Modeling the charging of geosynchronous and interplanetary spacecraft using Nascap-2k

Nascap-2k is the updated version of the NASCAP/GEO spacecraft charging analysis code. In addition to packaging the physical content of NASCAP/GEO in a modern way, Nascap-2k incorporates other plasma analysis codes (in particular, the DynaPAC code) in order to extend its applicability to a wide variety of plasma environments. Nascap-2k also includes an interactive Object Toolkit for defining spacecraft surface models for analysis. In this paper we focus on the tenuous plasma charging capabilities of the code, with application to DSCS-III (geosynchronous environment), STEREO (solar wind environment) and MESSENGER (solar wind environment near 0.4 AU).     

基于伪距和观测量的地球同步卫星动力学定轨研究

利用伪距和观测量对同步卫星进行了动力学定轨的研究，给出了伪距和观测量的测量方程和修正方法，采用国内4个监测站的模拟数据进行了仿真计算．结果表明，采用7天弧长伪距和数据进行轨道改进及轨道外推的精度，与5天弧长数据的计算结果相当，但远优于3天数据的计算结果．在观测随机误差为3m时，7天弧长数据定轨精度约为5m，预报7天径向精度优于20m．     

星载电子系统高能质子单粒子翻转率计算

文章对星栽电子系统空间高能质子单粒子翻转率计算方法进行了研究。总结了13种主要计算质子单粒子翻转率的方法,并对各种算法之间的相似性和差异性进行了比对分析。用Visual Basic语言编程,实现了高能质子单粒子翻转率计算模型软件化,为高能质子单粒子效应加固设计和验证评估提供技术依据。计算了几种典型轨道上的质子单粒子翻转率；在此基础上,与在轨观测数值进行比对分析验证,并分析了质子单粒子翻转率与空间轨道的关系。     

Optimising filtering of two-line element sets to increase re-entry prediction accuracy for GTO objects

Predicting re-entry epoch of space objects enables managing the risk to ground population. Predictions are particularly difficult for objects in highly-elliptical orbits, and important for objects with components that can survive re-entry, e.g. rocket bodies (R/Bs). This paper presents a methodology to filter two-line element sets (TLEs) to facilitate accurate re-entry prediction of such objects. Difficulties in using TLEs for precise analyses are highlighted and a set of filters that identifies erroneous element sets is developed. The filter settings are optimised using an artificially generated TLE time series. Optimisation results are verified on real TLEs by analysing the automatically found outliers for exemplar R/Bs. Based on a study of 96 historical re-entries, it is shown that TLE filtering is necessary on all orbital elements that are being used in a given analysis in order to avoid considerably inaccurate results.     

“多对多”模式下GEO卫星在轨加注任务规划

随着在轨服务技术的发展和对航天器发射运营成本的控制，航天器在轨服务模式将由“一对一”服务逐步发展为“一对多”“多对多”的服务模式。在具有多个服务目标的模式下，针对服务航天器的任务分配与规划将变得尤为关键。因此，本文研究了多服务航天器为多个地球同步轨道(GEO)卫星进行在轨加注的任务规划问题。首先，考虑服务航天器容量约束、服务路径约束等多类约束条件，以最小化燃料消耗为优化指标，以每个服务航天器的服务顺序为决策变量，建立“多对多”在轨加注任务规划模型。其次，针对遗传算法局部搜索能力差、易陷入局部最优的缺陷，设计了一种将大邻域搜索算法和遗传算法相结合的混合启发式算法(LNS-GA)，用以求解该任务规划问题。该算法利用大邻域搜索算法中的“破坏”和“修复”思想，对遗传算法每一代种群中的精英个体进行进一步的迭代搜索，从而增强算法的局部搜索能力。最后，通过设定的仿真场景与单一遗传算法进行仿真对比，验证了本文所提出算法的有效性和优越性。     

The Geostationary Earth Radiation Budget Edition 1 data processing algorithms

The Geostationary Earth Radiation Budget (GERB) instrument is the first to measure the earth radiation budget from a geostationary orbit. This allows a full sampling of the diurnal cycle of radiation and clouds – which is important for climate studies, as well as detailed process studies, e.g. the lifecycle of clouds or particular aerosol events such as desert storms. GERB data is now for the first time released as Edition 1 data for public scientific use. In this paper we summarise the algorithms used for the Edition 1 GERB data processing and the main validation results. Based on the comparison with the independent CERES instrument, the Edition 1 GERB accuracy is 5% for the reflected solar radiances and 2% for the emitted thermal radiances.     

Remote sensing of aerosol and radiation from geostationary satellites

The paper presents a high-level overview of current and future remote sensing of aerosol and shortwave radiation budget carried out at the US National Oceanic and Atmospheric Administration (NOAA) from the US Geostationary Operational Environmental Satellite (GOES) series. The retrievals from the current GOES imagers are based on physical principles. Aerosol and radiation are estimated in separate processing from the comparison of satellite-observed reflectances derived from a single visible channel with those calculated from detailed radiative transfer. The radiative transfer calculation accounts for multiple scattering by molecules, aerosol and cloud and absorption by the major atmospheric gases. The retrievals are performed operationally every 30 min for aerosol and every hour for radiation for pixel sizes of 4-km (aerosol) and 15- to 50-km (radiation). Both retrievals estimate the surface reflectance as a byproduct from the time composite of clear visible reflectances assuming fixed values of the aerosol optical depth. With the launch of GOES-R NOAA will begin a new era of geostationary remote sensing. The Advanced Baseline Imager (ABI) onboard GOES-R will offer capabilities for aerosol remote sensing similar to those currently provided by the Moderate Resolution Imaging Spectroradiometer (MODIS) flown on the NASA Earth Observing System (EOS) satellites. The ABI aerosol algorithm currently under development uses a multi-channel approach to estimate the aerosol optical depth and aerosol model simultaneously, both over water and land. Its design is strongly inspired by the MODIS aerosol algorithm. The ABI shortwave radiation budget algorithm is based on the successful GOES Surface and Insolation Product system of NOAA and the NASA Clouds and the Earth’s Radiant Energy System (CERES), Surface and Atmospheric Radiation Budget (SARB) algorithm. In all phases of the development, the algorithms are tested with proxy data generated from existing satellite observations and forward simulations. Final assessment of the performance will be made after the launch of GOES-R scheduled in 2012.     

Observations in the thermal IR and visible of a retired satellite in the graveyard orbit,and comparisons to active satellites in GEO

There exists a population of defunct satellites in the geo-stationary arc that potentially pose a hazard to current and future operational satellites. These drifting, non-station-kept objects have a variety of ages and sizes, and many are trapped in libration orbits around the Earth?s two gravitational potential wells (the non-spherical nature of the Earth gives rise to two geo-potential wells or “stable points” that affect objects in geostationary and geosynchronous orbits), whereas others were boosted to higher altitudes into so-called “graveyard” orbits.     

Longitude-dependent effects of fragmentation events in the geosynchronous orbit regime

The effects of on-orbit fragmentation events on localized debris congestion in each of the longitude slots of the geosynchronous orbit (GEO) regime are evaluated by simulating explosions and collisions of uncontrolled rocket bodies in multiple orbit configurations, including libration about one or both of the gravitational wells located at 75°E and 105°W. Fragmentation distributions are generated with the NASA Standard Breakup Model, which samples fragment area-to-mass ratio and delta-velocity as a function of effective diameter. Simulation results indicate that the long-term severity and consequence of a GEO fragmentation event is strongly dependent upon parent body longitude at the epoch of fragmentation, which can spawn bi-annual “fragment storms” in high-risk longitude slots, driven by lower-energy fragments that have been captured and have started librating around the nearby gravitational well.     

Long-term photometric signature study of two GEO satellites

Geostationary earth orbit satellites have been extensively used for unique high-orbit stationary characteristics. Long-term precise investigation is an important issue in the observation of GEO satellites, since it can provide valuable information on the satellites’ operation state, discrimination and early warning analysis. Ground-based optical-electronic devices play a significant role in the observation. 4-month photometric signature variation of two satellites is presented based on the successive observations using the 1.56-meter telescope of Shanghai Astronomical Observatory (SHAO). It can be concluded that the long-term brightness change mainly results from the sun declination angle and regular orbit maneuver. Moreover, the solar panel offsets of the two satellites are analyzed and found to be approximately 4 degrees. Estimation of photometric accuracy reaches 0.15 mag for the application of CCD drift-scan optical-electronic technique.