航天器再生伪码测距体制分析

再生伪码测距体制通过对上行伪码测距信号进行恢复,并重新调制到下行载波发送,可以获得可观的测距信号信噪比增益。对这部分增益的合理使用,可以获得较高的测距精度,也可以获得较短的测距时间,还可以提高遥测信号的功率。本文从测距码、捕获时间以及测距信号与遥控/遥测信号之间的相互干扰3方面介绍了再生伪码测距体制。     

Turbo码块同步参数优化设计

在信道码码块同步技术研究的基础上,针对CCSDS(空间数据系统咨询委员会)建议规定的Turbo码,为不同码块长度、不同编码效率的Turbo码设计一组最佳同步参数,以最优化平均入锁时间和数据有效率。利用理论推导出的解析公式,计算不同参数下的平均入锁时间和数据有效率,从而优选出最佳同步参数,并归纳总结最佳同步参数的特点。本文得到的同步参数可为实际工程提供参考。     

Empirical model of the TEC response to the geomagnetic activity over the North American region

The paper presents an empirical model of the total electron content (TEC) response to the geomagnetic activity described by the K_p-index. The model is built on the basis of TEC measurements covering the region of North America (50°W–150°W, 10°N–60°N) for the period of time between October 2004 and December 2009. By using a 2D (latitude-time) cross-correlation analysis it is found that the ionospheric response to the geomagnetic activity over the considered geographic region and at low solar activity revealed both positive and negative phases of response. The both phases of the ionospheric response have different duration and time delay with respect to the geomagnetic storm. It was found that these two parameters of the ionospheric response depend on the season and geographical latitude. The presence of two phases, positive and negative, of the ionospheric response imposed the implementation of two different time delay constants in order to properly describe the two different delayed reactions. The seasonal dependence of the TEC response to geomagnetic storms is characterized by predominantly positive response in winter with a short (usually ∼5–6 h) time delay as well as mainly negative response in summer with a long (larger than 15 h) time delay. While the TEC response in March and October is more close to the winter one the response in April and September is similar to the summer one.     

长波授时附加二次相位因子修正方法

附加二次相位因子（ASF）是影响长波授时精度的主要因素,而其理论计算复杂、实测成本太高,不便于工程推广。本文选取华北平原区域为研究范围,提出一种简单高效的ASF修正方法———建立对应的ASF数据网格,采用插值算法进行ASF修正研究。通过对ASF数据网格的验证和分析,得到了和预期效果相一致的实验结果。实验结果表明：建立区域性的ASF数据网格有利于快速地修正ASF误差,便于实际工程应用。     

脉冲星时间尺度的相关研究

在已有脉冲星时频率稳定度σZ算法基础上,提出了针对长时间跨度计时观测数据缺失（gap）的脉冲星时稳定度的处理方法,并以该类典型的脉冲星J1857＋0943于帕克斯天文台PARKES的实测数据为例,给出稳定度计算结果并讨论,简介了计时软件包Tempo2得到最小残差的拟合过程,并以Tempo2处理后的数据作为输入,由其时间尺度结果引发对Tempo2处理脉冲星时间尺度的相关分析与讨论,介绍了含gap的脉冲星观测数据在综合脉冲星时算法中的应用。     

GNSS geodetic techniques for time and frequency transfer applications

We performed an initial analysis of the pseudorange data of the GIOVE-B satellite, one of the two experimental Galileo satellites currently in operation, for time transfer.¹ For this specific aim, software was developed to process the GIOVE-B raw pseudoranges and broadcast navigation messages collected by the Galileo Experimental Sensor Stations (GESS) tracking network, yielding station clock phase errors with respect to the Experimental Galileo System Time (EGST). The software also allows processing the Global Positioning System (GPS) P1 and P2 pseudorange data with broadcast navigation message collected at the same stations to obtain the station clock phase errors with respect to the GPS system time (GPST). Differencing these solutions between stations provides two independent means of GNSS time transfer. We compared these time transfer results with Precise Point Positioning (PPP) method applied to GPS data in combined carrier-phase and pseudorange mode as well as in pseudorange-only mode to show their relative merits. The PPP solutions in combined carrier-phase and pseudorange mode showed the least instability of the methods tested herein at all scales, at few parts in 10¹⁵ at 1 day for the stations processed, following a tau^−½ interval dependency. Conversely, the PPP solutions in pseudorange-only mode are an order of magnitude worst (few parts in 10¹⁴ at 1 day for the stations processed) following a tau⁻¹ power-law, but slightly better than the single-satellite raw GPS time transfer solutions obtained using the developed software, since the PPP least-squares solution effectively averages the pseudorange noise. The pseudorange noise levels estimated from PPP pseudorange residuals and from clock solution comparisons are largely consistent, providing a validation of our software operation. The raw GIOVE-B time transfer, as implemented in this work, proves to be slightly better than single-satellite raw GPS satellite time transfer, at least in the medium term. However, one of the processed stations shows a combined GPS P1 and P2 pseudorange noise level at 2 m, a factor 2 worst than usually seen for geodetic receivers, so the GPS time transfer results may not be at their best for the cases processed. Over the short term, the GPS single-satellite time transfer instability outperforms the GIOVE-B by an order of magnitude at 1 s interval, which would be due to the different characteristics of the tracking loop filters for GPS P1 and P2 on one hand and the GIOVE-B signals on the other. Even at this preliminary stage and using an experimental satellite system, results show that the GIOVE-B (and hence Galileo) signals offer interesting perspectives for high precision time transfer between metrological laboratories.     

基于时间累计法的工时定额评估数学模型的建立

采用时间累计法对基本维修作业建立数学模型，解决了表格式工时定额数据多、误差大、使用不便和管理复杂等问题。而且，通过设计和建立数学模型数据库系统，为计算机辅助制定工时定额创造了条件。以基本维修作业为研究对象，系统地分析了基本维修作业划分和量化的方法及步骤，包括模型确定的方法和系数求解公式，并对基于累计法的基本维修作业数学模型进行了深入的研究，从而得到了工时定额评估的一般方法。     

Oxygen concentration variation in ullage influenced by dissolved oxygen evolution

To determine the oxygen concentration variation in ullage that results from dissolved oxygen evolution in an inert aircraft fuel tank, the CFD method with a mass transfer source is applied in the present study. An experimental system is also designed to evaluate the accuracy of the CFD simulations. The dissolved oxygen evolution is simulated under different conditions of fuel load and initial oxygen concentration in ullage of an inert fuel tank with stimulations of heating and pressure decrease. The increase in the oxygen concentration in ullage ranges from 0.82% to 5.92% upon stimulation of heating and from 0.735% to 12.36% upon stimulation of a pressure decrease for an inert ullage in the simulations. The heating accelerates the release of the dissolved oxygen from the fuel by increasing the mass transfer rate in the mass transfer source and decreasing the pressure, thereby accelerating the dissolved oxygen evolution by increasing the concentration difference between the gas and the fuel. The time constant that represents the oxygen evolution rate is independent of the initial oxygen concentration in ullage of an inert tank but depends closely on the fuel load, temperature and pressure. The time constant can be fitted using a polynomial equation relating the fuel load to temperature in the heating stimulation with an accuracy of 4.77%. Upon stimulation of a pressure decrease, the time constant can be expressed in terms of the fuel load and the pressure, with an accuracy of 5.02%.     

Combining GPS and GLONASS for time and frequency transfer

Geodetic time and frequency transfer (TFT) consists in a comprehensive modeling of code and carrier phase observations from Global Navigation Satellite System (GNSS) in order to determine the synchronization errors between two remote clocks connected to GNSS receivers. Using either common view (CV), or Precise Point Positioning (PPP), current GNSS time transfer uses only GPS measurements. This study combines GPS and GLONASS observations in geodetic TFT in order to determine the added value of the GLONASS data in the results. Using the software Atomium, we demonstrate on one hand that using both constellations improves the solution for both CV and PPP results when analysing short data batches. In that case, there are not enough GPS code data to calibrate the solution, and additional GLONASS code data allows us to retrieve a correct absolute value for the solution. On the other hand, the CV results of frequency transfer are not significantly affected by adding GLONASS data, while in PPP the combination with GLONASS modifies the frequency transfer results, and in particular the daily frequency offset, with maximum differences of 150 ps between the TFT solutions obtained with GPS-only or GPS + GLONASS.