Issues in planetary protection: policy, protocol and implementation

Planetary protection is NASA's term for the practice of protecting solar system bodies from Earth life while protecting Earth from life that may be brought back from other solar system bodies. Spacefaring nations will soon begin retrieving samples from Mars and other solar system bodies. For these samples, planetary protection is in order, and measures are already in place to prevent the forward contamination of Mars and other bodies by Earth microbes and the backward contamination of Earth by possible extraterrestrial life. A major goal of planetary protection controls on forward contamination is to preserve the planetary record of natural processes by preventing human-caused microbial introductions.     

Public opinion polls and perceptions of US human spaceflight

A belief exists in the United States about public support for NASA's human spaceflight activities. Many hold that NASA and the cause of the human exploration of space enjoyed outstanding public support and confidence in the 1960s during the era of Apollo and that public support waned in the post-Apollo era, only to sink to quite low depths in the decade of the 1990s. These beliefs are predicated on anecdotal evidence that should not be discounted, but empirical evidence gleaned from public opinion polling data suggests that some of these conceptions are totally incorrect and others are either incomplete or more nuanced than previously believed. This article explores the evolution of public support for space exploration since the 1960s. Using polling data from a variety of sources it presents trends over time and offers comments on the meaning of public perceptions for the evolution of space policy and the development of space exploration in the United States.     

Journey to the Moon: Recent results,science, future robotic and human exploration

The upcoming fleet of lunar missions, and the announcement of new lunar exploration initiatives, show an exciting “Journey to the Moon”, covering recent results, science, future robotic and human exploration. We review some of the questions, findings and perspectives given in the papers included in this issue of Advances in Space Research.     

基于修正Rife算法的脉冲回波相参积累算法

针对目标径向运动导致回波在波门内出现距离走动的情况,提出了一种针对径向匀速运动目标回波信号长时间相参积累的方法。该方法根据傅里叶变换的时移性质——不同时刻回波频谱相关序列的频率包含了各回波到达的时间延迟,通过修正Rife算法估计此时间延迟,最终确定并补偿各个回波的距离走动分量。仿真结果表明:提出的方法可以有效补偿各回波间的距离走动;信噪比低至-6dB时,算法的性能即可达到最优;补偿后积累信号的信噪比可以达到理想积累情况下的93%。     

The first new application of the Mathematical Theory of Stochastic Processes to lunar and planetary science: Topography-Profile Diagrams of Mars

The Mathematical Statistics Theory (MST) and the Mathematical Theory of Stochastic Processes (MTSP) are different branches of the more general Mathematical Probability Theory (MPT) that can be used to investigate physical processes through mathematics. Each model of a stochastic process, according to MTSP, can provide one or more interpretations in the MST domain. A large body of work on impact crater statistics according to MST exists, showing cumulative crater frequency (N km⁻²) as a function of age (years) for some particular crater diameter. However, this is only one possible representation in the MST domain of the bombardment of the planetary surface modeled as a stochastic process according to MTSP. The idea that other representations are possible in the MST domain of the same stochastic process from MTSP has been recently presented. The importance of the approach is that each such mathematical-based interpretation can provide a large amount of new information. Coupled with MOLA data, Topography-Profile Diagrams (TPD) are one of the many examples that can provide a large amount of new information regarding the history of Mars. TPD consists of: (1) Topography-Profile Curve (TPC), which is a representation of the planet’s topography, (2) Density-of-Craters Curve (DCC), which represents density of craters, (3) Filtered-DCC (FDCC), which represents DCC filtered by a low-pass filter, included with the purpose of reducing the noise, and (4) Level-of-Substance-Over-Time Curve (LSOTC), which represents interpretation of the influence on the distribution of craters shown by FDCC. TPC uniquely corresponds to the computation of TPD, whereas DCC depends on algorithms for computing the elevation of each crater according to the topography, center coordinates, and radius of impact crater, and FDCC relies on the architecture of the custom designed low-pass filter for filtering DCC. However, all variations of DCC and FDCC, which includes the various impact crater data sets, showed a correlation among the density of craters and elevation over 70–80% of the planet surface. Additionally, if we assume that the ocean primarily caused the noted correlation, LSOTC offers a mathematical approach for estimating topographic change of the ocean’s extent over time. Accordingly, TPD is the first new practical application of MTSP to lunar and planetary sciences, showing correlation of topography to a physical process.     

Four-month Moon and Mars crew water utilization study conducted at the Flashline Mars Arctic Research Station,Devon Island,Nunavut

A categorized water usage study was undertaken at the Flashline Mars Arctic Research Station on Devon Island, Nunavut in the High Canadian Arctic. This study was conducted as part of a long duration four-month Mars mission simulation during the summer of 2007. The study determined that the crew of seven averaged 82.07 L/day over the expedition (standard deviation 22.58 L/day). The study also incorporated a Mars Time Study phase which determined that an average of 12.12 L/sol of water was required for each crewmember. Drinking, food preparation, hand/face, oral, dish wash, clothes wash, shower, shaving, cleaning, engineering, science, plant growth and medical water were each individually monitored throughout the detailed study phases. It was determined that implementing the monitoring program itself resulted in an approximate water savings of 1.5 L/day per crewmember. The seven person crew averaged 202 distinct water draws a day (standard deviation 34) with high water use periods focusing around meal times. No statistically significant correlation was established between total water use and EVA or exercise duration. Study results suggest that current crew water utilization estimates for long duration planetary surface stays are more than two times greater than that required.     

Development of theoretical approaches to the control of a water-treatment system

The Advanced Life Support/NASA Specialized Center of Research and Training (ALS/NSCORT) focuses on research and development of technologies to support human habitation during space missions. This research was done as part of an effort to maintain crewmembers’ water supply in a closed life-support system. The water subsystem was the primary focus of this study because water is one of the most expensive and important resources for human survival.     

基于ADAMS的行星齿轮系刚柔耦合仿真局部缺陷识别

针对行星齿轮系在工作过程中出现的局部缺陷,将引起齿轮啮合异常,并导致冲击异常,其特征频率就会发生变化。现用ADAMS与ANSYS建立行星齿轮系的刚柔耦合模型,通过快速傅里叶变换（FFT）得到其啮合力的频域曲线,并分析无缺陷行星齿轮系的特征频率、行星轮齿局部缺陷的特征频率、太阳轮齿局部缺陷的特征频率。仿真结果与理论值吻合,说明了所建虚拟样机模型可靠,得到无缺陷行星齿轮系的特征频率是265.34Hz,行星轮齿局部缺陷的特征频率是17.67Hz,太阳轮齿局部缺陷的特征频率是36.13Hz,可用于识别行星齿轮系的行星轮或太阳轮局部缺陷。对行星齿轮系振动特性、可靠性的研究具有一定的指导意义。     

采样机械臂关节月表环境适应性设计

文章针对月球表面采样任务对机械臂关节防尘、耐高低温和轻量化的特殊要求,提出一种由永磁同步电机驱动、2K-H行星减速器+谐波减速器传动的关节设计方案。该方案采用电机的齿槽转矩提供关节制动力矩,并采用前馈力矩补偿控制的方法消除齿槽转矩引起的速度波动,节省了制动器的配置;通过控制减速器传动侧隙、电机定子与壳体的过盈量及密封垫片厚度,实现关节在-100~160℃高低温环境的热匹配和防尘。仿真分析和样机试验结果验证了关节设计方案可满足月表采样的月面特殊环境要求。     

对转螺旋桨/桨扇差动行星齿轮机构动力学设计方法及分析

在对转桨扇涡桨推进系统专有的外流对转桨推进器-对转减速齿轮机构-涡桨发动机的总体匹配设计问题中,给出了拖动共轴对转螺旋桨/桨扇类气动负荷的差动行星齿轮机构的一种设计与分析方法.不同于常规,该总体设计方法以机构的动力学参数为输入,诸传动比、诸半径、诸稳态传动受力等为输出,通过方程组得到了该类传动机构诸参数之间的联系.讨论了该类传动机构的设计原则,使用形式,适用的航空原动机类型.通过某当代算例给出了桨和传动机构诸参数的变化区间,变化特点,参数重要性的分析.结果表明:该方法可以快速得到一般总体设计问题中该类齿轮机构所有稳态设计参数的可行解区间与优化解,进而还可以为推进系统部件法数模的非设计点特性模拟提供计算方法.