Subjects: Geosciences >> Space Physics submitted time 2017-01-22
Abstract： Based on the 2755 days’ (2001-05-15~2008-12-31) density data derived from CHAMP accelerometer, the model errors of JB2008 and MSISE-00 are analyzed. It is found that the two modes both overestimate the atmospheric density, but the JB2008 is better than the MSISE-00, their average bias is 2.2% and 17.6% respectively. To brief classification of space environment, the model characteristics of latitudes and local time are analyzed in each class space environment. It is found that MSISE-00 model has better local time characteristic and JB2008 has good latitude characteristics. This study has certain significance to master model error characteristics and to improve atmospheric density model.
Peer Review Status:
Awaiting Review
Subjects: Geosciences >> Space Physics submitted time 2017-01-22
Abstract： The problem of minimum-fuel aeroassisted orbital transfer of a high lift-to-drag ratio vehicle from Low Earth Orbit (LEO) or Geostationary Earth Orbit (GEO) to low-Earth orbit with an inclination change is considered. Assuming impulsive thrust, the trajectory design is described in detail and the aeroassisted orbital transfer is posed as a nonlinear optimal control problem. Through comparison of the double-impusive orbit transfer and aeroassisted orbit Transfer in noncoplanar orbit, we concluded the influence of altitude difference from two noncoplanar orbits and the perigee choice of the middle transtion orbit. The main problem that aeroassisted orbital transfer may face is hypersonic flight in the upper atmosphere. In the end the technology used in X-37B flight was concluded.
Peer Review Status:Awaiting Review
Subjects: Geosciences >> Space Physics submitted time 2017-01-22
Abstract： Solar proton event forecast is very important to guarantee the security of spacecrafts and astronauts. According to the short to medium term space mission, the greater than 10 MeV, 30 MeV and 60 MeV solar proton event fluences are statistically analyzed. It is found that the probability distributions of solar proton event fluences basically satisfy the log-normal distributions, and their expectations and averages are logarithmic functions of the time periods. Based on these, a short to medium term forecast model of solar proton event fluences is built, which can forecast the greater than 10 MeV, 30 MeV and 60 MeV solar proton event fluences with some given confidence levels for 1 to 365 days. So, this model is very helpful to safely carry out the space mission with less than 1 year mission period.
Peer Review Status:Awaiting Review
Subjects: Geosciences >> Space Physics submitted time 2017-01-22
Abstract： Solar activity and Earth's space environment can effect the operation and safety of spacecraft, and they are also the main error source of navigation, positioning, and communication based on radio waves applications system. In this field, the L-band solar radio burst is regarded as a potential threat to Global Navigation Satellite System(GNSS) stability and performance. When the solar radio burst exceeds a threshold value, the radio noise from solar emission will increase dramatically, which can give rise to GNSS receiver tracking loss and positioning failure located in the sunlit hemisphere of the Earth. In this paper, by using the solar radio flux data, L-band scintillation data, and GPS receiver observation network data located in different regions, effect of the 13 December 2006 solar radio burst on GPS observations are investigated in detail. Results show that the disruption caused by this radio burst event is obvious, and the amplitude scintillation events occur and GPS signal losses of lock are detected. Furthermore, the GPS satellite signal locked at several GPS station is interrupted and the observed GPS satellite number is less than 4 during this solar radio burst. The event resulted in GPS service failure for about six minutes. By comparison, those stations located nearby sub-solar point are more serious than that of far away from it.
Peer Review Status:Awaiting Review
Subjects: Geosciences >> Space Physics submitted time 2016-05-13
Abstract： According to the databases of AP-8 and CRRESPRO proton radiation belt models, comparison between both models on the magnetic equator is carried out and reasons for their differences are presented. The model of proton radiation belt for the peak radiation region is developed by using the analytic function, which includes the submodel for relationship between the L value corresponding to the peak value of omni-directional proton differential flux (L_c) and the proton energy, and the submodel for relationship between the peak value of omni-directional proton differential flux J_(max) and the proton energy. Finally, the observation of energetic proton on the magnetic equator from RBSP A satellite's REPT telescope is used to compare with the results from AP-8 model,CRRESPRO model and the central radiation model. It is found that the values of omni-directional proton differential flux for 78.9, 102.6 and 208 MeV channels from RBSP A satellite are obviously larger than those from the three models, but the values of L_c from RBSP A satellite are very close to those from AP-8 model and the central radiation model, and RBSP satellite also observes the hidden secondary proton radiation belt presented by CRRESPRO Quiet model.
Peer Review Status:Awaiting Review
Subjects: Geosciences >> Space Physics submitted time 2016-05-13
Abstract： The outer radiation belt consists mainly of high energy electrons trapped by the Earth's magnetic field. The disturbance of the geomagnetic field caused by the Coronal Mass Ejection (CME) or the Co-rotating Interaction Region (CIR) can result in electron radiation belt variations. According to the variation feature of high energy electron flux in the outer radiation belt during magnetic storms, a novel index referred to as high electron flux fluctuation index was evaluated by using the 5-min resolution sampled electron flux data provided by GOES, and its correlation with geomagnetic Kp index was analyzed. It is found that high electron flux fluctuation index has a good correlation with geomagnetic Kp index, and the new index can be used as an indicator of geomagnetic storm occurrence. In comparison with 3-hour Kp index, which is wildly used in space environment operation prediction system, the suggested index in this paper can alert geomagnetic storm occurrence earlier.
Peer Review Status:Awaiting Review
Subjects: Geosciences >> Space Physics submitted time 2016-05-13
Abstract： The Reverse Monte Carlo (RMC) method is a powerful biasing technique available in Geant 4, also known as the Adjoint Monte Carlo method. In this method, particles are generated on the external boundary of the sensitive part of the geometry and then tracked backward in the geometry till they reach the external source surface, or exceed an energy threshold. By this way the computing time is focused only on particle tracks that are contributing to the tallies. The RMC method is much rapider than the Forward Monte Carlo (FMC) method when the sensitive part of the geometry is smaller compared to the rest of the geometry as well as the external source. Compared with the FMC method, accuracy of the RMC method applied to the radiation dose of the satellite is verified. Comparisons of RMC with the SHIELDOSE2, SSAT show that RMC is the preferred method of high-precision satellite radiation dose.
Peer Review Status:Awaiting Review
Subjects: Geosciences >> Space Physics submitted time 2016-05-13
Abstract： Solar activity and Earth's space environment can effect the operation and safety of spacecraft, and they are also the main error source of navigation, positioning, and communication based on radio waves applications system. In this field, the L-band solar radio burst is regarded as a potential threat to Global Navigation Satellite System(GNSS) stability and performance. When the solar radio burst exceeds a threshold value, the radio noise from solar emission will increase dramatically, which can give rise to GNSS receiver tracking loss and positioning failure located in the sunlit hemisphere of the Earth. In this paper, by using the solar radio flux data, L-band scintillation data, and GPS receiver observation network data located in different regions, effect of the 13 December 2006 solar radio burst on GPS observations are investigated in detail. Results show that the disruption caused by this radio burst event is obvious, and the amplitude scintillation events occur and GPS signal losses of lock are detected. Furthermore, the GPS satellite signal locked at several GPS station is interrupted and the observed GPS satellite number is less than 4 during this solar radio burst. The event resulted in GPS service failure for about six minutes. By comparison, those stations located nearby sub-solar point are more serious than that of far away from it.
Peer Review Status:Awaiting Review
Subjects: Geosciences >> Space Physics submitted time 2016-05-04
Abstract： The study of the ionosphere responses to Corotating Interaction Regions (CIRs) and Coronal Mass Ejections (CMEs) got much attentions in rencent years. With the comparison of different types of ionosphere response caused by different disturbance sources from solar activity and interplanetary solar wind, morphological changes and physical process of ionospheric storms can be understood more impressively and comprehensively. It provides a possibility to predict ionospheric disturbance states according to different solar wind conditions in advance as well. GPS-TEC data at a mid-latitude station (131 degrees E, 35 degrees N) are used to analyze the ionosphere response during geomagnetic disturbances induced by 109 CIRs and 45 CMEs over the period 2001 to 2009. Firstly, the TEC difference are determined to achieve the information of ionospheric positive or negative storms during the CIR and CME events. The definition of a ionospheric storms is relative TEC greater than or equal to 15% and persisting for more than 4 hours; Secondly, year dependence, seasonal dependence, time delay between ionospheric storms and geomagnetic storms, geomantic storm intensity dependence and time duration of ionospheric storms are analyzed in detail. Analysis results indicate that the types of ionospheric storms vary in different phases of a solar cycle. CIR-driven positive and positive-negative storms are more likely to occur in the declining phase of the solar cycle, while negative phase storms more in solar maximum and negative-positive storms mainly in solar minimum. CME-driven positive storms and negative storms mostly occur in solar maximum. There is no remarkable seasonal difference for the occurrence of different types of ionospheric storms except the positive-negative storms most likely to occur in summer. The time delays between geomagnetic disturbances and the start time of ionospheric storms are-6 to 6 hours in general, but CIR-driven ionopsheric storms involve in a wider range with a time delay of-12 to 24 hours and CME-driven storms is delayed from 6 to 6 hours. Moreover, for CIR-driven ionospheric storms, positive and negative storms mostly occur in main phase of magnetic storms, positive-negative storms mostly in initial and main phase, and negative-positive storms mainly in initial phase. For CME-driven storms, positive, negative and positive-negative storms basically occur in main phase. Our investigation also demonstrates certain correlation between the types of ionospheric storms and the AE maximum indices. Ionopsheric negative storms often occur in stronger geomagnetic activity, with the AE maximum intensity between 800 to 1200nT while positive-negative storms tend to occur with AE maximum intensity higher than 400 nT. Compared to CIR driven storms, AE maximum value during CME driven storms is higher. The duration of CIR-driven storms is longer (1 to 6 days) than that of CME-driven storms (1 to 4 days). The ionosphere response to interplanetary conditions contribute to the study the ionospheric disturbance. Statistical analysis of the ionosphere response to the CIR and CME in Mid-latitude regions indicate that there are some certain correlations among ionospheric changes, solar activities, interplanetary conditions and geomagnetic conditions. The ionospheric storms could be predicted more accurately and meticulously by distinguishing the different types of interplanetary conditions.
Peer Review Status:Awaiting Review
Subjects: Geosciences >> Space Physics submitted time 2016-05-03
Abstract： Drag coefficient sequence C_d is obtained by solving Tiangong 1 continuous 55 days (d)GPS orbit data with different arc length. The same period solar radiation flux f_(10.7)and geomagnetic index a_p,A_p sequences are high and low frequency multi-wavelet decomposed. Statistical analysis results of the multilayer sliding correlation between space environmental parameters and decomposition of C_d show that lag correlation between the satellite drag coefficient sequence after wavelet decomposition and the corresponding level of f_(10.7),A_p sequence is good. It is also verified that the C_d prediction is feasible. Prediction residuals of Cd with different regression models and different sample lengths are analyzed. The results show that the case setting sample length of 20 days and selecting f_(10.7)regression model is best. It is also show that NRLMSIS-00 model's response in the region of 350 km (Tiangong's altitude)and low-middle latitude (Tiangong's inclination)is excessive during the ascent phase of geomagnetic activity A_p and is inadequate during decline phase. Additionally,for the low-frequency decomposition sequence NRLMSIS-00 model's response is appropriate during the ascent rising phase of f_(10.7). For the high frequency decomposition sequence,NRLMSIS-00 model 's response is small-scale inadequate during the ascent phase of f_(10.7)and is excessive during the decline phase of f_(10.7). Finally,the summary of potential use and outlook are listed; this method has an important reference value for improving the spacecraft orbit prediction accuracy.
Peer Review Status:Awaiting Review
Subjects: Geosciences >> Space Physics submitted time 2016-04-22
Abstract： The planetary three-hour-range Kp index is widely used in space weather services. Due to the two weeks' time delay of the release of Kp index, the real-time estimation of the Kp index becomes essential for space weather forecasting organizations. In this paper, an improved algorithm for real-time Kp estimation on the basis of Takahashi's procedure was developed. The new algorithm improved the accuracy of Kp estimation by distinguishing the day-to-day variations of geomagnetic field's regular variation and taking account of both the diurnal and seasonal variations of magnetic disturbance. The statistical result shows that the Prediction Efficiency (PE) increased from 0.77 to 0.84 using Fredericksburg's data, from 0.88 to 0.92 using the nine stations network's data. Using the data from Beijing Ming Tombs observatory (BMT) from 2000 to 2006, the PE increased from 0.70 to 0.80 compared with the Takahashi procedure. The error of the estimations differs from universal time, season and the scale of magnetic disturbance. The RMS error reached maximum for Kp=7. Analysis of Kp using the SuperMAG indices indicated that the asymmetric distribution of Kp stations affects the Kp nowcast performance.
Peer Review Status:Awaiting Review
Subjects: Geosciences >> Space Physics submitted time 2016-04-22
Abstract： Forecasting the solar proton event fluence is very important to guarantee the safety of spacecrafts and astronauts.Within various periods less than 1 year,the occurrence probabilities of the solar proton events and their fluences were analyzed for solar active years and solar quiet years, respectively.It is found that the probability distributions of solar proton event fluence basically satisfy the log-normal distributions.Based on this,solar proton event fluence can be forecasted with some given confidence levels for different duration space missions ranging from 1 day to 365 days.
Peer Review Status:Awaiting Review
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