微重力火箭设计中减旋方案等问题

讨论了一种微重力火箭总体设计中减旋方案，飞行载荷，气动加热与壁温计算等几个关键问题。结合该火箭的具体特点，提出了一种简单实用的被动式减旋措施，即，安装反旋尾翼及辅助减旋机构，并分析了减旋与动稳定性的关系。对超高音速火箭的飞行载荷和气动热进行了分析计算。     

模糊控制在导弹瞬态气动热流试验中的研究

导弹与高速飞行器气动模拟试验瞬态热控过程的特点是变化复杂、瞬变、高度非线性、强耦合,很难或者根本无法建立控制的数学模型.模糊控制具有鲁棒性好,对参数变化的适应性强,过渡过程时间短等常规控制方法所不能比拟的优点.将模糊控制方法应用于导弹瞬态气动加热模拟控制系统,使该系统能够按照导弹高速飞行过程中弹体表面热流的瞬态连续变化对气动模拟加热过程实施快速的动态控制.     

Measuring atmospheric density using GPS–LEO tracking data

We present a method to estimate the total neutral atmospheric density from precise orbit determination of Low Earth Orbit (LEO) satellites. We derive the total atmospheric density by determining the drag force acting on the LEOs through centimeter-level reduced-dynamic precise orbit determination (POD) using onboard Global Positioning System (GPS) tracking data. The precision of the estimated drag accelerations is assessed using various metrics, including differences between estimated along-track accelerations from consecutive 30-h POD solutions which overlap by 6 h, comparison of the resulting accelerations with accelerometer measurements, and comparison against an existing atmospheric density model, DTM-2000. We apply the method to GPS tracking data from CHAMP, GRACE, SAC-C, Jason-2, TerraSAR-X and COSMIC satellites, spanning 12 years (2001–2012) and covering orbital heights from 400 km to 1300 km. Errors in the estimates, including those introduced by deficiencies in other modeled forces (such as solar radiation pressure and Earth radiation pressure), are evaluated and the signal and noise levels for each satellite are analyzed. The estimated density data from CHAMP, GRACE, SAC-C and TerraSAR-X are identified as having high signal and low noise levels. These data all have high correlations with anominal atmospheric density model and show common features in relative residuals with respect to the nominal model in related parameter space. On the contrary, the estimated density data from COSMIC and Jason-2 show errors larger than the actual signal at corresponding altitudes thus having little practical value for this study. The results demonstrate that this method is applicable to data from a variety of missions and can provide useful total neutral density measurements for atmospheric study up to altitude as high as 715 km, with precision and resolution between those derived from traditional special orbital perturbation analysis and those obtained from onboard accelerometers.     

Debris flux comparisons from the Goldstone Radar,Haystack Radar,and Hax Radar prior,during, and after the last solar maximum

The continual monitoring of the low Earth orbit (LEO) debris environment using highly sensitive radars is essential for an accurate characterization of these dynamic populations. Debris populations are continually evolving since there are new debris sources, previously unrecognized debris sources, and debris loss mechanisms that are dependent on the dynamic space environment. Such radar data are used to supplement, update, and validate existing orbital debris models. NASA has been utilizing radar observations of the debris environment for over a decade from three complementary radars: the NASA JPL Goldstone radar, the MIT Lincoln Laboratory (MIT/LL) Long Range Imaging Radar (known as the Haystack radar), and the MIT/LL Haystack Auxiliary radar (HAX). All of these systems are highly sensitive radars that operate in a fixed staring mode to statistically sample orbital debris in the LEO environment. Each of these radars is ideally suited to measure debris within a specific size region. The Goldstone radar generally observes objects with sizes from 2 mm to 1 cm. The Haystack radar generally measures from 5 mm to several meters. The HAX radar generally measures from 2 cm to several meters. These overlapping size regions allow a continuous measurement of cumulative debris flux versus diameter from 2 mm to several meters for a given altitude window. This is demonstrated for all three radars by comparing the debris flux versus diameter over 200 km altitude windows for 3 nonconsecutive years from 1998 to 2003. These years correspond to periods before, during, and after the peak of the last solar cycle. Comparing the year to year flux from Haystack for each of these altitude regions indicate statistically significant changes in subsets of the debris populations. Potential causes of these changes are discussed. These analysis results include error bars that represent statistical sampling errors.     

Structure of the migrating diurnal tide in the Whole Atmosphere Community Climate Model (WACCM)

As part of an ongoing effort to understand the migrating diurnal tide generated by the NCAR Whole Atmosphere Community Climate Model, version 3 (WACCM3), we compare the WACCM3 migrating diurnal tide in the horizontal wind and temperature fields to similar results from the Global Scale Wave Model (GSWM). The WACCM3 diurnal tidal wind fields are also compared to tropical radar measurements at Kauai (22°N, 200.2°E) and Rarotonga (21.3°S, 199.7°E). The large-scale features of the WACCM3 results, such as the global spatial structure and the semiannual amplitude variation are in general agreement with past tidal studies; however, several differences do exist. WACCM3 exhibits a much higher degree of hemispheric asymmetry, lower overall amplitudes around the equinoxes, and peaks which are more confined in latitude when compared with the GSWM. Factors which may contribute to such differences between WACCM3 and GSWM are the solar heating profiles from ozone and water vapor, dissipation, and the zonal mean zonal winds. We find that the internally generated heating in WACCM3 and eddy dissipation values are both smaller than the values specified in the GSWM; the eddy dissipation fields and zonal mean zonal winds of the two models also display measurable differences in spatial structure. Comparisons with radar data show several differences in spatial and seasonal structure. In particular, the diurnal tide zonal winds in WACCM3 above Kauai are considerably larger in amplitude than those observed in the radar data, due to contributions from nonmigrating tidal components including wave numbers eastward 1 through 3, westward 2, and stationary components, which interfere constructively with the migrating component around equinox in WACCM3.     

对接机构真空热试验外热流模拟方案研究

根据对接机构的结构特点和真空热试验要求,提出了红外笼、电加热片,以及红外笼+加热片组合3种对接机构外热流模拟方案.仿真计算了在真空罐模拟环境中各方案对接机构构件的稳态温度分布,并与轨道环境进行了比较.确定了最大温差构件.结果表明:红外笼方案较简单,适于正样飞行产品;电加热片和红外茏+加热片方案的地面模拟准确性较佳,适于初样地面产品试验.     

某卫星真空热试验中一些新要求的解决措施

某卫星在进行真空热试验时,对热流提出了三个方面的新要求：(1)对某些热流要求较低的加热区的加热笼进行修改,提高其低热流实现能力;(2)减小支架漏热;(3)实时计算设计热流和实际热流的周期积分偏差。由于修改时的约束条件较多,新的要求的满足非常困难。经过努力,最终解决了这些问题,通过对某些加热笼采取加热带双面涂黑漆的方法,实现了低热流;经过计算和针对性的设计,支架漏热不超过0．1188W;同时实现了设计热流与实际热流周期积分偏差的实时计算。     

大气密度对降落伞充气性能的影响

尽管火星表面大气非常稀薄,但降落伞仍是火星探测着陆系统中一种重要的减速装置。文章建立了一个降落伞的充气动力学模型,并根据此模型研究了大气密度对降落伞充气性能的影响。结果表明:降落伞的充气时间和充气距离是随大气密度的减小而增大,同时,随着大气密度的减小,降落伞开始张开的速度变得非常缓慢。     

对流层散射传播机制与特性分析

文章从对流层的一般特性入手,介绍了目前对流层散射传播机制研究的三种主要理论模型,分析了对流层散射传播所具有的一系列突出优点,同时重点讨论了传输损耗特性和衰落特性,并提出了克服其不足的有效措施,最后对未来的研究重点进行了展望。