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 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 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 2016-05-03
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： 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
Hits
Hits
Downloads
Comment