International Practices to Protect the Geostationary Ring

Since more than 20 years reorbiting of geostationary satellites at the end of their mission is recommended and partially performed to protect the GEO environment. Now a worldwide accepted reorbiting altitude was defined by the Inter-Agency Space Debris Coordination Committee (IADC). Still only one-third of the aging satellites follow this IADC rule. Based on orbital data in the DISCOS database, the situation in the geostationary ring is analyzed. From 878 known objects, 305 are controlled inside their longitude slots, 353 are drifting above, below or through GEO, and 125 are in a libration orbit (status of January 2001). In the last four years (1997–2000) 58 spacecraft reached end-of-life. Twenty of them were reorbited in compliance with the IADC recommendations, 16 were reorbited below this recommendation and 22 were abandoned without any end-of-life disposal manoeuvre.     

弹道导弹基于仿真的落点精度修正

介绍了利用计算机仿真技术预测、修正弹道导弹落点 ,从而提高其命中精度的原理和方法 ,给出了导弹射前初始状态的测量方法以及导弹仿真的程序模型 ,并对一枚具体的导弹作了落点的仿真预测与落点修正 ,仿真的结果与实际情况相吻合。此方法在弹道导弹的实弹演习与作战中具有十分重要的价值 ,可在相关单位广泛使用。     

一种简易的曲面隐藏线消去法

本文介绍一种简易的曲面隐藏线消去法。先将曲面上各网点分成可见与不可见两类,然后根据线与线相关性,判断各网格线段的可见性,最后只显示或绘制所有的可见网格线段,得到消隐后的曲面立体图形,本法比较简易,调用方便,通用性较强,不管曲面是根据什么方法构作的,只要顺序输入两个方向的网点数及所有网点的坐标值,调用本子程序,一般均能进行曲面消隐。     

数控机床参考点的回归及其常见故障诊断

结合具体数控机床介绍参考点回归原理及过程,并对机床回参考点过程中各种形式的故障进行分析、诊断及总结。     

关于Caristi不动点定理的一点注记

本文利用半序方法给出了一个新的Caristi型不动点定理，与原有结果不同的是：在我们的定理中，不动点可以用迭代方法求出。     

涡格法中二等分平板的升力和力矩的高精度解

本文从点涡和控制点位置的选取出发,研究涡格法中二等分二维平板的升力和力矩的高精度解。发现除传统的1/4和3/4法则之外,还有服从一定规律的无穷多种离散化格式存在,均可以得到精确的升力和力矩。这就为在保证升力和力矩精确的前提下,寻找优于传统涡格法的载荷分布提供了理论依据。     

Performance improvement of real-time PPP ambiguity resolution using a regional integer clock

Obtaining reliable GNSS uncalibrated phase delay (UPD) or integer clock products is the key to achieving ambiguity-fixed solutions for real-time (RT) precise point positioning (PPP) users. However, due to the influence of RT orbit errors, the quality of UPD/integer clock products estimated with a globally distributed GNSS network is difficult to ensure, thereby affecting the ambiguity resolution (AR) performance of RT-PPP. In this contribution, by fully utilising the consistency of orbital errors in regional GNSS network coverage areas, a method is proposed for estimating regional integer clock products to compensate for RT orbit errors. Based on Centre National d’Études Spatiales (CNES) RT precise products, the regional GPS/BDS integer clock was estimated with a CORS network in the west of China. Results showed that the difference between the estimated regional and CNES global integer clock/bias products was generally less than 5 cm for GPS, whereas clock differences of greater than 10 cm were observed for BDS due to the large RT orbit error. Compared with PPP using global integer clock/bias products, the AR performance of PPP using the regional integer clock was obviously improved for four rover stations. For single GPS, the horizontal and vertical accuracies of ambiguity-fixed PPP solutions were improved by 56.2% and 45.3% on average, respectively, whereas improvements of 67.5% and 50.5% in the horizontal and vertical directions, respectively, were observed for the combined GPS/BDS situation. Based on a regional integer clock, the RMS error of a kinematic ambiguity-fixed PPP solution in the horizontal direction could reach 0.5 cm. In terms of initialisation time, the average time to first fix (TTFF) in combined GPS/BDS PPP was shortened from 18.2 min to 12.7 min. In view of the high AR performance realised with the use of regional integer clocks, this method can be applied to scenarios that require high positioning accuracy, such as deformation monitoring.     

航空发动机用钛合金BT20组织分析及相变点的测定

为了实现航空发动机上外调节片等重要零件的再制造，对其所用材料BT20钛合金进行组织分析，采用计算法和连续升温金相法研究了BT20钛合金的相变点，为航空发动机零部件的再制造修理提供参考。     

4050润滑油前后闪点倒置现象的分析

针对油泵润滑系统存在的4050高温合成航空润滑油闪点前后倒置的现象．做了大量试验，在逐一排除干扰因素后，确定原因为现场操作不规范，使洗涤汽油混入润滑油中．导致前闪点大幅下降。     

一种高精度TVD格式中声速点处理方法

针对Ｃｈａｋｒａｖａｒｔｈｙ－ＯｓｈｅｒＴＶＤ格式，提出了一种处理声速点的方法，可使声速点和非声速点的计算统一起来 。