direction from these observations, which is correctable during our standard calibration pipeline procedures. We also calculated the pointing of the camera relative to the spacecraft bus within ~0.001°. Using these models, corrections, and the initial ephemeris provided by the Korea Aerospace Research Institute, images can be aligned within 60 m on the surface (95% confidence interval). This calibration and a precise radiometric model will enable reliable interpretation of ShadowCam images and the development of future derived products, including precisely mapped mosaics and meter-scale digital elevation models.
We present oscillating features from long-term neutral wind (meteor radar) and pressure (microwave limb sounder) measurements at Esrange (67°N, 20°E, 2007–2018) in the northern hemisphere and King Sejong Station (KSS; 62°S, 58°W, 2007–2017) in the Southern Hemisphere using the Lomb-Scargle periodogram and wavelet analysis. In zonal winds and pressure, we estimated the height profiles for the amplitude ratio between annual oscillation (AO) and semi-annual oscillation (SAO) at both sites. Over KSS, the ratio indicates that SAO increases with altitude, whereas AO decreases, with SAO becoming the dominant oscillating component at around 90 km. However, the ratio mostly remains constant with an altitude due to the steady formation of a westward wind field throughout the height in summer. More intensive gravity wave activity over KSS drives meridional residual circulation in summer mesopause, creating a more powerful SAO signature above 90 km.
A search coil magnetometer (SCM) is a common equipment to observe energy transmission and vibrations in space physics, enabling measurements across a wide frequency range of up to tens of kilohertz. This study proposes the designs of a magnetic core that allows a low-mass sensor and improves its performance: a rod core, sheet-stacked core, and rolling-sheet core. Subsequently, the performance of each sensor was investigated. The sheet-stacked core using the cobalt-based alloy exhibited the highest sensitivity, although it exhibited instability beyond 20 kHz. In contrast, the rod and rolling-sheet core sensors demonstrated stability in the magnetic field measurements (10 Hz–40 kHz). Moreover, the noise equivalent magnetic induction (NEMI) of the rod- and rolling-sheet core sensors were 0.014 pT Hz–1/2 and 0.012 pT Hz–1/2 at 1 kHz, respectively. The rolling-sheet core with high relative permeability achieved a mass reduction of over three times that of the rod core while exhibiting sufficient sensitivity.
This study developed a machine learning-based methodology to classify gravitational wave (GW) signals from black hole-neutron star (BH-NS) mergers by combining convolutional neural network (CNN) with conditional information for feature extraction. The model was trained and validated on a dataset of simulated GW signals injected to Gaussian noise to mimic real world signals. We considered all three types of merger: binary black hole (BBH), binary neutron star (BNS) and neutron star-black hole (NSBH). We achieved up to 96% correct classification of GW signals sources. Incorporating our novel conditional information approach improved classification accuracy by 10% compared to standard time series training. Additionally, to show the effectiveness of our method, we tested the model with real GW data from the Gravitational Wave Transient Catalog (GWTC-3) and successfully classified ~90% of signals. These results are an important step towards low-latency real-time GW detection.
