Expectations for Infrared Spectroscopy of 9P/Tempel 1 from Deep Impact

The science payload on the Deep Impact mission includes a 1.05R11;4.8 μm infrared spectrometer with a spectral resolution ranging from R∼200R11;900. The Deep Impact IR spectrometer was designed to optimize, within engineering and cost constraints, observations of the dust, gas, and nucleus of 9P/Tempel 1. The wavelength range includes absorption and emission features from ices, silicates, organics, and many gases that are known to be, or anticipated to be, present on comets. The expected data will provide measurements at previously unseen spatial resolution before, during, and after our cratering experiment at the comet 9P/Tempel 1. This article explores the unique aspects of the Deep Impact IR spectrometer experiment, presents a range of expectations for spectral data of 9P/Tempel 1, and summarizes the specific science objectives at each phase of the mission.     

Deep Impact: Working Properties for the Target Nucleus – Comet 9P/Tempel 1

In 1998, Comet 9P/Tempel 1 was chosen as the target of the Deep Impact mission (AR17;Hearn, M. F., Belton, M. J. S., and Delamere, A., Space Sci. Rev., 2005) even though very little was known about its physical properties. Efforts were immediately begun to improve this situation by the Deep Impact Science Team leading to the founding of a worldwide observing campaign (Meech et al., Space Sci. Rev., 2005a). This campaign has already produced a great deal of information on the global properties of the cometR17;s nucleus (summarized in Table I) that is vital to the planning and the assessment of the chances of success at the impact and encounter. Since the mission was begun the successful encounters of the Deep Space 1 spacecraft at Comet 19P/Borrelly and the Stardust spacecraft at Comet 81P/Wild 2 have occurred yielding new information on the state of the nuclei of these two comets. This information, together with earlier results on the nucleus of comet 1P/Halley from the European Space AgencyR17;s Giotto, the Soviet Vega mission, and various ground-based observational and theoretical studies, is used as a basis for conjectures on the morphological, geological, mechanical, and compositional properties of the surface and subsurface that Deep Impact may find at 9P/Tempel 1. We adopt the following working values (circa December 2004) for the nucleus parameters of prime importance to Deep Impact as follows: mean effective radius = 3.25± 0.2 km, shape R11; irregular triaxial ellipsoid with a/b = 3.2± 0.4 and overall dimensions of ∼14.4 15; 4.4 15; 4.4 km, principal axis rotation with period = 41.85± 0.1 hr, pole directions (RA, Dec, J2000) = 46± 10, 73± 10 deg (Pole 1) or 287± 14, 16.5± 10 deg (Pole 2) (the two poles are photometrically, but not geometrically, equivalent), Kron-Cousins (V-R) color = 0.56± 0.02, V-band geometric albedo = 0.04± 0.01, R-band geometric albedo = 0.05± 0.01, R-band H(1,1,0) = 14.441± 0.067, and mass ∼715;10¹³ kg assuming a bulk density of 500 kg m⁻³. As these are working values, {i.e.}, based on preliminary analyses, it is expected that adjustments to their values may be made before encounter as improved estimates become available through further analysis of the large database being made available by the Deep Impact observing campaign. Given the parameters listed above the impact will occur in an environment where the local gravity is estimated at 0.027R11;0.04 cm s⁻² and the escape velocity between 1.4 and 2 m s⁻¹. For both of the rotation poles found here, the Deep Impact spacecraft on approach to encounter will find the rotation axis close to the plane of the sky (aspect angles 82.2 and 69.7 deg. for pole 1 and 2, respectively). However, until the rotation period estimate is substantially improved, it will remain uncertain whether the impactor will collide with the broadside or the ends of the nucleus.     

随机疲劳裂纹扩展及动态可靠性分析

在确定性袭纹扩展模型的基础上，建立了疲劳裂纹扩展的随机模型。考虑裂纹扩展引起的强度衰减，建立了实用的动态可靠性分析模型。     

优化的GM(1,1)模型及其适用范围

在已有灰色理论的基础上,利用“最小二乘法”确定GM(1,1)白化权函数的时间响应函数中的常数c,摈弃了传统GM(1,1)把原始序列中x^(0)(1)作为初始条件的欠科学的做法,构建了时间响应函数的优化模型。经大量的数据模拟和预测,发现优化的GM(1,1)模型各项指标均优于传统的GM(1,1)模型,且拓宽了其适用范围。     

Atmospheric reentry hemisphere prediction for prograde orbits using logical disjunction

A unique logic-based algorithm for atmospheric reentry hemisphere prediction is presented for spacecraft in low-eccentricity, prograde low Earth orbits at altitudes of 300 km and lower. Using two-line element (TLE) data for initial orbit conditions, coupled with coarse estimates for spacecraft aerodynamic characteristics, the algorithm relies on logical disjunction operations based on a dual analysis of histogram and two-weighted Gaussian probability density function (PDF) fits of predicted reentry latitude data. The algorithm requires the execution of a series of parametric simulations to determine the reentry hemisphere for variations in spacecraft aerodynamic coefficients and drag reference area. When implemented, the algorithm yields accurate hemisphere predictions on average 15 days from reentry as demonstrated by historical reentry cases from 1979 to 2018. All reentry cases were selected to demonstrate the algorithm’s ability to deliver accurate reentry hemisphere predictions for spacecraft with varying physical size and mass, and reentering during different periods of solar cycle activity.     

国产工业摄影测量相机精度测评CSCD

专业的工业摄影测量相机作为摄影测量的基础,其成像质量对测量精度有着直接的影响。目前,国内的专业摄影测量相机的发展比较缓慢,且质量参差不齐,研究合适的测试方法对国内专业测量相机的精度进行测评已刻不容缓。以CIM-1相机为例,从坐标重复性、标准长度等方面对国内工业摄影测量相机的精度进行了分析研究。通过与目前国际上比较认可的INCA相机进行了实验对比,并对实验结果进行了分析评价,得到一些比较理想的结论。为我国工业摄影测量系统检定规程的制定提供参考依据。     

DME Interference mitigation for L-DACS1 based on system identification and sparse representation

L-band digital aeronautical communication system 1 (L-DACS1) is a promising candi-date data-link for future air-ground communication, but it is severely interfered by the pulse pairs (PPs) generated by distance measure equipment. A novel PP mitigation approach is proposed in this paper. Firstly, a deformed PP detection (DPPD) method that combines a filter bank, correlation detection, and rescanning is proposed to detect the deformed PPs (DPPs) which are caused by mul-tiple filters in the receiver. Secondly, a finite impulse response (FIR) model is used to approximate the overall characteristic of filters, and then the waveform of DPP can be acquired by the original waveform of PP and the FIR model. Finally, sparse representation is used to estimate the position and amplitude of each DPP, and then reconstruct each DPP. The reconstructed DPPs will be sub-tracted from the contaminated signal to mitigate interference. Numerical experiments show that the bit error rate performance of our approach is about 5 dB better than that of recent works and is closer to interference-free environment.     

不同冶炼工艺对1Cr18Ni10Ti钢夹杂物的影响

通过试验研究了1Cr18Ni10Ti不锈钢的4种冶炼工艺:真空感应+电渣重熔、真空感应(陶瓷过滤器)、真空感应(陶瓷过滤器)+电渣重熔、真空感应+真空自耗,得到钢锭中夹杂物的种类、大小以及数量的变化.对比试验结果可知,采用真空感应(陶瓷过滤器)冶炼工艺与真空感应+真空自耗之后的钢锭的夹杂物水平相当,D类夹杂物数量最少,大颗粒夹杂物占比也最小.     

基于三维裂纹尖端应力场的应力强度因子计算方法

提出一种基于无限大体裂纹尖端弹性应力场理论解的前几项多项式函数,对实际裂纹体弹性应力场有限元解进行拟合来计算应力强度因子的方法.该方法在计算应力强度因子时不需要预先假设裂纹尖端的应力应变状态,应力强度因子计算结果更符合三维裂纹体裂纹尖端实际的应力应变状态.首先基于二维无限大板中心穿透裂纹应力场理论解验证了方法的有效性,探讨了拟合确定应力强度因子需要的多项式应力函数的项数.然后分别以二维大板中心穿透裂纹、三维大体内埋圆裂纹和三维有限厚板中心穿透裂纹的应力强度因子计算为例,通过与无限大板和无限大体应力强度因子理论解以及基于位移外推法和1/4节点张开位移法的应力强度因子有限元解的对比分析,验证了该方法的有效性和合理性.研究表明该方法能够合理反映三维裂纹体裂纹尖端的实际应力应变状态,计算得到的应力强度因子数值更合理.